Attachment. The physical connection between the restrained component and its support or its restraint device and building structure using bolts, screws, welds, or otherwise positive fastening without relying on frictional resistance due to gravity.

Distribution system. Piping, ductwork, and electrical conduit/cable tray systems.

Effective shear force V_eff. Maximum shear force of one restraint or anchorage point.

Effective tension force T_eff. Maximum tension force or pullout force on one restraint or anchorage point.

Component. Any non-structural element attached to or part of a building such as a piece of equipment or a distribution system.

Resilient restraint. A device attached to a component that allows some limited movement.

Resilient support. Static support of a component which is flexible, such as a vibration isolator.

Response spectra. Relationship between the acceleration response of the ground and the peak acceleration of the earthquake in a damped single degree of freedom at various frequencies. The ground motion response spectrum varies with soil conditions.

Rigid restraint. Non-resilient device attached to a component to restrict its movement.

Rigid support. Static support of a component which is considered to be non-resilient, such as a steel frame.

Shear force V.Force generated parallel to the attachment plane.

Seismic restraint. Device designed to withstand seismic forces and hold a component in place during an earthquake.

Seismic force levels. Design forces on a component determined using various factors related to its weight, construction, position, contents, and function and related to the geographic location of a project.

Snubber. Restraint device that includes resilient material positioned to prevent a component from moving beyond an established gap.

Structure. Load-carrying element of a building, designed by a structural engineer of record.

Support. An element that holds a component in place; may be an external element such as a curb or rod hanger, or internal such as the component’s base frame.

Tension force T. Force generated axially, either perpendicular to the attachment plane or along the primary axis of a single-axis restraint such as a cable.

Sample calculations presented here assume that the equipment support is an integrated resilient support and restraint device. When the two functions of resilient support and motion restraint are separate or act separately, additional spring loads may need to be added to the anchor load calculation for the restraint device. Internal loads within integrated devices are not addressed in this chapter. These devices must be designed to withstand the full anchorage loads plus any internal spring loads.

Both static and dynamic analyses reduce the force generated by an earthquake to an equivalent statically applied force, which acts in a horizontal or vertical direction at the component’s center of gravity. The resulting overturning moment is resisted by shear and tension (pullout) forces on the tie-down bolts. Static analysis is used for both rigidly mounted and resiliently mounted equipment.

 Static Analysis as Defined in ASCE7

ASCE7 specifies a design lateral force F_p for nonstructural components as

(1)

but F_p need not be greater than

(2)

nor less than

(3)

where S_DS is determined by

(4)

where

ap = component amplification factor in accordance with Table 2.

SDS = design spectral response acceleration at short periods. SS is the mapped spectral acceleration for a specific location and is available at the ASCE website: asce7hazardtool.online. (Note: values are specific to certain editions of ASCE7, since they are periodically updated.)

Fa = function of site soil characteristics and must be determined in consultation with either project geotechnical (soils) or structural engineer. Values for Fa for different soil types are given in Table 3. (Note: Without an approved geotechnical report, the default site soil classification is assumed to be site class D.)

Rp = component response modification factor in accordance with Table 2.

Ip = component importance factor (see ASCE7 Chapter 13 for explanation and determination of Ip).

( 1 + 2z/h) = height amplification factor where z is the height of attachment in the structure and h is the average height of the roof above grade. The value of z for ground level and below (e.g., basements) should be taken as 0 and z/h shall not exceed 1.

Wp(D) = operating weight of component, which includes all items and contents attached or contained inside.

The forces acting on indoor components include the lateral and vertical forces at the center of gravity resulting from the earthquake movement, the force of gravity, and the forces of the restraint holding the component in place. Restraints must be designed for a concurrent vertical force F_pv at the center of gravity, defined as

(5)

Seismic coefficient values for both U.S. and Canadian locations can be found at the ASCE website (www.asce7hazardtool.online) and USGS website (www.USGS.gov). Seismic design values for many international locations that correspond with the ASCE7 methodology can be found at www.wbdg.org/additional-resources/tools/ufcsldt. Table 4 contains brief listings of historical S_s factors for international locations that may be used only for general comparisons; they have not been confirmed or updated for this publication and so should not be used for design purposes.

Table 3 Values of Site Coefficient F_a as Function of Site Class and Spectral Response Acceleration at Short Period (S_s)

Site Class	Soil Profile Name	Mapped Spectral Response Acceleration at Short Periodsa
		Ss ≤ 0.25	Ss = 0.50	Ss = 0.75	Ss = 1.00	Ss = 1.25	Ss ≥ 1.5
A	Hard rock	0.8	0.8	0.8	0.8	0.8	0.8
B	Rock	0.9	0.9	0.9	0.9	0.9	0.9
C	Very dense soil and soft rock	1.3	1.3	1.2	1.2	1.2	1.5
Dc	Stiff soil	1.6	1.4	1.2	1.1	1.0	1.0
E	Soft clay soil	2.4	1.7	1.3	b	b	b
F	Soils requiring site response analysis. See ASCE7-16, Chapters 11 and 20, for more information
a Use straight-line interpolation for intermediate values of mapped spectral acceleration at short period Ss. b Site-specific geotechnical investigation and dynamic site response analyses must be performed to determine appropriate values. c D is the default Site Class unless otherwise stated in the approved geotechnical report.

Table 4 S_s Numbers for Selected International Locations (Class Site B) (U.S. COE 2013)

Country	City	Ss		Country	City	Ss		Country	City	Ss		Country	City	Ss
Africa				India	Bombay	0.27		Denmark	Copenhagen	0.12		Mexico	Ciudad Juarez	0.19
Algeria	Algiers	1.01			Calcutta	0.52		England	Birmingham	0.23			Guadalajara	1.54
	Oran	0.63			Madras	0.15			Liverpool	0.24			Hermosillo	0.49
Angola	Luanda	0.06			New Delhi	0.74			Plymouth	0.21			Matamoros	0.02
Benin	Colonou	0.11		Indonesia	Bandung	1.72			Southport	0.24			Mazatlán	1.02
Botswana	Gaborone	0.03			Jakarta	1.45			South Shields	0.12			Merida	0.04
Burkina Faso	Ougadougou	0.46			Medan	1.17			Spurn Head	0.17			Mexico City	0.6
Burundi	Bujumbura	0.69			Surabaya	1.01		Finland	Helsinki	0.05			Monterrey	0.23
Cameroon	Douala	0.17		Iran	Isfahan	0.95		France	Bordeaux	0.17			Nuevo Laredo	0.16
	Yaounde	0.27			Shiraz	1.82			Lyon	0.3			Tijuana	0.97
Central African Republic					Tabriz	1.9			Marseille	0.47		South America
	Bangui	0.27			Tehran	2.15			Nice	0.43		Argentina	Buenos Aires	0.38
Chad	Ndjamena	0.06		Iraq	Baghdad	1.3			Strasbourg	0.45		Bolivia	La Paz	0.51
Congo	Brazaville	0.1			Basra	1.03		Germany	Ausbach	0.25		Brazil	Belem	0.01
Democratic Republic of Congo	Bukavu	0.78			Kirkuk	1.73			Babenhausen	0.36			Belo Horizonte	0.01
	Kinshasa	0.01		Israel	Haifa	1.44			Barnberg	0.22			Brasilia	0.01
	Lubumbashi	0.039			Jerusalem	1.12			Baumholder	0.26			Manaus	0.21
Cote d’lvoire	Abidjan	0.04			Tel Aviv	1			Berlin	0.05			Porto Alegre	0.01
Djibouti	Djibouti	1.02		Japan	Fukuoka	0.71			Bonn	0.44			Recife	0.11
Egypt	Alexandria	0.24			Itazuke AFB	0.77			Bremen	0.1			Rio de Janeiro	0.04
	Cairo	0.71			Iwo Jima	0.94			Dusseldorf	0.32			Salvador	0.33
	Port Said	0.68			Kobe	1.99			Frankfurt	0.4			Sao Paulo	0.1
Equatorial Guinea	Malabo	0.17			Misawa AFB	1.3			Hamburg	0.1		Chile	Santiago	2.21
Eritea	Asmare	0.45			Okinawa	1.73			Munich	0.27			Valparaiso	3.16
Ethiopia	Addis Ababa	0.58			Osaka	1.87			Stuttgart	0.46		Colombia	Bogota	0.99
Gabon	Libreville	0.27			Sagamihara	1.96			Vaihingen	0.41		Ecuador	Quito	2.12
Gambia	Banjul	0.1			Sapporo	1.05		Greece	Athens	0.85			Guayaquil	1.9
Ghana	Accra	0.37			Tokyo	1.96			Kavalla	1.14		Paraquay	Asuncion	0.07
Guinea Bissan	Bissau	0.31			Yokohama	1.96			Lartssa	1.47		Peru	Lima	2.3
Guinea	Conakry	0.38		Jordan	Amman	0.74			Makri	0.91			Piura	2.32
Kenya	Nairobi	0.32		Kuwait	Kuwait City	0.57			Rhodes	1.44		Uruguay	Montevideo	0.07
Lesotho	Maseru	0.07		Laos	Vientiane	0.57			Sauda Bay	1.26		Venezuela	Maracaibo	0.93
Liberia	Monrovia	0.22		Lebanon	Beirut	1.57			Thessaloniki	1.49			Caracas	1.07
Libya	Tripoli	0.6		Malaysia	Kuala Lumpur	0.59		Hungary	Budapest	0.49		Caribbean Sea
Madagascar	Antananarivo	0.19		Nepal	Kathmandu	2.58		Iceland	Keflavik	1.05		Bahamas	Eleuthero Island	0.02
Malawi	Blantyre	0.49		Oman	Muscat	1.3			Reykjavik	0.96			Grand Bahama Island	0.02
	Lilongwe	0.28		Pakistan	Islamabad	1.35			Thorshofn	0.51			Grand Turk Island	0.61
	Zomba	0.51			Karachi	0.77							Great Exuma Island	0.2
Mali	Bamako	0.1			Lahore	1.23		Italy	Aviano AFB	1.25			Nassuau	0.07
Mauritania	Nouakchott	0.08			Peshawar	1.1			Brindisi	0.21		Barbados	Bridgetown	0.39
Morocco	Casablanca	0.26		Qatar	Doha	0.06			Florence	0.62		Cuba	Havana	0.27
	Kenitra	0.28		Saudi Arabia	Dhahran	0.1			Genoa	0.35			Guantanamo Bay	1.32
	Rabat	0.27			Jeddah	0.51			Ghedi	0.75		Dominica	Santo Domingo	1.82
	Tangier	0.47			Jubail	0.37			Milan	0.27		Grenada	Saint George’s	1.13
Mozambique	Maputo	0.11			Khamis Mushayt	0.06			Naples	0.79		Guadeloupe	Basse-Terre	1.37
Niger	Niamey	0.01			Qadimah	0.25			Palermo	0.84		Haiti	Port-au-Prince	1.89
Nigeria	Ibadan				Riyadh	0.06			Rome	0.52			Cap-Haitien	1.5
	Kaduna	0.06			Tabuk	0.29			Siculiana	0.29		Jamaica	Kingston	1.52
	Lagos	0.01		Singapore	All	0.39			Trieste	0.55		Martinique	Fort-de-	1.02
Rwanda	Kigali	0.29		Sri Lanka	Colombo	0.03			Turin	0.28			France
Senegal	Dakar	0.08		South Korea	Camp Casey	0.16		Luxembourg	Luxembourg	0.22		Montserrat	Plymouth	1.7
Sierra Leone	Freetown	0.37			Camp Hialeah	0.31		Malta	Valletta	0.3		Saint Croix	Frederiksted	0.84
					Camp Hunpreys	0.2		Netherlands	Amsterdam	0.14		Saint John	Bethany	1.17
Somalia	Mogadishu	0.1			Chinhae	0.18			North Brunssum	0.58		Saint Kitts and Nevis	Basseterre	0.82
South Africa	Cape Town	0.27			Kimhae	0.19		Northern Ireland	Belfast	0.09		Saint Lucia	Castries	0.94
	Durban	0.3			Kimpo AFB	0.16		Norway	Oslo	0.16		Saint Thomas	Charlotte Amalie	1.17
	Johannesburg	0.03			Kunsan/Kunsan City	0.18		Norway	Stavanger	0.34		Saint Vincent and the Grenadines	Port Elizabeth	0.56
	Natal	0.07			Kwangju	0.14		Poland	Krakow	0.2		Tinidad & Tobago	Scarborough	1.17
	Pretoria	0.03			Osan AFB	0.2			Poznan	0.06			Trinidad	1.74
Swaziland	Mbabane	0.19			Pohang	0.015			Waraszawa	0.12			Port of Spain	1.8
Tanzania	Dar es Salaam	0.18			Seoul	0.18		Portugal	Azores/Lajes Field	1.73		Vieques	Isabel Segunda	0.99
	Zanzibar	0.12			Taegu	0.3			Lisbon	0.71		Indian Ocean Area
Togo	Lome	0.39			Uijongbu	0.18			Oporto	0.68		British	NSF Diego Garcia	0.73
Tunisia	Tunis	0.95			Yongsan/Seoul	0.18		Republic of Ireland	Dublin	0.1		Pacific Ocean Area
Uganda	Kampaia	0.46		Syria	Aleppo	0.68		Romania	Bucharest	1.1		Australia	Brisbane	0.32
Zambia	Lusaka	.0.23			Damascus	0.83		Russia	Moscow	0.07			Canberra	0.49
Zimbabwe	Harare	0.06		Taiwan	Changhua	2.88			St. Petersburg	0.07			Melbourne	0.49
Asia				Taiwan	Kao-hsiung	2.63		Scotland	Aberdeen	0.1			Perth	0.47
Afghanistan	Bagram	1.46			Tsinan	2.51			Edinburgh	0.18			Sydney	0.46
	Gardeyz	0.63			Taipei	3.41			Glasgow	0.22		Caroline Islands	Koror, Palau	0.73
	Herat	0.62			Tsoying	2.63			Renfrew	0.23			Ponape	1.08
	Jalalabad	1.06		Thailand	Bangkok	0.29			Stornoway	0.1			Yap	0.82
	Kabul	1.11			Chiang Mai	0.29		Serbia	Belgrade	1.02		Fiji	Suva	0.6
	Kandahar	0.32			Songkhia	0.31			Zagrebac	1.09		Johnson Island	All	1.43
	Lashkar Gah	0.16			Udom	0.25		Spain	Barcelona	0.63
	Mazar-e Sharif	0.78		Turkey	Ankara	1.04			Bilbao	0.34		Marcus Islands	All	1
	Pol-e Charkhi	1			Istanbul	1.53			Madrid	0.13		Atlantic Ocean Area
	Qalat	0.79			Izmir	2.54			Rota	0.76		Greenland	All	0.33
Bahrain	Manama	0.28			Karamursel	1.46			Seville	0.13
Bangladesh	Dhaka	0.73		United Arab Emirates	Abu Dhabi	1.12		Sweden
Brunei	Bandar Seri Begawan	0.39			Dubai	1.77		Sweden	Goteborg	0.15
				Viet Nam	Da Nang	0.19			Stockholm	0.08
					Ho Chi Minh City (Saigon)	0.15		Switzerland	Bern	0.46
				Yemen	Sanaa	0.36			Geneva	0.49
Burma	Mandalay	2.11		Europe					Zurich	0.41
	Rangoon	0.81		Albania	Tirana	1.17		Ukraine	Kiev	0.07
China	Beijing (Peking)	0.58		Austria	Salzburg	0.44		Central America
	Chengdu	0.46			Vienna	0.52		Belize	Belmopan	0.56
	Chongqing	0.09		Belgium	Antwerp	0.21		Canal Zone	All	0.97
	Guangzhou (Canton)	0.14			Brussels	0.34		Costa Rica	San Jose	2.94
	Harbin	0.13			Kester	0.38		El Salvador	San Salvador	1.79
	Nanjing	0.25			Kleine Brogel	0.33		Guatemala	Guatemala	1.77
	Shanghai	0.18			Shape-Cjoevres	0.57		Honduras	Tegucigalpa	1.05
	Shengyang	0.93		Boznia-Herzegovina	Tuzla AFB	0.97
	Tianjin (Tientsan)	0.76		Bulgaria	Sofia	1.22
	Wuhan	0.08		Cyprus	Nicosia	1.24
Hong Kong	Hong Kong	0.13		Czech Republic	Prague	0.13

The prescriptive method in ASCE7 allows that an equivalent static force can be calculated that represents the dynamic motions of an earthquake. The static forces acting on a piece of equipment are vertical and lateral forces acting on the center of gravity resulting from the earthquake, the force of gravity, and forces at the restraints that hold the equipment in place. The analysis assumes that the equipment moves with the structure during the earthquake and that the relative accelerations between its center of gravity and the ground generate forces that must be balanced by reactions at the restraints. Guidance from the code allows equipment to be analyzed as though it were a rigid component; however, a factor a_p is applied in the computation to address flexibility issues on particular equipment types or flexible mounting arrangements. (Note: for dynamic analysis, it is common to use a 5% damping factor for equipment and a 1% damping factor for piping.) Although the basic force computation is different, the details of load distribution in the examples that follow apply independently of the code used.

Once the overall seismic forces F_p and F_pv have been determined (as indicated in the section on Static Analysis as Defined by ASCE7 or per local code requirement), the loads at the restraint points can be calculated.

The primary forces acting on the restraints include both shear and tensile components. The application direction of the lateral seismic acceleration can vary and is unknown. Depending on its direction, it is likely that not all of the restraints will be affected or share the load equally. It is important to determine the worst-case combination of forces at all restraint points for any possible direction that the lateral wave front can follow to ensure that the attachment is adequate.

Under some instances (particularly those relating to life-support issues in hospital settings), code requirements indicate that critical equipment must be seismically qualified to ensure its continued operation during and after a seismic event. Special care must be taken in these situations to ensure that equipment has been shake-table-tested or otherwise certified to meet the maximum anticipated seismic load. Table 5 illustrates some load combination calculations.

ASCE Standard 7 is based on load- and resistance-factor design (LRFD). In the past, building codes have been based on allowable stress design (ASD). Both are allowed for seismic restraint design. Load factors and load combinations that must be considered in design are defined in Chapter 2 of ASCE7 (see Table 5). If a component is anchored with post-installed anchors, the design is usually accomplished using provisions of LRFD. It is rare now to find components or attachments rated based on their ASD capacity; nonetheless, it is important to recognize the difference between the two and apply the appropriate factors based on the design method and component rating system to ensure that they are consistent.

Restraints holding components in position must withstand shear and tensile forces. Restraint selection and design requires determining the number of fasteners, such as anchors and bolts, that are affected by earthquake forces. The lateral seismic design force can be applied in any horizontal direction and should be evaluated in at least two specific directions, as shown in Figure 1. Note that as many as all of the attachments, or as few as a single attachment, may be affected, depending on the restraint configuration and load direction. The simple case example following provides a basic design method and is made more complicated if the center of gravity (CG) is shifted or if the anchor spacing is not symmetrical. This basic method is called the polar method and is the most commonly used for seismic restraint design.

Some restraint designs consider how the mass is distributed and address all possible horizontal directions with some modification of the ASCE prescriptive design methodology. This is called the lump mass method.

Remember that vibration-isolated equipment will be restrained by snubbers that incorporate operating clearances. As the load is applied at all possible angles and the equipment tilts in response to these loads, not all of the snubbers will make contact and as such not all will be able to contribute to the resistance of vertical loads. Every restraint arrangement will experience differing abilities to share these loads, and the worst-case reactions at each restraint point should account for these factors.

When analyzing rigid equipment, it is reasonable to assume that vertical or horizontal loads will be shared among all restraints. Typically, the force that is generated by overturning or the rotational load created by an offset CG is shared among all restraint points. For lateral forces, the amplitude is equally divided over all the restraints. For rotational motion, the amplitude of the restraint force at each location is proportional to the distance that restraint point is from the geometric center of the mounting pattern. The worst-case load for the location at the maximum distance can be obtained by generating appropriate I_xx and I_yy terms for the restraint pattern and using that as indicated in the examples below.

When analyzing isolated equipment however, the ability to share rotational or rocking (compression/tension) loads beyond the four corner locations will become a function of the stiffness of the equipment. Some equipment, like packaged air handling units, is relatively flexible and will distort and spread the rotational and overturning loads among a number of restraints. Equipment with rigid bases, like a concrete inertia base mounted pump, will tend to distribute the load based on the rotational axis as described previously.

 Simple Case

Figure 1 shows a rigid floor-mount installation of a piece of equipment with the center of gravity at the approximate center of the restraint pattern. To calculate the shear force, the sum of the forces in the horizontal plane is

(6)

The equipment shown in Figure 1 has two bolts on each side, so that four bolts are in shear. Using a single-axis moment equation to calculate the tension force, the sum of the moments for overturning results in an overturning moment (OTM) and resisting moment (RM).

For Figure 1, two bolts are in tension. See Example 1 for applications of the OTM and RM. See ASCE Standard 7 for load combinations that adjust the D (dead load) and E (earthquake load). If the equipment is located outdoors, be sure to consider the W (wind load) forces as well. Shear and tension forces V and T should be calculated independently for both axes, as shown in the front and side views. See the examples for complete analysis.

 General Case

The classic method used to distribute seismic loads equally distributes lateral loads among the restraints and then modifies these loads as a function of the weight eccentricity. Worst-case weight, vertical seismic load, and overturning components are combined to determine a maximum vertical load component in two horizontal directions. This polar method is in common use and works well for most applications.

Equipment can be directly attached to the building structure or to a structural base made of steel shapes (like angles or I-beams). Using a structural base distributes the seismic loads more evenly and may reduce the size of the anchors by reducing the peak load. This results in less stress on the equipment point of attachment, which may not have sufficient strength to transfer the seismic load to the structure. If vibration isolation devices are used, stresses on the equipment points of attachment increase which may then require the use of a structural base.

Figure 1. Equipment with Rigidly Mounted Structural Bases

Larger equipment will have more than four anchor points at each of the corners. Depending on the weight distribution and anchor spacing, the seismic loads at the corners may be lower than the seismic loads in the middle.

Although only two methods of computing seismic forces are illustrated here, there are likely many other valid methods that can be used to distribute the restraint forces. It is important that any method used include the ability to account for equipment weight, seismic uplift or compression forces, overturning forces, and the impact of any offset of the center of gravity within the equipment.

 Lump Mass Method

In the lump mass method, the total equipment weight is distributed among the restraints in a manner that reflects the equipment’s actual weight distribution. There are many methods of determining the distribution analytically or by testing, although they are not addressed in this section. It is often possible that a weight distribution can be obtained from the equipment manufacturer, especially for equipment meant to be hoisted by crane.

Once the static point loads are obtained or computed for each restraint location, they can be multiplied by the lateral seismic acceleration factor (F_p/W_p) to determine lateral forces at each restraint point. Thus, if the weight at each restraint point is W_n, then

(7)

This method considers the loads at all the restraints individually and computes the overturning forces for each in 1° increments for a full 360° of possible approach angles; it is only practical to perform using a spreadsheet or computer routine. The methodology involves breaking the seismic force F_p into x- and y-axis components for each possible approach direction. These forces are multiplied by the height of the equipment center of gravity above the point of restraint h_cg. The resulting moments are then resolved into forces at each restraint based on the x- and y-axis moment arms associated with the particular restraint location and the distance between those restraint elements that will actually make contact to resist the overturning loads and the geometric center of the restraint layout.

For direct attachment with through bolts using ASD criteria, the design capacity of the attachment hardware should be based on criteria established in the American Institute of Steel Construction (AISC) manual. Based on the use of A307 bolts, the basic formula for computing allowable tensile stress when shear stresses are present is

(8)

where S_v is the shear stress in the bolt in psi. T_allow, the maximum allowable tensile stress, must not exceed 20,500 psi.

However, because these stresses are appropriate for dead- plus live-load combinations, they can be appropriately inflated by 1.33 when allowable stress design provisions are used and when they are used to resist wind and seismic loads as well. Peak bolt loads are based on the maximum permitted stress multiplied by the nominal bolt area.

Acceptable loads for lag screws into timber can be obtained from the National Design Specification^® (NDS^®) for Wood Construction (AWC 2015). Selected fasteners must be secured to solid lumber, not to plywood or other similar material. Withdrawal force design values are a function of the screw size, penetration depth, and wood density and can be increased by a factor of 1.6 for short-term seismic or wind loads. NDS identifies withdrawal forces on a force/embedment depth basis. Note that the values published in this table are capacities in both ASD and LRFD. In addition, NDS introduces deration factors for reduced edge distance and bolt spacing.

In timber construction, the interaction formula given in Equation (8) does not apply. Instead, per the NDS, the equation is

(9)

where

Concrete anchors can be divided into two main categories: cast-in-place and post-installed. The former are positioned prior to the concrete being poured and can be suitable for wood formwork, metal deck, or being fixed in place with rebar or other means. Post-installed anchors allow positioning after the concrete has cured and allow more flexibility in determining attachment point locations during construction.

Capacities are manufacturer and anchor-type specific and determined through testing using ACI Standard 355.2 or 355.4 for mechanical or adhesive anchors, respectively. Capacity data should be obtained from the most recent ICC-ES report available from the anchor manufacturer. The report will provide capacity strengths at specific installation conditions for use with strength-based design (LRFD) methods. For other installation conditions and for groups of anchors, special factors are required and American Concrete Institute Standard 318-11 should be consulted.

ASCE7 requires the use of an overstrength factor Ω₀, called “omega-naught” or “omega sub-zero,” applied to the demand side of the equation for attachments to concrete. This assumes the anchor failure mode may be brittle (a concrete breakout or pullout failure). The value of this overstrength factor has varied over the years with different codes. The ASCE7-16 version requires a value of 2 be used for most HVAC&R equipment with one exception, so-called fin-fans or condensing units that commonly come mounted on integral cold-formed sheet metal legs require an overstrength factor of 1.5 when attached to concrete. This factor is applied to F_p at the center of gravity. For some deep or cast-in-place anchors, the anchor failure mode may be determined to be in the steel anchor body in which case the overstrength factor need not be applied.

 ASD Applications

Interaction Formula. To evaluate the combined effective tension and shear forces that act simultaneously on the bolt, use the either of the following equations:

(10)

or

(11)

However, if T_eff ≤ 0.2; T_{allow ASD} the full T_eff can equal T_{allow ASD}, or if V_eff ≤ 0.2; V_{allow ASD} the full V_eff can equal V_{allow ASD}.

 LRFD Applications

The engineer must select an anchor for use from a current evaluation report for anchors that satisfy provisions of ACI 318 Appendix D or ACI 355 (the provisions are the same). From ACI 318, the capacity of the anchor must be reduced in accordance with the following:

(12)

(13)

The interaction equation for LFRD is modified as follows:

(14)

Weld capacities may be calculated to determine the size of welds needed to attach equipment to a steel plate or to evaluate raised support legs and attachments. A static analysis provides the effective tension and shear forces. The capacity of a weld is given per unit length of weld based on the shear strength of the weld material. For steel welds, the allowable shear strength capacity is 21,000 psi on the throat section of the weld. The section length is 0.707 times the specified weld size.

For a 1/16 in. weld, the length of shear in the weld is 0.707 × 1/16 = 0.0442 in. The allowable weld force (F_w)_allow for a 1/16 in. weld is

(15)

For a 1/8 in. weld, the capacity is 1400 lb/in.

The effective weld force is the sum of the vectors calculated in terms of effective shear and tension shall be reduced. Because the vectors are perpendicular, they are added by the method of the square root of the sum of the squares (SRSS), or

(16)

The length of weld required is given by the following equation:

(17)

Seismically rated snubbers allow floor-mounted restrained components to move within controlled limits and to be supported with resilient mounts such as spring or elastomer isolators. Several types of snubbers are manufactured or field fabricated. All snubber assemblies should meet the following minimum requirements to avoid imparting excessive accelerations to HVAC&R components:

Examples of typical snubbers and isolators with integral snubbers are shown as Types A through J in Figure 2. Types A through D are snubber styles corresponding to one isolator type referred to in Chapter 49 as Type 4 Restrained Spring Isolator and are referred to in ASHRAE Standard 171 as multidirectional, multi-axis, with integral isolation. Note that Table 47 of Chapter 49 uses the letters A through D to denote base mounting types which should not be confused with the snubber types below. Snubber Type E is a combination isolator and snubber referred to in that chapter as a Type 2 Rubber Mount and is also referred to in ASHRAE Standard 171 as multidirectional, multi-axis, with integral isolation. Typically all hold-down and mounting bolts are protected from housings and other components using elastomeric grommets and washers to minimize vibration short-circuiting and reduce seismic acceleration forces. Care must be taken during installation to ensure these bolts remain out of contact and free to move under normal operation. Snubbers types F through J are often used in conjunction with isolators that do not have integral snubbers. Per ASHRAE Standard 171, Types F, G, H, and J are called multidirectional, multi-axis with operating clearances, and Type I is called single-directional, single-axis, single angle.

For suspended equipment, pipes, ducts, conduits, and raceways, it is necessary to restrain lateral movement resulting from seismic acceleration applied to the component. Unrestrained, suspended equipment and related systems may sway violently back and forth, impacting nearby building elements and possibly overstressing the hanger rod supports or their attachments, leading to collapse. To prevent this swaying, suspended components are braced or restrained, typically by one of two methods: a wire rope system, or a rigid brace system using steel struts, angles, or other rigid elements.

Figure 2. Seismic Snubbers

Wire rope restraints are restraint assemblies typically used for suspended components consisting of galvanized steel wire rope (also known as aircraft cable). A typical cable restraint system is shown in Figure 3. Cable restraints should be tested for capacity in accordance with ASHRAE Standard 171. Cables are installed to prevent excessive seismic motion and arranged so they do not engage during normal operation. Equipment suspended with vibration isolators must use cable restraints instead of rigid restraints to avoid shorting out or degrading the isolation. Rod stiffeners are added as necessary, as shown in Figure 4, to prevent the hanger rods from buckling.

Figure 3. Cable Restraint

Secure the cable to structure and to the braced component through a bracket or stake eye designed to meet the cable restraint rated capacity. Cables ends are typically terminated using one of the following methods:

Figure 4. Rod Stiffener

When cables are looped through a bracket or support hole, a teardrop-shaped cable thimble matching the wire size should be used to protect the cable. Some specialty brackets are designed specifically for allowing a looped cable through without a thimble. Figure 5 shows typical cable restraint details with various attachment methods. Typical attachment methods to secure rigid braces to structures and components are shown in Figure 6.

Figure 5. Types of Cable Connections

When piping and ductwork run vertically through a structure, they are identified as risers. They are subject to the same seismic and (less commonly) wind forces as are piping and ductwork oriented horizontally. The primary difference is that the forces that act along the axis of the riser are the summation of the vertical seismic forces and gravity loads, whereas on horizontal systems, the axial forces are simply the horizontal seismic or wind force.

Figure 6. Strut End Connections

It is also important to recognize that restraining risers of any significant length and variation in temperature require support that allows thermally driven changes in the riser’s overall length to be accommodated. Because the vertical seismic and wind forces are small compared to gravity forces, axial restraint for the riser can normally be provided with only minor increases in the size of the specialized components used to support the system. Because of the potential of damage to the restraint or support systems as the system grows or shrinks due to thermal changes, it is not recommended that axial restraint systems be fitted to a riser. Instead, the primary support system should be designed or selected to meet the project design loads.

Risers of significant length are also fitted with some type of stabilization devices. These can be as simple as snug-fitting holes in the floors that the risers penetrate or specialized brackets or guiding devices that maintain the alignment of the piping or duct while still allowing it to expand or contract. As is the case with the vertical forces, the components used for guidance can frequently be used to provide resistance against seismic or wind events if they are sized and attached adequately.

If, in the lateral load case, the components used to provide guidance are not adequate to resist the design seismic or wind load conditions, additional seismically qualified restraint systems should be fitted to perform this task.

All axial and lateral restraints fitted to risers must be effective against forces that may act in any horizontal or vertical direction as applicable. In addition, the attachment hardware used must include seismically qualified components (e.g., anchors), installed in accordance with seismically qualified procedures.

The following examples should not be considered to cover all installation cases; they are a selection of simple cases that can be used for illustrative purposes. Many, if not most, cases are more complex and will require the engineer performing the analysis to consider the details of the application when creating a model. There are many potential configurations (far more than can be illustrated here) that impact the load path and add forces/moments at the restraint points. Efforts have been made in the examples to indicate qualifications and limitations specific to the particular model being used.

The following examples are provided to assist in the design of component anchorage to resist seismic forces. For Examples 1 through 4, assume the provisions contained in ASCE7-16 apply, I_p = 1.5, S_s = 0.85, site soil class is C, and the equipment is located at the top of a 50 ft building. Also include a vertical force component F_pv = 0.2S_DS D where D is the dead load for all examples. Examples 1 through 5 are solved using the polar method of analysis while Example 6 is solved by the lump mass method.

Note: These examples assume that I_p = 1.5. This assumes that the component being considered is required for the continued function an essential facility following an earthquake or contains hazardous materials. ASCE7-16 Section 13.2.2 requires that this component be certified as being operable after the design earthquake. Codes based on ASCE7 require that the anchor failure mode be considered when selecting an appropriate anchor. If, when using the baseline factors indicated above, it is found that the limiting failure mode of the anchor/restraint component is a brittle failure associated with the anchor (i.e., a concrete or anchor pullout failure) rather than a ductile (steel) failure, the analysis of the anchorage needs to be selected with the F_p load increased by the Ω₀ factor, which in most cases is 2. The general math is the same, but the force magnitudes will increase from those shown in the sample cases.

Example 1.

Anchorage design for equipment rigidly mounted to the structure (see Figure 7). This model is appropriate only for rigid-mounted equipment with four restraint points and the CG centered geometrically on the restraint point pattern. The equations can be adjusted when the equipment center of gravity is offset from the geometric center. There are other examples provided for vibration-isolated equipment.

From Equations (1) to (4), calculate the lateral seismic force and its vertical component. For rigidly mounted mechanical equipment (period < 0.06 s or > 16.7 Hz), a_p from Table 2 is 1.0, otherwise a_p = 2.5.

The first step in the load determination process is to determine S_DS using the following equation and F_a = 1.1 (from Table 3, site class C). Linear interpolation is allowed and the actual F_a for this application could be reduced to (1.0 – 0.75)/0.25 × 0.1 + 1.0, or 1.06. For this example, though, F_a = 1.1 is used.

Using this value for S_DS Equation (1) gives

Equation (2) shows that F_p need not be greater than

Equation (3) shows that F_p must not be less than

Therefore F_p = 450 lb.

When considering provisions of LRFD, a vertical acceleration component must be considered per ASCE7, Section 12.4.2.2.

A simplified method of calculating the resisting moment (RM) involves looking only at the diagonally opposite corners. For hard-mounted equipment, opposite corners could also be considered. The simplified method is shown next for both ASD and LRFD cases.

For Allowable Stress Design (ASD)

The load combinations of Section 2.4 of ASCE7-16 must be considered in the design. For rigidly mounted components, and when looking at worst-case tensile (uplifting) loads on the restraint component, Combination 8 is generally the critical combination to be considered.

Calculate the overturning moment OTM:

(18)

Calculate the resisting moment RM:

(19)

(20)

Calculate T_eff per bolt:

(21)

Calculate shear force per bolt:

(22)

Load and Resistance Factor Design (LRFD)

The load combinations of Section 2.3 of ASCE7-16 must be considered in the design. For rigidly mounted components, and when looking at the worst-case tensile (uplifting) loads on the restraint component, consider the most critical combination.

(23)

(24)

Case 1. Equipment attached to a timber structure

Before computing interaction forces, the computed loads must be reduced by a factor of 1.4 to make them compatible with the capacity data listed in the National Design Specification^® (NDS^®) for Wood Construction (AWC 1997). The lateral load V_eff becomes 112.5/1.4 or 80.4 lb per bolt and the pullout load T_eff becomes 103/1.4 = 73.5 lb per bolt. For the capacity of the connection, a resulting combined load and angle relative to the mounting surface must be computed. The combined load is

The angle α = arcs in (T_eff/Z′_α) = 42.5°, where Zα is the allowable lag screw load multiplied by applicable factors and Z′_αα is the factored allowable lag screw load at angle α from the mounting surface.

Selected fasteners must be secured to solid lumber, not to plywood or other similar material. The following calculations are made to determine whether a 1/2 in. diameter, 4 in. long lag screw in redwood will hold the required load. For this computation, it is assumed that bolt spacing, edge distance, temperature, and other factors do not reduce the bolt capacity (see NDS for further details) and that the load allowable factor for short-term wind or seismic loads is 1.6.

From Table 9.3A in the NDS, for redwood, G = 0.37, and Z perpendicular to the grain is 512 lb.

From Table 9.2A in the NDS, for G = 0.37 and 3.5 in. full thread, W = 385 × 3.5 = 1350 lb.

Substituting into the combined load for lag bolts [Equation (9)] gives

Therefore, a 1/2 in. diameter, 4 in. long lag screw can be used at each corner of the equipment.

Case 2. Equipment attached to steel

For equipment attached directly to a steel member, analysis is the same as that shown in case 1. Capacities for the attaching bolts are given in the Manual of Steel Construction (AISC). See Chapter J of the AISC Specification for design provisions.

For this example T_eff/T_ASD = 125/4410 = 0.02 < 0.2; therefore a combined tension shear check need not be performed on the connection.

Therefore, 1/2 in. diameter bolts can be used.

Figure 7. Equipment Rigidly Mounted to Structure (Example 1)

Example 2.

Anchorage design for equipment supported by external spring mounts (Figure 8) and attached to concrete using seismically rated post-installed anchors.

A mechanical or acoustical consultant may choose the type of isolator or snubber or combination of the two (restrained isolator), typically in collaboration with the product vendor to should select the actual spring and/or snubber devices appropriate for the application.

Note that there are different values for R_p and a_p in different versions of ASCE7. This example uses Table 1, which is drawn from ASCE7-16. S_DS remains as in Example 1. For resiliently floor-mounted mechanical equipment, R_p = 2.0 and a_p = 2.5.

The basic force equation is then

Equation (2) indicates that F_p need not be greater than

Equation (3) indicates that F_p must not be less than

The vertical force F_pv equals

Assume that the center of gravity CG of the equipment coincides with the geometric center of the isolator group.

If T = maximum tension on a restrained isolator and C = maximum compression on a restrained isolator, then

(25)

Note that the above equations hold true for all cases with four or more restraints on rigid equipment, assuming that the system is vibration isolated. This is because, for a very brief period of time, there is little or no load sharing with restraints that are not located on the diagonal corners as any remaining restraints would be operating in the clearance range of the snubbing elements and there would be no contact that would allow additional restraints to share the load.

To find maximum T or C, set dT/dθ = 0:

(26)

(27)

(28)

(29)

Calculate the shear force per isolator:

(30)

This shear force is applied at the centroid of the elevation of the snubbing element in the restraint device. Uplift tension T on the vibration isolator is the worst condition for the design of the anchor bolts. The compression force C must be evaluated to check the adequacy of the structure to resist the loads.

(31)

The value of (T₂)_eff per bolt due to overturning on the isolator is

(32)

where d is the distance from edge of isolator base plate to center of bolt hole.

(33)

(34)

(35)

See Example 1 for the design of the connections to the structural system.

Figure 8. Equipment Supported by External Spring Mounts

Figure 9. Spring Mount Detail (Example 2)

Example 3.

Anchorage design for equipment with a center of gravity different from the geometric center of the restrained isolator group (Figure 10).

Anchor properties

(36)

Angles:

(37)

(38)

(39)

(40)

Vertical reactions

(41)

Vertical reaction caused by overturning moment

(42)

Vertical reaction caused by eccentricity

(43)

Vertical reaction caused by W_p

(44)

(45)

(46)

Horizontal reactions

Horizontal reaction caused by rotation

(47)

(48)

(49)

See Example 1 for the design of the connections to the structural system.

The values of T_min and V_max are used to design the anchorage of the isolators and/or snubbers, and T_max is used to verify the structure’s adequacy to resist the vertical loads.

Figure 10. Equipment with Center of Gravity Different from Restrained Isolator Group (in Plan View)

Example 4.

Anchorage design for equipment with supports and bracing for suspended equipment (Figure 11). Equipment weight W_p = 500 lb.

Note that post-installed anchors may not withstand published allowable static loads when subjected to vibratory loads, so vibration isolators may be used between the equipment and the structure to damp vibrations generated by the equipment.

Anchor properties

(50)

Note that I_x and I_y will vary with the number of restraints for hard-mounted equipment, but since only the corner restraints come into play during initial contact caused by rocking or rotation, they will remain as indicated for vibration-isolated systems, no matter how many restraints are present.

Angle

(51)

From Equation (43),

From Equation (44),

From Equation (45),

From Equation (46),

From Equation (47),

From Equation (48),

Forces in the hanger rods:

Force in the splay brace = = 1587 lb at a 1:1 slope.

Because of the force being applied at the critical angle, as in Example 2, only one splay brace is effective in resisting the lateral load F_p.

Design of hanger rod/vibration isolator and connection to structure

When post-installed anchors are mounted to the underside of a concrete beam or slab, the allowable tension loads on the anchors must be reduced to account for cracking of the concrete. A general rule is to use half the allowable load. Some manufacturers have ICC reports that provide allowable values for anchors installed under the slab.

Determine whether a 1/2 in. wedge anchor with special inspection provisions will hold the required load.

Therefore, a 1/2 in. rod and post drill-in anchor should be used at each corner of the unit.

For anchors installed without special inspection,

Therefore, a larger anchor should be chosen.

Determine if the 1/2 in. hanger rod would require a stiffener if it is 36 in. long.

Design of splay brace and connection to structure

Force in the slack cable = 1587 lb.

Because all of the load must be resisted by a single cable, the forces in the connection to the structure are

Because the cable forces are relatively small, a 3/8 in. aircraft cable attached to clips with cable clamps should be used. The clips, in turn, may be attached to either the structure or the equipment.

The design of a post-installed anchor installation is similar to that shown in Example 1. Anchors installed through a metal deck will have lower capacities than anchors installed in a flat slab because of limited embedment depths. Take care to ensure that the design also satisfies the requirements contained in the evaluation report for the anchor specified.

Figure 11. Supports and Bracing for Suspended Equipment

Example 5.

This example is the same case as Example 1 (Figure 7), except that the lump mass method is used as a basis of analysis. Load combinations listed here are for LRFD, although the analysis can also be done using ASD in a similar manner to Example 1. The anchorage design is for equipment attached to concrete using seismically rated post-installed anchors. This model is also appropriate for vibration isolated equipment with no more than four restraint points and the CG centered geometrically on the restraint point pattern. It is not acceptable for systems where the CG is shifted away from the geometric center of the restraint point pattern.

When using the method, the F_p and F_pv acceleration terms are computed in the manner as when using the polar analysis; however the weight term would not be present. As such, the basic S_DS Equation (1) gives

Equation (2) shows that F_p(g) need not be greater than

Equation (3) shows that F_p(g) must not be less than

Therefore F_p(g) = 0.433 (g).

When considering provisions of LRFD, a vertical acceleration component would still be considered per ASCE7, Section 12.4.2.2:

The static mass load computation at each restraint location can be computed in many ways or may be provided by the equipment manufacturer. In this case the equipment is balanced, so the static mass load at each restraint point would equal the local weight/4:

Horizontal design force.

This is driven by the static mass load; at each of the four corners would be the mass load × F_p(g):

If the equipment were both vibration isolated and the CG was off center, a T_m component as shown in Equation (44) would be computed, divided by 4 for the four corners that would split the load and that would be added to the mass driven load.

Vertical seismic design force.

This is also driven by the static mass load at each of the four corners would be plus or minus the mass load x F_pv(g):

Dead load terms.

The maximum dead load terms would be the mass load × 1.2 per LRFD (Equation [5]):

The minimum dead load terms would be the mass load × 0.9 per LRFD (Equation [7]):

Overturning forces.

Per code for vertically cantilevered equipment, the overturning forces, must be computed for each possible seismic wavefront angle (from 0 to 360° in the plan view). This is accomplished by performing x and y axis static analyses using forces that are broken from the parent force F_p based on the angle of attack. The reaction forces for the load components are then summed for each restraint location and the worst-case upward and downward forces are retained. The method requires a spreadsheet or computer program to be accomplished efficiently. As such, the math behind a single load point and angle will be illustrated here.

Sample computation for the restraint in the bottom left hand corner as shown in Figure 8 at a wavefront angle θ = 30 degrees:

The x component of the F_p force = F_px = F_p(– cos θ)

F_px would generate a reaction on the corner restraint of

Similarly, the y component of the F_p force = F_py = F_p × (– sin θ)

F_py would generate a reaction on the corner restraint of

Summing, the overturning reaction at this restraint and this angle would be

After all 360° are analyzed an Overturning_max(+) and Overturning_min(–) would result.

For each restraint point, the peak vertical loads would be

Prescriptive provisions of ASCE7 can be summarized as follows:

The following should be considered when installing seismic restraints.

HVAC&R equipment in seismic design Categories C to F require certifications of compliance of HVAC&R components for seismic resistance. Certification of compliance for components, defined in ASCE7, Section 13.2.1, is based on analysis, testing, or experience data. These components include seismic restraint devices or force resisting systems in equipment. Equipment that is defined as designated seismic systems (essential for operation, I_p = 1.5) in ASCE7, Section 13.2.2, must meet special certification requirements. Certification of this essential equipment in seismic design Categories C through F is as follows (all section references in the following refer to ASCE7):

IBC Section 1703.5 identifies requirements for certification by an approved agency with in-plant inspections and labeling. The IBC further describes how the certification for seismically qualified equipment is supported with the in-plant inspections by an inspector knowledgeable to recognize the critical characteristics for seismic applications.

Classification. Buildings and other structures are classified for wind load design exposure according to Table 6.

Basic wind speed. The fastest mile-per-hour wind speed at 33 ft above the ground of Terrain Exposure C (see Table 6) having an annual probability of occurrence of 0.02. Data in ASCE Standard 7 or regional climatic data may be used to determine basic wind speeds. ASCE data do not include all special wind regions (such as mountainous terrains, gorges, and ocean promontories) where records or experience indicate that the wind speeds are higher than what is shown in appropriate wind data tables. For these circumstances, regional climatic data may be used provided that both acceptable extreme-value statistical analysis procedures were used in reducing the data and that due regard was given to the length of record, averaging time, anemometer height, data quality, and terrain exposure. One final exclusion is that tornadoes were not considered in developing the basic wind speed distributions.

Components and Cladding. Elements of the building envelope that do not qualify as part of the main wind-force resisting system.

Corner Zone. Areas of building walls and roofs adjacent to building corners that experience increased external pressure from wind.

Design wind force. Equivalent static force that is assumed to act on a component in a direction parallel to the wind and not necessarily normal to the surface area of the component. This force varies with respect to height above ground level.

Importance factor I. A factor that accounts for the degree of hazard to human life and damage to HVAC components (Table 7). For hurricanes, the value of the importance factor can be linearly interpolated between the ocean line and 100 miles inland because wind effects are assumed negligible at this distance inland.

Gust response factor G. A factor that accounts for the fluctuating nature of wind and the corresponding additional loading effects on HVAC components.

Minimum design wind load. The wind load may not be less than 16 lb/ft² multiplied by the area of the HVAC component projected on a vertical plane that is normal to the wind direction.

Two procedures are used to determine the design wind load on HVAC components. The analytical procedure, described here, is the most common method for standard component shapes, based on the requirements in ASCE7. The second method, the wind-tunnel procedure, is used in the analysis of complex and unusually shaped components or equipment located on sites that produce wind channeling or buffeting because of upwind obstructions. The analytical procedure produces design wind forces that are expected to act on HVAC components for durations of 1 to 10 s. The various factors, pressure, and force coefficients incorporated in this procedure are based on a mean wind speed that corresponds to the fastest wind speed.

 Analytical Procedure

The design wind force is determined by the following equation:

(52)

where

Fw = design wind force, lb

Qz = velocity pressure evaluated at height z above ground level, lb/ft2

G = gust response factor for HVAC components evaluated at height z above ground level

Cf = force coefficient (Table 9)

Af = area of HVAC component projected on a plane normal to wind direction, ft2

Certain of the preceding factors must be calculated from equations that incorporate site-specific conditions that are defined as follows:

Velocity Pressure. The design wind speed must be converted to a velocity pressure that is acting on an HVAC component at a height z above the ground. The equation is

(53)

where

Kz = velocity pressure exposure coefficient from Table 11

Kzt = topographic factor = 1.0

Kd = wind directionality factor = 1.0

V = velocity from Figure 11, mph

I = importance factor from Table 7

The force generated by the wind is calculated by

(54)

where

Fw = design wind force, lb

Qz = velocity pressure evaluated at height z above ground level, lb/ft2

G = gust response factor for HVAC components evaluated at height z above ground level

Cf = force coefficient (Table 9)

Af = area of HVAC component projected on a plane normal to wind direction, ft2

The following example calculations are for a 400 ton cooling tower:

.

Tower height h = 10 ft

Tower width D = 10 ft

Tower length l = 20 ft

Tower operating weight W_p = 19,080 lb

Tower diagonal dimension = = 22.4 ft

Area normal to wind direction A_f = 10 × 22.4 = 224 ft²

From Table 10, C_f = 1.0 for wind acting along diagonal with h/D = 10/10 = 1.

Example 5.

Suburban hospital in Omaha, Nebraska. The top of the cooling tower is 100 ft above ground level. Building width normal to the wind B = 3000 ft, and building height H = 90 ft.

Solution:

From Figure 12, the design wind speed is found to be 90 mph.

From Table 8, use Category IV.

From Table 6, use Exposure B.

From Table 7, I = 1.15.

From Table 11, K_z = 0.99.

From Figure 13, K_d = 0.9.

From Table 8, G = 0.85.

Substitution into Equation (58) yields

Building height is greater than 60 ft; therefore, E_f = 1.0.

Substitution into Equation (54) yields the design wind force as

Example 6.

Office building in New York City. Top of tower is 600 ft above ground level. Building wall normal to the wind B = 600 ft and building height H = 590 ft.

Solution:

From Figure 12, the design wind speed is 120 mph.

From Table 8, use Category II.

From Table 6, use Exposure B.

From Table 7, I = 1.0.

From Figure 13, K_d = 0.9.

Because z > 500 ft, K_z must be determined from Note 2 of Table 11.

From Table 8, α = 7.0, z_g = 1200, and G = 0.85.

Substituting into the first equation in Note 2 yields

Substituting into Equation (55) yields

Building height is greater than 60 ft, therefore E_f = 1.0.

Substituting into Equation (56) yields the design force wind as

The basic wind speed for design based on ASCE7-16 now uses individual maps based on whether a building is in design category I, II, III, or IV. Figures 12A to 12H (at the end of this chapter in the Appendix) show the basic wind speeds to be used.

Example 7.

Church in Key West, Florida. The top of the tower is 50 ft above ground level. Building wall normal to the wind B = 300 ft and building height H = 40 ft.

Solution:

From Figure 12, the design speed is found to be 150 mph.

From Table 8, use Category III.

From Table 5, use Exposure C (as this is a hurricane-prone region).

From Table 15, I = 1.15.

From Table 16, G = 0.85.

From Table 12, K_d = 0.9.

From Table 11, K_z = 1.09 (for exp category C).

From Equation (55):

Building height is less than 60 ft, A_f / (B × H) = 224/(300 × 40) = 0.02, therefore, E_f = 1.9

Substituting into Equation (56) gives the design wind force as

For many projects, the structural engineer of record will determine the components and cladding wind pressures provided on the structural notes drawing. If these wind pressures are not provided, the two following procedures (described previously) are used to determine the design wind load on HVAC cladding components.

 Analytical Procedure

Velocity Pressure. The design wind speed must be converted to a velocity pressure that is acting on an HVAC component at height z above the ground. This is done using Equation (54). Once the velocity pressure has been determined, the design wind pressure can be calculated.

Low-Rise Buildings and Buildings with h ≤ 60 ft

The design wind pressure for cladding is determined by the following equation:

(55)

where

Pw = design wind pressure, lb/ft2

Qh = velocity pressure evaluated at mean roof height h above ground level, lb/ft2

GCp = external pressure coefficient given in Figure 13

GCpi = internal pressure coefficient given in Table 13

Buildings with h > 60 ft

The design wind pressure is determined by the following equation:

(56)

where

Pw = design wind pressure, lb/ft2

Qz = velocity pressure for windward walls calculated at height z above the ground of the component being examined

Qh = velocity pressure for leeward walls, side walls and roofs, evaluated at height h of the roof

Qi = velocity pressure for windward walls, side walls, leeward walls, and roofs, evaluated at height h of the roof

GCp = external pressure coefficient given in Figure 14

GCpi = internal pressure coefficient given in Table 13

Example 8.

Office building in Houston, Texas. The top of the building is 30 ft above grade located in a newly developed suburban area. It is necessary to determine the wind pressures on louver 1 and louver 2 shown on the building elevation in Figure 15.

Solution:

From Figure 12, the design speed is found to be 120 mph.

From Table 8, use Category II.

From Table 6, use Exposure C.

From Table 7, I = 1.0.

From Table 11, K_z = 0.98, at roof height, h = 30 ft.

From Table 12, K_d = 0.85.

K_zt assumed to be 1.0.

Determine GC_p: Building height h is less than 60 ft; therefore, Equation (55) is used for the pressure evaluations. GC_p must be determined from Figure 15 for each of the louvers.

Louver 1: from the notes on Figure 15, it is necessary to determine the a dimension, which establishes the corner zone 5. The least horizontal dimension coming into the corner is 32 ft from the plan view. Ten percent of this value is 3.2 ft. The minimum value for the corner dimension is 3 ft. Louver 1 is located 1 ft 2 11/16 in. from the corner and is therefore in corner zone 5.

From Figure 15, GC_p = +0.95 or –1.3 for a 20 ft² wind area. A positive GC_p indicates a positive pressure on the windward side of the building. A negative GC_p indicates a suction pressure on the leeward side of the building. Both cases must be evaluated.

Louver 2: based on the corner calculation, louver 2 is in noncorner zone 4. From Figure 15, GC_p = +0.9 or –1.0 for a 30 ft² wind area.

Determine GC_pi: See Figure 14. Most buildings without significant wall openings are enclosed buildings. For the purposes of this example, an enclosed building is assumed. GC_pi = +0.18 or –0.18. A positive sign indicates pressure outward on all structure walls. A negative sign indicates pressure inward on all structure walls.

Determine velocity pressure at roof elevation h from Equation (55):

Determine design wind pressure P from Equation (56):

Louver 1, case 1: positive external, positive internal

Louver 1, case 2: positive external, negative internal

Louver 1, case 3: negative external, positive internal

Louver 1, case 4: negative external, negative internal

The controlling values for P for louver 1 are 34.7 lb/ft², – 45.4 lb/ft² and should be used to specify equipment performance levels.

Louver 2, case 1: positive external, positive internal

Louver 2, case 2: positive external, negative internal

Louver 2, case 3: negative external, positive internal

Louver 2, case 4: negative external, positive internal

The controlling values for P for louver 2 are 33.2 lb/ft², – 36.2 lb/ft² and should be used to specify equipment performance levels.

Figure 13. External Pressure Coefficient GC_p for Walls for h < 60 ft Reprinted with permission from ASCE (2016)

Figure 14. External Pressure Coefficient GC_p for Walls for h > 60 ft Reprinted with permission from ASCE (2005)

Figure 15. Office Building, Example 8

Table 10 Classification of Buildings and Other Structures for Wind Loads

Nature of Occupancy	Category
Buildings and other structures that represent a low hazard to human life in event of failure, including, but not limited to, agricultural facilities, certain temporary facilities, and minor storage facilities	I
All buildings and other structures except those listed in Categories I, III, and IV	II
Buildings and other structures that represent a substantial hazard to human life in event of failure, including, but not limited to, - Buildings and other structures where more than 300 people congregate in one area. - Buildings and other structures with elementary and secondary schools, day care facilities with capacity greater than 250 - Buildings and other structures with capacity greater than 500 for colleges or adult education facilities - Health care facilities with capacity of 50 or more resident patients, but not having surgery or emergency treatment facilities - Jails and detention centers - Power generating stations and other public utility facilities not included in Category IV - Buildings and others structures containing sufficient quantities of toxic or explosive substances to be dangerous to the public if released	III
Buildings and other structures designated as essential facilities including, but not limited to, - Hospitals and other health care facilities with surgery and emergency treatment facilities - Fire, rescue, and police stations and emergency vehicle garages - Designated earthquake, hurricane, or other emergency shelters - Communication center and other facilities required for emergency response - Power generating stations and other public utility facilities required in an emergency - Buildings and other structures with critical national defense functions	IV
Reprinted with permission from ASCE (2005).

Some jurisdictions require certifications of performance of HVAC&R components for wind resistance. These certifications focus on (1) the equipment’s ability to remain intact and/or (2) the equipment restraints and anchors to keep the item in place during a wind event.

In the United States, the State of Florida and the Building Code Compliance Office of Miami-Dade County have certification requirements that affect HVAC&R system designers. The HVAC products may have special requirements for wind performance and may need approval of the State of Florida. In addition to wind performance, the Florida Building Code (ICC 2007) requires impact resistance and wind-pressure resistance for items that protect openings in buildings in windborne debris regions. HVAC products provided for projects located in these regions may be required to have testing and product certification from the State of Florida before installation. Other states, such as Texas, also have requirements for wind-pressure and impact testing. To ensure that the HVAC&R equipment supplied is compliant, designers should contact the local building code official in their project location.

Overhead lines are generally not at a significant risk for flood damage. Energized power lines are elevated to prevent people from accidentally coming into contact with them, and the elevation protects much of an overhead electrical system from flood inundation damage. However, some portions of an overhead electrical system (most notably substations) are not elevated. Such portions of an overhead system may be vulnerable to inundation, particularly when located in low-lying areas or in SFHAs. Structures that support overhead lines can be damaged by moving floodwaters from scour, erosion, and hydrodynamic loads. Structures can be damaged by floating debris or soil saturation.

Underground portions of power lines are generally resistant to damage from freshwater flooding. Aboveground components of underground power line systems, such as pad-mounted transformers, medium-voltage sectionalizing switches, and pad-mounted switchgear, are vulnerable to floods. Like the supporting structures for overhead lines, pad-mounted equipment can be damaged by hydrostatic forces, hydrodynamic forces, flood-borne debris impact, scour, and erosion. Submersion can also short-circuit energized pad-mounted equipment, particularly the older style live-front equipment.

For many facilities, flood poses a risk of damage to building systems and can prevent a facility from functioning. Major components of buildings systems, such as boilers, electrical service and distribution equipment, fuel tanks and fuel pumps, other pumps, and IT servers, are often located in the lowest level of a building, which is the level most vulnerable to flooding. Another area that is vulnerable to flooding is rooftop equipment that is prone to overturning during high windstorms and can leave a hole in the roof curbs, thus allowing flooding of the building when it is raining.

The risk of flood damage is particularly high for buildings that were constructed before flood risks were quantified in the 2006 International Building Code (IBC). The 2006 International Building Code (IBC) is when the code first referenced ASCE 24-05, Flood Resistant Design and Construction (ASCE, 2005). ASCE 24-05 requires that building systems (referred to as “utilities” in that standard) either be elevated above design flood elevations or provided with flood protection.

Flooding historically has been disastrous for emergency power systems. Floodwater can damage or inundate fuel tanks that supply diesel generators, fuel oil pumping equipment, and emergency power distribution equipment, such as transfer switches, panels, and feeders. Many post-flood event investigations have shown that components of the emergency power and distribution system are often placed at lower elevations than components of the normal power distribution system and therefore are more vulnerable to flooding.

Base Flood. A term used in the National Flood Insurance Program to indicate the minimum size flood to be used by a community as a basis for its floodplain management regulations; presently required by regulation to be that flood which has a 1% chance of being equaled or exceeded in any given year. Also known as a 100-year flood or 1% chance flood.

Base Flood Elevation (BFE). The resulting elevation of the flood water at specific areas within identified in the FEMA flood maps based on the Base Flood.

Base Floodplain. The floodplain that would be inundated by a 100-year (1% chance) flood.

Critical Facilities. Structure or related infrastructure that if flooded may result in significant hazards to public health and safety or interrupt essential services and operations for the community at any time before, during and after a flood.

Deep. Deep flooding is where large amount of water flowing is restricted by barriers also known as a channel (natural occurring hills or buildings). As the water flow increases, the water levels raise and increase in water velocities causing major erosion.

FEMA. Federal Emergency Management Agency, the agency responsible for administering the National Flood Insurance Program (NFIP), or successor agency. FHAD (Flood Hazard Area Delineation) a flood study often prepared on a watershed basis by the Urban Drainage and Flood Control District. FHADs are adopted by the State and affected communities like LOMCs. FHADs are eventually submitted to FEMA as PMRs and become part of the updated FEMA FIRM map.

Flash Flood. Large amount of water is directed into natural occurring ravines. Flash flooding can be caused by heavy rains, snow melt, ice jams, or when dams or levees break.

Floatable Materials. Material that is not secured in place or completely enclosed in a structure, so that it could float off site during the occurrence of a flood and potentially cause harm to downstream property owners, or that could cause blockage of the channel or drainageway, a culvert, bridge, or other drainage facility. This includes, without limitation, lumber, vehicles, boats, equipment, trash dumpsters, tires, drums or other containers, pieces of metal, plastic or any other item or material likely to float.

Flood Duration. The length of time a stream is above flood stage or overflowing its banks.

Flood Hazard Boundary Map. An official map of a community issued by the Federal Insurance Administration on which the boundaries of the floodplain (i.e., subject to the 100-year flood), mudslide and/or flood-related erosion areas having special hazards have been drawn.

Flood Profile. A graph or plot of the water surface elevation against distance along a channel drawn for a specific flood or level of flooding.

Floodplain Regulations. A general term for the full range of codes, ordinances, and other regulations relating to the use of land and construction within stream channels and floodplain areas. The term encompasses zoning ordinances, subdivision regulations, building and housing codes, encroachment line statutes, open-space regulations, and other similar methods of control affecting the use and development of these areas.

Ground Water Recharge. The infiltration of water into the earth. It may increase the total amount of water stored underground or only replenish supplies depleted through pumping or natural discharge.

Hydrodynamic Loads. Forces imposed on structures by floodwaters due to the impact of moving water.

Hydrostatic Loads. The infiltration of water into the earth. It may increase the total amount of water stored underground or only replenish supplies depleted through pumping or natural discharge.

Letter of Map Amendment (LOMA). A letter from FEMA officially amending the effective National Flood Insurance Rate Map, which establishes that a property is not located in a FEMA SFHA.

Obstruction. Any physical barrier, structure, material or impediment in, along, across or projecting into a watercourse that may alter, impede, retard or change the direction or velocity of the flow of water, or that may, due to its location, have a propensity to snare or collect debris carried by the flow of water or to be carried downstream. Obstruction shall include, but not be limited to, any dam, wall, wharf, embankment, levee, dike, pile, abutment, protection, excavation, channelization, bridge, conduit, culvert, building, wire, fence, rock, gravel, refuse, fill, structure, and vegetation in, along, across or projecting into a watercourse.

Probable Maximum Flood. The most severe flood that may be expected from a combination of the most critical meteorological and hydrological conditions. It is used in designing high-risk flood facilities that shall be protected with minimal risk of flooding. The probable maximum flood is usually much larger than the 100-year flood.

Reservoir. A natural or artificially created pond, lake or other space used for storage and control of water. May be either permanent or temporary.

Shallow. Shallow flooding is defined as flooding with an average depth of one to three feet. Shallow flooding usually is where the water flow in the area is lower and covers more area. Water seepage in the ground is more prevalent and all construction below water level is subject to water pressure.

Special Flood Hazard Area (SFHA). Land subject to 1% or greater chance of flooding in any given year (i.e. the 100-year floodplain; see Figure 16 and Table 14). It is the land area covered by the floodwaters of the base flood on the Flood Insurance Rate Maps. The SFHA is the area where the National Flood Insurance Program’s floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The SFHA includes Zones A, AO, AH, AE, A99, AR, AR/AE, AR/AO, AR/AH, and AR/A.

Figure 16. Flood Levels

Structural Measures. Flood control works such as dams and reservoirs, levees and floodwalls, channel alterations, seawalls, and diversion channels which are designed to keep water away from specific developments and/or populated areas or to reduce flooding in such areas.

Subsidence. Sinking of the land surface, usually due to withdrawals of underground water, oil, or coal.

FEMA is the main agency that provides insurance for damage associated with flooding. Since this is a government agency, there are several prerequisites that need to be followed to receive government funding in terms of insurance coverage. Congress established the NFIP on August 1, 1968, with the passage of the National Flood Insurance Act (NFIA) of 1968, which has been modified over the years. The National Flood Insurance Program (NFIP) is managed by the FEMA and is delivered to the public by independent insurance companies.

Floods can happen anywhere, and just an inch of floodwater can cause significant damage. Most homeowners’ insurance does not cover flood damage. Flood insurance is a separate policy that can cover buildings, the contents in a building, or both, so it is important to protect these important financial assets. FEMA publication 348, Protecting Building Utilities from Flooding damage, is a good document to help protect HVAC, electrical, and plumbing systems for flooding. It provides principles and practices for the design and construction of flood resistant building utility systems.

The NFIP provides flood insurance to property owners, renters, and businesses. They work with communities required to adopt and enforce floodplain management regulations that help mitigate flooding effects. Flood insurance is available to anyone living in participating NFIP communities. Homes and businesses in high-risk flood areas with mortgages from government-backed lenders are required to have flood insurance. The National Flood Insurance Program's (NFIP) offer guidance on conducting daily operations for existing and new NFIP sellers and servicers. Information on the Write-Your-Own program, reinsurance, Risk Rating 2.0, plus the Flood Insurance Manual and other tools are available online. There also are publications, videos, graphics, and online tools that help policyholders, agents, and other servicers navigate the flood insurance process before, during and after disaster.

Most states adopt the FEMA regulations as written without any changes or additional regulations as it applies to buildings within the FEMA flood maps. Florida is the exception. Starting with the 2010 edition, the Florida Building Code (FBC) includes flood provisions that meet or exceed the NFIP requirements for buildings and structures. All counties, cities and towns are required to enforce the FBC. Many Florida communities enforce some higher standards than those required by the FBC.

The International Building Code^® (IBC) has minimal requirements for flooding. There are two locations that apply to HVAC equipment:

HVAC and utility systems are a potential target for flooding events. The first design question that is always the best is if the equipment and systems can be moved above the design flood elevation (DFE). Moving the equipment above the DFE is preferable. Check the local codes for restrictions when moving the equipment above the DFE. Moving equipment requires additional space above the DFE that is already assigned to other priorities. The spaces may require modifications to allow the equipment to be relocated. The design professionals should be involved with all relocation design application.

HVAC systems have several potential targets for flooding including equipment (boilers, furnaces, compressors, fans, and filters), piping, ductwork, and penetrations. Table 15 gives some examples of concerns for various building types. Some equipment that is below the DFE can be sealed with waterproof materials. Heat exchange or fuel-burning equipment would require barriers that reach above the DFE. Sealing ductwork is possible but expensive. Any ductwork affected by flood waters and not sealed would have to be replaced. Cleaning is not recommended because of the potential of bacterial left by the flood. Flood waters are contaminated, and equipment can be cleaned or refurbished. Flood waters also contain corrosive material. Most outdoor equipment has waterproof electrical connections at the compressor, but the controls may not be protected, and new control boxes needed for the refurbishment.

Penetrations like all normal building construction is not watertight. Even concrete construction has seams that allow a long-term flooding event to challenge. Normal construct walls are not watertight. Areas that need to be protected below the DFE will require as best as possible flood waterproofing, continuous monitoring during a flood (which means access to the areas), and a sump pump that removes any flood water entering the protected areas. HVAC, electrical, and piping penetrations need to be sealed.

Potable water systems outside of the buildings are protected by the nature of the piping systems are sealed. Any water access to the outside from the inside of the buildings and below the DFE may be contaminated and should be protected with a backflow preventer. The water supply can also be contaminated by the flooding condition. Contact local authorities for any restrictions on potable water systems during and after a flood. External piping above grade should be evaluated for potential impact of debris where water is moving.

Sewage systems are very different form potable water systems. Underground piping systems outside of the building are not sealed and will be contaminated by the flood conditions. Collection systems should be located above the DFE or protected with backflow preventers. Plugs or other methods to seal penetrations (sewage openings) in the building need to be sealed during and may be required sometime after a flooding event.

Fuel systems need attention for flooding events. Gas piping is sealed and usually protected from normal underground moisture. Aboveground thick-walled piping is susceptible to degrading from moving flood waters but will not require any additional special waterproofing treatment. Fuel tanks are outside and always a target for flooding events. Aboveground tanks need to be anchored to prevent flotation. Even if the tanks are full, at some time the fuel may be used during the flooding event and the tank to float. Protecting aboveground tanks from moving debris is also a concern and may require protection barriers (permanent to temporary).

Tanks installed below grade are anchored for potential water table issues. Waterproofing is usually performed below grade but not above grade. The access ports in a below grade tank need to be sealed and there is always a vent that needs to be elevated above the DFE. The other concern is refueling for long term events. If fuel and the generator/heating systems are required to be operational for long periods, that only solution is to move all the equipment and fuel tanks to a location that is above the DFE and accessible for refueling.

Electrical systems have many issues with flooding events. The main potential is short circuiting equipment, tripping breakers, and taking power supply systems offline. The potential targets are meters, panels, circuit breakers, appliances, electrical receptacles ground fault protection, and cables. This equipment is not waterproof and should be protected or moved is possible. Refurbishment of the electrical systems is required after a flooding event to determine all the devices that need to be replaced.

Fire protection systems are robust and not susceptible to damage or malfunction during a flood. Because of flooding, fires may start from the short circuiting of electrical systems. Design and construction of the electrical system can minimize but may never mitigate the issues associated with electrical systems and the risk of surges, sparks, and electrocution. If water is a threat from a flood or other potential water surge in the area, then the electrical system should be isolated as possible to stop all electrical circuits. Unplug electrical appliances and HVAC as appropriate. Isolate flammable or chemical substances (tanks and gas lines).

Emergency power and heating systems may be implemented at the facility. These items shall be designed and installed with flood mitigation features. These are in case of major power outages. Main power lines can also cause electrical shorts and fires in the area which could affect the building systems.

Building wall and floor construction as mentioned previously may be watertight. This is a rare case, and all construction buildings shall be evaluated to determine if the structure is worth and/or needs to be protected from flooding with flood mitigating features. Buildings can be constructed on piers to raise the building above the DFE (ASCE 24).

Wall construction made from standard non-concrete (perishable material) is susceptible to damage during flooding. These structures are not watertight and all inside contents are subject to water damage up to the DFE. When the flooding event is over, all material affected by the water damage must be remediated. This will include wood (structural framing, floors and any cabinetry), drywall, insulation, electrical (cables and receptacles), and HVAC systems (including ductwork).

Soil considerations in building system construction and design is important. Most important is when soil is saturated with water, it may heave and cause damage. No soil will protect building from water saturation and water seeking the DFE water level in all areas affected by the flood. And cavity (building space) below the DFE will see water seeping through the ground and into building structure. This water is contaminated and acidic in nature. Degradation of the building structure below grade is susceptible to damage. Cases have shown water flowing below grade can eat away metal due to electrolysis. Other considerations are degradation of the building foundation to be evaluated by design professionals. Soil outside of the building may be contaminated and treated before planting foliage.

Building categories looks at the different types of buildings and provides insight associated with that specific building type. Many items associated with systems have been discussed above about the systems and building construction. This section is in addition to the items previously discussed.

Most hospitals are designated to be functional during a flooding event. Before a flooding event, all aspects of the HVAC and utility design should have addressed mitigating the flooding potential effects. The items that need to be functional shall be protected or are located above the DFE plus 6 ft. Local codes may require more stringent requirements. Mold resistant materials should be used for the infrastructure HVAC and utility systems. This will reduce potential mold affects after a flooding event but may not eliminate all mold issues. All life safety equipment shall be protected including electrical, phones, data centers, and emergency trauma units. After a flooding event, the HVAC systems shall be evaluated for cleanliness. All equipment shall be evaluated for functionality. Mold should be removed and treated with UV systems or other types of removal. This treatment can be permanent or temporary/portable equipment. See Chapters 62 and 64 for information on UV and moisture management, respectively.

Clinics are emerging and needs to be reviewed for Flood mitigation as defined by the local authority having jurisdiction.

Museums are an important part of society and needs to be protected from a flooding event. All displays shall be moved to an elevation of the DFE plus 12 ft. All displays not being used shall be stored is a remote area that is not in any flood zone. After an event, all moisture and mold shall be quickly addressed as discussed in the hospital building category. Any displays that are susceptible to moisture degradation shall be moved or protected during and after a flooding event.

Airports, rail stations, and bus stations are in potential flood zones. These have been established and require flood mitigation evaluations. Before a flooding event airports or facilities (due to their size) shall have a plan for emergency access and egress. Areas and runways below the DFE need to be protected by levees (see ASCE 24). Planes, trains, and buses are a capital investment and will be moved as defined by their air carrier or owner. Alternate airport, train, or bus operation shall be negotiated prior to the event for continued operation. HVAC and utility systems shall be evaluated for emergency use during the flooding event. Those items necessary for safe operation of the airport or facilities shall be moved or protected from the flooding event plus 6 feet. This includes access to the airport control tower. The infrastructure that support airport operations such as baggage handling shall be addressed by each airline carrier.

Emergency facilities include incident command centers, emergency call centers, flood shelters, and potential sport stadiums that will house many displaced people during a flood shall be evaluated for mitigation during a flooding event. Emergency facilities category includes police stations, prisons, and detention centers. Before a flooding event emergency facilities shall be evaluated for a flooding event. HVAC and utility systems shall be evaluated for emergency use during the flooding event. Those items necessary for safe operation of the facilities shall be moved or protected from the flooding event plus 6 ft or as defined by the local authority have jurisdiction. This includes access of emergency personnel and operational personnel to oversee operating equipment. The infrastructure that support operations of all emergency facility functions shall be reviewed for mitigation features.

Petrochemical and industrial facilities have unique issues associated with flooding events. Caustic materials are a potential public hazard if the hazardous material is in contact with flood waters. Any potential water hazard or other airborne hazard that could be affected by a flooding event shall be evaluated for mitigation and protection of any toxic release.

Commercial and tall buildings are a potential target for a flooding event. These facilities do not usually have special requirements except for emergency egress. Some structural elements such as floating floors (isolation systems) are subject to water damage and should be mold resistant. For example, wood, plywood, fiberglass, perimeter boards, caulking material, and other elements be located above the DFE plus 6 ft.

Universities and dormitories have experienced damage from flooding. Each university shall review the infrastructure and identify the assets that need to be protected from flooding. Many facilities have the infrastructure HVAC and systems and shall evaluate the need to move or protect these items from a flooding event.

Residential and condominiums are governed by the local authority have jurisdiction.

A flood response plan is the most valuable tool when responding to a flooding event. The plan has step by step procedures for each facility to be implemented before an event and a timeline for implementing the procedures. The timeline to accomplish flood mitigation must be less that the amount of warning that would be received from the national emergency weather service. Each procedure must be validated so that it can be fully implemented in the time defined. The validation will identify if the flood doors really fit and if all the potential flooding vulnerabilities are addressed. The decision to implement the flooding procedures in not done lightly or without financial penalty. Waiting too long to implement the flooding procedures has a bigger financial penalty.

The response plan must address the equipment and personnel required to implement the flooding procedures, address the equipment and personnel that is required during the flood to keep all flood equipment (pumps and generators) running including delivery of fuel. Shift turnover must be addressed. The response plan shall address the actions required following a flooding event to restore the facilities to an operational status.

Flood plans and procedures will address the mitigation features for protecting capital assets and maintaining emergency functions. All the service within a flood target must be defined and addressed to ensure they will remain operational during a flooding event. The environment and air filtration are required to maintain air quality for all occupied areas. Outside areas that require personnel to be in flood waters shall be protected with personnel safety equipment (ropes and harnesses), handrails and nets, or elevated walkways.

Areas that are protected in the flood plans address potential entry points for water which include doors, drains, and any seam in a concrete structures. Permanent or temporary flood barriers are installed with gaskets, sealing material, and other isomeric products. Active pumping stations are implemented along with portable electrical power stations to provide power to pumps. Gas and diesel-driven pumps are usually outdoors and require hourly observation and refilling. Follow all equipment precautions for operating and refueling for safe operation of the equipment.

Flood plans will address permanent flood mitigation such a levees defined in ASCE 24. Mitigation will identify permanent or temporary barriers required to protect outdoor equipment from moving debris.