Handbook 1999 HVAC - Seismic and Wind Restraint Design

CHAPTER 53

SEISMIC AND WIND RESTRAINT DESIGN SEISMIC RESTRAINT DESIGN ............................................. 53. I Seisrnic Snu Tciwinolog~~ ............................................................................ 53.2 E.rtrriiples .................................. Ctiloil trrion.~ ............................................................................ 53.2 Instullotiort Applying S!crtic Anci1~wi.s Using I994 UBC ............................. 53.3 WIND RESTRAINT DESIGN ... Anclror B o l t s ........................................................................... 53.8 Terminology ................................................ 53.13 W d d Gl/"iciric.s ........... !. .......................................... _ _ 53.8 Calc fhr ion

LMOST all inhabited areas of the world are susceptible to tlie A tla~nnging effects of either eaitliquakes or wind. Restraints that are designed to resist one may not be adequate to resist the other. Consequently. when exposure to either earthquake or wind loading is a possibility. strength of equipnient and attachments should be evaluated for both conditions.

Earthquake tlamage to inatlequately restrained HVAC&R equipiiieiit can be extensive. Mechanical equipiiieiit that is blown off tlie support structure can become a projectile. tlveatening life and prop- erty. The cost of properly restraining the equipment is small com- Ixiretl to the high costs of replacing or repairing daniagetl equipment, or compared to tlie cost of building down-rim clue to

Design n u l installation of seismic antl wind restraints has the following primary objectives:

* Life safety to reduce the tlveat to life Reduce long-term costs due to equipment tlamage antl the resulr- ant down time

This chapter covers tlie design of restraints to limit the niove- ineiii of equipnient and to keep tlie equipment captive tluring an eanhquake or [luring extreme wind loading. Seisinic restraints and seismic isolators do not reduce the forces transmitted to tlie equip- nieiit to be restrained. Ingteatl, properly designed and installed seisinic restraints antl seismic isolators have tlie necessary strength to withstand tlie iiiiposetl forces. However, equipment that is to be restrained niust also have the necessary strength to remain attached to the restraint. Ec~uipnieiit iiianufacturers slioultl review structural aspects of tlie design i n tlie areas of atrachinent to ensure the equipment will remain attached to the restraint.

For ineclianical systems. analysis of seisiiiic and wind loading conditions is typically a static analysis, and conservative safety fac- rors Lire applied to reduce the complexity of earthquake antl wind loading response anal rid evnluatioii. T h e e aspects are consitl- eretl i n ;I properly designed restraint system.

1 . Arr(icliiiwnr of cqiiipti~t~nt ro re,srrtririt. The equipiiieiit must be positively attached to the restraint, and must have sufficient strength to withstand tlie imposed forces, and to transfer tlie forces to the restraint.

3. Rmrr i inr tksign. Strength of the restraint must also be sufficient to withstand tlie imposed forces. This should be tleterinioed by the ni:inufacturer by tests a n t h analyses.

3 . Att(ic1iiiwnt of rcsrrciinr to .siihstrir(:fnrt,. Attachment inay be by n i e m of bolts, welds or concrete anchors. The sub structure wust be capable of surviving tlie iniposetl forces.

The prepnl-nrion of rhis chnprer is nssignetl 10 TC 2.7. Seismic Restraint Design.

SEISMIC RESTRAINT DESIGN Most seismic requirements adopted by local jurisdictions in

North America are based on model codes developed by the Interna- tional Conference of Building Officials (ICBO). Building Officials and Code Administrators International (BOCA), the Southern Building Code Conference, Inc. (SBCCI). and the National Build- ing Code of Canada (NBCC); or on the requirements of the National Earthquake Hazards Reduction Program (NEHRP). The model code bodies are working through the International Code Council (ICC) to unify their model codes into the International Building Code (IBC) by the year 2000. Local building officials must be con- tacted for specific requirements that inay be more stringent than those presented in this chapter and to determine if the unified specification has been invoAetl.

Other sources of seismic restraint information include

Seisviie Restrciint Mnnuul: Guidelines for Mechanical Sysrerns, published by SMACNA (1998). includes seismic restraht information for mechanical equipment subjected to seismic forces of up to 4.7 m/s2 (0.48~). The National Fire Protection Association (NFPA) has developed staotlartls on restraint design for f i e protection systems. US. Department of Energy DOE f~430.1A and ASME AG-1 cover restraint design for nuclear facilities. Terlinicol Mwucil TM 5-809-10, published by the United States Army. Navy, and Air Force (1992). also provides guidance for seismic restraint design.

In seisinicallv active areas where governmental agencies regu- - - - late tlie earthquake-resistive design of buildings (e.g., California), the HVAC engineer usually does not prepare the code-required seismic restraint calculations. The HVAC engineer selects all the heat- ing and cooling equipiiient and, with the assistance of the acoustical engineer (if tlie project has one), selects the required vibration isolation devices. The HVAC engineer specifies these devices and calls for shop drawing submittals from the contractors, but the manufacturer employs a registered engineer to design and detail the iostal- lation. The HVAC engineer reviews the shop design and details the installation, reviews the shop drawings and calculations, and obtains tlie approval of the architect and structural engineer before issuance to tlie contractors for installation.

Anchors for tanks, brackets. and other equipment supports that do not require vibration isolation are designed by the building's structural engineer, or by the supplier of the seismic restraints, based on layout drawings prepared by the HVAC engineer. The building officials maintain the code-required quality control over the tlesigii by requiring that all building design professionals are registered (licensed) engineers. Upon completion of installation, the supplier of the seismic restraints. or a qualified representative, should inspect the installation antl verify that all restraints are installed properly and in compliance with specifications.

53.2 1999 ASHRAE Applications Handbook (SI)

TERMINOLOGY

Base plate thickness. Thickness of the equipment bracket fas- tened to the floor.

Effective shear force (Ve& Maximum shear force of one seismic restraint or tie-down bolt.

Effective tension force (T,II). Maximum tension force or pullout force on one seismic restraint or tie-down bolt.

Equipment. Any HVAC&R component that must be restrained from movement during an earthquake.

Fragility level. Maximum lateral acceleration force that the equipment is able to withstand. This data may be available from the equipment manufacturer and is generally on the order of four times the acceleration of gravity ( 4 ~ ) for mechanical equipment.

Resilient support. An active seismic device (such as a spring with a bumper) to prevent equipment from moving more than :I specified amount.

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 support. Passive seismic device used to restrict any movement.

Shear force (V). Force generated at the plane of the seismic restraints, acting to cut the restraint at the base.

Seismic restraint. Device designed to withstand an earthquake. Seismic zones. The geographical location of a facility tleter-

mines its seismic zone, as given in the Uniform Building Code or International Building Code.

Snubber. Device made of steel-housed resilient bushings ananged to prevent equipment from moving beyond an established gap.

Tension force (0. Force generated by overturning moments at the plane of the seismic restraints, acting to pull out the bolt.

CALCULATIONS

The 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. Such 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 static force, which acts in a horizontal direction at the component's center of mass. The resulting overturning moment is resisted by shear and tension (pullout) forces on the tie-down bolts. Static analysis is used for both rigid-mounted and resilient-mounted equipment.

Table 1 Coefficients for Mechanical Components Mechanical and Electrical Component or Element a, R, General Mechanical

Piping Boilers and furnaces 1.0 2.5

High deformability elements and attachments 1.0 3.5

Low deformability elements or attachments I .o I .25 Limited deformability elements and attachments I .(I 2.5

HVAC Equipment Vibration isolated 2.5 2.5 Non-vibration isolated 1.0 2.5 Mounted in line with ductwork 1.0 2.5

Dynamic Analysis I A dynamic analysis is based on site-specific ground motions

developed by a geotechnical or soils engineer. A coiniiio~i approach assumes an elastic response spectrum. The results of the tlynainic analysis are then scaled up or down :IS a percentage of the total lateral force obtained from the static analysis performed on the builtl- ing. The scaling coefficient is established by the UBC or by the governing building official. The scaled acceleration calculntetl by the structural engineer at any level in the structure c:in be tletermined and compared to the force calculated in Equation ( I ) . The greater of the two should be used in the anchor design. The horizontal force factor CIJ should be iiiultiplietl by a factor of two in either case, as shown in Table 5 .

Static Analysis as Defined in the International Building Code

The final tlrafi of the International Building Code (ICC 19YB) specifies a design lateral force Fl) for iioiistructur:iI coniponents ;IS

i I j

but FI, need not be greater than F], = l.6SD,yfI, WI, ( 2)

nor less than F = 0.3SS,,sII,W, i 3 j I'

A vertical force is specified as

Fpv = ".2SDSwp (4)

where

up = component amplification f i ' t . L or i n accordance with Table I SD,s = design spectral response acceleration at short periods as deter-

mined by SD,s = 2FUS,,/3. S,$ is the mapped spectral acceleratiuiis from Fignre I and 0 . X C F , 5 2 . 5 . F,, is a fiinction of the site soil characteristics and tiiiisl be determined i n consultntion wirh either the project geotechnical (soils) or strnctiirnl engineer. Valnes for F, are given i n Table 2.

K = component response motlilication factor in accordance wirh Table I . Nore: If expansive anchors, chemical aiichon. ur s h a l l u ~ eiiihedtled cast-in-place anchors are used. then K,, = 1.25.

I' = component importance factor in accordance with Table 3. I + 22Jh = height amplification factor where : is the height of attachment i n

the structnre and h is the average height of the roof ahove grade. The value of: should not be taken as less than 0.

W = mass of eqnipmeiit. which incliides all items attached or con- ' tained in the equipment

Table 2 Values of Site Coefficient F, as Function of Site Class and Mapped Spectral Response Acceleration at 1 s Period (S,)

Mapped Spectral Response Acceleration At Short Periods"

S,y C 0.25 S, = 0.50 S, = 0.75 S,< = 1.1111 S , 2 1.15 Site Soil Profie

Class Name

A Hardrock 0,s 0.8 0.4 (1.8 0.8

B Rock I .(I I .(I I .o I .o I . ( I

c Very dense soil 1.2 1.2 1 1 . 1 1.0 1.0

D Stiff soil profile 1.6 1.4 1.2 1.1 1.0

E Soft soil profile 2.5 1.7 I .2 0.9 n

F

nnd soft rock

See IBC Table I 6 15. I. I and Note b

Seisiiiic and Wind Restraint Design 53.3

Table 3 Seisniic Group and Occupancy Iniportance Factor

Occupancy Seismic Importance Group Factor Nature of Occupancy

I I .o All occnpancies excepr rhose listed helow

I I 1.25 I. Assemhly Group A i n which 300 or more people congregate in one area 2. E~lircarionnl Group E with an occupant load greater than 250 3. Day care centers i n Educational Group E with a capacity greater than 150 4, Insrinirioiial Group 1-2 (medical. etc.) with an occiipanr load greater than 50, no1 olherwise designated

5 . Instinitional Group 1-3 inhahired hy more [hail live persons who are under resrraint or security 6 . Any other occupnncy with an occripanl load greater than 5000 7. Power generating stations and orher puhlic utility lac

8. Water treatment facilities reqniretl for primary trearment antl disinfecrion for potable water 9. Was~e water ~reatiiient faciliries required for primary treatment.

2. Insriniiional Group I-? facilities that are hospitals 3. Designated lnsrirrrrional Group 1-2 faciliries having surgery or emergency rrenrmeiif facilities 3. Iksignared emergency preparedness ceiirers 5 . Desigiiared emergency operation centers h. Designared emergency shelters 7. Power generating stations or other utilities required as emergency hackup facilities for seismic group 111 fnc 8. Emergency vehicle garages antl emergency aircraft hangars 9. Designated commiinicatiuii cenrers

10. Avialion control lowers and air rraflic conrrol centers I I . Slriictiires containing highly toxic materials I?. Water treatmenr facilities required 10 niainraiti warer pressure for fire suppression

a Seismic Group 111 structure

es nor inclutlerl i n Seismic Group 111 and required for continued operation

111 1.5 I. Fire, rescue. and police starioiis

Table 4 Seisniic Zone Factor 2 The importance factor from the UBC (ICBO 1994) ranges from 1 to 1.5. depentling on the building occupancy and hazard level. For equipinent. f I , should be conservatively set at 1.5.

The horizontal force factor C,, is determined from Table 5 based 011 tlie type of equipment, the tie-down configuration, and the type

The weight WI, of the equipment should include all the items

Zone z

2A

28 0.20 of base. 3 4 0.40 attached or coiitaiiied in the equipment.

I 0.075 0. I 5

0.30

Table 5 Eqiiipnienr or Nonsrriicniral Components

Mechaiiical equipment. phimhing. alld electrical equipmenr alld

All eqiiipiiient resilienlly moiinred (maximiim 2.0)

Horizontal Force Factor Cp APPLYING STATIC ANALYSIS USING 1994 UBC The forces acting on tlie equipment are the lateral and vertical

forces resulting froill the earthquake. the force of gravity. and the forces of the restraint holding tlie equipment in place. The analysis assumes the equipment does not move during an earthquake, thus, the sum of the forces and iiioii~eiits must be zero. When calculating the ovenurlling lllolllellt, the vertical colnponent F ~ , ~ ~ ~ the mass is given as

I

0.75

2

assucinred piping rigidly moiiiited

h6m: S1:iok:. :lid t:inkr rllollld he c\~ahl;rIrd fol cul1lp~i:llice with Ihr :ipplic;lbk cdr?, hy :I q i ~ i l i t i e d ellgilleel:

Static Aiialysis as Defined in 1994 Uniform Building Code

The total design lateral seistiiic force is given as

Id f l~ro

F,, = total desigil laieral seismic force z = . '.

f,, = importance factor (set eqiial 10 I .5 for equipment) C,, = horizontal force factor W,, = weight of equipment i n newruns = maxs i n kilognms times stan-

Figure 2 and Table 6 may be used to tleterniine the seismic zone. The seisniic zone factor 2 can then be tletermined from Table 4. Scisirric n c . . \ . i g r r ~ ~ r . B i ~ i / t l i r l ~ , s (Army, Navy. and Air Force 1997) can also be used tu tleterniine the seisniic zone.

seismic zone facror

dard acceleration of gravity (9.8(17 lids')

The forces of the restraint holding the equipment in position include shear and tension forces. It is important to determine the number of bolts that are affected by the earthquake forces. The direction of the lateral force should be evaluated in both horizontal directions as shown in Figure 3. All bolts or as few as a single bolt may be affected.

Figure 3 shows a typical rigid floor mount installation of a piece of equipment. To calculate tlie shear force, the sum of the forces in the horizontal plane is

(7) 0 = F,, - v

"cf = Fp"/J,,/r (8)

The effective shear force V , i s

where N!,,,,, = the number of bolts in shear.


Fig. 1 Maximum Considered Earthquake Ground Motion for the United States 0.2 s spectral response acceleration (‘70 g) (S% of critical clamping) Sire Class B

Seismic and Wind Restraint Design 53.5

Fig. 1 Masiniuni Considered Eartkquake Ground Motion for the United States (Corzh'rzued) 0.2 s spectral response nccelerarioii (% s) (S% ofcriIical tlnniping) Site Class B


Table 6 International Seismic Zones Seismic

Conntrv citv Zone

Albania Tirana Algeria Alrien

Angola Antigua and Barbuda Argentina Armenia Australia

Austria

Azerbaijan Bahamas Bahrain Bangladesh Barbados Belams Belgium

Belize Benin Bennuda Boliuia Botswana Brazil

Bmnei Bulgaria Burkina Fasu Burma

Bumndi Camerwn

Can&

Cape Verde Central African Republic Bangui Chad Republic N’Diamena Chile China

Santiago Beijing (Peking!) Chengdu Guanrnhou (Canton)

Colombia

Congo Costa Rica Cuba

Czech Republic Denmark Djibouti Dominican Republic EcUdddOr

CypNS

Egypt

El Salvador Equatorial Guinea Ewnia Ethiopia

Fiji L\lantL\ Finland France

Gabon Gambia Georgia Germany

o r i n Luanda SI. lohns Buenos Aiies Yerevan Brisbane Canberra Melbourne Pellh Sydney Salzburg Vienna Baku Nassau Manama Dhaka Bridgetuwn Minsk Antwerp Brussels Belize City Cotonou Hamilton La Paz Gaborone Belo Horizonte BriLdia Pono Alegre Recife Rio de Janeiro si0 Paul0 Bandar Seri Begawm Sofia

Mandalay Rangoon B uj umbu t a Douala Yaounde Calgary Halifax Montreal Ottawa Quebec Toronto Vanwuvei Praia

Ouagadougou

Shanihai Shenyang (Mukden) Barranquilla

Branaville San Jose HavaIU Nicosia Prague Copenhagen Djibouti Santo Domingo Guay aquil Quito Alexandda

Bogota

Cairo San Salvador Malabo Tallinn Addis Ababa Asmura Suva Helsinki Bordeaux Lyon Mai>eille Pails Strasbourg Libreville Banjul Tbilisi Berlin

3 4 4 0 3 0 3 I 1 I I I ZB

3 (1 (1 3 3 I 1 I I 0 0 3 0 0 0 0 0 0 1 I 3 0 3

2B 3 0 (1 1 I

2A 2A 3 I 3 0 (1 0 4 3 3

2B

4 2B 3 0 3 1 3 1 I 3 3 3 4

ZB 2B 4 0

2A 3 3 3 I

2B I

2B 0

2B 0 0 3 0

2n

zn

~

Seismic Zone

Getm:iny (Ginrinired) Duaaeldot I Fr:inktiiit

Ghana Greece

Gi.rn:id:t Guatemala Guinm Guinea-Biss;iu guy an^ Haiti Hondura Hung Kong Hungary Iceland 1ndi:i

1ndonesi:i

Itaq Ireland Israel

Itilly

Ivoly Coast 1:im:iic;i Japan

lorilan K:lz;ikhstm Kenya Kotea Kuwait Kyrgyzstan L o s Latvia Lebzinun Lesotho Liberia Lithuania Luxembourg Madagascar Malawi Malaysia Mali Republic Miilta Martinique M;iuritani;i Mauritius Mexico

Moldo\,a Morocco

Moz;imbique Nep:il Netherlands

Netherhds Antillea New Zeal:ind

Nicaragua Niger Republic Nigeiia

Hiiiiibiitg Municli

Accr:t Athens Theaa;tloniki St. Geuige’s Gu;item:il:t City Conakry Biaa:iu Grorgetown Pon-:iii-Prince Teguci g:ilpn Hung Kong Biid;ipeat Reyk;:ivik Boinb:iy C:dcun:i M;idr:is New Delhi Jak~It1;l Med;in Suiah:ty:i Bzighd:id Dublin Jeiuaalem TeI Aviv Flot ence Genoa Milm N:iples Palermu Rome AbiiIj:iii Killguun Fukuoka Kube N‘lllil 0kin:iw:i 0aak:i s:lppoto Tokyo Ammm Almi-At:) Nairobi Seoul Kuwait Bislikek Vienti:ine Rig:) Beiiut Maseiu Mont w i : i

Vilnius Luxenibuuig Anfaniinaiivu Lilungwe Kuel:i Luitipur Barnako V:lllert:l M:titiniipe Nou:ikcliun Putt Louis

Sning:tit

M:it:inioi us Meild:i Mexico City Monterrey Nuevo L:~redo Tijii:iti:i Kishinev C:isabl;inc:i R:ibat Mtiputu K;rhm;lnlhl Ainateid:tm The Hague Ctir:ic:io Aiickl:tnd Wellinyuii M:in:igu:t Ni:iiney K:idun:i

I I (1 I

2B 3 3 4 3 4 0 0 0 3 3

2B

4 3

2B I

2B 3 3 3

0 3 I 3

2B 2B 2B 4

3 3 3 3 3 3 3 3 4 3 4

2B 2A

I 4 I I 3

I I I 0 3 I 0

3 0 0

2B 3 3 (1 0 3 0 0 3

2B 2B

2B 3 (1 0 3

4 4 0 0

?n

211

zn

2n

213

2n

2n

Seismic Coiintry City Zime

Oalo 28

P:iit:iina P:ipii:i New Ciuiiiea

Peru Philippines

P:uilgll:ly

Pol:lnd

Rw:inda Siiuili Ai;ihin

Spiiiii

Sii Liitik:~ Sutlm Surin:inte S w;izil;ind Swedert Switzer1:ind

Togo Trinidad :ind Tob;igo Tiiniai:, n l l k e y

TiirLiiienist:iii Ug:llLd:l Uki:iiiw United Arab Emii:rtea

United Kingdotii

u1ugu:ty Uzbekisr;ai Vaticm City Vellezue1;l

Metn:im Yeitten Acib Repiibli~

Yugual;wi;i

Zjire

Zimhi:i


Fig. 1 Seisniic Zone Map of the United States (Krpiudiiced from the 1994 edition of the L/it$mii Briildiiig Coik with permission of the puhlisher. rhe Iiileriinlionnl Conference of Building Ofticinls.)

J i T +- D 1

FRONT VIEW SIDE VIEW

Fig. 3 Ecluipntent with Rigidly Mounted Structural Bases

The restraints shown in Figure 3 have two bolts on each side, so t11at four bolts are in shear. To c:dculate the tension force, the sum of the I I I U I I I ~ I ~ ~ S for overturning are as follows:

Fl,h,,, - ( Wll - F1,/3)( D 112) - T D I = 0

For the exainple shown i n Figure 3 . two bolts are i n tension. The effective tension force Tfl, where overturning affects only one side. is

The shear and tension forces (Vaiiil T ) should be calculated intle- pentlenrly for both axes as shown in the front and side views. The worst case governs seismic restraint design; however, the direction of seisinic loading that governs the design in not always obvious.

For example. if three bolts were installed on each side, the lateral force applied as shown i n tlie side view affect six bolts in shear and a minimum of two i n tension. The lateral force applied as shown on the front view results in six bolts affected in shear and three in tension. Also. Dl and D? are different for each axis.

Equatioiis (6). (7). and (X) may be applied to ceiling-mounted equipment. Equation (9) must be modified to Equation (1 1) because the mass of the equipment adds to the overturning moment. Sum- ming the moineiit~ determines the effective tension force as

Interaction Formula. To evaluate the combined effective tension ancl shear forces that act simultaiieously on the bolt. the following equation applies:

The allowable forces TIII,,,,, and y,//,,H, are the generic allowable capacities given in Table 7 for wedge-type anchor bolts.

Tahle 7 Typical Allowable Loads for Wedge-Type Anchors

Diameter, mm Tfl//ow. kN V h w kN

13 2.6 5.3 16 4.0 9.8 19 6.0 13.3

No:e.v: I . The :illowable tensile IUICA ;W For imiall;ttions without speciill inxpeLrion (torque

2. Addition;il tension :ind slie:ir v:iIue\ inay be obtained from published ICBO repona. lest) nnd inay be doubled i t tlie imt;illation is inxpected.

1999 ASHRAE Applications Handbook (Sl) 53.8

ANCHOR BOLTS Several types of anchor bolts for insertion in concrete are manu-

factured. Wedge and sleeve anchors perform better than self-drilling or drop-in types. Epoxy-type anchors are stronger than other anchors, but lose their strength at elevated temperatures (i.e., on rooftops and in areas damaged by fire).

Wedge-type anchors have a wedge on the end with a small clip around the wedge. After a hole is drilled, the bolt is inserted aiid the external nut tightened. The wedge expands the small clip, which bites into the concrete.

A self-drilling anchor is basically a hollow drill bit. The anchor is used to drill the hole and is then removed. A wedge is then inserted on the end of the anchor, and the assembly is drilled back into place; the drill twists the assembly fully in place. The self-(lrill- ing anchor is weaker than other types because it forms a rough hole.

Drop-in expansion anchors are hollow cylinders with a tapered end. After they are inserted in a hole, a small rod is driven through the hollow portion, expanding the tapered end. These anchors are only for shallow installations because they have no reserve expaii- sion capacity.

A sleeve anchor is a bolt covered by a threaded, thin-wall, split tube. As the bolt is tightened, the thin wall expands. Additional load tends to further expand the thin wall. The bolt must be properly pre- loaded or friction force will not develop the required holding force.

Adhesive anchors may be in glass capsules or installed with various tools. Pure epoxy, polyester, or vinyl ester resin adhesives are used with a threaded rod supplied by the contractor or the adhesive manufacturer. Some adhesives have a problem with shrinkage; oth- ers are degraded by heat. However, some adhesives have been tested without protection to 590°C before they fail (all mechanical anchors will fail at this temperature). Where required. or if there is a concern. anchors should be protected with fire retardants similar to those applied to steel decks in high-rise buildings

The manufacturer’s instructions for installing the anchor bolts should be followed. Performance test data published by manufac- turers should include shock, fatigue, antl seismic resistance. IBCO reports have further information on allowable forces for design. Add a safety factor of two if the installation has not been inspected by a qualified firm or individual.

WELD CAPACITIES 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 if 110 MPa on the throat section of the weld. The section length is 0.707 times the specified weld size.

For a 1.5 mm weld. the length of shear in the weld is 0.707 x 1 .5 = 1.06 mm. ’The allowable weld force (FJollmw fur a 1.5 inin weld is

(Fw)ullow = 1.06 x 110 = 117 N per millimetre of weld

For a 3 mm weld, the capacity is 233 Nhnm. The effective weld force is the sum of the vectors calculated in

Equations (8) and (10). Because the vectors are perpendicular, they are added by the method of the square root of the sum of the squares (SRSS), or:

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

SEISMIC SNUBBERS Several types of siiubbers are manufiicturetl or field fabricated.

All siiubber assemblies should iiieet the following minimuin requirements to avoid imparting excessive accelerations ro rhe HVACRrR equipment:

Iinpact surface should have ;I high-quality elastuineric surface that is not cemented i n place Resilient material should be easy ru inspect fur damage ant1 be replaceable if necessary Assembly must provide restraint in :ill directions Siiubbers should be tested by an intlepentlent test laboratory (ant l analyzed by a registered engineer to ensure the stated load capacity and) to avoid serious design flaws.

Typical snubbers are classified as Types A through J (see Figure 4). Many devices are presently approved with Office of Statewide Health Planning Development (OSHPD) ratings.

Type A. Snubber built into :I resilient mounting. All-directional, inoltletl bridge-bearing quality neoprene element is ;I ininiinuin of 3.2 nini thick. Mounting must have :I minimum of two anchor bolt holes.

Type B. IsolatorRestraint. Stable isolation spring bears on the base plate of the fixed restraining member. Earthquake motion of the isolated equipment is restrained close to the base plate, ininimiz- ing pullout force tu the base plate anchorage.

‘Qpe C. Spring isolator with built-in all directional resrraints. Restraints have inoldeil neoprene eleinents with a miniinuin thickness of 3.2 min. A neoprene sound pad should be iiisralletl between the spring antl the base plate. Sountl pads below the base plnte :ire not recommentletl fur seismic installarions. The base plate shoultl have a minimum of four anchor bolt holes.

Type D. Integral all directional snubber/restrainetl spring isolator with AASHTO quality rep1 ible neoprene element. The all weltled housing has a miniinum of two nndhor bolt holes fur attachment to the structure.

Type E. Fully bonded neoprene mount capable of withstanding seismic loads in a11 directions with nu metal-to-mete1 cuiit:ict. Outer hosing must be ductile iron and have a minimum of two nnchor bolt holes.

Type F. All-directional with muliletl, replaceable neoprene ele- nieiit. Neoprene element of bridge-bearing quality is ii ininiinuin of 4.8 nim. Snubber must have a inininium of two anchor bvlt hvles.

Type G All-directional lateral siiubber. Reinforced AASHTO quality neoprene element is a minimum of 6.4 inin thick. Upper bracket is weltled to the equipment antl the base plate has :I inini- mum of two anchor bolt holes.

Type H. Restraint for fluor mounted equipment consisting of interlocking steel assemblies lined with resilient elastomer. Bolt to equipment antl anchored to structure through slotted holes tu allow field adjustment of restraint fur 6.4 i n i n clearance i n the hurizontnl aiid vertical directions. After final adjustment. weld anchor to floor bracket antl angle clip tu equipment to assure nu slip caii occur. Alternately, fill slots with epoxy grout tu prevent slip. The restraint assembly rating is certified by intlepentlent laboratory test.

Type I. Single axis, single direction lateral snubber, ribbed AASHTO quality neoprene element is a minimuni of 6.4 inin thick. Minimum fluor mounting is with two anchor bolts. Must be useil in sets of 4 or more.

Type J. Prestretcheil aircraft wire rope with galvanized end connections that avoid bending the wire rope across sharp edges. This type of snubber is mainly used with suspended pipe duct and equipment.


TYPE A

TYPE E

TYPE H

TYPE D

TYPE B TYPE C

TYPE F

TYPE I

& TYPE G

Fig. 4 Seismic Snubbers

EXAMPLES

The following exainples are provided to assist in the design of equipineiit :iiiciior:ige to resist seisinic forces. Assume seismic zone 4 Tor all ex;iinples.

Esatnplc 1. Aiichurnge tlesigii I’ur eqiiipmenr rigidly muiinretl I U rhe striic-

Froin Equations ( 5 ) niid (6) . cnlciilare the lateral seismic force nntl

r i m (see Figure 5 ) .

its vertical cuinputieiir:

F,, = 0.4 x I .5 x 0.75 x 4500 = 2025 N F,,,, = F , / 3 = 7-015/3 = 675 N

C‘nlciilale ihe overniriiitig iiiuiiietii (OTM):

0 T M = F p h C g = ( 1 0 2 5 X I .U) = 2025 N , 111 (14)

W, 4500 N ANCHOR BOLT

Fig. 5 Eqtiipnient Rigidly Mounted to Structure (Example 1)


Calculate the resisting moment (RM):

RM = (WP+Fp)dmi,/2

= (4500f675)0.70/2 = 1811 or 1339N . m (15)

Calculate the tension force T, using RM,”, to determine the maximum tension force:

T = (OTM- RMmin)/dmin = (2025 - 1339)/0.70 = 980 N

This force is the same as that obtained using Equation (9).

(16)

Calculate Te8per bolt from Equation ( 10):

Tc/, = 980/2 = 490 N/holt

Calculate shear force per bolt from Equarion (8):

k&, = 2025/4 = SO6 N/holr

Case 1. Equipment ottuched t~ (I riniher .structure

From the National Design Specification f o r W ~ o d Cr~nsrrrrction W S ) (AFPA 1997). Selected fasteners must he secured to solid Ium- her, not to plywood or other similar material. The following cnlcula- tions are made to determine whether a 13 mm diameter, I00 mm long lag screw will hold the required load.

From Table 8.IA in the NDS, which is inch-pound units, for Group IV (mixed species), G = 0.35, and from Tahle 8.6A the allowable with- drawal load is 203 Ib/in. X 4.45 N/lh/(2.5.4 iniiilinj = 35.6 N/rnni, and in the NDS,

TOrr,,,,, = (35.6 N/mm x 88 mm penerration)U3 = 2090 N

where the factor 2/3 accounts for rhe facr that ahout one-third of rhe length of a lag screw or bolt has no threads on the shank.

From Table 8.6C in the NDS,

VollOw = 800 N

Other types of wood may he used with appropriate factors from Table 8 andor other reductions as specified in Part I1 of the NDS.

In timber construction, the interaction formula given i n Equation (12) does not apply per Section 8.6.8 of the NDS. The ratios of the calculated shear and tension values ro the allowable values should each he less than 1 . 0

T / T = 490/2090 = 0.23 < 1.0,

v/ Vorr”w = 506/XOO = 0.63 < I .o

?herefore, a 13 mm diameter, 100 mni long lag screw can he used at each corner of the equipment.

Case 2. Equipment artuched tu concrete with p o s r insrulled onchor.~. It is good design practice to specify a minimum of 13 mm diameter

bolts to attach roof or floor-mounted equipmenr tu the strucnlre. Derer- mine whether 13 mm wedge anchors withour special inspection provisions will hold the required load.

From Table 7, Tu,,, = 2600 N and l$l,,,v = 5300 N From Equation ( 12).

Therefore, 13 mm diameter, IOU mm long post drill-in anchors can he used.

If special inspection of the anchor installation is provided by qualified personnel, TUlbw only may he increased hy a factor of 2.

Case 3. Equipment attached ~ I J steel For the case where equipment is attached directly to a steel mern-

her, the analysis is the same as that shown i n Case I ahove. The allowable values for the attaching holrs are given in the Manrid c!f Steel Construction (AISC 1989). Values for A307 bolts are given i n Table 8.

Table 8 Allowable Loads for A307 Bolts

Diameter, mm T,,ttnw,. kN v,,rt,>w,. jt b . mm2 13 17.3 8.7 I2h I 6 27. I 13.8 19s 19 39. I 19.6 2s5 25 69.8 3.5. I 506

The interaction formula given in Equation (12) does iiut apply ru steel-to-steel connections. Instead, rhe allowahle tension load int ist he modified as i n the following equation:

( 7 ; l / t , d ,,,,,,, = F, A,

where

F, = 116- I.X(V/N,,,,/,ArJ5 140(4/3) = 187

V/Nr,,,/, is i n kiluiiewlons and F, is i n kilopnscals. The 33%; stress incrense(4/3) is allowed for short-term loads such as witid or earthquakes.

Example 2. Anchorage design for eqiiipment supported hy exlernal spring mounts (see Figure 6).

A mechanical or acotrslical consultant should choose the type of isolator or sniihher or cotnhination of the two. Then the product v e n h r should selecr the acnial spring snuhher.

Assume that the center of mass, which is ahhreviared cg (center u t gravity) i n this chapter, (cg) of the equipment coincides with the ceiiler of mass of the isolator group.

If T = maximum tensioti on isolator. C = mnximiim compression on isolator, and

Fp,, = Fp /3. then

To find maximum Tor C, set dT/dq = 0:

W, = 4500 N

I I

EXTERNAL VIBRATION ISOLATOR/SNUBBER

Fig. 6 Equipnient Supported by Esternal Spring Mounts


f T o r C ANCHOR BOLT r--+-t--v HOLE (2)

Height =

.--

ELEV PLAN

Fig. 7 Spring Mount Detail (Esaniple 2)

From Eqnations ( 5 ) and (6 ) .

F , = 0 . 4 x l . 5 x 2 x U . 7 5 ~ 1 2 = 10.8 IrN

F,,>, = F,, /3 = 10.8/3 = 3.6 k N

From Eqiiations (I 8) and (19).

T = -2.IO+X.93 = 6.83 kN

c = -3 .90- s.93 = - 1 2 . ~ 3 ICN

Calciilate the shear force per isolator:

v = F / , / N i > , , = IO.X/J = 2.70 kN ( 2 0 )

This shear force is applied at the operating height of the isolator. Uplilt teiisioii Toil the vihration isulatiir is the worst conditioii for !he design u l he anchor holts. The cumpressiuii force C niust he evalnxteil 10 check the acleqlracy of h e striicttire to resist the loads (Figure 7).

(T ,&( perhqlt = T / 2 = h.R3/2 = 3.42 IrN

The valne uf(T2)<.tper bolt h e to overturning on the isolator is

V x Optimum height (Tr Lff = 0.85dN,,,,,

where d = distance from edge of isolator hase plate to center of hul l hole.

y,fl = 2.70/2 = 1.35 kN

Delermine whether I 6 inni post drill-in anchors with .spi&il i i is/~crtioii will handle this load. From Equation (12) and Tahle 7.

Therefore. Ih nini post ilrill-ill anchors will carry the load

Esainple 3. Anchorage design tor eqiiipment with a center of niass differ- en1 lrom that of the isolator group (see Figure 8).

~\irr/i,rrI,n,/ierties: I, = 48': I,. = JL'

PLAN

equip.

Wp = 11 kN h,, = 1 . 0 m

B = 0 .51 m L = 0.76 m

e, = 0.20 m ey = 0.10 m

Fig. 8 Equipnient with Different Center of Mass than Isolator Group (in Plan View)

LI L . T,,, = 5, cos+ + - sin+)

1 I? '

Vertical reaction h e to eccentricity:

Vertical reaction tlue to Wt;

( ' L ) r n m /min = ( )mux/min '4

Tmw = Tm + (T, + ('w)mo,

T,,,i, = T,,+(T.),,,i, +(T,+,),,,in (tensioaiPpositive)

Horizoirtd rccictioiis: Horizontal reaction due to rotation:

VJi, = F P / 4

yn0, = v,,;, + V , , ~ : - ~ V ~ , , , V ~ ~ , c 0 s ~ ) 0 . 5

From Equations ( 5 ) and (6 ) ,

F,, = 0 . 4 ~ 1 . 5 ~ 2 ~ 0 . 7 5 x I I = 9 . 9 k N

F,," = 9.9 /3 = 3.3 ldrl

I, = 4(0.51)' = 1.04 ni'; I, = 4(0.76)* = 2.31 m2

From Eqnations (21) throiigh (24).

e = 3 3 . ~ 6 ~ 5 = 63.430

p = 150.43" 0 = 33.R6'

53.12

From Equation (25),

(Wn)mar/n,in = 14.3 or 7.7 kN

From Equation (26),

T, = 9.9(0.407 + I).IR3) = 5 3 4 kN

From Equation (27).

(Tc),rrr,min = 0.1148(Wn) ,nu,/,n in = l . 6 4 k N o r 0 . 8 8 k N

From Equation (28),

(T,.)mar,min = 3.5X kN or 1.93 kN

From Equation (29),

T,,, = 5.84 + 1.64 + 3% = I I.O6 kN

From Equation (30).

Tmin = 5.84 +0.88 - 1.93 = 4.79 kN (tension)

From Equations (3 I), (32), and (33),

v ,,,, = 9.9X0.061 = 0.6OkN

Vdir = 9,9/4 = 2.48 kN

V,”,, = 3.02 kN

The values of Tmin antl V,, nre used to design the anchorage of the isolators and/or snubbers, and T,, is used to verify the adequacy of the structure to resist the vertical loads.

Example 4. Anchorage design for equipment with snpports antl bracing for suspended equipment (see Figure 9). Equipment weight W,, = 2200 N.

Because post drill-in anchors may not withstand published allowable static loads when subjected to vibratory loads, vibration isolators should be used between the equipment and the strucnire to dampen vibrations generated by the equipment.

From Equations (5 ) and (6),

Fp = 0.4 X 1.5 X 2 X 0.75 x 2200 = 1980 N Fpv = 1980/3 = 661) N

From Equation (14).

OTM = 1980 x 0.30 = 594 N . m

From Equation (10),

RM = (2200 f 660)0.90/2 = 1287 or 693 N m

Because RM is greater than OTM, overnrrning is not critical

Force to the hanger rods:

T = ( Wp + Fp,)/4 = (2200 + 6611)/4 = 7 15 N .ff

Force in the splay brace = f i F , = 2800 N at a I: I slope

Due to the force being applied a1 the critical angle, as i n Example 2, only one splay brace is effective in resisting the lateral load FF If eccentricities occur, as in Example 3, n similar method of analysis mnst be done to obtain the design forces.

Design of hanger ro&vihrurion isolutor crnd connecrion ro .striicfiir’

When installing post drill-in anchors in the underside of a concrete beam or slab, the allowable tension loads on the anchors must be reduced to account for the cracking of the concrete. A general rule is to use half the allowable load.

Determine whether a 13 mm wedge anchor with special inspection provisions will hold the required load.

1999 ASHRAE Applications Handbook (SI)

STRUCTURE ABOVE

VIBRATION ISOLATORS

HANGERROOS

SPLAY BRACE

0.30 m

PLAN Note: The splay braces are prestretched aircraft cables with enough slack so that the isolators can fully function vertically.

Fig. Y Supports and Bracing for Suspended Equipment

T = 2600 x 0.5 = I 300 N > T,,,;f = 7 15 N

Therefore. a 13 mrn rod and post drill-in anchor should he u\ed :iI each corner of the unit .

For anchors installed without special inspection.

7;,/ ,,,,“ = I300 x 0.5 = 650 N < TP,;, = 7 I S N

Therefore, a lnrger anchor would have to be chosen.

Design ojspIuy broce nnd corinrcriorr ro srriicrtire

Force i l l the slack cable = 28110 N

Force in the connection to the strucnire:

V,, ,,,, = 2 8 O O / f i = 19RON

Derertiiine whether a 19 mni wedge-type anchor will hold ihe required load. From Table 7:

T,, ,,,, = 5, = 19RON

= 6000/2 = 3OOll N Vullmv = 13 300 I\’

From Equation (12).

Therefore. i t is permissible to use a 19 mm anchor or mulliple anchors of a smaller size holred through a clip and to the structure.

Because the cnhle forcer are relatively small. n 9.5 mm aircl.nfl cable attached to clips with cahle clamps should be used. The clips. ill turn, may be attached to either the strticnire or the equipment.


INSTALLATION PROBLEMS TERMINOLOGY

T \ ~ ~ following slloultl be collsitlerell wllell installillg seislnic Classification. Buildings and other structures are classified for

Basic wind sneed. The fastest metre-oer-second wind weed at wind load design according to Table 9. restraints.

Anchor location affects the required strengths. Concrete anchors should be located away froin edges. stress joints, or existing frac- tures. ASTM Sfaiukird E488 should be followed as a guide for edge distances atid ceiiter-to-center spacing. Concrete anchors shoultl nut be too close together. Epoxy-type anchors can be closer together than expansioil-type anchors. Expansion-type aiichors (self-drilling and drop-in) can crush the concrete where they expand ant1 impose internal stresses in the concrete. Spacing of all anchor bolts should be carefully reviewed. (See nianufacturer's recominendations.) Suppletnent:iry steel bases and frames, concrete bases. or equipment inotlificarions may void sollie inanuf;icturer's warranties. Snubbers. for example, should be properly attached to a subbase. Buiiipers niay be used with springs. Static :inalysis does not account for the effects of resonant contli- tions within a piece of equipment or its components. Because all equipinent has different resonant frequencies during operation antl nonoperation, the equipiiieiit itself might fail even if the restraints do not. Equipment niouiitetl inside ii housing should be seisinically restrained to iiieet tlie same criteria as the exterior restr:iints. Snubbers uset1 with spring inuuiits should withstand motion i n a11 ilirectiuiis. Suine snubbers are only tlesignetl for restraint in one direction; sets of snubbers or snubbers tlesignetl for multitlirec- rion:il purposes should be used. Equipinent iiiust be strong enough to withstand the high deceler- ation forces developed by resilient restraints. Flexible connections should be provided between equipinent that is braced and piping and tluctwork that need not be braced. Flexible connections should be provided between isolated equip- inetit and braced piping antl tluctwork. Bumpers iiistalletl to liiiiit horizontal iiiotioii should be outfitted with resilient neoprene pads iu soften the potential inipact loads of the equipinent. Anchor installations should be inspected; in inany cases. damage occurs because bolts were not properly installed. To develop the rated restraint, bolts should be installed according to maiiufac- turer 's recoiiiiiientlati;ns. Brackets in structural steel iittacliiiieiits should be matched to reduce bending and internal stresses at the joint. Rigid seismic restraints should not have slotted holes.

WIND RESTRAINT DESIGN Dainnge done to I-IVACkR equipinent by both sustained antl

gusting wind forces has increased concern about the adequacy of the eiluipineiit protection that is defined in design tlocuments. The following calculative procedure generates tlie same type of total design lateral force that is used in the static analysis of the seismic restraint. This means that the value that is tleterinined for the design wintl force F,,, can be substituted for the total tlesigti lateral seismic force F,) when evaluating antl choosing restraint devices.

Odicr Sirrrcriirrs, includes design guitlelines for wind, snow. rain ant l earthquake loads. The equations. guitlelines. and data presented here are G.oin an earlier version o f this stantlard and only cover non- structural coinponents. The cuiyeiit stantlartl includes inore coinpre- heiisive antl rigorous procedures for evaluating wind forces antl wind resiraint.

ASCE S f ~ l i l ( / ( ~ ~ d 7-93. M ~ J I ~ I I I I I I I I D O . S ~ ~ I I LOCIC~S for B ~ ~ i k l i ~ t g , ~ ( I I ~

~~

10 in above the g k u n t l of Terrain Expos& C (see Table I0)having an annual probability of occurrence of 0.02. Data in ASCE Srun- ckird 7 or regional cliniatic data may be used to determine basic wind speeds. ASCE data does not include all special wind regions (such as iiiountainous 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 circunistances. regional climatic data may be used provided that both acceptable extreme-value statistical-analysis procedures were used in reducing the data and due regard was given to the

Table Y Classification of Buildings a n d Other Structures for Wind Loads

Repiinral with peiiiiisaioii from A X E SIMdard 7-93.

Nature of Occupancy Category All builtlings ant1 structiires except those listed below I

11 Builtlings nntl strnctures where the primary occupancy is one in which more thaii 300 people congregate in one mea

Biiiltlings nntl structures tlesignntetl as essential facilities, inclntlii~g. hut not limited to: - Hospital ant1 other medical facilities having surgery or

emergency trea~ment areas - Fire or rescue and police stations - Srriicrirres and equipment in government - Commtinicnrion centers and other facililies required for

-Power stations ant1 other iililities reyuiretl in an emergency - Structures having critical nationnl defense capabilities - Designnteil shelters for hnrricnnes

Builtlings and structures that represent a low huard 10 human life i n the event of failore, such as agricultural buildings, certain temporary facilities. ant1 minor storage facilities

111

emergency response

IV

Table 10 Definition of Exposure Categories Repiiinal with peiiiiisriuii hum ASCE Standard 7-93.

~ ~~~~

EspGure A. Large city ceniers with at least 50% of the buildings having a heighl i n excess of 2 I in. Use of this exposure category is limited to those areas for which terrain represenlolive of Exposure A prevails in the upwind direction for n distance of' at lens1 ROO m or 10 times the height of the building or structure, whichever is greater. Possible chnnneling effects or increased velocity pressures due to the building or striicnire being located in the wake of adjacent buildings needs to be considered.

Exposure E. Urhnn antl snhurban areas. wooded ueas, or other terrain with ~nimero~~s closely spaced ohstrnctions having the size of single-family dwellings or larger. Use of this exposure category shall be limited to those areas for which lerraiii representative of Exposure B prevails in the upwind direclion fora tlislnnce ofnr lens1 450 m or 10 times the height of the huilding or structure, whichever is grenler.

Esposure C. Open terrain with scntteretl obstructions having heights geiiernlly less than 9 111. This cnlegory includes flat open country and grasslantls.

Exposure D. Flat. nnohslructed areas exposed to wind flowing over large bodies of water. This exposlire shall apply only to those buildings and other slriiclures exposed 10 the wind coming from over the water. Notes: I . HVAC conipoiieiitr for biiildiiigr with :I i ~ i e m ruuf height of I R m or Itss are

derigned on f l ie h:irir of Expuriire C. 2. HVAC conipuneiitr UII hiiildings witli ii iiieiin iuuf height grater than I 8 m a i d other

r ~ r i i c ~ i i t e ~ :ire dr\igiied oil flu b:rsis ufthe exposure categolies defined in this ruble excepl iisrunie Exporum B f i r buildiugh and u i t w situdures sited in terrain repre- reiitiiti\'e of Expitire A.

53.14 1999 ASHKAE Applications Handbook (SI)

Table 11 Importance Factor (Wind Loads) Reprinted with permission fioin ASCE S t a d i d 7-93.

Importance Factor I, 160 km from hurricane ocean

Category line and in other areas At hurricane ocean line I I .oo I .os II I .07 1 . 1 1

111 I .07 1.11 IV 0.95 I .oo

NOteS: I . Table 9 lists the building and stmctuie classification ciitegurih. 2. Determine I , by linear interpolation for legions between the hurricane ocean h e

3. Typical hurricane ocean l i n s are the Atliintic ;ind Gulf of Mexico coastiil ;iieiih.

and 160 km inland.

length of record, averaging time, anemonleter height, data quality, and terrain exposure. One final exclusion is that tornadoes have not been considered in developing the basic wind-speed distributions.

Design wind force. Equivalent static force that is assumed to act on a component in a direction parallel to the wind and not necessar- ily 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 (see Table 11). For humcanes, the value of the importance factor can be lin- early interpolated between the ocean line and 160 kin inland because wind effects are assumed negligible at this distance inland.

Gust response factor (Gz). A factor that accounts for the fluctu- ating nature of wind and the corresponding additional loading effects on HVAC components.

Minimum design wind load. The wind load may not be less than 500 Pa multiplied by the area of the HVAC component pro- jected on a vertical plane that is normal to the wind direction.

CALCULATIONS Two procedures are used to determine the design wind load on

HVAC components. The analytical procedure, which is described here, is the most common analysis method for standard component shapes. The second method, the wind-tunnel procedure, is incorporated in the analysis of complex and unusual shaped components or equipment that are located on sites that produce wind channeling or buffeting due to upwind obstructions. The analytical procedure produces design wind forces that are expected to act on HVAC coinponents 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 metre-per-second wind speed.

Analytical Procedure The design wind force is determined by the following equation:

(34)

where F, = design wind force, N Q: = velocity pressure evaluated at height .f above ground level. Pa C: = gust response factor for HVAC components evaluated at height :

Cf = force coefficient (Table 12) Af = area of HVAC component projecretl on a plane normal ro wind

Certain of the above 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

h o v e ground level

direction. m2

Table 12 Force Coefficients for HVAC components, Tanks, and Siniilar Structures

Repriiiteil with pe~inission fiuin A S G Srnndrritl7-93.

Shape Square

(wind normal to face)

Square (wind along tlingonnl)

Hexagonal or octagonal

CO,& > 2.5)

Round (D& > 2.5)

Cf fur L/D Values ol:

Q p c of Surl‘ace 1 7 15

All 1.3 1.J 2.0

All 1.0 1 . 1 1.5

All 1.0 1.2 1.4

Moderarely smooth 0.5 0.6 0.7 Rough ( D / D = 0.02) 0.7 0.8 0.9 Very rough (DID = 0.08) 0.4 I . ( I I .2 All 0.7 (1.4 1.2

Table 13 Esposure Category Constants Repriinal with peiiii iaaioii fioiii ASCE Srn!atrn/ 7-93.

a ic n,, Exposure Categury

A 3.0 450 U.02S B 4.5 360 0.010

C 7.0 270 0.005 D 10.0 210 0.003

(35j

bvhrre

p = air mass density. At 1S”C and 101.315 kPa the densiry u t dry air is I .22 kg/m3.

Kz = velocity pressure exposure cueflicienl evnliinted nr heighl :, nhove groiind level. The valiie of K: is determined hy the fulluwiiig eqrintion that uses tlatn from Tnhle 13.

K; = 2.58(2/?J”U (36)

Valoes for K- from 0 5 : 5 150 in are given in Tnhle 14. The del- initions of Expostire A through D calegories x e shown i n Tahle 10.

I,, = imponance factor. Values are given i n Table I I . Detiniliuns tor categories I, II, 111. and IV nre found i n Tahle 9.

V = hasic wind speed tletermined from data in ASCE Sriiiiiliirrl 7 or appropriate regional darn. The hasic & i n c l speed used shuiild he 31

least 3 I .3 nl/s.

Gust response factor. The values of G, are deterinined by the following equations. Table IS lists values for G, for 0 5 i 5 150 i n .

GZ = 0.65 + 3.65T. (37j

where (38)


Table 14 Velocity Pi-essure Exposure Coefficient Kz Krpriiiled with pemiiraiuii ftuiii ASCE Srnruluril 7-93.

HI. Ahovc 4 Ground. in Esposure A Esposure U Esposure C Esposure D

11-5 0 13 0 39 0 83 I 2 2 h 0.15 0 42 0.87 1.27 8 0. I 8 0 48 0 94 1.34

I I 1

12 15 71) 25 30 35 4 0

SO 60 711 SO 90

0.20

11.23 0.27 0.32 0 .38 0.42 0.47 0 .5 I

O.hO

0.67 0.75 0.82 0.88

11.52 11.57 0.h3

0.7 I (1.79 (1.86

0.92 (1.97 I .07 I . l h 1.25 1.32 1.39

1 .1 ) l I .06 1.13 I .23 1.31 1.38

1.44

I .so I .59 I .hX I .75 1.82 1.88

I .40 I A6

I .s2 1.61

I .h9 I .75 1.80 I .85

I .94 2.01 2.07 2.13 2.18

I I)il 0.95 I .46 1.94 2.22 I10 I SI I I .52 2.~10 2.27 I20 I .07 1.58 2.05 2.3 I 130 1.13 I .h4 2.09 2.34 I 4 1 1.18 I .70 2.14 2.38 I 5 0 1.24 I .75 2.18 2.4 I

Table 15 Gust Response Factor Kepriiital with peiiiiissiuti fioiii ASCE Slrmnhnl 7-93,

Gust Response Factor GL Heighl Aliore Ground. in Espusure A Espusurc B Esposure C Esposure D

J-5 2.30 I .63 1.31 1.15 h 2.20 I .59 1.29 1.14 8 2.Oh 1.53 1.27 1.13 Ill 1.96 I .39 1.25 1 . 1 1 12 1.88 I .J5 1.23 1 . 1 1

I5 I .79 I .42 1.21 1.10

70 I .h9 1.37 1.19 I .08 25 1.61 1.33 1.17 I .1)7 30 1.56 1.31 1.16 I .07 35 I .5 I I .28 1.1s I .Oh 411 I .47 I .27 1.14 I .05

5 0 I .42 1.24 1.12 I .os hi1 I .37 1.21 1 . 1 1 I .04 70 1.33 1.19 1.10 I .03 8 0 I.30 1.18 I .09 I .03 90 1.28 1.16 1.09 I .02 I 00 1.26 1.15 I .os I SI2 I I l l I .24 1.14 I .07 I .02 I20 I 2 2 1.13 I .07 I .(I I 1311 1.21 1.12 I .Oh I .o I I40 1.19 1.12 I .Oh I .I) I I50 1.18 1 . 1 1 I ,l)6 I .oo

"WS:

I. Vdiieh ut' Ci, :lie C:IIUIII:I~~~ with Eqii:itiuiis (37) :lid (3X) :!id ~: I I : I huln T:iblr 13. 2. Liiieai. iitieipthtioii of r:ible \-:iIues is :~ccepi:lhlr fur iiiteniirdi:ite wItie\ of Iiriglii :. 3. TIE \s:ilue ut'ille C;; i i n y nut be less t h i 1.0.

wq DIAGONAL SECTION

\ FW

TOP VIEW

FRONT VIEW I SIDE VIEW TO GROUND LEVEL

Fig. 10 Equipnient Diniensions and Force Locations fur Wind Exaniples 5,6, and 7

Example Calculations: Analytical Procedure The following exaiiiple calculations are for a 1400 kW cooling

rower with dimensions shown in Figure 10:

Tower height = / I = 3 111 Tower width = D = 3 in

Tower length = I = 6 in

Tower operating mass = \Vp = 8650 kg

Tower diagonal dimension = (3* + 6*)".' = 6.71 m Area normal to wind direclion = A,= 3 X 6.71 = 20. I m2

From Tahle 12; C,= 1.0 tor wind acting along diagonal with hlD = 313 = I.

12sainplc 5 . Snhurhan hospital i n Omaha, Nebraska. The top of the cooling tuwer is 30 in. ahove ground level.

Solution: From appropriate wind data tables. the design wind speed

From Tahle 9, use Caregory 111

From Tahle l(1, use Exposure B

From Table I I, I,,, = I .07

From Table 14 or Equation (36), K: = 0.86

Siihstitntioii into Equation (35) yields:

is fo~rntl 10 he 40 mls.

QI = 0.61 X 0.86( 1.07 X 40)2 = 961 Pa = 0.961 lcPn

From Tahle 15 or Equations (37) and (38); G: = 1.31. Substitution into Equation (34) yields the design wind force as

F,,, = 0.96 I x I .3 I x I .I) x 20. I = 25.3 kN

Esample 6. Ollice huilding in New York City. Top of tower is I80 m ahove ground level.

Solution: From wind data iahles. the design wind speed is 54 m/s.

From Table 9. use Category 1.

From Tahle 10. use Exposure A From Tahle 1 1 . Iu, = I .05

Because :, > IS0 in. use Equations (36), (37), (38). and Tahle I 5 to

From Tahle 13. a = 3.0. zx = 450, antl D,, = 0.025 From Equation (36):

cletermine KI antl G,.

KI= 2.58(1801450)U3= 1.40

From Eqiiaiion (35)

Ql = O.61 x I .40( I .05 x S4)* = 2746 Pa = 2.746 kPn


Determine the gust response factor for I = 180 m using Equations (37) and (38).

2.35(0.025)”2 = 0,137 T: =

(I 80/9)”’

Gz=0.h5+3.h5(0.137)= 1.15

Equation (34) yields the design wind force as

F, = 2.746 x I, I 5 x 1.0 X 20. I = h3.5 kN

Example 7. Church in Key West, Florida. The top of the tower is 15 m above ground level.

Solution: From Table 9, use Category II

From Table 10, use Exposure D FromTable Il,I:= 1 . 1 1

From Table 14, Kz = I .52

From appropriate wind data, the design wind speed is found

From Equation (35):

to be 67 d s .

BIBLIOGRAPHY ACI. 1995. Biiilding code requirements for striicniral concrete. Smti~lnril

318-95 and comiiwiitur?: 3 18R-95. Americdii Concrete Iiisritiile. Farm- ington Hills, MI.

AISC. 1995. Mnnricil o j src,el coirsrrirctiori-Lori~l onil n~sisroiicr~ ,foetor rlesign, 2nd ed. American Institiite of Steel Constriictioii, Chicago.

Associate Committee on the National Biiiltling Code. 1985. Nurirriiril Biiild- iiig Codc ofCfiiifih 1985. 9th ed. National Research Coiincil of Canada. Ottawa.

Associate Committee on the National Biiilding Code. 1986. S i t / ) / h i i m t ro rhc Nritionrrl Bitilding Codr of Cwifirlu 1985, 2nd ell. National Research Coirncil of Canada, Ottawa. First errata. Jaiiuary.

AWS. 199h. Striicniral welding code. AWS DI. 1-96, Steel Aiiiericaii Weltl- ing Society. Miami.

Ayres. J.M. and R.J. Phillips. 1998. Water damage i n hospitals resiiliing from the Northridge earthqiiake. ASHME Tronsricrinns 104( 15): 1286- 96.

Barts, M.E.. M.R. Cordes, L.R Russell. J.R. Shaver. ancl E. Simiu. 19SO. Hurricane wind speeds ill the United States. NBS BSS 124. Nnrionnl Institiite of Stantlards and Technology, Gaithershiirg. MD.

Bolt, B.A. 1988. Eurthrprrkes. W.H. Freeman. New York. DOE. 1989. General design criteria. DOE Order 6430. IA. U S . Department

of Energy. Washington. D.C. FEMA 302 & 303. NEHRP recommeiided provisions for seismic regiila-

tions for new biiildinas and other structures. Part I. Provisions: Parr 2. Commentary. Biiiltling Seismic Safety Coiincil. Washington. DC.

lones, R.S. 1984. Noiw uiid idwiitioii cniitml iii l m i l d i i ~ ~ s . McGraw-Hill. Q: = 0.61 x 1.52(1.1 I x h7)* = 5128 Pa = 5.128 Wa

From Table 15, Gz = 1 .10 . Again using Equatioii (34). the design wind force is

F,=5.128~1.10xI .Ox20.1= 113.4W

REFERENCES AFPA. 1997. National design specijicution (NDS) f . r wood consrrricrion.

American Forest and Paper Association, Washington, DC. AISC. 1989. Manual of.stee/ wnsrrucrion-AlloH.rrhle .srre,ss design, 9th ed.

American Institute of Steel Construction, Chicago. Army, Navy, and Air Force. 1992. Seismic rlesigtlfor buildiitgs. TMS-809-

10, NAVFAC P-355, AFN 88-3. Chapter 13. ASCE. 1993. Minimum’ design loads for buildings and other ~tri~ctiires.

Standanl ASCE 7. American Society of Civil Engineers, Reston, VA. BOCA. 1996. The EOCA National hiiildiiig code, 13th ed. Building Ofli-

cials & Code Administrators International, Inc., Coontry Cluh Hills, IL. ICC. 1998. Internationol building code 2000, Final draft. International Code

Council, Falls Church, VA. ICBO. 1997. Uniform building code. International Conference of 511ilding

Officials, Whittier, CA. SBCCI. 1994. Standard building code 199h. Southern Building Code Con-

gress International. Inc., Birmingham. AL. SMACNA. 1998. Seisniic rerrruint moniiul: Grritlelinesfiu r!lechfinicril sy-

terns, 2nd ed. Sheet Metal and Air Conditioning Contractors’ National Association, Chantilly, VA.

New York. Kennedy, R.P., S.A. Short. J.R. McDoiialtl. M.W. McCanii. and R.C. Mur-

ray. 1989. Design and evahiation giiidelines for the Depaitment of Energy facilities subjected to nati~ral phenomena hazards.

Lama. P.J. 1998. Seismic codes. HVAC: pipe systems and practical suliitions. ASHKAE Trunxocrions IOU( 15): 1297-1304.

Maley. R., A. Acosta. F. Ellis. E. Etheredge. L. Foote, D. Johnson. R. Por- cella. M. Salsinan, and J. Switzer. 1989. Dep)vtment of the Interior. US. geological survey. U.S. geological siirvey strong-motion records from the Northern California (Loma Prieta) earthqiiake of Octoher 17. 1989. Open-file rcport R9-568.

Naeim. F. 1989. The .sei.sriiic rk,sign hcrtidbomk. Van Nostraiitl Reiiiliultl Inter- national Company Ltil.. London. England.

NFPA. I99 I. I i i s rd lur io i i of .vpriiiklor .syst~vn.v. National Fire Prutectiuii Association, Qiiincy. MA.

Peterka. J.A.. and J.E. Cermak. 1974. Wind pressiires on hiiiltlings-Proh- ability densities. J. Srriictiirril Di i . . ASCE l(Jl(6): 1255-67.

Simiii, E., M.J. Changery, and J.J. Fillihen. 1979. Extreme wind speeds n~ 129 stations in the contigiioiis United States. US. NBS BSS 118. National Institute of Standnrds and Technology. Gaithershiirg. MD.

SMACNA. 1995. HVAC h c / coiisrriicrinii srniiflrirrl-iiicrol n i i r l ,j7c~.rih/c~. 2nd ed. Sheet Metal and Air Conditioning Contractors’ National Asao- ciation. Chantilly, VA.

Wasilewski. R.J. 1998. Seismic restraints tor piping systems. ASHK.4E Troii.sucrioiis 104( le): 1273-95.

Weigels, R.L. 1970. Eurflrqriuke eiigiiiwrin.q. IOrh ell. Prentice-Hall. Engle- wood Cliffs. New Jersey.

Documents

Handbook 1999 HVAC - Seismic and Wind Restraint Design