PCI Report on

FIRE RESISTANCEOF ARCHITECTURALPRECAST CONCRETE

Prepared by

Armand H. GustaferroThe Consulting Engineers Group, Inc.

Glenview, Illinois

For the PCI Committee on Fireworking jointly with the

PCI Architectural Precast ConcreteDivision Management Committee

PCI FIRE COMMITTEE

John McGrew (Chairman)

Melvin S. AbramsGeorge AdamMerle BranderDonald R. BuettnerGary EhlenbeckR. P. Ellison, Jr.Frank G. ErskineFloyd FoxJames GastonWilliam D. Givens

A. H. GustaferroDavid W. HansonJohn B. HenryDaniel P. JennyPaul E. KraemerRobert A. MatthewsMilo J. NimmerWalter J. PrebisMerrill R. Walstad

18

This PCI committee report, which was preparedunder the direction of the PCI Committee on Fireand the PCI Architectural Precast Concrete DivisionManagement Committee, summarizes availableinformation on the behavior of architectural precastconcrete under fire conditions.Based on fire tests, the report presents design datafor calculating the thickness of many types of wallsthat will provide fire endurances of 1, 2, 3, and 4 hr.In particular, tables and design charts are includedfor determining the thickness of one- and two-coursepanels, ribbed panels, sandwich panels, andwindow panels. Several numerical examples areprovided to help the designer.Suggestions are offered for the treatment of jointsbetween wall panels, the protection of connections,and fire stopping between floors and wall panels.The report also contains a section dealing with thefire resistance of precast concrete columns andcolumn covers.

CONTENTSIntroduction ............................. 20

Standard Fire Tests of BuildingConstruction and Materials

PrecastConcrete Walls ................... 21One- and Two-Course PanelsRibbed PanelsSandwich PanelsWindow Walls

Detailing of Fire Barriers .................. 29Treatment of JointsProtection of ConnectionsFire Stopping Between Floors and Wall Panels

ConcreteColumns ........................ 32Precast Concrete Column Covers

References .............................. 32

PCI Journal/September-October 1974 19

INTRODUCTION

In the interest of life safety, buildingcodes require that the resistance to firebe considered in the design of build-ings. The degree of fire resistance re-quired is dependent on the type ofoccupancy, the size of the building, itslocation (proximity to property linesand within established fire zones) , andin some cases, the amount and type offire detection and suppression equip-ment available in the structure.

In addition to the life safety con-siderations, casualty insurance compa-nies and owners are concerned withthe damage that might be inflicted onthe building and its contents during afire. Insurance rates are often substan-tially lower for buildings with higherfire resistance ratings..

Fire resistance ratings are usuallyassigned on the basis of results of stan-dard fire tests. In recent years, therehas been a trend toward calculating thefire endurance of building componentsrather than relying entirely on fire tests.To facilitate this trend, much researchwork has been conducted on the be-havior of materials and building com-ponents in fires. The purpose of thisreport is to summarize available infor-mation on the behavior under fire con-ditions of architectural precast con-crete. e

Standard Fire Tests of BuildingConstruction and Materials

The fire resistance ratings of buildingcomponents are measured and specifiedin accordance with a common standard,ASTM E119. 1 Fire endurance is de-fined as the period of resistance to thestandard fire exposure which elapsesbefore an "end point" is reached.

The "standard fire exposure" re-quired by ASTM E119 is defined bythe time-temperature relation of the

Defined broadly in this report to cover all ap-plications of precast concrete to wall construction.

fire shown in Fig. 1. This fire repre-sents the combustion of about 10 lb ofwood (with a heat potential of 8000Btu per lb) per sq ft of exposed areaper hour of test.

In reality, the fuel consumed duringa fire test (generally fuel oil or gas)depends on the furnace design and theheat capacity of the test assembly. Forexample, the amount of fuel consumedduring a fire test of an exposed concretefloor specimen is likely to be 10 to 20percent greater than that used duringa test of a floor with an insulated ceil-ing, and considerably greater than fora combustible assembly. However, thisfact is not recognized when assigningor specifying fire resistance ratings.

The Standard, ASTM E119-73, spec-ifies the minimum sizes of specimens tobe exposed in fire tests. For floors androofs, at least 180 sq ft must be exposedto fire from beneath, and neither di-mension can be less than 12 ft. Fortests of walls, either load bearing ornon-load-bearing, the minimum speci-fied area is 100 sq ft with neither di-mension less than 9 ft. The minimumlength for columns is specified to be9 ft, while for beams it is 12 ft.

During fire tests of floors, beams,load-bearing walls, and columns, themaximum superimposed load, as re-quired or permitted by nationally recog-nized standards, is applied. The Stan-dard permits alternate tests of largesteel beams and columns in which asuperimposed load is not required, butthe end point criteria are modified.

Floor and roof specimens are ex-posed to fire from beneath, beams fromthe bottom and sides, walls from oneside, and columns from all sides. Thereare no standard fire tests, per se, ofcomponents such as connections orjoints.

Fire tests are generally terminatedwhen one or more of the end pointcriteria are reached. These criteria are:

20

(a) Load-bearing specimens mustsustain the applied loading—collapse isan obvious end point (structural endpoint) .

(b) Holes, cracks or fissures throughwhich flames or gases hot enough toignite cotton waste must not form(flame passage end point).

(c) When the temperature increaseof the unexposed surface of floors,roofs, or walls reaches an average of250 F or a maximum of 325 F at anyone point (heat transmission end point).

(d) In alternate tests of large steelbeams (not loaded during the test) theend point occurs when the steel tem-perature reaches an average of 1000 For a maximum of 1200 F at any onepoint.

(e) Walls and partitions must remainstanding during a hose stream test(simulating, in a specified manner, afire fighter's hose stream) and then sup-port twice the superimposed load.

In addition, there are steel tempera-ture limits for floors, roofs, and beamsfor unrestrained and restrained assem-blies.

PRECAST CONCRETE WALLS

Fire endurances of concrete walls, asdetermined by fire tests, are almost uni-versally governed by the ASTM E119criteria for temperature rise of the un-exposed surface (heat transmission)rather than by structural behavior dur-ing fire tests. This is probably due tothe low level of stresses, even in con-crete bearing walls, and the fact thatreinforcement generally does not per-form a primary structural function.

A report of a fire test conducted byUnderwriters' Laboratories, Inc. of adouble-tee wall assembly was publishedin the July-August 1972 PCI JOUR-NAL. 2 The assembly tested consistedof 4-ft wide double tees with 11/z-in.thick flanges. The stems, 12 in. deep

u' 2400

0 2000

W 160001

1200E-a sooW

400

W 0F

TIME , HR.

Fig. 1. Standard time-temperaturerelation.

and tapered from 4 1/2 in. at the flangeto 21/2 in., were not exposed to fire,i.e., the fire test simulated the usualapplication of double-tee wall panelswith the stems outside the building.

Despite the thin flange, the wall sup-ported a load equivalent to 9600 lb perlineal ft of wall length—the same loadgenerally applied to 10-in, concretemasonry walls during fire tests. Theassembly withstood a 2-hr fire test, ahose stream test, and subsequently adouble load test without distress.

Hence, structurally the assemblywithstood a large live load throughouta 2. hr standard fire exposure. The heattransmission criterion, i.e., an average250 F rise of the unexposed surface,was reached at 21 minutes. It is logicalto assume that a thicker slab (or aninsulated slab) would perform betterfrom a heat transmission standpointwithout sacrificing structural perfor-mance.

Some building codes modify or waivethe heat transmission criterion depend-ing on factors such as spatial separation,location, and occupancy. 3 ' 4 For manybuildings, however, the heat transmis-sion requirement is imposed.

From information that has been de-veloped from fire tests, it is possible toestimate accurately the thickness ofmany types of one-course and multi-

PCI Journal/September-October 1974 21

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WALL PANEL THICKNESS, IN.Fig. 2. Fire endurance (heat transmission) of concreteslabs as a function of thickness. Interpolation of varyingconcrete unit weights is acceptable.

course walls that will provide fire en-durances of 1, 2, 3, or 4 hr based onthe temperature rise of the unexposedsurface.Most of the information on heattransmission was derived from fire testsof assemblies tested in a horizontalposition simulating floors or roofs. Thedata are slightly conservative for as-semblies tested vertically, i.e., as walls.Nevertheless, it is suggested that nocorrection be made unless more specificdata derived from fire tests of wallsare used.

One- and Two-Course PanelsBased on fire test data, the thickness-es shown in Fig. 2 and Tables 1 and 2can be expected to provide the fireendurances indicated for single-courseand two-course walls.5.6As used in this report, concrete ag-gregates are designated as lightweight,sand-lightweight, carbonate, or sili-ceous.Lightweight aggregates include ex-panded clay, shale, slate, and fly ashwhich produce concretes having unit22

Table 1. Thicknesses (in inches) of solid concretewall panels for various fire endurances based on

results of fire tests.

Thickness in inches forfire endurance of

Aggregate 1 hr 2 hr 3 hr 4 hrAll lightweight 2.47 3.56 4.35 5.10Sand-lightweight 2.63 3.76 4.62 5.37Carbonate 3.25 4.67 5.75 6.63Siliceous 3.48 5.00 6.15 7.05

Table 2. Thicknesses of inside wythes (in inches) to provide various fireendurances for two-course panels based on Reference 6.

Siliceous aggregate Sand-lightweightFire Inside wythe concrete* concrete

endur- material (outside wythe) (outside wythe)ance (fire-exposed side)

11/2 in. 2 in. 3 in. 1 1/2 in. 2 in. 3 in.1 hr Carbonate aggregate concrete 1.9 1.4 0.45 1.70 1.00 01 hr Siliceous aggregate concrete 2.00 1.48 0.48 1.70 1.00 01 hr Lightweight aggregate concrete 1.50 1.20 0.25 1.13 0.63 01 hr Cellular concrete (30 pcf) 0.7 0.5 0.2 0.5 0.3 01 hr Perlite concrete (30 pcf) 0.8 0.6 0.2 0.7 0.4 01 hr Vermiculite concrete (30 pcf) 0.9 0.6 0.2 0.7 0.4 01 hr Sprayed mineral fiber 0.40 0.25 0.10 0.40 0.20 01 hr Sprayed vermiculite

-cementitious material 0.40 0.25 0.10 0.40

--0.20

- --0

2 hr Carbonate aggregate concrete 3.25-

2.8---1.9 3.20 2.60 1.25

2 hr Siliceous aggregate concrete 3.50 3.00 2.00 3.30 2.70 1.302 hr Lightweight aggregate concrete 2.50 2.10 1.40 2.26 1.76 0.762 hr Cellular concrete (30 pcf) 1.2 1.0 0.6 1.2 0.9 0.42 hr Perlite concrete (30 pcf) 1.4 1.1 0.7 1.3 0.9 0.42 hr Vermiculite concrete (30 pcf) 1.6 1-.3 0.8 1.4 1.1 0.42 hr Sprayed mineral fiber 1.1 0.80 0.50 1.00 0.80 0.302 hr Sprayed vermiculite

cementitious material 1.0 0.8 0.50 1.0 0.75 0.303 hr Carbonate aggregate concrete 4.4 3.9 3.0 4.2 3.7 2.43hr Siliceous aggregate concrete 4.65 4.15 3.15 4.4 3.8 2.53 hr Lightweight aggregate concrete 3.4 3.1 2.4 3.12 2.62 1.623 hr Cellular concrete (30 pcf) 1.6 1.3 0.9 1.6 1.3 0.83 hr Perlite concrete (30 pcf) 1.9 1.6 1.1 1.8 1.4 0.83 hr Vermiculite concrete (30 pcf) 2.2 1.8 1.3 2.0 1.6 1.03 hr Sprayed mineral fiber N.A. 1.40 0.90 N.A. 1.30 0.853 hr Sprayed vermiculite

cementitious material 1.60 1.35 0.85 1.60 1.30 0.804 hr Carbonate aggregate concrete 5.15 4.8 3.85 5.2 4.7 3.54 hr Siliceous aggregate concrete 5.55 5.05 4.05 5.5 4.9 3.74 hr Lightweight aggregate concrete 4.2 3.8 3.0 3.87 3.37 2.374 hr Cellular concrete (30 pcf) 2.1 1.9 1.4 2.0 1.7 1.14 hr Perlite concrete (30 pcf) 2.3 2.0 1.5 2.3 1.9 1.34 hr Vermiculite concrete (30 pcf) 2.7 2.3 1.7 2.6 2.2 1.54hr Sprayed mineral fiber N.A. N.A. 1.40 N.A. N.A. 1.404 hr Sprayed vermiculite

cementitious material N.A. 1.80 1.30 N.A. 1.75 1.25

*Tabulated values for thickness of inside wythe are conservative for carbonate aggregate concrete.N.A. means not applicable, i.e„ a thicker outside wythe is needed.

PCI Journal/September-October 1974 23

Table 3. Thicknesses of concretewall panels (in inches) faced with5/s-in. Type X gypsum wallboard

required to provide fireendurances of 2 and 3 hr.

icknesses of concretepanel for fireendurance of

Aggregate 2 hr 3 hrSand-lightweight 2.0 3.0Carbonate 2.3 3.7Siliceous 2.5 3.9

weights of about 95 to 105 pcf withoutsand replacement.

Lightweight concretes in which sandis used as part or all of the fine aggre-gate, and weigh no more than 120 pcf,are designated as sand-lightweight.

Carbonate aggregates include lime-stone and dolomite, i.e., those consis-ting mainly of calcium carbonate and/or magnesium carbonate.

Siliceous aggregates include quartz-ite, granite, basalt, and most hard rocksother than limestone and dolomite.

Table 3 shows the thicknesses of con-crete wall panels required to providefire endurances of 2 and 3 hr when thefire-exposed surface is covered with 5/s-in. Type X gypsum wallboard. Fasten-ing devices, not adhesives, must beused to attach the wallboard to thewall panels.

Ribbed PanelsHeat transmission through a ribbed

panel is influenced by the thinnest por-tion of the panel and by the panel's"equivalent thickness." Here, equiva-lent thickness is defined as the netcross-sectional area of the panel dividedby the width of the cross section. Incalculating the net cross-sectional areaof the panel, portions of ribs that pro-ject beyond twice the minimum thick-ness should be neglected, as shown inFig. 3(a).

The heat transmission end point canbe governed either by the thinnestsection, by the average thickness, or bya combination of the two. The follow-ing rule-of-thumb expressions appear togive a reasonable guide as to when theminimum thickness governs and whenthe average thickness governs.Let t = minimum thickness, in.

to = equivalent thickness ofpanel, in.

s = rib spacing, in.If t c s/4, fire endurance R is governed

by t and is equal to R.If t s/2, fire endurance R is governed

by to and is equal to R.

If s/2 > t > s/4:R = R t + (4t/s — 1) (R te — Rt) (1)

where R is the fire endurance of a con-crete panel and subscripts t and te re-late the corresponding R values to con-crete slab thicknesses t and t e, respec-tively.

N ^-

NEGLECT SHADED AREA S -IN CALCULATION OFEQUIVALENT THICKNESS

(a) (b)

Fig. 3. Cross sections of ribbed wall panels.

24

These expressions apply to ribbedand corrugated panels, but for panelswith widely spaced grooves or rustica-tions they give excessively low results.Consequently, engineering judgmentmust be used when applying the aboveexpressions.

Problem 1. Given the section of awall panel shown. Estimate the fireendurance if the minimum thickness is4 in. and the equivalent thickness is4.8 in. Assume that the panel is madeof sand-lightweight concrete.

r

a ro

n

Solution: t = 4 in., s/2 = 6 in., s/4= 3 in.

Therefore, s/2 > 4 > s/4, so useEq. (1):

From Fig. 2:Rt = fire endurance of 4-in, sand-light-

weight panel = 138 min.Rte = fire endurance of 4.8-in, sand-

lightweight panel = 194 min.Now, using Eq. (1):

R = 138 + [4(4)/12 — 1] [194 — 138]= 157 min.

Sandwich Panels

Some wall panels are made by sand-wiching an insulating material betweentwo face slabs of concrete.

Several building codes require thatwhere non-combustible construction isspecified, combustible elements in wallsshall be limited to thermal and soundinsulation having a flame spread classi-fication of not more than 75 when theinsulation is sandwiched between twolayers of non-combustible material suchas concrete.

When insulation is not installed inthis manner, it is required to have a

flame spread of not more than 25.Data on flame spread classification areavailable from insulation manufacturers.

A fire test was conducted of one suchpanel that consisted of a 2-in, baseslab of carbonate aggregate concrete,a 1-in, layer of cellular polystyrene in-sulation, and a 2-in, face slab of car-bonate aggregate concrete. The resulting fire endurance was 2 hr 00 min.

From Eq. (2) , 7 it is possible to cal-culate the contribution of the 1-in.layer of polystyrene:

R = (R1 0 ' 59 + R9019 ... R,zo • 1 9 )1.7 (2)

where R = the fire endurance of thecomposite assembly in minutes and R1,R.,, and R the fire endurance of eachof the individual courses in minutes.R = 2 hr 00 min. = 120 min.Rl = R3 = 28 min. for a 2-in, slab of

carbonate aggregate con-crete (from Fig. 2).

120 = [(28)°_59 + Rzo.os + (28)°.59] 1.7[7.14+R_,0.59+7.14]1.7

_ (16.85)1.716.85=14.28 ±R9059R; = (16.85 — 14.28) 1.7 = 5.0 min.

For most cases, Eq. (2) is approxi-mately equal to:R = K(R1 0 5 + R00 '... + Rno. 5)2 (2a)

whereK = 0.83 for n = 2, i.e., a two-course

assembly.K = 0.73 for n = 3, i.e., a typical

sandwich panel.K = 0.67 for n = 4.Whenever the R value for one of the

courses greatly exceeds the other Rvalues, Eq. (2a) underestimates the fireendurance. For example, in a two-course assembly where R1 = 20R2,Eq. (2a) yields a result about 6 percentlower than Eq. (2) .

It is likely that the comparable Rvalue for a 1-in, layer of cellular poly-urethane would be somewhat greaterthan that for a 1-in, layer of cellularpolystyrene, but test values are not

PCI Journal/September-October 1974 25

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2 3 4THICKNESS OF ONE COURSE, IN.

R, R 059MINUTES

60 11.20120 16.85180 21.41

240 25.37

MATERIAL R0.591- IN. CELLULARPLASTIC 2.573/4- IN. GLASSFIBER BOARD 4.031V2-IN. GLASSFIBER BOARD 8.571/2-IN. GYPSUMWALLBOARD 7.445/8-IN.GYPSUMWALLBOARD 8.492-IN. FOAM GLASS 10.61

20

15Ow2

wX10

0Imf 5O

Fig. 4. Design aid for use in solving Eq. 2b.

available. The above value for polysty-rene is probably conservative for cellu-lar polyurethane. Through the use ofthat value it is possible to estimate thefire endurance of sandwich panels con-sisting of concrete face slabs with 1-in.of polystyrene (and conservatively forpolyurethane) insulation sandwichedbetween the face slabs.

(It should be noted that the cellular

plastics melt and are consumed at about400 to 600 F. Thus, additional thick-ness or changes in composition probab-ly have only a minor effect on the fireendurance of sandwich panels. Thedanger of toxic fumes caused by theburning cellular plastics is practicallyeliminated when the plastics are com-pletely encased within concrete sand-wich panels.8)

Problem 2. Determine the thickness,of sand-lightweight concrete face slabsneeded to provide a 3-hr fire endurancewhen used in a sandwich panel con-taining a 1-in, layer of polystyrene.

Solution:R = [R1059 + (5.0)0.5 + R3059] 1.7

= 180Now R l = R1.( 2R10•59 + 2.57) 1.7 = (21.41)1.72R1059=21.41-2.57=18.84R l = 45 min.

From Fig. 2, the thickness of sand-lightweight concrete for a fire endur-ance of 45 min. is about 21/4 in. Thus,the wall should consist of 2'/4-in, faceslabs with a 1-in, layer of polystyreneinsulation.

Equation (2) can be restated in thefollowing form:RO.59 = R 1059 ± R105° ... + R 12o.59 (2b)

The design aid in Fig. 4 can be usedto solve Eq. (2b) as illustrated by thefollowing example.

26

Table 4. Fire Endurance of Precast ConcreteSandwich Walls [calculated, based on Eq. (2)]

Insidewythe Insulation

Outsidewythe

Fireendurance,

hr:min.

1 1/2 in. Sit 1 in. CP 11/2 in. Sil 1:231 1/2 in. Carb 1 in. CP 11/2 in. Carb 1:231 1/2 in. SLW 1 in. CP 11/2 in. SLW 1:452 in. Sit 1 in. CP 2 in. Sit 1:502 in. Carb 1 in. CP 2 in. Carb 2:002 in. SLW 1 in. CP 2 in. SLW 2:323 in. Sit 1 in. CP 3 in. Sil 3:071 1/2 in. Sil 3/4 in. GFB 11h in. Sil 1:392 in. Sil 3/4 in. GFB 2 in. Sil 2:072 in. SLW 3/a in. GFB 2 in. SLW 2:522 in. Sil 3/4 in. GFB 3 in. Sit 3:101 1/2 in. Sit 11/2 in. GFB 11/2 in. Sil 2:352 in. Sit 11/2 in. GFB 2 in. Sil 3:082 in. SLW 11/2 in. GFB 2 in. SLW 4:001 1/2 in. Sit 1 in. IC 11/2. in. Sit 2:121 1/2 in. SLW 1 in. IC 11/2 in. SLW 2:392 in. Carb 1 in. IC 2 in. Carb 2:562 in. SLW 1 in. IC 2 in. SLW 3:331 1/z in. Sit 11/2 in. IC 11/2 in. Sit 2:541 1/2 in. SLW 11/2 in. IC 11/2 in. SLW 3:242 in. Sit 11/z in. IC 3 in. Sil 4:162 in. Sit 2 in. IC 2 in. Sit 4:251 1/2 in. SLW 2 in. IC 1½ in. SLW 4:19

Notes: Carb = carbonate aggregate concreteSil = siliceous aggregate concreteSLW = sand-lightweight concrete (115 pcf maximum)CP = cellular plastic (polystyrene or polyurethane)GFB = glass fiber boardIC = lightweight insulating concrete (35 pcf maximum)

Problem 3. Determine the thicknessof the inside wythe of a sandwich panelthat must have a 3-hr fire endurance ifthe outside wythe is 2 in. of siliceousaggregate concrete and the insulationis 3/a in. of glass fiber board. The insidewythe is to be made of carbonate ag-gregate concrete.

Solution: R = 180 min; R°59 = 21.41(tabulated in Fig. 4).

For outside wythe, R1059 = 6.6 (2-in.siliceous aggregate concrete, Fig. 4).

For insulation, R2059 = 4.03 (tabu-lated in Fig. 4).

For inside wythe:R3059 =21.41-6.6-4.03= 10.78From Fig. 4, use 3 r/s-in, thickness of

carbonate aggregate concrete.

Table 4 lists fire endurances of sand-wich panels with either cellular plastic,glass fiber board, or insulating concreteused as the insulating material. Thevalues were obtained by use of Eq. (2)..

Window WallsMost building codes limit the area of

openings (windows and doors) in ex-terior walls that must be fire resistive..Limits are based on construction type,.occupancy, and spatial separation (dis-tance between a building and its neigh-bor or property line) . For example, the1973 Uniform Building Code° permitsno openings in exterior walls of officebuildings when the spatial separation isless than 5 ft, and requires the walls tobe of 4-hr fire resistive construction.

PCI Journal/September-October 1974 27

If the separation is between 5 and 10ft, openings must be protected and thearea of such openings is limited to halfthe total area of the wall in each story.(See later section for discussion of pro-tected openings.)

Unprotected openings are permittedin walls if the spatial separation is 10 ftor more. The area of these openings isnot limited. Bearing walls can be of 2-hr fire resistive noncombustible con-structiori.

Nonhearing walls may be of 1-hrnoncombustible construction where un-protected openings are permitted and2-hr fire resistive noncombustible con-struction where fire protection of theopenings is required. Nonbearing wallsfronting on streets or yards at least 50 ftwide in Fire Zone No. 1 (or 45 ft inZones 2 or 3) may be of unprotectednoncombustible construction.

The above pertains to the 1973 Uni-form Building Code requirements foroffice buildings. Requirements for otheroccupancies differ somewhat but gen-erally follow the same pattern. Require-ments in other codes also differ.

Perhaps the most comprehensive re-quirements are those in the NationalBuilding Code of Canada,3 which re-late spatial separation and maximumarea of unprotected openings to thearea and height-length ratio of the ex-posing building face. Percentages ofunprotected opening areas are tabulat-ed for various combinations of area ofbuilding face, height-length ratio, andspatial separation.

The percentage of openings permit-ted increases (a) as the spatial separa-tion increases, (b) as the area of theexposing building face decreases, and(c) as the ratio of either height-length(H/L) or length-height (L/H) increas-es, i.e., a greater percentage is permit-ted for H/L or L; H of 10:1 than forH/L orL;Hof3:1.

As an example, an exposing face ofan office building having an area of

3500 sq ft, an L/H = 2:1, and a limit-ing distance of 24 ft can have a maxi-mum of 18 percent of unprotectedopenings. If the ratio of L/H or H/Lwere 10:1 or more, the area of unpro-tected openings could be increased to33 percent, or if the spatial separationwere 40 ft and the L/H were 10:1,the area of unprotected openings per-mitted is 63 percent of the exposingface.

The National Building Code of Can-ada also permits a higher limit on theunexposed surface temperature if thearea of unprotected openings is lessth_.n the maximum allowed. The NBCCdefines an equivalent opening factor,F,,,„ to be:

_ (T,,_+_460) (3)F00 (T. + 460)1

whereT2, = average temperature in deg F

of the unexposed wall surfaceat the time required fire-resis-tive rating is reached under testconditions

T,; = 1638 F for a 3/a-hr fire-resistiverating1700 F for a 1-hr fire-resistiverating1850 F for a 2-hr fire-resistiverating

The equivalent opening factor is thenapplied in a formula to determine thecorrected area of openings:

A,, = A + AfFeo (4)where

A,. = corrected area of unprotectedopenings including actual andequivalent openings

A = actual area of unprotectedopenings

Af = area of exterior surface of theexposing building face exclu-sive of openings, on which thetemperature limitation of thestandard fire test is exceeded.

28`

-I J. 3 F

C'

0.2

O.1

n

F C.z QW F-Jo

> LLL.0W_z01d

(Lv'c

CARBONATE AGGREGATE

SILICEOUS AGGREGATE SAND- LIGHTWEIGHTCfMrPCTC (TVDC r.i\ CONr.RFTF (TVPF S) , r)NrPFTC (TVPr I C'

I 2 3 4 5 1 2 3 4 5 I 2 3 4 5

PANEL THICKNESS, IN.

Fig. 5. Equivalent opening factor, F e,, for concrete wall panels (for usewith the National Building Code of Canada).

Fig. 5 shows the relation betweenF,, (as defined in the National BuildingCode of Canada) and panel thicknessfor three types of concrete.

To illustrate the use of Fig. 5, sup-pose that for a particular building face,a 2-hr fire resistance rating is requiredand the area of unprotected openingspermitted is 57 percent. Suppose alsothat the actual area of unprotectedopenings is 49 percent and that thewindow wall panels are made of car-bonate aggregate concrete (referred to

as Type N in NBCC). Determine theminimum thickness of the panel.

In this case A, = 57 percent, A = 49percent, Af = 100 — 49 = 51 percent,hence:

F A,. 1 A 57-49 0.16Af — 51

From Fig. 5, for F,, = 0.16 at 2 hr,the minimum panel thickness is 2.1 in.Thus, if the panel is 2.1 in. thick orthicker, the code requirements will besatisfied.

DETAILING OF FIRE BARRIERS

case the wall must be tightly fittedagainst the underside of the roof. If the

One of the purposes of code provi- roof and walls are of combustible con-

sions for fire resistive construction is to struction, fire walls must extend notlimit the involvement of a fire to the only through the roof, but must extendroom or compartment where the fire through the sides of the building be-

originates. Thus, the floors, walls, and yond the eaves or other combustibleroof surrounding the compartment must projections.

serve as fire barriers. When protected openings are re-Most codes require that fire walls quired in walls, coverings for such

start at the foundation and extend con- openings must be fire resistive. Mosttinuously through all stories to and codes require that fire doors have fireabove the roof, except where the roof is resistive classifications of three-fourthsof fire resistive construction, in which of the classification required of the

PCI Journal/September-October 1974 29

TWO-STAGE JOINTVERTICAL SEALANTS

AIR SEAL

^e(OPTIONAL)

9

ASBESTOSROPE

FLUSH BUTT JOINT

AIR SEALASBESTOS ` (OPTIONAL)

ROPE

AIR SEAL(OPTIONAL)

CORNER JOINT DETAIL

AIR SEAL(OPTIONAL)

ii:::(ASBESTOS

ROPE

TWO -STAGE JOINTHORIZONTAL GASKET

ASBEST04ROPE

EXTERIORFACE

SEALANT (IF USED) MUST BEDISCONTINUED AT INTERVALS(VERTICAL JOINTS) TO DRAINAREA BETWEEN IT AND AIR SEAL.

TWO-STAGE JOINTHORIZONTAL SEALANTS

(a) (b)Fig. 6. Examples of one-stage and two-stage joint.

wall. Glazed openings in fire doors orfire windows are limited in area by codeprovisions, and the glass must be rein-forced with wire mesh. Fire dampersmust be used in ducts unless fire testsshow that they are not needed.

Treatment of JointsJoints between wall panels should be

detailed so that passage of flame or hot

gases is prevented, and transmission ofheat does not exceed the limits speci-fied in ASTM E119. These require-ments present a challenge to the archi-tect, particularly for joints that are de-signed to be weathertight while permit-ting thermal expansion and contractionand other movements.

Fortunately, the problem is simpli-fied somewhat by the fact that concrete

30

J

WI-Q

Z0I--UWI--0Xa-(I)

UJz

2I-

t=MINIMUM THICKI ESS OFSTEEL SUBJECTED TOFIRE FROM BOTH SIDES

. 5

2 h1\6 GCP\ y^\6

sj GMOR I 5 F 1 -^ I1

IMt> 5/16.,

02 3 4

(a)

CONCRETE ORDRY-PACK MORTAR

b = MINIMUM WIDTH OF

CONCRETE PROTECTI,>/

0

\2„by

2 3 4(b)

Z 4

FIRE ENDURANCE , HR.

Fig. 7. Thickness of protection material applied to connections consistingof structural steel shapes. (IM = intumescent mastic, SMF = sprayed

mineral fiber; VCM = vermiculite cementitious material).

expands when heated. Thus, duringfire exposure, the joints tend to close.Noncombustible materials that are flex-ible, such as asbestos rope, provideflame and smoke barriers, and whenused in conjunction with caulking ma-terials can provide the necessary resis-tance to heat transmission. Joints thatare not required to accommodatemovement can be filled with mortar.

It should be emphasized that in win-dow wall panels, the need for fire-resistive joints is minimized because theheat transmission and flame passagethrough the joints will usually be in-significant when compared to that ofthe windows.

From a standpoint of fire resistance,two-stage joints which incorporate flex-ible noncombustible materials, such asasbestos rope, are preferable to one-stage joints. However, either can be

made fire resistive. Fig. 6 shows severaltypes of such joints.

Protection of Connections

Many types of connections in pre-cast concrete construction are not vul-nerable to the effects of fire and, con-sequently, require no special treatment.For example, gravity-type connections,such as the bearings between precastconcrete panels and concrete footingsor beams which support them, do notgenerally require special fire protection.

If the panels rest on elastomeric padsor other combustible materials, protec-tion of the pads is not generally neededbecause deterioration of the pads willnot cause collapse. Nevertheless, aftera fire, the pads would probably have tobe replaced so protecting the padsmight prevent the need for replace-ment.

FCI Journal/September-October 1974 31

Connections that can be weakenedby fire and thereby jeopardize thestructure's stability should be protectedto the same degree as that required forthe structural frame. For example, anexposed steel bracket supporting a pan-el or spandrel beam will be weakenedby fire and might fail causing the panelor beam to collapse. Such a bracketshould be protected. The amount ofprotection depends on (a) the stress-strength ratio in the steel at the time ofthe fire and (b) the intensity and dura-tion of the fire. The thickness of protec-tion material required is greater as thestress level and fire severity increase.

Fig. 7 shows the thickness of variouscommonly used fire protection materialsrequired for fire endurances up to 4 hr.The values shown are based on a criti-cal steel temperature of 1000 F, i.e., astress-strength ratio (f / f y) of about65 percent. Values in Fig. 7(b) are ap-plicable to concrete or dry-pack mortarencasement of structural steel shapesused as brackets or lintels.

Problem 4. Determine the thicknessof vermiculite cementitious materialthat must be applied to an exposed

bracket made of 4 x 4 x 3/s-in. steelangles to provide a fire endurance of2 hr.

Solution: From Fig. 7(a) the thick-ness must be about 1% in.

Fire Stopping Between Floorsand Wall Panels

When precast concrete wall panelsare designed and installed in such amanner that no space exists betweenthe wall panel and floor, a fire belowthe floor cannot pass through the jointbetween the floor and wall.

However, some curtain wall pan-els are designed in such a manner that aspace exists between the floor and wall.This space is referred to as a "safe-off"area.

Fig. 8 shows two methods of firestopping such safe-off areas. Safing in-sulation is available in the form of min-eral fiber mats of varying dimensionsand densities. Care must be taken dur-ing installation to be sure that the entiresafe-off area is sealed. The safing insu-lation provides an adequate firestop andaccommodates differential movementbetween the wall panel and floor.

CONCRETE COLUMNS

Reinforced concrete columns havefor many years served as the standardfor fire resistive construction. Indeed,the performance of concrete columns infires has been excellent.

A concrete column possesses inherentfire resistance because of three factors:(1) the minimum size is generally suchthat the inner core of the column re-tains much of its strength even afterlong periods of fire exposure; (2) con-crete cover to the reinforcing bars isgenerally 17/s in. or more, thus provid-ing considerable protection for the re-inforcement; and (3) the ties or spirals

contain the concrete within the core.Table 5 shows a summary of typical

building code requirements for rein-forced concrete columns. It can be not-ed that most codes assign 4-hr classifi-cations for columns that are at least 12in. in diameter or 12 in. square, butsome codes require that columns madewith siliceous aggregate concrete mustbe larger.

The values shown in Table 5 applyto precast as well as cast-in-place con-crete columns. In addition, they applyto cast-in-place concrete columns cladwith precast concrete column coverswhether the covers serve merely ascladding or as forms for the cast-in-place columns.

32

SAFING INSULATION

CONTINUOUSCLOSURE PLATES

1 t/2" TO 6" MAXIMUMCURTAIN WALL PANEL

Fig. 8. Two methods of in-stalling safing insulationbetween floor slab and wallpanels. (Photo courtesy:

U.S. Gypsum Co.)

Table 5. Summary of building code requirements forconcrete columns.

Concrete cover, in.,for fire resistance

Model Minimum column dimension and classification of

Code aggregate type 1 hr 2 hr 3 hr 4 hr

UBC 12 in.

BOCA Carbonate or lightweight

BOCA Siliceous

NBC 16 in.; siliceous

NBC 12 in.; siliceous

NBC 12 in.; carbonate or lightweight

SSBC 16 in.; siliceous

SSBC 12 in.; siliceous

SSBC 12 in.; carbonate or lightweight

1½ 1½ 1 1a 1½* *

— — — 1½

— — 1 1/2 2

— — — 11

— 1 1h 1 1/2 i -

- — — 11

— — 1 1h 21

— — 11/2 -

- — — 11,12

Note: UBC = Uniform Building Code, 1973;9 BOCA = BOCA Basic BuildingCode, 1970;1 0 NBC— National Building Code, 1967;>>_ SSBC = South-ern Standard Building Code, 1969 Edition.12

*2 in. for siliceous aggregate concrete.•j Mesh in cover.

PCI Journal/September-October 1974 33

5 /7_O ry

b }}0 O} -

3 3 ^^

STRUCTURALLIGHTWEIGHT C 9 NCRETE

00

O NM ^} 'c

/NORMAL WEIGHT CONCRETE

3 4

Fig. 9. Fire endurance of steel columns afforded protection by concretecolumn covers. Calculated by use of Eq. (5).

XI

wUZ

X

0zw^wWU-

4

0

2 3 4 0 I 2

(Q) (b)

t, THICKNESS OF COLUMN COVER, IN.

Precast Concrete Column Covers

Steel columns are often clad withprecast concrete panels or covers forarchitectural reasons. Such covers alsoprovide fire protection for the columns.

Fig. 9 shows the relationship be-tween the thickness of concrete columncovers and fire endurance for varioussteel column sections. The fire endur-ances shown are based on an empiricalrelationship developed by Lie andHarmathy.13

The above authors 13 also found thatan air space between the steel core andthe column covers has only a minoreffect on the fire endurance. An air

space will probably increase the fireendurance but only by an insignificantamount.

Most precast concrete column coversare 3 in. or more in thickness, but someare as thin as 21 in. From Fig. 9, it canbe seen that precast concrete columncovers can qualify for fire endurancesof at least 21 hr, and usually morethan 3 hr. For steel column sectionsother than those shown, includingshapes other than wide flange beams,interpolation between the curves on thebasis of weight per foot will generallygive reasonable results.

For example, the fire endurance af-forded by a 3-in, thick column cover of

34

D

(a) (b)

(c) (d)

(e) (f)

Fig. 10. Types of precast concrete columncovers; (a) would probably be most vul-nerable to bowing during fire exposurewhile (f) would probably be the least vul-

nerable.

normal weight concrete for a 8 x 8 x 1/z-in. steel tube column will be about 3 hr20 min. (the weight of the section is47.35 lb per ft).

Precast concrete column covers (Fig.10) are made in various shapes such as(a) four flat panels with mitered sidesthat fit together to enclose the steelcolumn, (b) four L-shaped units, (c)two L-shaped units, (d) two U-shapedunits, and (e) and (f) U-shaped unitsand flat closure panels. There are, ofcourse, many combinations to accom-modate isolated columns, corner col-umns, and columns in walls.

To be fully effective the column cov-ers must remain in place without severedistortion. Many types of connectionsare used to hold the column covers inplace. Some connections consist of bolt-ed or welded clip angles attached to thetops and bottoms of the covers. Othersconsist of steel plates embedded in thecovers that are welded to angles, plates,or other shapes which are, in turn,welded or bolted to the steel column.In any case, the connections are usedprimarily to position the column coversand as such are not highly stressed. Asa result, temperature limits need not be

PCI Journal/September-October 1974 35

applied to the steel in most columncover connections.

If restrained, either partially or fully,concrete panels tend to deflect or bowwhen exposed to fire. For example,a steel column that is clad with fourflat panels attached top and bottom, thecolumn covers will tend to bulge atmidheight thus tending to open gapsalong the sides. The gap size decreasesas the panel thickness increases.

With L, C, or U-shaped panels, thegap size is further reduced. The gapsize can be further minimized by con-nections at midheight. In some cases,ship-lap joints can be used to minimizethe effects of joint openings. Fig. 10shows various column cover configura-tions.

Joints should be sealed in such a wayto prevent passage of flame to the steel

column. A noncombustible materialsuch as sand-cement mortar or asbestosrope can be used to seal the joint.

Precast concrete column coversshould be installed in such a mannerthat if they are exposed to fire, theywill not be restrained vertically. As thecovers are heated they tend to expand.Connections should accommodate suchexpansion without subjecting the coverto additional loads.

Fire resistive compressible materials,such as mineral fiber safing, can be usedto seal the tops or bases of the columncovers, thus permitting the columns toexpand. Similarly the connections be-tween the covers and columns shouldbe flexible (or "soft") enough to ac-commodate thermal expansion withoutinducing much stress into the covers.

REFERENCES

1. ASTM Designation: E119-73,"Standard Methods of Fire Tests ofBuilding Construction and Materi-als," ASTM Book of Standards,American Society for Testing andMaterials, Philadelphia, Pennsylva-nia, 1973.

2. PCI Committee on Fire ResistanceRatings, "Fire Endurance of Pre-stressed Concrete Double-Tee WallAssemblies," PCI JOURNAL, Vol.17, No. 4, July-August, 1972, pp.19-28.

3. National Building Code of Canada,1970 Edition, (NRC No, 11246),Associate Committee on the Na-tional Building Code, National Re-search Council, Ottawa, Canada.

4. Wisconsin Administrative Code,Rules of Department of Industry,Labor and Human Relations, Mad-ison, Wisconsin.

5. Abrams, M. S., and Gustaferro,A. H., "Fire Endurance of Con-crete Slabs as Influenced by Thick-ness, Aggregate Type, and Mois-ture," PCA Research DepartmentBulletin 223.

6. Abrams, M. S., and Gustaferro,A. H., "Fire Endurance of Two-Course Floors and Roofs," ACIJournal, Proceedings Vol. 66, No.2, 1969.

7. "Fire Resistance Classifications ofBuilding Constructions," ReportBMS 92, National Bureau of Stan-dards, Washington, D.C., 1942,70 pp.

8. Lie, T. T., "Constribution of Insu-lation in Cavity Walls to Propaga-tion of Fire," Fire Study No. 29,Division of Building Research, Na-tional Research Council of Canada,Ottawa, Canada.

36

9. Uniform Building Code, 1973 Edi-tion, International Conference ofBuilding Officials, Whittier, Calif.

10. Basic Building Code, 1970 Edition,Building Officials and Code Ad-ministrators International, Inc.,Chicago, Illinois.

11. National Building Code, 1967 Edi-tion, American Insurance Associa-tion, New York, New York.

12. Southern Standard Building Code,1973 Edition, Southern BuildingCode Congress, Birmingham, Ala-bama.

13. Lie, T. T., and Harmathy, T. Z.,"Fire Endurance of Concrete-Pro-tected Steel Columns," ACI Jour-nal, Proceedings Vol. 71, No. 1,1974.

Discussion of this report is invited.Please forward your discussion to PCI Headquartersby February 1, 1975, to permit publication in theMarch-April 1975 PCI JOURNAL.

PCI Journal/September-October 1974 37