dai 2009

ARTICLE IN PRESS

Fire Safety Journal 44 (2009) 376386Contents lists available at ScienceDirectFire Safety Journal0379-71

doi:10.1

CorrE-m

yong.wajournal homepage: www.elsevier.com/locate/firesafEffects of partial fire protection on temperature developments in steel jointsprotected by intumescent coatingX.H. Dai, Y.C. Wang , C.G. Bailey

School of Mechanical, Aerospace and Civil Engineering, University of Manchester, PO Box 88, Manchester M60 1QD, UKa r t i c l e i n f o

Article history:

Received 21 May 2008

Received in revised form

19 August 2008

Accepted 25 August 2008Available online 2 October 2008

Keywords:

Steelconcrete composite joints

Partial fire protection

Intumescent coating

Temperature

Fire tests

Fire resistance

Unprotected bolts12/$ - see front matter & 2008 Elsevier Ltd. A

016/j.firesaf.2008.08.005

esponding author. Tel.: +441613068968.

ail addresses: [email protected],

[email protected] (Y.C. Wang).a b s t r a c t

This paper presents experimental results of temperature distribution in fire in four typical types of

steelconcrete composite joint (web cleat, fin plate, flush endplate and flexible endplate) with different

fire-protection schemes. The test specimens were unloaded and the steelwork of each joint assembly

was exposed to a standard fire condition [ISO 834, 1975: Fire Resistance Tests, Elements of Building

Construction, International Organization for Standardization, Geneva] in a furnace. In total, 14 tests

were conducted, including 4 tests without any fire protection and 10 tests with different schemes of fire

protection. The main objective of these tests was to investigate the effects of three practical fire-

protection schemes as alternatives to full fire protection of the entire joint assembly. The three

alternative methods of fire protection were: (1) protecting a segment, instead of the entire length, of the

beams; (2) unprotected bolts and (3) protecting the columns only. The main results of these tests are:

(1) if all the steel work (excluding the bolts) in the joint assembly was protected, whether or not

protecting the bolts had very little effect on temperatures in the protected steelwork other than the

bolts. The bolt temperatures were higher if they were not protected than if they were protected, but the

unprotected bolt temperatures in a joint with fire protection to other steelwork were much lower than

bolt temperatures in a totally unprotected joint; (2) as far as joint temperatures are concerned,

protecting a segment of 400mm of the beam was sufficient to achieve full protection and (3) if only the

column was protected, only the joint components that were in the immediate vicinity of the column

(such as welds) developed noticeably lower temperatures than if the joint assembly was unprotected,

but due to heat conduction from the unprotected steel beams, these temperature values were much

higher than if the joint assembly was protected. Furthermore, the column temperatures in the joint

region were much higher than the protected column temperatures.

& 2008 Elsevier Ltd. All rights reserved.1. Introduction

Joints are critical members in steel-framed structures. Inparticular, how joints behave in steel-framed structure has acritical influence in controlling progressive collapse of thestructure under accidental fire attack. Despite extensive previousresearch on steel-framed structures in fire, which has resulted inthe development of fire engineering design methods that are nowbeing routinely adopted in steel structural design, large gaps stillexist in the understanding of joint behaviour in fire. Following theWorld Trade Center disaster, a number of authoritative organisa-tions [1,2] have identified joint integrity as key to maintainingstructural integrity in a fire and have called for extensive researchon joints under fire conditions.ll rights reserved.The current practice [3] to ensure that joints have sufficient fireresistance is simple: to protect joints to the highest level of fireprotection based on the connected members. This is based on theassumption that because joint components have lower sectionfactors compared to the connecting members (defined as the ratioof the fire-exposed surface area to the volume of steel beingheated) the temperature rise in the joint components is lowerthan in the connected members. One immediate shortcoming ofthis approach is that some joint components may be subject tohigher levels of loading than the connected members. Moreimportantly, under fire conditions, the behaviour of a steelstructure is complex with forces in different members changingduring the entire course of fire exposure. These forces aretransmitted from one connected member to another, mainlydependent on the behaviour and performance of the joints,making understanding joint behaviours in fire a key factor instructural fire design.

Understanding structural behaviour in fire involves threegeneral steps: quantifying the fire behaviour, assessment of

www.sciencedirect.com/science/journal/fisjwww.elsevier.com/locate/firesafdx.doi.org/10.1016/j.firesaf.2008.08.005mailto:[email protected],mailto:[email protected] FaisalHighlight

Arbab FaisalHighlight

Arbab FaisalSticky Notewhy study fire behavior of joints

ARTICLE IN PRESS

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386 377temperature development in the structure and understanding thestructural behaviour at elevated temperatures. For joints, thefocus has mainly been on joint structural behaviour at elevatedtemperatures [412]. This paper deals with quantification of thetemperature development in different joint components.Although there have been studies of temperature developmentin steel joints in fire [1316], these studies were concerned withthe temperatures in unprotected steel joints. The focus of thispaper is on protected steel joints. In particular, this paper dealswith temperatures in joints protected by intumescent coating.Steel being a thermally high conductive material, the temperaturerise in unprotected steel exposed to fire attack is quick, resultingin rapid loss in strength and stiffness of steel in fire. To ensuresufficient fire resistance of steel-framed structures, fire protectionis often required to limit temperature rises in steel. Currently,intumescent coating is the most popular type of fire protection,representing about 50% of the passive fire-protection market inthe UK. Application of intumescent coating fire protection tojoints can be a time-consuming process. Therefore, an importantassociated objective of this study is to develop rules for effectiveapplication of intumescent coating in practice. Intumescentcoating may be applied either on- or off-site. In on-site applicationof intumescent coating, unprotected steel members with suitableconnection components are assembled in the fabrication shop andapplication of the fire protection commences after site erection ofthe steel structure. In off-site application of intumescent coating,steel members together with the welded connection componentsare sprayed with intumescent coating and then assembled on site.Off-site application of intumescent coating is gaining popularityowing to better quality control and possible saving in constructiontime. Scope exists to improve the efficiency of both on- and off-site application of intumescent coating fire protection withoutcompromising fire-resistance performance of the joints. In thisresearch, fire tests on joints with different schemes of intumes-cent coating fire protection were conducted to investigate theeffects of the following three possible methods of reducing fireprotection to joints:(1) Full protection of joint components and connected membersexcept bolts.(2) Protecting a short segment of the connected beams. This isrelevant to joints in steel-framed structures where theconnected beams are unprotected but the joint and thecolumn are protected.(3) Protecting only the columns. This is relevant to joints in steel-framed structures where only the columns require fireprotection due to their critical importance to maintain globalstructural stability in fire.Conducting fire tests on loaded specimens is extremely timeconsuming and expensive. Therefore, the fire tests reported in thispaper were on unloaded specimens. Nevertheless, since this paperis mainly concerned with the relative temperature performance ofjoints with partial fire protection compared to those with total fireprotection, it is expected that the main conclusions of the paperwould be the same regardless whether or not the specimens areloaded. In total, 10 steel joint specimens with different schemes offire protection were fire tested in the gas furnace of the Universityof Manchester. In an earlier part of this study [17], 4 steel jointspecimens without any fire protection were also fire tested in thesame furnace. This paper will mainly present the experimentalobservations and results of the protected joints, but will also makereference to the unprotected fire tests. A follow on paper willpresent the results of analytical and numerical studies and thedevelopment of a design method for calculating temperatures indifferent connection components for implementation in subse-quent structural analysis of joints using either finite-elementmethod or the component-based joint characterisation method[18]. In addition, temperature calculation is only part of theprocess of quantifying structural fire resistance. Follow-onresearch studies are being carried out to investigate the effectsof partial fire protection on structural performance of joints.2. Research significance

Fire attack represents a significant risk to steel-framedstructures. Until very recently, joint behaviour in fire has receivedlittle attention from researchers, even though joint behaviour hasa critical influence on controlling progressive collapse of struc-tures under fire attack. Accurate prediction of temperatures injoints represents the first step towards thorough understandingand rational design of joints in steel-framed structures in fire.From a practical point of view, efficient application of intumescentfire protection can help to maintain the advantages of steel-framed structures. This paper will report results of temperaturesin partially protected steel joints in fire, which will have practicalimplications on how cumbersome fire protection to somecomponents of joints may be eliminated without compromisingsafety of the structure.3. Test specimens and set-up

3.1. Description of test specimens

A series of fire tests were conducted on steelconcrete compositejoint assemblies with four types of joints; web cleat, fin plate, flushendplate and flexible endplate, see Fig. 1. Four tests were performedon joints without any fire protection and 10 tests on joints withdifferent fire-protection schemes using intumescent coating. Itshould be pointed out that to enable extensive measurement oftemperatures and also to reduce the cost of fire tests, the jointspecimens were not loaded. Each joint assembly consisted of onecolumn, four beams (two bolted to the column flanges via theaforementioned four different types of joints and the other twobolted to the column web via fin plates) and a concrete slab withprofiled steel sheeting and mesh reinforcement. Fig. 1 shows the 3Dconfigurations of these joint assemblies. The column in all the testspecimens was the same, being UC254254 89 and with a lengthof 1000mm. The beam section in all the test specimens was also thesame, being UB30516540. The length of the steel beamsconnected to the column flanges was 605mm and the length ofthe steel beams connected to the column web was 485mm. Table 1gives detailed dimensions of joints for different test specimens,including the four unprotected specimens identified as USP1USP4and 10 protected specimens identified as SP1SP10. The dimensionof the concrete slab was 10001000mm with an overall depth of130mm. All columns, beams and joint components were in gradeS275 and grade 8.8 bolts of 20mm in diameter were used. To enableconnections of different dimensions to be directly compared, someof the tests used connectors of different dimensions in the same testto join the two steel beams connected to the flanges of the column.

3.2. Fire-protection schemes

As previously mentioned, the fire tests were designed toinvestigate the effects of different fire-protection schemes on thetemperature development within joint assemblies, focusing onthe following three principal aspects: (1) not protecting bolts;(2) protecting a small length of the beam near the joint and

ARTICLE IN PRESS

Fig. 1. Joint types and configurations: (a) web cleat joint assembly; (b) fin platejoint assembly; (c) flush endplate joint assembly and (d) flexible endplate joint

assembly.

Table 1Detailed dimensions of joint components

Specimen ID Join type to column flange Joint component to one

column flange

USP1 Flush endplate

USP2 Flexible endplate

USP3 Fin plate 20010010

USP4 Web cleats 1509010 (depth200SP1 Web cleats

SP2 Web cleats

SP3 Web cleat

SP4 Fin plate 20015010SP5 Fin plate

SP6 Fin plate

SP7 Flush endplate

SP8 Flush endplate

SP9 Flexible endplate

SP10 Flexible endplate

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386378(3) protecting the column only. Therefore, to achieve this aim, thefollowing four fire-protection options were adopted to theconnected beams:(1)32

2

)

32

2

Full protection including the bolts (to be referred to as FP+B): theentire beam length (including the unconnected end cross-sections of the beams) and the beam connectors including thebolts.(2) Full protection but not including bolts (to be referred to as FP_B):as in (1) but with the bolts unprotected.(3) Partial protection including bolts (to be referred to as P300+B orP400+B): a segment of 300mm (for beams connected to thecolumn web) or 400mm (for beams connected to the columnflanges) of the beams from the corresponding connection endswas protected, including all the beam connectors and bolts.(4) Partial protection not including bolts (to be referred to as P300_Bor P400_B): as in (3) but not including the bolts.The columns were fully protected but the column connectorshave two fire-protection options: (1) full protection includingbolts (FP+B) and (2) full protection not including bolts (FP_B).

Fig. 2 shows two fire-protected specimens before testing andTable 2 summarises the main features of the 14 tests, including the 4unprotected specimens identified as USP1USP4. In Table 2, Beams 1and 2 refer to the beams connected to the column flanges (605mmlong) and Beams 3 and 4 refer to the beams connected to the columnweb (485mm long). As shown in Fig. 2(a), the short beams (Beams 3and 4) were perpendicular to the span of the decking. Hence, theywere connected to the steel decking via shear connectors. The longerbeams (Beams 1 and 2) were not connected to the steel decking.Since intumescent coating was applied after the steel decking wasalready connected to Beams 3 and 4, the upper surface of Beams 3and 4 (which were connected to the steel decking) could not becoated. In contrast, all surfaces of Beams 1 and 2 were coatedaccording to the prescribed fire-protection schemes.

Intumescent coating fire protection was applied by theintumescent coating manufacturers own application team. Thenominal intumescent coating thickness was specified to limitthe steel temperature rise to 550 1C at 60min of the standard fireexposure to BS 476. Dry film thickness (DFT) measurements weretaken at a number of locations in each specimen prior to firetesting. Table 3 gives the average DFTs for different specimens. Itcan be seen that although the beams and columns used the samesection sizes in all tests, the actual average coating thicknesses forJoint component to the

other column flange

Fin plates welded

to column web

420010

20010010

00150820015010

909010 (depth200)

20010010

420010

001508

ARTICLE IN PRESS

Fig. 2. Examples of different fire-protection schemes: (a) unprotected bolts; (b) protected bolts.

Table 2Summary of fire-protection schemes

Specimen ID Join type to column flange Column Beam 1 Beam 2 Beam 3 Beam 4

USP1 Flush endplate Unprotected

USP2 Flexible endplate

USP3 Fin plate

USP4 Web cleat

SP1 Web cleat FP+B FP+B P400+B P300+B P300+B

SP2 Web cleat FP_B FP_B P400_B P300_B P300_B

SP3 Web cleat FP_NB None None None None

SP4 Fin plate FP+B FP+B P400+B FP+B FP+B

SP5 Fin plate FP_B FP_B P400_B FP_B FP_B

SP6 Fin plate FP_NB None None None None

SP7 Flush endplate FP+B FP+B P400+B FP+B P300+B

SP8 Flush endplate FP_B FP_B FP_B FP_B FP_B

SP9 Flexible endplate FP+B FP+B P400+B FP+B P300+B

SP10 Flexible endplate FP_B FP_B P400_B FP_B P300_B

Table 3Average dry film thickness (DFT) for different test specimens

Specimen ID Joint type to column flange Average coat thickness (DFT) in mm

Column Beam 1 Beam 2 Beam 3 Beam 4

SP1 Web cleat 0.67 1.02 1.18 1.12 1.15

SP2 Web cleat 0.73 1.02 1.29 1.05 1.09

SP3 Web cleat 0.60 / / / /

SP4 Fin plate 0.75 1.36 1.35 1.24 1.16

SP5 Fin plate 0.77 1.08 1.16 1.3 1.19

SP6 Fin plate 0.62 / / / /

SP7 Flush endplate 0.95 1.29 1.25 1.19 1.15

SP8 Flush endplate 0.84 1.14 1.19 1.43 1.35

SP9 Flexible endplate 0.78 1.21 1.19 1.25 1.33

SP10 Flexible endplate 0.86 1.22 1.16 1.21 1.31

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386 379different specimens varied considerably, being 1.021.43mm onbeams and 0.60.95mm on columns. Also DFT measurements(not presented here) at the different locations of the samemember showed large variations.3.3. Test set-up

Fire tests were carried out in a gas-fired furnace (internaldimensions: 3500mm3000mm2000mm) in the fire labora-tory of the University of Manchester. The interior faces of thefurnace were lined with ceramic fibre materials of thickness200mm that efficiently transferred heat to the specimen. Two gasburners and two exhausts were connected to the furnace. Thefurnace temperatures were recorded by six conventional beadthermocouples. To ensure that the concrete slab surface wasexposed to the ambient air environment, the test specimen wasrotated by 901 and hung inside the furnace via three well-protected steel ropes, as shown in Fig. 3. Fire exposure wasaccording to a standard fire condition [19].

ARTICLE IN PRESS

Fig. 3. Set-up of joint test specimen: (a) view from inside the furnace; (b) view from outside the furnace.

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C

)

Standard Fire Furnace testUSP1 USP2USP3 USP4SP1 SP2SP3 SP4SP5 SP6SP7 SP8SP9 SP10

USP2

SP5

Fig. 4. Average furnace temperatures calculated using furnace-control thermo-couples.

600

800

1000

atur

e (C

)

Standard fire Furnace testUSP2 USP3

USP2

X.H. Dai et al. / Fire Safety Journal 44 (2009) 3763863804. Furnace temperatures

In order to compare recorded temperatures in joints obtainedfrom different specimens, it was assumed that the temperaturefield inside furnace was uniform and identical for different tests.To verify this assumption, Fig. 4 shows the average gastemperatures calculated using readings from the six monitoringthermocouples in the furnace. It can be seen that the averagetemperatures in different tests were very similar and close to theISO 834 [19] standard fire temperature except for tests onspecimens USP2 and SP5, where the average gas temperatureswere slightly higher than the intended standard fire temperaturedue to failure of one control thermocouple. In each test, the gastemperature field around the test specimen was also measured bythermocouples around the test specimen. Fig. 5 shows the averagegas temperatures calculated using the thermocouples fixedaround the test specimens. It can be seen from Fig. 5 thatalthough there is some deviation from the intended standard firetemperature curve, the difference is small (typically less than50 1C), indicating that gas temperature in the fire-test furnace wasalmost uniform. To further confirm this, a supplementary fire testwas carried out, in which there was no test specimen butmeasurements were taken for gas temperatures near where thetest specimen would be placed. Fig. 6 shows the measured gastemperatures at different locations. The differences were small,further confirming uniformity of gas temperature around thetest specimen.00 10 20 30 40 50 60

200

400

Time (minutes)

Tem

per

USP4 SP1SP2 SP3SP4 SP5SP7 SP8SP9 SP10

Fig. 5. Average furnace temperatures calculated using thermocouples around test5. Temperature distributions in connection components withdifferent fire-protection schemes

A large amount of data was collected. As previously mentioned,the focus of this paper is to analyse the effects of three differentpartial fire-protection schemes. The results will be presentedunder these three headings.specimens.5.1. Effects of partial protecting beams

It is now well accepted that a significant number of beams insteel-framed buildings may be left unprotected, through the use offire engineering design methods such as tensile membrane actionin composite floor slabs [2022], control of load ratio or fireseverity [23]. Yet in the majority of buildings using unprotectedsteel beams, the columns and joints would normally have to beprotected to ensure stability of the whole structure and to preventprogressive collapse in fire. Under this circumstance, it isnecessary to decide a suitable length of the beams for fireprotection so that the cost of fire protection of a short segment ofthe beams is minimal, yet the columns and joints perform as iffully protected without suffering high temperature rises due toheat conduction from the unprotected beams away from thejoints. In the intumescent coating industry, a length of 400mmhas been considered adequate, although the basis of this practice

ARTICLE IN PRESS

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386 381is not clear. To investigate the validity of this practice, a series ofjoints, described in the previous sections, with partially protectedbeams (400 and 300mm from the connection zone) were firetested.

Figs. 7 and 8 compare typical temperature distributions in theweb cleat connected to the column flange of test SP1 (represent-ing web cleats and end plates in the column flange zone) and inthe bolts of the fin plates in test SP4 (representing web cleats/finplates/bolts/beam web in the beam web zone). The closeness oftemperature curves (typical difference being about 20 1C) betweenwith full beam fire protection and with partial beam fire00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C) T1 T3T4 T5

T6 T7T8 T10T11 T12T14 T15T16 T17T18 T19T20 T21T22 T23T24 T25T26 T27T-Average T-Standard fire

Fig. 6. Temperature distribution inside the furnace from a supplementary fire testwithout a joint specimen.

UB305X165X40

J-J View

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

90

50 40

J

J

X66

Web cleat150x90x10mm

605

0

100

200

300

400

500

600

Time (m

Tem

pera

ture

(C)

TC66 (full beam

TC51 (partial b

0 10 20 30

Fig. 7. Comparison of temperatures in web cleats connected to column flanges (Tprotection suggests that a length of 400mm of fire protectionon the beams would be sufficient to achieve effective full fireprotection to the connection components within 60min of fireexposure. Fig. 9 compares typical temperatures in a fin platewelded to the column web, where one beam was fully protectedand the other was protected for a length of only 300mm from thejoint end. It appears that temperatures associated with thispartially protected beam were noticeably higher than tempera-tures associated with the fully protected beam (temperaturedifference 450 1C), indicating that it would not be sufficient toachieve full protection to the joint if only 300mm of the adjacentbeam was protected.5.2. Effects of partial protecting bolts

In the general practice of steel structure construction, steelcomponents are fabricated in shops and then transported to sitefor erection. When using off-site intumescent coating, thefabricated steel components (including connection components)are usually applied with intumescent coating in the fabricationfactory. When protection of the bolts is necessary, this is carriedout on site after the steel frame is assembled using pre-coatedmembers and connection components. Application of intumes-cent coating to bolts on site may not be welcomed because of thetime necessary for site operation as well as the difficulty toguarantee quality of on-site application of intumescent coating tobolts. However, if the bolts are left unprotected, they may beoverheated in fire and cause structural failure. Therefore, if boltsare to be unprotected on site, it is important that the effects of thisaction are fully understood and considered in design. The effectsI-I View

90

50 40 4020

0

4060

6040

10

90

50 40

UC254X254X89

UB305X165X40

X52 Web cleat

90x90x10mm

I

I

X51

UncoatedZone

400605

inutes)

protection)

TC52 (partial beam protection: 400mm)

eam protection: 400mm)

40 50 60

est SP1): (a) locations of thermocouples (TC); (b) temperaturetime curves.

ARTICLE IN PRESS

UB305X165X4040

505050

4060

6040

10UC254X254X89

X Fin plate(200x150x10mm)

40

50 50

4060

6040

10

Fin plate(200X

100X10mm)

UB305X165X40

UncoatedZone

400605

605

0

100

200

300

400

500

600

700

800

0 10 20 30 40 50 60Time (minutes)

Tem

pera

ture

(C)


TC24 (full beam protection)TC18 (partial beam protection: 400mm)

TC25 (full beam protection)

X18

X25

17X

24

Fig. 8. Comparison of temperatures in bolts in fin plates welded to column flanges(Test SP4): (a) locations of thermocouples (TC); (b) temperaturetime curves.

0

100

200

300

400

500

600

700

Time (minutes)

Tem

pera

ture

s (C

) TC16 (partial beam protection: 300mm)

TC11(full beam protection)


TC12 (full beam protection)

X16

X17Beam3 Beam4

Unc

oate

d Zo

ne

300

UB305X165X40

485

40

5050

4060

6040

UC254X254X89Fin plate (200x100x10mm)

X11

12X

485

4060

6040

0 10 20 30 40 50 60

Fig. 9. Comparison of temperatures in fin plates welded to columnweb (Test SP7):(a) locations of thermocouples (TC); (b) temperaturetime curves.

UB305X165X40

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

J

J

X60


X58

605

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)

TC60TC58 Test USP4, unprotected specimen

Test SP2, protection scheme: FP_B

Test SP1, protection scheme: FP+B

Fig. 10. Comparison of temperatures in the web cleat on the beam web (TestsUSP4, SP1 and SP2): (a) locations of thermocouples (TC); (b) temperaturetime

curves.

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386382of unprotected bolts on joint and steel frame structural behaviourare being investigated by the authors research group. This paperwill focus on temperature developments.5.2.1. Temperature distributions in connection components on the

beam web

Figs. 10 and 11 compare typical temperature developmentin web cleats and associated bolts (representing connec-tion components on the beam web) between the followingthree fire-protection options: (1) unprotected (UP); (2) fullprotection of web cleats and bolts (FP+B) and (3) full protec-tion of web cleats but no protection of bolts (FP_B). From theresults in Figs. 10 and 11, it is possible to make the followingobservations:(1) If all the connection components were unprotected, theconnection temperatures were much higher than in connec-tions with fire protection regardless of whether or not thebolts were protected.(2) Fig. 10 shows that if the connection components (web cleats)were protected, then not protecting the bolts had a minorinfluence on temperature development in the protectedconnection components (web cleats). In fact, the differencein web cleat temperatures between the two different tests(SP1: with fire protection to bolts; SP2: without fire protectionto bolts) was no greater than the difference in web cleattemperatures at different locations (TC58 and TC60) in thesame test (SP1 or SP2). Results from tests on fin plateconnections were very similar.(3) Comparing the bolt temperatures in Fig. 11, it is clear that ifthe connection components (web cleats) were protected,whether or not protecting the bolts had noticeable effectson the bolt temperatures. As expected, not protecting the bolts(Test SP2) generated higher bolt temperatures than protectingthe bolts (Test SP1). Nevertheless, the difference in bolttemperatures in these two tests (about 100 1C at 60min) is

ARTICLE IN PRESS

Tem

pera

ture

(C)

Fig. 1locat

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386 383much less than the difference in bolt temperatures betweentests on unprotected connection (USP4) and fully protectedconnection including bolts (Test SP1), being about 450 1C at60min. Results from tests on fin plate connections weresimilar. Fig. 12 shows the unprotected bolts in a protected webcleat before and after the test. The bolts were not covered bythe expanded intumescent char so the conclusions of thesetests can be generally applied.5.2.2. Temperature distributions in connection components on the

column flange

Figs. 1315 compare typical temperatures in the connectioncomponents and in the bolts connected to column flanges. Theresults in Figs. 1315 suggest identical trends as described in thelast section. In fact, the results in Fig. 14 indicate higherFig. 12. Unprotected bolts in web cleat before

UB305X165X40

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

J

J

X

X

61

56


605

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

TC61TC56

Test USP4, unprotected specimen

Test SP2, protection scheme: FP-B


1. Comparison of temperatures in the bolts in web cleat on the beamweb: (a)ions of thermocouples (TC); (b) temperaturetime curves.connection temperatures when with full fire protection than withno fire protection on bolts. This is mainly caused by inconsistentintumescent coating behaviour such as coating thickness, but itdoes suggest that not protecting the bolts did not have asignificant detrimental effect. Furthermore, Fig. 15 shows that atthe early stage of the fire exposure, the temperature increasesin the unprotected bolts (fire-protection scheme FP_B) weremuch faster than in the protected bolts (fire-protection schemeFP+B). However, the differences in bolt temperatures almostdisappeared in the later stage of fire test. This is clearly a result ofthe expanded intumescent coating char covering the unprotectedbolts, as shown in Fig. 16(a). Unfortunately, it is not alwayspossible to rely on the expanded intumescent char to coverunprotected bolts. In most cases, the bolts were not coveredby the expanded intumescent coating char as shown in Figs. 12and 16(b).and after 60min fire exposure (Test SP2).

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)

TC64TC63




UB305X165X40

J-J View

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

90

50 40

J

J

64

63X

X


605

Fig. 13. Comparison of temperatures in the web cleat on column flange: (a)locations of thermocouples (TC); (b) temperaturetime curves.

ARTICLE IN PRESS

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)




6070

134

60

10

10605 200

X

50

25

E-E ViewE

E

UB305X165X40

45

Fig. 14. Comparison of temperatures in the flush endplate: (a) locations ofthermocouples (TC); (b) temperaturetime curves.

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)




6070

134

60

10

10605 200

X

50

E-E ViewE

E

UB305X165X40

48

Fig. 15. Comparison of temperatures in the bolts in flush endplate connections: (a)locations of thermocouples (TC); (b) temperaturetime curves.

Fig. 16. Unprotected bolts in protected endplates after 60min fire exposure:(a) bolts being covered by char after fire test (Test SP8); (b) bolts not covered by

char after fire test (Test SP10).

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)


Test SP3, protecting column only

Test SP1, total protection

UB305X165X40

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

J

J

X60


X58

605

Fig. 17. Temperatures in the web cleat on beam web: (a) locations of thermo-couples (TC); (b) temperaturetime curves.

X.H. Dai et al. / Fire Safety Journal 44 (2009) 3763863845.3. Effects of protecting columns only

Because columns are critical structural elements, they gen-erally will require fire protection. In the case of unprotectedbeams and joints, the following question arises: would connectioncomponents benefit from fire protection to the adjacent column?As shown in Table 2, two tests (SP3 and SP6) adopted the columnonly fire-protection scheme for web cleat and fin plate connec-tions. This section presents the effects of protecting columns onlyon the temperature distribution in these two types of connectioncomponents. Figs. 17 and 18 compare temperatures for the webcleat connections between full protection (FP+B, Test SP1),protecting column only (PC, Test SP3) and no fire protection (UP,Test USP4). Fig. 17 shows that for the connection components onthe beam web, protecting column only was of no benefit inreducing the connection temperatures. On the other hand, Fig. 18indicates that if the connection components were contacted to theprotected column flange (Test SP3), the connection temperatureswere noticeably lower than in the unprotected test specimen (TestUSP4). However, since the connection temperatures in the columnonly protection specimen were much higher than in the fullyprotected case (Test SP1), it is probably prudent to ignore thebenefit of reduction in connection component temperatures due

ARTICLE IN PRESS

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)




UB305X165X40

J-J View

4020

0

150

4060

6040

10

50 50 50

UC254X254X89

9050 40

J

J

64

63X

X


605

Fig. 18. Temperatures in the web cleat connected to column flange: (a) locations ofthermocouples (TC); (b) temperaturetime curves.

00 10 20 30 40 50 60

200

400

600

800

1000

Time (minutes)

Tem

pera

ture

(C)




40

505050

4060

6040

10

20

19X

X

UB305X165X40

UC254X254X89

Fin plate (200x150x10mm)

Fig. 19. Temperatures in welds on column: (a) locations of thermocouples (TC);(b) temperaturetime curves.

600

800

1000

ture

(C)



X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386 385to column protection only. Only Fig. 19 suggests that temperaturesin the welds, on the protected column flange, were much lowerthan if the joint assembly was completely unprotected (TestUSP3). Although the weld temperatures were higher than in thefully protected test specimen (Test SP4), the reduction in weldtemperature due to fire protecting the column alone wassubstantial and may be usefully exploited in joint design.

It is expected that for temperatures in the column in the jointregion, if only the column was protected by intumescent coatingand the connectionwas not protected, the fire protectionwould notbe as effective as when the entire joint assembly was protected,because the intumescent coating on the connection side would notbe able to expand and the column flange would receive conductedheat from the unprotected connection. Fig. 20 shows confirmation.Similar temperature trends were observed in the test using fin plateconnections. For safe design of joints, the column components ofthe joint should be assumed to be unprotected.00 10 20 30 40 50 60

200

400

Time (minutes)

Tem

pera

Test SP1, fully protected joint assembly

Fig. 20. Temperatures in column in the joint region: (a) locations of thermo-couples (TC); (b) temperaturetime curves.6. Conclusions

This paper describes fire experiments on unloaded steelcon-crete composite joints with four types of connection: web cleat,fin plate, flush endplate and flexible endplate. Results arepresented for representative temperature distributions in connec-tion components to demonstrate the effects of different fireprotection schemes, including protecting only a short segment ofthe connected beams, not protecting bolts in a protected joint andprotecting the column only. Based on comparisons and analyses oftemperature distributions in various connection components, thefollowing main conclusions may be drawn:(1) Protecting a segment of the connected beams by about400mm from the joint appeared to be sufficient to achievefull protection for the joint. As far as the joint is concerned, theeffect is similar in protecting the joint with steel of 400mm inlength. Thus, this conclusion indicates that the 400mm steel

ARTICLE IN PRESS

X.H. Dai et al. / Fire Safety Journal 44 (2009) 376386386protection has similar thermal resistance (thickness dividedby thermal conductivity) as the applied intumescent coating.Further numerical investigations are being carried out toassess whether this 400mm rule would be applicable underother conditions, e.g. different coating thickness.(2) In a protected joint with unprotected bolts, the unprotectedbolt temperatures were higher than those with full boltprotection, but the bolt temperatures were still much lowerthan those in completely unprotected joints.(3) In a protected joint, leaving the bolts unprotected had littleinfluence on temperatures in other connection components,i.e. end plates/fin plates/web cleats/beam/column.(4) Compared to unprotected joints, protecting the column onlyhad little benefit in reducing the temperatures in connectioncomponents except for the welds on the column.(5) Although protecting the column only did reduce columntemperatures in the joint region compared to a totallyunprotected joint, the column temperatures in the jointregion were substantially higher than those in a fullyprotected joint assembly due to the heat conducted from theunprotected connection components and beams. It would beprudent to assume the column is unprotected when calculat-ing column temperatures in the joint region.Due to limitations in sources and time, only representativeconnections were fire tested in this research. Nevertheless, it isexpected that the above conclusions would hold for connectionsof other practical dimensions. Further research studies are beingconducted to develop a method for calculation of temperatures indifferent types of joints with different fire-protection schemes andalso to understand the implications on structural behaviour byadopting different fire-protection schemes.Acknowledgements

This research is funded by a research grant from the UKsEngineering and Physical Science Research Council (EP/C003004/1). The authors would like to thank Mr. Jim Gorst and Mr. Jim Geefor assistance with the fire tests.

References

[1] Federal Emergency Management Authority (FEMA), World Trade CenterBuilding Performance Study, FEMA, USA, 2002.

[2] Institution of Structural Engineers (ISE), Safety in Tall Buildings and Buildingsof Large Occupancy, Institution of Structural Engineers, London, 2002.

[3] British Standards Institution (BSI, 2003), BS 5950 (2003), Structural Use ofSteelwork in Buildings, Part 8: Code of Practice for Fire Resistant Design,British Standards Institution, London.[4] K.S. Al-Jabri, I.W. Burgess, R.J. Plank, Spring-stiffness model for flexibleend-plate bare-steel joints in fire, J. Constr. Steel Res. 61 (11) (2005)16721691.

[5] F.M. Block, I.W. Burgess, J.B. Davison, R.J. Plank, The development of acomponent-based connection element for endplate connections in fire, in:P. Vila Real, J.M. Franssen, N. Lopes (Eds.), SIF06Fourth InternationalWorkshop on Structures in Fire, Aveiro, Portugal, vol. 1, 2006, pp. 345356.

[6] I.W. Burgess, Connection modelling in fire, in: F. Wald, F. Mazzolani, M.Byfield, D. Dubina, M. Faber (Eds.), Proceedings of the EU COST C26 ActionWorkshop in Prague, 2007, pp. 2534.

[7] J. Ding, Y.C. Wang, Experimental study of structural fire behaviour of steelbeam to concrete filled tubular column assemblies with different types ofjoints, Eng. Struct. 29 (12) (2007) 34853502.

[8] L.S. da Silva, A. Santiago, P. Vila Real, A component model for the behaviour ofsteel joints at elevated temperatures, J. Constr. Steel Res. 57 (11) (2001)11691195.

[9] S. Spyrou, J.B. Davison, I.W. Burgess, R.J. Plank, Experimental and analyticalinvestigation of the compression zone component within a steel joint atelevated temperatures, J. Constr. Steel Res. 60 (6) (2004) 841865.

[10] S. Spyrou, J.B. Davison, I.W. Burgess, R.J. Plank, Experimental and analyticalinvestigation of the tension zone component within a steel joint at elevatedtemperatures, J. Constr. Steel Res. 60 (6) (2004) 867896.

[11] Y.C. Wang, J. Ding, Experimental behaviour of steel joints to concrete filledsteel tubular column in fire, in: The Fourth International Symposium on SteelStructures, 1618 November 2006, Seoul, Korea, 2006.

[12] H.X. Yu, I.W. Burgess, J.B. Davison, R.J. Plank, Experimental investigation of thebehaviour of fin plate connections in fire, in: Wang, Choi (Eds.), Proceedings ofthe Third International Conference on Steel and Composite Structures(ICSCS07), Taylor & Francis Group, London, 2007.

[13] J. Ding, Y.C. Wang, Temperatures in unprotected joints between steel beamsand concrete-filled tubular columns in fire, Fire Saf. J., 2008, in press,doi:10.1016/j.firesaf.2008.02.004.

[14] F. Wald, et al., The temperature distribution in a full-scale steel framedbuilding subject to a natural fire, in: The Second International Conference onSteel and Composite Structures (ICSCS04), Seoul, Korea, September 24, 2004.

[15] F. Wald, L. Simoes da Silva, B.B. Moore, et al., Experimental behaviour of asteel structure under natural fire, Fire Saf. J. 41 (7) (2006) 509522.

[16] F. Wald, M. Pultar, J. Chlouba, Fire tests on industrial building. Steel andComposite Structures, in: Y.C. Wang, C.K. Choi (Eds.), Proceedings of the ThirdInternational Conference on Steel and Composite Structures (ICSCS07), Taylor& Francis Group, London, 2007.

[17] X.H. Dai, Y.C. Wang, C.G. Bailey, Temperature distribution in unprotected steelconnections in fire, in: Y.C. Wang, C.K. Choi (Eds.), Proceedings of the ThirdInternational Conference on Steel and Composite Structures (ICSCS07), Taylor& Francis Group, London, 2007.

[18] Committee of European Normalisation (CEN, 2005), BS EN 1993-1-8: 2005,Eurocode 3: Design of steel structuresPart 18: Design of joints, BritishStandards Institution, London.

[19] ISO 834, Fire Resistance Tests, Elements of Building Construction, Interna-tional Organization for Standardization, Geneva, 1975.

[20] C.G. Bailey, D.B. Moore, Structural behaviour of steel frames with compo-site floorslabs subject to fire: part 1: theory, Struct. Eng. 77 (11) (2000)1927.

[21] C.G. Bailey, D.B. Moore, Structural behaviour of steel frames with compositefloorslabs subject to fire: part 2: design, Struct. Eng. 77 (11) (2000) 2833.

[22] G.M. Newman, J.T. Robinson, C.G. Bailey, Fire Safe Design; A New Approach toMulti-storey Steel-Framed Buildings (second edition), SCI Publication P288,The Steel Construction Institute, Ascot, 2006.

[23] Y.C. Wang, Steel and Composite Structures, Behaviour and Design for fireSafety, Spon Press, London, 2002.

dx.doi.org/10.1016/j.firesaf.2008.02.004

Effects of partial fire protection on temperature developments in steel joints protected by intumescent coatingIntroductionResearch significanceTest specimens and set-upDescription of test specimensFire-protection schemesTest set-up

Furnace temperaturesTemperature distributions in connection components with different fire-protection schemesEffects of partial protecting beamsEffects of partial protecting boltsTemperature distributions in connection components on the beam webTemperature distributions in connection components on the column flange

Effects of protecting columns only

ConclusionsAcknowledgementsReferences

dai 2009

Documents

joint temperatures

protected column temperatures

joint assemblywas

joint components

entire joint assembly

lower temperatures

protected steelwork

lower thanbolt temperatures