Test Data on Intumescent Fire Protection for Structural Steel Sections in Thailand

Transcription

1 Artcle Test Data o Itumescet Fre Protecto for Structural Steel Sectos Thalad Thayawat Pothsr * ad Nattawut Hemathul Fre Safety Research Ceter, Departmet of Cvl Egeerg, Faculty of Egeerg, Chulalogkor Uversty, Bagkok, Thalad E-mal: fcetps@eg.chula.ac.th * Abstract. Curret fre safety regulatos Thalad requre that prmary structural steel compoets of buldgs be protected to acheve a mmum of 3-hour fre-resstace ratg. For steel roof structures, 1-hour or 2-hour fre-resstace ratgs may be specfed depedg o the umber of stores. The verfcato methods of fre-resstace ratgs set forth the regulatos are ISO 834 ad ASTM E119 stadards. The curret tred of fre protecto system for steel structures s tumescet pat due to aesthetcal reasos. However, the fre-resstace ratgs attaed by propretary tumescet systems curretly avalable the market are coclusve. It s therefore the am of ths paper to provde a sght of the fre-resstace ratgs of dfferet tumescet products based o the data collected from the fre tests coducted by the Fre Safety Research Ceter of Chulalogkor Uversty durg the perod of A statstcal aalyss was also coducted to compare the test data wth the fre-resstace ratgs specfed the curret fre safety regulatos. Keywords: Steel, tumescet, fre resstace, fre safety. ENGINEERING JOURNAL Volume 16 Issue 2 Receved 2 November 2011 Accepted 17 Jauary 2012 Publshed 1 Aprl 2012 Ole at DOI: /ej

2 1. Itroducto Fre safety regulatos for structural compoets of buldgs Thalad are geerally based o the requremets set forth Msteral Regulato (MR) 60, B.E. 2549, ssued by the Mstry of Iteror. Accordg to MR 60, prmary structural compoets whch are steel colums ad beams that are ot protected by cocrete coverg must be protected by other meas to meet a mmum of 3-hour freresstace ratg. For steel roof structures, a mmum of 1-hour fre-resstace ratg s specfed f the buldgs are oe-story hgh, otherwse a mmum of 2-hour fre-resstace ratg s requred. The freresstace ratg of steel roof structures ca be exempt for buldgs wth less tha 1,000 square meters of occupacy area, or the clearace heght of the roof structure exceeds 8 meters provded that the buldgs are equpped wth automatc sprkler system. The stadards referred MR 60 for the verfcato of fre resstace ratgs are ISO 834 [1] ad ASTM E119 [2]. It s well kow that uprotected steel members ca heat up at approxmately the same rate as the surroudg temperature rse, especally for th sectos wth a large exposed surface area [3]. To acheve the fre-resstace ratgs specfed by the curret buldg regulatos thus requres that the steel structures be protected. May alteratve methods for fre protecto of steelwork have bee adopted Thalad. A tradtoal method s ecasemet poured cocrete. Ths system has ot bee wdely used due to ecoomc ad aesthetc reasos. Board systems ad spray-o systems have also bee troduced the market the past few decades. However, these systems are ot popular amog archtects based o the aesthetc pot of vew. The curret tred of fre protecto system for steel structures s tumescet pat. Itumescet pat s a specal materal that expads to a sulatg foam layer upo beg heated. The pat may be waterbased or solvet-based ad several coats of pat must geerally be appled to obta the requred thckess. The key advatage of tumescet pats s that they allow the structural steel members to be see drectly, wthout ay coverg other tha the pat. However, the fre-resstace ratgs attaed by propretary tumescet systems curretly avalable the market are coclusve. It s therefore the am of ths paper to provde a sght of the fre-resstace ratgs of dfferet tumescet products based o the data collected from the fre tests coducted by the Fre Safety Research Ceter of Chulalogkor Uversty durg a 3-year perod ( ). A statstcal aalyss was also coducted to compare the test data wth the fre-resstace ratgs specfed the curret fre safety regulatos. 2. Fre-Resstace Test Data The data preseted ths paper were collected based maly o the test results obtaed from a seres of fre-resstace tests coducted at the Fre Safety Research Ceter (FSRC) durg the perod of wth a permsso grated by the Departmet of Cvl Egeerg, Chulalogkor Uversty. The followg paragraphs descrbe detals of the test set-up ad equpmet. The test furace of FSRC s equpped wth sx LPG-fueled burers located at two dfferet levels as llustrated Fg. 1. There are sx thermocouples stalled alogsde the burers to motor the temperature dstrbuto sde the furace chamber durg the fre test. The teral dmesos of the furace chamber are 900 mm x 2500 mm x 1700 mm. For the test data cosdered here, the tme-temperature relatoshp sde the furace was cotrolled to follow ASTM E119 stadard fre curve. The specmes were structural steel members of Grade ASTM A36 wth varyg cross sectos as show Table 1. The steel members were protected wth 15 dfferet propretary tumescet systems from 9 compaes. Detaled specfcatos of each tumescet product were tetoally excluded from ths paper to preserve dettes of these compaes. Because the rate of temperature rse of a protected structural steel member.e., the fre-resstace ratg s versely proportoal to the secto factor, whch s a measure of the rato of the heated permeter H to the area of the cross secto A [4], the defto of secto factor was also provded Table 1. The legth of the specmes was fxed at 1000 mm to eable them to ft wth the test furace. Each specme was stalled by bolts to the ld of the furace such that all sdes were exposed to heat whle the eds of the specme were protected wth thermal sulato to lmt drect heat trasfer from the furace. The alteratve test procedure as specfed ASTM E119 was used to evaluate the protecto of steel sectos wthout applcato of desg load. Temperatures of the steel were measured wth ot fewer tha three thermocouples at each of two levels 86 ENGINEERING JOURNAL Volume 16 Issue 2, ISSN ( p

3 located 300 mm from the eds of the steel member. Typcal thermocouple dstrbutos are show Fg. 2. The fre-resstace ratg was determed as the perod of fre exposure for whch the trasmsso of heat through the protecto dd ot rase the average temperature of the steel at ay oe of the two levels above 538 C, or dd ot rase the temperature above 649 C at ay oe of the measured pots. The fre-resstace ratg (FRR) data were plotted wth respect to the secto factor as show Fg. 3. The FRR data set cotas the test results of 138 I-shaped sectos (wth coatg thckesses the rage of m), 8 L-shaped sectos (wth coatg thckesses the rage of m), 7 rectagular hollow structural sectos (wth coatg thckesses the rage of m) ad 3 crcular hollow structural sectos (wth coatg thckesses the rage of m). It ca be see from the fgure that, for I-shaped sectos, 11.6% (16/138) of the test data fall below the 1-hour FRR crtero whle 87% (120/138) ad 99.3% (137/138) of the test data fall below the 2-hour ad 3-hour FRR crtera, respectvely. For L-shaped sectos, 75% (6/8) ad 100% (8/8) of the test data fall below the 1- hour ad 2-hour FRR crtera, whle for rectagular hollow structural sectos 42.9% (3/7) ad 100% (7/7) of the test data fall below the 1-hour ad 2-hour FRR crtera. For crcular hollow structural sectos, however, 100% (3/3) of the test data fall wth the 1-hour ad 2-hour FRR crtera. To exame the FRR data probablstc terms, a more rgorous statstcal aalyss was performed the subsequet sectos. It should be oted here that the FRR data used for the curret study were collected from a seres of approval tests whch the key objectve of these tests was to detfy whether the tumescet product could satsfy the FRR requremets specfed MR 60 (1-hour, 2-hour or 3-hour fre-resstace ratgs). The thckesses of each propretary tumescet product were specfed by the sposorg compay specfcally for the dvdual steel sectos to be tested. The am of the curret study s ether to vestgate the varato of FRR wth respect to the types of tumescet systems or the coatg thckess, but rather to vestgate FRR as a targeted varable. As such, the followg secto the FRR data were treated as depedet varables regardless of the coatg thckess ad the secto factor. 3. Statstcal Data Aalyss Ths secto provdes detals for evaluatg the fre-resstace ratgs (FRRs) of steel members protected wth dfferet tumescet systems. Because the uderlyg dstrbuto of the FRR data set s ot kow, a ormal dstrbuto s assumed ad the Kolmogorov-Smrov goodess-of-ft test [5] s mplemeted to verfy the dstrbuto assumpto. The set of observed FRR data ca be rearraged creasg order, x1, x2,, x, where x represets a -th FRR data pot ad s the sample sze ( 156). From the ordered sample data, a step-wse emprcal dstrbuto fucto s obtaed by the proporto of the data smaller tha x the data set. # of x's x F( x) ; 1,, (1) The measure of dscrepacy, D, betwee the assumed ormal dstrbuto fucto F ( ) 0 x havg a mea of 90.2 ad a stadard devato of 28.9, as computed from the FRR data set, ad the emprcal fucto F ( x ) ca be computed as follows: D max F ( x ) F ( x ) (2) 0 x For a specfed sgfcace level 0.05, the crtcal value D ca be obtaed from the lterature [5] through the followg relatoshp (for 50 ): ENGINEERING JOURNAL Volume 16 Issue 2, ISSN ( 87

4 Fg. 1. Test furace at Fre Safety Research Ceter (FSRC). Table 1. Typcal steel sectos ad defto of secto factor. Secto Secto Factor ( Hp A) h t 2( b h) 2( b t) Steel cross-sectoal area b D D Steel cross-sectoal area h t b 2( b h) Steel cross-sectoal area h b 2( b h) Steel cross-sectoal area 88 ENGINEERING JOURNAL Volume 16 Issue 2, ISSN (

5 Secto A Secto B Secto A Secto B Secto A Secto B Secto A Secto B A B Ut (mllmeters) Fg. 2. Typcal locatos of thermocouples. D 1.36 (3) The assumed dstrbuto s acceptable f the observed D s less tha the crtcal value D. Based o the Kolmogorov-Smrov goodess-of-ft test, t ca be see that the dstrbuto of the FRR data set s ormal as llustrated Fg. 4. As prevously dscussed, the FRR data set ca be characterzed by a ormal dstrbuto wth 90.2 ad Wth the kow statstcal dstrbuto, the probablty that the fre-resstace ratg would be less tha 1 hour, 2 hours ad 3 hours ca be computed as 0.148, ad 0.999, respectvely. The results ca be perceved from two dfferet agles. O oe had, t s obvous that egeers must be aware of the possbltes that the tumescet fre protecto systems may ot satsfy the requremets specfed MR 60. O the other had, gve that most of the propretary tumescet systems are mported ad have bee certfed for use other coutres, t may be useful to re-exame the curret regulatos regardg freresstace ratgs. The 3-hour fre-resstace ratg requremet seems vrtually uachevable for tumescet fre protecto systems. ENGINEERING JOURNAL Volume 16 Issue 2, ISSN ( 89

6 FRR (ms) FRR (ms) FRR (ms) DOI: /ej (a) H p /A (m -1 ) 240 (b) H p /A (m -1 ) (c) H p /A (m -1 ) Fg. 3. Varato of FRR data wth respect to secto factor for dfferet sectos: (a) I-shaped sectos; (b) L-shaped sectos ad (c) rectagular ad crcular hollow structural sectos. 90 ENGINEERING JOURNAL Volume 16 Issue 2, ISSN (

7 Frequecy CDF DOI: /ej Upper boud Normal dstrbuto Emprcal dstrbuto Lower boud FRR (ms) FRR (ms) Fg. 4. Hstogram ad cumulatve dstrbuto fucto (CDF) derved from the FRR data set. 4. Coclusos Fre-resstace ratg (FRR) data have bee collected based o a seres of fre tests coducted at the Fre Safety Research Ceter of Chulalogkor Uversty durg the perod of The FRR data were compled for 138 I-shaped sectos, 8 L-shaped sectos, 7 rectagular hollow structural sectos ad 3 crcular hollow structural sectos protected wth 15 propretary tumescet systems provded by 9 compaes. The tme-temperature relatoshps durg the fre tests were cotrolled to follow ASTM E119 stadard whch the fre-resstace ratg was defed as the tme that the average temperature of the steel at ay oe of the measured levels rose above 538 C, or the temperature at ay oe of the measured pots rose above 649 C. Based o the FRR data set, t has bee foud that 88.4% of I-shaped sectos, 25% of L-shaped sectos, 57.1% of rectagular hollow structural sectos ad 100% of crcular hollow structural sectos were able to meet the 1-hour FRR crtero. The percetages drop to 13% for I-shaped sectos ad 0% for other sectos whe the 2-hour FRR crtero s cosdered. The Kolmogorov-Smrov goodess-of-ft test was also performed o the FRR data set. It has bee foud that the data ca be characterzed by a ormal dstrbuto wth 90.2 ad Based o the derved statstcal dstrbuto, the probablty that the fre-resstace ratgs obtaed by ay of the tumescet systems tested would be less tha 1 hour, 2 hours ad 3 hours ca be computed as 0.148, ad 0.999, respectvely. It ca thus be cocluded that care must be take usg tumescet systems to meet the FRR requremets set forth the curret regulatos. Ackowledgemet The work preseted ths paper was facally supported by Stmulus Package 2 (SP2) of Mstry of Educato uder the theme of Gree Egeerg for Gree Socety. ENGINEERING JOURNAL Volume 16 Issue 2, ISSN ( 91

8 Refereces [1] ISO, Fre resstace tests elemets of buldg costructo, ISO , Iteratoal Orgazato for Stadardzato, [2] ASTM, Stadard test methods for fre tests of buldg costructo ad materals, ASTM E , Amerca Socety for Testg ad Materals, [3] A. H. Buchaa, Structural Desg for Fre Safety, Joh Wley & Sos Ltd, [4] J. A. Purkss, Fre Safety Egeerg Desg of Structures, Butterworth-Heema, Oxford, UK, [5] A. H-S. Ag ad W. H. Tag, Probablty Cocepts Egeerg Plag ad Desg Volume I Basc Prcples, Joh Wley & Sos Ltd, ENGINEERING JOURNAL Volume 16 Issue 2, ISSN (