ROLE OF THE FABRICATOR IN LABOR PRODUCTIVITY

Transcription

1 ROLE OF THE FABRICATOR IN LABOR PRODUCTIVITY By H. Rndolph Thoms 1 nd Victor E. Snvido 2 ABSTRACT: This pper describes the results of three cse studies in which the subcontrctor-fbrictor reltions hd significnt negtive effect on lbor productivity of the subcontrctor. Lte vendor deliveries, fbriction or construction errors, nd out-of-sequence deliveries plgued ech of the three projects. On two projects, there were work stoppges becuse there were no mterils. Unsequenced deliveries cused unnecessry crne movements nd rework. On the third project, the output of the fbriction shop ws not comptible with the output of the erection crew. The bseline productivity ws clculted, nd the loss of lbor efficiency in ech cse ws estimted to be 16.6, 28.4, nd 56.8%. These percentges were compred with similr percentges clculted from other published rticles tht described inefficient site storge conditions nd delivery methods. The lbor inefficiencies cused by mteril mngement rnge from low of 5.4% to high of 56.8%. The schedule slippge on the three cse study projects ws estimted to be between 50 nd 129%. INTRODUCTION Competent mteril mngement is recognized s n importnt component of effective project mngement. The uthors hve written previously bout other spects of mteril mngement, including delivery methods (Thoms et l. 1999) nd site storge prctices (Thoms et l. 1989). In ech previous publiction, the loss of lbor efficiency due to these spects ws quntified. However, those rticles did not ddress the role of the fbrictor. OBJECTIVE The objective of this pper is to demonstrte the quntittive impct of the fbrictor on construction lbor efficiency. This will be done by describing three cse study projects constructed on the Pennsylvni Stte University cmpus. The ctivities studied were the instlltion of windows nd louvers, erection of precst exterior concrete pnels, nd erection of sheet-metl duct. In ech instnce, the construction crew relied on the delivery of components tht were fbricted off site. The schedule slippge cused by ineffective mteril mngement will lso be documented. LITERATURE REVIEW Literture regrding the role of the fbrictor ws exmined. There is some discussion provided in publictions by the Americn Institute of Architects (Morog 1974). The publiction detils the reltionship of the fbrictor to the contrctor nd the responsibility of the rchitect to review the shop drwings. The stndrd contrct form between the owner nd contrctor, AIA A201 (AIA 1987) lso ddresses these responsibilities, mking it cler tht the contrctor is responsible for the mens nd methods of construction. AIA A201 lso provides tht prtil pyment cn be mde to the contrctor for mterils locted on site but not instlled. Once pyment is mde, the mterils belong to the owner. Fbricted items stored t the fbrictor s shop re presumbly not covered. A review of the literture reltive to the quntittive impcts of mteril mngement yield very little informtion, except for rticles written by the uthors (Thoms et l. 1989, 1999). 1 Prof. of Civ. Engrg., 203 Trnsp. Res. Bldg., University Prk, PA Prof. of Arch. Engrg., 103 Engr. Unit A, University Prk, PA. Note. Discussion open until Mrch 1, To extend the closing dte one month, written request must be filed with the ASCE Mnger of Journls. The mnuscript for this pper ws submitted for review nd possible publiction on June 16, This pper is prt of the Journl of Construction Engineering nd Mngement, Vol. 126, No. 5, September/October, ASCE, ISSN /00/ / $8.00 $.50 per pge. Pper No These show productivity inefficiencies in mnging the site storge process nd in the erection method selected. No study showing the quntittive effect of the fbrictor ws found. DESCRIPTION OF CASE STUDY PROJECTS Project A Multi-Sport Indoor Fcility The Multi-Sport Indoor Fcility is three-story, 130,000 ft 2 (12,082 m 2 ) building contining n indoor, hydruliclly elevted, ovl running trck, 60 yd (54.8 m) rtificil turf field for multiple uses, specttor seting, locker rooms, VIP res, nd offices. Other sports fcilities re lso included. The estimted cost is $16 million. The project ws built using the multiple-prime delivery system. The cse study is of the instlltion of luminum window frmes, glss, nd luminum louvers. The study lsted for 27 workdys. The frmes, glss, nd louvers were instlled seprtely. In totl, there were 270 frmes, 251 pieces of glss, nd 19 louvers. The triple-pne glss rnged in size from 3 ft 2 (0.28 m 2 )to49ft 2 (4.55 m 2 ) nd weighed pproximtely 10 lb/ft 2 (0.93 lb/m 2 ). On this project, the window subcontrctor experienced delys in mteril deliveries. The glss ws not delivered ccording to the plnned erection sequence. Some glss ws improperly sized nd did not meet the specifictions. The site storge res were dequte, lthough the re ws sometimes muddy. The initil pln ws to store the glss indoors; however, becuse of delys by other contrctors, the glss hd to be stored in remote loction outside the building. Thus, most of the glss ws double-hndled. Project B Erth nd Minerl Sciences Reserch Activities Building This four-story structurl steel building contins lecture clssrooms, fculty nd dministrtive offices, nd computer center. The construction budget ws $14.8 million. The project ws built using the multiple-prime delivery system. The ctivity studied ws the erection of exterior precst concrete pnels. The study period ws 22 workdys. Three types of pnels were involved in this work, the most common of which ws n exterior pnel ttched to the structurl steel frme. These pnels were bolted to connector pltes tht were welded to the columns. Another contrctor did the welding work. The size of the typicl exterior pnel ws 80 ft 2 (7.4 m 2 ). There were 175 exterior pnels or 14,000 ft 2 (1,301 m 2 ) erected during the study. The project lso contined 44 spndrel pnels whose verge size ws 50 ft 2 (4.7 m 2 ), or totl of 2,200 ft 2 (205 m 2 ). The third type of pnel ws louvered pnel tht rested on the ground. These pnels verged 185 ft 2 (17.2 m 2 ). There were 12 of these pnels or 17,570 ft 2 (1,633 m 2 ). 358 / JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000

2 The pnels were delivered dily from the fbriction yrd pproximtely 100 m (160 km) wy nd were erected directly from the delivery truck. The communiction between the erector nd fbrictor ws less thn stisfctory, which resulted in the pnels being delivered out of sequence. The end result ws tht seven crne setups were required insted of four or five. Problems were encountered becuse certin pnels did not fit properly, so tht swing, cutting, nd rewelding by field crews were required. Erection ws lso hmpered by muddy site conditions, which were not the responsibility of the erector, but could hve been voided by better site mngement by the generl contrctor. Pnel erection ws postponed for one dy becuse of the muddy conditions. Project C I & I Reserch Activities Building The I & I Reserch Activities Building is $12 million, three-story, reinforced concrete building with offices, clssrooms, nd lbortories tht contins 92,000 ft 2 (8,850 m 2 )of gross spce. The multiple-prime delivery system ws used. On this project, the erection of sheet-metl duct ws monitored for 37 workdys. The work ws divided into three sizes of duct bsed on the lrgest dimension of width or depth. Brnch duct ws identified s ny duct where the lrgest dimension (width or depth), x ws less thn 30 in. (75.9 cm). A totl of 1,492 ft (455 m) of brnch duct ws instlled. Feeder duct ws divided into two sizes. The smller feeder duct ws in the rnge of 30 x < 50 in. (75.9 x < cm), nd 220 ft (67 m) were instlled. Lrger duct included ll duct with the lrgest dimension of x 50 in. (x cm). A totl of 118 ft (36 m) were erected. In ddition, four verticl floor penetrtions nd 43 fire dmpers were instlled during the study period. The sheet-metl fbriction shop ws prt of the contrctor s firm. The production rtes of the fbriction shop nd the erection crew were not blnced. The contrctor shifted workers from the construction site to the fbriction shop on severl occsions, depending on where incresed production ws needed. The result ws tht deliveries were uneven, mteril shortges were common, nd field instlltion ws inconsistent during much of the work period. CALCULATION OF DAILY PRODUCTIVITY The dily productivity ws clculted seprtely for ech project. The clcultions follow recognized cost engineering principles. Rules of credit were used to ccount for work tht ws prt of finl unit of production (Thoms nd Krmer 1987). For exmple, on Project A, window frmes (55%) nd glss nd louvers (45%) when combined mke up the instlled window. Conversion fctors were used to convert different units of work into n equivlent quntity of bse or stndrd unit (Thoms nd Npolitn 1995). For exmple, one unit of re of louvered pnel on Project B equls 62% of the re of n exterior pnel, the bse unit. The method used to clculte the bseline productivity is explined below. Project A Multi-Sport Indoor Fcility TABLE 1. Work hours Dily Productivity Project A,b Frmes (ech) (0.55) Glss nd louvers (ech) (0.45) output (ech) Dily productivity (wh/ech) , Rules of credit re s follows: frmes = 0.55 nd glss nd louvers = b Boldfce indictes workdys in bseline subset. The unit of mesure for output is the number of windows. However, the windows were not instlled s unit, but rther frmes were instlled first, followed by the glss or louvers. Thus rules of credit or erning rules were pplied. Bsed on initil on-site observtions nd consulttion with contrctors nd stndrd estimting mnuls, the following rules were pplied: instlltion of frmes = 0.55, nd instlltion of glss or louvers = The dily output is the sum of the dily outputs for ll subtsks times the respective rule of credit. Dily productivity ws clculted s the (wh) divided by the dily output. The dt re shown in Tble 1, nd the dily productivity is shown in Fig. 1. Project B Erth nd Minerl Sciences Reserch Activities Building The unit of mesure for output is the number of squre feet (squre meters) erected. Pnels re erected in their entirety t one time; therefore, with no incomplete work, there is no need for rules of credit. However, the effort needed to erect pnels will vry ccording to the size. Thus the quntities need to be expressed s the equivlent squre footge of one common size. In this study, the exterior pnels re selected s the stndrd item. To determine conversion fctors, the quntities of spndrel pieces nd exterior pnels were combined. The nlysis continued with two pnel types: exterior nd louvered. A multiple regression model ws developed with the dily s the dependent vrible nd the dily quntities of the two pnel types s the independent vribles. The model ws developed without constnt term. The clculted model coefficients re the unit rtes (wh/ft 2 ) for the two independent vribles. The coefficients were determined s follows: exterior pnels = wh/ft 2 (0.90 wh/m 2 ), louvered (ground) pnels = wh/ft 2 (0.56 wh/m 2 ). The exterior pnel is selected s the stndrd item, mening tht its conversion fctor is The conversion fctor for the louvered pnels is the unit rte of the louvered pnel divided by the unit rte of the exterior pnel (stndrd item). The clcultion is s follows: conversion fctor (CF) Louvered = = (The conversion fctor for exterior pnels is 1.00.) The clcultion for expressing the quntity of louvered pnels s n equivlent quntity of exterior pnels is s follows: equivlent quntity = mesured quntity conversion fctor. JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000 / 359

3 FIG. 1. Dily Productivity for Multi-Sport Indoor Fcility Project A TABLE 2. Dily Productivity Project B,b Exterior pnels Louvered pnels output Dily productivity [wh/ft 2 (wh/m 2 )] (85) 0 (0) 910 (85) (0.88) ,120 (104) 0 (0) 1,120 (104) (0.76) ,090 (103) 0 (0) 1,090 (101) (0.89) (91) 0 (0) 980 (91) (0.88) (59) 0 (0) 640 (59) (0.84) (78) 555 (52) 1,182 (110) (0.82) (57) 925 (86) 1,181 (110) (0.77) (56) 0 (0) 600 (56) (1.53) (63) 0 (0) 680 (63) (1.08) (75) 0 (0) 810 (75) (0.85) (89) 0 (0) 960 (89) (0.89) (59) 0 (0) 640 (59) (1.43) ,080 (100) 0 (0) 1,080 (100) (0.89) (78) 0 (0) 840 (78) (0.96) (0) 370 (34) 228 (21) (4.24) (83) 370 (34) 1,118 (104) (0.69) (86) 0 (0) 930 (86) (1.04) (45) 0 (0) 480 (45) (1.12) (30) 0 (0) 320 (30) (2.02) ,060 (99) 0 (0) 1,060 (99) (0.71) (15) 0 (0) 160 (15) (3.02) (52) 0 (0) 560 (52) (1.15) 1,634 16,200 (1,506) 2,220 (204) 17,570 (1,633) (1.00) Conversion fctors re s follows: louvered pnels = 0.62 nd exterior pnels = b Boldfce indictes workdys in bseline subset. The totl dily quntity is the sum of the quntity of the stndrd item (exterior) plus the equivlent quntity of louvers. The clcultions re shown in Tble 2, nd the dily productivity is shown in Fig. 2. Project C I & I Reserch Activities Building The unit of mesure for ductwork is the liner feet (meters) of instlled work. The fire dmpers nd duct were instlled in different stges, thus necessitting the ppliction of rules of credit. The rules for fire dmpers were s follows: erect = 0.80 nd sel nd culk = The rules for duct instlltion were s follows: lyout nd hngers = 0.25, nd instll nd sel duct = The ppliction of these rules resulted in the quntities listed in Tble 3. The conversion fctors for the different size duct, fire dmpers, nd floor penetrtions were clculted in the sme mnner s ws done for the precst pnels. The multiple regression 360 / JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000

4 FIG. 2. Dily Productivity for E & MS Reserch Center Project B Penetrtions (ech) Fire dmper (ech) TABLE 3. Brnch duct Dily Productivity Project C Smll feeder duct Lrge feeder duct (7) output (8) Dily productivity [wh/ft (wh/m)] (9) (0) 0 (0) 0 (0) (14.3) 0.85 (2.79) (9.3) 0 (0) 0 (0) (6.3) 1.94 (6.36) (16.8) 0 (0) 0 (0) (8.9) 1.37 (4.49) (26.3) 0 (0) 0 (0) (13.90) 0.88 (2.89) (12.2) 0 (0) 0 (0) (9.8) 1.24 (4.07) (20.6) 0 (0) 0 (0) (10.9) 0.67 (2.20) (28.5) 0 (0) 0 (0) (15.10) 0.48 (1.57) (14.0) 0 (0) 0 (0) (7.40) 0.99 (3.25) (7.1) 0 (0) 0 (0) (5.5) 1.32 (4.33) (0) (5.3) 2.25 (0.7) (5.7) 1.28 (4.20) (6.8) 4.50 (1.4) 1.50 (0.5) (6.07) 1.21 (3.97) (8.8) 0 (0) 0 (0) (6.9) 1.07 (3.51) (12.7) 0 (0) 3.00 (0.91) (7.3) 1.66 (5.45) (24.4) 0 (0) 0 (0) (13.0) 0.94 (3.08) (16.7) 5.13 (1.6) 0 (0) (10.4) 1.17 (3.84) (7.7) 0 (0) 0 (0) (6.3) 1.16 (3.81) (27.7) 6.75 (2.1) 0 (0) (16.7) 0.44 (1.44) (5.0) 1.50 (0.5) 1.50 (0.5) (5.0) 1.48 (4.85) (8.0) 0 (0) 0 (0) (4.3) 1.72 (5.64) (17.7) 0 (0) 0 (0) (11.6) 0.63 (2.07) (0) (9.2) 0 (0) (9.1) 0.80 (2.62) (18.3) 0 (0) 0 (0) (9.7) 0.75 (2.46) (7.41) (6.8) (3.7) (13.2) 0.93 (3.05) (19.9) (5.8) (9.1) (22.4) 0.55 (1.80) (5.7) 0 (0) (6.2) (7.1) 1.72 (5.64) (14.3) (3.5) (6.3) (15.2) 0.80 (2.62) (10.5) 7.13 (2.2) 2.25 (0.7) (8.2) 1.49 (4.89) (12.1) 5.44 (1.7) (7.2) (12.8) 0.95 (3.12) (0) (11.61) 0.75 (0.2) (11.8) 0.83 (2.72) (3.64) (10.7) 0 (0) (12.7) 0.96 (3.15) (17.29) (4.9) 0 (0) (14.1) 0.87 (2.85) (10.3) 0 (0) 0 (0) (5.5) 2.23 (7.31) (15.2) 0 (0) 0 (0) (19.1) 0.64 (2.10) (5.2) 0 (0) 0 (0) (13.9) 0.88 (2.89) (5.2) 0 (0) 0 (0) (13.9) 0.88 (2.89) (23.4) 0 (0) 0 (0) (12.4) 0.59 (1.94) (15.1) 0 (0) 0 (0) (8.0) 0.91 (2.99) 1, ,492 (455) 220 (67) 118 (36) 1,293 (394) 0.94 (3.08) Boldfce indictes workdys in bseline subset. JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000 / 361

5 FIG. 3. Dily Productivity for I & I Reserch Activities Center Project C model yielded the following unit rtes: penetrtions = wh/ech, fire dmpers 3.38 wh/ech, brnch duct = 0.45 wh/ft (1.48 wh/m), smll feeder duct = 0.85 wh/ft (2.79 wh/m), nd lrge feeder duct = 0.56 wh/ft (1.84 wh/m). If the smller feeder duct is the stndrd item, the conversion fctors re s follows: penetrtions = 11.76, fire dmpers = 3.65, brnch duct = 0.53, smll feeder duct = 1.00, nd lrge feeder duct = The dily quntities in terms of equivlent footge of smll feeder duct re summrized in Tble 3. The dily productivity is shown in Fig. 3. CALCULATION OF BASELINE PRODUCTIVITY To quntify the productivity losses, it is now necessry to clculte the bseline productivity, which is the best productivity the contrctor chieves on project nd is bsed on work performed when there were no disruptions (Thoms nd Zvrški 1999). The bseline productivity is clculted s follows: 1. Determine the number of workdys tht comprise 10% of the totl workdys. 2. Round this number to the next highest odd number; this number, n, which should not be less thn 5, defines the size of (number of dys in) the bseline subset. 3. The contents of the bseline subset re selected s the n workdys tht hve the highest dily production or output. (The bseline subset is highlighted in Tbles 1 3 nd shown in Figs. 1 3.) 4. For these dys, mke note of the dily productivity. 5. The bseline productivity is the medin of the dily productivity vlues in the bseline subset. The bseline productivity is significnt becuse it is the dtum from which impcts cused by disruptions re mesured. The bseline productivity vlues were clculted s 2.01 wh/ ech, wh/ft 2 (0.77 wh/m 2 ), nd 0.55 wh/ft (1.80 wh/m) for windows (Project A), precst pnels (Project B), nd duct (Project C), respectively. IMPACT OF FABRICATOR The impct of the fbrictor on the field ctivities in terms of is clculted below. The cuse of this impct cn be the contrctor, fbrictor, or designer. No determintion of fult is mde in this pper. Project A Multi-Sport Indoor Fcility On the Multi-Sport Fcility, totl of six dys re shown in Fig. 1 s being impcted by mteril delys nd out-ofsequence deliveries. However, the impct extends beyond these dys lone. For instnce, just prior to workdy 8, limited shipment of glss ws mde tht ws insufficient to sustin norml production rtes. On workdys 9 12, the production output ws less thn hlf tht of the dys in the bseline subset. The crews were observed to djust their pce of work to the mount of work vilble to perform. This phenomenon hs been observed previously (Thoms et l. 1989). The sme sitution occurred on workdys nd gin on workdys The impcts on workdys 25 nd 27 re ssocited with the need to instll nd remove temporry, single-pne glss. This rework ws necessry becuse the triple-pne glss hd not been delivered on time. The mthemticl clcultions to quntify the inefficient re shown in Tble 4. Using the bseline productivity s the dtum, totl of 376 re clculted s hving been ineffectively used becuse of delys in nd outof-sequence mteril deliveries. Ineffective re defined s the difference between the ctul nd the required if the bseline rte hd been mintined. The percentge of lost cn be clculted using the following eqution: Workhour Percentge = / JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000

6 TABLE 4. Associted with Mteril Delivery Inefficiencies Project A Bseline productivity Actul Productivity Quntities (0) (0.75) (0.50) (0.38) (0.36) (1.13) (0.97) (0.80) (0.48) (1.17) (1.02) (0.67) (0.75) (0) The inefficiency percentge ws clculted s 56.8%, tht is, 56.8% more were used compred to the tht should hve been used to instll the window glss for tht period. At burdened lbor rte of $20/h, the 376 mounts to $7,520. Further, for the bseline productivity of 2.01 wh/ech nd n verge crew per dy of 40, the work should hve tken t lest (2.01)(270) 40 = 13.57, or 14 workdys. If the number of required is bsed on the totl minus the inefficient (or 1, = 662 ), then the number of dys required is clculted s 16.55, or 17 workdys. Thus, the work should hve tken between 14 nd 17 workdys. This is the unimpcted durtion. The ctul durtion of the work ws 27 working dys plus 5 dy dely becuse of lte deliveries, or 32 workdys. The schedule impct is expressed in equivlent workdys bsed on crew working 40 per dy. An equivlent workdy my not equte to workdy, one-to-one, becuse the contrctor hs the prerogtive to increse the crew size or to work overtime. Thus, the overll impct for delys in deliveries is clculted s $7,520 nd equivlent workdys of schedule impct. The smllest schedule impct, expressed s percentge, is clculted by dividing the lowest schedule impct, in this instnce, 15 equivlent workdys, by the longest unimpcted durtion, in this cse, 17 workdys. The lrgest schedule impct is clculted by dividing the highest schedule impct (18 equivlent workdys) by the shortest unimpcted schedule (14 workdys). The schedule impct then is between 88 nd 129%. Project B Erth nd Minerl Sciences Reserch Activities Building Compred to Project A, Project B experienced less noticeble impcts, which occurred in three res. First, pnel fit-up problems required some remedil work. It is not known if these were cused by fbriction errors, construction errors, or errors in the contrct drwings. However, some corrective work ws required t the time of instlltion. These problems occurred on workdys 4, 7, 20, nd 21; only on workdy 21 were the impcts clerly mesurble. Also, pnel deliveries mde out of sequence required excessive movement of the crne from one side of the building to nother. It is hrd to sy how mny crne loctions normlly would hve been required; however, if the deliveries re sequenced, the crne reloctions cn be mde t the beginning or end of the dy or in some wy tht is not disruptive to crew productivity. Most likely this ws done on workdys 3 nd 6, but most of the delivery problems occurred lte in the job. Therefore, the movements re considered unplnned, nd the impcts on workdys 12, 15, 17, nd 19 re clculted. There ws lso 5 dy schedule dely becuse there were no pnels. Lst of ll ws the impct of bd wether. Following rin nd snow events, the site becme very muddy. This impeded the movement of men nd equipment round the site, nd one dy even cused work to be hlted erly. The inefficiency clcultions re shown in Tble 5. It is clculted tht 232 were used inefficiently, minly becuse of the out-of-sequence deliveries, which required unscheduled crne movements. The lbor inefficiency percentge ws clculted to be 232 ( ) 100 = 16.5%. At $20/h, the economic loss is $4,640. The schedule dely is determined s follows. If the bseline is wh/ft 2 (0.77 wh/m 2 ), nd there is totl of 17,570 ft 2 (1,633 m 2 ) of work to be performed, then t 80 per dy, minimum of 16 workdys would be required. If the totl minus the inefficient re used s the required, then t 80 per dy, the work would tke 18 workdys. The ctul durtion of the work ws 22 workdys plus 5 dy dely for lck of mterils, or totl of 27 workdys. Thus, the unsequenced deliveries, corrective work, nd lck of pnels resulted in loss of $4,640 nd schedule impct of 9 to 11 equivlent workdys. The schedule dely is between 50 nd 69%. TABLE 5. Associted with Mteril Delivery Inefficiencies Project B Bseline productivity [wh/ft 2 (wh/m 2 )] Quntities for fbrictor errors for crne moves inefficient (7) (0.77) 1,090 (101.3) (0.77) 980 (91.1) (0.77) 1,182 (109.9) (0.77) 1,180 (109.7) (0.77) 640 (59.5) (0.77) 228 (21.2) (0.77) 930 (86.4) (0.77) 320 (29.7) (0.77) 1,060 (98.5) (0.77) Unplnned reloction during regulr work hours due to mteril rriving out of sequence. JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000 / 363

7 Project C I & I Reserch Activities Building The dily productivity for the I & I Reserch Activities Building is shown in Fig. 3. The impct of the fbriction opertion is not redily obvious from the figure. The production rte t the fbriction shop ws insufficient to support the production rte in the field. Therefore, the contrctor shifted workers from the field to the fbriction shop nd bck gin severl times. This led to n uneven delivery schedule nd periods of time where the field work ws slowed becuse of TABLE 6. Associted with Mteril Delivery Inefficiencies Project C Bseline productivity [wh/ft (wh/m)] Quntities inefficient (1.80) 49.6 (15.1) (1.80) 24.3 (7.4) (1.80) 18.2 (5.6) (1.80) 18.7 (5.7) (1.80) 19.9 (6.1) (1.80) 22.5 (6.9) (1.80) 24.1 (7.3) (1.80) 42.5 (13.0) (1.80) 34.1 (10.4) (1.80) 20.6 (6.3) (1.80) 54.9 (16.7) (1.80) 16.3 (5.0) (1.80) 14.0 (4.30) (1.80) 38.0 (11.6) (1.80) 30.0 (9.1) (1.80) 31.8 (9.7) (1.80) 43.2 (13.2) (1.80) 73.3 (22.3) (1.80) 23.3 (7.1) (1.80) 49.9 (15.2) insufficient duct being vilble. The period of time when this impct occurred ws workdys 7 through 26. Tble 6 shows the inefficient to be 245. The inefficient percentge is 245 (1, ) 100 = 25.2%. At $20/h, the loss is equl to $4,900. The mximum schedule dely is bsed on bseline of 0.55 wh/ft (1.80 wh/m), 40 h per dy, nd 1,293 ft (394 m) of instlled duct. The estimted workdys tht would hve been required re 18. If the totl minus the impcted re used (1, ), then the time required is estimted s 24 workdys. The ctul durtion of this work ws 37 workdys, which results in schedule impct of 13 to 19 equivlent workdys. The percentge of schedule impct is between 54 nd 105%. COMPARISON WITH OTHER STUDIES Two previous ppers deling with mteril mngement nd this cse study hve ddressed three mteril mngement issues t the project site tht relted directly to lbor inefficiencies. These res of deficient mngement re site storge conditions, delivery nd erection methods, nd contrctorfbrictor coordintion. Ech hs been nlyzed seprtely; however, it is recognized tht these fctors re not entirely mutully exclusive conditions. Tble 7 summrizes the losses of lbor efficiency ttributed to the three deficiency issues. The projects listed re ordinry nd typicl; none of the contrctors were involved in contrct clims relted to these projects. This tble mkes it clerly obvious tht mteril mngement problems hve significnt effect on lbor performnce nd tht these problems re common occurrences on mny sites. The losses of lbor efficiency rnged from 5.4 to 56.8%. The lrgest percentges ppered to be in the contrctor-fbrictor reltions ctegory, but this observtion my be just peculirity in the dt. These inefficiencies might explin strtegic resons why mny specilty contrctors elect to mintin in-house fbriction fcilities even when their fbriction costs re similr TABLE 7. Summry of Losses of Lbor Efficiency Project Project A (Thoms et l. 1989) Project B (Thoms et l. 1989) Reserch building (Thoms et l. 1999) Type of work Site Storge Conditions Percent Delivery/Erection Methods (7) Percent (8) (9) Contrctor/Fbrictor Reltions (10) Structurl steel 1, Structurl steel Structurl steel Project A Window instlltion 1, Project B Precst pnel erection 1, Project C Duct erection 1, Percent (11) TABLE 8. Summry of Schedule Slippges Project Type of work Actul durtion (workdys) Estimted unimpcted workdys required Equivlent workdys Schedule Slippge Dely (7) percent (8) Project A Window instlltion Project B Precst pnel erection Project C Duct erection b Equivlent workdys re totl schedule slippge less ny dely or work stoppge. Lowest number represents equivlent workdys cused by mterilrelted issues, wheres highest number represents delys cused by ll inefficiencies. b These numbers include dditionl delys becuse crew during most of impcted period were reduced from 40 per dy to 24. This trnsltes to schedule extension of nother six equivlent workdys. 364 / JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000

8 to, or in some cses, slightly higher thn other fbriction fcilities. The rel impct of in-house fbriction fcilities my be in superior coordintion between the shop nd field, resulting in field lbor nd schedule svings. Tble 8 summrizes the impct to the schedule. Only the three projects in this pper re summrized; however, it should be noted tht the first structurl steel project in Tble 7 experienced significnt delys due to delivery problems. Tble 8 shows the impct to the schedule to be between 50 nd 130% for the three projects, depending on how the estimted workdy durtion tht should hve been required is clculted. CONCLUSIONS This pper hs presented cse study of three projects tht experienced mteril mngement problems relted to fbricted components. Certin sttistics were compred to the results reported in erlier publictions. The results of this reserch hve led to severl significnt conclusions. Mteril mngement hs significnt effect on lbor efficiency. mteril mngement cn led to n increse in the field lbor hours of 50% or more. On the projects reported herein, the problems observed were poor site storge prctices, running out of mterils, lte deliveries, double-hndling of components, out-of-specifiction mteril nd fbriction errors, deliveries mde out of sequence, nd fbriction production rtes tht were incomptible with field production rtes. While not ll problems will occur on ll sites, there is clerly n enormous potentil for improving lbor performnce on ordinry commercil projects with the ppliction of few bsic mteril mngement principles. Poor mteril mngement prctices lso result in schedule delys. On the three projects fetured in this pper, the ctivities took 50 to 130% more workdys thn should hve been required. Schedule performnce ws function of delys in deliveries plus the inefficient use of lbor. The schedule slippge ttributed to inefficient ws equl to or greter thn the delys cused by lte deliveries. Although not ddressed in this pper, delys cused by lbor inefficiencies my rise questions bout conventionl dely nlyses on contrctor clims using the criticl pth method. APPENDIX. REFERENCES Americn Institute of Architects (AIA). (1987). Stndrd form of greement between owner nd contrctor. AIA Document A201, Wshington, D.C. Morog, J. V. (1974). Architect s hndbook for professionl prctice Construction contrct dministrtion, Americn Institute of Architects, Wshington, D.C. Thoms, H. R., nd Krmer, D. F. (1987). Construction productivity mesurement nd performnce evlution. Source Document 35, Construction Industry Institute, Austin, Tex. Thoms, H. R., nd Npolitn, C. L. (1995). Quntittive effects of construction chnges on lbor productivity. J. Constr. Engrg. nd Mgmt., ASCE, 121, Thoms, H. R., Riley, D. R., nd Snvido, V. E. (1999). Loss of lbor productivity due to delivery methods nd wether. J. Constr. Engrg. nd Mgmt., ASCE, 125, Thoms, H. R., Snvido, V. E., nd Snders, S. R. (1989). Impct of mteril mngement on productivity A cse study. J. Constr. Engrg. nd Mgmt., ASCE, 115, Thoms, H. R., nd Zvrški, I. (1999). Construction bseline productivity: Theory nd prctice. J. Constr. Engrg. nd Mgmt., ASCE, 125, JOURNAL OF CONSTRUCTION ENGINEERING AND MANAGEMENT / SEPTEMBER/OCTOBER 2000 / 365