estimating reinforcing bars_tcm45-340894

7/31/2019 Estimating Reinforcing Bars_tcm45-340894

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Sup p liers of re i n f o rcing b ars usu ally provide cer-tain ad de d services in ad dition to furn i s h i n gf a b ricat ed re i n f o rcin g b ar s to the job site. On ei m p o rtan t fun ction is estim at ing. This is p er-

form ed b y estima tor specialists who study a set of con -t ract d rawings an d specification s an d, from th eirk n owledge of c on stru ction an d re i n f o rcing ba rs, are

able to de velop a list of qu antities of m aterial whichth ey be lieve or e s t i m a t e are re q u i red to bu ild th es t ru c t u re un der con sidera tion . From th is inform a t i o nthe n ecessary pricin g is developed so that a b id can besubm itted to the general contractor. In a few metrop ol-itan a reas this estima ting service is provide d by esti-ma ting bureau s which con tract with a n um ber of re i n-f o rcing b ar su pp lier clients an d pro rate th e cost of theservice amon g the various u sers.

It is imp ortan t that th e contract dra wings and specifi-cations give complete detailed information a bout the re-i n f o rcing b ars. The estim ate is a line -by-line takeo ff an dcom plete d etails will usually insure a m ore accu rate es-

t i m a t e. Whe n the estimator ha s to guess a nd m ake a s-s u m p t i o n s, th e qu ality of th e e stim ate m ay b e im paire d .A pru den t estimator will tend to figure qu ant ities on th esafe side wh en there is a question of what is actually re-q u i red. This, of course, can increase the am ou n t of them a t e rial qu ota tion . Th e est ima tors oth er alter n a t i ve isto contact the architect or engineer and attempt to clar-ify tha t which is n ot clea r. This can be a ve ry fru s t ra t i n ge x p e rien ce as a nswer s a re n ot a lways fort hco m ing. Theestimator u sually works un der a tight de adline an d m ustm ove forw a rd a nd com plete th e estim ate. Of course th ebid can be qual if ied an d limited to the a ssumptionsm a d e, but this can lead to having the bid rejected a s be-ing non re s p o n s i ve.

EXTRAS ADDED TO BASE PRICEOne aspec t of p re p a ring qu an tity estimates for fabr i-

cated re i n f o rcing b ars is the way in which cha rges for ex-t ras (per h un dre d weight o f mate rial) ma y be ad ded toth e b ase p ri c e. The p rincip al extra s are for size, gra d e,bendin g and qu antity.

Si ze : Ex t ras for size m ay va ry; the re f o re it is n ecessar yfor the estimat or to segregate b y size. The tab le show s

the current p ublished size extras for fabricated barsf rom a m ajor reb ar fab ri c a t o r. Note th at the size extra for#3 bars is $4.00 per hu ndred p ound s or $80 per ton m orethan for #4 bars. This shows th at it is generally more eco-no mical to sp ecify #4 rath er th an #3 b ars for app rox i-m ately equa l areas of steel. Sim ilar com pa rison s couldbe m ade for other size s.

Quantity: Ex t ra ch arges m ay be incurred dep end ingon the total weight o f steel ord e red. The t able also sh ow sth e curr en t q u an tity extras for fab rica te d re i n f o rc i n gbars from the sam e fabricator wh ose size extras are giv-

Es t im a t in g r e in fo r c in g b a r s How the bid p rice is determ in ed

BY WILLIAM C. B LACKCHIEF ENGINEERREINFORCING BARS , P ILING AND CONSTRUCTIONSPECIALTY SALESBETHLEHEM STEEL CORPORATION

FABRICATED DEFORMED CONCRETEREINFORCING BARS

SIZE EXTRAS

Area Weight Extra perBar size sq. in. lb per ft 100 lb

#18 4.00 13.600 $ 2.00#14 2.25 7.650 2.00#11 1.56 5.313 1.00#10 1.27 4.303 1.00# 9 1.00 3.400 1.00# 8 0.79 2.670 1.00# 7 0.60 2.044 1.00# 6 0.44 1.502 1.25# 5 0.31 1.043 1.50# 4 0.20 0.668 2.00# 3 0.11 0.376 6.00

# 2* 0.05 0.167 15.00

QUANTITY EXTRAS

Extra perQuantity 100 lb

Over 300 tons None100-300 tons $0.25

50-99 tons 0.5020-49 tons 0.75

Under 20 tons** 1.25


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en. This shows that there m ay be a job size pen alty inb reaking down sm aller stru c t u res a t bidd ing time fors e p a rate acce pta nc e.

Grade: Som e grades of bars ha ve an extra, ma king itn e c e s s a ry for th e e stim ato r to segre gate by grad e a s we l las size.

Be n d i n g : Ex t ra ch arges are a pp lied for all shop ben d-ing. The estimator m ust segregate th e total qua ntity of ben din g into thre e classes a s follow s, based on cu rre n t

i n d u s t ry d efinitio ns : LIGHT BENDINGAll #3 ba rs, all stirr up s an d ties, and

all bars #4 through #18 which are ben t at m ore tha n sixpoints in one p lane, or bars which are ben t in mo rethan on e plan e (unless special ben ding). Also includ -ed are a l l one-plane rad ius bending with more tha none radius in any bar (three ma ximum ), and a ny com-bination of radius and other type bending in one p lane( radius be nd ing being defined as all ben ds ha ving a ra-dius of 12 inches o r m ore to inside of bar).

H E AVY BENDINGBar s izes #4 th ro ugh #18 , which are

bent a t not m ore than six points in on e plane (unlessclassified as light b end ing or special bend ing) and sin-g l e - rad ius b en din g.

S PECIAL BENDINGAll ben d ing to to leran ces m orere s t ri c t i ve th an th ose sh own in ind ust ry st an da rd s, allradius bend ing in m ore than one p lane, a l l m ult ipleplane ben ding containing one or mo re radius ben ds,and all bendin g for p recast un its. *

Typical extra ch arges m ay be o f the o rder of $4.00 perh u n d red p oun ds for light bend ing and $1.75 per h un -d red p oun ds for heavy ben ding. Since light b en dingcosts $2.25 per h un dred p oun ds ($45.00 per ton) morethan hea vy bend ing, it is more e conom ical to specify,for example, #4 ben t ba rs rather tha n #3 where total re-q u i red a reas a re ap proximately equ al. Multiple b en dssuch as con tinuou s truss bars in bridge deck slabs arem o re costly per h un dred p oun ds since th ey usually ha vem o re than six ben ds p er bar an d com e un der th e lightb e n d i n g ext ra .

LAP SPLICESId e a l l y, the len gth an d locatio n of all lap sp lices sho u ld

be shown in th e cont ract doc um en ts. Un f o rt u n a t e l y, th isis seldom the case in th e real world. Recent ly we sur-ve yed 139 jobs cu rrently being serviced a roun d th e con -tinen tal Un ited St a t e s. The results in dicate d tha t splicei n f o rm ation was given in th e following ways:

46 jobsindicated splice len gths inbar diam eters, generally 24,36 or 40.

22 jobsp rovided splice d imen sionson plans, sections, or details.

23 jobss h owed class o f splice, p erACI 318.

24 jobsg a ve a t ab le of sp lice length s(inch es), generally con form -ing to ACI 318, but n ota l w a y s.

10 job sm e rely re f e ren ced ACI 318 or

CRSI Man ual of St a n d a rdPractice (or silen t).

14 jobshad m iscellaneou s otherc o m b i n a t i o n s.

One of our conclusion s is that som e of the odd com -binations are d ue to different d esigners working on thesam e con tra c t .

Figure 1. Using contract drawing information (top) theestimator visualizes how the detailer would handle the bars(bottom) before he can estimate quantities. See Figure 2for a much better way for the designer to treat this corner.

Figure 2. Preferredway of showing wallcorner in Figure 1.Overall cost ofhorizontal wallreinforcement isreduced because onlythe bent corner bar ischarged the heavybending extra.

* Standard tolerances are given in the Manual of Standard Practice publishedby Concrete Reinforcing Steel Institute, 180 N. LaSalle Street, Chicago, Illi-nois 60601.


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Splice locationThe estimator m ust first determ ine the location of all

sp lices so as to calculate th e to tal qu an tity re q u i red . Th isis fa irly str a i g h t f o rw a rd for co lum n s w he re th e typ icaldetail m ay show a splice at each floor level. It is not soo bvious for elemen ts such as walls with long run s of hor-i zontal bars. The estimato r has a d oub le problem here :(1) he n eeds to d eterm ine the q ua ntity of splices re-q u i red in each ru n o f bars; and (2) he also m u st m ake a

judgem en t d ec isio n as to h ow m an y fee t o f th e r un willbe estimat ed as b en t a nd h ow m any as stra i g h t .An exam ple is shown in Fi g u re l. The con tract dra w-

ings show a wall cross section and indicate #5 at 12 hor-i zontal b oth faces. The ou tside face ba rs are ben ta roun d each co rner an d extend ed 2 feet 2 inches. The in-side face bars extend in straight. The estimato r mu st vi-s u a l i ze h ow t he det ailer wou ld a ctu ally han dle it. In th isexamp le the estim ator has assumed three bars per run in30-foot stock lengths, plus a bent b ar at each en d for theoutside ba rs. This app roach m inimizes the weight of ben t bar re q u i red, an d the re f o re th e qu oted price o f them a t e rial, withou t a dd ing e xtra splices. A far b etter an d

m o re econ om ical solution would b e for the designer tos h ow separa te corn er b ars 2 feet 2 in ches o n a side (Fi g-u re 2). The estimat or wou ld then figure th e inside an doutside h ori zontal bars in an iden tical m an ne r, ass t raight bar s. The o n ly bars t ha t wo uld re q u i re th e h eavyben ding extra would be the b ent corner bars, there by re-du cing th e ove rall co st of t he ho ri zon ta l wa ll re i n f o rc e-m en t. The inside face bars would pro bab ly be figured asa ru n of fou r bars, each app roxima tely 30 feet long, witht h ree splices. It is im por tan t t o re c o g n i ze th at th e stan -d a rd indu stry method of pricing bend ing is on a hu n-d re d weight basis. Placing a ben d at th e en d of a longerbar causes the b en ding extra to be ap plied to th e entireweight o f the bar.

Fa b rication, tra n s p o rtat ion an d con stru ction lim ita-tions shou ld h ave been co nsidered by the designer whend e t e rm inin g p erm issible splice loca tion s (o r p ro h i b i t i o nof splices). The estim ator is not in a po sition to m akethese de cision s.

Length of lapOnce the estimator has determ ined where the splice

i s, he m ust d eterm ine its length. If the splice lengths a respecified as a certain nu mb er of bar diam eters for allsplices (33 percent of jobs in survey) or clearly dim en -sioned on the plan s and sections (16 percent ) there isn o pr oblem . If th e splice is specified as Class A, B or C ac-c o rding t o ACI 318 (17 pe rcent) the estima tor m u st cal-culate this len gth or have look-up tables such as th osein th e ACI Detailing Man ual1980. Even then there areq u e s t i o n s, as spacin g a nd edge cover are va ri a b l e, an d areduction can be m ade when spirals are invo l ved. Anestimat or would no rma lly ap ply the top bar factor re-q u i red by th e co de * to all splices with m ore t ha n 12 in ch-es of con crete u n der the bars. Howe ve r, he m ay have a

p roblem if the contract docu men ts do not ind icatewheth er ho ri zonta l wall bars are to p bars o r not . The d e-signe r shou ld state e xplicitly if he ha s provide d for topba r effect an d wh ich splices are affected , includ ing hor-i zonta l wall bars. If the con tract do cum en ts are silent ont h i s, the estima tor wou ld u sually assum e th at n o top bareffect is re q u i red for walls, an d sp lices wou ld be figure das o t h e r.

Prob ably the m ost fru s t ratin g experien ce for an esti-

m ator or a detai ler is to h ave the con tract documen tsspell out sp lices in accorda n ce with ACI 318 an d b eo t h e rwise silen t. This is of ab solute ly n o h elp to the esti-m a t o r; he is in n o p osition to dete rm ine co nd itions of ten sion o r com pression, class of splice, top bar e ffect,confinem ent, and th e like. He m ust then con tact the ar-chitect or en gineer t o d eter m ine wh at is re q u i red. All toooften the re spo nse is You fellows are the experts; work ou t th e solu tion yo u r s e l f , or Wha t do you re c o m -m e n d ?

BUTT SPLICESBu tt sp lices, which are less frequen tly encou n tere d ,

m ay be eith er m echa nical or arc welded. The m ajori t yof butt splices used tod ay are mech anical. There are nu -m e rous p ro p ri e t a ry types, includ in g t he follow i n g :

m eta l filled sleeve

ho t forged sleeve

cold forged slee ve

forged sleeve with t hread ed stu d

tap er threaded sleeve

thread deform ed rebar with m atching sleeve

cem ent mo rtar filled sleeve

end bea ring sleeve

Det ailed de scriptio ns are given in th e Co n c rete Re i n -f o rcing Steel In s t i t u t es public at ion , Re i n f o rcem en t An-c h o rage s an d Sp l i c e s.

It is the job of the architect-en gineer to indicate wherebu tt sp lices a re re q u i red and to furth er define wheth erthey are to be end bear ing (comp ression only), m etalfilled sleeves (com press ion o nly), or ten sion splices. Fo r

* Building Code Requirements for Reinforced Concrete (ACI 318-77) is sp e-cific regarding top reinforcement requiring a multiplier of 1.4 and definingtop reinforcement as horizontal reinforcement so placed that more than 12inches of concrete is cast in the member below the reinforcement. However,the commentary to the code states that Recent research studying other mat-ters has seemed to reflect a lessening of this effect when the horizontal topbar is in a wall or wall-like beam with multiple runs of other horizontal barsplus vertical bars and/or ties and stirrups. This suggests that some water andair may be entrapped by other reinforcement and not be free to reach thetop bars. However, judgment regarding interpretation of these provisionsshould be made by the designer, not the estimator.


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tension splices, the en gineer de cides whether they mu std e velop 125 p ercen t of m inimu m specified yields t rength (per ACI 318) or th e m inim um ultima te ten siles t rengt h (p er ACI 359 and oth ers). If splices m ust be stag-g e red, the designer m ust also indicate this as well as theamo unt of stagger.

The estimat or mu st know which kin ds of splices arep e rm itted a s th is affects his e stimate. The firm for whichhe is doing the estim ating ma y include t he sp lice sleeve

itself in th e b id or m ay on ly includ e sp ecial end pre p a-ration of th e b ars, if re q u i red. If the sleeve is inclu de d,the estimator obviously must figure the quantity of splices re q u i red for ea ch bar size a nd m ust follow re a-son ing similar to that for lapp ed sp lices. Even if oth ersa re fur nishin g the splice sleeve, the e stima tor m ust d e-t e rm ine an y end pre p a ration necessary a nd the qu anti-ty of en ds invo l ved for each b ar size.

ANCHORAGESAn c h o rages are usu ally n ot a p roblem for th e estima-

tor since h e generally is able to follow the co ntract doc-u m e n t s. When hoo ked an cho rages are specified t heyp robab ly would be estimat ed witho ut re g a rd to wheth erthe m inimum code anchorage lengths have been pro-vided . Usually the h ooks are on b eam or slab bars sh ow na n c h o red fully into th e sup po rt. Colum n dowe ls aresom etim es a pro blem . Fi g u re 3A shows a d owel app ar-en tly exten din g d own to th e foot ing m at re i n f o rc e m e n t ,with a stand ard 90-degree ho ok. In th is case, the esti-m ato r w ou ld pr ob ab ly figure it ju st th at way, re g a rd l e s sof wheth er the anch orage length exceeded or even m etcod e re q u i re m e n t s. Howe ve r, if th e foo tin g o r m at de pt h ,as illu stra ted in Fi g u re 3B is ve ry larg e, th e estim ato rm ight ch eck th e re q u i red a n ch orage len gth p er CRSI Re-i n f o rcem en t An ch orage s a n d Splices o r th e ACI De s i g nHand book (SP 17) to d eterm ine if he sh ould u se it. In c i-d e n t a l l y, t he se two do cum en ts are n ot in agre e m e n t .

This makes it all the m ore importan t that the designershou ld indicate h is wants clearly and concisely.

If a straight bar length o f anchorage or em bedm ent iss h own a nd the contra ct drawings are n ot sp ecific as toam oun t, the estimator figures either all the way to thebottom of the footing (the usual way) or assum es ten-sion b ar an chora g e. He is never in a po sition to assum ec o m p ressio n an ch ora g e.

COLUMN TIESThe est imator m ust determ ine th e s ize , length and

quan tity of colum n ties. Where the contract docum entsa re comp lete with sche du les and typical colum n de tails,th is is fairly st ra i g h t f o rw a rd . Howe ve r, wh ere n o typ icalsections are shown, the estima tor does h ave decisions tom a k e. He either mu st con tact th e a rchitect-engineer forc l a rification or ass um e an arran geme nt such as sh ow nin Fi g u re 4 for m ultiple stor y heights, wh ich h as b eentaken from th e ACI Deta iling Man ua l. These d etails as-sum e tha t at least som e of the ve rtical colum n bars areoffset ben t an d that extra ties are re q u i red a t th e b end lo-cation. This is true o f the m ajority of bu ilding de signs. If bu tt sp lices are invo l ved, the e stimato r ha s to m ake an -other decision: whether to add extra colum n ties adja-cent to t he bu tt sp lice, as sh own in Fi g u re 5. The extraties are p resum ab ly re q u i red to replace ties elimina ted atthe splice. This is a judgmen t call and dep end s on th etie sp acin g an d th e len gth o f the splice sleeve. Ne ve rt h e-l e s s, it is possible t ha t tie sp acin g is large eno ugh so th atno ties would b e elim inated by the splice. This becom es

Figure 3. Anchorage for dowels in Drawing A would probablybe estimated exactly as shown, whereas for the deepfooting (B) a check of the required anchorage length mightbe made by the estimator.

Figure 4. Extra column ties may be required at the locationof bends in column steel which is offset bent, as shown inthis detail reproduced from the ACI Detailing Manual.


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m o re com plicated if the splices are sta ggered. It is esp e-cially imp ortan t that the estim ator be accurat e with ties,as all ties (and stirrup s) are sub ject to the light b end inge x t ra an d affect th e q uo ted price ou t o f pro p o rtion toth eir we i g h t .

BAR SUPPORTSSup pliers of re i n f o rcing b ars frequ en tly include as pa rt

of th eir service a qu ant ity survey for b ar sup po rt s. Ba rs u p p o rts m ay co n sist o f con cre t e, m etal or oth er ap -p roved m ate ri a l s. St a n d a rd spe cificatio ns for wire ba rs u p p o rt s a re inc lud ed in th e CRSI M an u al of St a n d a rdPra c t i c e, wh ich is re vised pe riod ically to reflect late stp ra c t i c e. The con tract docum en ts shou ld indicate typesof bar supp orts perm itted an d for wire supp ort s, theclass of pro tection . Most wide ly u sed are st an dard i ze d

f a c t o ry-m ad e wire ba r sup port s an d re i n f o rcing ba rs.After iden tifying t he types of ba r sup po rts pe rm i t t e dand the class of protection re q u i red, th e estim ator m ustma ke a q uan tity su rve y. He will base h is quan tities on re-q u i rements shown in the con tract docum ents or as cov-e red in th e CRSI Ma n ua l o f St a n d a rd Pra c t i c e. This in -vo l ves first determ ining th e n um ber of rows of sup port sre q u i red. In continu ous elemen ts suc h as slab bolstersor rebar sup port bars the num ber of rows m ust be con-ve rted into line al feet. For individu al elemen ts such ashigh cha irs or reba r s t a n d e e s, th e nu m ber of p ieces p errow m ust also b e d eterm i n e d .

Unless otherwise shown in th e contract docum ents,

the estim ator wou ld figure ba r supp orts for slabs o ng rade for sup po rt of top ba rs on ly. For foun dat ion m atsm o re th an 4 feet th ick, su pp orts are no t no rm a l l yp rovided for top b ars. The estima tor wou ld u sually takeoff ind ividu al stan dee s sp ace d a t 4 feet in ea ch dire c t i o nand assume th at bars in the top m at in one direct ion( a p p roxim at ely eve ry 4 feet) wou ld b e lowe red twobar d iameters to be used as a cont inuo us ho ri zontalbar su pport .

The estim ator has a choice, when ma kin g a quan tity

s u rvey for o ne-way su pp orted slabs, if n ot ot herwise de-fined in th e contract docum ents. When estimating thebar sup port s for the top re i n f o rceme nt , h e co uld figure

cont inuou s high chairs or ind ividua l high chairs with #4s u p p o rt b ars. Econ om y usu ally de term ines h is decision .W h e re it is feasible to use a tem pera t u re b ar as a sup -p o rt bar, individua l high ch airs will almo st a lways bem o re econ om ical for b uilding slabs. In certain areas of the coun try con tinu ou s high cha irs, with ru n n e r s, arespecified for bridge decks to sup port the t op m at fro mthe bott om m at o f re b a r s, where an all-straight-b ar d e-sign is invo l ved. The estimat or wou ld figure on the con-tinu ou s ch airs in th is instan ce a s a con tract re q u i re m e n t .

Fu rn ishing o f spacer s again st ve rtical or slop ing form sto main tain p re s c ribed s ide cover a nd cross position o f re i n f o rcing b ars ha s no t bee n stan dard i zed within there i n f o rcem ent ind ust ry. Estimatin g or de tailing su chspacers with th e re i n f o rcem ent is no t a nor m al indu stryp ra c t i c e, an d th e CRSI m an ua l ind icates th at the y are tobe furn ished by the gen eral contracto r (see related art i-cle on page 825).

SUMMARYAn attemp t has b een m ade to give som e insight into

the bu siness of m aking a qu ant ity survey (estim ating) of re i n f o rcin g b ars. On ly a few of t he m an y va riab les h ave

Figure 5. Extra ties may alsobe required in the region ofbutt splices in column bars,presumably to replace tieswhich may have beendisplaced by the splicelocation.

Figure 6. Supports for bars in foundation mats and slabs onground include individual high chairs wit h sand plates forsoil bearing (HCP) and continuous high chairs for upper barsupport (CHCU). Standeesreinforcing bars fabricated toorder with bent legs resting on lower mat of barsare alsoused. Dowel blocks are common in western areas of theUnited States. Drawing from CRSI Manual of StandardPractice.


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been br ief ly touched on . It ha s been said m any t imesthat an estima tor s qu antity survey ma y determine (1)whether the rebar fabricator is successful in securing ac e rtain con tract an d (2) whether it tu rn s ou t to b e a pro f-itable contract o r not . In ot her word s, the rebar e stima-tor is a ve ry im po rtan t cog in th e re i n f o rced con cre t ec o n s t ru ction whee l.

Editors note:

Publications of the Concrete Reinforcing Steel Institute citedin this article are for sale by CRSI. Address all inquiries to

their office at 180 North LaSalle Street, Chicago, Illinois60601.ACI Detailing Manual1980 is available from Concrete Con-struction Publications, 426 S. Westgate, Addison, Illinois60101 for $39.95 postpaid; check should accompany order.ACI members may wish to order directly from ACI to obtainmember discount.

P U BL I C AT I O N# C 8 1 0 7 9 3Copyright 1981, The Aberdeen Gro u pAll rights re s e r v e d

estimating reinforcing bars_tcm45-340894

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