6 barcharts

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Bar Gant Charts

Lake excavation at a d evelopment si te in Ft . Mye rs Flor ida. Co urtesy of Terra Excav ating In c.La rgo FLorid a

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10 Chap ter 2

DEFINITION AND INTROD UCTION

A bar cb ar t is a grap hic r epre sentat ion of p roject ac tiv ities shown in atime-scaled b ar line w ith n o link s shown between activities (popescu an dCh aro en ng am 1995 , 96 ). Th e bar chart was or igi nally develo ped b y Henry L. antt in 1 917 an d is altern atively calle d a G an tt c ba rt t quickly becamepo pular es pecially in th e const ru ction in dus t r be cause of t s lltt y togra ph ically re present a proje ct s acti vitie s o n a t ime s ca le.

Befo re a ba r chart can be co nst ructed for a project , th e pro jec t m us t bebrok en in t o sm aller , usuall y h o mog eneou s co m po nen ts, each of w hi ch isca lled an ac t iv i ty or a task No abso lutely correct or in co rrect way to br eakdow n a project exi sts; h o weve r, th e schedu ler sh ould take a balan ced approac han d br eak it down int o a reaso nab le nu m ber of activitie s that are easily m ea:sured an d con trolled with ou t be ing o verly d eta iled. (Project br eakd own i s d iscu ssed further in ch apter 7.)

An activity , or a ta sk , ma y b e as large as laying th e fou nd ati on o f abui lding, as small a s erecting t he f or mwork of on e footing, or a nywh ereb etween. The durat i on of e ach ac tivity must be estimated . Bars are t h end rawn to show, fo r ea ch activi ty, t h e dura tion a nd t he sta rtin g an d en d ingpo in ts. As me n tioned p rev io usly, li n ks be t we en activ it ies are n ot u suallysh ow n.

On a b ar chart, t h e b ar ma y n ot in d ica te co ntinu ou s wo rk from th e st art

o f th e activit y until it s e n d. For exampl e, th e ac tivit y Ge tt in g a Buil dingPermit ma y be repre sen ted by a 2 -mo nth-lon g bar. Ho wever , m os t of th ist im e is a waiting p er iod . Likew ise, a Conc rete Fou nd ation su m ma ry activitym ay i nclude se veral day s of wait in g fo r con crete to cure. No nc o n t in u ous(da sh ed) b ar s are so met imes u sed to di sting ui sh betw ee n rea l work (so lidli ne) and in active perio d s (gapsb etwee n solid line s) (Ca llaha n , Quac kenb ush ,and Rowing s 1992 ).

Bar charts ha ve beco m e a ve h icle f or repr esenting m any pieces of a pro ject sin form a tio n . Man y v aria tio ns of bar chart s h ave evo lved; so me simp ly sh owth e sta r t a nd e nd of ea ch activ ity (Figu res 2. 1 an d 2.2), some are loa ded withresou r ce or b udge t nu m be rs (Figure s 2.3 an d 2 .4), an d o ther s com pare th eas p lanned scbedule with the as built scbedule (Figur e 2. 5). UsingPrim avera Pro ject Plann er (P3) so ftware (primavera S ystem s, In c., Bala Cy nwyd,PA), we can show a ctivities wit h in ter ruptions as co nt i n uou s bars o r as nec ked ba rs (Figure 2.6).


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Prepa re Si te

Va po r Barri e r

Fo rm Edges

Wel ded Wi re Fa bri c

Pour Conc ret e

Fin ish Top

Str ip Form )

ar G an Ch arts 11

I , , ; , ;

l l ll l ll -t- -

- L , L i - , ,j ~ , l

~ ~~~,~ , =I .- ,~~t , ; ~ T_= [ ~~t =J ~ ; ~ l - - ~ i ~ ~

____ _ fi__: L---_ ;..._...._l .i.__ ~_ . ; . l _ _ J

: j :: i_ _j

. i.I ~ _ 1 -. : __i.r_r - .- v -

. ...._ , .... ..__ . .__.__..._fi._... __ .1._ ._ _ .- ; ; .

~J =r ~. t~~ - T ~I ~ t=:: r- - -i ~ T ~I ~~ 1, i ~ , ;--l-. ---t---- ._ ~ _ i t_- - : L . . -,2 4 6 8 10 11 H o urs

FIGURE 2. 1 Bar chart for placing a simpl e slab on a grad e

Sinc e bar ch art s ba sicall y use th e x-axis o n ly (to depict time) , th e y xi s isuse d (in add itio n to sh owing indi vidual ac tivitie s) to re pre se n t a var iabl eacross t im e, such as m an -hours (Figur e 2,3), bu dg et (Figur e 2 ,4), percentco mp lete (Figur e 2,5 ), and so for th, Thi s va riable i s usually shown as a cu rvesuperim pose d o n the bar ch art ,

Excav at e

Form Footin gs

Place Reba r

--Place Co ncrete I - - - - I - - - -i- - - --

,..

St rip For m s

2 4 6 8 10 12 14 16 18 Days

FIGURE 2 .2 Alter n ati ve ba r chart for pl acin g a s i mp le slab o n a grad e


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12 Chapter 2

Man hou rsFo undatio n

ir s t l oo r

e ond l oo r

Th ir d H oor

our th loor

R oof

Site

~ - -~-, - .- -f - r f - - '

.~ : ~ : L i ~ _ __L l ~ L. .

.......-._ __t _.:--. -l---]. L L.L.

7.000

6.000

5.000

4.00 0

3.00 0

2.000

1.000

6 8 10 12 14 16 18 20 22 2 4 26 28 Days

FIGUR E 3 Bar ch art oaded with man hours or co ns t ruction o f a two-story b uildin g

In Figure 2.5, S curves (also called la zy es repres en t the per cen tco mplete for the projec t:

Th e th in cont inu o us lin e ( ) represents th e as-plan ned curv e. Th e th ick con tinu o us line ( ) represen t s t he as-buil t curve, The thick da shed lin e (- - - - - - represen t s th e p redict ed cu rve based

o n ext rapol atio n from th e as-built curve.

3 60

12 0

180

6 00

240

720

BUdg et k

8 40

-+-;--+-T+- v , 1 , I. '' T . ~ ~ _ , '_. i. Li...~ .. . __-t- .. .. ..L.. L...L_

I i ~ j

i I:; -[ ;~ ~ - r t -4--i .. --i-i L

- l , i -H--+-

rs t Floo r

Roo f

o un da tion

o ur t h l oor

T hird loor

Site

Se con d Flo or

2 4 6 8 10 12 14 16 18 20 22 24 26 28 Days

FIGU RE 2 4 Bar char t loa de d with th e bud get for con stru cti o n of a tw o stor y buildin g


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Bar Ga ntt C harts 13

Data Dat e

____ __ L _ i _ _ _ _

Re mo ve O ld Roof

Repla ce Rott en Rafters

Insta ll Shea thing

Insta ll Felt

Install Sh ingles

Clean Up

.._ . - - _ ~ - - - - - - -- - - .

Percen t

mplete10 0

90

80

70

60

50

40

30

20

10

2 3 4 5 6 7 8 9 10 11 12 13 14 15 D ays

ilAs Plan ned As Bu ilt IFIGURE 2. 5 Bar chart for rep laceme n t of an ol d roo f, showi ng a co mparison be tw een th e

pe rcent compl et e of th e planned (as-pl anned) a ct ivities thin lin e) and th a tof t he actu al (as-bui lt) activ it ies (thi ck lin e)

Excavate

Form Footing s

Place Rebar

IlIII Place C oncret e _ st ip fo rms

FIGUR E 2. 6 Bar chart f or p lacing a simp le slab on a grade, wit h activities necked durin gn onwork perio ds

ADVA NTAGES OF BAR CHART SBar c ha rts h ave gai ned wide acce ptance an d popular ity ma inly beca use oftheir simp licity an d ease of prepa ration and under sta nding. No th eory orcomplic ated cai cula ti ons a re involved. Anyone can u nderstand them . They


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14 Chapter 2

can be pre pared anywhere wi th just a pen cil an d paper.S o, alth o ugh ba r chart scan ca rry r b e loaded wi th the r in formation , the u ser m ust be ca reful n o tto ove rload th em an d t hus eliminate th eir ma in a dv an t age : simp licity .

Ano ther ad vantage i s that bar cha rts parti cularly ap peal t o pe rsons wh o dono t have a tech nical bac kgro un d . For exa mple, s ome clien t s an d up per-lev elmanage rs may b etter un derstand th e plan for carrying ou t a co nstruct ion pro jectby looki ngat a bar char t th an by looking at a sc hematic of a logic n etwork.

A f inal advantage of ba r cha r ts is that , with th e advent o f th e critical p athmethod e PM an d th e evol ution of powerful com puter s, bar cha rt s did no tper ish or lose importance. Instead, th ey evolved to a differ en t suppor ting rol eth at m ade them mo re valuable an d popular. This ro le is e xplained in chapte rs3 and 4 .

DISA DVANTAGES OF BAR H RTS

The mai n disad va nt age of bar ch a rts is lack o f logical repre sentation relationsh ips : W hy did th i s ac tiv ity st art on that date? B ar ch arts do n ot revea l th eanswer. t could be a logica l relations h ip , a res ourc e co nstraint, o r a s u bjectiv edec ision by th e pro ject m anager. Alth ou gh so me softw are progra mmers tri edto depict logical re lationships on bar ch arts, th e re sult was no t always cl ear.The logic lin es wo uld ge t t an gled, an d u nlik e networks, b ar cha rts do notallow th e len gth of t he bar s to be changed or moved around to m ake item s

clearer or look b etter.Anoth er lim itati on , rat he r t han a d isadvantage, for ba r cha rt s is th e size

an d comp lexity of pro jects . Bar chart s may not be pra ctica l for proj ects withlarge nu mbers of tivit i s unless you u se th em in two way s:

1 u show a subset o f th e work a ctivities to m aintain t he s impli dty ofthe chart . For exam ple, th e genera l con tractor can prod uce b ar cha rtsfor activiti es du r ing on ly a certain perio d, for cr i t ica l ac t i vi es a ctivities th at can n o t be d elay ed or th e en tire project would bedelayed ; a full d efinition an d discuss io n follows in c h ap ter 4 oniy ,for ac tiviti es in a c ertain sect ion of t he p roject , or for ac tivities undera certain subcon tractor.

2. u sho w sum mary bars eac h bar represents a grou p of activ itie scombined on t he b asis of a certai n cr iterion suc h as depart me nt ,m ajor componen t, or re sponsibili ty . Thi s can be d on e during t heearly plannin g phase , when details are no t available s ee, f or examp le,


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Bar G antt Chart s

Pr epare S ite

Pilin g

Columns Pier H eads

Beam s Deck

arri ers Joints

pproach Slabs

Road way Stripi ng

2 4 6 8 10 12 14 16 18 20 21 We eks

FIGURE 7 Bar cha rt rep resen ting th e summary a ctivities for c ons tructing a bridge

Figure 2.7 , nd when yo u are reporting the inf orma tion to h igh-l evelma nagem en t.

New tech nology com puters, sof tware, p rinters, p lotters, etc. has arn ellorat ed so me of the disa dvantages o f bar chart s by en abling th e us er to o rgani ze filt er, ro ll up, summarize, or do alm ost a ny thing t o cu stomize th e ba rcha rt. Bar chart reporting a nd p resentati on is d iscussed in ch p ter

1. Wha t i s a bar c hart? W hat o ther te rm is syno nymo us? H ow d id th e otherter m originate?

2. Wha t are the m in advantages of bar cha rts th at m ade th em so popular?Wh at are the i r m ain disa dvantages?

In t he foll owing e xercises, dra w a bar ch art showing th e tim e scaie on th ex-axls. Usee ngineering pap er, or d raw light ve rtical li nes every ce rtain in t erval

- e.g. , ever y 5 d ays to h elp yo u read t he starting and e nd ing dates of a ny activit y.Make si mplifying assum p tions whe never necessa ry. Be sure t o me nt ion th eseassum p tions.

3. You a re runn ing o ut o f space i n yo ur h ouse, so yo u h ave decided totransform yo ur t wo- car g arage in to a family ro om . In add it ion , y ou willbuild a simpl e carpo rt in your driveway. Make a ba r chart for this proj ect,breaking your proj ect i nt o 10 t o 15 work ac tivities.


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Chapter 2

4. Thi n k of co llege education as a pro ject. u a re advis in g a fri end, a

senior in hi gh sc hool wh o pla ns t o at ten d co llege n ext year. Prepare a barchart for him , de p icti ng all th e co urs es he m ust take from th e start ofcoll ege u ntil grad ua tion . Obta in t he program course list. Make sure youdo n ot o verlook a ny prerequis ite requir ements. Make the fo llowing simpli fying assumptions :

a. ur frien d is smart. H e will n ot fail any cour se.

b . All co ur ses a re ava ilable ever y f all nd spri n g semester.

c. No sum mer sem esters are in clud ed . ur fri end will w ork d ur ing thesu m mer .

d . TI,e total load every seme ster sho uld be no less th n 15 credit h o ur sand n o m ore th n 18. Yo u can le t hi m ta ke as m any as 20 c redith ours in on e semester only, and on ly during t h e last yea r.

e. Your f riend must graduate in eig ht semesters.

After fi nishing th e bar chart , show it to yo ur ad viser and get his or h er approv alo n your sequ ence of courses. Note th t several correct solutio n s to th is prob lemm ay be possibl e which is often th e case with cons truction pro jects .

5. Draw a b ar chart fo r buildin g a d etached s hed in yo ur b ackyard . Breakyo ur p roject in to 10 t o 15 work activitie s.

6.

u are gi ven th e ta sk of ch anging th e worn -out carpe t in your o ffice.Draw a ba r chart sho wing all activiti es invo lved in clud in g removing a ndreinstalling b aseboa rd s; rem oving nd di sposing of o ld carpet and th epad; selectin g, pur chasi ng , a nd de live rin g ne w carp et a nd a n ew p ad;clea n ing u p b efor e nd after i nstallin g the n ew c arp et; an d an y otherreleva n t act ivity .

7. Prepa re a bar c hart for b uilding a n in ground swimm ing poo l. yo u don ot know the steps in v olved , ask a fr ien d or a l oca l cont ractor .

8. Con tact a con tractor a nd ask hi m or h er whe th e r h e o r she u ses b archarts t hey m ay be ca lled Gantt cha rt s Ask ab ou t t he m in t ypesof bar c h art r eports . h ich groups of ac tivities are includ ed? Ask ifthe bar ch rts are p rep ared a s bar cha rts o r as an out pu t for a CPMsch edul e.

9. To de mo n stra te th e con cept o f sum m ary bars, d raw b ar ch arts forbuilding a n ew h om e. Use a few s ummary activ ities, su ch as laying th efound ati on , p ut t ing a slab o n a grade , fram ing , doi n g e lectrica l work,


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Bu r G untt C harts

puttin g in the plu m in g , ins talling an HVAC h eating, ven tilation ,

and air-c ondi tioning syst em, putt ing on t he roo f, ins talli ng door s andwi ndows, n d do ing the finishing. u m ay n eed to show so me of theseactivities e .g., th e e lectrica l work , t he p lum ing as di scontinuou s ba rsbecause yo u start th e activity do a rou gh -in , s top, th en ret ur n an dfin ish it. Take the char t to a specializ ed contracto r and expan d one o fth ese bar s. Expa nding a summ ry ba r me ans bre aking it d own in to th edetailed activities th t com pose th e summ ary ac tivit y. For ex am ple , youc n expand Fram ing to Ins talling First- Floor Bottom Pla tes , Ins tallingFirst -Floor Studs, Ins talling First -Floor Blocking , In stalling First -Floor To pPlat es, Installing Se con d-Floor Joist s, and so fo rt h . No te th t th e tot aldur ati on of th e su mm ary activi ty m ust equ al th e total du r ati on n otn ecessarily th e alg ebraic summ at io n of th e de tailed activ itiesun d er n eath the summary activ ity .


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6 barcharts

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