Planning Repetitive ActivitiesfLine of Balance

Sabah Alkass PhD PEng FASCEProfessor

Line of Balance Planning Techniques

PROCEDURE FOR LOB SCHEDULINGPROCEDURE FOR LOB SCHEDULINGWhen preparing a line of balance schedule the

following stages should be systematically undertaken:

1. Preparation of logic diagram2. Assessment of manhours per operation3. Selection of buffer times4 Assessment of the ate of const ction fo t o

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4. Assessment of the rate of construction for two related operations

5. Assessment of start and finish times for first and last unit

Line of Balance Planning Techniques

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Line of Balance Planning Techniques

1. Preparation of logic diagramThe logic diagram illustrates the sequence ofThe logic diagram illustrates the sequence of

undertaking the construction operations relative to the finish and start of related activities.

FABRICATE

C-COLUMN SEQUENCE

SITESTRIP FNDNS EXT. BWK

FDNDSSUPER

1ST FIX JOINER

A-FOUNDATION SEQUENCE

B-HOUSING SEQUENCE

FABRICATE

REINFTFIX

REINFT

FIX FWK

CONCRETE

COLUMNS

FABRICATE fwk

PILINGPILE CAPS

GROUND BEAMS

ERECT STEEL

EXTERNAL BRICKWORK

ROOF

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FDNDS STRUCTURE ROOF1ST PLUMBER

1ST FIX

ELECTRICIAN

PLASTERROOF CLADDING

D-STEEL FRAMED FACTORY BUILDING

Line of Balance Planning Techniques2. Assessment of manhours per operationThe manhour allocation is required To calculate the operational duration once the gang size

has been established. Assessment of the rate of construction based upon the

forecast completion or handover ratelExample: Operation foundations

Gang size - 2 labourersManhours allocated per unit 64 manhours

Duration for one unit based on an 8 hour working day

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Duration = manhours allocated

Gang size x 8 hours/day

= 64 hours / (2 x 8) = 4 gang days

Line of Balance Planning Techniques

3. Selection of buffer times Th b ff ti i th ti i d i d b t th The buffer time is the time period in days between the

finish of one operation and the commencement of the succeeding one in the construction sequence.

The buffer period allows flexibility to be built into the planning process and is intended to prevent operations p a g p ocess a d s te ded to p e e t ope at o soverlapping.

It enables one trade to be clear of the work area before the next trade commences.The buffer period may be directly affected by

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construction constraints such as allowances for curing times or drying out periods.

Line of Balance Planning Techniques

4. Assessment of the rate of construction for4. Assessment of the rate of construction for two related operations

Example: Foundations project shown in logic diagram ARate of construction 2 house units per week.Number of units to be constructed 10 NosSite Strip 32 hours / unit Operation 1Foundations 120 hours / unit Operation 2

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Ext Bwk - 160 hours / unit Operation 3

Line of Balance Planning Techniques

SITE STRIP OPERATION 1SITE STRIP OPERATION 1Manhours required for 2 units = 2 x 32 hours = 64 manhoursPlanned nos of men to achieve 2 units/week = 64 mh /(40 hours per week)

= 1.5 menOptimum number of men in gang = 2 menNumber of gangs to be used = 1 no.

Actual rate of construction =

Actual no. of men to be used on site strip1 gang consisting of 2 men = 2 menPlanned no. of men to achieve forecast rate of construction of 2 units/week = 1.5 men Actual construction rate = (2.0/1.5) x 2.0 = 2.66

Actual no. of men

Planned no. of menX reqd rate of construction

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Rate of construction required = 2.0 houses/weekUtilizing the labour resources as shown the rate of construction on site strip will be faster than the required rateThe duration of the site strip for each unit will be: (32 manhours / unit ) / (2 men x 8 hours)

= 32 / 16 = 2 days

Line of Balance Planning TechniquesFOUNDATIONS OPERATION 2Manhours required for 2 units = 2 x 120 hours = 240 manhoursPlanned nos of men to achieve 2 units/week = 240 mh /(40 hours per week)

= 6 0 men= 6.0 menOptimum number of men in gang = 3 menNumber of gangs to be used = 2 no.

Actual rate of construction =

Actual no. of men to be used on foundations = 2 gangs consisting of 3 men = 6 men

Actual no. of menPlanned no. of men

X reqd rate of construction

Planned no. of men to achieve forecast rate of construction of 2 units/week = 6 men Actual construction rate = (6.0/6.0) x 2.0 = 2.0Rate of construction required = 2.0 houses/weekUtilizing the labour resources as shown the rate of construction on foundations will be at the required rateThe duration of the foundations work for each unit will be: (120 manhours / unit ) / (3 men x 8 hours) =120 / 24 = 5 days

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hours) 120 / 24 5 days

The rate of construction for the site strip (2.66 units/week) is faster than the rate of construction for the foundations (2.0 units / week). The balance line for the site strip will therefore be at a greater slope than that of the foundations.

Line of Balance Planning Techniques5. Assessment of start and finish times for first and

last unitIn order to develop the balance lines for each operation the start and finish timeIn order to develop the balance lines for each operation, the start and finish time

of the first and last unit must be calculated. Assume that a minimum buffer time of 2 days is to be allowed between the site strip and foundation works.

SITE STRIP - OPERATION 1For the first house unit site strip operationsCommencement of first unit = Day 0Commencement of first unit = Day 0Completion of first unit = Day 0 + Duration = 0+ 2 Days = Day 2

Start of last unit =

Start of last unit = Day 18

(No. of unit 1) x durationNo. of gangs =

(10 1) x 21 =

18

1=18

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Finish of last unit = Day 18 + Duration = Day 18 + 2 = Day 20.Summary: Site stripHouse unit 1 Starts Day 0, Finishes Day 2House unit 10 Starts Day 18, Finishes Day 20.

Line of Balance Planning TechniquesFOUNDATIONS OPERATION 2Commencement of first unit = Unit 1C l i f i i U i 1 D 2 2 d b ffCompletion of site strip to Unit 1 = Day 2 + 2 day buffer =

Day 4 Completion of foundations to Unit 1 = Day 4 + 5 day duration = Day 9

Start of last unit = (No. of units 1) x durationStart of last unit = = Day 4 + (10 1)5 /2 = (9x5)/2= Day 4 + Day 22.5 = Day 26.5

Completion of last unit = Day 26.5 + 5 day duration = Day 31.5

Summary: Foundations

no of gangs

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yHouse unit 1 Starts Day 4, Finishes Day 9House unit 10 Starts Day 26.5, Finishes Day 31.5

Line of Balance Planning Techniques

EXTERNAL BRICKWORK OPERATION 3Manhours required for 2 units = 2 x 160 hours = 320Planned no. of men to achieve 2 units/week = (320 mh) / (40 hours/week) = 8.0Optimum gang size = 3.0 menNumber of gangs to be used = 3 nosActual rate of construction = (9.0 / 8.0) x 2 = 2.25 units/weekRate of construction required 2 00 units/weekRate of construction required = 2.00 units/weekUsing 3 gangs of 3 men the rate of construction will be faster than the required

rateDuration for 1 unit = 160 mhs / (3 men x 8 hours) = 160 / 24 mh = 6.7 days =

say 7 daysAs the rate of construction for the external brickwork is faster than the foundation

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operation, the balance line will be at a steeper gradient. The external brickwork balance line must

therefore relate to the completion of the last house unit on foundations in order to prevent operations overlapping.

Line of Balance Planning TechniquesCommencement of last house unit unit 10.Completion of foundations to Unit 10 = Day 31.5 + 2 day bufferCommencement of external brickwork for Unit 10 = Day 33.5Completion of external brickwork for Unit 10 = Day 33.5 + 7 day duration =

Day 40.5

Commencement of Unit 1 for ext. bwk

Commencement of ext. bwk to Unit 10 = (No. of units 1) x duration

No of gangs

= Day 33.5 -= Day 12.5

Commencement of external brickwork Unit 1- 12.5Completion of brickwork Unit 1= Day 12.5 + 7 days duration

= Day 19.5

No of gangs

(10-1) x 73

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ySummary: External brickworkHouse Unit 1 Starts Day 12.5, Finishes Day 19.5House Unit 10 Starts Day 33.5, Finishes Day 40.5

Line of Balance Planning Techniques

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Line of Balance Planning Techniques

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Techniques

Line of Balance Planning Techniques

TechniquesResource bar chart

Use of RatiosPlanned performancePlanned performancePlanned liability/planned earning

Actual performanceActual liability/actual earning

Effi i

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EfficiencyActual performance/planned performance

Planning repetitive work

Line of balanceBased on establishing a delivery or a

handover ratehandover rateThe basic construction logic of the

repetitive unit is expressed in a form of a network called a production diagramNormally a constant rate of delivery is

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Normally a constant rate of delivery is used which is expressed in (no.of units/unit time)

Determining the handover rateExample- Road project

6 3 5 7 4

Handover rate

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Determining the handover rate (cont.)Example Road project

Waitingtime

Handover rate

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G1G2

Preparing a L.O.B schedule

In order to avoid non-productive time(Waiting Time) in parallel scheduling, resources are taken into account as part of the scheduling procedure.

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Preparing scheduling information

1 2 3 4 5 6 7 8

M Q g

Example project ( in road project based on R=4)

1 2 3 4 5 6 7 8op. M G Q g U T Ssub str 120 12 3 12 4 5 36 25=37sub.str 120 12 3 12 4 5 36.25=37

sup. str 290 29 6 30 4.14 6.04 35.02=35int.part. 250 25 4 24 3.84 7.81 37.76=38plumb. 40 4 3 3 3 1.67 48.33=49

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pelectr. 30 3 2 2 2.67 1.87 54.31=55finish. 220 22 5 20 3.64 5.5 39.84=40

1 2 3 4 5 6 7 8op. M G Q g U T Ssub.str 120 12 3 12 4 5 36.25=37sup. str 290 29 6 30 4.14 6.04 35.02=35int.part. 250 25 4 24 3.84 7.81 37.76=38plumb. 40 4 3 3 3 1.67 48.33=49electr. 30 3 2 2 2.67 1.87 54.31=55finish. 220 22 5 20 3.64 5.5 39.84=40

Time (days)

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