139 workplan

WORKPLANWORKPLANPART-1PART-1

helpdesk@construction-productivity.co.ukhtt://www.construction-productivity.co.ukhtt://www.construction-productivity.co.uk

WORKPLANWORKPLAN Construction Planning is a Construction Planning is a

fundamental and challenging fundamental and challenging activity in the management and activity in the management and execution of construction projectsexecution of construction projects

It involves:It involves:1.1. Managerial Managerial 2.2. TechnologicalTechnological3.3. Social factors.Social factors.

WORKPLANWORKPLAN Managerial

Factors

Technological

Factors

SocialFactors

WORKPLANWORKPLAN A good construction plan is the basis for A good construction plan is the basis for

developing the budget and the schedule developing the budget and the schedule for work.for work.

Developing the construction plan is a Developing the construction plan is a critical task in the management of critical task in the management of construction. construction.

In developing a construction plan, it is In developing a construction plan, it is common to adopt a primary emphasis on common to adopt a primary emphasis on either cost control or on schedule control. either cost control or on schedule control.

WORKPLANWORKPLANConstruction

Plan

Resourcesand cost

ResourceOrientated

Criticalpath

NetworkAnalysis

TimeOriented

Scheduleof

workbased plan

IndirectCost

involved

DirectCost

involved

Budgetbasedplan

WORKPLANWORKPLAN A database program called WorkPlan A database program called WorkPlan

has been developed to systematically has been developed to systematically provide weekly work plans. provide weekly work plans.

WorkPlan adopts the Last Planner WorkPlan adopts the Last Planner methodology, which implements a methodology, which implements a number of lean construction number of lean construction techniques.techniques.

WORKPLANWORKPLAN A week before the actual work starts A week before the actual work starts

WorkPlan guides the management team WorkPlan guides the management team step by step through the process of step by step through the process of producing work packages in order to producing work packages in order to identify issues such:identify issues such:

checking constraintchecking constraint resolving constraintsresolving constraints Sending out work packagesSending out work packages allocating resourcesallocating resources

WORKPLANWORKPLAN Then at the end of the week, Then at the end of the week,

collecting site progress data such as:collecting site progress data such as: reasons for cost overrunreasons for cost overrun reason for time overrunreason for time overrun reason for delaysreason for delays DisruptionsDisruptions etcetc

WORKPLANWORKPLAN This well planned and systematic This well planned and systematic

approach helps the management approach helps the management team to create quality work plans.team to create quality work plans.

They learn from any failureThey learn from any failure a good WorkPlan is a weekly work a good WorkPlan is a weekly work

planplan based lean constructionbased lean construction production schedulingproduction scheduling

WORKPLANWORKPLAN screeningscreening work packagework package ConstraintConstraint percentage of planned completed (PPC)percentage of planned completed (PPC) Scheduling of construction work is Scheduling of construction work is

often done with the help of computer often done with the help of computer toolstools

It implement the critical-path method It implement the critical-path method (CPM)(CPM)

WORKPLANWORKPLAN based on activities of given duration based on activities of given duration

and unit resources allocated to themand unit resources allocated to them as well as predecessor relationships as well as predecessor relationships

between activitiesbetween activities for different parties involved in a for different parties involved in a

construction project to communicate construction project to communicate with one another whom should be with one another whom should be doing what work and when.doing what work and when.

WORKPLANWORKPLAN The application of lean production The application of lean production

techniques in construction has been techniques in construction has been triggered by its success in manufacturing triggered by its success in manufacturing (Womack and Jones 1996).(Womack and Jones 1996).

Weekly work plans can be developed as Weekly work plans can be developed as valuable tools for production planning and valuable tools for production planning and control.control.

This is possible through the application of This is possible through the application of lean construction techniques.lean construction techniques.

In the application weekly work plans are In the application weekly work plans are generated using a database (generated using a database (Choo, Choo, Tommelein, Ballard, and Zabelle -1998).Tommelein, Ballard, and Zabelle -1998).

WORKPLANWORKPLANChoice of Technology and Construction Choice of Technology and Construction

Method Method For example, a decision whether to pump For example, a decision whether to pump

or to transport concrete in buckets will or to transport concrete in buckets will directly affect the cost & duration of directly affect the cost & duration of tasks involved in building construction. tasks involved in building construction.

A decision between these two A decision between these two alternatives should consider the costs, alternatives should consider the costs, reliabilities, and availability of reliabilities, and availability of equipment for the two transport equipment for the two transport methods. methods.

WORKPLANWORKPLAN Formulate a number of construction Formulate a number of construction

plans based on alternative methods.plans based on alternative methods. Once the full plan is available, then the Once the full plan is available, then the

cost, time and reliability impacts of the cost, time and reliability impacts of the alternative approaches can be reviewed. alternative approaches can be reviewed.

In bidding competitions in which several In bidding competitions in which several alternative designs may be proposed. alternative designs may be proposed.

value engineeringvalue engineering for alternative for alternative construction may be considered.construction may be considered.

WORKPLANWORKPLAN The planner will prepare his/her The planner will prepare his/her

workplan based on past knowledge workplan based on past knowledge and work experience or by using a and work experience or by using a formal computer based simulation formal computer based simulation technique is used.technique is used.

By observing the result, comparisons By observing the result, comparisons among different plans or problems among different plans or problems with the existing plan can be with the existing plan can be identified. identified.

WORKPLANWORKPLAN Defining Work Tasks. Defining Work Tasks. Defining Work Tasks can also be Defining Work Tasks can also be

accomplished. accomplished. These work tasks represent the These work tasks represent the

necessary framework to allow necessary framework to allow schedulingscheduling of construction activities.of construction activities.

Along with estimating the Along with estimating the resourcesresources required by the individual work tasks, required by the individual work tasks, and any necessary and any necessary precedenceprecedence or or required sequence among the tasks. required sequence among the tasks.

WORKPLANWORKPLAN The The scheduling problemscheduling problem is to determine is to determine

an appropriate set of activity such as: an appropriate set of activity such as: start time; start time; resource allocations;resource allocations; completion times;completion times; will result in completion of the project in will result in completion of the project in

time and within the budget. time and within the budget. In this planning, defining work tasks, In this planning, defining work tasks,

technology and construction method is done technology and construction method is done either simultaneously or in a series of either simultaneously or in a series of iterations. iterations.

WORKPLANWORKPLANPrecedence Definition for Site Preparation Precedence Definition for Site Preparation

andandFoundation WorkFoundation Work Suppose that a site preparation and concrete Suppose that a site preparation and concrete

slab foundation construction project consists of slab foundation construction project consists of nine different activities:nine different activities:

A.A. Site clearing (of vegitation and minor debris) Site clearing (of vegitation and minor debris) B.B. Removal of trees Removal of trees C.C. General excavation General excavation D.D. Grading general area Grading general area

WORKPLANWORKPLAN E.E. Excavation for utility trenches Excavation for utility trenches F.F. Placing formwork and Placing formwork and

reinforcement for concretereinforcement for concrete G.G. Installing sewer lines Installing sewer lines H.H. Installing other utilities Installing other utilities I.I. Pouring concrete. Pouring concrete.

WORKPLANWORKPLAN Activities A (site clearing)Activities A (site clearing) B (tree removal) do not have B (tree removal) do not have

preceding activities since they depend preceding activities since they depend on none of the other activities on none of the other activities

Activities C (general excavation)Activities C (general excavation) and D (general grading) are preceded and D (general grading) are preceded

by activity A (site clearing). by activity A (site clearing).

WORKPLANWORKPLANActivity Description Predecessors

A Site clearing ---

B Removal of trees ---

C General excavation A

D Grading general area A

E Excavation for utilitytrenches B,C

F Placing formwork andreinforcement for concrete B,C

G Installing sewer lines D,E

H Installing other utilities D,E

Pouring concrete F,G

WORKPLANWORKPLANActivity-on-Arrows Representation of a Activity-on-Arrows Representation of a

Nine Activity Project Nine Activity Project

WORKPLANWORKPLAN Defining Precedence Relationships Defining Precedence Relationships

Among Activities Among Activities

Illustrative Set of Four Activities with Precedence

WORKPLANWORKPLAN More complicated precedence More complicated precedence

relationships can also be specified. relationships can also be specified. For example, one activity might not For example, one activity might not

be able to start for several days after be able to start for several days after the completion of another activity.the completion of another activity.

For example-concrete might have to For example-concrete might have to cure (or set) for several days before cure (or set) for several days before formwork is removed. formwork is removed.

WORKPLANWORKPLAN This restriction on the removal of This restriction on the removal of

forms activity forms activity is called a is called a laglag between the completion of one between the completion of one activity (i.e., pouring concrete in this activity (i.e., pouring concrete in this case) and the start of another activity case) and the start of another activity (i.e., removing formwork in this case). (i.e., removing formwork in this case).

Many computer based scheduling Many computer based scheduling programs permit the use of a variety programs permit the use of a variety of precedence relationships. of precedence relationships.

WORKPLANWORKPLAN Three mistakes should be avoided in specifying Three mistakes should be avoided in specifying

predecessor relationships for construction plans. predecessor relationships for construction plans. First, a circle of activity precedence will result in an First, a circle of activity precedence will result in an

impossible plan. impossible plan. For example:For example: if activity A precedes activity B,if activity A precedes activity B, activity B precedes activity C,activity B precedes activity C, and activity C precedes activity A, and activity C precedes activity A, then the project can never be started or completed! then the project can never be started or completed!

Figure below- illustrates the resulting activity Figure below- illustrates the resulting activity network.network.

Formal scheduling methods and good computer Formal scheduling methods and good computer scheduling programs will find any such errors in the scheduling programs will find any such errors in the logic of the construction plan. logic of the construction plan.

WORKPLANWORKPLAN

Example of an Impossible Work Plan

WORKPLANWORKPLAN Estimating Activity Durations. Estimating Activity Durations. In most scheduling procedures, each In most scheduling procedures, each

work activity has an associated time work activity has an associated time duration. duration.

These durations are used extensively These durations are used extensively in preparing a schedule. in preparing a schedule.

Suppose that the durations shown in Suppose that the durations shown in Table-below were estimated for the Table-below were estimated for the project diagrammed in Figure below. project diagrammed in Figure below.

WORKPLANWORKPLAN

Activity Predecessor Duration (Days)

Excavate trench --- 1.0

Place formwork Excavate trench 0.5

Place reinforcing Place formwork 0.5

Pour concrete Place reinforcing 1.0 1.0

WORKPLANWORKPLAN The entire set of activities would then The entire set of activities would then

require at least 3 days, since the activities require at least 3 days, since the activities follow one another directly and require a follow one another directly and require a total of 1.0 + 0.5 + 0.5 + 1.0 = 3 days. total of 1.0 + 0.5 + 0.5 + 1.0 = 3 days.

If another activity proceeded in If another activity proceeded in parallelparallel with this sequence, the 3 day minimum with this sequence, the 3 day minimum duration of these four activities is duration of these four activities is unaffected. unaffected.

More than 3 days would be required for More than 3 days would be required for the sequence if there was a delay or a lag the sequence if there was a delay or a lag between the completion of one activity and between the completion of one activity and the start of another. the start of another.

WORKPLANWORKPLAN All formal scheduling procedures rely All formal scheduling procedures rely

upon estimates of the durations of the upon estimates of the durations of the various project activities.various project activities.

As well as the definitions of the As well as the definitions of the predecessor relationships among tasks. predecessor relationships among tasks.

The variability of an activity's duration The variability of an activity's duration may also be considered. may also be considered.

Formally, the Formally, the probability probability distributiondistribution of an activity's duration of an activity's duration as well as the expected or most likely as well as the expected or most likely duration may be used in scheduling. duration may be used in scheduling.

WORKPLANWORKPLAN A probability distribution indicates A probability distribution indicates

the chance that a particular activity the chance that a particular activity duration will occur. duration will occur.

In advance of actually doing a In advance of actually doing a particular task, we cannot be certain particular task, we cannot be certain exactly how long the task will exactly how long the task will require. require.

WORKPLANWORKPLAN A straightforward approach to the A straightforward approach to the

estimation of activity durations is to keep estimation of activity durations is to keep historical recordshistorical records of particular activities. of particular activities.

Including rely on the average durations Including rely on the average durations from this experience in making new from this experience in making new duration estimates. duration estimates.

Since the scope of activities are unlikely to Since the scope of activities are unlikely to be identical between different projects, be identical between different projects, unit productivity rates are typically unit productivity rates are typically employed for this purpose. employed for this purpose.

WORKPLANWORKPLAN For example, the duration of an For example, the duration of an

activity Dij such as concrete activity Dij such as concrete formwork assembly might be formwork assembly might be estimated as:estimated as:

WORKPLANWORKPLAN where Aij is the required formwork where Aij is the required formwork

area to assemble (in square yards). area to assemble (in square yards). Pij is the average productivity of a Pij is the average productivity of a

standard crew in this task standard crew in this task (measured in square yards per (measured in square yards per hour). hour).

Nij is the number of crews assigned Nij is the number of crews assigned to the task. In some organizations, to the task. In some organizations, unit production time, unit production time,

WORKPLANWORKPLAN Tij, is defined as the time Tij, is defined as the time

required to complete a unit of required to complete a unit of work by a standard crew.work by a standard crew.

It is used as a productivity It is used as a productivity measure such that Tij is a measure such that Tij is a reciprocal of Pij. reciprocal of Pij.

A formula such as Eq-can be used for A formula such as Eq-can be used for nearly all construction activities nearly all construction activities

WORKPLANWORKPLAN

Figure-above  Illustration of Productivity Changes Due to Learning

WORKPLANWORKPLAN Random factors will also influence Random factors will also influence

productivity rates and make productivity rates and make estimation of activity durations estimation of activity durations uncertain. uncertain.

For example:For example: A scheduler will typically not know at A scheduler will typically not know at

the time of making the initial schedule the time of making the initial schedule how skilful the crew and manager will how skilful the crew and manager will be that are assigned to a particular be that are assigned to a particular project. project.

WORKPLANWORKPLAN The productivity of a skilled The productivity of a skilled

site worker may be many times site worker may be many times that of an unskilled workforce. that of an unskilled workforce.

In the absence of specific In the absence of specific knowledge:knowledge:

The estimator can only use The estimator can only use average values of productivity. average values of productivity.

WORKPLANWORKPLAN Weather condition are very important and Weather condition are very important and

thus requires particular attention in thus requires particular attention in estimating durations. estimating durations.

Weather has both Weather has both systematic and randomsystematic and random influences on activity durations.influences on activity durations.

Whether or not a heavy snow will fall on a Whether or not a heavy snow will fall on a particular day is certainly a random effect that particular day is certainly a random effect that will influence the productivity of many will influence the productivity of many activities.activities.

However, the likelihood of a sub zero However, the likelihood of a sub zero temperature is likely to vary systematically temperature is likely to vary systematically from one month or one site to the next. from one month or one site to the next.

WORKPLANWORKPLAN Adjustment factors for inclement weather as Adjustment factors for inclement weather as

well as meteorological records can be used well as meteorological records can be used to incorporate the effects of weather on to incorporate the effects of weather on durations. durations.

As a simple example, an activity might As a simple example, an activity might require 15 days in good weather, but the require 15 days in good weather, but the activity could not proceed in the snow. activity could not proceed in the snow.

Suppose that rain is expected ten percent of Suppose that rain is expected ten percent of the days in a particular month.the days in a particular month.

In this case, the expected activity duration is In this case, the expected activity duration is eleven days including one expected rain day. eleven days including one expected rain day.

WORKPLANWORKPLAN Finally, the use of average Finally, the use of average

productivity factors themselves productivity factors themselves cause problems in the calculation cause problems in the calculation presented in Equation-above. presented in Equation-above.

The expected value of the The expected value of the multiplicative reciprocal of a variable multiplicative reciprocal of a variable is not exactly equal to the reciprocal is not exactly equal to the reciprocal of the variable's expected value. of the variable's expected value.

WORKPLANWORKPLANFor example:For example: If productivity on an activity is either six If productivity on an activity is either six

in good weather (ie., P=6)in good weather (ie., P=6) or two in bad weather (ie., P=2)or two in bad weather (ie., P=2) and good or bad weather is equally and good or bad weather is equally

likely,likely, then the expected productivity is P = (6)then the expected productivity is P = (6)

(0.5) + (2)(0.5) = 4,(0.5) + (2)(0.5) = 4, and the reciprocal of expected and the reciprocal of expected

productivity is 1/4. productivity is 1/4.

WORKPLANWORKPLAN The expected reciprocal of productivity The expected reciprocal of productivity

is E[1/P] = (0.5)/6 + (0.5)/2 = 1/3. is E[1/P] = (0.5)/6 + (0.5)/2 = 1/3. The reciprocal of expected productivity The reciprocal of expected productivity

is 25% less than the expected value of is 25% less than the expected value of the reciprocal in this case.the reciprocal in this case.

By representing only two possible By representing only two possible productivity values, this example productivity values, this example represents an extreme case.represents an extreme case.

but it is always true that the use of but it is always true that the use of average productivity factors in average productivity factors in Equation-above will result in Equation-above will result in optimisticoptimistic estimates of activity durations. estimates of activity durations.

WORKPLANWORKPLAN The use of actual averages for The use of actual averages for

the reciprocals of productivity the reciprocals of productivity or small adjustment factors or small adjustment factors may be used to correct for this may be used to correct for this non-linearity problem. non-linearity problem.

A Hierarchical Estimation Framework A Hierarchical Estimation Framework for Masonry Constructionfor Masonry Construction