Planning and Control of Construction Projects

Importance of Schedule

A Schedule is dynamic and therefore will always change
It must be accurate and reflect all the changes and impact
The schedule is a critical management tool
- A current and accurate schedule facilitates a successful project
- Responsively managing changing conditions
- Stakeholders' engagement for a timely decision making

Scheduling on Three Levels

Master plan - milestones for the whole project
- Examine Construction methods
- General plan of resources, cash flow, etc.
- Critical Path Method (CPM), Location-based scheduling
Look ahead plan - monthly
- Reveal barriers to actual construction and coordination with partners
- Notification of resource activation
- Critical Path Method (CPM), Location-based scheduling
Work assignments – weekly production management
- Notification of barriers to actual construction
- Coordinations of actual construction plan
- Production control
- Last planner system

Critical Path Method - Components

Work
- Specify the activities, translate the design
- Work Method, Quantity, Space
- Work Breakdown Structure (WBS)
Link
- Work dependencies
- Define the start and end time
- Gantt chart and network diagram
Resource
- Constraints of resource allocation
- Resource leveling

CPM - WBS

100% rule
Mutually exclusive elements
Level of detail
Coding scheme

CPM - Activity and Dependency

Activity Duration

Work Dependency

Shortening Project?

CPM - Network Method

Activity-on-node diagram

ES	Activity	EF
LS		LF
TF	Duration	FF

ES	Activity	EF
LS		LF
TF	Duration	FF

FF = Maximum delay of an activity that does not cause a delay in the start of any successor activities (ESs-EFp)

TF = Maximum delay of and activity that does not cause a delay in completion of all the project (LS-ES)

Critical path: nodes with TF = 0

Algorithm

Activity	A	B	C	D	E	F	G
Duration	1	2	1	3	2	3	2

Level Method

Predecessor activity	Successor activity
A	C
B	D
G	A
F	C
B	G
D	A
E	G
D	F

Activity-on-arrow diagram

CPM - Example

Activity-on-node diagram

0	B	2

	2

2	D	5

	3

5	F	8

	3

0	E	2

	2

2	G	4

	2

5	A	6

	1

8	C	9

	1

0

1

0

2

0

9

8

7

5

2

5

2

0

5

3

0

3

2

0

FF = Maximum delay of an activity that does not cause a delay in the start of any successor activities (ESs-EFp)

TF = Maximum delay of and activity that does not cause a delay in completion of all the project (LS-ES)

Critical path: nodes with TF = 0

ES	Activity	EF
LS		LF
TF	Duration	FF

ES	Activity	EF
LS		LF
TF	Duration	FF

CPM - Exercise

Activity code	Length (weeks)	Predecessor	Type of connection	Total float
A	7	-
B	9	-
C	12	-
D	14	A B C	FF=7 FS=2 SS=8
E	11	D	FS=0
F	17	D	SS=11
G	13	E	FS=0	0
H	6	E F	FS=3 FS=0
I	?	F	SS=12	0

Sketch the network of activities and calculate ES and EF for each activity
Calculate LS and LF for each activity
Calculate TF and FF for each activity
Identify the critical path
How do you calculate the duration of a task I ?
Is it possible to shorten the project by shortening activity D ? Explain.
What will be the project duration if the length of activity D is 18 weeks instead of 14 weeks?
How will the critical path change?
What will be the new duration of the project?

CPM - Resource

Resources: workers, equipment, material, money, space
- Consumed resource : consumed (e.g. materials).
- Required resource: used but not consumed (e.g. equipment).
Allocation of resources for activities;
- Costs, cost allocation (at start, uniform, at end)
- Required resources
Resource optimization
- Resource Allocation
- Resource Leveling

CPM - Resource Allocation

Activity	Duration	Early Start	Total Float
A	32	90	30
B	25	102	10

Project delay 147-137= 10

Project delay 159-152= 7

If both A and B require the same resource, and only one unit of that resource is available, and the activities must be performed continuously, which activity should be given the resource first, in order to minimize the impact on the project as a whole?

CPM - Resource Leveling

CPM - Time Cost Tradeoff

A highway project has four tasks: A, B, C and D.

Site overheads are ¥ 2,000/day, and the client has offered a bonus of ¥ 500 for every week short of the 15th week

The contractor can perform the work in two different construction methods

CPM - Summary

Components
- Task, link, resource
Techniques
- WBS, network diagram, resource allocation/leveling
Constraints
- Task dependencies, resource, time cost tradeoff, etc.
Limitations?
- Activities are represented as 'black boxes'
- Network method does not describe the flow of workers
- Mainly preventing task overlap rather than waiting time

Modular Building

Modular Project
- Project with similar units in which tasks repeat themselves periodically.
Work Section
- A defined area in a building where some craft is performed by a trade crew.
Tasks
- Single craft performed by one crew at one work section

Work section / Floor
1
2
3
4

Trades
Structure
Plastering
Tiling

Empire State Building

102-story
200,000 m2 rental space
381 m / 443 m with antenna
Stood as world's tallest building for 40 years
Construction involves 3,500 workers
57,000 t of structural steel
48,000 m3 of concrete
10 million bricks
The framework rises 4 ½ stories per week
Construction completed in 410 days

Modular Building

Line of Balance Chart

Work section / Floor
1
2
3
4

Trades
Structure
Plastering
Tiling

Line of Balance Chart

Task Dependencies

Specialization

The following is a list of trades in construction.

Specialization due to professionalization
Designed to enable improved quality
Professional responsibility/liability
Allows improvement of local productivity

Continuity in Construction - 'Rapid' Tasks

Continuous workflow

‘Anchors’

Why continuity
- Restart of work costs money
- Maximum productivity
- Labor availability
Treat the 'Rapid' tasks
- Delay the beginning
- Slow down by resource dilution
- Merge with other tasks

Rapid tasks

Continuity in Construction - 'Slow' Tasks

How to treat the 'Slow' tasks

Accelerate the pace of work
Split plastering into ceiling plastering and walls plastering
Splitting the work section and adding additional teams as needed

Interim Summary

Reduce waiting time - waste
Mismatch in work rates causes discontinuities
To achieve a fixed rate in tasks
- Slow down or merge the 'rapid' tasks
- Speed up or split the 'slow' tasks
Limitation in determine the rhythms of cyclic tasks
- The rate is limited by section size and the number of workers\resources that can be used in each section
- Lower limit of construction rate: rate limited by the method of construction and minimum group size; not less than one floorer and assistant

Technical Constraints and Work Section Conflict

Structure work = formwork + pouring concrete
Task Specialization & Work Section Conflicts

Division of Work Section

1

2

3

4

A

B

C

D

E

F

G

H

Proper division of independent work sections on each floor .
Division of floors into two allows continuous progression for the formwork and pouring teams.
The work rate of teams in different sections is the same.

In Practice

Sections of work are not completely identical

Uncertainty of Production Rate

Production rate is a nonlinear function of:
- Work section size
- Team (equipment compared to workers)
- Local variability (such as weather, learning curve)

Pouring concrete with a pump

Learning curve

Uncertainty of Task Duration

0	F	10

	10

0	A	12

	12

12	C	18

	6

2

0

2

18

12

0

2

0

0	F

	9-12

0	A

	10-13

	C

	6

If the durations of the tasks are uncertain

What is the probability curve of the earliest project completion date?
What are the chances task F will be critical?
When would you instruct the crew performing task C to start? Why?

Assume that:

Activity F will take 9-12 days (uniform distribution)
Activity A will take 10-13 days (uniform distribution)

Uncertainty of Task Duration

Note: Only one plaster crew is available

Suppose a uniform distribution of the probability of durations from D-1 to D+1 days

Case # 1: All minimal durations

Probability of this case: 0.5*0.5*0.5*0.5=0.125

Summery - Location Based Scheduling vs CPM

Clearer representation with work section and crews for modular project
'Minimum' constraint vs. 'Maximum' constraint
- Continuity
- 'Rapid' tasks
- 'Slow' tasks
- Split work section
Task Duration vs. Production Rate

Production in Automotive Industry

Vulcan 20 HP Tourer

Henry Ford Model T

Disassembly and Assembly Line

Disassembly line at the Chicago Meat Packing Factory

Assembly line at Ford

Construction as a Production Process

A process in which inputs are converted to products
The product of any stage is raw material for the next stage
Crews on site are comparable to production workstations
Understanding of production theory is essential for optimal planning and management of production systems on site

Production Performance Measure

Cycle Time

Throughput Rate and Process Capacity

Exercise

Work begins at the machining center. Two identical lines form the heads of the hammers and place them in a buffer.
- Set up time is 80 min. processing takes 4 min per unit in each line. Batch size: 200 in each line.
Handles are attached at the assembly step.
- Manual by two workers (no set up). Each hammer requires 40 min processing. 34 workers available.
Finished hammers are sent to the next stage, where they are packed and shipped.
- 30 min set up, 2 min per unit processing. Lot sizes of 100.

Throughput Rates?
Bottleneck Task?
Process Capacity?

WIP and Little's Law

Impact of WIP on Cycle Time

Exercise

2 hr

X

T=0

T=2?

T=4?

T=6?

WIP=1

Station 1

Station 2

Station 3

Station 4

X	X

WIP=2

Station 1

Station 2

Station 3

Station 4

WIP	1	2	3	4	5
CT
TH

Critical WIP

6 mins

W0?

Recheck the Little's Law

Batch size

4 hr

Impact of batch size on TH and CT?

2 hr

Processing time

Batch size

2

1

Total processing time T0 = ___

Bottleneck rate rb = ___

Critical WIP W0 = ___

WIP	2	4	5	7
CT	12
TH	2/12

WIP=2

4 hr

2 hr

Processing

time

Batch size

2

1

t=0	#2, #1
t=1	#2, #1
t=2	#2, #1
t=3	#2, #1
t=4		#2	#1
t=5		#2	#1
t=6			#2	#1
t=7			#2	#1
t=8				#2	#1
t=9				#2	#1
t=10					#2	#1
t=11					#2
t=12						#2
t=13
t=14

WIP=4

t=0	#4, #3		#2	#1
t=1	#4, #3		#2	#1
t=2	#4, #3			#2	#1
t=3	#4, #3			#2	#1
t=4		#4	#3		#2	#1
t=5		#4	#3		#2
t=6			#4	#3		#2
t=7			#4	#3
t=8				#4	#3
t=9				#4	#3
t=10					#4	#3
t=11					#4
t=12						#4
t=13
t=14

First, distribute the WIP to the system

It takes 12 days for the last two items - #3 and #4 to complete

The cycle time = 12 days

TH=WIP/12=4/12

WIP=5

t=0	#4, #5		#3	#2	#1
t=1	#4, #5		#3	#2	#1
t=2	#4, #5			#3	#2	#1
t=3	#4, #5			#3	#2
t=4		#5	#4		#3	#2
t=5		#5	#4		#3
t=6			#5	#4		#3
t=7			#5	#4
t=8				#5	#4
t=9				#5	#4
t=10					#5	#4
t=11					#5
t=12						#5
t=13
t=14

First, distribute the WIP to the system

The system is fully loaded when WIP=5. min(CT)=12, max(TH)=5/12, rb=5/12
When WIP>5, the items needs to stay outside the line, e.g., #6 and #7 need to wait for 4 days. Therefore, it will take 16 days to complete them. so CT = 16 days and TH=WIP/12=7/16
If WIP>5, then CT>12 and TH<5/12, this follows Little's law

Conclusion - Batch Size

Increasing batch size increases cycle time
Increasing batch size increases WIP
In a project, increasing batch size extends the project duration

Unbalanced Line

2 hr

4 hr

3 hr

Total processing time T0 = ___
Bottleneck rate rb = ___
Critical WIP W0 = ___
The unfinished units are usually located in which workstations?
Utilization of the process = W0/Number of operators = ___

Variations and 'Parade of Trades'

2 hr

4 hr

3 hr

Software simulation – the ‘Parade of Trades’

http://www.ce.berkeley.edu/~tommelein/parade.htm

A three-round experiment in which production rates vary.

The average production rate at each workstation will be 5 units/ round, but the actual instantaneous rate will depend on the throw of a dice.

Summary - Fundamental Concepts

Push Production vs. Pull Production

Minimum inventory - Just in Time (JIT)

Traditional Scheduling in Construction

As the Project Manager

I divide the project into activities, which are ordered according to technological constraints
The schedule is set according to the Critical Path (the longest path in a CPM network)
All the activities are scheduled for earliest possible start
I dictate and push the schedule to the trades and ensure they follow the schedule

Problems?

No input from the trades
Work conflict in the field
Costly delays and waste
Due-date driven

PUSH

Design Change?

PULL

Pull Scheduling in Construction

Pull scheduling meeting

Planning backwards along the time
Each trade uses a distinct color
The post notes specify the duration and handoff of the activity

Pull Scheduling in Construction

Design

White paper and post notes

Reference to the design
Colored notes on white paper
Keep track of the constraints
Big room

White sheets

Planning backwards

Pull Scheduling in Construction

Scheduling Reliability

Variability in CPM

Variability in LBS

Variability in Production Line

0	F

	9-12

0	A

	10-13

	C

	6

Scheduling Reliability

Schedule is dynamic
Crash the system when an activity is not completed
Improving planning reliability can improve project performance

Good Schedule?

Construction Preconditions

Many more ...

Construction Preconditions Game

Build a 4-story concrete structure

Tie the rebar
Formwork
Pour the concrete

Preconditions (Roll the dice)

Drawing
Equipment
Material
Crew

Look Ahead Plan

Six week look ahead plan
Project manager, owner, subcontractors, key vendors, etc.
Resolve constraints

Last Planner System

Weekly Work Plan

Which one will you choose?

Weekly Work Plan

The "Physics" of Coordination

Last Planner System

Percentage of Plan Complete (PPC)

Percentage of Plan Complete or PPC is the number of actual completions divided by the number of assignments for a given week.
PPC assesses the extent to which the Last Planner was able to anticipate what work would get done in the upcoming week. It measures if WILL matches DID.
- PPC thus reflects the reliability of planning system.
- The higher PPC, the higher the planning reliability.
- The higher PPC, the higher workflow predictability.

Percentage of Plan Complete (PPC)

When an assignment is not completed by the end of the plan week, the Last Planner must record the reasons for non-completion (RNC). Reasons for plan failure fall into categories pertaining to directives, prerequisite work, resources, and process or output failures.

Percentage of Plan Complete (PPC)

PPC Evolution

Record of PPC

Last Planner System

Summary - Scheduling Principles

Identify the critical path
- Critical Path Method
  - Technological constraints
  - Network diagram
Reduce batch size and balance the production system
- Location based scheduling
  - Treat the 'rapid' tasks and 'slow' tasks
  - Continuous workflow
  - Split workspace
Stabilize the environment and reduce the uncertainty
- Last planner system (Should -> Can -> Will -> Did)
  - Pull scheduling (reduce WIP)
  - Look ahead plan
  - Weekly work plan
  - Percentage of plan complete (PPC)

	Quality	Safety
Basis (desired)	Plans and technical specifications	Safety procedures
Measure (reality)	Physical condition and function	Accidents

Apartment, 1-3 Story Construction Cost Assumptions
Location:	US National Average
Stories:	3
Story Height (L.F.):	10.00
Floor Area (S.F.):	22500
Basement Included:	No
Data Release:	Year 2013
Cost Per SF:	$$113.96
Total Cost:	$2,564,000

	PV	EV	AC
Foundation	$15,394	$15,394	$15,850
Patio	$8,166	$8,166	$7,200
Exterior Walls	$8,748	$6,608	$6,250
Stairway	$5,961	$2,981	$3,100
Project Total	$38,269	$33,149	$32,400

	Duration	Cost
Basis (desired)	Schedule	Budget
Measure (reality)	PPC	Actual cost

Resource Code	Resource Description	Unit	Cost [NIS]	Notes
10	Gravel	m3	100	Waste factor of 8%
20	White marble tiles of size 30/60 cm	m2	200	Waste factor of 3%
30	Flooring crew	day	2,000	300m2/day
40	Gravel pump	m3	30

Planning and Control of Construction Projects

Introduction

Dr. Ling Ma