Work Scheduling in Bridge Construction

Work Scheduling In Bridge Construction

Work Scheduling • Work scheduling is a tool of planning of project, which decide in advance about what to do and when to do considering how to do and who is to do . • It is a time phased plan for performing the work necessary to complete the project • It is a graphical representation of plan which shows the starting and completion dates of each activity and the sequential relationship among the various activities • It – – – – –

Predicts project completion time and activity completion time Controls financing and payment Serves as a record Helps to plan resources required for construction Supports to cash management

Scheduling Tools Different Scheduling Tools

• Bar Chart /Gantt Chart • Critical Path Method (CPM) • Program Evaluation and Review Techniques (PERT)

Bar charts are mostly used in work scheduling of simple small and medium span bridges and CPM is mostly used in complex medium and large span bridges in Nepal

Bar Chart Graphical representation of various activities/works with their starting and completion time and duration. In bar chart, activities/works are represented by horizontal bars and the length of bar indicates the time/duration required for accomplishment of that particular activity/work

Bar chart may be linked bar chart or milestones chart Linked bar chart Modified bar chart in which links between succeeding and preceding activities are shown. Links helps to show the effects of delay if any in the activities and helps to calculate float or extra time available for the activities. Milestone chart Improved bar chart in which important events are shown

Steps for preparing Bar Chart 1.

Break down the whole project in to various activities or sub activities Identify different works within the activities

2. Estimate the time/duration required for each work. For each work, estimate how long it will take to do that work. The time required for execution of a work depends on the method of execution, volume of the work , nature of the work and the time available for completion of the project.

3.

Develop a logical and practical sequence of the works One by one, put everything in order. Make a note of any dependencies, the situations where you can’t do one thing until another is started or finished. For example Until the laying out of reinforcing bars is completed concreting can not be performed in a structural member. Eliminate interdependencies of work as far as possible in planning

4. Chunk up the works/activities After having the sequential order of works/activities with their time duration, reduce the list without losing any specificity. Division of time depends on the total period available for project. If it is only one year long, you might list items by month. If your project is three years long, then you might list items by quarter. If you are planning over five years, you might break it down to sixmonth periods.

5. Draw bar chart Draw bar chart by hand or by word-processing/spreadsheet or any software. Mark the milestones and link lines if any in bar chart

Best scheduling can only be achieved when there are • Clearly defined activities • Realistic duration • Knowledge of construction techniques • Knowledge of resources available • Knowledge of construction procedures

Example on Bar Chart Method of Scheduling Example 1

Prepare a schedule for the activities involved in detail engineering survey and design of a bridge using Bar Chart

S.N.

Activities/Works

Time required (Days)

1

Document preparation for tendering of Detail survey and design works

3

2

Call for tender

10

3

Evaluation of tender and selection of consultant

4

4

Mobilization of study team

5

5

Detail Engineering Survey

8

6

Gological/Goetechnical Investigation

14

7

Hydrological Study

5

8

Design and detailing

35

9

Submission and approval of report

9

Total no of days -93

Bar Chart for Detail Engineering Survey and Design of Bridge

S.N .

Duration / Time Activities/Works

Mangsir 2069 1

1

Document preparation for tender Detail survey and design works

2

Call for tender

3

Evaluation of tender and selection of consultant

4

Mobilization of study team

5

Detail Engineering Survey

6

Gological/Goetechnical Investigation

7

Hydrological Study

8

Design and detailing

9

Submission and approval of report

2

3

Paush 2069

4

1

2

3

Falgun 2069 4

1

2

3

4

3 days 10 days 4 days 3 days 8 days

Completion of study for design 14 days Draft report submission

5 days

Approval of report

35 days 9 days

Project completion period 79 days

Example 2

S.N.

Prepare bar schedule and resource aggregation chart for the activities involved in the construction of the two well foundations by using Bar Chart

Activities/Works

Days required to complete Labour the work

Human Resources Mason

Carpenter

Bar bender

Welder

1

Diversion of stream

1

4

-

-

-

-

2

Construction of platform of well

1

4

-

-

-

-

3

Fabrication and placement of well curb

2

2

1

-

-

1

4

Form works of well up to 3 m height

2

2

-

1

-

-

5

Bar cutting and bending

2

1

-

-

1

-

6

Reinforcement layout in well

2

2

-

-

1

-

7

Concreting of well steining up to 3m ht.

1

4

2

-

-

-

8

Dredging and sinking of well

2

2

1

-

-

-

9

Concreting of lower plug

1

3

1

-

-

-

10

Filling of granular materials

2

4

1

-

-

-

11

Concreting of upper plug

1

3

1

-

-

-

12

Placement of reinforcement for well cap

2

2

-

-

1

-

13

Form works for well cap

1

1

1

-

-

14

Concreting of well cap

1

3

-

-

-

1

Bar Chart of Well Construction

Well at right bank Well at left bank

S.N.

Activities/Works

1

Diversion of stream

2

Construction of platform of well

3

Fabrication and placement of well curb

4

Form works of well up to 3 m height

5

Bar cutting and bending up to 3 m height

6

Reinforcement layout in well up to 3 m height

7

Concreting of well steining up to 3m height

8

Dredging and sinking of well up to 3m height

9

Concreting of lower plug

10

Filling of granular materials

11

Concreting of upper plug

12

Placement of reinforcement for well cap

13

Form works for well cap

14

Concreting of well cap

Duration (Days) 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Human Resources Aggregation Chart/Table S.N.

Activities/Works

1

Diversion of stream

2

Construction of platform of well

3

Fabrication and placement of well curb

4

Form works of well up to 3 m height

5

Bar cutting and bending up to 3 m height

6

Reinforcement layout in well up to 3 m height

7

Concreting of well steining up to 3m height

8

Dredging and sinking of well up to 3m height

Labour Mason Carpenter

Duration (Days) 1

2

3

4

5

6

7

8

9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

4 4 7 3 5 5 4 4 6 2 5 1 1 1 0 0 0 2 2 2 2 2 2 4 4 6 2 4 1 1 1 1

2

2

1 1 1 1

Bar bender

1 1 1 1 1 1 1 1 1 1 1 1

Welder

1 1 1 1

2 1 1 1 1 1 1 1 1

2

Critical Path Method (CPM) It is a logical representation of different activities and their interrelationships in a diagrammatic form (Network Diagram). Arrows and nodes are used in a network diagram and they represent activities and events respectively. Activity is a task to be performed, which takes time for completion. Event is an important instance in a project’s life from where an activity starts or where an activity ends. Critical path is the longest path in a network diagram, which takes maximum time among the alternative paths through which a project will be completed.

Rules for preparing Network Diagram •

Initial event should be one in network diagram and should contain only out going arrow.

•

Until and unless all activities leading to an event are completed no event is occurred.

•

Until and unless the preceding events are completed no activity is started.

•

Network path shall not be turned back. Event should not be dependent on the succeeding events.

•

Before reaching the objective, every activity should be completed.

•

Final event should be only one.

•

Network should contain all constraints and interdependencies

•

In network, time flows from left to right

•

The length of an arrow in a network diagram does not represent time.

•

Number given to a preceding event should be smaller than the number given to the succeeding events.

Example on Critical Path Method of Scheduling A bridge requires six intermediate piers consisting of concrete cap supported by steel piles. All piles will be driven before any caps are started. Sequential information about the activities of this project is given below. Draw network diagram Proceeded by

Followed by

Days require for the activity

A Drive piles

-

B

20

B Erect forms for caps 1 and 2

A

C,E

4

C Place reinforcement for caps 1 and 2

B

D,F

2

D Place concrete for caps 1 and 2

C

G

2

E Erect forms for caps 3 and 4

B

F,H

4

F Place reinforcement for caps 3 and 4

C,E

G,I

2

G Place concrete for caps 3 and 4

D,F

J

2

E

I

4

I Place reinforcement for caps 5 and 6

F,H

J

2

J Place concrete for caps 5 and 6

G,I

-

2

Activity

H Erect forms for caps 5 and 6

Network diagram

4 days

20 days

1

A

2

B

3

2 days

4 days

4 days

E

H

5

6

C 2 days

F

4

2 days

7

I

9

2 days D 2 days

8

Path ABCDGJ = 32 days Path ABEFGJ = 34 days Path ABEHIJ = 36 days

G

2 days

10

J

Critical path is 1-2-3-5-6-7-9-10-11

11