Holloway Consulting is a leading Construction Consulting firm providing services to U.S. and International clients, including law firms, public agencies, developers, owners, design professionals, construction managers, general and trade contractors. Holloway are experts in all aspects of construction project scheduling, both contemporaneous and retrospective scheduling. This page addresses the use of Bar Charts.
Bar Chart Schedules
Prior to the advent of the CPM scheduling methods developed in the 1950s, the most common method used for construction project scheduling was the bar chart, which was developed in the early 1900s by Henry Gantt and Frederick Taylor. Hence, schedule bar charts are frequently referred to as “Gantt” charts.
The bar chart method presents work activities as bars on a horizontal time scale. Work activities are listed vertically on the bar chart and the bar for each activity is drawn to graphically illustrate the time frame required to complete each activity. Bar charts are usually kept rather simple and uncomplicated, but can become very sophisticated by adding labor resource requirements and distributing budgeted costs or manhours to the various bars or activities. Predecessor and successor relationships can be added between activities, and an “S” curve may be used to illustrate the cumulative budgeted man-hour and percent complete projections over the duration of the project. A “bell curve” may be used to illustrate the schedule for daily or weekly manpower requirements.
The demonstration of physical project progress using a bar chart is normally simple and straightforward. A progress line indicating “time now” is drawn or overlaid on the bar chart and activity bars are filled in to represent the physical progress and completion status of activities. The physical representation of this progress in comparison with the progress time line identifies whether an activity is ahead, behind or on schedule. The bar chart can also be revised to reflect changes in activity sequencing and durations that vary from the original plan.
Although the bar chart has been used for many years and is still in use today, Holloway has found that the method has fundamental weaknesses which limit their usefulness in both planning and scheduling large, complex projects and retrospective analyses. For example, bar charts cannot accurately distribute or control manpower and project cost. Data entered into a bar chart does not lend itself to computer analysis of scheduled starts and finishes, and is usually limited to the visual depiction of activities which, on a large scale, may be fine for determining completion dates, but is often inadequate for controlling the project or measuring performance.
A bar chart typically does not show the amount of float for an activity, which is the amount of time an activity or chain of activities may “slip” before downstream activities or the project completion date are impacted. The amount of slack or potential slippage is referred to as “float”. A bar chart also does not usually display the interrelationships between activities necessary to accurately plan a project or measure the performance of the parties. The absence of activity logic and available float makes it difficult to assess the delay impact of one activity upon another. Also, because bar charts are prepared manually, the time and effort required to prepare and maintain bar charts for large, complex projects can be quite burdensome. Finally, detailed bar charts may be difficult to read, understand and maintain. For these reasons, Holloway believes bar charts have limited value and are most often used by field personnel as short-term planning tools.
Call Steve Holloway – – at (303) 984-1941 to discuss your construction scheduling consulting needs.
Construction and Project Scheduling Consultants
12081 W. Alameda Pkwy., #450
Lakewood, CO 80228-2701
Denver Phone: (303) 984-1941
International : (888) 545-0666
Fax: (303) 716-0432
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