SYSTEMS FUNDAMENTALS
A project schedule becomes operable when the scheduling system has a func- tioning network diagram of all the activities of production. Working flow- charts with all job logic sequences developed, plus total durations required for completion added, create a network timeline. A project schedule’s primary purpose is to keep the production activities on schedule. However, much use- ful data from the schedule can be used in other ways for added cost-efficiency in many areas of project production. As we have seen, critical path manage- ment increases productivity, efficiency, and time management, thereby reduc- ing overall project cost.
The fundamentals of the system can be illustrated by a simple project such as a room addition. The activities could be as simple as starting and finishing dates for the foundation, walls, and roof. A more complex project, such as the entire residence, will add phases of activities completion. These phases serve as benchmarks in construction completed to date and accord- ing progress payments to the activity subcontractors. In scheduling systems fundamentals, these benchmarks of phases completion are called milestones. Financial milestones set by the lender are typically tied to the dates progress payments are due.
Systems fundamentals of project scheduling came into being on capital projects in the early 1940s with preplanned, written schedules. During World War II, the military began to develop its own type of project scheduling to deal with multiproject management of many different types of project con- tractors. The first is an activity duration estimate system developed by the
military, called PERT, which we will examine later. In the civilian market, two traditional systems have evolved from hand spreadsheet methods: bar charts and logic-diagram-based schedules. Both methods are used extensively and interchangeably in both project planning and actual construction work. Nat- urally, each method has its advantages and disadvantages.
Bar charts are the simplest form of project scheduling and have been in use the longest of any of the systems we have available today. They offer the advantage of being cheap and simple to prepare, they are easy to read and update, and they are readily understood by anyone with a basic knowledge of the construction business. They are still in wide use today, even as one of the final sort reports of computerized CPM scheduling systems. The main disad- vantage of the bar chart is its inability to show enough interactive relation- ships between all of the activities on larger, more complex projects.
Figure 3.1 is an example of how visual data overload doesn’t allow for one clear path made up of many smaller paths to become apparent. In the bar chart illustrated here, there is no critical path method of scheduling. Simple job logic of placing the activities in order of their construction sequence was used. Note how the many activities have been condensed into single group bars to get the complete chart to fit on one page. Any time you condense something by compressing it into something else, you lose control over that item. In network scheduling, the approach is just the opposite. We‘‘explode’’ the activities, subactivities, tasks, and work items out into a network so that each has complete tracking and controlling. Each of the macroactivity bars in Fig. 3.1 needs to be broken down into a series of individual tasks, to control the microactivities within the macroactivity. Only by having control at those levels will we have ultimate control of the macroactivity.
The bar chart here shows macroactivity progress, which is useful and will suffice on small jobs, but no interrelationship between the activities that would allow for alternate routes if progress hits a bottleneck. This ability to switch paths is crucial to critical path management. It’s much like tap dancing in a minefield: You can’t stop moving or you lose. If project production stops, everyone loses. So it’s in everyone’s best interest that things keep moving to a timely completion. Bar charts, such as that shown in Fig. 3.1, have no capacity for contingency planning. And your job as the project scheduler is to be ready to pull a rabbit out of the hat by having a workaround ready to go if a production activity encounters a bottleneck. So this type of bar chart is useful, but it is not enough.
This example has excellent comparison and completion capabilities, and bar charts have a number of other very useful methods of processing data. Note that some of the activities finish ahead or behind where they would in smooth progression. This is vital information and must be tracked accord- ingly, but no option exists in Fig. 3.1 for critically analyzing the activities’ interrelationship or doing something about them. CPM offers those options
F IGURE 3.1 Bar chart by early s tart.
and, if float is used correctly, also offers the time management necessary for critical path workarounds. Our example here shows the strategic dates for starting and finishing major portions of the overall project, along with a few milestones. Intuitively, one can grasp that there is little or no ability to control changes or manipulate time-scale interlinkage between activities in such macroactivity grouping.
Control comes at the microgrouping, or individual task, level. Manually generated bar charts and spreadsheets that cover the whole project involve a lot of detailed record keeping and summary reports, which soon absorb too much of the project manager’s time to allow managing the field end of the project’s production work properly. This means, in our example, that each bar would also need another series of bars to show subactivity tasks within each activity noted.
For example, under the contract phase, the Supplementary Conditions bar chart might have a large quantity of subactivities covering workplace safety requirements, public pedestrian barricades, or specific traffic control plans. These would all be individual activities in CPM on a larger project. But showing the production activities and their subactivities in that sort of detail could easily take 20 pages of bar chart schedules just to list all those phases- related construction activities, subactivities, tasks, and work items.
The primary reason for the cost overruns and late completions of proj- ects in the 1960s was this lack of control over the project’s scheduled timeline. This became a focal point of change for more efficient construction manage- ment. Delay overruns on commercial and industrial projects can run into millions of dollars. Bar charts used up to that time proved inadequate. Sched- uling larger projects in that sort of detail, with bar charts like the example in Fig. 3.1, simply does not offer the time manipulation advantages of modern critical path management.
Computerized CPM makes up for bar chart’s inherent disadvantages by interlinking activities and producing integrated progress summary reports called sorts that contain specific current data, instantly available to any end user on demand. By first monitoring and recording production activities progress on each production development activity, computerized CPM then integrates the data through the sorts, some of which produce progress reports in a bar chart sort. Experts are saying that in a few short years we’ll have remote terminals the size of credit cards to input this data from a foreman’s pick-up back to a host computer in the office that does instantly the sum- mary work.
PERT SCHEDULING
The PERT scheduling system was developed in the military for government production scheduling control while contracting with multiple and different
types of defense contractors. PERT (Program Evaluation Review Technique) is a scheduling system that uses inside and outside figures to make a best-guess estimate on each activity duration.
These ‘‘guesstimates’’ are then strung together by the prevailing job logic. In the PERT system, the elapsed time of an activity is calculated by assessing an optimistic activity finishing event date and a pessimistic activity finishing event date, then calculating an average duration of the activity. This average time is then used as the only factoring used for activities durations in the network schedule.
This‘‘inside and outside best-guess estimate’’ will work for averages in data processing, but PERT serves no other scheduling functions in mod- ern construction project management. Accordingly, most modern CPM soft- ware programs for construction projects do not include the PERT-type scheduling system, but instead use the data from precise activity events, both early and late, calculate with all four of those factors, then average the duration. Float can also be taken into account. The proper selection of the elapsed duration times for the work activities is an important part in preparing an accurate CPM network schedule, because exact events deter- mine the exact activity duration times, which in turn directly affect the critical path and succeeding activities float times. The PERT system does not offer these scheduling advantages.
In the PERT system, generalized time estimates for activities through- out the total project are made, with a timing leeway built-in cushion allowed for optimism or pessimism of activities duration. However, the linkage of activities and establishing a critical path through a PERT system is very diffi- cult to establish and impossible to maintain workaround options in the event of changing critical paths. To be accurate in event time estimating, the project scheduler breaks out all activities into manageable units of time. The elapsed- time estimate is based on the unit labor and materials quantities taken off the project’s specifications, which are used to estimate the project cost. This quantitative survey estimate contains a wide variety of bidding pre-estimated information, such as cubic yards of import fill or excavation, tons of structural steel, numbers of block masonry units, and cubic yards of concrete.
That information combined with previously recorded labor and mate- rial costs from the company’s own records or activity subcontractor is used to calculate the expected elapsed-time duration for each activity. The unit number to be used as a computation factor is then adjusted for delay by factoring in prevailing local conditions, such as seasonal inclement weather, variations in delivered materials costs, area union labor rates, trucking strikes, etc.
Note the way that‘‘etc.’’ just hangs at the end of that last paragraph. Looks nice and easy, doesn’t it? And it sure was easy to write. Just dropped it on the page. But in real-life application, any etc. in that last paragraph will
cost thousands of dollars of unrecoverable lost profit. Part of the project scheduler’s job is to know and account for the unpredictable events that will delay the schedule, such as inclement weather or materials shortages. Just because it was ordered doesn’t mean you’re going to get it on time. Follow-up on every line item is part of the job for a professional project scheduler. SCHEDULING PHILOSOPHY
The dichotomy between scheduling planning and real-world construction exe- cution are the two main factors affecting the preparation of the project sched- ule. Practical limitations of the project’s production must be established, then prepared for in the planning stages. We call this conception and critical think- ing stage scheduling philosophy. Once the project commencement occurs, the basic ground rules for its construction schedule must have already been es- tablished. These ground rules will address the scope of construction phases, materials procurement procedures, contingency critical paths planning, and long-lead items procurement.
These ground rules will be different in specifics with the job logic of each project, but large or small, they will all be determined by following basic scheduling philosophy. Scheduling philosophy refers to the selection of the scheduling system. The questions that must be answered prior to the first scheduling meeting will determine the scheduling philosophy, which in turn will determine the production contracting basis. Scheduling philosophy uses critical analysis to determine
The scheduling management needed for CPM Identification of critical path activities
Workarounds (alternative option activities that can be substituted if a critical path activity hits a bottleneck)
Job logic (sequence of activities) Timing of schedule recycling
Contractual requirements for progress reporting from field supervisors Assignment of CPM-trained personnel to areas of production
responsibilities
Typically, it is the project team’s responsibility to establish the schedul- ing philosophy, critically analyze their decisions, and then get owner approval of the scheduling system selection. The scheduling philosophy must be a cohesive decision among all vested parties because changing the system later during the project’s phases is disruptive of the production continuity and, accordingly, very costly.
The scheduling philosophy should also account for the start-up se- quence of the various activities making up the production phases. Activities
that start up first must also be the activities that finish first. The project schedule must also interlink with the other major project considerations, such as design and long-lead items procurement. That is easy enough where, traditionally, the design is completed before the project goes to construc- tion bidding.
But in other production execution modes, such as fast-tracking, design should be 30 to 50% complete if a reliable CPM schedule is to be developed and executed. By getting this advance start on a project without a finished project design, error is obviously probable if the operation has not been done previously to provide accurate activities duration.
FIELD SCHEDULING
Even a detailed CPM schedule with a comprehensive work breakdown struc- ture is not an adequate tool for controlling the daily progress of the activities in the field. Field scheduling is necessary to coordinate reporting data with the main scheduling system. On smaller construction projects, the production progress milestone schedule may be the only one used. Sequential completion of phases is simple enough on small jobs and usually will be adequate.
On larger projects, however, the project schedule also functions as the basis for making more detailed weekly work plans in the field, for each major activity. In either case, the approved project schedule will, in turn, determine the type and detail of the field scheduling the owner and the prime contractor use to set the production phases milestones and monitor the projected sched- ule progress versus the actual completed progress. Detailed field scheduling is necessary continually throughout the entire project production to interlink the two for critical analysis and control.
Complete detailed field planning makes the most efficient use of field manpower on the priority list of tasks within those activities required to meet the CPM milestone dates. This detailed planning first concentrates on those items of work that are on the critical path, then on secondary activities that are noncritical. The field scheduling personnel of the project team are responsible to the project manager for planning the construction activities each week for the following week. Field schedulers list sequentially the work activities that are scheduled to be completed by the following week. This list of pending activities is then discussed in the weekly scheduling meeting with the project manager, project scheduler, prime contractor, major subcontractors, chief field engineer, and site superintendent all present. The project manager and/or the project scheduler typically chairs these weekly meetings.
Prior to the meeting, the site supervisor will have checked to see that all the necessary labor, materials, and equipment are on site to perform next week’s scheduled work. The site supervisor will then report production
readiness or deficiencies at the meeting. After the meeting, the weekly task lists are distributed to all responsible personnel, so the activities subcon- tractors can plan weekly production execution. Scheduled work not com- pleted in the previous week is also examined at the meeting, and plans are made to bring those activities up to speed. The outlook for the next two weeks is critically analyzed and projected. The project scheduler then prepares the longer-range quarterly field scheduling plans by checking the critical CPM milestone dates four weeks ahead, and plotting the appropriate courses for the next quarter.
PROPOSAL SCHEDULING
The project schedule first comes under serious discussion by the contractors when the bidding documents or the request for proposal (RFP) arrives at the individual contractor’s office. The RFP or bidding documents contain a section devoted to the construction schedule. Usually the documents ask the contractors to develop preliminary bar chart schedules showing the major construction activities (and their durations) in the contractors’ proposals. The purpose of that request is to get the contractors to look at their strategic end dates in general terms to see if they are still feasible. The owners use the con- tractors’ preliminary bidding schedule to compare it with the schedule the project team has developed. This is typically the project team’s first oppor- tunity to get the activities subcontractors’ professional opinion as to how long the activities’ construction work will actually take. This is then compared to projected scheduled duration and adjustments made accordingly.
Now, the contractors are not paid for doing this; it’s just part of the business. So typically, contractors don’t like to spend much time developing construction schedules during the bidding process. At this point they are not assured of getting any contracts. The only exception to this reluctance of contractor input is when the selection of that activity contractor may depend on a previous track record of being able to meet a tight completion date. This is normally the case in‘‘fast-track’’ project production execution. Then the contractor’s schedule becomes a bidding edge that is worth the extra bidding expense to the contractor. In the case of fast-track projects, the contractor’s proposed schedule will undergo intensive examination by the project team during bid openings and must be viable within the owner’s project schedule. At this proposal stage, the project scheduler must evaluate the schedule in relation to the contracting plan and the construction technology available to improve the production timeline. For example, there could be company policies affecting the contracting plan that could be changed for this project to improve this particular project schedule. If they are, both the owner’s project team and the prime contractor determine if the proposed changes are
viable and then review the new suggestions. This is the same procedure for substituting construction technology improvements that will shorten an activity’s completion duration.
As the project scheduler, you must be aware of where the‘‘hot spots’’ are that will make or break you. Proposal scheduling is a critical juncture of one of the hotter spots. Here you must show your experience and critical analysis to the project team. At this point, project schedulers must make their opinions known to the owner, client, or project management team if they