CONSTRUCTION SCHEDULING FACTORS, EMPHASES, IMPEDIMENTS AND PROBLEMS, AS SEEN BY CONSTRUCTION EXPERTS

INTRODUCTION

A schedule for a future construction process is the best method of controlling the subsequent actual construction process given the type, location, and surrounding circumstances under which it is to be built. However, construction scheduling in textbooks has not included heuristic factors and emphases that should be included in such schedules. Therefore, the need for this study was apparent. The results provide information from construction experts to improve the quality of scheduling of construction work necessary to create high quality construction schedules.

Sources of Information

The findings from which this paper was written came from approximately 100 experts in both general contracting and subcontracting. Each construction company from which an expert was drawn is based in one of three urban areas in northern Florida, and was randomly selected from lists from their trade associations and peers as being from the upper quality levels of all their members.

Fifty senior executives of general contractors were interviewed by using a questionnaire designed, tested, and applied for the purpose of gathering their scheduling expertise. Twenty of these were site-based managers or superintendents responsible for day-to-day on-site control of ongoing construction work with or without schedules. Thirty were either office-based senior executives responsible for the strategy of construction processes, or project managers and schedulers who have more direct construction supervisory and scheduling duties.

A questionnaire designed specifically for subcontractor scheduling and control was created, tested and applied to thirty-two subcontractor executives in the electrical and mechanical trades as representing all subcontractor trades. Again, both office and site executives were interviewed to achieve an appropriate balance to scheduling and control of construction by subcontractors.

From the carefully structured research pro­cess, the report's findings can be considered repre­sentative of most normal construction activity in the whole of Florida, and even of construction in the whole nation.

Uses of the Scheduling Research Results

There are at least three major uses of this report; (1) general educational reading for constructors, (2) a guide to better scheduling of future construction processes for specific types of buildings, and (3) to bring to general contractors and subcontractors a better understanding of the objectives and needs of the other for scheduling and controlling construction work. The report concentrates on the features of construction processes which should be of major concern in creating optimum scheduling to minimize problems in the construction process for all participants, and that such processes will be comparatively easy to control from the schedule so created.

To achieve the optimum potential, these fac­tors of construction processes should be included and emphasized, and construction schedules and control problems should be dissolved or minimized by management's careful scheduling of future work during the preconstruction scheduling process.

THE FACTORS TO BE INCLUDED IN CONSTRUCTION SCHEDULING

From an earlier pilot study on construction scheduling, forty-five factors were found from interviewing senior construction executives. These were the factors considered by that group of executives as being worthy of consideration by the scheduler in creating a construction schedule and by the construction controller in controlling construction work with a schedule.

Each interviewee was asked if he used that factor Always, Most Times, Sometimes, or Never in his scheduling work or use of construction schedules during construction work. The responses from all interviewees were collated and, for each factor, the percentage of responses to each of Always, Most Times, Sometimes and Never was calculated.

For example, the factor "Expected Productivity" scored 60% for Always, 22% for Most Times, 10% for Sometimes, and 8% for Never. Thus (for it) the sum of Always plus Most Times was 82%. This calculation was repeated for each of the forty-five factors.

This single list of percentages was then examined and it was found that there were twelve factors rated greater than 80%, fifteen factors rated greater than 75%, nineteen factors rated greater than 66%, and thirty-five factors rated equal to or greater than 50%. That thirty-five out of a total of forty-five factors rated greater than 50% for use to the extent of Always plus Most Times expresses further validity to the whole set of factors. Further validity of this set of factors was provided because when each interviewee in this main study was asked to state any additional factors, there were comparatively few and only scattered responses, and of those suggested quite a number were other ways of stating a factor already in the list presented to them.

Based on the above analysis, it was concluded that fifteen factors which were rated at greater than 75% on the sum of responses to Always and Most Times, should be considered as Most Important Fac­tors in scheduling and controlling construction work. Those twenty-one factors whose Always plus Most Times rating was between 75% and 50% inclusive should be considered as being of medium importance. Those nine factors whose Always plus Most Time rating was below 50% should be considered as factors of lesser importance.

Most Important Factors

The fifteen Most Important Factors for in­clusion in a schedule for a future construction process, in order of priority from all the general contractor interviewees will now be outlined and the remainder listed because of space limitations in this paper.

1) Optimum Completion Date. The expected completion date should be arrived at after consideration of the construction input factors and their interactions in a schedule rather than as a global guess without carefully thinking about their interplay for this project. The optimum completion date is then realistically achievable in a construction sense, even though it may be set up to be slightly optimistic to motivate participants. Some ingredient forces are: the various possible logical formats of the construction process, the realistic availability and cost of construction resources, and the nature of

the building and its location.

 

2) Lead Time for Material Delivery. By having a sensible construction process thought out and expressed in a carefully prepared schedule, including realistic durations for deliveries, the date by which each work task should begin, is known. This enables all parties involved in their delivery to work to these dates in a rational way rather than by guessing and hoping. To ignore this factor in scheduling results in a high probability of the actual construction process being very different from the planned schedule which, in turn, makes it a poor guide for the actual construction.

 

3) Type of Construction (Materials and Methods). The schedule should express the most efficient construction methods and sequences of work having regard to the nature of the materials in the designed building, and their quantities in various locations in the building. A search of contract documents should be made to establish the nature of all conditions as well as the materials and methods required. This greatly reduces the chance that some constituents will go unnoticed as being required until or after their construction begins on site.

 

4) Critical Items. "Construction critical" as well as "time critical" activities are those to which onsite management should pay special attention. These critical items should exist in the schedule and be highlighted to guide and control the actual construction process.

 

5) Work and Material by Others. Establishing required work or materials by others is another major input which should be in the construction schedule. "Others" are participants such as utility companies which have work to do but are not direct members of the construction team. Their position in the work process and the realistic lead durations for their work should be found and built into the construction schedule.

 

6) Previous Experience of Each Contractor. The written expression of the schedule to the contractor should consider flow to best communicate that schedule information to each participant so that its use can be maximized. To carry this out, the sched­uler has to find out the work experience, the level of knowledge of scheduling techniques, and the willingness to develop forward looking attitudes of all the important participants to the construction process.

 

7) Complexity of the Project. Scheduling can and should transform a potentially complex construction process into one which can be managed as a normal construction process. If information in the form of a schedule is written down in a diagram and words, then careful thinking and schedule modification can be applied to, it in each part of the initial sched­ule to improve its construction realism, effectiveness, efficiency, and simplicity. Thus, complex schedules can be simplified and clarified and communicated to others rather than be left as complex schedules.

 

8) Previous Experience of the Scheduler. The sche­duler selected for a project should have or seek out knowledge and information particular to that type of project as well as the available array of scheduling techniques. It is wise that for a project schedule to be most effective, the "scheduler" should be a team comprised of the office-based project manager responsible for the project and the site superintendent who will control the work on site. They should take input from at least major subcontractors, but remain the author and controller of the schedule for the whole construction process.

 

9) Subcontractor Input. Since the majority of the construction work is usually carried out by trade subcontractors, it is very important in the creation of the construction schedule that input is sought and obtained from subcontractors or at least, from those of the major trades for that future construc­tion process. It follows that the greatest benefits from a schedule can come from having it focussed on the multi resource and complex phases of the construction process.

 

10) Contract Documents. It is essential in the creation of the construction schedule that the conditions of the contract, especially the modifications to typical general conditions and supplementary conditions, and the drawings and specifications, are searched for features which are important as input to the scheduling process.

 

11) Restraining Items (Work and Material). Work scheduled later in the sequence may not be able to begin because an earlier piece of work is not completed or has not taken place. For each piece of work in the schedule, it should indicate preceding restraining items of work so that those managing the actual construction process can identify these preceding items as being of "construction critical" importance for subsequent work, even though in themselves, and may not be costly or time consuming.

 

12) Expected Productivity. Establishing the productivity of local work crews on each trade's work tasks is very important in establishing the planned duration of such work tasks given their quantities of work. The more realistic are these durations the higher the probability that actual work will occur closer to the scheduled durations and, thus, the whole schedule will be more valid as a construction control instrument.

 

13) Size of the Project. On a small project, the required logic choices for that construction process could be expressed on one schedule for ease of comprehension by all participants. The schedule for a large project may have to be developed as a hierarchy of interrelated schedules so that each provides a balance between overall strategic validity of the whole construction process and the required level of detail and logic interactions between required construction tasks for the schedule to be an effective guide and control to the participants in the actual construction process.

 

14) Communications With Others. The schedule is the best tool by which to control the actual construction process. The information in the schedule must be communicated to each construction participant in a format and content understandable and useful by each to guide and control his work. The format in which the schedule has been thought out, revised and produced may not be best for use by each participant.

 

15) Conditions Which Affect Productivity. The scheduler should search the local marketplace for factors that may exist or change in the future during the overall construction duration of the project being schedule that might change or invalidate the original productivity rates used to create the initial construction schedule durations. Seeking out "what ifs" regarding these major construction resources can increase the realism of the durations of work tasks in the schedule which also may have impact on the preferred logic of the schedule.

Medium Important Factors

The following factors were found to be of Medium Importance in the responses of the top quality general contractor experts who form the source of the information from whom the report and this

paper was produced. These factors are listed in descending order of their score.

Availability of Materials

Anticipated Problems

Owner's Requirements

Flexibility of Schedule

Availability of Workers

Balancing Manpower and Equipment

Scheduling Experience of the Superintendent

Ease of Updating

Maintenance of a Consistent Workforce

The Estimate

Weather

Availability of Highly Skilled Workers

Intended Use of the Building

Availability of Construction Equipment

Placement of Equipment on the Site

Interference from Utilities

Optimum Movement of Crews During Construction

Location

Traffic Patterns around the Site

Job Safety

Least Important Factors

Of the scheduling factors presented to the general contractor expert interviewees; the following were found to be of Lesser Importance than the others. These factors are listed in descending order of their score.

Cleanliness of the Workplace Scheduling

Experience of the A/E Scheduling

Experience of the Owner

Possible Claims and Lawsuits

Type of Neighborhood

Specific Billing Requirements

Cash Flow

Craft Work Assignments

Prevailing Winds

EMPHASES TO BE INCLUDED IN CONSTRUCTION SCHEDULES

Because different types of buildings require somewhat different emphases in their construction processes for each to maximize construction effi­ciency, the construction schedule should emphasize the construction process features meaningful to that type of building.

The construction executives were asked to state what features of the construction process should be emphasized in the construction schedule to facilitate construction efficiency in different building variations. General contractor scheduling experts responded to these variables: (i) types of buildings, (ii) heights of buildings, (iii) quality of material in the buildings, (iv) the neighborhood location of the construction process and (v) the repeatability of work activities in the construction process.

These various emphases for scheduling the construction of different buildings should be con­sidered in combinations. For example, a hospital can be high-rise or low-rise and it could be in a city center or rural or suburban situation. For the construction process for a particular hospital, the scheduler should blend the emphases stated in each of five categories of variables. That blend or combination creates the conceptual framework from which to express the details of that specific build­ing in a construction schedule.

(i)                 Types of Buildings

A specific set of building types were pre­sented for comments. Emphases in schedules for other types of buildings could be derived from interpolation from this array of building types.

(a)      Office Buildings, Shell Only. The schedule should facilitate high speed continuous construction work flows by all participants with minimum time buffers between the work of each flow. Provision of utilities and other such services should be on the schedule as they impact the work of participants. The desired scheduled dates of the beginning of tenant work and the obtaining of all government permits and inspections should be on the schedule along with dates for delivery of materials. Early enclosure of the building shell, and beginning of site finishes should be as early as possible on the schedule.

 

(b)      Office Buildings - Shell Plus Finishes In this type of building, considerable importance should be given to the tasks of establishing what the tenant finishes will be and when such work will begin. The better the fit between tasks of the shell building and that of the tenant finishes, the better will be the efficiency of the whole construc­tion process which should be scheduled as one process.

(c)      Apartment Buildings. Scheduling should try to achieve high speed of construction by all resource flows by approaches similar to that in office buildings described above. Again, the exis­tence of a schedule of desired completion dates for sub groups or sequences of sub groups, of specific apartments is of great use as input to scheduling the construction process.

(d)      Schools. The school calendar year is a major boundary condition for scheduling construction of a school as are including in the schedule the various required inspections by the required autho­rities of work done. The food services, mechanical and electrical systems tend to require detailed attention in the schedule due to their importance in school buildings and auditoria and gymnasia have special requirements to be recognized in the sched­ule as do lead durations for their materials to match timing of their direct work in the schedule.

(e)      (e) Factories. The buildings of a factory tend to be the envelope surrounding the production machinery and the schedule should reflect the build­ings secondary role to the machinery procurement and delivery schedule.          If the work is altering an

(f)        existing factory, it is wise to find out if the ongoing factory labor force is unionized and to carefully include consideration of set geographic boundaries between ongoing factory work and con­struction work. Also, what services such as can­teens and corridors can be used by construction forces and the calendar timing of work to enable the factory to continue operations are strategic factors in scheduling.

(g)      Hospitals. Hospitals are extremely complex buildings in which the details are really important to the user and hence to the constructor. The detailed scheduling of construction is extremely important if a realistic early completion is to be expected. There are extremely stringent inspections of construction work and these should be incorpora­ted into the construction schedule. Constructor quality control work should also be stated in the schedule.

(h)      Lead times for deliveries of complex medical machines should be built into the schedule and controlled from it as should the integration of all services to each user space in the building.

(i)        The schedule should express the best thought out construction process given the complexity, inhibitors and problems to be faced in building that hospital, then it should become the focal point of all communications to control the actual construc­tion process. The schedule should include the work of all parties required in the hospital building and not only the work of the construction contractors.

(j)        (g) Housing Sub Divisions. The continuity of work for all of the required work forces is important in building housing sub divisions. Toler­ating the fluctuating work load in each resource flow from the houses of different design charac­teristics requires careful scheduling. Dates by which delivery of each finished house is required is also important to scheduling this type of work.

(k)      Changes in such dates are also major problems for the scheduler and construction controller.

(l)        Realism in establishing resource availability in the locality of the project should be a major input to scheduling housing sub divisions. Site infrastructure work should be scheduled as early and fast as possible because their completion usually is required prior to the beginning of construction of the houses.

(ii)                Heights of Buildings

The second emphasis presented is in regards to height of a building. The construction executives' responses were directed at the two extremes of high­rise and low-rise building construction. The major features in each which should be emphasized in construction schedules as mentioned.

(a)      High Rise. Eight major emphases were suggested for the high-rise construction processes and their scheduling. The first emphasis was cycle time and its process for each floor. This focusses on the duration from the start of the first specific trade on a typical floor to the finish of the last trade on that floor. It tries to establish the best and fastest sequence of the repeatable construction process for all work required.

The second emphasis was vertical movement of materials for all trades and its scheduling. While not part of the direct building work, this vertical movement scheduling enables control and expeditingof all work and facilitates all trades, not just the "pushiest". Cross-site flow of materials and crews was the third emphases of importance and it is related to the second emphases above.

(b)      Low Rise. Again, eight emphases were suggested for low-rise construction. The first was maximizing continuous harmonious work flows with minimum interference between each. To achieve this requires a schedule which presents continuous flow harmony of speed, and geographic flow direction of all work through the building with sufficient time spaces or buffers between adjacent and sequential work crews to enable each work crew to do its own work efficiently.

The layout of the site support services for the construction process was the second emphasis in importance. The position of site services around the building should facilitate the selected generic flow of all construction work in the building, as well as being a linkage with surrounding roads.

The third emphasis was the availability of required materials. The construction schedule should represent the speed of the construction process from the potential of local availability of common materials by volume and speed of delivery to the site.

(iii) Quality of Materials

This third scheduling emphasis considers the quality of the materials and finishes chosen in the design for the building which is one major force in the value of the building subsequent to construc­tion. The required quality of materials and finishes will be stated in the specifications and in its plans.

High quality materials is usually coupled with the need for high skilled construction work to ensure the desired quality. Most designed low quality buildings require only normally skilled construction to satisfy their design requirements.

In buildings of high quality materials, it appears that scheduling emphasis should be placed on realistic and somewhat longer delivery durations than for normal materials. Also, scarce high quality craftsmen are beneficial to the execution of such work. Provision of adequate durations for such work and that appropriate on-site construction quality control is provided has to be considered as other components of the durations for such work activities. Implied from high quality materials, the schedule should move the support and framing work for such materials to as early as possible in the overall schedule to balance the longer durations for high quality finishes work.

In buildings of low quality materials, the creation of a realistic schedule requires considera­tion of the availability of workers, with high productivity rates on simple work and the appropri­ate durations for such work, the logic to enable fast construction with coordination of adjacent and sequential work activities, and a realistic ap­praisal of the availability and speed of flow of the delivery of these low quality materials in the locality of the project.

(iii)               Locations of the Building

Each location has a different array of factors of emphasis to be expressed in the construction schedule of any building's construction process in that location

(a) Suburban Location. Most of these emphases are not directly involved in the construction process but influence the flow of resources which feed the construction process. Also, providing inhibitions to stop the wrongful movement of materials off the site and the movement of invalid people onto the site is important. More specifically, these are: security fencing for children

and against theft and vandalism, county and neigh­borhood ordinances controlling working hours, and site access and delivery of materials.

(b) City Center Location. The major emphases in city center locations are off-site movement and deliveries of materials and access to the site, onsite storage of materials, security interface between the site and the public and workers, employee parking, sub-surface conditions, site utilities, and early and sufficient notice to subcontractors.

(c) Rural Location. The major emphases in rural locations are balancing betwen (i) availability of materials and material deliveries, availability of labor and their transportation to site, and (ii) site security for theft and vandalism, including scheduling to minimize materials store on-site. Also, when utilities and power are available on-site is important.

(v) Repeatability of Work Activities In The Construction Process

The design of the building can vary in degrees of repeatability of work processes in the building. If there are features or components which are re­peated many times in the design, then there can be a highly repetitive but still complex construction process. If there are a very few repeated design features, then the construction process will be made up from an array of diverse types of work activi­ties. The more astute and observant the scheduler or construction controller of this phenomenon of repetitive potential, the more opportunity there is for seeing repetitive patterns of work in the design of a building that overtly appear to have only a few repetitive features. Moving the schedule towards repetition maximizes the use of the learning curve in sequences of work tasks, but maximizing the quality of logical interactions in construction processes is required where there is little repetition.

The major input factors to construction scheduling for buildings with many repetitive work pro­cesses are: the learning curve, work cycles, sequence or flow of work resources, availability of resources, and inspections of work. Of course, all of these facets of scheduling of buildings with many repetitive features should be considered on an interactive basis on each schedule produced.

Maximizing the use of the learning curve in the actual construction process requires the sche­dule to maximize (i) long chains of similar type work and (ii) parallelism of the maximum number of these chains in the schedule.

Evaluating work cycles requires the schedule to minimize the downtime between work tasks in the cycle of work in the construction of the typical location or zone in the designed building.

Considering the sequence or flow of work resources requires the scheduler to arrange the work of each type of resource so that all such resources on-site are usually fully employed while on-site.

The reality of availability should not be taken for granted, but should be examined and carefully considered as input to scheduling. Inspections of completed construction work are vital activities in the construction process and should be included in the schedule.

The major component of schedules for construction of buildings which have few repetitive features is that emphasis should be placed on the logical and sequencing interactions among their ingredient work activities. This is mainly because such buildings have a diverse array of work activities which have to be scheduled as one holistic construction pro­cess. Other factors of lesser importance are: the durations and efficiency of each work activity, the information flows for management, availability of workers with flexible trade skills, availability, delivery and required lead time of materials, and careful pre-construction thinking and action to control the actual construction.

IMPEDIMENTS IN ACTUAL LABOR AND MATERIAL FLOWS RELATED TO AND FROM THE SCHEDULE

This part of the paper summarizes the views of general and subcontractors on labor flows and material flows in the construction process but related to scheduling. Most such impediments should be considered and dissolved by the scheduler as he does his work creating the schedule, which is to guide actual construction.

Major Impediments To Labor Flows As Seen by General Contractors

From the general contractor's point of view, on-site labor flows can be impeded by a number of factors such as lack of material deliveries, including on-site moving equipment for materials, schedules having work activities which lack their work locations and resources required, and poor quality labor and its management. To a lesser extent, also considered as impediments were lack of or poor communication, considering site conditions, and poor or changing design information.

The scheduler should consider these potential impediments to the execution of construction work in creating the schedule. At the very least, they can influence the productivity and speed of construction labor working on that project and, hence, affect the realism of the durations of work activities in the schedule.

Simply getting the proper material delivered across the site to the work places of labor was cited as the major impediment to construction labor's being ability to do its work. It appears that a major cause of this impediment to construc­tion work is the non-existence of proper haulage equipment on-site, and the lack of hoisting capacity to move the materials to the required work places in the building.

Too many work crews scheduled to work in particular work locations at the same time is one result of having construction work activities which lack their work location and resources required. To eliminate or at least greatly reduce this negative aspect of poor construction schedules, requires that the location within the building and the resource requirements of each work activity be stated in task descriptions.

The use of labor which is not skilled enough to carry out the scheduled work required is a fun­damental impediment to labor flow. This can be made worse by labor being in short supply, being incon­sistent in attendance on-site, being put into work crews of unusual sizes, or there being poor balance among its skills. These features in the labor force has a demotivating effect on workers of any skill level which reduces their productivity and can cause a domino effect through the whole work force onsite.

A serious impediment to labor flow efficiency occurs when the general contractor fails to or poorly communicates to each subcontractor and, hence, to his work crews what work he wants them to do and when and where they should do it. The sched­ule, either in total or relevant parts, must be communicated to the people managing the work forces building the project for that fundamental guidance to take place.

Major Impediments To Labor Flows As Seen By Subcontractors

In the pre-construction phase, subcontractors use the schedule to arrange the required size, flow, and segmentation of their labor forces against time. The schedule should provide the framework of such requirements to the subcontractor by enabling him to establish the number of workers he will need in each broad phase of time. Within such global numbers, it should also enable him to establish the number of each labor skill type the construction process will need from him.

When the overall schedule requires the sub-contractor to operate with a labor force profile/ histogram different from his most efficient one, the subcontractor will tend to work according to what is the most efficient use of his labor resources. This usually implies that he will not operate his work force in numbers, resource mixes, and work locations sequence dictated by' the needs of the schedule. Thus, the schedule tends not to be followed by each such subcontractor which also impinges on the work of other subcontractors which tends to cause an overall downward spiral from construction efficiency. It follows that the schedule should be drawn in such a way as to enable each subcontractor to create a labor profile/histogram for his work that generally allows each, or at least each major subcontractor, to operate according to an economically efficient, desired labor flow profile/histogram.

The gap between the general contractor's usually optimistic pre-construction schedule and the expected under manning by the subcontractor in order to minimize the risk of unproductive labor force is a major grey area in construction scheduling which reduces the validity of the pre-construction schedule as a guide to actual construction. This gap exacerbates all problems which arise when the actual construction process is divergent or diverging from the pre-construction schedule. To close this gap on a particular schedule and construction process, scheduling attention should be directed towards construction realism in logic, durations, and labor flow and volume demands in the construction schedule for subcontractors.

For each subcontractor, the incomplete and uncompleted or out of sequence work by other sub-contractors disturbs the state of the workplaces for his work and his labor force. This can lead to inefficiency in his productivity which leads him to try to redress the imbalance by operating more independently of the overall schedule which further reduces coordination of the whole construction process by the schedule.

Deliveries of materials to the site which arrive later than required to meet an original or revised construction schedule or whose arrival is a random occurrence from any schedule can cause vari­ances in the demand for labor. This is especially severe once the labor force is on-site because the lack of materials delivered leaves the site management of the subcontractor with few options other than putting men to work on activities from the future remainder of the schedule which can disrupt many work activities of other subcontractors onsite, as well as cause discontinuity within his own work.

Variable quality of work supervision at the level of the general contractor site-superintendent may cause variances in labor flow for a subcontractor. In the control process, if the site superintendent makes major changes in actual work logic or timing of work activities from that stated in the schedule which gave labor allocations to a subcontractor, then there will likely be major variances on the demands of the subcontractor's labor force. The subcontractor's response will be to reduce his work force to a size below that demanded by the original construction schedule so that his forces can be fully employed (and note all such changes in work to be done as potential future claims for extra payment).

Within the work forces of subcontractors there appears to be both positive and negative variables to be considered in working to a schedule for a building. The positive variables tend to occur by treating workers humanely, building up a multi-project work force of competent workers with seniority in their trades, hiring new workers for short durations to work which is over and above the normal work load for his regular workers, and trying to have materials ready at on-site work locations prior to workers moving to that work location. All of these will improve the attitude of the workers and raise their productivity. The variables causing low productivity include: drug and alcohol problems, sickness, personal problems, worker apathy, absen­teeism, inefficient management, and a lack of training in the trade.

Major Impediments To Material Flows As Seen By General Contractors

The unavailability of proper equipment to handle cross-site movement of materials was cited as the impediment most often encountered by material flows. This can be seen as any of the proper equip­ment simply not being on-site or being on-site but for too short a duration, or inadequate numbers of pieces of appropriate equipment, or simply inap­propriate equipment being put on-site.

The availability of on-site space on the ground for staging areas or lay down areas for materials as they move to their work places of temporary on-site storage areas is a potential impediment to the flow of materials across the site. Their existence or non-existence may affect the speed of the

flow of materials, and these areas should be sought out and considered as input to the scheduling, especially in establishing work durations.

The movement of materials across the site are affected by both underfoot conditions and weather. Underfoot conditions are related to maintaining the temporary roads, hardstands, and storage areas onsite so that materials can be moved in and out under all expected weather conditions.

The non availability of men to move materials across a construction site and handle hoists, elevators, cranes, trucks, and stores, can seriously impede the flow of materials which can impede construction and change durations in the actual construction process from the scheduled progress.

The lack of carefully considered logistics of which materials are moved when and by whom and from where to where on-site is a major factor in slowing all material flows and the whole construction process. It is beneficial that the schedule represents the reality of these site conditions.

Major Impediments To Material Flows As Seen By Subcontractors

The duration of ordering, procuring, manufacturing, and delivery tends to be derived from the requisite parts of the supply channel of each material rather than from the duration from time of the beginning of all construction to the points in time in the schedule when such pieces of material should be optimally built into the building. Hence, the schedule should reflect the realistic points in time at which the deliveries of these special pieces of material can be delivered.

The major cause of false delivery dates stated by subcontractors is that they have been given false delivery dates by suppliers of materials. Other causes can extend from the supplier not knowing his inventory of materials and presuming that stocks exist and that the longer the lead time for a component, the higher the probability of inaccuracy in the forecast of a delivery date for its arrival onsite. False delivery dates lead to an invalid and unrealistic schedule from which to control the actual construction process. Furthermore, the wrong item might be delivered to the site, or the material or component might be delivered in parts and only some parts reach the site. In other instances, the correct component reaches the site but is damaged so that it would be futile to build it into the build­ing. Some deliveries may be correct, but an inadequate quantity is delivered so that only some of the on-site work can take place and the remainder must wait, thus perturbing the schedule. The proper material arriving at the site later than expected was seen as improper delivery, but was probably the less injurious compared to the above. If the pre-construction schedule is valid and realistic, then improper deliveries can make it invalid.

Interestingly, shop drawings and submittal papers were hardly cited as a problem by subcontractors with deliveries; whereas during actual construction their focus of concern was on the delivery of the physical object to be built into the building.

SUBCONTRACTORS VIEWS OF GENERAL CONTRACTORS SCHEDULE

Subcontractors provided their views of the general contractor's schedules under which they work during the construction process. First, they dealt with a comparison between the general contractor's final pre-construction schedule and the work schedule of a subcontractor. Secondly, the views of subcontractors are presented on the realism of durations in general contractors' final pre-construction schedules. Thirdly, they discussed the changes in management control by the general contractor as it varies from the pre-construction schedule.

Comparison Between theGeneral Contractors Final Preconstruction Schedule and the Subcontractor's Work Schedule

While the general contractor will provide his own schedule for the whole construction process which causes differences from the pre-construction schedule of the subcontractor (if he has such a schedule), it should be recognized that the subcontractor has input to make as to whether or not such changes should be made. That input can be in the pre-construction negotiations or even in the post-bid negotiations between the general contractor and each subcontractor.

Once the pre-construction schedule is agreed upon by the general contractor and the subcon­tractor, it is very clear that virtually all sub­contractors then make up their own work schedule by which to control their work. The major factors which were brought out by this comparison appear to group around: the start and finish dates of sub­contractor's work, material and labor availability, manpower loading, work phasing, schedule logic, and durations of work activities.

The subcontractors tend to see the expected delivery dates of materials and labor to that site as being more fixed than are the work activities of the general contractor's pre-construction schedule. To minimize the differences between the agreed pre-construction schedule and the subcontractor's work control schedule, the agreed pre-construction schedule prepared by the general contractor should be scheduled by logic and durations that each subcontractor will have work to do for approximately the same total work force over the majority of the duration of his stay on the site.

The logic of the general contractor's and subcontractor's schedules tends to be the same in overall work sequence and each follows that of the agreed pre-construction schedule. Where different, the subcontractor may tend to emphasize the roughing, equipment, and finishes sequencing nature of his work within each work activity.

While the overall logic of the schedule tends to remain approximately as agreed, the durations of the work activities desired by and thought appro­priate by the subcontractor may be different from those in the general's schedule for his work. The subcontractor will tend to modify slack time on his schedule by reducing the peaks and filling the troughs of demands on his on-site labor force. The man-hour volume for the whole of the subcontractor's work will tend to stay about as scheduled and its minimization is the subcontractor's major objective.

Realism of Durations in General Contractors' Final Preconstruction Schedule

The major problems for a subcontractor in change his work activity durations and dates during the construction process deal with the need for: changes in manpower allocations, changes in material deliveries, and problems in subsequent worker prod­uctivity. The major approach used by subcontractors to minimize the surprise of such changes is by knowing what is occurring in that construction process among all participants and their own work and work force, and all interactions that may affect their work.

By carefully considering the simultaneity of work activities in his work schedule, the subcon­tractor should have created for himself some flexibility in moving his labor force across an array of types of work activities and work locations on-site at any point in time. While best productivity is usually achieved by focusing on one type of work over a short period of time to benefit from the learning curve, his primary objective is to keep all of his workers working all the time. So the subcontractor will move surplus men away from work that is delayed or slowed down to other work which can be done.

The subcontractor's overall objective is to maintain full workload for his full work force onsite over their duration on-site. The schedule should try to provide satisfaction to that objective for each subcontractor on-site.

If the duration, or more likely, the calendar time of a work activity changes there may be interaction with the delivery dates for materials for such activities. When the move is to an earlier calendar date than scheduled, the delivery problem is one of speeding up the logic of the delivery process. When the move in time is towards a later calendar date, there are the alternatives of changing the delivery process to a later date or leaving the deliveries as originally scheduled and paying for the materials at the original date, but having to pay the demurrage for a longer duration and the added risk of damage from storage on-site.

Even if such changes in duration or their calendar dates are made, there is always the completion date for the whole project which tends not to change. Given that there are delays which cause later calendar timing for some work activities and that the completion date remains valid, then there will be work acceleration in the later stages of the work of the subcontractor. This implies more work to be done in a shorter calendar time which, at very least, means a more complicated management load on the subcontractor's site staff which, in turn, increases the risks of mistakes and more confusion, and the work momentum is usually affected in a negative way. Such changes have an effect on workers because they then tend to be moved from one work activity or work location to another in a seemingly random manner. This changeability in the process reduces worker productivity and may even lead to inducing apathy in the workers' morale which further decreases productivity.

A possible construction solution to this is to try to schedule for an array of work crews to work in parallel on the same type of work rather than working in sequence in the schedule. This will execute more work in the same calendar time. These strategic changes may require subcontractors to place more work crews on-site and require greater management forces. Also, under parallelism, there is less benefit from the shorter and more numerous learning curves for each work crew.

Effects of Changes in Management Control By The General Contractor From His Preconstruction Schedule

There are problems for the subcontractor in controlling his construction work under the management of the general contractor. Factors which cause a negative impact on construction work, in descending value, were found to be: poor supervision, poor performance of work, work performed out of scheduled sequence, incomplete work in work zones, and lack of respect or concern for the work of others. All such activities slow the construction process, increase its costs, and create unnecessary divergences from even a very good construction schedule.

Poor supervision of the actual construction process appears to be derived from either poor control on-site or poor logic in the construction schedule from which the control originates, or both. It can occur in the situation of workers controlling their work and interactions with others, rather than being controlled in a coordinated manner by the site superintendent. Every change that is made to the construction contract should be in writing, and every change order should reach all parties on the site affected by that change. It is important that such changes be incorporated in the construction schedule. Poor supervision can also include: poor, relations between subcontractor staff and both the general's site superintendent and the staff of other subcontractors on-site, and lack of clear and adequate communications.

Poor work performance points up the issues of what quality of work is required on each activity, and the concurrent, or immediately following inspection of quality of work done. By proper timing of inspections and quality clearances, there is a higher probability that when a work activity is finished the next work crew can begin their work fully without interference from subsequent rework by the poorly performing preceding work crew.

Work being executed out of sequence may be caused by a work crew simply falling behind in time or not starting their work on time so that they are constantly behind their schedule, by a holdup in material delivery, or because too many workers of different crews are in one work location at one time thus causing all of them to be delayed.

The result of the above is that the whole construction process becomes more random than scheduled because the work to be done has to occur upon the work already in place. This randomness causes inefficiencies in the execution of that subsequent work as well as the deleterious work in place having been executed out of the most efficient sequence of work.

A work crew may be unable to complete its work in a work location because of a lack of materials or unavailability of particularly skilled labor or some tradesmen, because of poor control by the subcontractor of his labor force allowing them to do as much work quickly in as many locations as possible

without finishing any one work location, or because the work crew completely finished its work in a location, but left waste and debris lying around which has to be moved by someone else. All of these delays impact the progress of each subcontractor and

the whole construction process.

COMPUTER SOFTWARE PACKAGES FOR CONSTRUCTION SCHEDULING AS SEEN BY GENERAL CONTRACTORS

Since the widespread use of many different computer software programs for scheduling may be presumed, general contractors pointed up the beneficial and detrimental features of such programs.

The forty percent of the general contractors interviewed who use a scheduling software package do so by their own choice, and not just because it is called for in the contract. There is not a clear preference for one particular commercial package. The scheduling software package is seen as a tool to do a job, and is usually housed in the office or on­site with the project manager.

Ease of use of particular packages was found to be advantageous because such programs do not require considerable prior computer knowledge. Changes are easily made and the package can be used at the construction site. Other individual features seen as strengths of programs are: the package can easily identify work activities which are time critical, the earliest starts and latest starts of each work activity can be calculated and output, resource analysis can be done, scheduling can be coordinated with accounting and estimating, and a variety of required output reports can be produced directly from the package. The major strength seen in a package is that the pre-construction schedule and post-monitoring schedule can both be produced as time-scaled schedules of work activities showing their logical interactions in the construction process. A more elaborate strength mentioned was the ability to summarize the schedule and produce it without the burden of large amounts of detail. The complement was also considered a strength, i.e., the ability to derive detail sub schedules from an overall schedule.

Minor individual weaknesses included the required human capability to use a computer of any type, the time to learn the contents and procedures of the package, and the software package was not user-friendly. There was also seen an array of lesser individual weaknesses, such as the high cost of the software packages, the difficulty in revising or updating the schedule, that weekends and holidays could not be built into the calendar, and that there may be a maximum number of work activities allowed in the schedule for it to be handled by the package.

CONCLUSIONS

The major conclusion which can be drawn from all of the above is that construction schedules used today lack construction realism which weakens their potential to guide actual construction work.

The quality of a construction schedule affects the work carried out on a construction site, and thus affects the durations and costs of a construction process.

The payoffs from considering and using the contents of the report's findings outlined in this paper will show in their effects on the durations and costs of the actual construction process.

The general contractor construction executives stated that if the normal construction schedule used by their top quality companies were replaced with the best schedule for construction work, that the construction duration would be reduced by about 15% from their normal duration. If that normal schedule were replaced with the worst schedule, then construction durations would increase by about 30% over the normal durations.

Likewise, the best schedule for construction work would reduce the overall cost by 10% from the normal cost. If that normal schedule was replaced by the worst schedule, then construction costs would increase by about 17% over their normal costs. The payoffs are shown in the diagram below.

The differences between these "save" and "lose" percentages on good and bad scheduling can be seen as the minimum ranges for the extent of improvements in duration and costs of construction work which can be achieved by improving the quality of construction scheduling.

It should be remembered that all construction executives, and office and site staff interviewed in this research project came from construction companies recommended by their peers and trade associations as the top quality construction organizations in the industry. Hence, their initial normal construction schedules from which they consider duration and cost effects and construction productivity are probably of a quality greater than that of the average contractor organization. Because the normal scheduling of the average contractor is probably of lesser quality than the normal schedule of the top quality contractors, the beneficial effects could well be greater than the improvements of 15% of duration and 10% of costs stated above for top quality contractors.

To achieve the potential improvement in duration, cost, and productivity of actual construction requires the scheduler to include the factors and emphases in his construction schedules. Also, the control problems and impediments stated should be dissolved or minimized by management thinking during the pre-construction scheduling process.

ACKNOWLEDGEMENT

This paper was derived from a research report titled "Construction Scheduling Factors, Emphases, Impediments and Problems As Seen By Construction Experts" by George S. Birrell. The underlying research was funded by the Florida Building Con­struction Industry Advisory Committee, whose Executive Secretary, School of Building Construction, University of Florida, Gainesville, Florida, 32611 can supply copies of the report to any interested party.