COMPUTER-AIDED DESIGN AND DRAFTING AS A CONSTRUCTION MANAGEMENT TOOL

INTRODUCTION

In today's highly competitive construction environment, successful project management requires the use of increasingly sophisticated tools. Computerized estimating, scheduling and cost control programs are becoming industry standards for project management. New products and technologies are continually being developed to assist the construction manager.

Estimating is one construction management task to which new technologies are being applied. Computer programs have been developed to assist the estimator in quantifying and pricing the materials. These programs require the estimator to interpret information contained in the plans and specifications. When the estimator has determined the architect's intentions, the project data must be entered into the computer. Data entry can be a time consuming and expensive oper­ation. In addition, the data entry process is subject to misinterpretation and error.

A procedure is needed to enable automatic input of the architect's intentions for estimating analysis., Linking the design process with the estimating process should significantly reduce the chance for omission and error by the estimating team.

Significance of the Problem

The Importance of the Quantity Take-Off

Preparation of the quantity take-off is a key function in the estimating process. "Perhaps the most basic as well as the most important aspect of the contractor's estimating and bid functions is the taking off of work quantities from the two-dimensional drawings representing a project," (Adrian, 1982). Clough wrote:

"A major cost incurred in preparing an estimate is the procedure of organizing and counting the materials and equipment required to complete the work. This procedure, known as the quantity take-off, produces a complete listing of the materials and items of work that will be required. Using these work quantities as a base, the contractor computes the costs of the materials, labor, equipment, subcontractors, taxes, insur­ance, overhead and contract bond. The sum total of these individual items of cost constitutes the anticipated overall cost of the construction." (Clough, 1981)

Preparing the quantity take-off with conventional procedures can be a time-consuming and costly process. With conventional practices, an architect prepares drawings and specifications which define a construction project. These construction documents are typically provided to several bidding contractors who must interpret them. Each contractor must independently determine the quantity of materials, labor and equipment required for construction of the facility. As Spradlin has noted, this practice often results in confusion.

"If 20 estimators or contractors were furnished the same set of plans and specifications and told to prepare an estimate of cost from them so that the different methods might be compared, it is safe to assume there would be not more than two estimates in the entire twenty that had been prepared on the same basis or from the same units." (Spradlin, 1982)

A tool is needed which is capable of providing all bidding contractors with an identical quantity take-off. This will insure that all contractors compete on an equal level. The low bid will result from a contractor's expertise at finishing the job, not an overlooked component of work. The redundant costs incurred when several competing firms prepare quantity take-offs for the same project will be avoided. This will lower the overhead expense of all contractors and should eventually be reflected in lower construction costs.

Computer-Aided Design and Drafting as a Take-Off Tool

Computer-aided design and drafting (CADD) may be the tool which is capable of providing the uniform quantity take-offs needed by the industry. An age-old adage states, "A picture is worth a thousand words". In simple eloquence this phrase captures the power of CADD.

Individuals who use CADD systems are familiar with the benefits of producing graphic images with computers. However, there is also a great deal of useful non-graphics information contained in CADD drawings, (Breslin, 1987). For example, a line on a computer screen representing a

wall to the draftsman is actually stored in great detail in the drawing file. A list of the typical information stored for a single line includes:

The very specific and detailed information stored in CADD drawing files offers considerable potential to the construction estimator. If this information can be used to provide quantity take-offs, more accurate and detailed estimates may be attainable. Instead of manually measuring the drawings for quantities, the CADD system could provide the required infor­mation. Transferring information directly from the CADD drawings would insure that the architect's intentions for material usage will be clearly relayed to the estimating team. Clear communication between the designer and the estimator will eliminate uncertainty, confusion and delays from the construction process.

"CADD-generated drawings offer incred­ible potential at integrating the flow of information within the construction industry. With CADD systems, archi­tects are able to create drawings and drawing files that contain geometry and attribute information. This quanti­tative information can be passed to the estimating system." (Robinson, 1986)

Purpose Statement

The purpose of this study was to investigate the use of Computer-Aided Design and Drafting as an estimating tool. Drawing files prepared with a microcomputer-based CADD system served as the data base for quantity take-off preparation.

Delimitations and Limitations

PROCEDURES

This study investigated the use of CADD-generated drawing files to produce quantity take-offs. Research was delimited to producing concrete quantity takeoffs for a simple foundation system. The study proceeded in the following steps:

Step 1

Creation of the Foundation Master Drawing

A master drawing for a simple foundation system was created using the Synthesis and AutoCAD programs (Figure 1, "Foundation Master Drawing"). The Synthesis Master Drawing file defines a standard shape with variable dimensions. These variable dimensions are easily recognized by the "$" preceding the variable number. This variable-labeling convention is required by the Synthesis program.

The variables created in the master drawing can be defined, or "rectified", to create infinite variations of the drawing. This allows a designer to create one drawing file for each standard shape. For example, the foundation system shown in Figure 1 can be altered to represent any other rectangular foundation system.

The Foundation Master Drawing contains a simplified quantity take-off. This section of the drawing, labeled "AUTOMATIC QUANTITY TAKE-OFF", was updated auto­matically to reflect dimensional changes of the master drawing variables. The "AUTOMATIC QUANTITY TAKE-OFF" is part of the drawing file and is stored on the layer named "Quantities". For clarity, the "Quantities" layer was turned off when the foundation plan was plotted. This layer was plotted separately and is presented in Table 1, "Foundation Master Drawing, Quantities Layer".

Nine items were automatically calculated when the Foundation Master Drawing file was updated. These quantities were:

The quantity take-off is reported twice in Table 1. The first take off was plotted directly from the drawing file. The second quantity take-off was created by exporting information from the drawing file to a word processing program. The take-off data was then printed with a daisy wheel printer.

Step 2

Development of the Foundation Master Spec Sheet

The SpecSheet which defines the master drawing variables is presented in Table 2, "Foundation Master SpecSheet". The SpecSheet was completed during a para­metric design session provided by the Synthesis software. The parametric design session prompts the user for needed input and creates an updated SpecSheet and drawing file.

The Synthesis SpecSheet provides many functions normally found only in spread­sheet programs. For example, formulas may be entered in SpecSheet cells. These formulas are used to calculate dimension variables specified in the master drawing. The Foundation Master SpecSheet requires the user to supply values for six of the thirty-nine variables shown in Figure 1. (The thirty-nine variables are listed in column one of Table 2.) The remaining thirty-three variables are calculated by formulas contained in the SpecSheet.

Step 3

Definition of Foundation Master Drawing Variables

The dimension variables contained in Figure 1 were defined using the parametric design feature of the Synthesis program. Figure 2, "Rectified Foundation Drawing", presents the revised foundation drawing. The quantity take-off for the revised foundation drawing is presented in Table 3, "Rectified Foun­dation Drawing, Quantities Layer". The quantity take-off for the foundation drawing revision is presented in plotted format and in standard type.

Step 4

Presentation of Data

The results of the study were plotted using a Hewlett/Packard 7475-A pen plotter or exported to a word processing program for text editing.

SUMMARY

This study was conducted to determine if the data stored in a microCADD drawing file could be used to generate a quantity take-off. Research was performed using AutoCAD 2.5 and Synthesis 2.5 software. A master drawing and accompanying SpecSheet were created for a foundation system. The variables shown on the master drawing were then defined to create a drawing and quantity take-off.

Using the procedures previously described, a quantity take-off was prepared for a simple concrete foundation system. This was accomplished by direct manipulation of the drawing data. Repetitive data entry (once to create a drawing and again to produce a quantity take-off) was completely eliminated. The quantity data was then exported to another program (work processing) to explore the flexibility of the system. Exporting data was easily achieved.

Procedure Analysis

The System

The Synthesis software was easy to learn and required little train­ing. This should allow rapid system implementation. However, the user must be thoroughly familiar with AutoCAD software in order to use the Synthesis program. When creating the master drawing, the Synthesis software was almost transparent to the user. The basic AutoCAD structure and commands were not changed and could be invoked from within the Synthesis program. A user that is well acquainted with the AutoCAD software should have little difficulty adapting to the Synthesis program.

The Synthesis master SpecSheet was also relatively simple to learn. The SpecSheet performed much like most popular spreadsheet programs. However, the SpecSheet does impose certain restrictions on the user. For example:

After the master SpecSheet was created and tested, revision of the drawing and subsequent creation of an updated quantity take-off was very simple. The screen prompts were answered and the program did the rest. The culmination of this parametric design session was the creation of a functional version of the foundation drawing and an automatic update of the quantity take-off.

Foundation Master Drawing Analysis

Creating and rectifying the Master Foundation Drawing revealed some important factors about applying the Synthesis software to the construction environment. The most important discovery was the degree of complexity required for the master drawing layout. The complexity required by the master drawing is apparent in Figure 1. The Synthesis program requires that all variables be referenced to a common point. This results in a master drawing that is complex and time consuming to create.

The simplistic foundation system chosen for this study would be the exception in actual practice. A more complicated foundation system would be typical. Using the Synthesis/AutoCAD programs to manage a complex construction project would be cumbersome. However, after the Master drawing was created, rectifying the foundation drawing was simple to perform. The problems encountrered in design of the drawing would seem to over-ride this utility.

CONCLUSIONS

The research has conclusively shown that volumetric quantity take-offs can be produced from the data stored in drawing files prepared with a microCADD system. Furthermore, the software chosen for this study provided complete automation of the process through parametric design. This parametric design function allowed the user to make changes to pre-defined variables of the master drawing. These design changes were then rapidly reflected in both the drawing and the material takeoff.

An added utility of the system was the ability to easily export data to other software. The updated bill of materials was exported to a word processing package for reporting. It should be equally

simple to export the data to spreadsheet, scheduling and other software. Linking the data stored in the drawing files to other software may provide integration of the many construction management functions.

This study has effectively demonstrated that the two-dimensional environment of many microCADD software packages is not a significant barrier to producing volumetric (three-dimensional) quantity take­offs. The ability to include all views (plan, elevation, section and detail) in one drawing, in effect, creates a three dimensional data base. This practice proved very functional for this study.

RECOMMENDATIONS

Construction Applications for AutoCAD/Synthesis Programs

The results of this study prove that data stored in AutoCAD files can be used to prepare accurate and detailed material take-offs. However, due to the considerable effort required to produce these take-offs, the practical application of the Synthesis program to the construction environment must be questioned.

The Synthesis master drawing and master SpecSheet should be created when a project drawing is first produced. While it is possible to alter an existing drawing to conform to the Synthesis standards, this is not an easy process and would likely prove to be uneconomical. Preparing the Synthesis master drawing and SpecSheet during the design stage would become the responsibility of the architect. This is an added responsibility the architectural community is not likely to accept.

A construction firm involved in design work may want to consider using the Synthesis and AutoCAD software combination. The parametric design feature provided by the Synthesis program can produce any variation of the original master drawing. (Provided all variables have been anticipated and defined). If master drawings and SpecSheets were created for typical building systems, considerable time and effort might be saved when creating variations of these systems.

The ability to provide accurate and detailed quantity take-offs for concrete, as demonstrated by this study, shows great potential for construction management. Applying the techniques outlined in this study to other quantity take-off problems should be feasible. The problems encountered in producing the quantity take-off indicate that further software development is needed. Software should allow quantity

take-offs to be prepared without requiring the intensive master drawing and SpecSheet design. If this modification were accomplished, the Synthesis/AutoCAD combination could prove to be an invaluable tool to the construction estimator.

CADD Applications to Other Management Tasks

Further study on microCADD applications for the construction environ­ment are both needed and justified. The potential advantages to be gained by tapping the vast information stored in a typical drawing file are many. This approach should provide increased speed and accuracy in processing the voluminous project information. In addition, using CADD files as a data base for project management may provide the integration of information which is needed to effectively manage a construction project. Further study exploring the application of a CADD data base to cost control, scheduling and estimating functions is needed.

CADD-Based Scheduling and Cost Control

The scheduling requirements for many construction projects are becoming increasingly rigorous. As owners become more sophisticated, they are requiring construction management personnel to provide comprehensive construction schedules. Unfortunately, many detailed job schedules wind up as wall paper for the construction shack and are not really used to control the job.

Obsolescence is a major factor in the lack of schedule use. A detailed schedule prepared at the beginning of the project will often become outdated within weeks. Schedules must be continually revised to provide useful information. Updating a schedule with conventional techniques often requires greater effort than the perceived benefits. A mechanism is needed to automatically link the scheduling process with project revisions.

Exporting data from CADD-prepared drawing revisions to the scheduling program may provide such a link. As revised drawings are prepared, the data can be exported to scheduling programs. Revised schedules can then be prepared with a minimum expenditure of effort. This would eliminate much of the effort associated with schedule revision.

Another common problem facing construction managers is the lack of an integrated approach to cost control. The construc­tion schedule must be combined with the estimate to produce an effective cost control system. Scheduling, estimating and cost control are therefore inseparably linked by function. Costs cannot be controlled without effective scheduling and estimating.

A CADD-based management approach may provide the means to effectively integrate estimating, scheduling and cost control. Integration of these functions would provide cohesive control of project cost and duration. Using the construction drawings as a data base for the other management functions could insure a smooth flow of information between all management groups.

Educator's Role

Microcomputer-based CADD systems offer incredible potential to the construction industry. Linking the design process with estimating, scheduling and cost control will improve the entire construction process. However, further study on microCADD applications are needed.

Educators have traditionally provided leadership in exploring the development and application of new technologies. Using CADD technology for construction management should be no exception. The exhaustive project information stored in CADD drawing files represents an untapped resource for construction management.

The rapid expansion of CADD technologies in recent years forecasts increased reliance of this technology in the future. If educators are to maintain their pro­active position in technology development, CADD research and training are neces­sities.

REFERENCES

DEFINITIONS