Using the Shack Project to Introduce Parametric Construction Management

Introduction

 Computer methods can be used to improve accuracy and efficiency in many phases of the construction process.  Most employers that hire students with Bachelor degrees in Construction Management expect them to have experience using popular computer programs such as Microsoft Excel, Timberline Software Corporation Precision Collection, Primavera Project Planner P3 and Microsoft Project.  However, they should be more than just technicians running a computer program.  Through a course of study that integrates theory and practice, students also develop an understanding of the methods used in the commercial software.  This well-rounded graduate will be able to quickly learn how to perform basic tasks on unfamiliar commercial software and independently explore more advanced methods.  For example, a student who learned Primavera in a rigorous scheduling course should be able to use Microsoft Project for simple jobs with little additional instruction.

One of the advantages of using computer software is the ability to automate repetitive calculations.  This can be as simple as programming and copying an equation in Excel or as complex as developing a Model with Timberline software.  “A model is a set of instructions for taking off everything for a specific building element” (Timberline Software Corporation, 2001).  An example of a Model Takeoff algorithm available with Precision Estimating performs a preliminary design and estimate of a “Tilt-Up Warehouse On Spread Footings” after the user inputs 16 parameters describing the dimensions and layout of the facility.  The program can also be configured to export some scheduling information to popular scheduling programs.

Construction management graduates should be aware of the options available with commercial software to develop customized programs to automatically perform repeated tasks, and some will be motivated to develop their own applications.  These computer programs can be as simple as a spreadsheet set up to automatically calculate the volume of an excavation given a length, width and depth, to a standalone application with a sophisticated user interface.  Although a complicated computer programming assignment would intimidate many students, all technical graduates should be aware of the available tools and have experience in the fundamentals of the most common applications.

An exercise has been developed to introduce construction students to some simple computer programming tasks and, in the process, familiarize them with the function of typical estimating, scheduling, drawing and analysis software.  The project involves completing the development of software to perform “Parametric Construction Management.”  This term is derived from the concept of parametric design in engineering.  In parametric design, custom computer software is developed to create a complete model of a standard part from a limited number of parameters.  Conventional analysis methods can then be used to evaluate the performance.  The designer can then use this solution or easily modify parameters to improve and optimize the design.  For example, an engineer that designs highway overpass bridges may take advantage of similarities in most designs to automate much of the design/analysis process.  The use of Assemblies in Timberline’s Precision Estimating is an example of parametric estimating.  For example, a concrete footing assembly automatically estimates the cost of a footing after the user defines a few simple parameters to describe the geometry and reinforcing.  Parametric Construction Management will take the parameters used in the estimate to also schedule the project, create drawings when required and possibly perform analysis and design operations for temporary structures such as formwork.

The project scenario in that the student works for a company specializing in designing and constructing custom “shacks” for customers.  Given the value of roughly ten input parameters describing the overall dimensions and some design details for the structure, the computer software completes the structural design and develops a detailed estimate, construction schedule, and sketches of the proposed structure.  Students are given software templates that must be modified and completed in the assignment.

Shack Description

The shack is a simple, rectangular wood structure.  Architectural details, such as doors and windows, are kept to a minimum to maintain simplicity while preserving essential components to meet the objectives of the project.  The shack is to be constructed on a reinforced concrete floor placed on gravel and framed with 2 by 4’s covered by 4’X 8’ sheathing.  The flat roof must be designed for a 20-psf-snow load.  It will be supported with 2 by X (to be determined by structural requirements) joists and covered with 4’X 8’ sheathing.  Students are told to assume that an adequate system is provided to attach the walls to the floor slab.

Students are supplied with a Microsoft Excel file that provides a template for estimating the project.  Visual Basic for Applications (VBA) modules are supplied with the Excel file to create output files that are later read by VBA routines in AutoCAD and Microsoft Project to complete the drawings and schedule.

Students are required to complete the spreadsheet to include:

1)       A User Form to accept the design parameter input and transfer the numbers to the spreadsheet

2)       Valid calculations on the Summary sheet to properly estimate all quantities from the input parameters

3)       Bid Item sheets to estimate the Labor, Material and Equipment costs for each bid item and the Duration in hours

4)       An allowance for indirect costs, overhead and profit as a percentage of the direct costs distributed over the bid items

Output from the VBA routines will then be used to create

1)       A solid model of the selected design

2)       A schedule

3)       An early-start schedule of payments

Estimating using Microsoft Excel

The students are provided with a Microsoft Excel Workbook, Estimate.xls, which was developed based on the format suggested by Paulson (1995).  The baseline spreadsheet is shown in Figure 1.  The design parameters and many of the formulas to perform quantity calculations are developed in class and entered on the Summary sheet.  Students are required complete these calculations to automatically calculate the required quantities of materials in an appropriate format for estimating.  Students that have completed the required Structures course are expected to develop formulas to calculate the required Joist Size based on beam theory calculations.  Other students are provided with a lookup table to select the joists based on the width of the structure.

The baseline spreadsheet includes additional sheets for resource costs and bid items.  The necessary links between the Summary sheet, the Bid Item sheets and the Resource summary are provided in the baseline.  Students are required to develop cost data for the Labor, Material and Equipment to be used in the project and enter it on the appropriate sheet using the sample format provided.  The Resource Summary Sheet is shown in Figure 2.

The baseline project uses nine bid items.  Students were required to select crews and estimate productivity for each bid item in order to calculate the labor, material, and equipment costs and to estimate the duration of each task.  Students were encouraged to modify these items based on their own interpretation of the project.  Once the spreadsheet is completed and all calculations are fully integrated, the user can simply modify the values of input parameters on the summary sheet and obtain a new estimate of the construction costs for the desired shack.  The development of the Estimate spreadsheet required students to apply principles taught in earlier classes in the Construction Management curriculum.  The practical estimating exercise also provided a valuable experience.

Visual Basic for Applications

Visual Basic for Applications is becoming the standard for developing sophisticated “Macros” in many commercial software applications.  It is available in Microsoft Office, Microsoft Project and most commercial Computer-Aided Drafting (CAD) packages.  VBA provides the user with greater flexibility to develop user interfaces for both input and output and to program complex algorithms.  The Shack project requires students to create a typical User Form for parameter input and write the supporting computer code.  They also use VBA programs to create drawings and schedules.  The project requirements are defined so that students can be successful without extensive software development training.  The exercise exposes them to the components of a computer program, and motivated students can make incremental changes to the programs in addition to the minimum requirements for the project.

Input Form in Microsoft Excel

All students are required to create a User Form to provide an interface to the user.  The form contains Labels, Text Boxes and Command Buttons.  Figure 4 is an example of one student’s work.  This student also used text boxes to output some results of the analysis and estimate.  A subroutine must be written to take the input from the text boxes and insert it on the Summary sheet in the spreadsheet.  A fragment of the VBA subroutine that transfers values to the spreadsheet when the Enter command button is clicked is provided in Figure 5. 

All students can complete this User Form development requirement with minimal coaching.  It develops a useful skill that can be applied by anyone using Excel without any additional programming experience and provides the student with some insight into computer programming.

Solid Model Generation in Microsoft Excel

The completed shack is an assembly of layers of gravel and concrete, dimensioned lumber and plywood.  These entities are hexahedrons that can be defined by the X, Y, and Z coordinates of opposite corners.  The parameters that define each part of the shack can be written to a file in a generic format.  Students are provided with a VBA subroutine that automatically generates this generic file given the parametric description of the shack.  There are six numbers in each line in the file -- X1, Y1, Z1, X2, Y2, Z2 – that give the coordinates of opposite corners of each component.  The last line of the file is six zeros.

Solid Model Creation in AutoCAD

AutoCAD is used to view the solid model.  The fundamentals of this CAD program are also taught in the Computer Applications course.  A VBA program can be loaded in AutoCAD to read the information in the output file from Excel and create the solid model.  The AutoCAD command

    Set boxObj = ThisDrawing.ModelSpace.AddBox(center, Length, Width, Height)

calls for the length, width, height and the location of the centroid of each component.  These are calculated from the data provided in the file.  The Hide option is selected to see an actual view of the structure.  The sheathing was drawn on a separate level that is turned off in Figure 6 to expose the skeleton.  Students are required to plot views of the solid model and add dimensions.  This type of sketch would be sufficient to show a potential customer or to give instructions to carpenters building the project.

Scheduling using Microsoft Project

Figure 7 shows the final bid summary and estimated task durations for a 20’ X 16’ X 10’ shack.  Software is being developed in the current course offering to extract the durations and prompt the user to describe task dependencies.  This information will be written to a file that will be read by a VBA program in Microsoft Project to create the schedule. 

Conclusions

Although the average construction student does not wish to become a computer programmer, most will be expected to use computers to perform their work, and those who can apply some simple computer programming techniques will be more efficient.  Feedback from students and graduates working with local companies indicates that they frequently become the computer expert and use their computer skills extensively and effectively.  The Shack Project, as a component of the Computer Applications in Construction course, introduces students to useful programming techniques and will motivate some to further develop these skills.

References

Paulson, B.C. Jr. (1995). Computer Applications in Construction. New York: McGraw-Hill, Inc.

Timberline Software Corporation. (2001). Model Estimating Training Workbook.