Chapter One
BIM Handbook Introduction
1.0 EXECUTIVE SUMMARY
Building Information Modeling (BIM) is one of the most promising developments in the architecture, engineering and construction (AEC) industries. With BIM technology, an accurate virtual model of a building is constructed digitally. When completed, the computer-generated model contains precise geometry and relevant data needed to support the construction, fabrication, and procurement activities needed to realize the building.
BIM also accommodates many of the functions needed to model the lifecycle of a building, providing the basis for new construction capabilities and changes in the roles and relationships among a project team. When implemented appropriately, BIM facilitates a more integrated design and construction process that results in better quality buildings at lower cost and reduced project duration.
This chapter begins with a description of existing construction practices, and it documents the inefficiencies inherent in these methods. It then explains both the technology behind BIM and recommends ways to best take advantage of the new business processes it enables for the entire lifecycle of a building. It concludes with an appraisal of various problems one might encounter when converting to BIM technology.
1.1 INTRODUCTION
To better understand the significant changes that BIM introduces, this chapter begins with a description of current paper-based design and construction methods and the predominant business models now in use by the construction industry. It then describes various problems associated with these practices, outlines what BIM is, and explains how it differs from 2D and 3D computer-aided design (CAD). We give a brief description of the kinds of problems that BIM can solve and the new business models that it enables. The chapter concludes with a presentation of the most significant problems that may arise when using the technology, which is now only in its earliest phase of development and use.
1.2 THE CURRENT AEC BUSINESS MODEL
Currently, the facility delivery process remains fragmented, and it depends on paper-based modes of communication. Errors and omissions in paper documents often cause unanticipated field costs, delays, and eventual lawsuits between the various parties in a project team. These problems cause friction, financial expense, and delays. Recent efforts to address such problems have included: alternative organizational structures such as the design-build method; the use of real-time technology, such as project Web sites for sharing plans and documents; and the implementation of 3D CAD tools. Though these methods have improved the timely exchange of information, they have done little to reduce the severity and frequency of conflicts caused by paper documents.
One of the most common problems associated with paper-based communication during the design phase is the considerable time and expense required to generate critical assessment information about a proposed design, including cost estimates, energy-use analysis, structural details, etc. These analyses are normally done last, when it is already too late to make important changes. Because these iterative improvements do not happen during the design phase, value engineering must then be undertaken to address inconsistencies, which often results in compromises to the original design.
Regardless of the contractual approach, certain statistics are common to nearly all large-scale projects ($10 M or more), including the number of people involved and the amount of information generated. The following data was compiled by Maged Abdelsayed of Tardif, Murray & Associates, a construction company located in Quebec, Canada (Hendrickson 2003):
Number of participants (companies): 420 (including all suppliers and sub-sub-contractors) Number of participants (individuals): 850 Number of different types of documents generated: 50 Number of pages of documents: 56,000 Number of bankers boxes to hold project documents: 25 Number of 4-drawer filing cabinets: 6 Number of 20 inch diameter, 20 year old, 50 feet high, trees used to generate this volume of paper: 6 Equivalent number of Mega Bytes of electronic data to hold this volume of paper (scanned): 3,000 MB Equivalent number of compact discs (CDs): 6
It is not easy to manage an effort involving such a large number of people and documents, regardless of the contractual approach taken. Figure 1-1 illustrates the typical members of a project team and their various organizational boundaries.
There are two dominant contract methods in the U.S, Design-Bid-Build and Design-Build, and many variations of them (Sanvido and Konchar 1999; Warne and Beard 2005).
1.2.1 Design-Bid-Build (DBB)
A significant percentage of buildings are built using the DBB approach (almost 90% of public buildings and about 40% of private buildings in 2002) (DBIA 2007). The two major benefits of this approach are: more competitive bidding to achieve the lowest possible price for an owner; and less political pressure to select a given contractor. (The latter is particularly important for public projects). Figure 1-2 illustrates the typical DBB procurement process as compared to the typical Design-Build (DB) process (see section 1.2.2)
In the DBB model, the client (owner) hires an architect, who then develops a list of building requirements (a program) and establishes the project''s design objectives. The architect proceeds through a series of phases: schematic design, design development, and contract documents. The final documents must fulfill the program and satisfy local building and zoning codes. The architect either hires employees or contracts consultants to assist in designing structural, HVAC, piping, and plumbing components. These designs are recorded on drawings (plans, elevations, 3D visualizations), which must then be coordinated to reflect all of the changes as they are identified. The final set of drawings and specifications must contain sufficient detail to facilitate construction bids. Because of potential liability, an architect may choose to include fewer details in the drawings or insert language indicating that the drawings cannot be relied on for dimensional accuracy. These practices often lead to disputes with the contractor, as errors and omissions are detected and responsibility and extra costs reallocated.
Stage two involves obtaining bids from general contractors. The owner and architect may play a role in determining which contractors can bid. Each contractor must be sent a set of drawings and specifications which are then used to compile an independent quantity survey. These quantities, together with the bids from subcontractors are then used to determine their cost estimate. Subcontractors selected by the contractors must follow the same process for the part of the project that they are involved with. Because of the effort required, contractors (general and subcontractors) typically spend approximately 1% of their estimated costs in compiling bids. If a contractor wins approximately one out of every 6 to 10 jobs that they bid on, the cost per successful bid averages from 6% to 10% of the entire project cost. This expense then gets added to the general and subcontractors'' overhead costs.
The winning contractor is usually the one with the lowest responsible bid, including work to be done by the general contractor and selected subcontractors. Before work can begin, it is often necessary for the contractor to redraw some of the drawings to reflect the construction process and the phasing of work. These are called general arrangement drawings. The subcontractors and fabricators must also produce their own shop drawings to reflect accurate details of certain items, such as precast concrete units, steel connections, wall details, piping runs, etc.
The need for accurate and complete drawings extends to the shop drawings, as these are the most detailed representations and are used for actual fabrication. If these drawings are inaccurate or incomplete, or if they are based on drawings that already contain errors, inconsistencies or omissions, then expensive time-consuming conflicts will arise in the field. The costs associated with these conflicts can be significant.
Inconsistency, inaccuracy, and uncertainty in design make it difficult to fabricate materials offsite. As a result, most fabrication and construction must take place onsite and only when exact conditions are known. This is more costly, more time consuming, and prone to produce errors that would not occur if the work were performed in a factory environment where costs are lower and quality control is better.
Often during the construction phase, numerous changes are made to the design as a result of previously unknown errors and omissions, unanticipated site conditions, changes in material availabilities, questions about the design, new client requirements, and new technologies. These need to be resolved by the project team. For each change, a procedure is required to determine the cause, assign responsibility, evaluate time and cost implications, and address how the issue will be resolved. This procedure, whether initiated in writing or with the use of a Web-based tool, involves a Request for Information (RFI), which must then be answered by the architect or other relevant party. Next a Change Order (CO) is issued and all impacted parties are notified about the change, which is communicated together with needed changes in the drawings. These changes and resolutions frequently lead to legal disputes, added costs, and delays. Web site products for managing these transactions do help the project team stay on top of each change, but because they do not address the source of the problem, they are of marginal benefit.
Problems typically arise when a contractor bids below the estimated cost in order to win the job. He will then abuse the change process to recoup losses incurred from the original bid. This, of course, leads to more disputes between the owner and project team.
In addition, the DBB process requires that the procurement of all materials be held until the owner approves the bid, which means that long lead time items cannot be ordered early enough to keep the project on schedule. For this and other reasons (described below), the DBB approach often takes longer than the DB approach.
The final phase is commissioning the building, which takes place after construction is finished. This involves testing the building systems (heating, cooling, electrical, plumbing, fire sprinklers, etc.) to make sure they work properly. Final contracts and drawings are then produced to reflect all as-built changes, and these are delivered to the owner along with all manuals for installed equipment. At this point, the DBB process is completed.
Because all of the information provided to the owner is conveyed in 2D (on paper), the owner must put in a considerable amount of effort to relay all relevant information to the facility management team charged with maintaining and operating the building. The process is time consuming, prone to error, costly and remains a significant barrier.
As a result of these problems, the DBB approach is probably not the most expeditious or cost-efficient approach to design and construction. Other approaches have been developed to address these problems.
1.2.2 Design-Build (DB)
The design-build process was developed to consolidate responsibility for design and construction into a single contracting entity and to simplify the administration of tasks for the owner (Beard et al. 2005). Figure 1-2 illustrates this process.
In this model, the owner contracts directly with the design-build team to develop a well-defined building program and a schematic design. The DB contractor then estimates the total cost and time needed to construct the building. After all modifications requested by the owner are implemented, the plan is approved and the final estimate cost for the project is established. It is important to note that because the DB model allows for modifications to be made to the building''s design earlier in the process, the amount of money and time needed to incorporate these changes is also reduced. The DB contractor establishes contractual relationships with specialty designers and sub-contractors as-needed. After this point, construction begins and any further changes to the design (within predefined limits) become the responsibility of the DB contractor. The same is true for errors and omissions. It is not necessary for detailed construction drawings to be complete for all parts of the building prior to the start of construction on the foundation, etc. As a result of these simplifications, the building is typically completed faster, with far fewer legal complications, and at a somewhat reduced total cost. On the other hand, there is less flexibility for the owner to make changes after the initial design is approved and a contract amount is established.
The DB model is becoming more common in the U.S. and is used widely abroad. Data is not currently available from U.S. government sources, but the Design Build Institute of America (DBIA) estimates that, in 2006, approximately 40% of construction projects in the U.S. relied on a variation of the DB procurement approach. Higher percentages (50%-70%) were measured for some governmental organizations (Navy, Army, Air Force, and GSA). The trend toward increasing use of DB is very strong (Evey 2006).
1.2.3 What Kind of Building Procurement Is Best When BIM Is Used
There are many variations of the design-to-construction business process, including the organization of the project team, how the team members are paid, and who absorbs various risks. There are lump sum contracts, cost plus a fixed or percentage fee, various forms of negotiated contracts, etc. It is beyond the scope of this book to outline each of these and the benefits and problems associated with each of them (see Sanvido and Konchar 1999 and Warne and Beard 2005).
With regard to the use of BIM, the general issues that either enhance or diminish the positive changes that this technology offers depends on how well and at what stage the project team works collaboratively on the digital model. The earlier the model can be developed and shared, the more useful it will be. The DB approach provides an excellent opportunity to exploit BIM technology, because a single entity is responsible for design and construction and both areas participate during the design phase. Other procurement approaches can also benefit from the use of BIM but may achieve only partial benefits, particularly if the BIM technology is not used collaboratively during the design phase.
1.3 DOCUMENTED INEFFICIENCIES OF TRADITIONAL APPROACHES
This section documents how traditional practices contribute unnecessary waste and errors. Evidence of poor field productivity is illustrated in a graph developed by the Center for Integrated Facility Engineering (CIFE) at Stanford University (CIFE, 2007). The impact of poor information flow and redundancy is illustrated using the results of a study performed by the National Institute of Standards and Technology (NIST) (Gallaher et al. 2004).
(Continues...)
Excerpted from BIM Handbookby Chuck Eastman Paul Teicholz Rafael Sacks Kathleen Liston Copyright © 2008 by Chuck Eastman. Excerpted by permission.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.
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