Despite tremendous industry buzz about Building Information Modeling (BIM), the greatest success has occurred within the “silos” of the designer, the builder and the fabricator. Designers are finding productivity gains and better coordinated designs. Construction management companies are identifying system clashes before they occur in the field. Steel fabricators have used 3-D modeling for years to better automate their fabrication processes. This practice is now growing in the precast industry as well.
In a growing number of projects these three groups are now sharing their BIM information to provide leverage up and down the value chain. One recent example is a stadium project where the general contractor used the precast fabrication model to place and track the precast elements using RFID technology.1 Other examples include a steel fabricator’s use of the structural engineer’s BIM model to expedite the steel detailing and fabrication schedule.2
But the cast-in-place construction industry has not captured the benefits of 3-D modeling and BIM to the same degree as the structural steel and precast industries. A significant contributor to this disparity is the highly fractured nature of the industry, from design through installation.
With design-build project delivery, however, cast-in-place projects can benefit, where project information is shared along the value chain using BIM technology.
The School of Cinematic Arts project currently under construction at the University of Southern California is a good example. By sharing the designer and concrete builder’s knowledge and expertise about constructability early in the design process, the project owner was able to recognize several benefits.
Located in Los Angeles, the School of Cinematic Arts is funded in part by a gift from the Lucasfilm Foundation. The foundation, USC and architect, Urban Design Group, worked together to identify the many contexts within which the project must be built. It required weaving together solutions that take into account climate, uses, location, the industry, and budgets.
The plans for the new complex reflect the vision of the foundation and university. The necessary durability, efficiency and usability of the structure had to be solved simultaneously with the mass and positioning, taking advantage of winds, sun and view corridors.
With a project team that includes Urban Design Group (architect), Gregory P. Luth & Associates (structural engineer), IPE (mechanical engineer), Hathaway Dinwiddie (contractor) and View By View (model manager). Key subcontractors include Fontana Steel (rebar fabricator/erector) and Schroeder Iron (steel fabricator), the foundation’s vision to use the latest in technology led to the project team’s use of BIM technology.
With past experience with BIM, the foundation was influential in the project’s adoption of an integrated project delivery method. Once the project is complete, the university plans to use the design and construction “as-built” 3-D BIM models for future facilities management.
Concrete Effects
The structural design’s lateral system is comprised of a revolutionary, never-before-used, repairable “fused rocking wall” cast-in-place concrete system. Located around the exterior of the building, this structural system acts as the seismic resisting frame. Cast-in-place concrete was used instead of precast or tilt-up wall construction due to the tight site conditions and the architectural requirement to have a jointless, stucco exterior wall. The structural design’s gravity system consists of a traditional steel frame with composite metal deck. The lateral and gravity systems are linked together utilizing repairable “butterfly” shear plates that are fastened along the seams of the CIP walls and to the vertical steel frame columns.
Research conducted at Stanford University verified the structural performance of the butterfly plates as required for city approval. Because this multi-material, complex structure was designed in a high-seismic zone, many challenges were introduced requiring the structural design to be sensitive not only to the architectural design intent, but also to how the structure would be built.
Constructability-Driven
With high seismic zone design requirements, it was critical that the structural steel frame to the concrete shear wall interfaces maintained very tight tolerances. Therefore, any site modifications of reinforcing bar placement or embed plates was prohibitive.
To ensure a good constructible design, the owner invited rebar detailers to participate in pre-bid meetings with the general contractor and structural engineer to review and recommend methods for constructability of the rebar panels. Once a rebar detailer was brought on board after construction documents were issued, further pre-coordination meetings were held to discuss potential clash issues between the steel frame, steel-to-concrete embedments and shear wall reinforcement.
To better facilitate discussions with the rebar detailer, the structural engineer used the rebar modeling capabilities of Tekla Structures to create the desired placement positions of the wall reinforcing bars in addition to the steel embed plates and structural steel elements.
The majority of the reinforcing bars were designed for shop assembly and site installation as rebar cage panels. The engineer visited the rebar fabricator’s shop to review the rebar cage panels before they were shipped to the job site.
Staging and erection of the rebar cages was of critical concern to the site erector. The initial estimation was to erect two panels per day over several months. However, the erector was able to increase that to 10 per day, due in large part to the pre-coordination efforts that went on before erection.
In addition, the structural engineer modeled the structural steelwork frame and some critical steel connections during the design phase of the project for design coordination, constructability review and pre-contract detailing of the frame for the benefit of the selected steelwork contractor. A structural steel model was given to the steel detailers, who used the model to generate the detailing model using the same modeling platform.
Collaborative Cast-In-Place
Great benefits can come to cast-in-place projects that are delivered in a design-build, collaborative setting, especially when teams are BIM-enabled.
For the USC School of Cinematic Arts project, the visualization of construction-level details and connections in 3-D during the design development stage of the project proved critical for the designers and builders to gain a better understanding of the scope and complexity of the project.
The use of the structural engineer’s BIM information downstream during fabrication also showed significant benefits.
Both technology and the industry are evolving rapidly. Since the beginning of the project’s Phase I in 2006, the tools have evolved substantially.
At the same time, BIM, in one form or another, has moved into the mainstream for the design community and is increasingly adopted by builders.
This technological evolution continues at a substantial pace, and the School of Cinematic Arts project team is setting its goals high for Phase II.
The team realizes that in order for BIM to have a significant impact on the entire project, an integrated project delivery approach should be used to truly capture the expertise of the designers and builders in parallel throughout the project.
“Using the Tekla Structures BIM,” says Gregory P. Luth, owner of Gregory P. Luth & Associates, “we are truly transforming the way concrete projects are designed and delivered, and to the benefit of the project team.”
End Notes:
1 “Smart Tracking”, Engineering News-Record, April 2008.
2 “Are You Ready for BIM?”, Civil Engineering, May 2008, p. 44
3 Luth, G.P., Krawinkler, H., and Law, K.H., “Representation and Reasoning for Integrated Structural Design,” CIFE Technical Report #55, Center for Integrated Facility Engineering, Stanford University, June 1991.
Gregory P. Luth is with Gregory P. Luth & Associates; Clifford Bourland is with Urban Design Group and Michael Gustafson is with Tekla Inc.