Engineers have been working with 2D drawings for a long time. These drawings used to be sufficient for most design work. For more important or complex projects, engineers would resort to physical models made out of wood, clay, or other appropriate materials. This brought into play the all-important third dimension: height. These models generally were built to demonstrate aesthetic aspects of the structure. They were expensive and often times of limited practical utility, especially for capturing design details.

A good engineer could visualize the third dimension. In his mind, the engineer would visualize a 3D object that he could use to draw 2D plan sheets. However, this system was far from perfect; The leap from 2D on plan sheets to 3D in the real world would sometimes show several conflicts in connection details and geometry, rebar placement, post-tensioning hardware, et cetera. Some of these conflicts could be corrected in the field, but the more complex ones would hold up construction, cause delays, and often result in disputes and expensive claims for the owner.

Enter the world of 3D, data-driven, and intelligent object-oriented bridge information modeling (BrIM). BrIM may be defined as the process of documenting bridge geometry and other data through the project design and construction phases as well as through its service life in a data-centric, 3D model. This process results in a BrIM model that includes bridge geometry, material and section properties, quantities, erection sequences, maintenance data, et cetera. This is, in effect, similar to building information modeling (BIM), which is used increasingly and commonly in the building industry. The term BIM was coined by Charles Eastman at the Georgia Institute of Technology and used extensively in his papers since the late 1970s.

Imagine a 3D model of a prestressed concrete segmental bridge. All elements of the bridge are shown in 3D, using precise spatial geometry. For concrete bridges, the outline of the concrete form is shown, and all rebar and post-tensioning is laid out and modeled precisely in 3D. In the case of structural steel, all elements and connections are detailed fully and modeled. Embedded elements, drainage, electrical and mechanical systems, as well as utilities supported off the bridge are fully detailed and modeled. Foundations, piles, and the surrounding soil layers also are systematically modeled. A 6-inch-thick stack of civil, structural, electrical, and mechanical plans is transformed into a compact 3D digital model. The engineer can rotate the model; pan, zoom in, and look closely at a component; cut sections; turn on and off whole groups of elements to reduce the clutter; and zero in on the area of study. The time and cost savings for the design process can be significant. The elimination of potential conflicts and delay issues before construction commences can be invaluable.

The design engineer can use this model to generate classical 2D design drawings and details. The BrIM model also can generate shop drawings for steel bridges for use in fabrication shops. Similarly, in the case of precast concrete bridges, BrIM can generate integrated shop drawings showing concrete, rebar, and post-tensioning details for the casting yard, resulting in significant time and cost savings for the project. In addition, the BrIM model can be used to generate data for analysis programs, node point locations, section and material properties, et cetera. Several different types of analyses can benefit from this. For example, global analysis for dead and live loads as well as local finite element analysis of a connection can tap into the same model for their data. The BrIM model and the analysis process can interact with each other progressively throughout the design process, ensuring that the 3D aspects of the structure are captured fully by the analysis models.

So far, we have looked at an intelligent, data-driven 3D model used to evaluate the structure with still shots or views, which are 3D, but, as the name implies, not animated. Naturally, the next milestone in the BrIM evolution process is the introduction of real-time digital animation to simulate construction processes. In the beginning, the focus of animation was on aesthetic elements — clouds floating in the sky, trees moving in the breeze, and traffic running on the bridge. The next logical construct is an animation of the detailed construction sequence and procedures. The objective is to build the structure virtually before it is actually constructed. This is an order of magnitude more complex, but it is an immensely rewarding development in capable hands.

The construction sequence of a modern bridge is of great interest to both designers and builders. For major bridges, it is important that the designer establish the feasibility of the construction sequence carefully. This includes substructure construction, including coffer dams, pile installation sequence, and pile-cap and pier construction. The superstructure erection schemes can be extremely complex and challenging. Consider the construction sequence of a segmentally erected, precast prestressed concrete box girder bridge. The designer needs to address several important questions, namely: How is the pier head segment installed atop the pier? How is the form traveler connected to the structure? Is there space for two travelers to be mounted onto the pier table? Which segment shall be erected first? What is the sequence of stressing temporary and permanent prestressing? This list goes on. A 3D virtual BrIM simulation of the erection sequence can be invaluable in refining the construction procedure; that is, making it more rational, efficient, and constructible, thereby enabling the engineer to produce a more competitive design.

The construction sequence is coupled with the all-important variable: time. The animation can be controlled to run in accordance with the construction schedule, generally called 4D BrIM, highlighting construction operations on the critical path. Using the simulation model, the engineer now operating on a more intuitive visual plane can experiment with different construction sequences, selecting the fastest and most efficient method to be implemented in the field. This can translate into real and significant savings on a construction job.

During the construction of the bridge, the model can be used for planning, estimating, scheduling, ordering materials, and keeping track of inventories for various elements. The model can be used to explain the construction of an intricate and complicated component to several subcontractors belonging to different disciplines, highlighting critical activities and helping coordinate the effort. As the bridge is constructed, the contractor and the owner keep a record of as-built information. If rebar arrangement is changed for an element, a tendon is placed in the spare duct, a pile hits refusal before making it to the specified tip elevation, or the concrete strength is different from that specified, then it must be recorded for subsequent use by maintenance teams as well as for any future rehab and retrofit work. Individual elements in the 3D model can be linked with a database; a mouse click on the element can bring up an inspector’s notes, photographs of a detail, pile driving records, or anything else recorded during construction. These are termed “smart elements” because they remember their history and data associated with them.

A properly developed BrIM model can be applied effectively to manage the entire lifecycle of the bridge, from conceptual design to detailed design, construction, and bridge maintenance. After construction is completed, the owner can use the BrIM model along with the associated database to develop a maintenance program for the structure. Imagine a truss element that remembers when it was painted last, or a connection that knows when the rusted gusset plates were replaced, or an expansion joint that remembers the upcoming replacement date. During the lifetime of the structure, the database is updated with the latest maintenance data. This presents a treasure trove of information that would typically fill several storage rooms in the native hard copy format. Over the years, more often than not, hard copy information is misplaced or lost, with the owner then incurring additional costs for reassembling the lost information.

Several software packages currently are available for developing BrIM models for both steel and reinforced and post-tensioned concrete bridges. Most major analysis and design software for bridges produces 3D BrIM models — mostly member solid profiles, concrete profiles, and post-tensioning layouts as a byproduct of the development of analytical models. Detailed BrIM models can be prepared using several different software packages, including Autodesk’s AutoCAD, Navisworks Manage, and Revit; and Bentley’s Microstation, RM Bridge, ProSteel 3D, and Rebar. Tekla Structures provides powerful and comprehensive multi-user capabilities for modeling large steel and reinforced concrete structures, with bridge concrete profiles being generated in AutoCAD or Microstation.

Development of a comprehensive and all-inclusive software package to generate both design and construction BrIM models remains a current challenge for the bridge design software industry. Another major challenge, which requires special engineering, CAD, and BrIM skills, is the management of the model and the central database, and its communication with the design and construction teams throughout the design and construction process. Development of comprehensive specifications governing the development of BrIM models, standardization of BrIM, BrIM management, liability, and model ownership issues also need to be addressed by the industry.

The California Department of Transportation (Caltrans) has been aggressively introducing some of these concepts into the construction for the East Spans of the San Francisco Oakland Bay Bridge. Extensive use of BrIM models was made for the design and construction of the East Tie-In structure of the South-South Detour of the San Francisco Oakland Bay Bridge. This structure presented a unique challenge in terms of bridge engineering, requiring the replacement of 300 feet of an existing double-deck bridge truss with a new truss in a 72-hour window through a roll-out/roll-in process that took place 150 feet up in the air. Timelines for the project required an extremely challenging schedule for design, detailing, fabrication, and erection of nearly 5,000 tons of structural steel designed to the exacting seismic performance standards required by Caltrans.

Given the extremely challenging schedule requirements, Caltrans and the design joint venture of T.Y. Lin International/Moffatt & Nichol Engineers decided to develop fully detailed BrIM models of the East Tie-In structures during the design phase. The primary objective was to use the BrIMs for a virtual simulation of the construction procedure and to evaluate the sequence for the roll-out/roll-in to identify and eliminate all possible steel fit-up, geometrical conflicts, and space requirement issues, thus eliminating any surprises and subsequent schedule impacts during the actual execution of the process. The secondary objective was to use the BrIM models of the new structures to generate shop drawings to facilitate the fabrication and erection of structural steel in order to significantly accelerate overall construction schedules.

Fully detailed BrIM models for the East Tie-In structures, including the new skid bents and towers, skid beams, and the new roll-in truss were developed in AutoCAD and Bentley ProSteel 3D (see Figure 1). The software used intelligent objects for modeling various structural elements in new and existing construction, allowing the design team to access information regarding member and structure geometry and associated structural properties. Autodesk Navisworks Review & Simulate software was employed for model viewing and simulation.

Figure. 1: San Francisco-Oakland Bay Bridge – East Tie-In – complete structure

The ProSteel 3D BrIM models generated for the skid bents, towers, and beams were used to generate structural steel shop drawings for fabrication. The development of the detailing models along with the design effort eliminated fit-up and fabrication issues and allowed for smooth and on-schedule completion of the steel fabrication of the East Tie-In structures. Each individual connection was fully detailed (see Figure 2).

Figure. 2: San Francisco-Oakland Bay Bridge – East Tie-In – truss connection details

Detailed BrIM models also were developed for the existing truss spans, including the roll-out truss and the adjacent existing and new structures as well as the viaduct, truss, and cantilever structures of the existing east spans. The structures were modeled as solid 3D elements with complete as-built detail right down to connection details in critical areas. The jacking systems used to move the existing and new spans also were modeled in complete detail to ensure proper fit-up of all components (see Figure 3). BrIM models were generated to simulate the critical phases of the construction process step-by-step, as a ”playbook” through the 72-hour-roll-out/roll-in window. This simulation provided the designers thorough studies of critical details of the construction procedures in 3D and allowed the design team to refine and fine tune the structural systems and details, thereby eliminating potential construction issues that could result in schedule delays.

Figure. 3: San Francisco-Oakland Bay Bridge – East Tie-In – truss jacking details

Use of fully detailed BrIMs for the East Tie-In was a first for Caltrans and the joint venture design team of T.Y. Lin International/Moffatt & Nichol Engineers. Successful use of this technology was critical in allowing the designers to simulate the construction and movement of the various structures in the East Tie-In in true 3D. Generation of shop drawings from the BrIM models accelerated and facilitated the fabrication and erection schedule significantly. The pre-construction virtual simulation of the roll-out/roll-in resulted in minimization and elimination of issues that could have potentially caused schedule delays in actual construction of a critical link for the San Francisco-Oakland Bay Bridge seismic safety project.

Caltrans also is extensively using BrIM models for the design and construction of Yerba Buena Island (YBI) Transition Structures. The westbound and eastbound bridges at the island are prestressed concrete multi-cell, box girder structures. The models include all concrete forms, rebar details, post-tensioning, and utilities embedded or suspended off the bridge (see Figure 4). The models have helped resolve conflicts between rebar, post-tensioning, and any embeds in the concrete.

Figure. 4: San Francisco-Oakland Bay Bridge – utilities on YBI structures

In addition, BrIM models also were employed to develop details of the 1,400-foot span cantilever truss of the existing Bay Bridge. These models were used to study the existing eyebar chains in the structure and their potential retrofits as developed by Caltrans engineers (see Figure 5).

Figure. 5: San Francisco-Oakland Bay Bridge – cantilever truss joint at eyebar chain

The trend for using BrIM models in the United States as well as in international markets is increasing at a remarkable pace. Owners are realizing that investing in BrIM models at the onset of a project can offer significant time and cost saving benefits. The design details are integrated in 3D models, thereby reducing the owner’s exposure to lengthy construction claims. The contractor can use the model for a virtual simulation of the construction program. The inspectors can use it to record as-built information for the bridge. When the structure is completed and handed over, the owner’s maintenance group can use it as a visual, 3D database to keep a record of the bridge’s lifecycle maintenance and upgrade. A few decades down the road, when rehabilitation is needed, the new design team will have the advantage of all of the pertinent information at their fingertips with a BrIM model.

Expect BrIM to become an integral component of design and construction for major bridges in the future. It is an idea whose time has come, and it is here to stay.

Ali H. Abbas, P.E., is president of NorCal Structural, Inc. He can be contacted at ali@ncstructural.com. Sajid Abbas, Ph.D., P.E., is vice president of T.Y. Lin International. He can be contacted at sabbas@tylin.com. Brian Maroney, D.Eng., P.E., is deputy program manager, Caltrans, San Francisco Oakland Bay Bridge, East Spans Seismic Safety Project, at the California Department of Transportation. He can be contacted at brian.maroney@dot.ca.gov.