Prof explores ways to speed up bridge construction

Faster bridge construction projects may be in store for California through the efforts of a Sacramento State civil engineering professor. Eric Matsumoto, in conjunction with researchers from UC San Diego and state departments of transportation including CalTrans, is exploring the feasibility of constructing bridges in the seismic regions using precast concrete. The research focuses on a precast bridge element call the bent cap which connects the bridge girders to columns.

It’s an approach to rapid bridge construction already used in some parts of the country but which especially challenges earthquake-prone areas like California.

The research is being funded by a $550,000 contract from the National Cooperative Highway research program, which develops practical solutions to problems facing transportation agencies.

Using precast concrete eliminates much of the bulky falsework and wood forms that currently are used in California bridge construction. Precasting is less labor-intensive at the construction site, Matsumoto says, because it removes the concrete forming, pouring and curing from the work zone, increasing safety for both construction crews and motorists, and decreasing traffic tie-ups and traffic control. “Essentially what it does is speed up construction so there is a reduced impact on the traveling public,” Matsumoto says.

Precasting also improves quality and durability, he says, because the work is performed in a controlled environment. “Precast concrete is typically more durable than cast-in-place concrete. It’s built under controlled plant conditions so higher quality materials, construction techniques and inspections can be employed and there is less impact due to adverse weather conditions,” Matsumoto says.

Among the most appealing features of precast is speed of construction. It allows crews to get in, get out and stay out, making it safer for workers and the traveling public. On the Lake Ray Hubbard Bridge in Texas, for example, the use of precast bent caps reduced construction time by one week per bent cap on a 43-span structure, shortening the total construction time by 43 weeks.

The California research is an extension of Matsumoto’s doctoral work at the University of Texas at Austin which has been implemented in several bridges including the Lake Belton Bridge. That bridge recently won national recognition for its innovative use of precast concrete.

The concern over using pre-cast concrete in California stems from the state’s high level of seismic activity. California is the one of the few states that still relies primarily on site-cast concrete for the entire bridge including the bent cap. Although this approach ensures the bridge is well connected, Caltrans and other states are beginning to consider alternative construction approaches such as bent caps because of the need to accelerate bridge construction.

Matsumoto’s goal is to develop new design and construction guidelines for precast bent cap systems that provide cost-effective seismic resistance while accelerating construction. “What we don’t know is how bridge systems using precast bent caps will behave in a major seismic event,” he says.

“But I think the research will successfully develop new systems that will work,” Matsumoto says. And if it does, he adds, it will affect the way business is done today because California and other states need to replace bridges in congested urban environments by the thousands.

Matsumoto and his students previously conducted preliminary on-campus tests for one type of bent cap connection. The new research at Sacramento State will involve more complex beam-column connection tests based on developments of the research team and information obtained from a nationwide survey currently under way. Matsumoto’s crew will conduct four of the six beam-column tests. The other tests will take place at UC San Diego, where a large-scale bridge system test will also be performed.

— Laurie Hall