Research Highlight - James Wight and Gustavo Parra-Montesinos

Professors in the Civil and Environmental Engineering Department at the University of Michigan simulated the effects of a large earthquake in the Structural Engineering Laboratory to test their new technique for constructing high-rise reinforced concrete buildings. Their proposed design procedure for coupling beams in a core-wall structural system passed the test, withstanding more lateral deformation than an earthquake would typically demand.

The engineers used steel fiber-reinforced concrete to develop a better kind of coupling beam that requires less reinforcement and is easier to construct. Coupling beams connect the shear walls of high rises around openings such as those for doorways, windows, and elevator shafts.

"We simulated an earthquake that is beyond the range of the maximum credible earthquake and our test was very successful. Our fiber-reinforced concrete beams behaved as well as we expected they would, which is significantly better than the coupling beams in use today," said James Wight, the Frank E. Richart Jr. Collegiate Professor in the U-M Department of Civil and Environmental Engineering. Working with Professor Wight on this project are Gustavo Parra-Montesinos, an Associate Professor, and Remy Lequesne, a doctoral student in the Department of Civil and Environmental Engineering.

Today, coupling beams are difficult to install and require intricate reinforcing bar configurations. The University of Michigan engineers created a simpler reinforcement configuration that is used in conjunction with a flowable, steel fiber-reinforced concrete. "We took quite a bit of the cumbersome reinforcement out of the design and replaced it with steel fibers that can be added to the concrete while it's being mixed," Professor Parra-Montesinos said. "Builders can use this fiber-reinforced concrete to construct coupling beams that do not require as much reinforcement." The fiber-reinforced concrete has other benefits as well. "The cracks that do occur are narrower because the fibers hold them together," Professor Parra-Montesinos said. The fibers are about 30 mm long and have a diameter of about 0.4 mm.

Professors Wight and Parra-Montesinos envision that their coupling beams could be precast either on-site or at a precasting yard, and then delivered to the job-site. Currently, contractors construct the walls and beams, including all the reinforcement, member by member as they build skyscrapers.

The U-M researchers performed their test in December on a 40-percent replica of a 4-story coupled-wall system that was constructed under the supervision of Remy Lequesne in the Structural Engineering Laboratory. They applied a peak lateral load of 300,000 pounds to the coupled wall system, pushing and pulling it with hydraulic actuators.

To quantify the results, they measured strains in the concrete and reinforcing bars at several locations in the coupling beams and the adjacent shear walls. They also measured the building's drift, which is the lateral displacement at the top of the building expressed as a percentage of the height of the building. During a large earthquake, a coupled-wall building might sustain a drift of 1 to 2 percent. The U-M structure easily withstood a drift of 3 percent.

The new coupling beams could provide an easier, cheaper, and more ductile way to provide lateral strength and stiffness to buildings in earthquake-prone areas. The researchers are now working with a structural design firm to install the beams in some high rises soon to be under construction on the west coast.

This research is funded by the National Science Foundation under the Network for Earthquake Engineering Simulation Program.