Multi-table bridge test
Photo courtesy of Tongji University
Multi-table curved bridge test
Photo courtesy of University of Nevada - Reno
Biaxial table with structural actuator
Photo courtesy of Tongji University
Photo courtesy of Kajima Corporation
Innovative Shake Table System ConfigurationsSeismic simulation requirements are changing due to a variety of factors: these include the need to incorporate ever larger scale test articles to increase simulation fidelity, as well as demands for replicating the longer displacements and durations of recent earthquakes (Kobe 1995 and Tohoku 2011, respectively). MTS provides the expertise, advanced control techniques and extensive product portfolio that civil engineers and researchers need to meet these challenges. The following case studies represent a cross-section of how MTS is helping address these issues with innovative solutions, from multi-table configurations to additional actuators to table-on-table designs.
Multi-table configurations for long-span bridges
Tongji University is at the forefront of shake table testing models of long-span bridges. As with other large structures, these tests involve relatively small scale models that provide less than optimal results. This challenge was particularly daunting for models of Jiangsu’s Taizhou Bridge, which spans 62 km.
To complete seismic testing for large-scale models, including a replica of the Taizhou Bridge, Tongji University worked with MTS to commission a one-of-a-kind shaking table solution that supports models weighing up to 200 tons. Housed in the largest multi-table seismic test facility in the world, it features two 70-ton shake tables and two 30-ton shake tables that can be arranged in multiple configurations anywhere within two adjacent trenches.
Most important, the motion of all four tables can be synchronized to replicate seismic waves as if they were one very large platform, or the tables can be operated independently. Using a high-speed, real-time, shared memory application, the solution allows all tables to “see” data from all other tables. All of the data is integrated into a master controller that interprets the commands and feedback to keep everything in synch. This gives the lab more extensive control over the entire testing environment and makes it feasible to use a 1:40 scale model that is 65 meters long—instead of one that is only three meters long.
Flexible positioning for testing curved bridges
Due to their irregular shape, curved bridges have unique requirements for large-scale seismic simulations. Traditional multi-table test systems installed in trenches have limited positioning flexibility, which makes it difficult to accommodate these complex specimens. This is why the University of Nevada, Reno NEES Equipment Site (UNR-NEES) began to investigate seismic impact using a 2/5-scale model of a three-span curved bridge, measuring 44.1 meters (145 feet) long with a 24.4-meter (80-foot) radius at the model’s centerline. It was the biggest bridge test the lab had ever attempted.
The UNR-NEES facility includes three biaxial shake tables, a 6DOF shake table and a custom hydrostatic bearing designed by MTS that allows the tables to be installed directly on the strong floor instead of in a trench.
All four tables were used for the curved bridge seismic simulations, including the 6DOF table set in biaxial mode. This arrayed, portable configuration allowed UNR-NEES to test the curved-bridge scale model in unprecedented ways. Tests included column design with and without conventional columns; abutment design with and without backfill; seismic isolation with and without response modification; and live load, with and without trucks positioned on the superstructure surface. The resulting data helped establish new industry design guidelines for curved-span bridges.
Adding a structural actuator to large-scale hybrid simulation
Large, heavy specimens often make it impractical to conduct shake table tests with full-scale civil structures in the lab. One innovative approach to this problem is to combine shake table tests with structural actuators of large-scale, partial physical structures and employ hybrid simulation techniques to simulate the remainder of the structure and/or mass. Although the concept is not new, it had only been pursued at scales too small for meaningful seismic simulation on very large civil structures.
Working with Tongji University and the University of California at Berkeley, MTS helped prove the concept could work on a significantly larger scale. MTS was brought to the project to address the control challenges associated with integrating and synchronizing a dynamic structural actuator with a biaxial shake table and real-time hybrid simulation system. To do this, MTS employed new system tuning techniques and control calculations.
To test the solution, the team set up a seismic test of a bridge bearing component that featured a 1:4 scale bridge section with a greatly reduced deck mass mounted on a large, biaxial seismic simulator that was attached to a dynamic structural actuator mounted to an adjacent strong wall. This physical system was driven by a real-time hybrid simulation system. As the simulation played out, results proved the system had effectively employed the extra actuator to represent the missing bridge deck mass, resulting in an accurate seismic simulation of the full structure. This approach gives researchers a powerful new tool for performing high-fidelity seismic simulation on larger structures, yielding far more realistic data.
Table-on-table design to increase stroke length and power
Kajima Corporation, a major Japanese general contractor, worked with MTS to upgrade its shake table lab. The goal was to increase the stroke and power needed to test the earthquake resistance of skyscrapers and other important structures, such as nuclear power plants. The most important characteristics were high accuracy control, increased payload and longer stroke capacity to reproduce long-period earthquakes.
MTS provided a high-performance, three-dimensional shake table configuration, consisting of a two-layer system: a lower main shake table that reproduces large seismic motions and an upper shake table that can be mounted on the main table, which provides the stroke capacity to replicate long-period motions.
The resulting table-on-table configuration is the world’s highest performing large-scale privately owned shake table system. It can reproduce nearly every major recorded earthquake. Its long-period motion capabilities help reproduce and examine large oscillations of skyscrapers located far from the quake’s seismic center. Kajima has used the solution to improve earthquake countermeasures, such as earthquake proofing, vibration control and seismic isolation.
Seismic testing expertise
MTS has the experience and technology to help civil engineers and researchers explore new testing opportunities. Contact MTS today to learn more about our standard and custom seismic simulation solutions.
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>> TONGJI UNIVERSITY CASE STUDY #1
>> TONGJI UNIVERSITY CASE STUDY #2
>> UNIVERSITY OF NEVADA, RENO - NEES CASE STUDY
>> KAJIMA CONSTRUCTION CO., LTD. CASE STUDY
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