Herrera, Ricles, and Sause 2008

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The behavior and seismic performance of a composite moment resisting frame was evaluated. A four-story prototype building was designed using a performance-based methodology and a scale model of the frame was tested using a hybrid pseudo-dynamic test method. The test structure was a two bay three-fifths scale frame with rectangular CFT columns, wide flange beams, and split tee moment connections.

Analytical Study

The frame was modeled using component models developed by previous researchers (CFT distributed plasticity, wide flange beam, and connection) in addition to a panel zone model created for this research. Before the experimental tests, the prototype structure was analyzed to assess its performance under the various seismic hazard levels. After the experimental tests, to test the performance of the analytical model, the experiments were recreated in the analytical model. An overall good agreement was found between the experimental and analytical results.

Experimental Study, Results, and Discussion

The prototype building was six bays by six bays with four stories and a basement. The lateral resistance system consisted of two four bay moment resisting frames in the perimeter of the building in either direction. The test structure was a three-fifths scale model of two of the bays of one of the moment resisting frames. The square steel tubes for the columns had a side length of 12 in., a thickness of 0.35 in., and a yield strength of 81 ksi. The concrete was measured to have a compressive strength of 9.8 ksi. The beams were A992 wide flange beams with a nominal yield strength of 50 ksi. Split-tee connections were used at all beam-to-column joints. The concrete slabs were excluded from the test structure to facilitate easier measurement of the internal forces in the beams.

The physical model was coupled with an analytical leaning column which represented a portion of the interior gravity frame. Loads were applied to the structure with actuators at each of the four floors. The load from the actuator was distributed to both bays of the test frame with a loading beam. The loading beams also simulated the restraint imposed by the floor slab.

Using the pseudo-dynamic hybrid method, a series of four tests were performed. The test corresponded to different seismic hazard levels. First, the frame was subjected to a frequently occurring earthquake. The maximum roof displacement was measured as 0.6% of the building height and the structure remained primarily elastic. Second, the frame was subjected to a design basis earthquake. The maximum roof displacement was measured as 3.0% of the building height and the frame experienced inelastic deformation but no significant strength degradation. After this test the frame was straightened to eliminate the residual drift. Third, the frame was subjected to a maximum considered earthquake. The maximum roof displacement was measured as 3.7% of the building height. Plastic hinges formed in the beams and a crack developed at the bottom of the first story middle column, resulting in a drop in shear capacity. Lastly, the frame was subjected to a second design basis earthquake, representing an aftershock. The maximum roof displacement was measured as 3.3% of the building height. The crack from the previous test propagated and another crack was formed, however the frame did not collapse.

References

Herrera, R., Ricles, J., and Sause, R. (2006). “Experimental Study of a Large-Scale Composite MRF System with CFT Columns under Seismic Loading,” Proceedings of the 8th U.S. National Conference on Earthquake Engineering, San Francisco, California, 18-22 April 2006, EERI, Oakland, California.

Herrera, R. A., Ricles, J. M., and Sause, R. (2008). “Seismic Performance Evaluation of a Large-Scale Composite MRF Using Pseudodynamic Testing.” Journal of Structural Engineering, Vol. 134, No. 2, pp. 279-288.