Experimental and numerical investigation of the seismic performance of an A-frame–truss–column hybrid supporting structure

A hybrid structural system designed for use in large thermal power plants in China to house air-cooled condenser systems is investigated. The hybrid structure consists of a series of metal A-frames resting on a steel space truss supported by an array of reinforced concrete columns. To gain a better understanding of this structural system, a one-eighth (1:8) scale test structure modeled after a prototype structure was constructed and tested. The test structure was subjected to both free vibration and forced excitation tests with the following objectives: (1) determining its modal properties and seismic response characteristics, (2) gaining insight into its response and most probable failure modes under dynamic excitations, (3) obtaining some useful experimental data for future research, and (4) providing important data to complement the Chinese seismic design code as well as to guide the design of this type of structure in practical engineering applications. The free vibration tests were carried out by inducing an initial displacement to the structure and measuring its natural frequencies and mode shapes. The forced excitation tests consist of a series of quasi-static and pseudo-dynamic tests. For the quasi-static tests, 10 reciprocating displacement excitations with peaks ranging from 6 to 100 mm were used, and for the pseudo-dynamic tests, six ground motions with scaled maximum accelerations ranging from 50 to 800 cm/s² were employed. Based on the results of these tests, modal properties of the hybrid structure such as natural frequencies, mode shapes, and equivalent damping ratios, as well as some seismic response characteristics such as seismic shears, accelerations, deformations, interstory drifts, roof drifts, and hold-down forces were determined and presented. In addition, nonlinear analysis of the test and prototype structures was conducted using the finite element software ANSYS and compared with the test results. Detailed damage inspection was performed, and important findings were summarized.