## 3 Overview of Pseudo-Dynamic Testing and Result Analysis
### Pseudo-Dynamic Testing System and Test Methods  
The impact of an earthquake on a structure depends on the ground acceleration and the type, weight, and stiffness of the structure. The horizontal earthquake acceleration induces shear stress on the vertical members of the structure, which support the structure. This then subjects the structure to relative transverse motion. In general, when an earthquake occurs, many structures, even after large deformation, support themselves without structural collapse. In the process, however, they are likely to absorb some energy through non-elastic behavior. More specifically, while the seismic load is being transmitted to a structure, some materials in the structural system reach their yield points, thereby causing localized plastic deformation to occur. The resultant large amount of earthquake input energy then starts to be absorbed by the structure through non-elastic behavior. It is, however, still very difficult or impossible to theoretically assess such non-elastic behavioral characteristics even though a wide range of relevant computing programs have been developed. For that reason, the non-elastic seismic response of a structure has been mostly experimentally studied with various test methods, including shaking table tests, quasi-static tests, and pseudo-dynamic tests. The shaking table test method is considered to be the most effective way to assess the seismic behavior of structures, but the maximum weight and size of specimens are limited by the size and capacity of the applied shaking table. Thus, in most cases, reduced-size models are used, and this may lead to issues arising from the discrepancy between the model and the actual structure. In an attempt to overcome this limitation, quasi-static tests have been widely used to assess the non-elastic behavior of full-size structures, in which the test conditions are controlled by the displacement or load. Meanwhile, the pseudo-dynamic test method was developed to conduct realistic experimental tests on full-scale structures subjected to earthquake ground motions [31]. This test uses an online computer and associated test instrumentation to monitor and control a structure, such that displacement thereof closely resembles the consequences of real seismic excitation. The pseudo-dynamic test is as realistic as shaking table-based testing, where discretization of the model is feasible; its advantages over shaking tables include (a) versatility, where it allows for detailed observation of the specimen during the test, (b) the ability to test full- and large-scale models, thus circumventing the problem of dynamic similitude, (c) lack of requirement for physical structures, because the method uses a numerical model, (d) greatly reduced equipment, installation, and operation costs, (e) circumventing the problems associated with the interactions of a shaking table with heavy specimens, and (f) improved actuator control and data acquisition reliability due to the relatively slow rate of loading. In principle, the test can be performed in real time; however, physical limitations of the instrumentation dictate that the test must be conducted step-by-step, i.e., pseudo-dynamically. Shaking table tests may be more appropriate in cases where strain rate effects are significant and/or in distributed parameter systems. Experimental measurements of restoring forces are performed during the test. These measured forces are then fed into the computer, together with a set of mathematical equations for inertial response characteristics, to determine the structural displacement that would occur as a consequence of a given ground acceleration. This procedure is superior to quasi-static testing because non-linear structural characteristics are based on instantaneous experimental feedback rather than hypothetical mathematical models.