Prototype Frame

The prototype frame is idealized as an interconnected set of columns and beams contained in the same vertical plane, interacting to resist the inertia forces induced by the seismic event. No gravitational load effects are considered in the evaluation of the state of strain and stress in the material. The purpose of this assumption is to simplify the mathematical model and to avoid the difficulty in establishing the most representative initial state of stress and strain at the instant when the seismic event starts.

In general, the geometric and mechanical properties of the two frames in the X direction can be different to the two frames in the Y direction, but the two frames in the same direction have identical properties, except for their location. Dissertation Plans

Frame Configuration

The prototype frame is defined by two continuous lines of columns and one beam at each story level, as shown in figure 2. The columns at one story level have identical geometric and mechanical properties, but they can be different to the pair of columns at the adjacent levels. The columns at the fist level are assumed to be fixed at their lower end, and have a continuous moment and shear connection with the beam located at their top. This simple structural system was chosen to facilitate the parametric study.

Figure 2: Prototype Frame Configuration

The interstory heights have different values. The columns at each story level have identical properties, but the columns or beams at different levels can have different properties. Dissertation Plans

Plastic Mechanisms Developed by a Frame

As an extension of the criteria adopted for one story frames, the multi story prototype frame is dimensioned with the intention of enforcing a strong column-weak beam (SCWB) plastic mechanism. Plastic hinges (PH) are used to model the plastic deformations that could be developed at some beams or column ends. The occurrence of these PH’s providing the global non linear behavior of the frame.

For one story frames, it is possible to enforce the developing of a SCWB plastic mechanism, as imposed by the designer, but for multistory frames it is not possible to attain this mechanism for all the possible lateral displacement patterns, which could be generated during an arbitrary seismic event. Therefore, a different approach must be taken to enforce the SCWB mechanism.

The approach used hereafter is a trial and error procedure to dimension the frame and get the desired type of plastic mechanism. Dissertation Plans