General Design Framework
Figure 1. General Value Based Design Framework
The workflow of Endurance Time Method, follows the general framework for Value Based Seismic Design as shown in Figure 1. The building model and environmental conditions are required inputs for Endurance Time analysis. Building model is ideally a BIM model, but simplified structural dynamics models are usually adequate. Environmental conditions translate into seismic hazard in ET analysis. Structural response is calculated using ET method considering input parameters from building model and seismic hazard. Based on the results of ET analysis, various objectives, such as design code compliance, seismic performance, life cycle cost, or any other objective can be evaluated. Construction costs should also be evaluated based on building model specifications. In general, maintenance, demolition, and similar costs can also be derived from the building model specifications. Based on the weights given to various design objectives and priorities, the Value of the current design can be evaluated. If design improvement seems to be possible, the building model can be updated and the process can be repeated until a design with optimal value is achieved.
A more detailed design workflow using the ET method is described in Figure 2. The first step is the preparation of an appropriate dynamic model of the dynamic system. Conventional codified methods can be used to produce a design. The next step is to select a set of ET excitation functions (ETEFs) compatible with design objectives. If compatible ETEFs are not available, a standard scaling procedure can be adopted to match acceleration response from 0.2T to 1.5T (or other appropriate IM) of ETEFs at a target time to required design spectra. In the next step, the structure is subjected to the ETEF and a response history analysis is carried out. Then, ET curves based on significant EDPs are sketched and compared with the allowable limits at relevant target times. If the performance of the structure is acceptable, and the optimality criteria is satisfied, the design can be considered as final. Otherwise, the design is modified and the analysis cycle is repeated until a satisfactory design is achieved.
Figure 2. General design workflow