Optimization and simplification of performance-based seismic design for ladder and outrigger systems

The implementation of Performance-Based Seismic Design (PBSD) for assessing the performance of high-rise structures necessitates the sustainable evolution of the approach and the enhancement of its execution to achieve an effective ultimate design. The innovative PBSD methodologies are initiated by incorporating optimization and simplification strategies during the preliminary design phase, which facilitates the expeditious acquisition of an optimal initial quantity of materials essential for formulating models of ladder and outrigger systems. Subsequently, a nonlinear time history analysis is implemented using Perform-3D and ETABS software to assess the proximity of the primary design to the ultimate design and to evaluate the effectiveness of both systems in scenarios of various seismic occurrences. Under each of the three performance levels-immediate occupancy (IO), life safety (LS), and collapse prevention (CP)-the global and component responses are analyzed. The implementation of optimizing and simplifying methodologies during the initial design phase has significantly reduced the amount of effort required to generate and prepare an optimum initial design for ladder and outrigger structures. The results obtained from the nonlinear time history analysis demonstrate that the ladder system, in comparison with the outrigger system, leads to a significant decrease of 37.29 % in lateral displacement and 15 % in base shear as part of the overall structural response. The examination of the acceptance criteria for individual components, however, confirms that this system amplifies the dispersion of damage in plastic within the elements in the outer design while simultaneously reducing it within the internal elements. From a broader perspective, the primary design converges towards the ultimate design through diverse ratios. This is evident in percentages ranging from 60 to 80 % within the ladder system and 60-90 % within the outrigger system across distinct components. Therefore, this approach can be utilized to optimize the functionality of the outrigger system and enhance the performance of the ladder system. The focus of this investigation is primarily on an efficient original design that progressively aligns with the ultimate design, thereby reducing the number of iterations in PBSD procedures. This limitation highlights the critical need for further research efforts, essential for both enhancing and broadening the applicability of these procedural methodologies.