## 11 Optimal Design Strategies for Earthquake-Resistant Composite Buildings  
### Optimal Design Strategies for Earthquake-Resistant Composite Buildings: State-of-the-Art  
Achieving the optimal design of earthquake-resistant composite buildings involves a complex interplay of structural engineering principles, material science, and seismic analysis. Strategies for designing cost-effective steel-concrete composite structures aim to strike a balance between safety, performance, and economic efficiency. These strategies typically focus on optimizing the distribution of steel and concrete elements to maximize strength and ductility while minimizing material usage. Advanced analysis techniques, including nonlinear dynamic analysis and performance-based design, are often utilized to evaluate and enhance the seismic response of composite buildings. The ultimate goal is to create structures that can withstand earthquake forces while maintaining occupant safety and minimizing structural damage, all within reasonable cost constraints. [PERSON] et al. (2020) [168] compared the cost-effectiveness of three seismic retrofit methods for framed structures with composite columns that did not meet building codes. The first two methods involved strengthening individual composite columns with reinforced concrete jackets or steel cages. The third method upgraded the building frame by adding steel bracings. A specialized optimization procedure was used to minimize retrofit material costs while meeting the design requirements. Thirty cases of under-designed composite buildings were analyzed, revealing the most cost-effective retrofit approach for different conditions. Similarly, [PERSON] and [PERSON] (2020) [169] examined the cost-effectiveness of seismic buildings with pure steel or steel-concrete columns using a structural optimization process for unbiased comparison. An Evolution Strategies algorithm minimized material cost while meeting safety provisions from Eurocodes 4 and 3 and considering seismic behavior. The results from 154 optimization runs suggested the benefits of using concrete to partially replace steel in column designs for earthquake-resistant structures. Moreover, [PERSON] and [PERSON] (2016) [170] focused on optimizing the design of earthquake-resistant multi-story composite buildings with steel-concrete columns. The composite columns consist of steel members fully encased in concrete, along with steel beams and optional steel bracings. The goal was to minimize materials costs while meeting design code constraints, including Eurocodes. The optimization procedure included constraints on member capacity, inter-story drifts, and top-story displacements, as well as limits on the fundamental period. The Evolution Strategies algorithm was used to solve the optimization problem and was linked with structural analysis software for evaluation purposes. [PERSON] and [PERSON] (2023) [171] introduced a practical method for life-cycle cost analysis for composite structures, combining the economic loss rate with probabilistic seismic demand modeling. A framework using a multi-objective cuckoo search algorithm was proposed for seismic design optimization. An eight-story composite frame prototype was used to compare design alternatives. The over-strength factor was identified as critical for construction, seismic damage, and life-cycle costs. Improved fiber models were developed to evaluate spatial composite effect on designs using the OpenSees software ([[https://opensees.berkeley.edu/](https://opensees.berkeley.edu/)]([https://opensees.berkeley.edu/](https://opensees.berkeley.edu/))). It was found that certain design parameters, like over-strength factor and flexibility, significantly affected costs. Moreover, [PERSON] et al. (2016) [172] developed a seismic optimization framework for composite structures through an extensive parametric study of steel-concrete composite moment-resisting frames with steel I-beams and CFT columns.