Methods and case study for optimizing seismic life cycle cost of buildings

Structural engineers are tasked with the responsibility of designing economical structures that can safely resist earthquakes. Current building regulations are intended to protect against human casualties, but focus less on protecting against economic losses during seismic events. Therefore, this research formalized and tested methods to minimize seismic life cycle cost (SLCC), that considers both the lifetime damage cost from seismic events and construction or capital cost. There are three research objectives for this study. The first objective is to develop a new method to optimize the member sizing and beam-column connection types for steel frame structures that minimize capital cost (Chapter 2). To accomplish this, I built a Dimension Increasing Search (DIS) algorithm which assesses the geometric constraints of connection and safety and serviceability constraints. I compared the DIS algorithm against three existing optimization methods (genetic algorithm, ant colony search, harmony search) on three steel frames ranging in size from small to large. The results show that the DIS algorithm generates designs with the lowest capital cost and least computational effort among all optimizers when applied to mid-size and large-size frames. Thus, the DIS algorithm is found to be suitable for practical applications given its ability to handle problems of greater complexity that more closely mimic real-world situations. The second research objective is to develop an extended seismic life cycle cost (SLCC) model that includes the critical components of the capital cost and the lifetime damage cost (LDC) that need to be considered for seismic events (Chapter 3). This model extends the existing model by incorporating fabrication, erection, and demolition costs. The extended SLCC model is then compared against two other cost models: a model which only considers the capital cost and an existing simplified SLCC model. I compared the structural designs optimized for these two models for a case-study building, which is a 5-bay, 5-story office building located in San Francisco, CA. Applying the extended SLCC model produces a structural design with 13% lower SLCC than that of applying the capital cost only and 14% lower SLCC than that of applying the existing SLCC model. The differences between applying the extended SLCC model and the capital cost demonstrates the impact of including LDC in design objective on structural design. The difference between applying the extended and existing SLCC model indicates the potential significant impact of incorporating fabrication, erection, and demolition costs in the design objectives for structural design. The last research objective is to explore the impact of the façade system on a building's SLCC (Chapter 4). This involves adding a façade system as a passive vibration damper (PVD) to the structural design scope and applying the extended SLCC model established on Chapter 3. This façade system, a concept called "Smart Façade", improves the seismic structural response of the building, but the impact of such a system on a building's SLCC has not been studied. There are three components in this framework: (1) a structural analysis step that simplifies the system into a 2DOF model, (2) an SLCC estimator, and (3) a proposed bi-level surrogate optimizer. I then applied this approach onto the same 5-bay 5-story office building as in Chapter 3. This test case shows that the benefits of a Smart Façade depend on which floor the façade is attached to. When attached peripherally to each floor, the SLCC increases by 2.8%, while installation on only the top two floors reduces the SLCC. Lastly, I determined the performance of the bi-level surrogate optimizer by comparing it with two other methods: a simultaneous surrogate model and a genetic algorithm (GA). The results based on the case study show that, with the same number of iterations, the bi-level surrogate optimizer generates a solution with 10% less SLCC than that of the simultaneous surrogate model and 13% less SLCC than that of the GA. This thesis contributes a refined assessment for a building's SLCC and an initial study on the impact of a Smart Façade on a building's SLCC. These findings aim to further the potential uses of the extended SLCC model and Smart Façades in real-world settings. Future work should study the generality of the findings by testing them on different building types and sizes and for different structural designs and material selections. As the need for stronger yet more cost-effective buildings grows, it is likely that the extended SLCC model will be an increasingly important metric in the design for economical buildings

Advisor: Fischer Martin
Baker Jack W. 
Miranda Eduardo (Miranda Mijares)