The reliability of capacity-designed components in seismic resistant systems [electronic resource]

Capacity design principles are employed in structural design codes to help ensure ductile response and energy dissipation in seismic resisting systems. In the event of an earthquake, so called "deformation-controlled" components are expected to yield and sustain large inelastic deformations such that they can absorb the earthquake's energy and soften the response of the structure. To ensure that this desired behavior is achieved, the required design strength of other components (capacity-designed components) within the structure is to exceed the strength capacity of the deformation-controlled components. While the basic concept of capacity design is straightforward, capacity design provisions have tended to be established in an ad-hoc manner. This has led to concerns as to whether the current seismic provisions are over-conservative, leading to uneconomical designs, or un-conservative, potentially creating unsafe designs. The objectives of this research are to contribute to the understanding of the reliability of capacity-designed components in seismic resistant systems and to develop a reliability-based methodology for establishing the required design strengths of capacity-designed components in seismic resistant systems. Topics that are explored in this research are: (1) quantifying the expected demand on capacity-designed components, (2) assessing the influence of the structural response modification factor, R-factor, and member overstrength on the reliability of capacity-designed components, (3) assessing the impact of the seismic hazard curve on the reliability of capacity-designed components and (4) assess the consequences of capacity-designed components' failure on the overall system reliability. Dynamic analyses of 1-story, 6-story and 16-story Special Concentrically Braced Frames are conducted and the reliability of the brace connections and columns investigated. The results demonstrate that the initiation of connection failures is associated with the initiation of brace yielding. As structural building systems are typically designed for only a fraction of the estimated elastic forces that would develop under extreme earthquake ground motions, failure of brace connections can occur at low ground motion intensities with high frequences of exceedance. Based on the analysis results, the ground motion intensity, or spectral acceleration at which braces yield, Say, exp, can be related to the R-factor and member overstrength. Dynamic analyses where brace connection failures are included in the simulations show that the probability of collapse given connection failure depends on the ground motion intensity and at spectral accelerations close to the MCE demand, the probability of collapse due to connection failure was 25%-30% for the cases studied. The demand on columns in braced frames is very system, height and configuration dependent The braced frame analysis results demonstrate that unless there are only a couple of braces exerting demand on columns, capacity design principles overestimate the expected demand on them and the difference increases as the number of stories increases. This is caused by the low likelihood of simultaneous yielding of all braces, different member overstrength between stories and further complicated in the case of braced frames with the differences in brace tension and compression strength capacities.The proposed reliability framework considers the main factors believed to influence the reliability of capacity-designed components and the end result is a framework for establishing required component design strength that provides risk consistency between different seismic resistant systems and seismic areas. The factors considered are the system R-factors and member overstrengths, site seismic hazard curves, assumed influence of failure of capacity-designed components on system collapse behavior, and the tolerable increased probability of frame collapse due to the failure of capacity-designed components.

Advisor: Deierlein Gregory G. (Gregory Gerard)
Baker Jack W. advisor. Thesis advisor
Krawinkler Helmut advisor. Thesis advisor