Advances in Structural Engineering Research
Full Session with Abstracts
337103-11 - Performance-Based Assessment and Retrofit of Nonductile Existing Reinforced Concrete Structures
Friday, April 20
1:30 PM - 3:00 PM
How does this session impact and improve the Structural Engineering Profession?
The session focuses on advancements in nonlinear analysis methods for performance based earthquake engineering (PBEE). The session involves accurate modeling of all structural components, nonlinear dynamic analysis, and development of structural fragilities through a performance based approach. These methodologies can easily and directly used from the structural engineering profession in order to have optimization procedures about the design or the retrofit of the buildings.
In different high seismic regions around the world, post-earthquake reconnaissance has shown that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames. Therefore, for this type of structures, it is necessary to accurately model materials and members to capture the flexure, shear and flexure-shear failure modes in members and the potential collapse of the structure. In this paper, alternative retrofit methods are evaluated for these older frame buildings using a probability-based framework, based on nonlinear dynamic Cloud Analysis, in order to assess the structural performance and safety at each chosen performance level. As a case study, the longitudinal and the transversal frames of an existing building are modeled, including the effect of flexural-shear-axial load interaction and the bar slip deformational component in order to be able to capture column shear and axial failures. The critical demand to capacity ratio, corresponding to the component or mechanism that leads the structure closest to the onset of limit state (e.g., near collapse), is adopted as the structural response parameter. This structural response parameter, that is equal to unity at the onset of limit state, can encompass both ductile and fragile failure mechanisms. It can also register a possible shift in the governing failure mechanism with increasing intensity. Finally, the estimates of expected life cycle cost are compared for the retrofit methods considered in this research.
Is this topic of regional, national or international interest?
The topic of the work has an international interest.
Who is the target audience?
The proposed work can be presented both to the professional and to the academic audiences in the context of structural engineering. In fact, the whole performance-based procedure can be formalized as an optimization procedure that minimizes/maximizes a utility function (e.g., economic losses, functional benefits, etc.) and satisfies code-based (or desirable) safety constraints. This type a procedure can be useful both as research point and as instrumentation for professional users.
What will the audience take away from your presentation?
The paper focuses on a critical process needed to assess and retrofit an existing building. The presented methodology involves accurate modeling of all structural components, nonlinear dynamic analysis, and development and assessment of structural fragilities through a performance based approach. At the end of this process, through the application of the cut-sets method and the DCFD method, a direct comparison is possible between a demand and a capacity value, which is easily and directly applicable for assessment of different retrofit methods. So, the procedure can be considered as a debate point for researchers and can be easily used in some practical applications.