Graduate Thesis Or Dissertation

 

Studies of Earthquake Pounding Risk and of Above-Code Seismic Design Public Deposited

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https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/z029p494z
Abstract
  • This thesis tests three hypotheses: (1) Some US practice to determine the required separation distance to preclude pounding between neighboring buildings is overly conservative. (2) Pounding between buildings with aligned floors significantly contributes to collapse. (3) Above-code design of a common engineered commercial building type is cost effective in many though perhaps not all US locations, at least from a benefit-cost-analysis perspective.

    The first part of this thesis reexamines the required minimum permissible space between two adjacent buildings to preclude earthquake pounding. This part of the thesis employs and compares three analytical approaches to estimate the minimum safe distance conditioned on the occurrence of risk-targeted maximum considered earthquake (MCER) shaking. 1) First, safe separation distance between buildings is estimated using elastic spectral displacement response of adjacent buildings at the top of the shorter building, accounting for mode shape and the height difference. 2) ASCE 7-16’s equivalent lateral force procedure is also examined. 3) Finally, multiple linear elastic dynamic structural analyses of two adjacent buildings are performed, factoring drift estimates by ASCE 7-16’s Cd/R to approximate nonlinear response. To examine diverse, though not exhaustive, conditions, this thesis examines 3 combinations of shearwall and steel moment frame buildings; 5 building heights between 2 and 26 stories; fundamental periods of vibration vary between 0.2 sec and 2.8 sec; and 4 locations with degrees of seismicity in roughly equal increments corresponding to short-period mapped spectral acceleration response SMS from 0.8 to 3.0g.

    Part 2 repeats much of the analysis of part 1, but with an additional structural analysis procedure (nonlinear dynamic analysis) but with a narrower set of building types. As with part 1, this part evaluates the required minimum permissible space between two adjacent buildings to preclude earthquake pounding. Unlike part 1, this part develops a set of conversion factors to relate the separation distances calculated by any of the simpler methods (elastic spectral displacement, equivalent lateral force, and multiple linear elastic dynamic structural analyses) to multiple nonlinear dynamic structural analyses method. This part examines 3 combinations of special reinforced concrete moment frame buildings, SMF, and ordinary reinforced concrete moment frame buildings, 𝑂𝑀𝐹 (i.e. ductile and non-ductile reinforced concrete frame structures); 5 building heights between 2 and 20 stories for SMF; 4 building heights between 2 and 12 stories for 𝑂𝑀𝐹; two risk-targeted shaking levels (i.e. shaking of 2/3 𝑀𝐶𝐸𝑅 and 𝑀𝐶𝐸𝑅).

    While parts 1 and 2 address the estimation of safe separation distance, part 3 examines what happens when two buildings are not safely separated but have aligned floors. It examines how pounding affects (and either reduces or does not reduce) the collapse capacity of adjacent buildings. Its focus is limited to post-2000 reinforced concrete moment frame buildings with aligned floors and various separation gaps. This methodology includes applying the framework of performance-based earthquake engineering to assess seismic safety concerns of pounding. In addition to the analytic study, part 3 includes a limited empirical validation, using a photo survey of California building collapses in the last 5 decades to search for evidence of the effect of pounding on collapse.

    Part 4 examines a wholly different topic: is design of new buildings to exceed certain current seismic design criteria worth the added cost, in terms of reduction in the present value of future losses avoided? Does the answer vary by geographic location? This part employs standard benefit-cost analysis procedures, using a suite of buildings analyzed with FEMA P-58. The building suite is designed to reflect important variability within a building type using the Global Earthquake Model’s (GEM) analytical methodology. The buildings represent a common engineered type: a single-story reinforced concrete shearwall building used for commercial purposes. The suite is designed so that its most seismically salient features vary similarly to actual buildings observed in a survey. Part 4 complements another study, not documented here, that addressed the same question but using a risk analysis procedure closely related to Hazus, entitled Natural Hazard Mitigation Saves (MMC 2017). The present study avoids the structural analytical simplifications of the Hazus methodology, albeit at the cost of a much narrower set of buildings and locations.

    Each part includes a methodology, implements the methodology with a number of case studies, and presents results and conclusions. Parts 2 and 3 employ overlapping, though not identical, methods. They differ in the case study buildings so as to use available structural models.

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  • 2019
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  • 2020-02-13
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