Deformation Problems Of Reinforced Concrete Structures Subjected To Gravitational And Seismic Type Loading

Author : Elham Moore
Publisher :
ISBN 13 :
Total Pages : 542 pages
Book Rating : 4.:/5 (129 download)

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Download or read book Experimental Study and Retrofit of a Non-Ductile Concrete Moment Frame Building Subjected to Biaxial Quasi-Static Seismic Loading written by Elham Moore and published by . This book was released on 2021 with total page 542 pages. Available in PDF, EPUB and Kindle. Book excerpt: ABSTRACT OF THE DISSERTATION Experimental Study of a Non-Ductile Concrete Moment Frame Building Subjected to Biaxial Quasi-Static Seismic Loading by Elham MooreDoctor of Philosophy in Civil Engineering University of California, Los Angeles, 2021 Professor John Wright Wallace, Chair The ability of reinforced concrete (RC) columns to continue to deform with reduced capacity depends on the ability of the floor system to redistribute some of the axial load from heavily damaged element to adjacent members to prevent the collapse of the structure when that happens. Physical testing of columns, although does not fully capture the behavior of the building as a system, is the closest approach to simulate behavior of columns that undergo high constant or varying axial forces. That is by choosing boundary conditions that are representative of actual conditions, as accurately as possible. However, physical testing of a building subassembly is a more powerful tool to provide realistic information on the performance level of existing buildings under seismic loads, as well as to better demonstrate the governing failure modes of the system working together, rather than evaluating members individually. Two large-scale beam-column-slab subassemblies were tested under biaxial quasi-static, reversed cyclic loading are discussed in this report. The test specimens are replicas of elements from a non-ductile concrete moment frame building located on the UCLA campus, the Franz Tower (currently named the Pritzker Hall). The reinforced concrete building originally constructed in the late 60s consists of six levels with closely spaced perimeter columns supported on a transfer girder, with two open lower levels supported on a widely spaced column grid. The lateral force resisting system at the upper six levels consists of trapezoidal columns spaced at 4 ft. (1219 mm) on center along the perimeter of the structure, with trapezoidal beams spanning between the columns. Traditional retrofit techniques in accordance with the governing building codes and the University of California Seismic Performance Rating (UCSPC), suggested a high cost retrofit scheme with significant disruption to the architecture of the building. This is believed to be attributed to these main reasons: 1- The governing standard for seismic evaluation and rehabilitation of existing buildings, ASCE/SEI 41-13 Seismic Evaluation and Retrofit of Existing Buildings, herein referred to as ASCE 41-13, was conservative in predicting deformation capacity of building components when subjected to lateral (seismic) loading, especially when the building components fell under the non-conforming criteria, hence underestimating their performance. 2- The cross sections of the frame beams and columns were not rectangular which is the common type of cross section for typical moment frames. As a result, there was an inherent ambiguity in the capability of the non-linear modeling parameter offered by ASCE 41-13 to predict the performance achieved by the moment frames in the Franz Tower. 3- Another uncommon characteristic of this building was the aspect ratio of the moment frames (bay width/story height), which is less than 0.3 (with the beam span of 4 ft. (1219 mm) and column height of about 12. ft 9 in. (3886 mm), while aspect ratios of more than or equal to 1 are more common. Therefore, the beams were rigid and would not be able to sustain a double curvature deformation, as common in the moment frame beams. 4- The repetitive frame system around the perimeter of the building provided a high level of redundancy that was not observed in typical buildings, nor in the test data used to derive the ASCE 41-13 modeling parameters. To evaluate all the issues mentioned above, a detailed physical testing program was designed with an emphasis on obtaining the overall force-deformation backbone curve for the subassembly. In order to use the data obtained from the physical testing, it was imperative to recreate the experimental backbone curve in Perform-3D, by making necessary modifications to the modeling parameters of the building components. These modifications were based on the observed damage at each drift level, and at each building component, and included the plastic deformation capacity of the columns, flexural residual strength of the columns, and shear capacity of the beams. Those modifications were later applied to the Perform-3D model of the actual building in an attempt to assess its actual performance under seismic loading. This study presents the findings of the two biaxial tests conducted on two building subassemblies and reveals that the test specimens sustained damages beyond the Collapse Prevention and Life-Safety limits of ASCE 41-13. The specimens did not lose their gravity load-carrying capacity during the test (even after exceeding 2.5% lateral drift ratio), which also provided for a higher Expected Seismic Level Performance per UCSPR, performance rating III (seismic safety policy compliant). Finally, this study provides a holistic overview on the proposed retrofit program that includes downtime and repair costs in case of a major ground shaking, utilizing the FEMA P-58, Seismic Performance Assessment of Buildings, Methodology which was developed by the Applied Technology Council (ATC) and funded by FEMA. (ATC, 2020) This study includes building assessments per the Seismic Performance Prediction Program (SP3), including analyses per the governing standards, as well as analyses per the experimental test observations. Downtime and repair cost are of great importance to the public while not directly considered in ASCE 41-13 and other local building documents. Hence, the SP3 Risk Model Engine, was used to calculate the mean loss and time to regain function. Implementation of test data in the SP3 analysis input showed not only the retrofit program enhanced building performance in terms of life safety of the occupants, but it also showed lower expected loss, as well as significantly lower downtime in comparison to prescriptive retrofit methods.