Seismic Analysis of Multi-Story Unreinforced Masonry Buildings with Flexible Diaphragms PDF Download
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Author: Juan Aleman Hernandez
Publisher:
ISBN:
Category :
Languages : en
Pages : 374
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Book Description
Studies regarding the regional seismicity of New York City (NYC) indicate that earthquakes of magnitude greater than or equal to 5 have a 20-40% probability of occurring in a 50 year period. Considering that more than 50% of the large population of the region (19.1 million) is living in an area where 80% of the buildings are of old Unreinforced Masonry (URM) construction, it is likely that even a moderate earthquake could have critical consequences on public safety and the economy of this area. The main goal of this study was to develop simulation capabilities supported by experimental testing to evaluate the seismic performance of typical unreinforced masonry buildings with flexible diaphragms located in NYC. Simplified nonlinear macro-models of wood diaphragms, masonry walls and floor-to-wall connections were developed and validated individually using data from past experiments. The models are implemented in both commercial and research software to demonstrate their practical use. In particular, a new approach for modeling flexible diaphragms is proposed that is shown to provide similar accuracy to detailed finite element models at a fraction of the computation cost. The models developed were also validated as at the system level, through shake table testing of two full-scale specimens conducted as part of this study. The specimens were designed and constructed to represent the expected loading conditions of a central portion of a one-story URM building and constructed of materials representative of older masonry construction. The tests provide a unique data set that captures the interaction between flexible floors, out-of-plane walls and their connections at, full scale.The validated macro-models can be used for performance-based seismic assessment of unreinforced masonry building in NYC and elsewhere. To demonstrate their use, preliminary studies were conducted to develop out-of-plane URM fragility curves, a building-specific collapse fragility function, and estimate the seismic response of the building when subjected to a ground shaking intensity similar to the 2011 Virginia Earthquake. The probabilistic framework and new performance definitions provided by the FEMA P58 project were used to conduct a performance-based seismic assessment for an archetype unreinforced masonry building in New York City with an emphasis on out-of-plane behavior. This preliminary study served to demonstrate the applicability of the proposed models for applications in performance-based design.
Author: Juan Aleman Hernandez
Publisher:
ISBN:
Category :
Languages : en
Pages : 374
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Book Description
Studies regarding the regional seismicity of New York City (NYC) indicate that earthquakes of magnitude greater than or equal to 5 have a 20-40% probability of occurring in a 50 year period. Considering that more than 50% of the large population of the region (19.1 million) is living in an area where 80% of the buildings are of old Unreinforced Masonry (URM) construction, it is likely that even a moderate earthquake could have critical consequences on public safety and the economy of this area. The main goal of this study was to develop simulation capabilities supported by experimental testing to evaluate the seismic performance of typical unreinforced masonry buildings with flexible diaphragms located in NYC. Simplified nonlinear macro-models of wood diaphragms, masonry walls and floor-to-wall connections were developed and validated individually using data from past experiments. The models are implemented in both commercial and research software to demonstrate their practical use. In particular, a new approach for modeling flexible diaphragms is proposed that is shown to provide similar accuracy to detailed finite element models at a fraction of the computation cost. The models developed were also validated as at the system level, through shake table testing of two full-scale specimens conducted as part of this study. The specimens were designed and constructed to represent the expected loading conditions of a central portion of a one-story URM building and constructed of materials representative of older masonry construction. The tests provide a unique data set that captures the interaction between flexible floors, out-of-plane walls and their connections at, full scale.The validated macro-models can be used for performance-based seismic assessment of unreinforced masonry building in NYC and elsewhere. To demonstrate their use, preliminary studies were conducted to develop out-of-plane URM fragility curves, a building-specific collapse fragility function, and estimate the seismic response of the building when subjected to a ground shaking intensity similar to the 2011 Virginia Earthquake. The probabilistic framework and new performance definitions provided by the FEMA P58 project were used to conduct a performance-based seismic assessment for an archetype unreinforced masonry building in New York City with an emphasis on out-of-plane behavior. This preliminary study served to demonstrate the applicability of the proposed models for applications in performance-based design.
Author: Steven C. Sweeney
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 80
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Book Description
Author: Franklin Lehr Moon
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 1298
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Book Description
As a capstone to several Mid-America Earthquake Center (MAE Center) projects, a full-scale two story unreinforced masonry (URM) building was tested following the application of several retrofit techniques, which included the use of fiber reinforced polymer (FRP) overlays, near surface mounted (NSM) rods, vertical unbonded post-tensioning, and joist anchors. The test structure was composed of four URM walls, flexible timber diaphragms and interior stud walls, and was designed and built following construction practices consistent with those used in Mid-America prior to 1950. Initial testing subjected both the roof diaphragm and in-plane walls to slowly applied lateral load reversals in an unreinforced sate. Following this series of tests, each in-plane wall was retrofit and retested. Experimental results indicated that global issues such as flange participation and the effects of overturning moment substantially impacted the response of primary components both before and after retrofit. FRP retrofit techniques resulted in strength increases up to 32% and displayed a pseudo-ductile response caused by progressive debonding. For cases where such retrofits forced sliding failures, large increases in energy dissipation resulted. The use of vertical unbonded post-tensioning resulted in strength increases between 40%-60%; however, piers displayed a tendency to switch from a ductile rocking/sliding mode to a more brittle diagonal tension mode. In addition, results highlighted the need for retrofit schemes to employ both horizontal and vertical reinforcement to prevent progressive crack opening that can decrease wall displacement capacity. Based on the experimental results, the model implied by the "Prestandard for the Rehabilitation of Existing Structures," FEMA 356, for the analysis of in-plane URM walls was modified and extended to (1) include the effect of FRP pier retrofits and (2) consider the global effects of URM structures. The resulting model displayed reasonable estimates of measured response both before and after retrofit, with an average error of 14%. In addition, the proposed model displayed improvements over the current model from 14% to 66%. Based on the results of sensitivity analyses this improved accuracy was primarily attributed to the consideration of global effects.
Author: Andrew Christopher Costley
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
As seismic awareness increases, especially in traditionally non-seismic regions, there is an ever-increasing need to evaluate the lateral resistance of existing structures. Unreinforced masonry (URM) structures are perceived to be seismically unsafe due to dramatic media coverage of these structures following earthquakes. However, well-built URM structures can possess substantial seismic resistance, although quantifying this strength can be difficult. Through a combination of experimental and analytical investigations, the overall objective of the study is to provide recommendations for the evaluation and rehabilitation of URM buildings. To accomplish this objective, the study was broken down into three primary tasks: (1) an experimental investigation, (2) the development of a simple dynamic model, and (3) a review of current analysis methods. The experimental investigation consisted primarily of the construction and dynamic testing of two, two-story, URM buildings with flexible floor and roof diaphragms on the University of Illinois shaking table. The two buildings were subjected to a total of nine simulated earthquakes. Experimental results indicated that (first-story) pier rocking was a ductile mode of response. Based on experimental results, a simple (3-DOF), nonlinear elastic model was developed. This model, in conjunction with a nonlinear time-step integration program, was used to estimate peak displacements during the rocking portions of the later earthquake simulations. The third task was a review of existing static and dynamic methods for analyzing URM structures. The static methods studied included two design codes, two rehabilitation codes, finite element modeling, and a pushover analysis. Dynamic methods included an elastic time-step integration, response spectra analysis, equivalent frame modeling, and finite element modeling. After a thorough examination of the measured results from the dynamic testing and a comparison between these results with those calculated during the analytical studies, a number of recommendations for the evaluation and rehabilitation of unreinforced masonry buildings with flexible diaphragms were made.
Author: United States. Department of Defense. Tri-Service Seismic Design Committee
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 472
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Book Description
Author:
Publisher: SPA Risk LLC
ISBN:
Category :
Languages : en
Pages : 16
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Book Description
Author: Steven C. Sweeney
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 114
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Book Description
Author: Gregory L. Cohen
Publisher:
ISBN:
Category :
Languages : en
Pages : 360
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Book Description
This study compares the responses from shaking-table testing and analytical predictions evaluated in the context of geometric scaling, to provide a coherent description of the seismic response of low-rise masonry buildings with flexible roof diaphragms. Two half-scale, low-rise reinforced masonry buildings with flexible roof diaphragms are subjected to carefully selected earthquake ground motion on the Tri-axial Earthquake and Shock Simulator at the Construction Engineering Research Laboratory. Damage to the half-scale specimens is assessed using published protocols. Geometric scaling analysis relates response and damage of the half-scale specimens to those of the full-scale prototype structures. Linear elastic modeling is simplified to a generalized two-degrees-of-freedom idealization. Response-spectrum analysis of such an idealization is accurate and justified for prediction of dynamic response of the half-scale specimens and the corresponding full-scale prototype. It is shown that low-rise masonry buildings with flexible roof diaphragms can be designed for seismic loads as single-degree-of- freedom systems, using the degree of freedom associated with the in-plane response of the diaphragm in the building's transverse direction, rather than the degree of freedom associated with the in-plane responses of the shear walls.
Author: A. C. Costley
Publisher:
ISBN:
Category : Building, Brick
Languages : en
Pages : 298
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Book Description
Author: Steven C. Sweeney
Publisher:
ISBN:
Category : Flexible diaphragm
Languages : en
Pages : 38
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Book Description
This paper provides an integrated approach to the seismic evaluation of low-rise reinforced masonry buildings with flexible roof diaphragms. The paper is divided into four phases. In Phase 1 (Behavior), results from shaking-table testing, quasi-static testing, and analytical predictions are integrated to provide a coherent description of the seismic response of low-rise reinforced masonry buildings with flexible roof diaphragms. Two half-scale, low-rise reinforced masonry buildings with flexible roof diaphragms are subjected to earthquake ground motions on the Tri-axial Earthquake and Shock Simulator at the United States Army Construction Engineering Research Laboratory, Engineer Research and Development Center. Following the shaking-table tests, diaphragms and top four courses of attached masonry walls are salvaged from the half-scale structures and tested quasi-statically in their own plane. A new index, the diaphragm drift ratio, is introduced to describe the potential for diaphragm damage. In Phase 2 (Analysis), coordinated analytical modeling is developed and implemented to corroborate and extend the results of that experimental work, and to examine the efficacy and accuracy of different analytical modeling approaches. Linear elastic finite-element models, simplified two-degree-of-freedom models, and nonlinear lumped-parameter models are developed; all agree well with measured responses. In Phase 3 (Seismic Evaluation), the first two phases are used to develop and verify a simple extension to FEMA 310, the predominant seismic evaluation methodology for low-rise reinforced masonry buildings with flexible diaphragms. In Phase 4 (Application and Verification), the proposed extension, applied to four existing buildings, is shown to be simple, useful, and necessary.
