Author: Matthew Ronald LeBorgne
Publisher:
ISBN:
Category :
Languages : en
Pages : 602
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Book Description
Numerous reinforced concrete buildings vulnerable to earthquake induced collapse have been constructed in seismic zones prior to the 1970s. A major contributor to building collapse is the loss of axial load carrying capacity in non-seismically detailed columns. Experimental investigations have shown that non-seismically detailed columns will only experience axial failure after shear failure and subsequent lateral shear strength degradation have occurred. Therefore, column shear failure and degrading behavior must be modeled accurately before axial collapse algorithms can be properly implemented. Furthermore, accurate modeling of the degrading lateral-load behavior of columns is needed if lateral load sharing between structural elements is to be assessed with reasonable accuracy during seismic analyses. A calibrated analytical model was developed that is capable of estimating the lateral strength degrading behavior of RC columns prone to shear failure. Existing analytical models poorly approximate nonlinear column behavior and require several nonphysical damage parameters to be defined. In contrast, the proposed calibrated model provides the engineering community with a valuable tool that only requires the input of column material and geometric properties to simulate column behavior up to loss of lateral strength. In developing the model, a database of RC columns was compiled. Parameters extracted from database column-tests were scrutinized for trends and regression models relating damage parameters to column physical properties and boundary conditions were produced. The regression models were implemented in the degrading analytical framework that was developed in this project. Two reinforced concrete columns exhibiting significant inelastic deformations prior to failing in shear were tested in support of the analytical work. A newly developed Vision System was used to track a grid of targets on the column face with a resolution of three-thousands of an inch. Surface column deformations were measured to further the understanding of the fundamental changes in column behavior that accompany shear and axial failure and validate the proposed analytical model. This research provides the engineering community with an analytical tool that can be used to perform nonlinear dynamic analysis of buildings that are at risk of collapse and help engineers improve retrofit techniques. Further insight into shear behavior attained through this project is an important step toward the development of better shear and axial degradation models for reinforced concrete columns.
Author: P. Benson Shing
Publisher: ASCE Publications
ISBN: 9780784474969
Category : Technology & Engineering
Languages : en
Pages : 636
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Book Description
Proceedings of the U.S.?Japan Seminar on Post-Peak Behavior of Reinforced Concrete Structures Subjected to Seismic Loads: Recent Advances and Challenges on Analysis and Design, held in Tokyo and Lake Yamanaka, Japan, October 25-29, 1999. Sponsored by the National Science Foundation, U.S.A.; Japan Society for the Promotion of Science; Japan Concrete Institute. This collection presents the latest ideas and findings on the inelastic behavior of reinforced concrete (RC) structures from the analysis and design standpoints. These papers discuss state-of-the-art concrete material models and analysis methods that can be used to simulate and understand the inelastic behavior of RC structures, as well as design issues that can improve the seismic performance of these structures. Topics include modeling of concrete behavior; modeling of RC structures (finite element approach and macro-element approach); and experimental studies, analysis, and design issues.
Author: Jinsong Fan
Publisher:
ISBN:
Category : Buildings, Reinforced concrete
Languages : en
Pages :
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Book Description
The collapse of most non-ductile reinforced concrete buildings is caused by the loss of column support under gravity loads when subjected to lateral seismic loads. Although some modeling approaches of reinforced concrete columns can generate a reasonably accurate prediction of flexural response, the determination of shear displacement still needs further developments. Very few models could accurately simulate the shear failure and axial collapse of non-ductile columns under seismic loading. This dissertation focuses on the development of more accurate lateral displacement models including more focus on flexure-shear interaction for total lateral deformation response of lightly confined reinforced concrete columns. Experimental studies and post-earthquake reconnaissance demonstrated that reinforced concrete columns with light or widely spaced transverse reinforcement are vulnerable to shear failure and axial failure during earthquakes. Based on experimental results, a critical crack surface is selected to analyze and predict the onset of axial failure for damaged columns. When the lateral response of the column reaches the failure limit, the shear or axial strength begins to degrade. This research proposes two simplified analytical models that incorporate the shear failure and axial load failure limit state for predicting ultimate lateral displacements. An analytical model is developed to estimate the shear strength degradation and shear displacement at shear failure. Accordingly, a modified shear response envelope of shear-critical columns is proposed to predict shear behavior after peak shear strength is reached. The proposed model for calculating ultimate shear displacement is implemented and compared to experimental data. Another analytical model is developed to predict lateral displacements at axial load failure. Shear friction mechanisms are introduced to analyze the force equilibrium condition at the onset of axial load failure along a critical crack surface of the damaged column. Parametric studies are carried out to investigate and identify the most relevant factors used in calculations. The calculated results show that the proposed models can predict the lateral load-lateral displacement relationship of the test specimens with reasonable accuracy. A modified method is presented to calculate the total lateral displacements as a combination of flexure, longitudinal bar slip, and shear components. Comparison of the calculated response and experimental data show that the axial-shear-flexure interaction approach is basically suited to predict the lateral response of RC columns dominated by shear or shear-flexure failure.
Author: Eric John Setzler
Publisher:
ISBN:
Category : Columns, Concrete
Languages : en
Pages : 404
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Abstract: Prior studies have shown that many reinforced concrete buildings located in seismically active regions do not have the necessary lateral strength and ductility to perform adequately in earthquakes. In particular, it has been noted that reinforced concrete columns with poor transverse reinforcement are susceptible to shear failure and loss of axial capacity under cyclic lateral loads. The research reported here is focused on modeling the lateral deformation behavior of lightly reinforced concrete columns subjected to lateral loads. Lateral deformations in a column are comprised of three parts: flexural, reinforcement slip, and shear deformations. The monotonic response for each of these deformations was modeled separately. Flexural deformations were modeled using moment-curvature analysis and a plastic hinge model. A review of existing models for reinforcement slip was completed, and an existing model was modified based on experimental data and a parametric study. A comparison of models showed that the proposed slip model performs well in terms of accuracy and efficiency. A shear model was adopted from a previous study, and combined with an available computer program to predict shear behavior in this study. These three component models were found to predict the lateral response envelopes acceptably well for several sets of experimental data. A model for the overall lateral force-deformation relationship of reinforced concrete columns was created by combining the effects of each of the component models. The behavior of a column is classified into one of five categories based on a comparison of the shear, yield, and flexural strengths. The expected behavior in each category determines rules that govern the combination of the deformation components. For columns that are susceptible to shear failure after the onset of flexural failure, the response envelope is modified based on an available shear capacity model. An axial capacity model is also employed for the prediction of ultimate deformations. The proposed model was compared with experimental data from 37 column tests by various researchers. It was found that the classification system employed in the model was successful in representing column behavior. Overall, the model did a reasonable job of predicting the lateral response envelope for the columns in the test database. The model predicted the peak lateral strength well, and successfully represented the onset of shear failure in columns initially failing in flexure.
Author: Fawad Muzaffar Shaikh
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Inelastic response of reinforced concrete frame members to combined gravity and lateral loads involves the complex interaction of axial, moment and shear forces and deformations. Whereas there is a considerable body of experimental data and knowledge on the behavior of members that respond predominately in either inelastic shear or moment effects, the behavior of frame elements that are sensitive to combined shear-flexure interaction is less understood. At present, there is little agreement as to how to analyze the behavior of concrete frame elements that experience strength degradation under the combined nonlinear interaction of shear and moment. This study takes a closer look at existing analytical models that have been proposed for simulation of shear effects in frame elements. Experimental behavior of beam-columns as reported by other researchers is catalogued in order to develop an understanding of the actual physical behavior of concrete frame elements. Available experimental data of ductile and non-ductile columns is analyzed to identify key parameters which affect shear deformation behavior of beam-column elements. Bond slip penetration within the plastic hinge regions of the concrete frame elements is found to play a key role in causing shear failure and subsequent post-peak force deformation response of beam-columns. Existing concrete and steel material models are studied and an improved steel material model capable of simulating cyclic hardening, cyclic softening and mean stress relaxation is proposed. The proposed steel model is verified by comparing its simulated response with reported behavior of reinforcing bars. The suitability of the proposed steel material model to simulate random loading history is demonstrated. A numerical framework (i.e. kinematic description, solver routine and control algorithms), capable of simulating large rotation, large deformation, post-peak shear deformation behavior of frame elements is developed. A new analytical model for simulating shear deformation behavior of concrete frame elements subjected to axial, flexural and shear loading is proposed. While the modeling concepts are general, the implementation and verification of the proposed model is limited to two-dimensional response. The proposed element model is based on behavioral effects and parameters that are identified through careful analysis and interpretation of previously published tests of ductile and non-ductile beam-columns. This analytical model is then used along with the proposed numerical framework to simulate local and element level behavior of four non-ductile columns (tested by Sezen and Moehle at U.C. Berkeley), two ductile column stubs (tested by Ichinose, Imai, Okano and Ohashi at Nagoya Institute of Technology) and two beam specimens (tested by Popov, Bertero and Krawinkler at U.C. Berkeley). The proposed element formulation, along with the supporting computational framework (e.g., solution control algorithms), are shown to be capable and robust to simulate the post-peak response of beam-columns due to large flexural and shear deformations. The proposed formulation is shown to be capable of simulating the effect of cumulative flexural deformations, axial load and strength of longitudinal bars on shear strength of beam-columns. Complicated behavioral features, such as the opening of stirrups in non-ductile columns and degradation of aggregate interlock behavior with cycling, are captured in the analysis. The element model was shown to be capable of simulating the correct mode of failure observed in four tests of non-ductile columns. In addition, shear strain, stirrup strain and axial strain of beam-columns were simulated and compared with corresponding available experimental values. The values of the input parameters of the proposed element model were justified and the resulting response was compared with experimental behavior. Generally good agreement was observed between experimental and simulated values.
Author: Stan W. Zagajeski
Publisher:
ISBN:
Category : Buildings
Languages : en
Pages : 660
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Author: Marvin E. Criswell
Publisher:
ISBN:
Category : Columns, Concrete
Languages : en
Pages : 434
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The objectives of this investigation were to study the strength and behavior of slowly (statically) loaded reinforced concrete slab-column connections and to determine the effect of rapid (dynamic) loading on the strength and behavior by comparison with the static test results. Nineteen full-scale models of a connection and adjoining slab area, consisting of a simply supported slab 84 or 94 inches square and 6-1/2 inches thick loaded concentrically on a 10- or 20-inch-square stub column at the center of the slab, were tested. The main variables were the amounts of reinforcement in the slab (p = 0.75 and 1.50 percent), the column size, and the loading speed. Eight specimens were loaded to failure statically, two were subjected to a very rapidly applied load of short duration, and nine were loaded to failure by a rapidly applied load with a rise time chosen to represent the conditions in a blast-loaded structure. The static test results are compared with 12 shear strength prediction methods. Differences between the mechanism of shear failure in slabs and beams are examined. (Author).
Author: Chaitanya Patwardhan
Publisher:
ISBN:
Category : Columns, Concrete
Languages : en
Pages : 318
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Book Description
Abstract: Effect of transverse loading, e.g., as in an earthquake, on reinforced concrete column behavior has been an attractive topic of research for the last few decades. The column behavior is typically represented by its lateral load-displacement relationship. The past research has been primarily focused on estimation of the maximum lateral load capacity rather than the load-displacement relation, which includes flexure, bond-slip, and shear deformation components. The major goal of this study is to model lateral load-shear displacement relationship. Existing models are evaluated using available experimental data. A new model is developed using one of the existing models, Modified Compression Field Theory (MCFT). The results from MCFT appear to be accurate, but the theory is very complicated to implement as it uses an iterative algorithm. Thorough investigation of MCFT analyses is performed in this study. The results show that the theory can be simplified to simple equations, which are proposed here. The proposed model is compared with the predictions obtained using existing models as well as the experimental data. The proposed model is fairly simple, and proves to be accurate.
Author: Tanmoy Chowdhury
Publisher:
ISBN:
Category : Columns
Languages : en
Pages : 396
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Abstract: Prior studies have shown that older reinforced concrete buildings designed before the introduction of the modern seismic code in the early 1970s are vulnerable to damage and collapse during an earthquake. In particular, building columns did not have the lateral strength or ductility to withstand the demands imposed by the effects of a severe earthquake ground motion, and were often the most critical components of such earthquake damage-prone structures. They were typically characterized by insufficient and poorly detailed transverse reinforcement, widely spaced stirrups and low longitudinal reinforcement ratios. The focus of this research is to develop a suitable hysteretic model that would predict the lateral deformation behavior of lightly reinforced or shear-critical columns subjected to seismic and gravity loads. Tests of reinforced concrete columns under lateral loads have shown that the total drift stems from deformations owing to flexure, reinforcement slip, and shear. The monotonic response is initially established for the separate components in order to serve as a primary backbone curve for the cyclic force-displacement relationships. Existing analytical and experimental research on lightly reinforced columns is examined. This information is used, and when required, modified to ultimately develop a suitable overall hysteretic model that would accurately predict the lateral response of this class of columns with a limited computational effort. Cyclic models are developed for each deformation component that incorporate the strength, stiffness, and energy dissipation characteristics of the structural members. The total hysteretic response was derived by coupling flexure, reinforcement slip, and shear responses as springs in series. The behavior of a column is classified into one of five categories based on a comparison of the shear, yield, and flexural strengths. The expected behavior in each category determines rules that govern the combination of the deformation components. The proposed hysteretic model is calibrated against experimental results for correlation and verification studies. Overall, the model did a reasonable job of simulating the loaddeformation relationships of shear-critical columns. It provides a suitable platform to analyze older reinforced concrete buildings with a view to determining the amount of remediation necessary for satisfactory seismic performance.
Author: Ngan Ha D. Vu
Publisher:
ISBN:
Category : Columns, Concrete
Languages : en
Pages : 108
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