The Experts below are selected from a list of 27 Experts worldwide ranked by ideXlab platform
Hardy Cross - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Continuous Frames By Distributing Fixed-End Moments
Transactions of the American Society of Civil Engineers, 2020Co-Authors: Hardy CrossAbstract:A METHOD IS EXPLAINED WHICH HAS BEEN FOUND USEFUL IN ANALYZING BRIDGE FRAMES WHICH ARE STATICALLY INDETERMINATE. THE ESSENTIAL IDEA INVOLVES NO MATHEMATICAL RELATIONS EXCEPT THE SIMPLEST ARITHMETIC. IT IS TRUE THAT IN ORDER TO APPLY THE METHOD IT IS NECESSARY TO DETERMINE CERTAIN CONSTANTS MATHEMATICALLY, BUT THE MEANS TO BE USED IN DETERMINING THESE CONSTANTS ARE NOT DISCUSSED IN THE PAPER, NOR ARE THEY PART OF THE METHOD. THESE CONSTANTS HAVE BEEN DERIVED BY SO MANY WRITERS AND IN SO MANY SLIGHTLY DIFFERENT WAYS THAT THERE IS LITTLE NEED TO REPEAT THE WHOLE PROCEDURE. THE REACTIONS IN BEAMS, BENTS AND ARCHES WHICH ARE IMMOVABLY Fixed AT THEIR EndS HAVE BEEN EXTENSIVELY DISCUSSED. THEY CAN BE FOUND COMPARATIVELY READILY BY METHODS WHICH ARE MORE OR LESS STANDARD. THE METHOD OF ANALYSIS HEREIN PRESENTED ENABLES ONE TO DERIVE FROM THESE THE MomentS, SHEARS AND THRUST REQUIRED IN THE DESIGN OF COMPLICATED CONTINUOUS FRAMES. FOR CONVENIENCE OF REFERENCE, DEFINITIONS OF THREE TERMS ARE INTRODUCED. THESE TERMS ARE Fixed-End Moment, STIFFNESS AND CARRY-OVER FACTOR. /ASCE/
Achintya Haldar - One of the best experts on this subject based on the ideXlab platform.
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Seismic response and energy dissipation in partially restrained and fully restrained steel frames: An analytical study
Steel and Composite Structures, 2001Co-Authors: Alfredo Reyes-salazar, Achintya HaldarAbstract:The damage suffered by steel structures during the Northridge (1994) and Kobe (1995) earthquakes indicates that the fully restrained (FR) connections in steel frames did not behave as expected. Consequently, researchers began studying other possibilities, including making the connections more flexible, to reduce the risk of damage from seismic loading. Recent experimental and analytical investigations pointed out that the seismic response of steel frames with partially restrained (PR) connections might be superior to that of similar frames with FR connections since the energy dissipation at PR connections could be significant. This beneficial effect has not yet been fully quantified analytically. Thus, the dissipation of energy at PR connections needs to be considered in analytical evaluations, in addition to the dissipation of energy due to viscous damping and at plastic hinges (if they form). An algorithm is developed and verified by the authors to estimate the nonlinear time-domain dynamic response of steel frames with PR connections. The verified algorithm is then used to quantify the major sources of energy dissipation and their effect on the overall structural response in terms of the maximum base shear and the maximum top displacement. The results indicate that the dissipation of energy at PR connections is comparable to that dissipated by viscous damping and at plastic hinges. In general, the maximum total base shear significantly increases with an increase in the connection stiffness. On the other hand, the maximum top lateral displacement does not always increase as the connection stiffness decreases. Energy dissipation is considerably influenced by the stiffness of a connection, defined in terms of the T ratio, i.e., the ratio of the Moment the connection would have to carry according to beam line theory (Disque 1964) and the Fixed End Moment of the girder. A connection with a T ratio of at least 0.9 is considered to be fully restrained. The energy dissipation behavior may be quite different for a frame with FR connections with a T ratio of 1.0 compared to when the T ratio is 0.9. Thus, for nonlinear seismic analysis, a T ratio of at least 0.9 should not be considered to be an FR connection. The study quantitatively confirms the general observations made in experimental results for frames with PR connections. Proper consideration of the PR connection stiffness and other dynamic properties are essential to predict dynamic behavior, no matter how difficult the analysis procedure becomes. Any simplified approach may need to be calibrated using this type of detailed analytical study.
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Nonlinear seismic response of steel structures with semi-rigid and composite connections
Journal of Constructional Steel Research, 1999Co-Authors: Alfredo Reyes-salazar, Achintya HaldarAbstract:Abstract The nonlinear seismic responses of steel frames with fully restrained, partially restrained and composite connections are evaluated and compared in terms of the maximum interstory and maximum top lateral displacements. Steel frames are usually analyzed assuming all the connections are fully restrained. However, considering the practical design aspects of connections, this is rarely true. This practice introduces unintEnded flexibility in the frame. Using a nonlinear time domain seismic analysis algorithm developed by the authors, three steel frames are excited by 13 earthquake time histories. Twelve of them were recorded during the Northridge earthquake of 1994. Any one of these 12 earthquake time histories can be used to represent the Northridge earthquake in future designs. To define the rigidity of a connection, a parameter called the T ratio is introduced. It is the ratio of the Moment the connection would have to carry according to the beam line theory and the Fixed End Moment of the girder. Initially, the T ratio of all the connections is assumed to be 0.9, making them fully restrained. The results indicate that this assumption is inappropriate and gives unconservative responses depEnding upon which time history of the same earthquake is being used. Several frames with a T ratio of 0.95 developed very large lateral displacements causing instability, although they behaved properly when the ratio was assumed to be 1.0. For composite connections, slab steel has a significant beneficial effect on the overall structural response. It increases the T ratio, making it closer to the FR connection. Even for composite connections with a T ratio of 0.95, the frames developed large lateral displacement. Further parametric study indicates that, at least for seismic analysis, PR or composite connections should be designed for a T ratio as close to 1 as possible to represent an FR connection. Otherwise, the lateral displacement failure criterion should also be checked for less than ideal FR connection conditions. Improvements in both the analysis and design of steel frames are necessary to make them more seismic load tolerant.
Wang Hai-b - One of the best experts on this subject based on the ideXlab platform.
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Approximate Calculation on Elemental Stiffness Matrix for Poles of Steel Portal Frame
Journal of Heilongjiang August First Land Reclamation University, 2020Co-Authors: Wang Hai-bAbstract:An approximate calculation method on elemental stiffness matrix for light-weight steel portal frame was presented in this paper. According to this method, Fixed End Moment could be calculated. So we can regard it as a calculation basis for designing computer programs by means of displacement of matrix, and also can provide conveniences for designers to check the data of the light-weight portal frame.
Alfredo Reyes-salazar - One of the best experts on this subject based on the ideXlab platform.
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Seismic response and energy dissipation in partially restrained and fully restrained steel frames: An analytical study
Steel and Composite Structures, 2001Co-Authors: Alfredo Reyes-salazar, Achintya HaldarAbstract:The damage suffered by steel structures during the Northridge (1994) and Kobe (1995) earthquakes indicates that the fully restrained (FR) connections in steel frames did not behave as expected. Consequently, researchers began studying other possibilities, including making the connections more flexible, to reduce the risk of damage from seismic loading. Recent experimental and analytical investigations pointed out that the seismic response of steel frames with partially restrained (PR) connections might be superior to that of similar frames with FR connections since the energy dissipation at PR connections could be significant. This beneficial effect has not yet been fully quantified analytically. Thus, the dissipation of energy at PR connections needs to be considered in analytical evaluations, in addition to the dissipation of energy due to viscous damping and at plastic hinges (if they form). An algorithm is developed and verified by the authors to estimate the nonlinear time-domain dynamic response of steel frames with PR connections. The verified algorithm is then used to quantify the major sources of energy dissipation and their effect on the overall structural response in terms of the maximum base shear and the maximum top displacement. The results indicate that the dissipation of energy at PR connections is comparable to that dissipated by viscous damping and at plastic hinges. In general, the maximum total base shear significantly increases with an increase in the connection stiffness. On the other hand, the maximum top lateral displacement does not always increase as the connection stiffness decreases. Energy dissipation is considerably influenced by the stiffness of a connection, defined in terms of the T ratio, i.e., the ratio of the Moment the connection would have to carry according to beam line theory (Disque 1964) and the Fixed End Moment of the girder. A connection with a T ratio of at least 0.9 is considered to be fully restrained. The energy dissipation behavior may be quite different for a frame with FR connections with a T ratio of 1.0 compared to when the T ratio is 0.9. Thus, for nonlinear seismic analysis, a T ratio of at least 0.9 should not be considered to be an FR connection. The study quantitatively confirms the general observations made in experimental results for frames with PR connections. Proper consideration of the PR connection stiffness and other dynamic properties are essential to predict dynamic behavior, no matter how difficult the analysis procedure becomes. Any simplified approach may need to be calibrated using this type of detailed analytical study.
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Nonlinear seismic response of steel structures with semi-rigid and composite connections
Journal of Constructional Steel Research, 1999Co-Authors: Alfredo Reyes-salazar, Achintya HaldarAbstract:Abstract The nonlinear seismic responses of steel frames with fully restrained, partially restrained and composite connections are evaluated and compared in terms of the maximum interstory and maximum top lateral displacements. Steel frames are usually analyzed assuming all the connections are fully restrained. However, considering the practical design aspects of connections, this is rarely true. This practice introduces unintEnded flexibility in the frame. Using a nonlinear time domain seismic analysis algorithm developed by the authors, three steel frames are excited by 13 earthquake time histories. Twelve of them were recorded during the Northridge earthquake of 1994. Any one of these 12 earthquake time histories can be used to represent the Northridge earthquake in future designs. To define the rigidity of a connection, a parameter called the T ratio is introduced. It is the ratio of the Moment the connection would have to carry according to the beam line theory and the Fixed End Moment of the girder. Initially, the T ratio of all the connections is assumed to be 0.9, making them fully restrained. The results indicate that this assumption is inappropriate and gives unconservative responses depEnding upon which time history of the same earthquake is being used. Several frames with a T ratio of 0.95 developed very large lateral displacements causing instability, although they behaved properly when the ratio was assumed to be 1.0. For composite connections, slab steel has a significant beneficial effect on the overall structural response. It increases the T ratio, making it closer to the FR connection. Even for composite connections with a T ratio of 0.95, the frames developed large lateral displacement. Further parametric study indicates that, at least for seismic analysis, PR or composite connections should be designed for a T ratio as close to 1 as possible to represent an FR connection. Otherwise, the lateral displacement failure criterion should also be checked for less than ideal FR connection conditions. Improvements in both the analysis and design of steel frames are necessary to make them more seismic load tolerant.
Can Balkaya - One of the best experts on this subject based on the ideXlab platform.
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Behavior and Modeling of Nonprismatic Members Having T-Sections
Journal of Structural Engineering-asce, 2001Co-Authors: Can BalkayaAbstract:This paper emphasizes the discrepancies in conventional methods of analyzing nonprismatic members having T-sections. In practice, the change in the location of the centroidal axis over the length of nonprismatic members is ignored in structural analysis. Commonly used Portland Cement Association tables for Fixed-End Moment and stiffness factors are based on the assumptions of a straight-line centroidal axis and variable rectangular cross section. However, discontinuities in the centroidal axis produce strong coupling between the End Moments and horizontal thrust. Nonprismatic members behave similar to an arch, and this creates an axial force that is neglected in conventional methods. Moreover, beams are considered as T-beams in the structural models because of the effect of RC slabs. Consequently, nonprismatic T-sections require special consideration in structural analysis. The purpose of this paper is to present the behavior of nonprismatic T-section beams based on a 3D finite-element investigation. Base...