Experimental study on seismic performance of steel reinforced concrete T-shaped columns

Zuqiang Liu,Chaofeng Zhou,Jianyang Xue,Roberto T. Leon 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.3

This study investigates the seismic performance of steel reinforced concrete (SRC) T-shaped columns under low cyclic loading tests. Based on test results of ten half-scale column specimens, failure patterns, hysteretic behavior, skeleton curves, ultimate strength, ductility, stiffness degradation and energy dissipation capacity were analyzed. The main variables included loading angles, axial compression ratios and steel ratios. The test results show that the average values of the ductility factor and the equivalent viscous damping coefficient with respect to the failure of the columns were 5.23 and 0.373, respectively, reflecting good seismic performance. The ductility decreased and the initial stiffness increased as the axial compression ratio of the columns increased. The strength increased with increasing steel ratio, as expected. The columns displaced along the web had higher strength and initial stiffness, while the columns displaced along the flange had better ductility and energy dissipation capacity. Based on the test and analysis results, a formula is proposed to calculate the effective stiffness of SRC T-shaped columns.

Fragility Analyses of Mid-rise T-stub PR Frames in the Mid-America Earthquake Region

김도환,Roberto T. Leon 한국강구조학회 2013 International Journal of Steel Structures Vol.13 No.1

Mid-America region is defined as the region of the central and southeastern United States compromising those states that have expected large but infrequent seismicity. Although earthquakes in this region are less frequent than in western U.S., they affect much larger areas than those of similar magnitude in western U.S. due to the deep and loose subsurface conditions. However, as little research has been carried out for partially restrained (PR) steel moment frame structures in this region, it is necessary to evaluate their seismic performance. To achieve this, seismic performance of three proto-type 6-story steel moment frames with T-stub PR connections was evaluated in accordance with FEMA 273/356 limit state criteria using fragility analyses. Three PR frames were designed using the appropriate design codes representing mid-1950s, late 1980s, and current practice. Two different types (“Conventional” and “New”) of fragility curves are developed and compared. In addition, the fragility curves at Los Angeles site representing western U.S. were generated and compared with those at the Mid-America region. Two different fragility analysis results show the same trends. Three proto-type 6 story PR frames in the Mid-America earthquake region performed well and may not collapse. It can be concluded that the seismic performance of the mid-rise PR frames in the Mid-America region will be satisfactory even under large but infrequent ground motions

강재보와 합성기둥에 사용된 새로운 반강접 접합부의 설계

Hong Min Son,Roberto T. Leon,Jong Wan Hu 한국복합신소재구조학회 2014 복합신소재구조학회논문집 Vol.5 No.1

This study describes the development of innovative connections between steel beams and concrete-filled tube columns that utilize a combination of low-carbon steel and super-elastic shape memory alloy components. The intent is to combine the recentering behavior provided by the shape memory alloys to reduce building damage and residual drift after a major earthquake with the excellent energy dissipation of the low-carbon steel. The analysis and design of structures requires that simple yet accurate models for the connection behavior be developed. The development of a simplified 2D spring connection model for cyclic loads from advanced 3D FE monotonic studies is described. The implementation of those models into non-linear frame analyses indicates hat the recentering systems will provide substantial benefits for smaller earthquakes and superior performance to all-welded moment frames for large earthquakes.

Investigation on the Inelastic Behavior of Full-scale Heavy Clip-angle Connections

허종완,Roberto T. Leon,최은수 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.1

This paper describes the investigation on the inelastic behavior of steel heavy clip-angle connections subjected to static loading. The work depends on the results of a large experimental investigation into the cyclic behavior of full-scale connections involving thick clip-angle components. The results of these experimental tests are described first, and then a methodology to simulate the response of clip-angle connections numerically using nonlinear finite element (FE) models is mainly treated in this study. Extensive studies utilizing numerous 3D models are discussed, including the introduction of the pretension force into the bolts and the effects of small changes in geometry on the deformation capacity of the angles. Generally, FE test results show a good agreement with experimental test results. These outcomes indicate that it is possible to model such connections successfully if care is exercised in the modeling phase. Moreover, these FE models provide useful instrumentation which is difficult to obtain during an experiment. They have widely been used to understand the parametric effect of connection components and establish a comprehensive study of their inelastic behavior including slip deformation and prying action.

Design of Innovative SMA PR Connections Between Steel Beams and Composite Columns

손홍민,Roberto T. Leon,허종완 한국복합신소재구조학회 2014 복합신소재구조학회논문집 Vol.5 No.1

This study describes the development of innovative connections between steel beams and concrete-filled tube columns that utilize a combination of low-carbon steel and super-elastic shape memory alloy components. The intent isto combine the recentering behavior provided by the shape memory alloys to reduce building damage and residual drift after a major earthquake with the excellent energy dissipation of the low-carbon steel. The analysis and design of structures requires that simple yet accurate models for the connection behavior be developed. The development of a simplified 2D spring connection model for cyclic loads from advanced 3D FE monotonic studies is described. The implementation of those models into non-linear frame analyses indicates hat the recentering systems will provide substantial benefits for smaller earthquakes and superior performance to all-welded moment frames for large earthquakes.

Shear strength analyses of internal diaphragm connections to CFT columns

Liping Kang,Roberto T. Leon,Xilin Lu 국제구조공학회 2015 Steel and Composite Structures, An International J Vol.18 No.5

Previous theoretical equations for the shear capacity of steel beam to concrete filled steel tube (CFT) column connections vary in the assumptions for the shear deformation mechanisms and adopt different equations for calculating shear strength of each component (steel tube webs, steel tube flanges, diaphragms, and concrete etc.); thus result in different equations for calculating shear strength of the joint. Besides, shear force-deformation relations of the joint, needed for estimating building drift, are not well developed at the present. This paper compares previously proposed equations for joint shear capacity, discusses the shear deformation mechanism of the joint, and suggests recommendations for obtaining more accurate predictions. Finite element analyses of internal diaphragm connections to CFT columns were carried out in ABAQUS. ABAQUS results and theoretical estimations of the shear capacities were then used to calibrate rotational springs in joint elements in OpenSEES simulating the shear deformation behavior of the joint. The ABAQUS and OpenSEES results were validated with experimental results available. Results show that: (1) shear deformation of the steel tube dominates the deformation of the joint; while the thickness of the diaphragms has a negligible effect; (2) in OpenSEES simulation, the joint behavior is highly dependent on the yielding strength given to the rotational spring; and (3) axial force ratio has a significant effect on the joint deformation of the specimen analyzed. Finally, modified joint shear force-deformation relations are proposed based on previous theory.

Analytical Investigation on Ultimate Behaviors for Steel Heavy Clip-angle Connections Using FE Analysis

Hu, Jong Wan,Leon, Roberto T.,Park, Taehyo The Iron and Steel Institute of Japan 2010 ISIJ international Vol.50 No.6

<P>This paper describes an analytical investigation on the strength, stiffness, and mechanical behavior of heavy clip-angle connections subjected to static loading. The work is based on the results of a large experimental investigation into the cyclic behavior of connection components incorporating with thick clip-angles. The results of these tests are described first, and then methodologies to generate the response of connection components, utilizing nonlinear finite element (FE) models with the advanced modeling methods such as the pretension force in the bolts and the interaction between two contact surfaces, are presented in this study. Numerical test results obtained from FE analyses are compared with experimental test results in an effort to verify that 3D FE models can simulate the overall and detailed behavior of a various type of clip-angle connections accurately. These FE models provide useful instrumentation, which is difficult to obtain during an experiment, such as the distribution of the plastic strain, prying forces induced by the initial bolt pretension, and friction forces on the interface between a clip-angle and a steel beam. These valuable results can support the basic knowledge for developing strength models consistent with the AISC-LRFD component method of the clip-angle design. They are also utilized to better understand the parametric effect of connection components and achieve a comprehensive study of their behavior.</P>

강재보와 합성기둥에 사용된 새로운 반강접 접합부의 설계

손홍민 ( Hong Min Son ),( Roberto T. Leon ),허종완 ( Jong Wan Hu ) 한국복합신소재구조학회 2014 복합신소재학회논문집 Vol.5 No.1

This study describes the development of innovative connections between steel beams and concrete-filled tube columns that utilize a combination of low-carbon steel and super-elastic shape memory alloy components. The intent is to combine the recentering behavior provided by the shape memory alloys to reduce building damage and residual drift after a major earthquake with the excellent energy dissipation of the low-carbon steel. The analysis and design of structures requires that simple yet accurate models for the connection behavior be developed. The development of a simplified 2D spring connection model for cyclic loads from advanced 3D FE monotonic studies is described. The implementation of those models into non-linear frame analyses indicates hat the recentering systems will provide substantial benefits for smaller earthquakes and superior performance to all-welded moment frames for large earthquakes.

Vibration analysis of steel frames with semi-rigid connections on an elastic foundation

Anh Q. Vu,Roberto T. Leon 국제구조공학회 2008 Steel and Composite Structures, An International J Vol.8 No.4

An investigation on the combined effect of foundation type, foundation flexibility, axial load and PR (semi-rigid) connections on the natural frequencies of steel frames is presented. These effects were investigated using a suitable modified FE program for cases where the foundation flexibility, foundation connectivity, and semi-rigid connections could be treated as equivalent linear springs. The effect of axial load on the natural frequency of a structure was found to be significant for slender structures subjected to high axial loads. In general, if columns of medium slenderness are designed without consideration of axial load effects, the frequency of the structure will be overestimated. Studies on the 3-story Los Angeles PR SAC frame indicate that the assumption of rigid connections at beam-column and column-base interfaces, as well as the assumption of a rigid foundation, can lead to significant errors if simplified design procedures are used. These errors in an equivalent static analysis are expected to lead to even more serious problems when considering the effect of higher modes under a non-linear dynamic analysis.