Shear Failure Of Columns Research Articles

Investigation and Analysis of Buildings Damaged during the September 2007 Sumatra, Indonesia Earthquakes

Earthquakes occurring on September 12 (8.4 ML) and 13 (7.9 ML), 2007, in South and West Sumatra, Indonesia, respectively, damaged many buildings. This paper reports investigation results on damaged buildings in and around Padang, West Sumatra, and discusses the seismic performance of two reinforced concrete (RC) frame structures with unreinforced masonry (URM) brick walls.Observations revealed that several RC structures with URM walls suffered severe damage such as shear failure of columns, buckling of column longitudinal reinforcements, and collapse of brick walls. In confined and simple URM structures, damage mainly to brick walls was observed. On the contrary, timber structures performed relatively well during the earthquakes.Two calculations were performed—one with and one without infill walls, focusing on two three-story collapsed and surviving RC buildings in Padang. A distinct difference was identified between the seismic performance of the two buildings when considering infill walls. Therefore, these samples of earthquake-damaged buildings verify that nonstructural infill walls can significantly contribute to the seismic performance of this type of structure.

Analytical Collapse Study of Lightly Confined Reinforced Concrete Frames Subjected to Northridge Earthquake Ground Motions

Review of older non seismically detailed reinforced concrete building collapses shows that most collapses are triggered by failures in columns, beam-column joints, and slab-column connections. Using data from laboratory studies, failure models have previously been developed to estimate loading conditions that correspond to failure of column components. These failure models have been incorporated in nonlinear dynamic analysis software, enabling complete dynamic simulations of building response including component failure and the progression of collapse. A reinforced concrete frame analytical model incorporating column shear and axial failure elements was subjected to a suite of near-fault ground motions recorded during the 1994 Northridge earthquake. The results of this study show sensitivity of the frame response to ground motions recorded from the same earthquake, at sites of close proximity, and with similar soil conditions. This suggests that the variability of ground motion from site to site (so-called intra-event variability) plays an important role in determining which buildings will collapse in a given earthquake.

Model for the Lateral Behavior of Reinforced Concrete Columns Including Shear Deformations

This research is focused on modeling the behavior of reinforced concrete columns subjected to lateral loads. Deformations due to flexure, reinforcement slip, and shear are modeled individually using existing and new models. Columns are classified into five categories based on a comparison of their predicted shear and flexural strengths, and rules for combining the three deformation components are established based on the expected behavior of columns in each category. Shear failure in columns initially dominated by flexural response is considered through the use of a shear capacity model. The proposed model was tested on 37 columns from various experimental studies. In general, the model predicted the lateral deformation response envelope reasonably well.

Shear deformation model for reinforced concrete columns

Column shear failures observed during recent earthquakes and experimental data indicate that shear deformations are typically associated with the amount of transverse reinforcement, column aspect ratio, axial load, and a few other parameters. It was shown that in some columns shear displacements can be significantly large, especially after flexural yielding. In this paper, a piecewise linear model is developed to predict an envelope of the cyclic shear response including the shear displacement and corresponding strength predictions at the first shear cracking, peak strength, onset of lateral strength degradation, and loss of axial-load-carrying capacity. Part of the proposed model is developed using the analysis results from the Modified Compression Field Theory (MCFT). The results from the proposed model, which uses simplified equations, are compared with the column test data.

STUDY ON SEISMIC PERFORMANCE OF R/C WALL-FRAME STRUCTURES BASED ON LARGE-SCALE SHAKING TABLE TEST

The Response of reinforced concrete wall-frame structures subjected to earthquake motion was investigated by testing a full-scale six-story specimen on the world's largest tri-axial shaking table “E-Defense”. The test specimen consisted of three parallel three-bay frames in the longitudinal direction. The central frame had a multi-story structural wall in the center bay continuous from the 1st to the 6th story. To be able to monitor shear force carried by the structural wall at the 1st story, 3-component force transducers were instrumented between foundation beams and the shaking table.The test specimen was subjected to a series of strong earthquake motions and finally nearly collapsed caused by shear failure of short columns and shear slipping failure of the structural wall at the 1st story. This paper outlines measurement plan of 3-component force transducers and also examines the shaking table test results for rigidity at the bottom of the wall, restoring force characteristics of the structure, and measured shear force carried by the 1st-story structural wall.

Life-Safety and Near-Collapse Capacity Models for Seismic Shear Behavior of Reinforced Concrete Columns

In seismic assessment of existing reinforced concrete (RC) structures, it is important to reliably predict potential column shear failure. Shear strength and deformation capacities can be used to evaluate this failure. This paper evaluates the reliability of three available strength models for estimating the shear strength of RC columns using existing experimental test results. Deformation capacity models are developed for life-safety and near-collapse performance levels. The models account for the difference between the deformation of double-curvature and double-ended columns, in which damage can concentrate on one end of the specimen, and that of cantilever columns. The models include the effects of the transverse reinforcement, axial load, and the aspect ratio of columns on their deformation capacities. Using shear force transfer mechanics, a shear strength capacity model is also developed for RC columns that can estimate column shear strength significantly better than the currently available models. In addition to the section and material characteristics, the shear strength capacity model accounts for the effects of the aspect ratio, compressive load, and displacement ductility on the column strength.

SEISMIC RISK ASSESSMENT OF RC STRUCTURES WITH THE “2000 SAC/FEMA” METHOD

The applicability of a new, fully probabilistic approach to seismic design and assessment of reinforced concrete (RC) structures is investigated. Fundamental advantages of the method are mathematical simplicity and comparatively light computational effort. The original formulation, which was developed for steel structures, is first illustrated; ah extension which allows consideration of multiple failure mechanisms, typical of RC structures, is then proposed. The applicability of the method is demonstrated through an example: the seismic risk of a four storey RC building that was not designed for seismic resistance is evaluated. Three failure mechanisms are considered: joint failure, column shear failure and drift failure.

Performance Assessment for a Reinforced Concrete Frame Building

This paper evaluates the performance of a seven-story reinforced concrete frame building that was severely damaged during the 1994 Northridge, California, earthquake. The building was designed and constructed in the 1960s and contains details that are typical of that construction era in the western United States. The building sustained severe damage that included column shear failures. The building was analyzed independently by three research teams using analysis methodólogies that were similar in concept but different in details. An objective of each analysis was to correlate observed and calculated performance. The different analyses were successful to varying degrees. The results provide a test case of the effectiveness of various seismic performance assessment methodologies.

Shear failure and ductility of RC columns after yielding of main reinforcement

During the Hanshin-Awaji Earthquake, catastrophic shear failure accompanying plenty of diagonal shear cracks was experienced in RC structures and bridge piers serving transportation facilities. In this paper, shear capacity and ductility of RC columns in the post-yield range of longitudinal reinforcement are discussed for seismic-resistant-design. First, the shear failure of large-scale RC columns is computationally simulated for an understanding of the mechanism of shear collapse of bridge piers. FEM computational results on ductility are compared with the experiments and a parametric study is conducted concerning factors that affect the post-yield deformability of RC columns. Finally, a simple formula for ductility is presented for summarizing the sensitivity of influential factors.

Modeling Nonductile R/C Columns for Seismic Analysis of Bridges

A stress resultant plasticity-based formulation with shear failure criteria and post-shear failure effects is presented for modeling the response of nonductile reinforced concrete bridge columns subjected to biaxial seismic loading. The formulation consists of a single component model, in which plastic hinges exist at each end of an elastic beam-column. Deterioration in column strength following a shear failure, kinematic flexural strain hardening, and degradation of elastic unloading stiffness under cyclic load reversal are accounted for in the hinges' force-deformation relationships. The degradation of the transverse shear strength in a reinforced concrete column's flexural plastic hinge zone is also accounted for. The formulation is shown to predict reasonably well the cyclic response of nonductile beam-column experimental test specimens that develop either ductile flexural yielding, a brittle shear failure, or a ductile shear failure in the flexural plastic hinge zone when subjected to uniaxial or biaxial nonproportional cyclic lateral loading. Inelastic seismic time-history analysis is also presented to illustrate the significance of including nonductile effects in a model of a bridge structure susceptible to column shear failure during an earthquake.

SHEAR RESISTANCE AND DUCTILITY OF RC COLUMNS AFTER YIELD OF MAIN REINFORCEMENT

During Hanshin-Awaji Earthquake, catastrophic shear failure accompanying plenty of diagonal shear cracks were experienced in RC structures and bridge piers serving transportation facilities. In this paper, shear capacity and ductility of RC columns in the post-yield range of longitudinal reinforcement are discussed for seismic resistant design. First, the shear failure of large scale RC column is computationally simulated for understanding the mechanism of shear collapse of bridge piers. FEM computational results on ductility are compared with the experiments and parametric study is conducted concerning factors that affect the post-yield deformability of RC columns. Finally, a simple formula for ductility is presented for summarizing the sensitivity of influential factors.

Behavior of reinforced concrete buildings during the Hyougoken-Nanbu earthquake

The Hyougoken-Nanbu earthquake caused serious damage to reinforced concrete building structures. Investigation results indicated that most buildings which suffered serious structural damage were built before 1981, i.e. new modern buildings behaved well, because the current seismic design provisions were enforced by the ministry of construction in 1981. Typical damage patterns of reinforced concrete building structures were: (1) collapse of soft first story construction; (2) collapse of a mid-height story; (3) torsional failure resulting from eccentricities of stiffness and mass; (4) inadequate spacing and anchorage of transverse reinforcement; (5) shear failure of short columns; (6) fracture of re-bar splices by gas-pressure welding; (7) damage to separation joints and elevated corridors; and (8) damage to non-structural members (Preliminary Reconnaissance Report of the 1995 Hyougoken-Nanbu earthquake, Architectural Institute of Japan, 1995 (English version)).

The collapse mechanism of a subway station during the Great Hanshin earthquake

The Great Hanshin earthquake, on 17 January 1995, brought about serious damage to some underground reinforced concrete (RC) structures serving the subway in Kobe city, Japan. In this study, the seismic response of Daikai subway station during this earthquake is computed by FEM code WCOMD-SJ, which is a two-dimensional dynamic finite element program including path dependent RC smeared model, soil foundation model and interfacial model. The shear failure of intermediate column of the station can be reasonably simulated and it is concluded that the failure of the intermediate column is caused by low shear capacity and poor ductility. Enhancement of seismic resistance is also discussed using this FEM code.

A study of the damage of subway structures during the 1995 Hanshin-Awaji earthquake

During the 1995 Hanshin-Awaji earthquake, underground subway structures suffered significant damage, including middle column shear failure which has never been experienced in the past. The present paper describes analytical studies for damage verification and for failure mechanism investigation. Focusing on box culvert structure with middle columns at Kamisawa station, Kobe city municipal subway, the following three series of analytical studies have been conducted. In the first study, soil deposit dependent ground response are investigated using equivalent linear response analysis computer program based on multi-reflection theory. The increase of the deposit layer thickness provides less acceleration, but more displacement responses, which causes more in the way of damage in the present underground structure. In the second study, structure and ground responses are investigated with using two-dimensional soil-structure interaction computer program. As a result, the horizontal motion dependent flexural shear section force has more of an effect, but the vertical motion dependent axial force has less of an effect on the middle column damage. That section force is more affected by displacement amplification of ground dependent on deposit layer. In the third study, three-dimensional FE static nonlinear analysis is conducted to investigate failure mechanism of the damaged structure subjected to earth pressure load, which is obtained in the second study. Analytical results predict shear failure of the top story middle column prior to the flexural yielding of the slabs and walls.

Seismic Repair and Strengthening of a Severely Damaged Concrete Frame

A repair technique designed to strengthen and repair reinforced concrete frames with heavily damaged columns was tested experimentally. A two-thirds scale model of two bays and two stories of an exterior moment-resisting frame with heavily damaged columns was repaired and strengthened by completely encasing the damaged columns. The damage was characterized by heavy shear cracking and spalling of the concrete in the window space between the spandrel beams. In addition to repairing the damage to the columns, the new columns were designed to increase the lateral capacity of the frame and to shift the mode of failure from shear in the columns to flexural hinging in the beams. Test results of the frame was successfully shifted from column shear failure to flexural hinging of the beams. The results also showed that the encased columns behaved monolithically, and that the lateral strength of the frame was substantially increased

構造目地を有する鉄筋コンクリート造腰壁付き骨組の力学的特性に関する研究 : そのIII-腰壁付き柱の最大荷重の決定過程と腰壁の反力挙動

This paper focusses seismic behavior of reinforced concrete columns with a gap, called the "Structural Slits" in this paper. The purpose to provite the Structural Slits is to mitigate the undesirable effects of spandrels on reinforced concrete frames, such as shear failure of columns during an earthquake. The reaction condition of a spandrel in the maximum lateral load of a column Q_<SLU> caused by [he crush of concrete at Structural Slits is cleared up by the analysis of a test results and the finite element analysis.

Behavior of RC Frame Strengthened Using Structural Steel Bracing

A retrofit strengthening technique for improving the seismic behavior of a nonductile reinforced concrete (RC) frame was investigated experimentally. The original frame contained deep, stiff spandrel beams and short, flexible columns that were susceptible to shear failure under lateral loads. The strengthening technique used a steel X‐bracing system attached to the exterior of the frame using epoxy‐grouted dowels. A two‐thirds‐scale frame model consisting of two bays and three levels was subjected to statically applied cyclic lateral load. Test results indicated substantial increases in both lateral stiffness and strength. The lateral capacity of the strengthened frame was governed by brace buckling and eventual connection failures and column shear failures. Measured brace buckling loads agreed well with predicted capacities assuming fixed (K=0.5) connections, and dowel performance was excellent. Bracing‐system elements attached to the side faces of the concrete columns also substantially increased column...

鉄筋コンクリート造腰壁付柱に設けたスリットの効果に関する研究

Spandrel-walls frequently adopted for reinforced concrete buildings such a school and hospital sometimes cause shear failure of columns, which accidentally bring brittle failure of whole structure. Typical earthquake damages of building in which the existence of spandrelwalls was considered as one of majar reason of their damages were seen in the 1968 Tokachi-oki Earthquake and the 1983 Nihonkai-Chubu Earthquake. Recently structural design method where columns are intentionally separated from spandrel walls by slit have been adopted so that such brittle failure of columns with spandrel wall might not occur and that total structure might resist earthquakes by ductility capacity. This paper describes experimental results of column and spandrel wall assemblies with or without slits subjected to reversing static lateral loads, focusing on the effect of slit on the crack and failure patterns, yielding sequences of reinforcing bars and deformation capability. The test results of the strength of slit were compared to the analytical results based on strain distribution along the height of slit and stress vs. strain relations of concrete. Through the tests results and comparisons between test and analytical results, the following conclusions were drawn ; i) specimen without slit and specimens with thick slit faild in shear while specimens without spandrel wall and specimens with thin slit faild in flexure, ii) the strength of slit was expressed by the thickness of the concrete of a slit, the height of a slit and the compressive strength of concrete, and iii) the dimension of the concrete of a slit should be designed by based on the comparison between the strength of a slit and those of columns and beams.

十勝沖地震における鉄筋コンクリート造校舎の耐震性について : 被害建物と無被害建物の比較検討

Failures of reinforced concrete school buildings due to 1968 Tokachi-oki earthquake, May 16, 1968, were investigated by comparing failed buildings with similar buildings in the same area which survived the earthquake. Most remarkable and important mode of failure of these buildings was the shear failure of the first story columns, mostly short columns. Natural period was measured, and structural analyses showed that calculated period, based on the uncracked section including finishings, was very close to the measured value if the building was safe or only partially damaged. However there was no remarkable diflerence between the calculated periods of safe and damaged buildings. Earthquake response was calculated for these buildings, As to the maximum relative displacement of the first story, again, there was no remarkable diflerence. Based on the elastic theory, shear strain and stress in the columns of the first story were calculated. It was shown that ther was remarkable diflerence in the shear strain and stress, and that shear stress may be approximately estimated if the base shear coefficient was evaluated. The base shear coefficient of low, rigid reinforced concrete buildings may be assumed to be approximately constant, or in other words, it dous not depend on the natural period of the structure. Thus, safety against shear failure of columns may be estimated by means of W_e/A, where W_e is the effective weight of the building as related to the particular column, and A is the cross-sectional area. Furtheremore, relation between shear strength and shear span ratio was studied. It was found that an empirical equation by Dr. Arakawa showed a very good agreement with the observed failure in the earthquake. Also it was shown that short columns were apt to fail because the stress concentration due to its high rigidity exceeds the increase in the strength.

1968 年十勝沖地震における鉄筋コンクリート柱の剪断破壊に関する一考察

Three series of tests on reinforced concrete columns were carried out with regard to the damage to reinforced concrete structures due to the Tokachi-oki Earthquake, 1968. In these tests the following items were preliminarily investigated; i) the eflects upon ductility of columns due to eccentricity of wall girders with regard to the axes of centroid of columns, ii) apprehensions of under-estimation of resisting capacity of columns for bending when one compares the bending resistance with the shear resistance for the purpose of providing the ductility of columns, iii) Shear resistance behaviors of columns of frame-works under repeated alternating lateral forces. The test results are compared with actual failing feature of columns damaged by the Tokachi-oki Earthquake. Some problems on shear failure of columns are pointed out, which should be further investigated ; especially we are interested in the relations between bond collapse and shear failure.