Dynamic analysis of reinforced concrete frames including joint shear deformation (original) (raw)
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Effect of Joint Flexibility on the Overall Performance of Reinforced Concrete Structure
The Fourth International Conference on Concrete and Development, 2013
The rehabilitation of existing buildings requires an assessment of their lateral load resisting capacity which may be limited by the strength and ductility capacity of their critical regions. From this assessment, a rehabilitation strategy can be formulated. Lack of adequate confinement and shear reinforcement in the beam-column joints of existing reinforced concrete frames may be the cause of brittle failure during a seismic event. Most of the analysis programs assume infinitely rigid beam-column joints in concrete frames regardless of the reinforcement detail. In this paper a beam-column joint element in OpenSees software platform verified with experimental result and then the response of five and ten story existing frames with beam-column joint elements subjected to dynamic and static loading was compared with the response of frames with rigid joint assumption. The results show that the modelling of inelastic shear deformation in joints has a significant effect on the seismic response in terms of drift and damage. The rigid joint assumption was found to be inappropriate when assessing the behaviour of existing non-ductile structures.
A Beam-Column Joint Model for Simulating the Earthquake Response of Reinforced Concrete Frames
Experimental investigation of the earthquake response of reinforced concrete subassemblages indicates that stiffness and strength loss resulting from beam-column joint damage may be substantial. To simulate inelastic joint action, a joint element is developed that is appropriate for use with traditional beam-column elements in two-dimensional nonlinear frame analysis. The proposed element formulation includes four external nodes with a total of 12 external degrees-of-freedom; however, the element is a super-element and includes four additional internal degrees-of-freedom. The super-element comprises 13 one-dimensional components that explicitly represent the three types of inelastic mechanisms that may determine the earthquake response of beam-column joints: anchorage failure of beam and column longitudinal reinforcement embedded in the joint, shear failure of the joint core, and sheartransfer failure at the beam-joint and column-joint interfaces. Calibration models are proposed for each of the three types of components. These calibration models enable a user to predict response as a function of concrete compressive strength, transverse steel ratio, frame-member longitudinal steel properties and joint geometry. Comparison of simulated and observed response for sub-assemblages tested in the laboratory indicates that the proposed model is appropriate for use in simulating the earthquake response of building joints with moderate earthquake load demands.
Effects of joint flexibility on lateral response of reinforced concrete frames
Engineering Structures, 2014
It is known that shear deformation of beam-column joints have a significant contribution to lateral response of reinforced concrete structures. Most of the available analysis programs assume rigid joints regardless of reinforcement details in the joint region. Slip of the beam longitudinal reinforcement in the joint and shear deformation of joint panel significantly decrease rigidity of the joint, especially in non-seismically detailed beam-column joints. In the current study, these effects were modelled in the OpenSees software framework and a modified joint element for analysis of multi-storey frames was used. The model was verified by experimental results and the verified model was used to analyze five and ten storey frames with various joint details using nonlinear static and incremental dynamic analyses. The results of frames with flexible joints were compared with those of frames with rigid joints assumption. The analytical results confirmed that the modified joint element successfully predicted experimental cyclic behaviour of beam-column joint specimens and also was found that existing RC structures with deficient beam-column joints are very vulnerable when subjected to severe earthquakes and the rigid joint assumption was not appropriate when assessing the behaviour of existing non-seismically detailed structures. The results also showed that the effect of joint deformation on lateral response of RC frames depends on the peak acceleration values of the ground excitation.
The seismic performance of reinforced concrete buildings cannot be fully understood aside from the beam-column joints. The capacity design (and the subsequent strength hierarchy) or the displacement ductility design are modern design principles and they are strongly subordinates to the beam-column joint panels behavior which can reduce substantially the global ductility, if the joint is subjected to a premature failure. Both the cracking of the joint panel zone, the slipping of the passing through steel reinforcement rebars can generate additional deformability and they can alter the strength hierarchy between the elements converging into the beam-column joint. The present work focuses on these two aspects using a refined finite element non-linear modeling technique. A numerical-experimental comparison is discussed that validate the adopted numerical model. Numerical results were compared to experimental data and were found to be in good agreement with the test data, thus validating the methodological approach.
Beam-Column Joint Model for Nonlinear Analysis of Non-Seismically Detailed Reinforced Concrete Frame
An efficient and simplified plane beam-column joint model that can describe the strength deterioration , stiffness degradation, and pinching effect was developed for the nonlinear analysis of non-seismically detailed reinforced concrete frames. The proposed beam-column joint model is a super-element consisting of eight spring components and one panel zone component, representing the bond-slip mechanism of the longitudinal reinforcement and the shear deformation mechanism of the joint concrete core region, respectively. In order to represent the dynamic response at the system level, the elastic constitutive law is applied to the eight connector springs, while the Bouc-Wen-Baber-Noori (BWBN) model is adopted to describe the hysteretic behavior of the panel zone component. For the implementation of the finite element analysis, the algorithmically consistent tangent of the BWBN model is derived as a uni-axial constitutive model, while the initial stiffness of the panel zone component is determined by the concrete compression strut assumption. The accuracy and efficiency of the proposed beam-column joint model were calibrated at both the component and structural levels by comparing the simulated results with the experimental data for non-seismically detailed joint sub-assemblages and a reinforced concrete plane frame.
Static force-based seismic analysis of reinforced concrete frames having weaker beam-column joints
European Journal of Environmental and Civil Engineering, 2020
Shake table tests were conducted on three 1:3 reduced scale two-story RC frames having weaker beam-column joints. The models were subjected to multi-levels input acceleration time histories to understand the seismic behaviour of test models. The models incurred severe damages in beamcolumn joint panels, forming shear hinging in joint panels, and were found in the incipient collapse state under input excitation below the design level excitation. Elastic hypothetical structures were considered having fundamental frequency that of test structures, which were subjected to actually recorded input excitation, in order to assess the seismic demands (base shear force and lateral roof displacement) using simplified analytical static procedure. The analytically predicted demands were correlated with the measured inelastic response, in order to calculate seismic response parameters (force reduction factor R and displacement modification factors C d). On average, R ¼ 2.0 and Cd ¼ 1.86 were obtained for the considered structures. The derived seismic response parameters can be employed in the analytical static force-based procedure for the seismic vulnerability assessment of RC frame structures having weaker beam-column joints. Example study is presented for the vulnerability assessment of considered structure using the proposed analytical static force procedure and the derived seismic response parameters.
The paper discusses how joint damage and deterioration affect the seismic response of existing reinforced concrete frames with sub-standard beam-column joints. The available simplified modeling techniques are critically reviewed to propose a robust, yet computationally efficient technique for simulating the nonlinear behavior of substandard beam-column joints. Improvements over the existing models include simulation of the cyclic deterioration of joint stiffness and strength as well as pinching in the hysteretic response, implemented considering a deteriorating hysteretic rule. A fibre-section forced-based inelastic beam-column element is developed; considering improved material models and fixed-end rotation due to bond failure, rebars-slip and inelastic extension, to simulate the deteriorating cyclic behavior of existing pre-cracked beam-column members. For the assessment of frames with substandard exterior beam-column joints, a nonlinear model for the exterior joint is developed a...
MATEC Web of Conferences
For an earthquake resistant structure, reinforced concrete building must have certain performance level under certain level of earthquakes such as when it is subjected to a strong level earthquake, it may experience severe damages, but without partial or full collapse, thus some reparations could be done to recover the functions of those damaged structures. However, repairing methods were usually done to slightly-damaged structures, while for severely-damaged structures, more studies are still needed to optimize the effectivity of the repair. Therefore, the objective of this study is to evaluate the performance of a structure that is retrofitted using high strength concrete after experiencing severe damage from an earthquake. Reinforced concrete beam column joints - that are used as specimens for this study - were initially subjected to cyclic loading up to 5% drift. The specimens’ beams are then repaired by replacing the damaged concrete with the new, stronger concrete without repl...
SEISMIC RESPONSE OF A CONCRETE FRAME WITH WEAK BEAM-COLUMN JOINTS
A reduced-scale, planar, two-story by two-bay reinforced concrete frame with weak beam-column joints was subjected to earthquake simulations on a shaking table. The beam-column joints did not contain transverse reinforcement, as is typical in older-type construction designed without attention to detailing for ductile response. A series of linear and nonlinear analytical models of the frame were developed in accordance with ASCE 41 and were subjected to the input base motions. The goodness of fit between analytical and measured results depended on the details of the analytical model. Reasonably accurate reproduction of the measured response was obtained only by modeling the inelastic response of both the columns and the beam-column joints. The results confirm the importance of modeling nonlinear joint behavior in older-type concrete buildings with deficient beam-column joints.
In seismic assessment of existing reinforced concrete buildings, the plastic behavior of beams and columns are typically represented by concentrated plastic hinges at the end of the members and the beam-column joint is considered rigid or partially rigid. This approach; however, does not account for the joint deterioration caused by cyclic seismic loading as observed during past earthquakes and also in experimental tests. The observations indicate that the potential for joint deterioration is higher in older concrete buildings. In this paper, the seismic behavior of a full-scale reinforced concrete beam-column connection extracted from an earthquake-damaged building is evaluated using structural testing and also numerical analysis. Cyclic testing is performed up to a column drift of 3%. Two analytical models of the connection are developed considering the joint flexibility; one model considers the rigid end offset approach recommended by ASCE/SEI 41, and the other model uses a lumped-plasticity joint spring model which is calibrated using the experimental test results. The test results show that the plastic mechanism of the connection is controlled by the joint flexibility in shear and that slippage of the beam bottom bars occurred after plastic hinges developed at the beam ends. These results are validated using the analytical model with joint lumped-plasticity. The model with end offsets, on the other hand, fails to adequately represent the specimen behavior. These findings indicate that nonlinear modeling of beam-column joints is critical in seismic assessments of older reinforced concrete buildings.