Seismic Performance Of Reinforced Concrete Frames Research Articles

Experimental results of reinforced concrete frames with masonry infills with and without openings under combined quasi-static in-plane and out-of-plane seismic loading

Reinforced concrete (RC) frames with masonry infills can be encountered all over the world, especially in earthquake prone regions. Although masonry infills are usually not considered in the design process, in the case of seismic loading they are subjected to in-plane and out-of-plane forces that can act separately or simultaneously. In recent earthquakes it was observed that seismic loads can severely damage masonry infills or even cause their complete collapse, especially when the loads act simultaneously. Due to this, effects of interaction of in-plane and out-of-plane loads on seismic performance of masonry infills have received more attention recently. However, most of studies focus only on fully infilled frames, even though openings, such as windows and doors are essential parts of infills that substantially affect the seismic response of masonry infills. Therefore, this article presents the results of a comprehensive experimental study on nine full-scale traditional masonry RC frames infilled with modern hollow clay bricks for configurations with and without window and door openings under separate, sequential and combined in-plane and out-of-plane loading. Based on the results, a detailed comparison and interpretation for the different infill and loading configurations is presented. The test results clearly show the unfavourable influence of openings and combined loading conditions as well as the importance of the quality of execution of the circumferential mortar joint between infill and frame. The new findings can be used as a basis for the required development of innovative solutions to improve significantly the seismic performance of RC frames with masonry infills.

Optimum buckling-restrained braces application to enhance seismic performance of RC frame with curtailed walls

Reinforced concrete (RC) frames are commonly built together with shear walls. In high seismicity regions, constructing shear walls along the frame’s height is proven ineffective. Thus, in numerous studies, using shear walls at a certain height is beneficial, and this kind of structure is popularly known as curtailed shear walls. However, the area above the curtailed walls could suffer significant deformation under high seismic load and upgrading the seismic performance in those upper parts is needed. In this study, the seismic performance of 2-dimension RC frame building with curtailed walls is improved by installing buckling-restrained braces (BRBs). The seismic response is performed through non-linear dynamic analysis using an open-licensed software, STERA_3D. To determine the ideal number and location of the BRBs above the curtailed walls, a classical genetic algorithm is exercised using Python language programming. The parameters involved in optimizations are inter-story drifts, the number of BRBs, and damage indices surround the frames. The result shows that the configuration of BRBs resulted from the optimization could reduce the excessive amount of displacement along the building height. Moreover, the genetic algorithm could give the fittest number and location of BRBs installation to upgrade the seismic response of RC frames with partial shear walls.

The Influence of Vertical Arrangement and Masonry Material of Infill Walls on the Seismic Performance of RC Frames

This study presents a finite element (FE) model, the accuracy of which is verified by the comparison between the numerical and test results. The calibrated model is used to investigate the influence of vertical arrangement and masonry material of infill walls on the seismic performance of reinforced concrete (RC) frames through pushover analysis and time–history analysis. The lateral capacity, interstorey drift ratio, and plastic hinge distribution of structures is discussed. It was found that the damage of frames with irregular vertical infill arrangement is more serious than that of bare frames, which should be limited in the seismic design process. Moreover, the disadvantages induced by the elastic modulus of masonry material should be considered in the seismic design and assessment of the frames with vertical irregularly arranged infill.

Design parameters and material‐scale damage evolution of seismic upgraded RC frames by viscoelastic haunch bracing‐dampers

AbstractTo improve the seismic design of reinforced concrete (RC) frame structures and upgrade existing RC frame structures that have insufficient seismic design, a new suitable seismic upgraded solution, the installation of viscoelastic haunch bracing‐dampers (VHBD) to increase the seismic performance of RC frames, is proposed in this paper. For a comprehensive and systematical research about this new upgraded frames system, a comparative study on the seismic performance between 15 RC frame structure specimens by adding the VHBD with different design parameters and one common RC frame structure specimen is performed under sinusoidal dynamic loading. The specific items of seismic performance mainly include hysteresis performance, load‐bearing capacity, stiffness degradation, energy dissipation capacity, and additional damping ratio, and so on. First, on the basic of this, the material‐scale damage evolution of structure specimens at each stage is qualitatively analyzed. Then, six reasonable material‐scale damage indexes that can describe the damage evolution of the structures precisely are proposed. Finally, a quantitative comparative analysis on the material‐scale damage evolution of structure specimens in the whole process is carried out under different design parameters. The research results indicate that the upgraded scheme (reasonable design parameters of and ) proposed in this study can improve the seismic performance of RC frame structures to the appropriate level required for the design, in terms of load‐bearing capacity, stiffness, energy dissipation capacity, and damping ratio. At the same time, the failure mode of the structures can be well controlled. The occurred damage at beam‐column joints is reasonably transferred to the beam area, which can guarantee the seismic design requirements of “strong joints and weak components.”

English

The seismic performance of non ductile reinforced concrete (RC) buildings with eccentric steel bracing of inverted Y type is investigated. 10, 15 and 20 storey buildings are analyzed by using pushover analysis. The analysis is carried out by using software SAP2000v17. The effect of distribution of steel bracing over the height of RC frame was studied. The study also concentrates on effect of link length of eccentric bracing on seismic performance of RC frame. The performance of RC frame with inverted eccentric bracing is evaluated in terms of energy absorption capacity, stiffness of frame and ductility. The behavior of eccentric braced frame (EBF) is compared with conventional RC frame and inverted V bracing.

Seismic performance evaluation of RC frames with uniform infilled walls based on adaptive CMS

In the development of performance-based seismic engineering, the capacity spectrum method (CMS) has been widely used in seismic performance evaluation because of its merits of clarity in concept and simplicity in computation. The lateral force resistance of nonstructural components and the influence of bidirectional loading are usually neglected in current seismic performance evaluation. Three archetype reinforced concrete (RC) frames were designed according to current Chinese standards and three-dimensional finite element models accounting for infilled walls or not at different modeling fidelity levels were created. Influences of infilled walls and bidirectional loading on seismic performance of RC frames are studied by CMS based on adaptive Pushover analysis. Results show that uniform infilled walls significantly improve seismic performance of RC frames. The bearing capacity under bidirectional loading is less than that under unidirectional loading. And bidirectional loading makes influences of infilled walls become somewhat inefficient.

Effect of Different Bracing Systems in Reinforced Concrete Frames under Cyclic Loading

Reinforced concrete (RC) framed structures are widely used as load transferring system in residential and commercial buildings. Even though the RC frames are designed for gravitational and seismic forces, but they are week under severe seismic events. The main disadvantage of the framed structures is inefficient bracing systems designed in it. This investigation is conducted mainly to study the effective bracing system in the RC framed structure to transfer the seismic force. This research aims to study the seismic performance of RC frames influenced by the various types of cross bracings under cyclic loading. The finite element analysis software package ABAQUS is used to investigate the braced RC frames analytically. The research scheme consists of three RC frames; the bare frame, the bare frame with single X-bracing (X frame), double X bracing (D-X frame) along the height. The structural parameters include, load-displacement hysteresis envelope, stiffness degradation and energy absorption were studied to analyze the performance of bracings. The results showed that the X frame and D-X frame noticeably increased the lateral strength, stiffness and energy dissipation properties compared to the bare RC frame. The results also indicated that the addition of X bracing along the height significantly enhanced the structural parameters of the RC frame.

Seismic performance of RC frames with EPSC latticed concrete infill walls

An expansive polystyrene granule cement (EPSC) latticed concrete wall, which has advantages of higher load-bearing and better environmental-friendly construction, has been widely applied in reinforced concrete (RC) frames to form a new structural system, and its seismic performance has become a hot topic in the field of earthquake engineering. This paper presents the experimental and numerical studies on the seismic performance of RC frames with EPSC latticed concrete infill walls. A full-scale single-storey model structure with openings in the walls, various spacings of steel rebar and binding methods between the walls and the RC frame was designed, and then tested on a shaking table to investigate the seismic performance. A numerical analysis model was constructed using the nonlinear dynamic modelling software ABAQUS. The comparative analysis of the test data and simulation results indicate that the designed RC frame with EPSC latticed concrete infill walls has satisfactory seismic performance, including the good collapse resistance and energy dissipation capacity. Especially the latticed concrete walls can significantly strengthen the RC frame and increase its lateral stiffness, and the model structure undergoes a super-major earthquake with minor inter-storey rotational displacements (only 1/513). Reduction in spacing of bars can delay the growth of cracks in the walls and increase the ductility of the structural system. Both local binding method and through-rebar binding method can effectively restrain the walls. Compared with local binding method, the through-rebar binding method can play an effective role in the out-of-plane stability of the wall, thus improve the integrity of the structural system. The proposed analytical procedure can be also applied in simulating the seismic performance of infilled multi-storey RC frames. To achieve more comprehensive assessment the performance of the RC frames with latticed concrete infill walls, further study on its global and local ductility relationships and the failure model of the infilled multi-storey frame should be carried out.

Seismic performance of non-ductile RC frames strengthened with CFRP

To study the seismic performance of non-ductile reinforced concrete (RC) frames strengthened with carbon fiber-reinforced polymer (CFRP), two 1/2-scale, 2-bay, 2-story RC frames were prepared and tested under combined axial load and cyclic lateral load. One of the RC frames served as a control specimen (bare specimen) and the other was strengthened with CFRP sheets (strengthened specimen) at its joint regions. Based on the hysteretic curves, the envelop curves, and several important indexes (e.g., strength, stiffness, ductility, energy dissipation capacity) of the two specimens, the performance of the employed seismic strengthening technique in improving the seismic performance of RC frames was discussed in detail. The experimental results indicated that the externally bonded CFRP reinforcement had little influence on the lateral stiffness of the RC frame. While the lateral strength of the strengthened RC frame increased by about 20% compared to the control RC frame. Furthermore, it is worth noting that the energy dissipation capacity of the strengthened RC frame is as much as 3.01 times that of the control RC frame. The test results of the current study indicate that the employed strengthening method can substantially improve the seismic performance of the strengthened RC frames.

Ductility damage indices based on seismic performance of RC frames

This paper presents an analytical procedure for determining ductility damage indices using static collapse mechanism analysis for ductile reinforced concrete (RC) frames subjected to prescribed drift limits corresponding to different seismic performance levels. This assessment benefits from performance-based seismic design (PBSD) concept that employs rotation ductility factors, pre-defined target damage indices and beam sidesway mechanism as key performance objectives to estimate curvature ductility demands at pre-designated plastic hinges of beam sidesway mechanism. The proposed ductility-based damage indices (DBDI) assessment procedure considers regular frames with secondary effects such as P-Delta and soil–structure interaction (SSI) within a simple non-iterative process suitable for practical applications. A 12-story RC moment frame was chosen to implement the proposed procedure considering P-Delta effect. Pushover analysis using SAP 2000 was carried out for the frame to verify the results of the DBDI method. The results show that the DBDI seismic assessment procedure can be used to quantify the damage potential at different performance levels and relate that to local flexural ductility of critical frame members. The research presented in this paper provides a simple yet conservative damage assessment tool for use by practicing engineers.

Full-scale experimental study on masonry infilled RC moment-resisting frames under cyclic loads

The reinforced concrete (RC) moment-resisting frames with masonry infill walls are widely used in buildings. It has been well recognized that the arrangement and constructional detail of infill walls have significant effects on the seismic performance of RC frames. During 2008 Wenchuan Earthquake, a lot of masonry infilled RC frame structures suffered serious damages due to detrimental effects brought about by infill walls rigidly connected to the main structure. In the updated Chinese seismic design code, the flexible connection between infill walls and RC frames is recommended in order to reduce the unfavorable interaction between them. In this study, seven full-scale, single-bay and single-storey RC frame specimens, five with masonry infill wall and flexible connection, one with masonry infill wall and rigid connection, and one without infill wall, were tested under low-cycle reversed loads. For the specimens with flexible connection, the variable parameters are the type and amount of constructional column, the amount of tie steel bar, and the amount of vertical slit set in the infill wall. Based on the test results, the damage behavior, lateral strength, displacement ductility ratio, stiffness degradation, and energy dissipation of the specimen are compared. The influence of constructional details of infill walls on the seismic behavior of RC frames is analyzed. It is found that with the addition of masonry infill wall rigidly connected to the frame, the lateral strength, the stiffness and the energy-dissipation capacity of the bare RC frame increase significantly while the displacement ductility ratio decreases significantly. Compared with the infill wall with rigid connection, the strength, the stiffness and the energy-dissipation capacity contributed by the infill wall with flexible connection drop significantly, but the displacement ductility ratio of the frame rises up.

Earthquake Response Characteristics of Contained Masonry Infilled Frames

The strength and stiffness contribution of infill masonry is generally ignored in the design, due to the uncertainty in the strength properties of masonry, separation of infill from frame, low tensile strength, brittle characteristics of masonry walls, less out of plane strength and stiffness, etc.. They are considered as nonstructural elements which is reasonable for the frames under gravity loads but it is not true for the frames under seismic loads. Contained masonry as infill in RC (reinforced concrete) frames provides better contact at the interface and a higher out of plane strength and stiffness. Considering the seismic action on the frames which are likely to be subjected to in-plane as well as out of plane shaking, a research work has been carried out by the authors to investigate the seismic performance of RC frames with and without contained masonry infill panels using FE (finite element) computer program (ANSYS-Ver.11) and experimentally using the tri-axial shake table to evaluate the methods proposed in IS-1893-2002 to calculate the fundamental natural frequency. The RC frames were designed and detailed as per IS (Indian Standard) specifications such as IS 456-2000, IS 1893-2002 and IS 13920-1993. Based on the experimental and analytical investigations, the contained masonry infill panels significantly affect the seismic load resisting characteristics of the RC frames. The IS 1893-2002 formulation does not predict the values and hence the recommendation needs to be validated with experimental results.

Restoring Force Model of Joints of RC Frame Retrofitted by FRP

In order to evaluate the seismic performance of reinforced concrete (RC) frames retrofitted by FRP, the experiment of RC frames retrofitted at joints by FRP was carried out. The enhancement in seismic performance of the retrofitted frames is evaluated in hysteretic performance, bearing capacity, stiffness degradation and energy dissipation. And the strengthening effect of the frame retrofitted by CFRP and C/GFRP was compared in the experiment. The restoring force model of RC frame joints retrofitted with FRP was proposed and ranges of the characteristic parameters were determined. The equation of restoring force model for joints strengthened by C/GFRP was suggested. The result show that seismic performance of RC frame retrofitted by FRP based on joints can be improved remarkably. The restoring force model which proposed can be used in seismic elasto-plastic analysis of RC frame structure retrofitted by FRP and practical engineering seismic retrofitting design by FRP.

A Beam-and-Column Based Macro Model for Masonry Infill Walls in RC Frames under Cyclic Loading

Reinforced concrete (RC) frame with masonry infill walls is a very common structural system in low and medium rise buildings. The infill walls are usually considered as non-structural components in the design or assessment of buildings. However, many damages in earthquakes have shown that the infill walls can significantly change the structural response to seismic action. Consequently the evaluation of the seismic performance of RC frame with masonry infill walls becomes very important, and also turns to be a major challenge for structure engineers. In this paper a beam-and-column (BAC) macro model for walls is proposed to simulate the masonry infill walls in RC frames. In this model, the masonry panel is replaced by an equivalent rigid frame which is made up of some beam-and-column members. The geometric parameters of each member can be determined simply by equivalent stiffness combined with the original dimensions of wall panel. The physical characteristics are described directly by material properties of wall panel under investigation. To validate the rationality of proposed model, a masonry-infilled RC frame under cyclic reversed loading is analyzed by the proposed model. The results, including crack pattern, load versus displacement relation are then compared with the experiment response. Good agreements are found.

Reconsideration of Seismic Performance and Design of Beam-Column Joints of Earthquake-Resistant Reinforced Concrete Frames

Seismic performance requirements for beam-column joints of earthquake-resistant reinforced concrete (RC) frames are discussed, and the experimental data of RC joints under cyclic loading collected from the literature are analyzed. It is observed that joint shear failure under cyclic loading is characterized by significant inelastic joint shear deformation. Joint shear strength should thus be formulated by limiting the influence of joint shear deformation on the seismic performance of RC frames. It is noticed that joint transverse reinforcement does not have significant influence on joint shear deformation and bond deterioration in the joints but may have significant influence on joint axial capacity under cyclic loading. Hence, the requirement for joint transverse reinforcement may be formulated by keeping the joint axial capacity not lower than the column axial capacity under seismic action. The influence of bond deterioration in joints on the seismic performance of RC frames and the anchorage requirement for beam reinforcement in joints are analyzed and discussed.

Analytical investigation of the seismic performance of RC frames rehabilitated using different rehabilitation techniques

The objective of this study is to investigate analytically the effectiveness of different rehabilitation patterns in upgrading the seismic performance of existing non-ductile reinforced concrete (RC) frame structures. The study investigates the performance of two RC frames (with different heights representing low- and high-rise buildings) with or without masonry infill when rehabilitated and subjected to three types of ground motion records. The ground motion records represent earthquakes with low, medium and high frequency contents. Three models were considered for the RC frames; bare frame, masonry-infilled frame with soft infill, and masonry-infilled frame with stiff infill. Four rehabilitation patterns were studied, namely: (1) introducing a RC shear wall, (2) using steel bracing, (3) using diagonal FRP strips (FRP bracings) in the case of masonry-infilled frames, and (4) wrapping or partially wrapping the frame members (columns and beams) using FRP composites. Incremental Dynamic Analysis was conducted for the studied cases. The seismic performance enhancement of the studied frames is evaluated in terms of the maximum applied peak ground acceleration resisted by the frames, maximum inter-storey drift ratio, maximum storey shear-to-weight ratio and energy dissipation capacity.

Analytical Evaluation of Seismic Performance of RC Frames Rehabilitated Using FRP for Increased Ductility of Members

Many reinforced concrete (RC) frame structures designed according to pre1970 strength-based codes are susceptible to abrupt strength deterioration once the shear capacity of the columns is reached. Fiber composites are used to increase the shear strength of existing RC columns and beams by wrapping or partially wrapping the members. Increasing the shear strength can alter the failure mode to be more ductile with higher energy dissipation and interstorey drift ratio capacities. The objective of this study was to analytically evaluate the effect of varying distributions of fiber-reinforced polymer (FRP) rehabilitation on the seismic performance of three existing RC frames with different heights when subjected to three types of scaled ground motion records. The FRP wrapping is designed to increase the displacement ductility of frame members to reach certain values representing moderate ductility and high ductility levels. These values were assumed based on previous experimental work conducted on members wrap...

The effects of construction practices on the seismic performance of RC frames with masonry infills

A number of construction practices, implemented during the design process of a reinforced concrete (RC) structural system, may have significant consequences on the behaviour of the structural system in the case of earthquake loading. Although a number of provisions are imposed by the contemporary Greek national design codes for the seismic design of RC structures, in order to reduce the consequences, the influence of the construction practices on the seismic behaviour of the structural system remains significant. The objective of this work is to perform a comparative study in order to examine the influence of three, often encountered, construction practices namely weak ground storey, short and floating columns and two combinations on the seismic performance of the structural system with respect to the structural capacity and the maximum interstorey drifts in three earthquake hazard levels.

Seismic performance of RC frames with concentric internal steel bracing

Steel bracing has proven to be one of the most effective systems in resisting lateral loads. Although its use to upgrade the lateral load capacity of existing Reinforced Concrete (RC) frames has been the subject of numerous studies, guidelines for its use in newly constructed RC frames still need to be developed. In this paper, the efficiency of using braced RC frames is experimentally evaluated. Two cyclic loading tests were conducted on a moment frame and a braced frame. The moment frame was designed and detailed according to current seismic codes. A rational design methodology was adopted to design the braced frame including the connections between the brace members and the concrete frame. Test results showed that the braced frame resisted higher lateral loads than the moment frame and provided adequate ductility. The adopted methodology for designing the braced frame resulted in an acceptable seismic performance and thus represents the first step in the development of design guidelines for this type of frames.

Experiments on Seismic Performance of RC Frames with Hinging Columns

The seismic behavior of reinforced concrete (RC) frames with hinging columns, also known as strong‐beam–weak‐column (SBWC) frames, is studied from earthquake‐simulation test results of two small‐scale models. The models were subjected to scaled earthquake motions of various intensities on a unidirectional shake table. The paper describes some of the dynamic response measurements and their implication for SBWC‐frame performance. The response of the model structures to the “design” motion is found to be acceptable when large discontinuities in the vertical distribution of lateral strength are avoided. Maximum inelastic drifts of the structures were controlled through appropriate member proportioning, and stories comprising hinging columns exhibited adequate force‐deformation behavior and developed moderate displacement ductility factors.