Strong Column-weak Beam Research Articles

Behaviour of fibre-reinforced high-performance concrete in exterior beam-column joint

This paper presents the effect of reinforced high performance concrete (HPC) in exterior beam-column joint with and without fibre under monotonic loading. In this experimental investigation, cross-diagonal bars have been provided at the joint for reducing the congestion of reinforcement in joints, and also M75 grade of concrete with optimum mix proportion of 10 % silica fume and 0.3 % glass fibre was used. Four exterior beam-column joint sub-assemblages were tested. The specimens were divided into two types based on the reinforcement detailing. Type A comprises two joint sub-assemblages with joint detailing as per construction code of practice in India (IS 456-2000), and Type B comprises two joint sub-assemblages with joint detailing as per ductile detailing code of practice in India (IS 13920-1993). In each group there was one specimen of control mix and the remaining one specimen of fibre-reinforced mix. All the test specimens were designed to satisfy the strong column–weak beam concept. The performances of specimens were compared with the control mix and the fibre-reinforced mix. The results show that exterior beam-column joint specimens with silica fume and glass fibre in the HPC mix showed better performance.

Analysis of Influencing Factors on Outer Annular-Stiffener Type Steel Castellated Beam-Concrete Filled Steel Tuber

In order to provide a basis for designing outer annular-stiffener type steel castellated beam (OATSCB) - concrete filled steel tube (CFST) joint, the factors that influence the load-displacement skeleton curve of this kind of joint is analyzed. OATSCB - CFST joint with different influencing factors are designed, and their loading process is simulated by using finite element software ABAQUS. Before simulating, the simulating method is verified by previous test result. The corresponding load-displacement skeleton curves of those joints are also extracted. By comparing these curves in diagram, the following conclusions can be gotten: OATSCB - CFST joint has good seismic performance; steel yield strength, steel ratio and beam to column linear stiffness ratio are the important factors that influences the skeleton curve of this type of joint; opening rate is an important factor for this type of joint to form "strong column weak beam" yield mechanism.

Seismic Performance Analysis of a High-Rise Structure with Multi-Short Columns

This paper aimed at a tall frame-shear wall structure contains multi-short columns, and did pushover analysis to this structure with finite element software, and evaluated its seismic performance under rare earthquake in seismic intensity of 6 degrees. It concluded that the structure can meet the "earthquake does not fall" seismic requirements, and will not appear the cut destruction of shear frame short columns, and can achieve "strong column weak beam" design requirements.

The Influence of Slab on Yield Mechanism of RC Frame Structure

"Strong column weak beam" form of frame structure is widely considered to be a reasonable framework structure yield mechanism in the seismic damage. The current structure design is mostly on the basis of that yield mechanism for structural seismic design. Generally the structural engineers ignore the bearing capacity contribution of frame beams that comes from the slab in the seismic design. The structure engineers considered the slab as a rigid component and simply calculate the slab stiffness by magnification factor method, which ignores the core of the problem. This paper analyzes mainly the influence of the destruction of slab form frame structure , studying further how slab affect the yield mechanism of frame structure, and explores the destruction form of difference between two models after analyzing two structure models by the method of Push – over. It shows that the existence of slab make the yield mechanism of RC frame structures different from the design.

Analysis on Axial Compression Ratio to Strong Column Weak Beam Effect in Framework Node

Nodes of Column ends, included ordinary Intermediate nodes and nodes in the model of carbon fiber, have been established based on finite element program, have analyzed the comparison of the deformation, bearing capacity, ductility in Quasi static state under three conditions of axial compression ratio reinforcement (0.2, 0.4, 0.6) between reinforcement nodes and ordinary nodes, have researched the impact caused by the change of axial pressure ratio on seismic performance of node, The result have shown that size of the axial compression ratio and bearing capacity of reinforced nodes follow basic plastics performance, but ductility of nodes in low axial compression ratio is more effective.

Investigation into the behaviour of shear stud applied weak column–strong beam connections

The behaviour of weak column–strong beam reinforced concrete (RC) connections with the application of specially manufactured steel plates with shear studs (SPwSS) under cyclic loads was investigated, both experimentally and analytically. The aim of the work was to improve the seismic behaviour of the joint by using SPwSS. In total, 15 full-scale RC connections were tested under reversed-cyclic lateral loads. The specimens were formed as an exterior joint of a frame. The compressive strength of concrete, the width of the shear stud heads and their spacing on the steel plates were adopted as the main test parameters, whose effects on the weak columns were investigated. It was observed that plastic hinges occurred at the beams after SPwSS application. The obtained experimental results were compared with analytical results and similarities in the behaviours were observed.

Experimental study on mechanical performances of lattice steel reinforced concrete inner frame with irregular section columns

Based on the test on a 1/2.5-scaled model of a two-bay and three-story inner frame composed of reinforced concrete beams and lattice steel reinforced concrete (SRC) irregular section columns under low cyclic reversed loading, the failure process and the features of the frame were observed. The subsequence of plastic hinges of the structure, the load-displacement hysteresis loops and the skeleton curve, load bearing capacity, inter-story drift ratio, ductility, energy dissipation and stiffness degradation were analyzed. The results show that the lattice SRC inner frame is a typical strong column-weak beam structure. The hysteresis loops are spindle-shaped, and the stiffness degradation is insignificant. The elastic-plastic inter-story deformation capacity is high. Compared with the reinforced concrete frame with irregular section columns, the ductility and energy dissipation of the structure are better. The conclusions can be referred to for seismic design of this new kind of structure.

Research on Influence of Moment Augment Factor of Column on Building Cost

The new moment augment factor of column of the national Code for Seismic Design of Buildings (GB500112010) were increased, the strong column weak beam reliability of reinforced concrete structure were improved, at the same time, the cost of building were improved also. Influence of moment augment factor column on building cost was discussed by computer design software Guang Sha CAD. Result indicates that the increase of cost is very small.

Experimental tests on retrofitted RC beam-column joints underdesigned to seismic loads. General approach

This paper presents an experimental program designed to determine the behaviour of steel jacketing used as a seismic strengthening system for reinforced concrete frame structures. Tests were carried out on a total of 20 full scale interior beam-column joints. Geometry and reinforcements were selected according to existing buildings, designed solely to gravity loads under strong beam-weak column concept. Column strengthening was performed in all specimens, and four different types of column-joint connection strengthening have been tested. Two types of beam reinforcement have been included in the experimental program. Tests were carried out by subjecting specimens to gravity and cyclic loads. The paper shows general results and conclusions, describing the failure modes of the specimens. Results show that the strengthening techniques and the axial loads applied on columns can have significant influence on the seismic behaviour of the joints.

Plastic hinge length of RC columns considering soil-structure interaction

During an earthquake, soils filter and send out the shaking to the building and simultaneously it has the role of bearing the building vibrations and transmitting them back to the ground. In other words, the ground and the building interact with each other. Hence, soil-structure interaction (SSI) is a key parameter that affects the performance of buildings during the earthquakes and is worth to be taken into consideration. Columns are one of the most crucial elements in RC buildings that play an important role in stability of the building and must be able to dissipate energy under seismic loads. Recent earthquakes showed that formation of plastic hinges in columns is still possible as a result of strong ground motion, despite the application of strong column-weak beam concept, as recommended by various design codes. Energy is dissipated through the plastic deformation of specific zones at the end of a member without affecting the rest of the structure. The formation of a plastic hinge in an RC column in regions that experience inelastic actions depends on the column details as well as soil-structure interaction (SSI). In this paper, 854 different scenarios have been analyzed by inelastic time-history analyses to predict the nonlinear behavior of RC columns considering soil-structure interaction (SSI). The effects of axial load, height over depth ratio, main period of soil and structure as well as different characteristics of earthquakes, are evaluated analytically by finite element methods and the results are compared with corresponding experimental data. Findings from this study provide a simple expression to estimate plastic hinge length of RC columns including soil-structure interaction.

Numerical Simulation of Column-End Damages of Reinforced Concrete Frames Caused by 2008 Wenchuan Earthquake in China

This paper aims to investigate into the reasons for the widespread column-end damages of reinforced concrete (RC) frame buildings caused by the 2008 China Wenchuan earthquake. A six-story office building is used as the prototype building, and ten RC frames under different combinations of Seismic Intensity and Seismic Category are designed for the prototype building in accordance with the Chinese codes. Two joints of the second floor of each frame are selected for calculating the column-to-beam flexural strength ratio (CBSR), and the effects of the following four factors on the CBSR during a strong earthquake are analyzed: (1) the detailing practice of beam longitudinal reinforcement adopted in China; (2) slab participation in beam flexure; (3) reduction of joint concrete strength; and (4) variation of column axial force. The numerical results of CBSR indicate that the code requirement for the “strong column-weak beam” design in China is not sufficient for the RC frames designed for a Seismic Intensity of 0.2 g or lower to avoid column-end damages during a strong earthquake. Suggestions are made for improving the “strong column-weak beam” design of RC frames in China.

Analysis and seismic tests of composite shear walls with CFST columns and steel plate deep beams

A composite shear wall concept based on concrete filled steel tube (CFST) columns and steel plate (SP) deep beams is proposed and examined in this study. The new wall is composed of three different energy dissipation elements: CFST columns; SP deep beams; and reinforced concrete (RC) strips. The RC strips are intended to allow the core structural elements — the CFST columns and SP deep beams — to work as a single structure to consume energy. Six specimens of different configurations were tested under cyclic loading. The resulting data are analyzed herein. In addition, numerical simulations of the stress and damage processes for each specimen were carried out, and simulations were completed for a range of location and span-height ratio variations for the SP beams. The simulations show good agreement with the test results. The core structure exhibits a ductile yielding mechanism characteristic of strong column-weak beam structures, hysteretic curves are plump and the composite shear wall exhibits several seismic defense lines. The deformation of the shear wall specimens with encased CFST column and SP deep beam design appears to be closer to that of entire shear walls. Establishing optimal design parameters for the configuration of SP deep beams is pivotal to the best seismic behavior of the wall. The new composite shear wall is therefore suitable for use in the seismic design of building structures.

Role of cast-in situ slabs in RC frames under low frequency cyclic load

This paper presents an investigation on the seismic behaviors of two spatial reinforced concrete (RC) frames: RC frame with slabs and RC frame without slabs. The study is focused on the effect of the cast-in situ slabs on the seismic performance of the RC frames. Based on the low frequency cyclic loading test for two spatial RC frames, the energy dissipation, bearing capacity, ductility, effect of cast in situ slabs on the flexural capacity, effective slab width, shear distribution of columns, rotation of members and joint shear force were experimentally investigated. Research findings indicated that, due to the effect of slab, the energy dissipation capacity of specimens changed slightly while the corresponding flexural moment at the beam ends increased obviously. Compared to the RC frame without slabs, the RC frame with slabs exhibited a higher bearing capacity while inferior deformation capacity. Test results also showed that the effective slab width varied with the variation of inter-story drift and joint pattern. The torsion cracks appeared in the transverse beams and the joints shear force increased due to the effect of slabs. The failure pattern of RC frame without slabs was “strong column–weak beam” while that with slabs turned into the “strong beam weak column”. The shear distribution of columns was affected by slabs.

The seismic performance of new detailing for RCS connections

Over the past few decades considerable experimental and numerical studies have been conducted on the Reinforced Concrete columns to Steel beams (RCS) connections. Most of those researches have focused on studying the joint failure modes and ultimate joint strength of specimens utilizing strong beams and columns with weak joints. In this paper, two interior RCS connections were designed based on the Strong Column–Weak Beam (SCWB) criterion. Both specimens were tested under quasi-static reversed cyclic loading. The tested specimens were modeled by a finite element method, which verified with experimental results. Several models with different joint details were investigated using the verified FEM. Lateral load–story drift response, vertical bearing stresses, joint shear forces, shear strains at the joints, and axial stresses of the joint stirrups were studied in those models. The results indicated that the performance of models directly depends on joint detailing, effectiveness of shear keys, and the amount of confinement provided for a joint region.

Force Behavior of Outer Annular-Stiffener Type Steel Castellated Beam-Concrete Filled Steel Tuber

The force behavior of outer annular-stiffener type steel castellated beam (OATSCB) - concrete filled steel tube (CFST) is analyzed, and the feasibility of this kind of join is discussed. The loading process of the joint is simulated by using finite element software. By analyzing the hysteretic loops, skeleton curves, energy dissipation coefficient, equivalent viscous damping coefficient and ductility coefficient, the bearing capacity and seismic performance of this type of joint is studied. Before simulation, the validity of the simulation method is verified by using the previous experiment data of outer annular-stiffener type steel beam (OATSB) - CFST. It shows that the results from the finite element simulation method and the experiment are similar to each other, and the hysteretic loops is plump , the energy dissipation coefficient, equivalent viscous damping coefficient and ductility coefficient of this type of joint are high. It can be seen that this type of joint has good mechanical properties, and is easy to realize the yield mechanism of strong column weak beam.

Experimental Study and Finite Element Analysis of Hysteretic Behavior of End-plate Connection Semi-Rigid Space Steel Frames

To investigate the seismic behavior of end-plate connection semi-rigid space steel frames, three 1/4-scale specimens were tested under cyclic load. Finite element analysis which took initial geometric imperfections into consideration was also conducted, and the results conform to experimental results. The failure modes, hysteretic behavior, deformation capacity and energy-dissipation capacity of the end-plate connection semi-rigid space steel frame have been explicated in this paper. The investigation in this paper indicates that: (1) the end-plate connection semi-rigid space steel frames exhibit full hysteretic loops under horizontal cyclic load and have good ductility as well, indicating that this kind of frames can satisfy the deformation demand in strong earthquakes. (2) Plastic hinges formed at beam ends, and the stress and deformation amplitudes of joint-panels were smaller than those of column base and beam ends. It shows that this kind of frames satisfy the design principle “strong column weak beam, strong joint weak component”.

The Effect of Cast-In-Place Floor Slab on Strong Column-Weak Beam Mechanism of RC Frame Structures

For understanding the influence of cast-in-place floor slab on the failure mechanism of "Strong column-weak beam", nonlinear finite element simulation of a 1/2-scale one-story, two-bay RC frame specimen has been carried on using DIANA software. The analysis model was designed and constructed according to the design drawings of Xuankou middle school building. Through the comparison and analysis, it shows that the 3 D solid finite element model established is feasible to analyze the mechanical performance of RC frame, and the contribution of cast-in-place floor slab on the negative flexural capacity of frame beam, which is disadvantageous to realize the failure mechanism of "Strong column-weak beam", should not be neglected.

Seismic Evaluation of Reinforced Concrete Frames Using Pushover Analysis(eng)

Ten stories–five bays reinforced concrete frame (two dimensional beams and columns system) subjected to seismic hazard of the Mosul city/Iraq is analyzed. Plastic hinge is used to represent the failure mode in the beams and columns when the member yields. The pushover analysis is performed on the present building frame using SAP2000 software (V.14) to verify code's underlying intent of Life Safety performance under seismic effects. The principles of Performance Based Seismic Engineering are used to govern the present analysis, where inelastic structural analysis is combined with the seismic hazard to calculate expected seismic performance of a structure. Base shear versus tip displacement curve of the structure, called pushover curve, is an essential outcomes of pushover analysis for two actions of the plastic hinge behavior, force-controlled (brittle) and deformation-controlled (ductile) actions. Lateral deformations at the performance point proved that the building is capable of sustaining certain level of seismic load. The building clearly behaves like the strong column-weak beam mechanism, although the formed hinges are in the dangerous level according to Applied Technology Council (ATC-40) categories of structural performance and they need to be strengthened. Keywords: Building frame, Nonlinear response spectrum, Pushover analysis, Reinforced concrete, Seismic performance.

Observations on the Van Earthquake and Structural Failures

Turkey is located in one of the most seismically active regions in the world. In the 1999 Marmara earthquake in Turkey, more than 20,000 people died. On October 23, 2011, an earthquake with a magnitude of 7.2 on the Richter scale struck the Van and Ercis cities, causing more than 600 casualties. The epicenter was located in Zone 1 in the earthquake zones map of Turkey. In this paper, the results of a field reconnaissance survey of the affected earthquake area were reported and common structural failures in reinforced concrete (RC) structures were summarized. The observed failure modes included weak column–strong beam formations, hinging in the columns, column–beam joint failures, lap splice inadequacies, poor concrete quality, insufficient transverse reinforcement, buckling of longitudinal column reinforcement, pancake type of collapse mechanism, soft- and weak-story failures, and short column formations. The buildings in Van and Ercis have also several undesired architectural features, such as the presence of mezzanine floors and penthouses, commercial use of ground floors, etc.

Push-over Analysis on the Failure Mechanism of Reinforced Concrete Frame Structure

A reinforced concrete frame model was designed by PKPM software and then a push-over analysis is performed in this paper. Values of plastic hinges were calculated by Section Builder software, which based on constitutive relations of material and the section forms, then the data was written into corresponding components in the model to carry out push-over analysis. The plastic hinges first appeared at the ends of beams in the first story ,spread to the second story and the ends of columns in the first story. At last plastic hinges spread to the top story. The story drift and interstory displacement rotation of the model in different cases tended to decrease as structural height increase. It can be demonstrated that failure mechanism satisfies the design requirements of strong column weak beam.