Beam Bars Research Articles

Fatigue behavior assessment for steel fiber reinforced concrete beams through experiment and Fatigue Prediction Model

The fatigue flexural behavior of steel-fiber-reinforced concrete (SFRC) beams was assessed through the experiment on SFRC beams subjected to fatigue loading and the analysis of Fatigue Prediction Model (FPM). The stress level, tensile reinforcement strength, and steel fiber volume fraction were considered in the program. Test results indicated that steel fibers can improve the fatigue performance of the beams. The fatigue life of the beams increased significantly with the increase of steel fiber volume fractions from 0 to 1.0%, and slightly decreased for 1.5% steel fiber volume fraction because of the fiber cluster. A FPM of SFRC beam was proposed based on the fatigue properties of constituent materials and cross-section analytical method. This model can simulate the development of strains in concrete and steel bars of beams under fatigue loading, and can also be extended to assess the effects of reinforcement ratio upon the fatigue life and failure mode of SFRC beams.

Fatigue performance of an innovative shallow-buried modular bridge expansion joint

Bridge expansion joint can accommodate the deformation under the effects of vehicle load and temperature. Fatigue damage readily occurs because it is directly subjected to repeated load. In this paper, fatigue and static loading tests were conducted on modular bridge expansion joint (MBEJ). This is an innovative type of shallow-buried modular bridge expansion joint, and the anchoring depth is reduced by 40%-50% compared with traditional ones. The reduced overall height can well adapt to the slide shutter rapid construction method in practical engineering. A loading device was designed to simulate vertical and horizontal load. The load-deflection relationship after fatigue loading were discussed. The fatigue crack types, crack initiation locations, failure criteria, and fatigue failure modes of MBEJs were also studied. Following that, a finite element model was established to calculate the internal force of welded connections. Structural analysis on MBEJs was used to calculate the stress range within center beam and support bars under the test conditions. A theoretical fatigue performance assessment method on MBEJs was introduced, which is based on the nominal stress method and a linear Miner damage accumulation rule. The theoretical prediction agreed well with the experimental observations.

Bond Behavior of Upper Reinforcing Steel Bars in Self-Compacting Concrete Beams at Shear Zone

Bond Behavior of Upper Reinforcing Steel Bars in Self-Compacting Concrete Beams at Shear Zone

Nonlinear Response Study and a Rotational Spring Model for Degrading Cyclic Behavior of Interior Reinforced Concrete Connections

ABSTRACT A parametric study is performed on the cyclic behavior of reinforced concrete connections. A number of 64 analytical cases are developed being different in the value of the axial force of column, volume of the transverse reinforcement in the connection, ratio of the bending capacity of column and beam, and the continuity index of the longitudinal bars of beam in the connection. The stiffness, dissipated energy, ductility, and ultimate shear stress and strain of the connections are calculated. Finally, a cyclic model for the nonlinear behavior of the connection is proposed that includes stiffness and strength degradation and longitudinal bar slip.

Effect of deviation angle between principal stress and diagonal reinforcement direction on seismic performance of RC coupling beams

In a coupled shear wall system, the reinforced concrete (RC) coupling beams are allowed to form plastic deformations in order to dissipate seismic energy while maintaining the stability of overall structural system. However, the coupling beams are generally shear-dominated members because of their short shear span-depth ratio, which is usually less than 2. Therefore, under high seismic shear demand, the energy dissipation capacity and ductility of these members are sharply reduced compared to RC beams with larger shear span-depth ratio due to severe pinching effect. In order to avoid any undesirable structural behavior, the current standards stipulate the use of diagonal reinforcing bars in RC coupling beams with short span-depth ratio. Previous studies show that the diagonal reinforcement arrangements improve the structural performance of coupling beams, but the behavior of such members under cyclic bending and shear may significantly vary depending on the orientation of diagonal reinforcement. In this study, the effects of deviation angle between principal stress and diagonal reinforcement direction in the failure region, were experimentally investigated considering the potential failure modes of the coupling beams. Six RC coupling beams were tested under reversed cyclic bending and shear during this research. Experimental results show that the ductility ratio and the energy dissipation capacity of RC coupling beams vary, depending on the orientation of the diagonal reinforcement even when the same amount of diagonal reinforcement is provided. The structural performance of RC coupling beams improves as the deviation angle between direction of principal stress and the diagonal reinforcement becomes smaller. Finally, a finite element method (FEM) analysis was carried out for the test specimens. The FEM analysis results closely agreed with experimental observations that both the ductility ratio and energy dissipation capacity were larger for members with lowest deviation angle.

Analytical investigation of the role of reinforcement in perpendicular beams of beam-column knee joints by 3D meso-scale model

This paper presents an analytical investigation of the role of the reinforcing bars in the perpendicular beams of beam-column knee joints with mechanical anchorages. A computer simulation using 3D Rigid Body Spring Model (3D RBSM) is used for the analysis of RC beam-column joints in consideration of the effect of multidirectional arrangement of reinforcing steels. Simulation results provide beneficial information for understanding the macroscopic behavior because the internal stresses and crack conditions can be investigated. In this study, the beam-column joint simulation models are varied in the number of reinforcements to study the role of the reinforcing bar in perpendicular beam. Simulation results show that the capacity can be increased when reinforcing bars are added in the perpendicular beams. Through the study of the internal stresses and cracks using numerical simulation, the function of the longitudinal reinforcement in the perpendicular beams is to transfer the stresses from the joint to the perpendicular beams by means of the dowel action which is obtained by utilizing the multiple layers meshing of reinforcement and the local strain distribution. Ultimately, this research also shows that 3D RBSM can be a useful tool for the analysis of the RC beam-column joints with multidirectional arrangement of reinforcing steels based on a case-by case basis that cannot be addressed by the design code and conventional numerical methods.

Structural designation and mechanical properties of TiNi/Ti2Ni laminated composites

TiNi/Ti2Ni laminated composites were fabricated using hot isostatic pressing (HIP) furnace together with structural designation by the control of Ti and Ni foil thicknesses. During HIP processing, Ti reacts with Ni, leading to the formation of softer TiNi and harder Ti2Ni. Through adjusting the thickness ratio of Ti and Ni foils, the ratio of TiNi and Ti2Ni fraction can be controlled. Hard-soft-hard, soft-hard-soft and hard-intermediate-soft laminated composites were designed, where hard layer was made by 50 μm Ti and 20 μm Ni, soft layer was made by 40 μm Ti and 20 μm Ni, and the intermediate structure between hard and soft ones was made by 45 μm Ti and 20 μm Ni. The mechanical properties were characterized using uniaxial tension, uniaxial compression, single edge-notched beam and split-Hopkinson pressure bar. The results show that all three laminated composites have compression strength of 1690 ∼ 1853 MPa and fracture toughness of 27.2 ∼ 37.9 MPa• m1/2 due to the same constituents of TiNi and Ti2Ni. However, the soft-hard-soft structure shows the best response under high strain rate because it was fractured into larger pieces while the other two structures were fractured into smaller pieces together with smaller fracture strain.

Experimental study of flexural behavior and serviceability of hybrid concrete beams reinforced by steel and G/BFRP bars

In this paper, the flexural behavior and serviceability performance of concrete beams reinforced with hybrid glass/basalt fiber-reinforced polymer (G/BFRP) bars and steel bars were investigated. From the viewpoint of reducing the risk of steel corrosion, two kinds of hybrid reinforced beams were designed, eleven concrete beams including 3 steel-reinforced beams and 8 hybrid-reinforced beams were tested. The effect of the hybrid reinforcement ratio on the flexural performance was analyzed and the applicability of replacing steel bars with GFRP or BFRP bars in concrete beams was discussed. The results show that the ultimate bending moment of hybrid-reinforced concrete beam was about 91-97% of that of steel-reinforced concrete beam with the same reinforcement ratio. Since the reduction of the bearing capacity of hybrid-reinforced beam was small, it can be proved that it is feasible to replace the corner steel bar of concrete members with G/BFRP bars. For the serviceability performance of beams hybrid-reinforced with G/BFRP bars and steel bars, however, their deflection and maximum crack width were 20%-60% higher than that of steel-reinforced beams under the same load levels within the limit state of serviceability. It showed that the stiffness and crack resistance of hybrid beams weakened greatly. Finally, it was found that the FRP-to-steel ratio of bar areas had great influence on the flexural behavior and serviceability performance of concrete beams hybrid-reinforced with FRP and steel bars.

Assessing provisions in Eurocode2 for anchoring reinforcing bars with bends

In Eurocode2, the design provisions allow for the anchorage length of reinforcing bars with bends to be calculated as the center line of the bar from the critical section of the member to the end of the straight portion of the bar beyond the bend, with no limit on the maximum value of the length beyond the bend (extension length). This paper thus presents statistical analysis for test results of reinforcing bars anchored with bends, collected from the literature, as a means to assess the performance of the provisions of Eurocode2. Strength of bent bars at an anchorage length depends on many parameters, including concrete compressive strength, embodied as a constant bond stress along the anchorage length; diameter of the bar; concrete side cover; spacing between bars, and confining reinforcement. Test results incorporated in this analysis include 113 simulated beam-column joint specimens with 16, 19, 22, 25, and 36 mm beam bars with stresses at anchorage failure ranging from 213 to 943 MPa, and concrete compressive strengths ranging from 18 to 114 MPa. Each specimen contained 2, 3, or 4 bent beam bars with clear spacing between them ranging from 2db to 11.4db. All specimens contained no confining reinforcement within the joint region and a constant concrete side cover of either 65 mm or 90 mm. The analysis showed that, for a given bar diameter, the predicted bar stress at anchorage failure with limitations as originally integrated on bond stress, concrete cover, and spacing between bars is reasonably safe. However, the ratio of test-to-calculated bar stress decreases as the ratio of extension to embedment length increases, resulting in an unconservative design when the extension length exceeds half of the embedment length. For rational designs, an upper limit on the extension length of half the embedment length is thus suggested.

Experimental Investigation of Progressive Collapse of Prestressed Concrete Frames after the Loss of Middle Column

Accidental loads such as explosion and vehicle impact could lead to failure of one or several load‐bearing members in the structures, which is likely to trigger disproportionate progressive collapse of overall structures. Prestressed concrete (PC) frame structures are usually at great risk of collapse once load‐bearing members fail, because the members in PC frame structures are usually subjected to much more load than those in common reinforced concrete (RC) frame structures. To investigate the progressive collapse behaviors of PC frame structures, five one‐fourth reduced scaled frame substructures were fabricated and collapse tests were conducted on them. Influence of span‐to‐depth ratios of frame beams and prestress action modes on the collapse performance of PC frame structures was discussed. Experimental results indicated that PC frame substructures with different prestress action modes, including bonded prestress and unbonded prestress, presented different collapse resistance capabilities and deformability. Tensile force increment of the unbonded prestressing strands almost linearly increased with the vertical displacement of the failed middle column. Catenary action is one of the most important mechanisms in resisting structural collapse. Prestressing strands and longitudinal reinforcing bars in the frame beams benefited the formation and maintaining of catenary action. The ultimate deformability of the PC frame structures was tightly connected with the fracture of prestressing strand. In addition, a calculation method of dynamic increase factors (DIFs) suitable for PC frame structures was developed, which can be used to revise the design collapse load when static collapse analysis is conducted by the alternative path method. The DIFs of the five substructures were discussed on the basis of the proposed method; it revealed that the DIFs corresponding to the first peak loads and the ultimate failure loads for the PC frame substructures were less than 1.49 and 1.83, respectively.

Collapse Responses of Concrete Frames Reinforced with BFRP Bars in Middle Column Removal Scenario

Six concrete beam-column frame sub-assemblages reinforced with basalt fiber-reinforced polymer (BFRP) bars in the frame beams were designed to investigate the collapse resistance after a middle column removal. Effect of parameters, including span to depth ratio of frame beams, prestressing, as well as material types of stirrups in the beams, on the collapse resistance of the sub-assemblages, was investigated. Experimental results showed that the initial stiffness of the frame beams was apparently lower due to low elastic modulus of BFRP bars. The collapse resistance of the sub-assemblages presented wave-like increasing tendency with the vertical displacement of the failed middle column, and it mainly attributed to the cracking or crushing of concrete and rupture of BFRP bars in the frame beams. Top longitudinal BFRP bars at the beam ends near to the side column (BESCs) and bottom longitudinal BFRP bars at the beam ends near to the middle column (BEMCs) kept tensile during the loading process, which played an important role in resisting structural collapse. Adjacent structural members such as frame beams and columns could provide horizontal reaction forces to constrain the free deformation of the residual sub-assemblages after the middle column failed, and it was beneficial to mitigate the structural collapse risk. The vertical deformation of the frame beams was nearly linear and proportional to the vertical displacement of the failed middle column. Finally, the dynamic increase factor (DIF) of collapse load was discussed using energy conservation method, and a calculation method of DIF for prestressed concrete frame structures was developed. It was suggested that the DIF values for the non-prestressed frame structures reinforced with BFRP bars in the beams should be taken as 2.0, while those for the prestressed sub-assemblages can be taken between 1.44 and 2.0.

Flexural Performance of Laced Reinforced Concrete Beams under Static and Fatigue Loads

This paper introduces experimental results of eighteen simply supported reinforced concrete beams of cross sections ( ) and length 3000 mm to study the effect of lacing reinforcement on the performance of such beams under static and fatigue loads. Twelve reinforced concrete beams (two of them are casted with vertical shear reinforcement used as control beams) are tested under four points bending loading with displacement control technique and six laced reinforced concrete beams were exposed to high frequency (10 Hz) by fixing the fatigue load in each cycle. Three parameters are used in the designed beams, which are: lacing bar diameter (4mm, 6mm, and 8mm), lacing bar inclination angle to horizontal , and lacing steel ratio depending on number of lacing bar in each longitudinal face of beam and lacing bar diameter. The comparison results of experimental tests revealed that the ultimate loads of laced reinforced concrete beams are higher than the conventional reinforced concrete beams due to increasing lacing bar diameter, angle of inclination lacing bar, and lacing steel ratio, while the deflection is reduced. Also, the laced reinforced concrete beams can safely withstand the fatigue loading.

Analysis of the Effect of Column-to-Beam Strength Ratio on Seismic Performance of RC Frame Structure

Strong column-weak beam is one of the important concepts in seismic design of RC frame structure. The experience of earthquake damage shows that the structure designed according to the existing codes cannot achieve the expected failure mode of strong column-weak beam due to the effects of factors such as axial compression ratio, slab and so on. In this paper, the RC frame structures are designed with column-to-beam strength ratio of 1.2, 1.4, 1.6, 1.8 and 2.0, and the structural responses are obtained using Push-over analysis. The effect of column-to-beam strength ratio on failure modes of RC frame structure is studied. The results show that the existence of slab affects the yield mechanism of steel bars in beams and columns, and further affects the possible failure modes of structures. In case of considering slab, increasing column-to-beam strength ratio can effectively enhance structural seismic capacity. The failure mode of strong column and weak beam can be achieved when the column-to-beam strength ratio is 1.8.

Development and testing of precast concrete beam-to-column connections with high-strength hooked bars under cyclic loading

A traditional reinforcing detail—hooked bars anchored in the joint core—for the bottom bars in precast beams was improved by using small-diameter high-strength bars to reduce the steel congestion in the cast-in-place connection zone. Five full-scale beam-to-column connections, including a monolithic specimen, were tested under reversed cyclic loading. The primary test variables were the type of beam longitudinal bars, manner of roughening the inner surface of the precast U-shell, presence or absence of the small-diameter stirrups inside the U-shell, and height of the precast columns. An analysis of the strength, ductility, stiffness, and energy dissipation showed that the proposed connection exhibited a comparable, although slightly inferior, seismic performance relative to the monolithic connection. Among the precast specimens, the existence of additional stirrups slightly improved the total performance. The use of high-strength steel bars as beam top longitudinal bars further decreased the loading capacity and energy dissipation. The air bubble film technique used to roughen the interfaces ensured the structural integrity.

Flexural fatigue behaviour of steel reinforced PVA-ECC beams

This paper presents an experimental investigation of the flexural fatigue behaviour of steel reinforced polyvinyl alcohol-engineered cementitious composite (PVA-ECC) beams. The influence of the PVA-ECC matrix and stirrups on the fatigue strength of steel reinforced beams was studied. Eleven beams, including three steel reinforced normal concrete beams (RC beams), four reinforced PVA-ECC beams with stirrups (RECC beams) and four reinforced PVA-ECC beams without stirrups (RECC-NS beams), were tested under a constant amplitude cyclic loading. The minimum load of each cycle was set at 20% of the static strength of the corresponding beam while the maximum loads ranged from 60% to 90%. Experimental results showed that the RC and RECC beams exhibited flexural failure with fracture of tensile reinforcement bars. By contrast, RECC-NS beams tested under 20–90%, 20–70% and 20–60% load ranges were respectively failed by shear, combined of shear and flexural, and flexural with tensile reinforcement bars yielded. The test results showed that the RECC beams generally had shorter fatigue life than the RC beams when tested under relatively high load ranges. This could be due to greater stiffness degradation which eventually led to a higher stress increasing rate in tensile reinforcement bars of the RECC beams.

Shear strength model for reinforced concrete beam-column joints based on hybrid approach

Behavior of RC beam-column joint is very complex as the composite material behaves differently in elastic and inelastic range. The approaches generally used for predicting joint shear strength are either based on theoretical, strut-and-tie or empirical methods. These approaches are incapable of predicting the accurate response of the joint for entire range of loading. In the present study a new generalized RC beam-column joint shear strength model based on hybrid approach i.e. combined strutand-tie and empirical approach has been proposed. The contribution of governing parameters affecting the joint shear strength under compression has been derived from compressive strut approach whereas; the governing parameters active under tension has been extracted from empirical approach. The proposed model is applicable for various conditions such as, joints reinforced either with or without shear reinforcement, joints with wide beam or wide column, joints with transverse beams and slab, joints reinforced with X-bars, different anchorage of beam bar, and column subjected to various axial loading conditions. The joint shear strength prediction of the proposed model has been compared with 435 experimental results and with eleven popular models from literature. In comparison to other eleven models the prediction of the proposed model is found closest to the experimental results. Moreover, from statistical analysis of the results, the proposed model has the least coefficient of variation. The proposed model is simple in application and can be effectively used by designers.

Tests and analysis of RC building, with or without masonry infills, for instant column loss

Abrupt loss of a ground story column was experimentally simulated on a 0.8:1-scaled model of a 2 × 3 bay, two-story concrete building with masonry infills along the perimeter of the second story. Three cases were investigated in the infilled building: loss of a column at a corner of the building, inside the plan area or at the perimeter; loss of the perimeter column was also studied with the infills removed and the weight on the model structure increased, to simulate a third story. In general, there was almost no visible damage after each test, neither in the concrete structure nor in the infills. Residual diagonal cracks were visible at the bottom face of slabs, starting from the removed interior column, and especially from the removed exterior column in the repeat test without infills; after the additional load on the floors had been removed, these cracks were not visible anymore. The excellent performance even without the infills is due to the continuity of the bottom bars of beams through the beam/column joints and to the placement of two-way top and bottom reinforcement throughout the slabs, continuous across the supports on beams. During the quasi-stationary free vibration stage that followed column removal, the accelerations measured on the slabs adjacent to the column being removed exceeded only marginally the acceleration of gravity upwards and downwards. This confirms that it is good practice to place two-way top reinforcement in slabs, as well as to use a magnification factor of 2 on the gravity loads of these slabs in pushdown analyses performed to investigate loss of column incidents. Numerical simulation of the tests was successful as far as the prediction of the residual deflections and the decay of vertical vibrations are concerned, but could not capture the high frequency features of the transient vibration.

Analytical Model for Tensile Membrane Action in RC Beam-Slab Structures under Internal Column Removal

An analytical approach was developed at Nanyang Technological University, Singapore, to predict structural capacities of RC beam-slab structures under the internal column removal scenario, taking into account the contribution of tensile membrane action in the slab. The model considers both commonly used loading methods in the laboratory, namely, concentrated and uniformly distributed loads. Catenary action in internal beams is neglected for conservatism, and tensile membrane action is assumed to rely solely on the yielding force of the top reinforcement arranged along negative yielding lines in the slab. The failure criterion of the model is based on fracture of longitudinal bars in internal beams, either near the middle or near the edge of beam-column joints. The proposed approach is shown to be reasonable because it provides conservative estimates compared with actual tests, which had high rotational restraints at the slab perimeter, and still gives good predictions for cases of semirigid rotational restraints.

A Review on Pull out Test on Exterior Beam-Column joint

Conventional concrete loses its tensile resistance after the formation of multiple cracks. However, fibrous concrete can sustain a portion of its resistance following cracking to resist more loading. Use of the headed bar can offer a potential solution for these problems and may also ease fabrication, construction, and concrete placement. There have been many catastrophic failures reported in the past earthquakes, with Turkey and Taiwan earthquakes occurred in 1999, which have been attributed to beam–column joint failures. To achieve this performance level, special steel reinforcement details are required in the beam–column joint region of reinforced concrete framed structures. The experimental work carried out on four different arrangements of reinforcement of beam column joints. The aim of the research is to investigate the pull-out behavior such as strength, failure mode, and crack patterns of different arrangements of reinforcement in exterior beam column junctions. The transverse reinforcement of a joint reduces stresses by improving the confinement of concrete. All joints were tested by using reversed cyclic loading. In the first arrangement, the beam bars are extended in the column for distance Ld + (10xDia) from the inner face of column. This research studies the experimental behavior of full-scale beam-column space (three-dimensional) joints under displacement-controlled cyclic loading. Eleven joint specimens, included a traditionally reinforced one (without adequate shear reinforcement), a reference one with sufficient shear reinforcement according to ACI 318, and nine specimens retrofitted by ferrocement layers, were experimentally tested to evaluate a retrofit technique for strengthening shear deficient beam column joints.

Bond Strength of Reinforcing Steel Bars In Self-Compacting Concrete Beams at Shear zone

Bond Strength of Reinforcing Steel Bars In Self-Compacting Concrete Beams at Shear zone