Seismic Behavior of Diaphragm-Through Connections of Concrete-Filled Square Steel Tubular Columns and H-Shaped Steel Beams

Based on the introductions of a type of diaphragm-through connection between concrete-filled square steel tubular columns (CFSSTCs) and H-shaped steel beams,a finite element model of the connection is developed and used to investigate the seismic behavior of the connection.The results of the finite element model are validated by a set of cyclic loading tests.The cyclic loading tests and the finite element analyses indicate that the failure mode of the suggested connections is plastic hinge at the beam with inelastic rotation angle exceeding 0.04 rad.The suggested connections have sufficient strength,plastic deformation and energy dissipation capacity to be used in composite moment frames as beam-to-column rigid connections.

Experimental Research on Shear Behavior of Reinforced Concrete Composite Beams Under Uniformly Distributed Load

An experimental program was carried out to study the shear behavior of the reinforced concrete composite beam (RCCB) subjected to two-phase uniformly distributed load. A total of 12 reinforced concrete composite beams were tested: 10 of them were the RCCB subjected to two-phase uniformly distributed load, the other 2 were the comparative reinforced concrete beams cast at the same time as the RCCB subjected to one-phase uniformly distributed load. The interface of precast unit and recast concrete was natural and rough. The test range of the main composite factors: the ratio of precast section depth to composite section depth was from 0.35 to 0.65, the ratio of first-phase load moment to precast section ultimate bearing moment was from 0.25 to 0.65. Based on the test results, the stresses of the longitudinal reinforcements and stirrups, the load-bearing properties of the interface, the crack state and the failure characteristics of the RCCB under uniformly distributed load are discussed. The effects of the stirrups, the concrete strength and the composite factors on the shear resistance of the RCCB are analyzed, and the method for evaluating the shear resistance of the RCCB is proposed.

Fatigue properties of special kind of reinforced concrete composite beams

The special reinforced concrete composite beam consists of a steel fiber reinforced self-stressing concrete composite layer and a reinforced concrete T-beam, and constructional bars are set up at their bonding interface. Fatigue properties of the composite beam under the action of negative moment were experimentally studied. Through inverted loading mode the load-bearing state of a composite beam was simulated under the action of negative moment. With the ratios of constructional bars being 0, 0.082% and 0.164% respectively as parameters, the effects of constructional bars on the properties of composite beam, such as fatigue life, crack propagation, rigidity loss as well as damage behavior of bonding interface, were studied. The mechanism of the constructional bars on the fatigue properties of the composite beams and the restriction mechanism of crack widths and rigidity loss were analyzed. The test results show that the constructional bars can enhance the shear resistance of the bonding interface between composite layer and old concrete beam and restrict expanding of steel fiber reinforced self-stressing concrete, which are beneficial to synergistic action of composite layer and old concrete beam, to reducing the stress amplitude of bars and the crack width of composite layer, and to increasing the durability and fatigue life of the composite beam.

Fatigue tests of composite beam by steel fiber reinforced self-stressing concrete in the hogging bending

Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete （SFRSC） as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar’s stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone.

Bending Stiffness of Truss-Reinforced Steel-Concrete Composite Beams

This paper is concerned with a special steel-concrete composite beam in which the resisting system is a truss structure whose bottom chord is made of a steel plate supporting the precast floor system. This system works in two distinct phases with two different resisting mechanisms: during the construction phase, the truss structure bears the precast floor system and the resisting system is that of a simply supported steel truss;once the concrete has hardened, the truss structure becomes the reinforcing element of a steel-concrete composite beam, where it is also in a pre-stressed condition due to the loads carried before the hardening of concrete. Within this framework, the effects of the diagonal bars on the bending stiffness of this composite beam are investigated. First, a closed-form solution for the evaluation of the equivalent bending stiffness is derived. Subsequently, the influence of geometrical and mechanical characteristics of shear reinforcement is studied. Finally, results obtained from parametric and numerical analyses are discussed.

Structural Behavior of Continuous Prestressed Steel Fiber Reinforced High Strength Concrete Beam

The flexural behaviors of continuous fully and partially prestressed steel fiber reinforced high strength concrete beams are studied by experiment and nonlinear finite element analysis. Three levels of partial prestress ratio （PPR） are considered, and three pairs of two-span continuous beams with box sections varying in size are designed. The major parameters involved in the study include the PPR and the fiber location. It is concluded that the prestressed high strength concrete beam exhibits satisfactory ductility; the influences of steel fiber on the crack behaviors for partially prestressed beams are not as obvious as those for fully prestressed ones; steel fibers can improve the structural stiffness after cracking for fully prestressed high strength concrete beams; the moment redistribution from mid-span to intermediate support in the first stage should be mainly considered in practical design.

Closed-form solution for shear lag effects of steel-concrete composite box beams considering shear deformation and slip

Based on the consideration of longitudinal warp caused by shear lag effects on concrete slabs and bottom plates of steel beams,shear deformation of steel beams and interface slip between steel beams and concrete slabs,the governing differential equations and boundary conditions of the steel-concrete composite box beams under lateral loading were derived using energy-variational method.The closed-form solutions for stress,deflection and slip of box beams under lateral loading were obtained,and the comparison of the analytical results and the experimental results for steel-concrete composite box beams under concentrated loading or uniform loading verifies the closed-form solution.The investigation of the parameters of load effects on composite box beams shows that:1) Slip stiffness has considerable impact on mid-span deflection and end slip when it is comparatively small;the mid-span deflection and end slip decrease significantly with the increase of slip stiffness,but when the slip stiffness reaches a certain value,its impact on mid-span deflection and end slip decreases to be negligible.2) The shear deformation has certain influence on mid-span deflection,and the larger the load is,the greater the influence is.3) The impact of shear deformation on end slip can be neglected.4) The strain of bottom plate of steel beam decreases with the increase of slip stiffness,while the shear lag effect becomes more significant.

Hysteretic behavior of special shaped columns composed of steel and reinforced concrete(SRC)

This paper describes a series of experimental investigations on seventeen specimens of steel reinforced concrete special shaped(SRCSS) columns under low cyclic reversed loading using parallel crosshead equipment. Nine T-shaped SRC columns, four L-shaped SRC columns and four +-shaped SRC columns were tested to examine the effects of shape steel confi guration, loading angle, axial compressive ratio and shear-span ratio on the behavior(strength, stiffness, energy dissipation, ductility, etc.) of SRCSS column specimens. The failure modes and hysteretic performance of all the specimens were obtained in the tests. Test results demonstrate that the shear-span ratio is the main parameter affecting the failure modes of SRCSS columns. The specimens with small shear-span ratio are prone to shear failure, and the primary failure planes in SRCSS columns are parallel to the loading direction. As a result, there is a symmetry between positive and negative loading directions in the hysteretic curves of the SRCSS columns. The majority of displacement ductility coeffi cients for all the specimens are over 3.0, so that the SRCSS columns demonstrate a better deformation capacity. In addition, the equivalent viscous damping coeffi cients of all the specimens are greater than 0.2, indicating that the seismic behavior of SRCSS columns is adequate. Finally, the superposition theory was used to calculate the limits of axial compressive ratio for the specimens, and it is found that the test axial compressive ratio is close to or smaller than the calculated axial compressive ratio limit.

A new 3-D element formulation on displacement of steel-concrete composite box beam

Slip of a composite box beam may reduce its stiffness, enlarge its deformation and affect its performance. In this work, the governing differential equations and boundary conditions of composite box beams were established. Analytic solutions of combined differential equations were also established. Partial degree of freedom was adopted to establish a new FEA element of three-dimensional beam, taking into account the slip effect. Slip and its first-order derivative were introduced into the nodes of composite box beams as generalized degree of freedom. Stiffness matrix and load array of beam elements were established. A three-dimensional nonlinear calculation program was worked out. The results show that the element is reliable and easy to divide and is suitable for special nonlinear analysis of large-span composite box beams.

Mechanical Behavior of Rectangular Steel-Reinforced ECC/Concrete Composite Column under Eccentric Compression

In order to improve the seismic performance, deformation ability and ultimate load-carrying capacity of columns with rectangular cross section, engineered cementitious composite(ECC) is introduced to partially substitute concrete in the edge zone of reinforced concrete columns and form reinforced ECC/concrete composite columns.Firstly, based on the assumption of plane remaining plane and the simplified constitutive models, the calculation method of the load-carrying capacity of reinforced ECC/concrete columns is proposed. The stress and strain distributions and crack propagation of the composite columns in different states of eccentric compressive loading are analyzed. Then, nonlinear finite element analysis is conducted to study the mechanical performance of reinforced ECC/concrete composite columns with rectangular cross section. It is found that the simulation results are in good agreement with the theoretical results, indicating that the proposed method for calculating the load-carrying capacity of concrete/ECC composite columns is valid. Finally, based on the proposed method, the effects of ECC thickness, compressive strength of concrete and longitudinal reinforcement ratio on the mechanical performance of reinforced ECC/ concrete composite columns are analyzed. Calculation results indicate that increasing the thickness of ECC layer or longitudinal reinforcement ratio can effectively increase the ultimate load-carrying capacity of the composite column with both small and large eccentricity, but increasing the strength of concrete can only increase the ultimate loadcarrying capacity of the composite column with small eccentricity.

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.

Nonlinear finite element analysis of steel-concrete composite beams

Proposes a simplified finite element model for steel-concrete composite beams. The effects of slip can be taken into account by creating a special matrix of shear connector stiffness and using the iteration method. Meanwhile, the effect of material non-linearity of steel and concrete on rigidity and strength of composite beams is considered. With the age-adjusted effective modulus method, the analysis for the whole process of shrinkage and creep under long-term load can be performed. The ultimate load, deflection, stress and slip of continuous composite beams under short-term and long-term load are computed using the proposed finite element model. The numerical results are compared with the experimental results and existing values based on other numerical methods, and are found to be in good agreement.

Experimental research on mechanical properties of prestressed truss concrete composite beam encased with circular steel tube

Tests of 4 simply supported unbonded prestressed truss concrete composite beams encased with circular steel tube were carried out. It is found that the ratio of the stress increment of the unbonded tendon to that of the tensile steel tube is 0.252 during the using stage,and the average crack space of beams depends on the ratio of the sum of the bottom chord steel tube's outside diameter and the secondary bottom chord steel tube's section area to the effective tensile concrete area. The coefficient of uneven crack distribution is 1.68 and the formula for the calculation of crack width is established. Test results indicate that the ultimate stress increment of unbonded tendon in the beams decreases in linearity with the increase of the composite reinforcement index β0. The pure bending region of beams accords with the plane section assumption from loading to failure. The calculation formula of ultimate stress increment of the unbonded tendon and the method to calculate the bearing capacity of normal section of beams have been presented. Besides,the method to calculate the stiffness of this sort of beams is brought forward as well.

Experimental research on shear carrying capacity of H-steel concrete composite beam with small shear span ratio

In order to investigate shear carrying capacity of H-steel concrete beam with small shear span ratio,shear test on 5 H-steel concrete composite beams with small span ratio (from 0.7 to 1.1) are reported,including test design,test scheme,test method,failure characteristics and test results. Influences of shear span ratio,web of H steel and concrete on shear carrying capacity of this kind of beam are investigated. The main components comprising shear bearing capacity are analyzed. The results show that with the shear span ratio increasing,the contribution of web of H steel and concrete on shear carrying capacity decrease. Based on test data,the calculation formula of shear carrying capacity for this beam is established by curve fitting.

Mechanical performance of shear studs and application in steel-concrete composite beams

This work experimentally investigates the effects of shear stud characteristics on the interface slippage of steel-concrete composite push-out specimens. ABAQUS is used to establish a detailed 3D finite element(FE) model and analyze the behavior of push-out specimens. The modeling results are in good agreement with the experimental results. Based on parametrical analysis using the validated FE approaches, the effects of important design parameters, such as the diameter, number, length to diameter ratio, and yield strength of studs, concrete strength and steel transverse reinforcement ratio, on the load-slip relationship at the interface of composite beams are discussed. In addition, a simplified approach to model studs is developed using virtual springs with an equivalent stiffness. This approach is demonstrated to be able to predict the load-displacement response and ultimate bearing capacity of steel-concrete composite beams. The predicted results show satisfactory agreement with experimental results from the literature.

Seismic Behaviour of Beam-Column Joints of Precast and Partial Steel Reinforced Concrete

A beam-column joint of precast and partial steel reinforced concrete( PPSRC) is proposed for precast reinforced concrete frames. The PPSRC consists of partial steel and reinforced concrete. The partial steel is located in the core joint region and the connections between concrete members. This paper presents an experimental study of a series of PPSRC specimens. These specimens are tested under low cyclic loading.Experimental results demonstrate that the bearing capacity of the PPSRC specimens is 3 times that of the ordinary reinforced concrete( RC) beam-column joints. The strength and stiffness degradation rates are slower compared with that of the RC beam-column joints. In addition,the strength of the core joint region and the connections is higher than other parts of the PPSRC specimens. Beam failure occurs firstly for the PPSRC specimens,followed by column failure and connections failure. The failure of the core joint region occurs finally.Test results show that the seismic performance of the PPSRC is better than that of the ordinary RC beam-column joints.

Nonlinear Finite Element Analysis of Steel Fiber Reinforced Concrete Deep Beams

By the nonlinear finite element analysis （FEA） method, the mechanical properties of the steel fiber reinforced concrete （SFRC） deep beams were discussed in terms of the crack load and ultimate bearing capacity. In the simulation process, the ANSYS parametric design language （APDL） was used to set up the finite element model; the model of bond stress-slip relationship between steel bar and concrete was established. The nonlinear FEA results and test results demonstrated that the steel fiber can not only significantly improve the cracking load and ultimate bearing capacity of the concrete but also repress the development of the cracks. Meanwhile, good agreement was found between the experimental data and FEA results, if the unit type, the parameter model and the failure criterion are selected reasonably.

The Design and Analysis of Long-Span and Low-Depth Prestressed Composite Steel-Concrete Beam Bridge

The design scheme of long span and low depth composite steel concrete beams is introduced, and the methods of avoiding the cracking of concrete deck in the negative moment regions are proposed. Moreover, significant exploration for problems of the composite beams has been made, such as optimizing construction steps to regulate the stress, applying jacking technique to exert prestress on the concrete deck, investigating the uplifting force principle of the shear connectors by means of model test and non linear finite element analysis, and pointing out the countermeasure to reduce tension force of the shear connectors.

Static behavior of semi-rigid thin-walled steel-concrete composite beam-to-column joints with bolted partial-depth flush end plate:experimental study

A new type of semi-rigid thin-walled steel-concrete composite beam-to-column joint has been proposed in this paper.Five semi-rigid composite beam-to-column joint specimens subjected to hogging moments under monotonic loading were tested to study the static behavior of this new type of joint.The main variable parameters for the five joint specimens were the longitudinal reinforcement ratio and the joint type.The experimental results designated that the magnitude of extension of the longitudinal reinforcement is the most important factor that influenced the moment-rotation characteristic of the new type of joint.The concrete slabs could resist 3.8%-19.1% of the total shear load applied to the cross-sections near the beam-to-column connection.The edge stiffened elements,such as the flange of the lipped I-section thin-walled steel beam,were capable of having considerable inelastic deformation capacity although they had comparatively large width-to-thickness ratios.The shear failure of the concrete cantilever edge strip must be taken into account in practical design because it has significant influence on the anchorage of the longitudinal reinforcement in the new type of external joints.