Experimental Study on Force Behavior of Steel Rein forced Concrete Transfer Beam Structure with Basement of Large Space

Based on comparative test of two transfer story models, in one of which the transfer beam and basement column is constructed of steel reinforced concrete, and the other is constructed of ordinary reinforced concrete, its force behavior, ductility and failure mechanism under vertical and horizontal loads are studied. The results show that loading bearing and seismic behavior of transfer story structure with steel reinforced concrete beam and basement column is good. The relative design suggestion is put forward.

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.

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.

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.

Behavior of reinforced concrete beams and columns subjected to blast loading

In this study, the blast performance of steel reinforced concrete(RC) beams was experimentally and analytically investigated. The experiment consists of a total of 10 one-half-scale beams subjected to different levels of blast loading using live explosives. The reflected pressure-time histories were recorded and different damage levels and modes were observed. The blast resilience of the damaged beams was quantified by measuring the time-dependent displacements. Experiment results show that the damage in steel reinforced concrete beams with higher explosive mass is enhanced compared with that of the beams with smaller explosive mass at the same scaled distance. Based on the experiment data, an empirical expression is developed via dimensional analysis to correct the relationship between the midspan displacement and scaled distance. Besides, a complex single degree of freedom model(SDOF)incorporating complex features of the material behavior, high strain-rate effect and the column geometry was proposed and validated by test results.

Research on Flexural Behavior of Coral Aggregate Reinforced Concrete Beams

Through the flexural behavior test of coral aggregate reinforced concrete beams(CARCB) and ordinary Portland reinforced concrete beams(OPRCB), and based on the parameters of concrete types, concrete strength grades and reinforcement ratios, the crack development, failure mode, midspan deflection and flexural capacity were studied, the relationships of bending moment-midspan deflection, load-longitudinal tensile reinforcement strain, load-maximum crack width were established, and a calculation model for the flexural capacity of CARCB was suggested. The results showed that with the increase in the reinforcement ratio and concrete strength grade, the crack bending moment(Mcr)and ultimate bending moment(Mu) of CARCB gradually increased. The characteristics of CARCB and OPRCB are basically the same. Furthermore, through increasing the concrete strength grade and reinforcement ratio, Mcr/Mu could be increased to delay the cracking of CARCB. As the load increased, crack width(w) would also increase. At the beginning of the loading, w increased slowly. And then it increased rapidly when the load reached to the ultimate load, which then led to beam failure. Meanwhile, with a comprehensive consideration of the effects of steel corrosion on the loss of steel section and the decrease of steel yield strength, a more reasonable calculation model for the flexural capacity of CARCB was proposed.

Experimental study and analysis on fatigue stiffness of RC beams strengthened with CFRP and steel plate

The objective of this work is to investigate the fatigue behavior of reinforced concrete(RC) beams strengthened with externally bonded carbon fiber reinforced polymer(CFRP) and steel plate. An experimental investigation and theoretical analysis were made on the law of deflection development and stiffness degradation, as well as the influence of fatigue load ranges. Test results indicate that the law of three-stage change under fatigue loading is followed by both midspan deflection and permanent deflection, which also have positive correlation with fatigue load amplitude. Fatigue stiffness of composite strengthened beams degrades gradually with the increasing of number of cycles. Based on the experimental results, a theoretical model by effective moment of inertia method is developed for calculating the sectional stiffness of such composite strengthened beams under fatigue loading, and the calculated results are in good agreement with the experimental results.

Experimental and Numerical Analysis of High-Strength Concrete Beams Including Steel Fibers and Large-Particle Recycled Coarse Aggregates

In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.

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.

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-beating 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.

Durability of Reinforced Concrete Beams under Simultaneous Flexural Load in Corrosive Environment

The deterioration of concrete over time is the result of various mechanical, physical, chemical and biological processes, with the corrosion of reinforcement being the most serious problem of durability of reinforced concrete structures. Over the last 50 years, a tremendous effort has been spent by the international scientific community with laboratory research and experimental field studies in order to increase the resistance of concrete over corrosion. This paper presents an experimental study of the corrosion behaviour of reinforced concrete beams with simultaneous sustained flexural loading. For this purpose, 40 reinforced concrete beams of 5 different compositions were constructed and exposed in simulated harmful environmental conditions in 3 different stress ratios for a total period of 42 months. Their behavior against corrosion was determined via regular measurements of the electrical resistance of concrete (according to ASTM G57) and the corrosion potential of the steel-reinforced bars with the use of copper sulphate (CSE) as reference electrode (according to ASTM C876). A theoretical calculation of the corrosion rate was conducted based on the electrochemical measurements of the beams. The results indicate that the corrosion potential of steel decreased in time and more rapidly after the initiation of the corrosion process;the electrical resistance firstly increased, remained stable for a short period and then decreased with the corrosion development, as expected. An inversely proportional relationship of the water/cement ratio of a composition with its corrosion behaviour as well as an analogous relationship between the cement content of a composition and its corrosion behaviour was observed. Also, the corrosion rate of steel is increased gradually with increasing load.

Experimental and analytical study on seismic behavior of steel-concrete multienergy dissipation composite shear walls

In this paper, a steel-concrete multi-energy dissipation composite shear wall, comprised of steel-reinforced concrete （SRC） columns, steel plate （SP） deep beams, a concrete wall and energy dissipation strips, is proposed. In order to study the multi-energy dissipation behavior and restorability after an earthquake, two stages of low cyclic loading tests were carded out on ten test specimens. In the first stage, test on five specimens with different number of SP deep beams was carried out, and the test lasted until the displacement drift reached 2%. In the second stage, thin SPs were welded to both sides of the five specimens tested in the first stage, and the same test was carried out on the repaired specimens （designated as new specimens）. The load-bearing capacity, stiffness, ductility, hysteretic behavior and failure characteristics were analyzed for both stages and the results are discussed herein. Extrapolating from these results, strength calculation models and formulas are proposed herein and simulations using ABAQUS carried out, they show good agreement with the test results. The study demonstrates that SRC columns, SP deep beams, concrete wall and energy dissipation strips cooperate well and play an important role in energy dissipation. In addition, this study shows that the shear wall has good recoverability after an earthquake, and that the welding of thin SP＇s to repair a deformed wall is a practicable technique.

Analytical theory of flexural behavior of concrete beam reinforced with textile-combined steel

Textile-reinforced concrete (TRC) is a new high performance cementitious composite material,which not only has superior corrosion resistance but also can effectively limit the development of concrete cracks and make the crack width and spacing of concrete become smaller.However,due to the brittle feature of fiber materials,the TRC structural member has no distinct failure symptom when it arrives at its ultimate load.At the same time,ordinary reinforced concrete (RC) elements have large dead weight and can not efficiently restrict the expansion of the main crack of structures because of the restriction of their special cover thickness.In order to overcome the disadvantages of both the TRC and the RC,a new architecture reinforced with textile-combined steel is proposed in this study,making full use of the advantages of the above two structures.The cover concrete at the tension zone of an RC element is partially replaced with TRC and thus the steel reinforcements replaced with textiles are subtracted.Compared with the old one,the new structure has less dead weight and has the merits of service safety and good durability.The flexural development process of the proper beam with this new structure is investigated in this paper and based on the plane section assumption,analytical equations are derived by using nonlinear analysis theory,including the load-carrying capacity at different stages and moment-curvature relationship and mid-span deflection during the entire loading process.Comparison between the calculated and the experimental results reveals satisfactory agreement and thus verifies the feasibility of the equations.

Elastic-plastic study on high building with SRC transferring story

A new type of transferring structure for steel reinforced concrete (SRC) beams is used in high building. The pushover analysis method was used to study the failure mechanism and ductility of SRC transferring structure through consulting pseudo-static test results for the structure. And, the occurrence order and position of the plastic hinge, the weak story and seismic capacity of high building with SRC transferring story were also studied through consulting shaking table test results for the high building, showing that the seismic behavior of high building with SRC transferring story is good.

预制装配式型钢混凝土梁抗剪承载力的智能模型研究

通过建立计算预制装配式型钢混凝土(PSRC)梁抗剪承载力的智能模型,在一定程度上提高了计算精度与适用性。基于BP人工神经网络算法,通过对影响PSRC梁抗剪承载力的相关参数进行梳理,选取14个主要影响参数作为输入层,以试算法确定隐含层节点数为5,初步构建了3层结构人工神经网络系统;以收集的76组试验数据作为学习样本,对构建的神经网络系统进行训练,建立了对PSRC梁及SRC梁抗剪承载力计算的N14-5-1智能模型。使用智能模型对6个PSRC梁构件及6个SRC梁构件进行抗剪承载力计算,并通过与规范公式计算结果、试验结果的对比分析,证明了智能模型具有良好的计算精度及较好的泛化能力,具有一定的工程参考意义。运用Garson算法对输入参数进行敏感性分析,结果表明箍筋间距、型钢屈服强度、箍筋屈服强度、型钢腹板含钢率对抗剪承载力影响较大。随着研究试验的开展,在收集更多具有代表性的试验数据以扩充学习样本后,可对智能模型进一步优化。

反复荷载下圆钢管型钢再生混凝土组合柱恢复力模型研究

为建立圆钢管型钢再生混凝土组合柱的恢复力模型,对11根圆钢管型钢再生混凝土组合柱试件进行了低周反复荷载试验研究,考虑了再生骨料取代率、配钢率及钢管径厚比等不同设计参数的影响,分析了组合柱的地震破坏形态及滞回性能。基于组合柱的力学特征及曲线形状,提出了圆钢管型钢再生混凝土组合柱骨架曲线的三折线参数模型,采用理论推导与数据拟合的方法确定了组合柱骨架曲线的模型参数。在此基础上,给出了组合柱的滞回规则和卸载规律,构建了组合柱的恢复力模型,计算滞回曲线与试验滞回曲线吻合良好,表明该恢复力模型较好地反映了反复荷载下组合柱的受力特征点及滞回性能,可为此类组合柱的推广提供技术参考。

端钩型钢纤维混凝土简支梁受弯承载力试验

为改善普通钢筋混凝土梁自重大、易开裂、承载力低等缺点,在混凝土中常加入钢纤维,端钩型钢纤维,作为常见的一种高性能钢纤维得到广泛关注,中外学者针对端钩型钢纤维混凝土的基本力学性能开展了较多研究,而对端钩型钢纤维混凝土受弯构件的正截面受力性能有待深入研究。为研究端钩型钢纤维混凝土简支梁受弯性能,制作4根端钩型钢纤维混凝土梁及1根普通混凝土梁,对其进行受弯性能试验,根据试验得到的破坏形态、承载力、荷载-挠度曲线、荷载-应变曲线,分析端钩型钢纤维体积掺量对试件受弯承载力及破坏形态的影响。结果表明:端钩型钢纤维混凝土简支梁与一般混凝土简支梁受弯过程类似,均经历了弹性、开裂、带裂缝工作、破坏4个阶段;端钩型钢纤维混凝土简支梁与一般混凝土简支梁受弯过程均基本符合“平截面假定”;端钩型钢纤维限制了裂缝的产生和发展,使得纤维混凝土梁变形能力增强;与一般混凝土梁相比,端钩型钢纤维混凝土梁抗裂性及极限承载力得到提高,且构件承载力与钢纤维体积掺量基本呈现正相关;基于试验数据,对现行规范中开裂弯矩及极限承载力计算公式进行优化,开裂弯矩方面考虑对截面抵抗矩塑性影响系数进行修正,极限承载力方面引入纤维混凝土正截面承载力影响系数ζ,经修正计算值可较好吻合试验值。

CFRP-PCPs复合筋加固钢-混组合梁负弯矩区抗裂试验与理论计算

为解决钢-混组合梁负弯矩区混凝土板易开裂而造成刚度减弱的行业难题,以预制的CFRP-PCPs(carbon fibre reinforced polymer-prestressed concrete prisms)复合筋作为中支座的腹筋,并以复合筋的数量、预应力张拉水平和截面尺寸为主要参数设计制作了五根复合筋钢-混组合连续梁和一根普通组合连续梁,研究其在单跨单点荷载下负弯矩区的抗裂性能。结果表明:复合筋能显著增强中支座截面刚度,对负弯矩区的裂缝控制能力提升显著;与普通组合梁相比,复合筋梁的开裂荷载提高近30%,裂缝数量与裂缝宽度减少近50%;复合筋面积是提高裂缝控制能力的主要因素,预应力水平和截面尺寸对开裂荷载的影响较弱;复合筋的开裂荷载与预应力水平、面积正相关,其中预应力水平是影响复合筋效用时长的关键因素。基于现有理论和试验数据,本文提出CFRP-PCPs复合筋钢-混组合梁负弯矩区开裂荷载和复合筋的开裂荷载计算公式,计算结果与试验值较为吻合,可为复合筋在钢-混组合梁桥实际工程中应用提供参考。

考虑粘结滑移本构模型的托换梁承载特性分析

粘结滑移有限元分析是掌握型钢混凝土托换梁变形特性的关键手段。采用有限元分析软件建立了考虑和不考虑型钢与混凝土粘结滑移两种有限元模型,分析了托换梁荷载-挠度曲线、型钢应变及箍筋应变的变化规律。结果表明:不考虑粘结滑移时,托换梁的极限荷载、跨中挠度与试验值差值百分比范围分别为1.0%~6.8%和11.3%~24.5%,受剪段中部、梁跨中位置的腹板应变和内、外侧箍筋应变与试验值的差值百分比分别为23.1%、46.4%、15.8%和45.8%;考虑粘结滑移后,托换梁的极限荷载、跨中挠度与试验值差值百分比范围分别为0.7%~4.5%和5.7%~18.2%,受剪段中部、梁跨中位置的腹板应变和内、外侧箍筋应变与试验值的差值百分比分别为2.7%、1.3%、11.6%和27.7%;考虑型钢与混凝土粘结滑移的有限元模型可更准确地模拟梁的承载力和变形。