Experimental study on ultimate flexural capacity of steel encased concrete composite beams

Based on the experimental study and inelastic theory, the ultimate flexuralcapacity of steel encased concrete composite beams are derived. The difference between steel encasedconcrete composite beams with full shear connection and beams with partial shear connection,together with the relationship between the inelastic neutral axis of steel parts and concrete parts,are considered in the formulae. The calculation results of the eight specimens with full shearconnection and the three specimens with partial shear connection are in good agreement with theexperimental data, which validates the effectiveness and efficiency of the proposed calculationmethods. Furthermore, the nonlinear finite element analysis of the ultimate flexural capacity of thesteel encased concrete composite beams is performed. Nonlinear material properties and nonlinearcontact properties are considered in the finite element analysis. The finite element analyticalresults also correlate well with the experimental data.

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.

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.

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.

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.

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.

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 study on seismic behaviors of steel-concrete composite frames

Steel-concrete composite frames are seeing increased use in earthquake region because of their excellent structural characteristics, including high strength, stiffness, and good ductility. However, there exist gaps in the knowledge of seismic behavior and the design provisions for these structures. In order to better understand the seismic behaviors of composite frame systems, eight steel-concrete composite frames were designed. These composite frames were composed of steel-concrete composite beams and concrete filled steel tube columns. The axial compression ratio of column, slenderness ratio and linear stiffness ratio of beam to column were selected as main design parameters. The low reversed cyclic loading tests of composite frame system were carried out. Based on test results, the seismic behaviors of composite frames such as failure mode, hysteresis curve, strength degradation, rigidity degradation, ductility and energy dissipation were studied. Known from the test phenomenon, the main cause of damage is the out-of-plane deformation of steel beam and the yielding destruction of column heel. The hysteretic loops of composite frame appear a spindle shape and no obvious pinch phenomenon. The results demonstrate that this type of composite frame has favorable seismic behaviors. Furthermore, the effects of design parameters on seismic behaviors were also discussed. The results of the experiment show that the different design parameter has different influence rule on seismic behaviors of composite frame.

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.

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.

Identification of Connection Flexibility Effects Based on Load Testing of a Steel-Concrete Bridge

In the case of composite girders, an effective cooperation of both parts of the section is influenced by deformability of connectors. Limited flexural stiffness of welded studs, used commonly in bridge structures, does not provide full interaction of a steel beam and a concrete slab. This changes strain distribution in cross-sections of a composite girder and results in redistribution of internal forces in steel and concrete element. In the paper partial interaction index defined on the basis of a neutral axis position, which can be used for verification of steel-concrete interaction in real bridge structures rather than in specimens is proposed. The range of the index value changes, obtained during load testing of a typical steel-concrete composite beam bridge, is presented. The investigation was carried out on a motorway viaduct, consisting of two parallel structures. During the testing values of strains in girders under static and quasi-static loads were measured. The readings from the gauges were used to determine the index, characterizing composite action of the girders. Results of bridge testing under movable load, changing position along the bridge span is presented and obtained in-situ influence functions of strains and index values are commented in the paper.

工艺孔对大截面部分包覆钢-混凝土组合梁受弯性能影响的试验研究

为了研究工艺孔对大截面部分包覆钢-混凝土组合梁(大截面PEC梁)受弯性能的影响,对5根不同构造的大截面PEC梁进行了静力试验,研究了两点加载下主次梁腹板开洞方式对大截面PEC梁试件受弯性能、延性、破坏模式等的影响规律。结果表明:静力荷载作用下,各个试件均表现出良好的延性,腹部开孔对试件承载力和截面刚度有一定的削弱作用。型钢主钢件的应变与混凝土的应变沿截面高度方向均大致呈线性变化,符合平截面假定。按《部分包覆钢-混凝土组合结构技术规程》(T/CECS 719—2020)计算得到的开工艺孔的大截面PEC梁抗弯承载力与试验值误差较小,受尺寸效应影响不大,所采用计算公式安全可靠。

局部半包裹部分包覆钢-混凝土组合梁受弯性能试验研究

针对部分包覆钢-混凝土组合梁柱节点区域后浇筑混凝土不易密实的问题,研究了受拉侧混凝土对局部半包裹部分包覆钢-混凝土组合梁(局部半包裹PEC梁)受弯性能的影响,进行了2根不同构造的局部半包裹PEC梁的四点弯曲试验,模拟局部半包裹PEC梁负弯矩区受力状态,对其受弯性能、延性、破坏形式等展开分析。结果表明:局部半包裹PEC梁表现出良好的延性,挠度达到l_(0)/50时截面抗弯承载力并未下降。型钢主钢件、混凝土的应变沿截面高度方向大致呈线性变化,可引用平截面假定计算受弯承载力及刚度。局部半包裹PEC梁受拉侧混凝土对其极限承载力与破坏模式影响不大,在计算局部半包裹PEC梁柱节点受力时可不考虑受拉侧混凝土作用,节点后浇筑区域可采用半包裹填充,以加快施工进度。此外,对局部半包裹PEC梁进行建模,进行梁受弯过程的有限元分析,对比模拟结果与试验结果,二者荷载-挠度曲线吻合较好,误差均在10%以内。

部分包覆钢-混凝土组合梁柱节点抗震性能试验研究

为研究不同连接构造的部分包覆钢-混凝土组合梁柱节点(PEC梁柱节点)的抗震性能,对2个PEC梁柱节点试件进行了拟静力加载试验,研究了低周往复荷载作用下PEC梁柱节点试件的破坏现象、滞回曲线、骨架曲线、延性、耗能能力和刚度退化等抗震性能。结果表明:强轴连接PEC梁柱节点的滞回曲线呈梭形和弓形,在达到极限承载力后仍能保持一定的延性和耗能能力;弱轴连接PEC梁柱节点牛腿与梁间的焊缝处发生破坏,未展现出预期的耗能能力,PEC梁仍在弹塑性状态,没有达到极限状态;PEC梁柱节点核心区混凝土替换为加劲肋板后,试件仍具有较好的承载力、延性和耗能能力,刚度退化规律无明显变化,且强轴连接节点与弱轴连接节点刚度变化规律基本一致;PEC柱牛腿设计过短会导致焊缝连接处断裂,试件延性和耗能能力得不到发挥,剩余刚度较大。

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。

部分充填式窄幅钢箱-UHPC组合梁抗裂性能

为研究部分充填式窄幅钢箱-UHPC组合梁的抗裂性能,开展了4根不同钢纤维掺量的部分充填式窄幅钢箱-UHPC组合梁与1根部分充填式窄幅钢箱-NC组合梁静力加载试验。试验表明:在负弯矩作用下,部分充填式窄幅钢箱-UHPC组合梁裂缝呈现数量多、短小且密集的特点;同等配筋率的条件下,不同钢纤维掺量(0、1%、2%和3%)部分充填式窄幅钢箱-UHPC组合梁与部分充填式窄幅钢箱-NC组合梁相比,在弹性阶段其刚度明显提高,最大裂缝宽度随钢纤维掺量的增加而减少,开裂强度分别提高了36.0%、48.8%、82.0%和112.0%,UHPC显著提高了组合梁的抗裂性能;可以参考按照JTG 3362—2018中裂缝宽度式乘以0.8的修正系数来计算部分充填式窄幅钢箱-UHPC组合梁裂缝宽度。

钢-混凝土组合梁螺栓连接件受剪性能试验研究

传统螺栓连接件的直径小于钢梁预留孔的孔径,导致螺栓与孔壁存在间隙,容易引发钢梁与上部混凝土板间发生相对滑移使组合梁挠度增大。为尽量减小或消除上述间隙,本文引入铰制孔螺栓和螺纹孔螺栓作为组合结构的剪力连接件,并提出锥套自锁螺栓连接件。设计并开展了8个螺栓连接件推出试验,基于各试件的荷载-滑移曲线,研究了3种螺栓连接件与传统螺栓连接件间的抗剪承载力、滑移能力及抗剪刚度等受剪力学性能的具体差异。研究结果表明:3种螺栓连接件的破坏形态与传统螺栓连接件表现一致,均为螺栓杆剪断,混凝土无压溃现象;3种螺栓连接件的抗剪承载力均接近于传统螺栓连接件的抗剪承载力;基于试件的荷载-滑移曲线,3种螺栓连接件均可分为弹性阶段、塑性阶段及破坏阶段;3种螺栓连接件的延性系数和抗剪刚度均明显优于传统螺栓。综合考虑力学性能、施工性能和经济性,本文建议选用铰制孔螺栓用于组合结构的剪力连接件。

新型部分填充钢-混凝土组合梁受剪性能试验及有限元模拟研究

采用合理的材料本构关系,利用ABAQUS有限元软件建立足尺有限元模型,对新型部分填充钢-混凝土组合梁进行受剪承载力分析。结合试验研究,通过改变剪跨比、型钢强度等级、梁高度、型钢腹板厚度、翼缘栓钉间距等因素对新型组合梁组合截面受剪承载力进行了研究。结果表明,新型组合梁有较好的受剪承载力,混凝土强度等级和新型组合梁高度对峰值承载力的影响不显著,但混凝土显著提高了新型组合梁的整体稳定性;而新型组合梁高度每增加50mm,其峰值剪力值约提高7%~21%;型钢腹板厚度每增大2mm,新型组合梁峰值剪力就提高10%左右,腹板对其受剪承载力影响较大。运用叠加原理,结合腹板、翼缘内侧混凝土、翼缘栓钉和箍筋的受剪贡献,对《组合结构设计规范》(JGJ 138—2016)中组合梁截面受剪承载力计算公式进行了优化。结果表明,修正后的计算公式具有良好精度。