Modeling and investigation of elasto-plastic behavior of steel–concrete composite frame systems

This paper presents a mixed finite-element model combining the fibered beam and layered shell elements using the general finite-element program MSC.MARC (2005r2) based on the discussion and comparison of the previous models. The proposed modeling procedure is intended for integrated elasto-plastic analysis of fully connected steel–concrete composite frames subjected to the combined action of gravity and monotonic lateral loads. The model is verified by extensive experiments and examples, and the behavior of composite frames is also investigated intensively. The slab space composite effect and the beam–column semi-rigidity are the two critical factors influencing the structural behavior. These two factors have not been considered simultaneously in some previous models but can be both included in the proposed model. Due to the complex slab space composite effect in composite frames, the previous models with a constant-width effective flange of slab can not trace the actual nonlinear slab behavior, but the proposed model can give accurate results. Since the slip effect between the steel beam and RC slab has negligible influence on the global calculation results of the structural system verified by the calculation examples, the slip effect is neglected in the present study to simplify the modeling procedure and enhance the calculating efficiency. The proposed model possesses good accuracy and broad applicability with simple modeling procedure and high calculation efficiency, and has a great advantage for the large-scale integrated analysis of multistory and high-rise composite frames.     

多高层钢-混凝土组合框架结构体系弹塑性分析模型

以通用有限元软件MSC.MARC (2005r2)为平台,建立了纤维梁单元和分层壳单元的混合有限元模型,用于完全剪力连接多高层钢-混凝土组合框架在竖向荷载和单调水平荷载作用下的整体弹塑性分析,并得到试验和算例验证。给出了钢梁、钢柱以及混凝土楼板的有限元建模方法以及相关参数的取值建议,并就楼板和钢梁的协同工作以及半刚性梁柱节点在模型中的实现展开讨论。算例表明：节点半刚性和楼板的空间作用是影响结构性能的关键因素,而已有的相关模型并未同时解决这一问题。建议的模型忽略了钢梁与混凝土楼板之间的滑移效应,算例表明滑移效应对结构体系的整体计算结果影响不大,但能有效简化建模,提高计算效率。图23表2参31     

考虑收缩徐变影响的两跨钢-混凝土连续组合梁长期性能预测方法

为量化混凝土翼板收缩徐变对多跨钢-混凝土连续组合梁长期性能的影响,提出相应的预测方法,基于现有两跨连续组合梁长期试验结果对典型的组合梁设计方法进行适用性评述; 在此基础上,基于龄期调整的有效模量法并考虑混凝土的收缩徐变、开裂及组合梁界面相对滑移的综合影响,提出两跨连续组合梁长期中支座弯矩与跨中挠度的计算公式,并采用长期试验结果验证预测方法的可靠性; 进一步对比不同混凝土翼板类型(收缩徐变分布模型)对组合梁长期性能的影响。结果表明:采用龄期调整的有效模量法模拟混凝土徐变特征,考虑收缩产生的附加弯矩,采用折减刚度考虑混凝土开裂与界面滑移的影响,提出的两跨连续组合梁长期性能计算公式,可有效预测组合梁长期中支座弯矩分布与跨中挠度,计算结果与试验结果最大相差25.3%; 混凝土的收缩变形对组合梁长期性能影响显著,当不考虑混凝土收缩变形时,组合梁中支座弯矩与跨中挠度仅分别为试验值的41.1%和60.6%; 组合梁长期性能设计时,应根据楼板类型采用不同的收缩徐变模型,针对钢筋混凝土楼板采用均匀收缩、均匀徐变模型,针对组合楼板采用非均匀收缩、非均匀徐变模型。     

Dynamic response of composite frames with different shear connection degree

The influence of partial composite action between concrete slab and steel beam and of partial-strength connections on the seismic response of composite frames is evaluated. To this end, experimental tests were carried out at the Laboratory of the National Technical University of Athens. The specimens, one-story one-bay moment-resisting frames with steel–concrete composite beams, were tested under base acceleration on the shaking table. Experimental results demonstrated that for different degrees of partial interaction between the slab and the beam the response of the specimens varied significantly. Specimens with intermediate and low shear connection degree showed the most favourable performance, in terms of ductile behavior and energy dissipation. The slip between the slab and the beam interface contributed to the energy dissipated by the system and the ductility demands decreased on other parts like the beam ends and the joints. Then, finite element models simulating the behavior of the tested specimens were developed and, after validation, extended parametric studies were carried out. The main objective is to investigate the influence of the partial interaction and the employment of partially restrained beam-to-column joints on the dissipative capacities of composite frames under strong ground motions. Numerical results confirmed the experimental conclusions and revealed that the use of intermediate and low shear connection degrees with partial-strength joints results in an advantageous seismic design.     

Seismic behavior of CFRSTC composite frames considering slab effects

This paper reports on an experimental and numerical investigation conducted on the seismic behavior of concrete-filled rectangular steel tubular columns (CFRSTC) composite frames. The experimental study was conducted by subjecting two full-scale composite frames to simulated seismic loads. Both frames were composed of CFRSTC and steel beams. One specimen was placed on a reinforce concrete (RC) floor slab and the other was not. The purpose of the test was to investigate the elasto-plastic performance of the CFRSTC composite frame system and to examine the effects of composite action on the behavior of composite frames. The test results showed that the stiffness, strength and energy-dissipating capacity of the CFRSTC frame increased significantly with the presence of the floor slab. Compared with a bare steel beam, the composite beam experienced a decrease in the rotation capacity from 0.046 rad to 0.026 rad. The shear deformation of the panel zone grew because of the composite action, which delayed the fracture of the beam. Finite element (FE) models were established to simulate the tested frames. The results of the FE model fit well with that of the test model in terms of stiffness, strength, hysteretic behavior and component deformation.     

考虑楼板空间组合效应的组合框架体系纤维模型

将正常使用极限状态和承载能力极限状态有效宽度公式与传统纤维模型相结合,通过修正楼板钢筋和混凝土材料的单轴本构关系,实现了一种改进的考虑楼板空间组合效应的纤维模型,利用该模型可以在组合框架体系非线性分析中采用高效的全杆系单元合理地考虑复杂楼板空间组合效应的影响。基于考虑楼板空间组合效应的纤维模型,开发了一套较为完整的组合结构非线性有限元分析程序COMPONA-MARC (Version 1.0)。最后,将开发程序应用于多个组合框架抗震试验的模拟,结果表明了本文模型可较为准确地模拟组合框架弹塑性全过程的楼板空间组合效应。     

GFRP型材-混凝土组合梁受弯性能试验

为了研究玻璃纤维增强复合材料(GFRP)型材-混凝土组合梁在静载作用下的受弯性能,将GFRP工字型材的上翼缘埋于混凝土板内,完成了8根GFRP型材-混凝土组合梁三分点加载受弯性能试验,得到了其破坏形态、荷载-跨中挠度曲线、荷载-应变曲线以及荷载-滑移曲线,分析了界面连接方式及型材厚度对组合梁受弯破坏机理、正截面受弯承载力及延性的影响。通过比较分析组合梁截面应变、跨中挠度、界面相对滑移的变化规律,验证了将GFRP工字型材的上翼缘置于混凝土板内作为剪力键的可行性。结果表明:接触面喷砂和GFRP型材上翼缘设置螺栓的界面连接方式可以显著降低GFRP型材与混凝土板界面间的滑移,从而提高组合梁的整体工作性能; GFRP型材厚度对试件的承载力影响不明显,但是型材厚度提高48%,其挠度降低20%左右; 所得结论可为该组合梁的理论分析与实际工程应用提供参考。     

Long-term deflection of cracked composite beams with nonlinear partial shear interaction: I — Finite element modeling

In this paper, a uniaxial nonlinear finite element procedure for modeling the long-term behavior of composite beams at the serviceability limit state is presented. The finite element procedure follows a displacement-based approach. The nonlinear load-slip relationship of shear connectors as well as the creep, shrinkage, and cracking of concrete slab are accounted for in the proposed finite element procedure. The effects of creep and shrinkage of the concrete slab are considered only for uncracked concrete. The nonlinear iterative procedure adopted for tracking the nonlinear behavior of the composite beam implemented the total nodal deformations, not the incremental deformations, as the independent variables of any iteration. The results of the proposed finite element procedure were compared with the experimental results of four composite beams reported in the literature. The proposed finite element procedure was capable of predicting the deflections and stresses of the four beams with an acceptable degree of accuracy. A parametric study was conducted to study the effect of the nonlinearity of load-slip relationship of shear connectors and the cracking of the concrete deck on the long-term behavior of simply-supported composite beams.     

Modeling of curved composite I-girder bridges using spatial systems of beam elements

A new way of modeling steel composite bridges has been presented by Vayas et al. (in press, 2010)  [3.] and [4.]. The proposed model is based on the representation of steel I-girders by equivalent trusses. The concrete slab is suitably represented by a set of bar elements, and the bearings by appropriate springs. Diaphragms and stiffeners may also be taken into account. In comparison to the grillage model, which is usually used for the analysis of bridges, the proposed three-dimensional model allows a more reliable prediction of deformations, internal forces, and stresses. Curved bridges display unique behavior characteristics, and for this reason a grillage analysis is not always suitable. The new way of modeling composite bridges, using a spatial system of beam-like structural elements, is applied in this paper for the modeling of curved composite bridges. Worked examples are provided to illustrate the set-up procedure of the proposed modeling and to compare its results with those of corresponding finite element models.     

腹板嵌入式组合梁抗弯性能理论和试验研究

提出了一种新型腹板嵌入式钢-混凝土组合梁,并对该组合梁的整体抗弯性能和抗剪性能进行了研究.首先阐述了腹板嵌入式钢-混凝土组合梁的构成、受力特点和主要优点,然后介绍了该组合梁的抗弯承载力、钢梁与混凝土翼板之间的滑移以及挠度计算公式.通过竖向荷载作用下的静力加载试验对4个腹板嵌入式钢-混凝土组合梁试件的抗弯承载力、滑移影响...     

New evaluation and modeling procedure for horizontal shear bond in composite slabs

A new method for modeling the horizontal shear bond in steel deck-concrete composite slabs is proposed. The method considers the slab slenderness as the strength parameter that affects the accuracy of horizontal shear bond modeling. A calculation procedure called the Force Equilibrium method is developed to generate shear bond stress versus end slips relationship (shear bond property) from bending tests. An interpolation procedure is also presented to estimate the shear bond property curves for slabs of varying slenderness using two sets of bending test data. The shear bond property curves are applied to connector elements of finite element models to model the horizontal shear bond behavior in composite slabs. The results of this study show that the shear bond of composite slabs under bending varies with the slenderness parameter, and hence influences the slab strength and behavior, as well as affecting the accuracy of the finite element analyses. The finite element analyses conducted on slabs with different slenderness utilizing a single shear bond property, which are not varied according to the slenderness parameter, may lead to either safe or unsafe results, depending on the geometry of the slabs.     

钢-混凝土蜂窝组合梁抗剪性能分析

对腹板开孔后的蜂窝梁和考虑混凝土板组合作用下的蜂窝组合梁抗剪性能进行分析。以试验为基础,建立有限元模型,对不同开孔率、翼缘尺寸、混凝土板尺寸和连接程度下的蜂窝梁和蜂窝组合梁进行分析。结果表明:蜂窝梁翼缘宽度变化对抗剪贡献影响不大,翼缘厚度变化对其影响较大,翼缘厚度的抗剪贡献与开孔大小、形式有关;混凝土板和连接程度对蜂窝组合梁抗剪强度贡献不可忽略。给出了蜂窝梁、无连接蜂窝组合梁和有连接组合梁抗剪强度计算方法;通过分析不同剪跨比蜂窝组合梁的受力性能,给出弯-剪相关曲线公式;通过提高蜂窝组合梁孔洞竖向位置,可以提高其承载能力。     

可拆卸组合梁剪力连接件抗剪性能数值分析

为避免传统螺栓剪力连接方式的缺陷,提出了一种用于可拆卸组合梁的新型插块式螺栓剪力连接件。以螺栓直径、缩颈杆段长度、插块材料和插块尺寸为研究参数,共设计了9个静力推出试件,研究了插块式螺栓剪力连接件的抗剪性能。以推出试件为原型,建立ABAQUS有限元分析模型进行数值分析,并通过试验进行验证。结果表明:插块式螺栓剪力连接件的荷载-滑移曲线呈现出预期的明显二次刚度特性,具有良好的剪切滑移延性; 破坏模式为预设的缩颈杆段区段内的螺栓发生剪断,而此时预制混凝土板和钢梁无明显损伤; 增大螺栓直径可以显著提高连接件的抗剪承载力和抗剪刚度; 增加缩颈杆段长度可以提高连接件延性变形能力,但会降低连接件屈服抗剪承载力和抗剪刚度,对极限抗剪承载力则无显著影响; 相比于普通混凝土和高强砂浆,使用超高性能混凝土作为插块材料使得插块式螺栓剪力连接件的抗剪承载力和抗剪刚度均得到了提高; 插块尺寸对连接件力学性能没有明显影响,但螺栓缩颈杆段和混凝土板预留孔孔壁之间应确保螺栓有足够的剪切滑移变形空间。     

箱型钢——混凝土组合梁滑移影响下的分析模型

分析了定量研究钢-混凝土组合梁的界面滑移对组合箱梁刚度和挠度影响的必要性,建立了考虑滑移效应的箱型钢一混凝土组合梁的变形模型,并提出了利用最小势能原理,推导组合梁变形微分方程的建议,可供结构设计人员参考。     

Creep behaviour modelling of a composite steel-concrete section

Long term behavior modelling of steel-concrete composite beams requires the use of the time variable and the taking into account of all the sustained stress history of the concrete slab constituting the cross section. In this context, a research contribution of the time-dependent behavior of composite sections under the creep influence of a concrete slab is presented in the present work. The concrete creep influence upon the composite section strength is taken into account as part of the concrete linear viscoelasticity. Thus, by considering the assumption of a complete composite connection made up of a steel beam and concrete slab, with no slip at the interface, and owing to the irreversible law of concrete, we obtain an analytical model, based upon a system of two differential linear equations governing the long term behavior of composite beam cross sections in bending. Results obtained from the application of the suggested model to a steel-concrete composite beam are satisfactory.     

Nonlinear analysis of reinforced concrete cross-sections exposed to fire

A nonlinear structural analysis of cross-sections of three-dimensional reinforced concrete frames exposed to fire is presented. The analysis includes two steps: the first step is the calculation of the transient temperature field in cross-sections exposed to fire and the second step is the determination of the mechanical response due to the effect of thermal and mechanical load. A nonlinear finite-element procedure is proposed to predict the temperature field history. In this thermal analysis, the effect of moisture has been taken into account by introducing a water vapor fraction function to define the variation of enthalpy. A mechanical nonlinear analysis of the cross-sections is performed for each temperature distribution and for the applied exterior load using an algorithm of arc-length control. The mechanical and thermal properties of concrete and steel are taken according to the European Standard ENV 1991-1-2 [ENV. Eurocode 2, design of concrete structures, part 1–2: general rules—structural fire design. ENV 1992-1-2, 1995]. In order to validate the proposed thermal and mechanical models, comparisons between numerical and experimental results have been performed. The agreement found is in both cases, fairly good. In addition, a numerical example of the structural analysis of several cross-sections of a reinforced concrete waffle slab under external load and fire is shown.     

矩形钢管混凝土组合桁梁负弯矩区受力性能试验研究

矩形钢管混凝土组合桁梁由混凝土板和矩形钢管混凝土桁架组成,在竖向荷载作用下,其正弯矩区可充分发挥混凝土板和桁架的组合作用,但负弯矩区的力学性能较为薄弱且受拉混凝土板容易开裂。针对这一问题,提出了在负弯矩区混凝土板施加预应力以及布置局部释放剪切作用的剪力钉相结合的组合桁梁结构形式。采用跨中施加反向集中荷载模拟连续梁支点反力的方法,对2榀承受负弯矩的矩形钢管混凝土组合桁梁进行了静力加载试验,对其荷载-位移关系、裂缝发展规律、混凝土板应变分布、桁梁荷载-应变关系、钢与混凝土界面滑移及承载力进行了分析。还根据组合桁梁的简化力学模型对不同加载阶段的结构特征荷载进行了讨论。结果表明：采用局部释放剪切作用的剪力钉和混凝土板施加预应力的组合桁梁结构形式可有效提高其抗裂性能,但对受弯承载力影响较小;在加载过程中混凝土板的开裂和杆件的屈服导致结构塑性变形增大,最终节点处焊缝撕裂,组合桁梁丧失承载力;由简化力学模型计算得到的结构特征内力与实测值吻合较好,可为矩形钢管混凝土组合桁梁负弯矩区的设计和计算提供参考。     

Elastic rigidity of composite beams with full width slab openings

Openings often exist in the concrete slab of composite floors due to the functional requirements of structures. The strength and rigidity of steel-concrete composite beams are reduced by openings. Based on three tests of steel-concrete composite beams with full openings in the concrete flange, the elastic rigidity of composite beams is analyzed. Finite element analysis (FEA) considering the slip effect between the steel and concrete is conducted to simulate the composite beams with full openings in the concrete slab, and the results show that the FEA method is reliable. The analytical calculation method for the deflection of composite beams with full openings in the concrete slab is also proposed, and the results are verified by tests. The predicted deflections using the analytical method and FEA method both agree well with the test results. It is further verified that openings near the supports have insignificant effects on the deflection at the mid-span and this effect can be thus ignored. The simplified method to calculate the rigidity reduction factor is developed by a regression analysis. The analytical method and FEA method can be used for the serviceability limit state design of steel-concrete composite beams with full openings in the concrete flange.     

Experimental study on the bend and shear behaviors of steel-concrete composite beams with notched web of inverted T-shaped steel section

A new steel-concrete composite beam with notched web of inverted T-shaped steel section is proposed in this paper. This composite beam is composed of concrete slab and inverted T-shaped steel beam. Experimental studies on the bend and shear behavior of the composite beam are conducted. Four specimens are tested to investigate the bend behavior of the novel composite beam, and the formula for predicting the bend capacity is proposed and verified by comparing the results between predicted with the formula and the measured from the tests. Six specimens are also tested to study the shear behavior and the formula for estimating the shear capacity of the novel composite beam is recommended on the base of the test results. The formulas proposed in this paper may be employed to estimate the bend and shear capacity of the composite beam with notched web of inverted T-shaped steel section for application in practice.     

Modeling the response of composite beam–slab assemblies exposed to fire

This paper presents the development of a three-dimensional nonlinear finite element model for evaluating the response of composite beam–slab assemblies subjected to a combination of gravity and fire loading. The behavior of typical beam–slab assemblies with different shear connection types (welded–bolted shear tab and all-bolted double-angle connection), exposed to different fire scenarios, was modeled using ANSYS. The finite element model accounts for temperature dependent thermal and mechanical properties of constituent materials, connections, and composite action. Transient time domain coupled thermal-stress analysis is performed to obtain the temperature distribution and deformation response of the composite beam–slab assembly. The finite element model is validated by comparing the predicted and measured thermal and structural response parameters of three composite beam–slab assemblies tested under fire conditions. The comparisons show that the proposed model is capable of predicting the fire response of beam–slab assemblies with good accuracy. Research from the analysis clearly shows that the composite action between the beam and slab significantly enhances the fire performance of composite beam–slab assemblies. It is concluded that the proposed finite element model could be used as a feasible tool to evaluate the fire response of composite floor systems.