Seismic behavior of connections composed of CFSSTCs and steel-concrete composite beams—experimental study

In order to investigate the seismic behavior of connections composed of concrete-filled square steel tubular columns and steel-concrete composite beams, fourteen cruciform connection specimens were tested. The strength, deformation, and energy dissipation capacity of these composite connections were analyzed. The test results showed that the strength of connections with interior diaphragms is adequate, but their ductility is low. Also, the deformation capacity of connections with anchored studs is good, but their strength is low. In comparison, the connections with exterior diaphragms have adequate strength, good ductility, and high-energy dissipation capacity, and as a result, it can be concluded that they are more suitable for applications in moment resisting frames in seismic regions.     

Seismic behavior of composite connections — flexural capacity analysis

Based on the experimental results of connections composed of concrete-filled square steel tubular columns and steel-concrete composite beams with interior diaphragms or anchored studs, the flexural capacity of connections is studied theoretically in the present paper. Analytical models are proposed, with consideration of the effects of axial load, concrete slab, middle interior diaphragm, beam and column width condition, and punching shear failure mode. Formulae in different conditions are established based on these models. The predictions and the test results are compared and they are in good agreement.     

方钢管混凝土柱和钢-混凝土组合梁连接节点的抗震性能试验研究

为研究方钢管混凝土柱和钢-混凝土组合梁的抗震性能,对14个十字型连接构件进行试验。分析了这些构件的强度、变形和耗能能力。试验结果显示:内隔板式节点的强度是足够的,但延性较差。同时,螺栓节点具有较强的变形能力但其强度较低。相比之下,外隔板式节点具有足够的强度、良好的延性和高耗能能力,因此这类节点更适用于地震区抗弯结构的设计。     

预应力钢-混凝土连续组合梁的非线性有限元分析

以六根两跨预应力钢-混凝土连续组合梁的系列试验结果为基础,以通用有限元程序MSC.MARC(2005r2)为平台,提出了用于模拟预应力连续组合梁非线性全过程受力行为的精细有限元模型,并给出了单元选取、材料建模以及整体组装的详细过程。有限元分析基于弹塑性本构模型,能充分考虑材料非线性和几何非线性,反映结构受力全过程中预应力筋内力变化、滑移效应、内力重分布、应力分布、曲率分布以及塑性铰形成等复杂特性,深入揭示了预应力连续组合梁的受力机理和特点。模型计算结果和实测结果以及理论分析结果吻合良好,表现出良好的数值特性。文中模型对于预应力连续组合梁的精细化分析具有较高的精度和广泛的适用性,为研究预应力连续组合梁受力性能提供了强有力的工具。     

钢—混凝土组合梁单调静力性能有限元分析

利用ANSYS软件建立了钢—混凝土组合梁的有限元模型,并对其进行了非线性分析,通过与试验结果的对比验证了建模方法的正确性,在此基础上,分析了栓钉间距、有效预应力等参数对钢—混凝土组合梁静力性能的影响,以期为钢—混凝土组合梁的设计计算提供指导。     

方钢管混凝土柱与钢-混凝土组合梁连接的内隔板式节点的抗震性能试验研究

为研究方钢管混凝土柱与钢-混凝土组合梁连接的内隔板式节点的抗震性能,本文对3个节点试件进行了低周反复荷载试验,在此基础上对节点的受力过程、破坏形态、滞回曲线、骨架曲线、变形恢复能力、延性、刚度退化和耗能能力等抗震性能进行了较为深入的研究与分析。试验结果表明:内隔板式节点能够有效地传递梁端弯矩及剪力,其滞回曲线呈明显的梭形,单周耗能能力较强;节点在梁端塑性铰破坏模式下具有较好的承载力、耗能性能及滞回特征,而在剪切破坏及局部焊接破坏模式下则延性较低,抗震性能相对较差;节点在整个加载过程中刚度退化明显,持续均匀,同时表现出一定的变形恢复能力;楼板组合作用对于节点的抗震性能具有一定程度的影响。     

Invisible elastic bolt model concept for finite element analysis of bolted connections

In accurate numerical modeling of bolted connections challenges are introduced due to the complexities encountered in meshing and providing non-conforming mesh for the exact modeling of bolt assemblages which may undermine the monotonic convergence in the solution algorithms. Thus, an elastic invisible bolt model is introduced to represent the bolt’s effect in the finite element modeling of bolted connections. The proposed algorithm assigns three degrees-of-freedoms (DOF) to each bolt’s end that include; one translational, in the bolt axial direction, and two rotational. Constraints are introduced for the DOF of the nodes in contact with the bolt head (or nut) such that they are permitted to move in the normal direction of the bolt based on the bolt elongation and end rotations. This introduces a variable-sized element stiffness matrix for the elements in contact with bolt ends. This bolt model is implemented in a general purpose cyclic plasticity-based finite element computer program, capable of predicting energy dissipation of bolted surfaces. Finally, the proposed algorithm is validated using a benchmark case and a sensitivity study on a hypothetical connection to ensure that the expected trend in energy dissipation is observed when geometric variables are varied.     

Finite element analysis of precast hybrid-steel concrete connections under cyclic loading

In this paper, a nonlinear finite element (FE) analysis of hybrid-steel concrete connections is presented. The detailed experimental results of the four full-scale hybrid-steel concrete connections with limited seismic detailing have been discussed in a different paper. However, due to the inherent complexity of beam-column joints and the unique features of the tested specimens, the experimental study was not comprehensive enough. Therefore, in this paper, an analytical investigation based on the FE models and using the DIANA software is presented. The FE models were validated using the experimental results of the hybrid-steel concrete connections tested in Nanyang Technological University, Singapore. The critical parameters influencing the joint’s behaviour, such as the axial load on column, the connection plate thickness, and the continuation of beam bottom reinforcement, are varied, and their effects, especially implications on code specifications, are studied.     

Finite element modelling of composite beams with full and partial shear connection

The present investigation focuses on the evaluation of full and partial shear connection in composite beams using the commercial finite element (FE) software ANSYS. The proposed three-dimensional FE model is able to simulate the overall flexural behaviour of simply supported composite beams subjected to either concentrated or uniformly distributed loads. This covers: load deflection behaviour, longitudinal slip at the steel-concrete interface, distribution of stud shear force and failure modes. The reliability of the model is demonstrated by comparisons with experiments and with alternative numerical analyses. This is followed by an extensive parametric study using the calibrated FE model. The paper also discusses in detail several numerical modelling issues related to potential convergence problems, loading strategies and computer efficiency. The accuracy and simplicity of the proposed model make it suitable to predict and/or complement experimental investigations.     

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.     

The finite element analysis of the ultimate behavior of thin-walled carbon steel bolted connections

Finite element analysis (FEA) procedures were recommended for predicting the structural behaviors of single shear bolted connections in thin-walled stainless steel and carbon steel based on a previous numerical study with Kuwamura’s test results. The ultimate behaviors such as ultimate strength, fracture mode and curling occurrence predicted by FEA were in good agreement with those of test results. Especially, the effect of curling on the mechanical behavior of a stainless steel bolted connection has been focused. In this paper, an additional experiment for estimating in detail the block shear fracture mechanism and curling influence on thin-walled carbon steel bolted connections has been conducted. Finite element analysis was performed for test specimens. Bolted connections with a short end distance showed the typical block shear fracture. In contrast, connections with a relatively long end distance led to the ultimate state accompanied by out-of-plane deformation; curling. The ultimate strength reduction gets larger with the increase of end distance and the reduction ratio ranged from 4% to 17%. Moreover, this paper describes the comparison of strain distribution between specimens with curling and specimens without curling.     

钢-混凝土组合空间框架拟动力有限元分析

基于混凝土的塑性-损伤本构模型与钢材的弹塑性混合强化本构模型,采用ABAQUS有限元分析软件,对圆钢管混凝土柱-钢筋混凝土框架梁2层空间框架的三维实体精细有限元模型进行拟动力分析。模型中考虑了钢管与核心混凝土的约束作用以及连续地震作用下引起的塑性耗能累积效应。对钢管混凝土柱轴压比、钢管横向变形系数以及各关键点的钢管与核心混凝土、框架梁、环梁与楼板中的钢筋和混凝土的应力-应变滞回曲线以及框架结构的塑性耗能分布情况进行分析。结果表明：连续工况地震作用使框架结构产生塑性耗能累积效应,进而使楼层的位移响应明显增大,层间刚度减小;连续工况地震作用后,钢管和所有钢筋都屈服,钢管、环梁钢筋的约束作用使核心混凝土、环梁混凝土强度超过其轴心抗压强度,楼板混凝土因受拉而开裂;短边柱的轴压比有明显波动,罕遇地震作用下其值大于角柱、中柱和长边柱的轴压比;钢管混凝土柱为主要的塑性耗能构件,环梁次之。     

Nonlinear finite element analysis of CFT-to-bracing connections subjected to axial compressive forces

The Abaqus finite element program together with nonlinear material constitutive models for concrete-filled tube (CFT) and steel gusset plate is used to analyze the behaviors of the gusset plate type CFT-to-Bracing connections subjected to axial compressive forces. It is found that the failure of CFT-to-Bracing connections occurs below the connecting area. Local bulged shapes of the steel tube might take place in the areas close to the gusset plate and the fixed end under the failure stage. The ultimate strengths of the CFT columns slightly increase with the increasing of the load ratio and the thickness of the gusset plate. The introduction of the cutouts on the gusset plates slightly increases the ultimate strength of the CFT column and causes more local bulged shapes on the steel tubes below the connection area under the failure stage.     

Parametric finite element study on slotted rectangular and square HSS tension connections

A parametric finite element analysis study was carried out on slotted rectangular and square hollow structural section (HSS) tension connections without welding at the end of the gusset plate for different weld length ratio, slot orientation, weld size and level of HSS corner strength compared to its flat segment. Finite element models for the parametric study were developed and validated against test results of the connection with the tube slotted. The modified weld length ratio was found to be a better parameter than the modified eccentricity ratio in characterizing the net section efficiency of a slotted HSS tension member when the weld length is short. Improvements to provisions in CSA-S16-01 and ANSI/AISC-360-05 for slotted tubular tension connections were proposed based on results of the study.     

Numerical analysis on mechanical behavior of steel-concrete composite beams under fire

This paper investigated the fire behavior of steel-concrete composite beams (SCB) and partially encased steel-concrete composite beams (PEB) through numerical analysis. The numerical models established by the software ABAQUS were verified against experimental results. Parametric studies were performed to study the influences of load ratio, strength of concrete and steel, width of concrete slab, size of steel beam, fire protection layer, and degree of shear connection on the fire behavior of SCB and PEB. The analysis results show that the deformation stages of SCB and PEB under fire both go through four stages: elastic, elastic–plastic, plastic small deformation, and plastic large deformation. The web of SCB experiences a tension–compression–tension process under fire, and the bottom flange of PEB may even change from tension to compression at a lower load ratio. The failure mode of PEB, whether the concrete is crushed, depends on the load ratio. When SCB fails, the concrete is crushed and only the bottom flange of the steel beam yields. Under various parameters, the fire resistance of SCB is about 22 min, while the fire resistance of PEB is 82–93 min under a load of 0.4. When the load ratio increases from 0.2 to 0.6, the fire resistance of SCB decreases by 8 min, while that of PEB decreases by 110 min. To meet class I fire resistance rating under a normal service load ratio of 0.4, additional measures for PEB are still required, and at least 15 mm of fire protection layer is required for the steel beam of SCB. Finally, considering the temperature internal fore, a coefficient related to the fire time was introduced to modify the formula of ultimate flexural capacity of SCB and PEB, which showed good accuracy.     

The behavior of top and seat bolted angle connections under blast loading

Abnormal loading generated by blast or impact may cause local damage in a building that may evolve to affect the whole structural system. Therefore, structures have to be designed to prevent such disproportional consequences. Connection is an important contributor to ductility and robustness of the structural steel systems in mitigating such consequences. Considering this importance, finite element analysis is used in this paper to study the behavior of top and seat bolted angle connections under blast loading. The two frequent angle connections including top and seat angle bolted connections with and without web angles are studied using the ANSYS finite element software. The finite element models are verified by comparing the predicted results obtained from the models and the values measured in the experimental tests. Simplified blast loading is then applied to the verified connection models and the behavior of these connections under blast loads is evaluated with the connection critical areas being determined. The connection failure modes as well as the applicability of the connection under blast loading are briefly discussed.     

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.     

轻钢-混凝土组合梁的试验研究及非线性有限元分析

针对轻钢-混凝土组合梁这种新的结构形式,本文进行了六个试件的试验研究,分析了构件的破坏形式、荷载-位移曲线、荷载-应变曲线、钢材和混凝土的应变分布及板宽度方向应变分布等。通过试验研究,初步了解了轻钢-混凝土组合梁的特点和各种截面的粘结性能。采用组合梁单元模型,对轻钢-混凝土组合梁进行了非线性有限元分析,理论计算结果与试验结果吻合较好。     

Free vibration analysis of laminated FG-CNT reinforced composite beams using finite element method

In the present study, the free vibration of laminated functionally graded carbon nanotube reinforced composite beams is analyzed. The laminated beam is made of perfectly bonded carbon nanotubes reinforced composite (CNTRC) layers. In each layer, single-walled carbon nanotubes are assumed to be uniformly distributed (UD) or functionally graded (FG) distributed along the thickness direction. Effective material properties of the two-phase composites, a mixture of carbon nanotubes (CNTs) and an isotropic polymer, are calculated using the extended rule of mixture. The first-order shear deformation theory is used to formulate a governing equation for predicting free vibration of laminated functionally graded carbon nanotubes reinforced composite (FG-CNTRC) beams. The governing equation is solved by the finite element method with various boundary conditions. Several numerical tests are performed to investigate the influence of the CNTs volume fractions, CNTs distributions, CNTs orientation angles, boundary conditions, length-to-thickness ratios and the numbers of layers on the frequencies of the laminated FG-CNTRC beams. Moreover, a laminated composite beam combined by various distribution types of CNTs is also studied.