Seismic behaviour of beam-to-column partial-strength joints for steel-concrete composite frames

The paper presents a large experimental campaign carried out on ten steel-concrete composite beam-to-column sub-assemblages employing monotonic and cyclic loading test protocols. Structural members (beams, columns and slabs) were defined through the design of a full-scale 3D prototype frame subjected to PSD testing campaign; main design hypothesis was to dissipate seismic energy in the joints designed as partial-strength. Testing programme on beam-to-column sub-assemblages was executed in order to assess seismic performance varying structural details at beam-to-column connection level and material qualities. Different mechanical connecting systems between concrete slab and column, two end-plate configurations, weak and strong column web panel, two steel qualities and different concrete strengths.The analysis of sub-assemblages performance was realized in two steps: a first step in which the joints behaviour was assessed, characterizing response at local level (e.g. moment-rotation curves); a second step in which the response was assessed at global level (e.g. force-displacement curves). The structural behaviour (i.e. resistance, plastic deformation and stiffness) was evaluated at three stages-identified as initial, service and maximum load-in order to monitor the evolution of sub-assemblage response increasing solicitation level. Moreover, seismic behaviour of specimens-in terms of dissipated energy, ductility, over-strength and equivalent viscous damping-was also executed. Comparison between experimental results was made in order to identify those parameter suitable for improved and reliable seismic behaviour of steel-concrete composite partial-strength joints.     

Behavior of beam-to-column moment connections under fire load

The welded flange-bolted web type moment connections are commonly used in the construction of modern steel buildings. The behavior of this type of connection under service load and seismic load has been studied extensively; however, the knowledge of its performance under fire load is limited. In this paper, the experimental studies of the welded flange-bolted web moment connections under fire loads are presented. Four full-size steel beam-to-column assemblages, with and without fire-proofing materials, were selected to simulate the moment connection commonly used in steel buildings. The fire load was simulated either by a steady state method to reach a fully-developed fire or by a transient state method following the standard temperature-time curve. Parametric studies were also conducted to examine the strength degradation of steel moment connection at elevated temperature. From these studies, it was found that the beam-to-column connection is able to retain its design strength up to 650 ^°C. However, the stiffness dropped to 25% of the value at ambient temperature. Ductile behaviors were observed on the connections, with necking and tearing at the top flange and local buckling at the bottom flange. It was also found that the stability and integrity of steel connections can be ensured if proper fire-proofing materials were provided.     

Experimental and numerical study on cyclic behaviour of steel beam-to-column joints

Ten specimens are tested to investigate the cyclic behavior of beam-to-column joints of steel frames with joint panels. The performances of the joints with respect to strength, rigidity, and hysteretic performance are examined. Three different load-carrying mechanisms can be identified. Panel resistance ratio (R _p ) is presented for predicting the buckling patterns. The validity ofR _p is confirmed through the present experimental results. On the basis of the experimental results of steel beam-to-column moment joints, 3-D nonlinear finite element models are established to analyze the mechanical properties of these connections. The load-displacement curves of the finite element analysis are in good agreement with those of the tests in terms of strength and unloading stiffness. A shear lag phenomenon was captured in the beam flanges by not only experimental results but also numerical analysis. Parametric studies are conducted on the connections under monotonic loading to investigate the influences of connection dimension, resistance ratio on the connection behavior. It was found that the failure modes are influenced by the resistance ratio, while the thickness of joint panels resulting in large effects on the strength and stiffness under shear failure mode.     

Bolted large seismic steel beam-to-column connections Part 2: numerical nonlinear analysis

A large bolted steel moment-resisting connection was studied by nonlinear numerical analysis. This connection was a single-sided beam-to-column assembly that is representative of exterior beam-to-column connections. It was composed of a W36 × 150 Grade 50 beam and a W14 × 283 Grade 50 column. The T-stubs were cut from W40 × 264 sections of Grade 50 steel. The T-stub stems were welded and prestressed by high-strength bolts to the beam flanges in a fabricating shop. Final beam-to-column assembly required no additional welding: the T-stub flanges were bolted to the column and the column shear tab was bolted to the beam web. During cyclic testing the beam deformation was minimal due to the active participation of the T-stub flanges. A separation was observed between the T-stub flanges and the column flange. The separation occurred due to plastic bending deformation in the T-stub flanges. This phenomenon allowed energy dissipation and prevented severe buckling in the beam flanges and beam web. The tests revealed the importance of the numerical analysis of the connection to obtain a better understanding of the critical performance parameters. A finite element analysis was conducted on a specimen with rectangular- shaped stems. The analysis consisted of two parts: a solid element analysis of the T-stub under tension load in the stem and a shell element modeling with buckling and instability analysis. The solid element analysis was conducted to study the local behavior of the T-stub, whereas the shell model analysis was performed to study the global behavior of the connection.     

钢框架梁柱T型钢连接节点滞回性能的研究

用ANSYS对T型钢连接节点进行滞回性能的分析,在考虑材料、几何和状态非线性的基础上,系统分析了各种参数对连接滞回性能的影响,分析表明:T型钢的尺寸、是否设柱加劲肋、T型钢翼缘上螺栓的竖向间距对连接的滞回性能影响比较大,并在非线性有限元分析结果的基础上,提出了钢框架T型钢连接的滞回模型.     

Bolted large seismic steel beam-to-column connections Part 1: experimental study

Two large bolted steel moment-resisting connections were studied by experiments. These connections were single-sided beam-to-column assemblies that are representative of exterior beam-to-column connections, and they were composed of W36×150 Grade 50 beams and W14×283 Grade 50 columns. T-stubs were cut from W40×264 sections of Grade 50 steel. The T-stub stems were welded to the beams and prestressed by bolts to the beam flanges in the shop. Final beam-to-column assembly required no additional welding: the T-stub flanges were bolted to the column and the column shear tab was bolted to the beam web. The specimens had two symmetrically located T-stubs with different stem geometry: Specimen 1 had rectangular-shaped stems, whereas Specimen 2 had U-shaped stems. During the cyclic testing the beam deformation was minimal controlled by active participation of the T-stub flanges: a separation between T-stub flanges and the column flanges was observed. This separation was caused by bending plastic deformation in the T-stub flanges and plastic deformation in the high-strength bolts. This phenomenon allowed energy dissipation and prevented severe buckling of the beam flanges and beam web.     

钢框架梁柱连接分类系统

针对我国半刚性连接判定尚无相关研究,介绍了国外已有的几种梁柱连接分类系统,分析总结了现有分类系统的适用范围及应用中存在的问题,提出了修改建议,以供设计研究人员参考.     

组合效应对高层钢框架梁柱节点脆性破坏的影响分析

美国北领地震中,不少钢框架梁柱连接出现了意想不到的脆性破坏。观察表明,大部分破坏发生在节点区的梁下翼缘与柱翼缘之间的全熔透焊缝以及相邻板件的焊缝热影响区。由此可知,焊缝质量不良是节点断裂的主要因素。此外,连接缺乏有效的延性也是破坏的一个原因。节点抗震性能试验中多数采用的是钢节点,没有考虑钢梁上的混凝土板。实际结构中,混凝土楼板的存在提高了节点连接的强度和刚度,这也就加剧了下翼缘发生脆性破坏。通过有限元方法,分析了混凝土板组合效应对梁柱节点脆性破坏的影响。     

Cyclic testing and parametric study of bolted beam-height adjustable steel beam-to-column connections

A kind of bolted beam-height adjustable beam-to-column connections (BHA connections) is proposed for moment-resisting steel frames. It is applicable when the height of beams change in small ranges. A BHA connection is composed of a T-shaped connector, an L-shaped connector with ellipse-type blot holes and bolts. A cyclic test on four full-scaled subassemblies and a series of numerical parametric analyses of BHA connections were conducted to study their mechanical performance. The test results show that the BHA connections with properly stiffened L-shaped connectors possessed good hysteretic properties, stabile secant stiffness and load-carrying capacity degradation and excellent energy dissipation capacity. And the effect of connector slippage and beam web eccentricity was negligible. It can be found in the parametric study that the flange thickness of T-shaped connectors played a pivotal role both in the load-carrying capacity and elastic stiffness of BHA connections, and the elastic stiffness was also affected by the thickness of T-shaped connector webs, L-shaped connector flanges and webs, and column stiffeners. Moreover, the numerical results also demonstrated that the column stiffeners in joint regions could improve the efficiency of load transfer between beams and columns. This kind of connections can be used to assemble steel frames expediently.     

Experimental study and numerical analysis of a composite truss joint

This paper presents a model test and numerical finite element analysis (FEA) on the mechanical behavior of a composite joint in a truss cable-stayed bridge. The model test with the scale of 1:2.5 for the truss joint was conduct to fully understand the safety and serviceability. In the experiment, stress distribution, crack resistance ability and shear resistance of headed studs were carefully measured to investigate the mechanical performance, force transmission of the joint part. The maximum strain of the steel plate and concrete chord remained in the linear elastic region until 1.7 times the design load, which means there is a significant safety margin for such composites. On the basis of the experimental results of composite truss joints, three-dimensional finite element models are established. The results of the finite element analysis are in good agreement with those of the tests in terms of strength and stiffness. It is also expected that the results presented in this paper would be useful as references for the further research and the design of composite truss bridges and composite joints.     

半刚性T型钢梁柱连接的滞回性能研究

为了研究T型钢梁柱连接的滞回性能,对T型钢梁柱连接节点进行了循环加载的有限元模拟和模型试验研究。分析了连接节点关键部件在荷载作用下的应力应变发展情况,并对有限元分析结果和试验结果进行了对比。结果表明:T型钢连接在循环荷载作用下表现出了良好的延性。     

梁柱连接中端板厚度讨论

在考虑撬力按不做功考虑,并采用小变形几何关系原理及内外功相等条件,提出端板厚度的计算公式,并和我国现行规范对比,按屈服理论要比按弹性理论计算的板薄,降低了板厚。     

Behavior of composite beams prestressed with external tendons: Experimental study

The paper deals with the failure mechanisms and behavior of composite steel-concrete beams prestressed with external tendons and subjected to positive bending. Experimental tests were carried out on beams with straight and draped tendons as well as on a non-prestressed beam. Six simply supported beams subjected to a positive static bending moment were tested up to failure. The influence of shear connection flexibility was taken into account and slip was measured along the beam axis. Concurrently, push-out specimens were made and tested to determine shear force vs. slip curves. It was found that at the same eccentricity of tendons (draped or straight without saddle points) the tendon shape has no significant effect on the behavior and ultimate resistance of composite steel-concrete beams. It is also shown that steel-concrete bond cohesion can significantly influence the behavior of the shear connection in composite beams. This influence is comparable with the design shear resistance of a single stud connector.     

The unilateral contact problem in composite slabs: Experimental study and numerical treatment

The shear connection between concrete and profiled steel sheeting in composite slabs is a highly nonlinear problem as far as boundary conditions, material and geometry are concerned. It can be treated as a unilateral contact problem where sticking, sliding and frictional phenomena at the interface of the bodies are all present. Unilateral contact problems, where the contact and noncontact regions between bodies or structures are not a priori known, can be described by the use of nonmonotone material laws. This leads to a hemivariational inequality, which describes the problem under consideration mathematically. The study is also extended experimentally and numerically. The results of both analyses are presented and compared.     

Behaviour and design of beam-to-column connections under fire conditions

In this paper, the main approaches used for developing a component-based connection model are presented and discussed. The model is capable of simulating the behaviour of typical connection configurations in both steel and composite framed structures under monotonic and cyclic loading conditions at ambient as well as elevated temperatures. Validation of the proposed connection model is carried out by comparison against a range of available experimental results, and implementation is undertaken within an advanced finite element program that accounts for material and geometric non-linearities. A series of sensitivity studies are then presented in order to demonstrate the scope of application of the proposed model, and to examine the influence of connection behaviour on the overall structural performance in fire. A number of structural configurations are investigated starting from isolated members and reaching more detailed representations. Several factors are assessed including connection type, boundary conditions and temperature effects. Finally, key parameters and considerations related to connection design are examined.     

Shear instability of panel zone in beam-to-column connections

In this paper, the problem of shear buckling in the panel zone of beam-to-column connections is examined. In particular, following the application of the shear buckling theory for rectangular plates, both in the elastic and in the plastic field, and a critical review of American and European provisions for panel zones, a parametric FEM analysis using ABAQUS Code is carried out on beam-to-column connections. The comparison of the analysed code provisions with the numerical and experimental results shows a good agreement of the American provisions; on the contrary, some drawbacks are identified in the application of the European provisions. Thus, in order to exclude any buckling phenomena, some possible improvements are proposed in terms of panel zone slenderness limit.     

复合锚杆承载性能试验研究与数值模拟分析

复合锚杆具有承载力高、耐久性好、成本低、污染小等优点.为了解复合锚杆的极限承载力以及杆身受力特点,通过现场试验及数值模拟对比分析,得到认识如下:①半杆长粘结复合锚杆及底部锚固无粘结复合锚杆极限承载力高于全杆长粘结复合锚杆;②复合锚杆极限抗拔承载力估算可采用《建筑桩基技术规范》(JGJ 94-2008)中抗拔桩的估算方法...     

Experimental study on low cycle fatigue strength of beam-to-column connections in steel bridge bents with different plate assembling and material mismatching

This study examined the effects of inherent defects due to plate assembling and material mismatched condition between base and weld metal on the fatigue strength of beam-to-column connections. Low cycle fatigue tests were carried out on specimens with different plate assembling systems and material mismatched conditions. The test results revealed that the global load-displacement relationships from specimens with different plate assembling systems and material mismatched conditions are similar, meaning these effects involve only local behavior of specimens. However, the fatigue strength of the specimens strongly depends on the location of defects resulting from plate assembling and mismatched conditions. The specimen with the undermatched conditions and the existing defect located closer to the corner of beam-to-column connection tends to have lower fatigue strength. The fracture surfaces indicated that failure patterns of specimen are different regarding mismatched conditions. While the crack propagated through the weld metal for the undermatched condition, it propagated towards the boundary between base and weld metal for overmatched condition. Elasto-plastic shell analysis was performed under the same condition as the experiments. And it is found that when evaluating fatigue strength of beam-to-column connections, the effects of plate assembling system and material mismatched condition should be considered.     

Experimental and numerical study on restrained composite slab during heating and cooling

In this paper, a series of fire tests on restrained composite slabs, carried out at the University of Manchester, is presented. A total of six composite slabs were tested under different fire scenarios, with different load ratios. The tests were particularly concerned with the variation of internal forces within the slabs during both heating and cooling phases. In addition to the testing programme, two separate nonlinear finite element models have been developed to simulate the thermal and mechanical behaviour of composite slabs during heating and cooling, which is introduced in detail in this paper. In the thermal analysis model, plane elements were adopted to obtain a detailed thermal behaviour. In the structural analysis model, the concrete, steel deck and mesh were simulated by solid elements, shell elements and truss elements respectively. The interaction between the concrete and steel sheet was simplified to spring elements. According to the experimental results and FE modelling, the behaviour of composite slabs was analysed in detail. At last, the parametric study was performed where the effect of concrete strength, steel deck thickness and mesh size was analysed.     

Numerical modeling of the fire-structure behavior of steel beam-to-column connections

This study proposes a numerical model to investigate the behavior of steel beam-to-column connections in fires. Two strategies have been employed to transfer thermal results from a fire simulation to structural analysis. A full scale fire test was performed on a steel beam-to-column connection following the ISO 834 standard fire curve; it was simulated to verify the proposed methods. The wall temperatures obtained by FDS were used as an interface for fire exposure on the surface of the structure. The numerical results are in agreement with the experimental data. In addition, the size effect of the furnace and a sensitivity analysis on insulation materials had been studied. Two reduced beam sections were analyzed and compared with the simulation results of an unreduced beam section. Both sections were able to withstand the severity of the blaze with the runway phenomenon occurred after a similar period of time for each beam.