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.     

Finite element modeling of bolted connections in thin-walled stainless steel plates under static shear

The recently performed experimental study indicates that the current Japanese steel design standards (AIJ) cannot be used to predict accurately the ultimate behavior of bolted connections loaded in static shear, which are fabricated from thin-walled (cold-formed) SUS304 austenite stainless steel plates and thus, modified formula for calculating the ultimate strength to account for the mechanical properties of stainless steel and thin-walled steel plates were proposed. In this study, based on the existing test data for calibration and parametric study, finite element (FE) model with three-dimensional solid elements using ABAQUS program is established to investigate the structural behavior of bolted shear connections with thin-walled stainless steel plate. Non-linear material and non-geometric analysis is carried out in order to predict the load–displacement curves of bolted connections. Curling, i.e., out of plane deformation of the ends of connection plates which occurred in test specimens was also observed in FE model without geometric imperfection, the effect of curling on the ultimate strength was examined quantitatively and the failure criteria which is suitable to predict failure modes of bolted connections was proposed. In addition, results of the FE analysis are compared with previous experimental results, failure modes and ultimate strengths predicted by recommended procedures of FE showed a good correlation with those of experimental results and numerical approach was found to provide estimates with reasonable accuracy.     

静剪切力作用下薄壁不锈钢板螺栓连接的有限元建模

最近的试验研究表明,日本现行钢结构设计标准(AIJ)不能准确预测薄壁(冷加工)SUS304不锈钢板的螺栓连接在静剪力作用下的极限状态,因此本文提出极限强度计算公式,说明不锈钢和薄壁钢板的机械特性。以现有试验数据作为参数研究的基础,采用ABAQUS程序对三维实体单元进行有限元分析,以探究薄壁不锈钢板中螺栓剪切连接的结构性能。采用材料非线性和几何非线性分析法以预测螺栓连接的荷载-位移曲线。试验中试件发生的卷曲等连接板端部的平面外变形在不考虑几何缺陷的有限元模型分析中同样可观察到;在对卷曲对极限强度的影响进行量化检验外,提出适合于预测螺栓连接破坏模式的破坏准则。此外,有限元分析结果与以前试验结果相比可知,破坏模式和有限元推荐步骤预测的极限强度与试验结果具有良好的相关性,数值方法可提供具有合理精度的评估。     

Tests of single shear bolted connections of thin sheet steels at elevated temperatures—Part II: Transient state tests

A total of 62 single shear bolted connection specimens were tested using transient state test method. The specimens of single shear bolted connections were fabricated by three different thicknesses of thin sheet steels. The tests were conducted at three different load levels of 25%, 50% and 75% of the failure load at ambient temperature. The tendency of the test strength reduction of the single shear bolted connections conducted using the transient state test method is generally similar to that for the steady state test method. However, it is shown that the transient state test results are always conservative compared with the steady state test results. Three main failure modes, namely the bearing, tear out and net section tension, were observed in the transient state tests. The failure modes of the specimens in transient state tests for the load level of 0.25 of the failure load at ambient temperature are generally consistent with those specimens in the steady state tests.     

Numerical study on seismic behavior of H-beams with wing plates for bolted beam-column connections

Many experiments have been studied for bolted beam-column connections for past years to prevent the demerit of welding at the site. Wing plates welded at beam ends of bolted beam-column connections in CFT structures have been studied experimentally by authors to ensure that plastic hinges are away from the welding. This paper studies the effect of wing plates numerically by simulating H-beams in bolted beam-column connections as cantilever beams using ABAQUS. Through convergence and cyclic loading analyses, simulation agrees well with the experimental results. The brittle failure due to developed crack can be predicted once equivalent plastic strain exceeds the maximum plastic strain. From numerical results, the effect of wing plates is verified. Furthermore, suitable formulas for the width of wing plates are derived to prevent the brittle failure of beams. Consequently, it is suggested that the length and the width of wing plates in application should be designed by using the suggested design process proposed in this paper.     

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.     

Behavior of bolted angle connections subjected to combined shear force and moment

In this paper, the effect of web angle dimensions on moment-rotation behavior of bolted top and seat angle connections, with double web angles is studied. Several 3D parametric finite element (FE) models are presented in this study whose geometrical and mechanical properties are used as parameters. In these models, all of the connection components, such as beam, column, angles and bolts are modeled using solid elements. The effect of interactions between components, such as slippage of bolts and frictional forces, are modeled using a surface contact algorithm. To evaluate the behavior of connection more precisely, bolt pretensioning force is applied on bolt shanks as the first load case. The results of this numerical modeling are compared with the results of experimental works done by other researchers and good agreement was observed. To study the influence of shear force on behavior of these connections, several models were analyzed using different values of shear force. The effect of important parameters, especially the effect of web angle dimension, is studied then. An equation is proposed to determine the reduction factor for initial rotational stiffness of connection using connection initial rotational stiffness, yield moment, the expected shear force and web angle dimension. The proposed equation is compared with other existing formulations and it was observed that the proposed model is a better estimator of connection behavior.     

Analysis of cold-formed purlins with slotted sleeve connections

In multi-span purlin design, it is customary to assume beam continuity, avoiding joint analysis. This analysis is safe when employing full strength and stiffness connection. There are two usual joint typologies: overlapping and sleeve connections. The main advantage of sleeve joints is reduction of cost and time in the assembly process. Overlapping joints can be correctly designed selecting the overlap length to depth ratio, for a wide range of Z-shaped profiles. In this paper, a partial strength and stiffness Z profile sleeve joint is experimentally and numerically analyzed, studying their structural behavior and characterizing their rotational stiffness and strength.     

Effect of shear force on the initial stiffness of top and seat angle connections with double web angles

This study focused on the moment-rotation behavior of bolted top and seat angles with double web angle connections, especially the initial stiffness of this type of connection under the combination of shear force and moment. Several 3D parametric finite element models are presented in this regard, with the geometrical and mechanical properties of connections are as parameters. In the models, all the connection components such as beam, column, angles and bolts are modeled using eight node brick elements. The effects of all component interactions, such as slippage of bolts and frictional forces, are modeled using a surface contact algorithm, and to evaluate the connection behavior more precisely, bolt pre-tensioning is applied on the bolts shanks as the first load case. The results of numerical modeling are compared with test results of experiments that have been done by researchers, and show good agreement with them. To evaluate the effect of shear force on the behavior of such connections, several models were analyzed under different magnitudes of shear force, and the results of the analyses showed that the shear force has a reducing effect on the initial stiffness of bolted angle connections. Therefore, an equation is proposed to determine the reduction factor of a connection’s initial stiffness in terms of the connection’s initial stiffness and yield moment in the case of no shear force, and any expected shear force that might be applied.     

Tests of single shear bolted connections of thin sheet steels at elevated temperatures—Part I: Steady state tests

The current design rules on bolted connections of thin sheet steels for cold-formed steel structures are applicable for ambient temperature condition only. Investigation of single shear bolted connections at elevated temperatures is limited. In this study, 120 single shear bolted connection specimens involving three different thicknesses of thin sheet steels and 30 coupon specimens were conducted by using steady state test method in the temperature range from 22 to 900 °C. There are three main failure modes observed in the single shear bolted connection tests, namely the net section tension, bearing, and tear out. The test results were compared with the predicted values calculated from the American, Australian/New Zealand and European specifications for cold-formed steel structures. In calculating the nominal strengths of the connections, the reduced material properties were used due to the deterioration of material at elevated temperatures. It is shown that the strengths of the single shear bolted connections predicted by the specifications are generally conservative at elevated temperatures. The comparison between the deterioration of the tested connection strengths and that of the material properties at elevated temperatures showed a similar tendency of reduction.     

State-of-the-art on resistance of bearing-type bolted connections in high strength steel

With the recent development of material science, high strength steel (HSS) has become a practical solution for landmark buildings and major projects. The current codes for design of bearing-type bolted connections of steel constructions were established based on the research of conventional steels. Since the mechanical properties of HSS are different from those of conventional steels, more works should be done to develop the appropriate approach for the design of bearing-type bolted connections in HSS. A review of the research carried out on bearing-type bolted connections fabricated from conventional steel and HSS is presented. The up-to-date tests conducted at Tongji University on four connection types fabricated from three grades of HSS with nominal yield strengths of 550, 690, and 890 MPa are presented. The previous research on failure modes, bearing resistance and the design with consideration of bolt hole elongation are summarized. It is found that the behavior of bolted connections in HSS have no drastic difference compared to that of conventional steel connections. Although the ductility is reduced, plastic deformation capacity of HSS is sufficient to ensure the load redistribution between different bolts with normal construction tolerances. It is also found that behavior of each bolt of multi-bolt connections arranged in perpendicular to load direction is almost identical to that of a single-bolt connection with the same end distance. For connections with bolts arranged in parallel to load direction, the deformation capacity of the whole connection depends on the minimum value between the end distance and the spacing distances in load direction. The comparison with existing design codes shows that Eurocode3 and Chinese GB50017-2017 are conservative for the design of bolted connections in HSS while AISC 360-16 may overestimate the bearing resistance of bolted connections.     

Analysis of the behaviour of stainless steel bolted connections

This study is focused on two types of bolted connections that are common in steel structures. They concern cover plate connections and T-stubs, where the bolts are loaded in shear or in tension. The Eurocode 3 requirements for stainless steel connection design are essentially the same as for carbon steel. The study considers the case of austenitic stainless steel for which the conventional elastic limit is relatively low compared to the ultimate strength. In bearing, criteria on deformation limits have to be considered for cover plate connections. In T-stubs, strain hardening of stainless steel exhibits a continuous increase of the applied load and can influence the failure mode. A finite element model is developed and validated for the two types of connections. A more extensive parametric study should be carried out to develop a better understanding of the behaviour of stainless steel connections.     

Analysis of bolted moment connections in cold-formed steel beam-column sub-frames

An extensive experimental investigation on bolted moment connections between cold-formed steel sections was carried out, and a total of 16 internal and external beam-column sub-frames with various connection configurations were tested under lateral loads. It is found that for those six beam-column sub-frames with large bolt pitches and thick gusset plates in the connections, flexural failure of connected sections is always critical. The moment resistances of the connections attain at least 85% of the moment capacities of the connected sections.This paper presents a theoretical investigation for predicting the structural behaviour of bolted moment connections between cold-formed steel sections. An analysis and design method for internal force distribution of the connections is presented, and hence a set of design rules for section failure of connected sections under combined bending and shear is proposed. Moreover, a non-linear finite element model of the beam-column sub-frames incorporating the effect of semi-rigid joints is also presented. On the basis of the measured moment joint rotation curves of the bolted moment connections, the overall lateral load-deflection curves of the sub-frames are predicted, and they are found to follow closely the curves obtained from tests. Furthermore, a semi-empirical formula for flexibility prediction of the bolted moment connections is also proposed after careful calibration against test data.It is demonstrated that the proposed rules are highly effective for predicting the structural performance of cold-formed steel frames with bolted moment connections. Hence, structural engineers are encouraged to design and build cold-formed steel structures with bolted moment connections to achieve practical and efficient construction.     

Numerical investigation on ultimate shear strength of steel plate shear walls

Ultimate shear strength of steel plate shear walls, SPSW, was conventionally computed as the sum of base shear supported by in-fill plate and boundary frame elements. The base shear supported by the in-fill plate was computed assuming that it was fully yielded after buckling whereas the base shear supported by the boundary frame elements was computed by plastic analysis assuming uniform yielding mechanism. In this paper the ultimate shear strength of SPSW was investigated by the finite element method. A detailed three-dimensional finite element model was established using ANSYS software at which the in-fill plate and the boundary frame elements were modeled using finite strain iso-parametric shell elements. The analysis included material and geometric non-linearities. Numerical results obtained from cyclic and pushover loading of SPSWs were verified by comparison to test results published in the literature. A comprehensive parametric analysis was conducted to assess the effect of geometric and material parameters of the wall on its ultimate shear strength. Discrepancies between numerical results and conventional theory were attributed to interaction of in-fill plate and boundary frame elements at ultimate load. When the flexural rigidity of boundary frame elements decreased, the in-fill plate did not achieve full yield strength. On the other hand, the base shear supported by boundary frame elements increased when thicker in-fill plates were utilized. Numerical results were used to update the theoretical expression of ultimate shear strength of SPSWs. The proposed expression was assessed by comparison to test results published in the literature.     

Application of steel channels as stiffeners in bolted moment connections

This paper proposes a stiffening method to meet some architectural needs. This method uses bolted channels as alternatives to both continuity and doubler plates in bolted moment-resistant beam-to-column connections. The present study investigates the performance of channels as stiffeners to: increase yield load in the tension zone of connection, gradually increase overall moment capacity of connection, and avert shear failure of the column web panel zone. We conducted experiments to examine the tension region of the connection loaded from T-stubs. The moment capacity of full connection was predicted by considering T-stub idealization and shear effects on the column web panel. T-stub tensile behavior and overall connection behavior were also monitored using three-dimensional finite element simulations in ANSYS simulation software because this problem is three-dimensional in nature. Effects of geometrical and material non-linearities on interaction among connecting members should be clarified. This study showed marked strength improvement in connection by use of channels. The performance of channel stiffeners was examined through comparison of results.     

Modal analysis of cold-formed pallet rack structures with semi-rigid connections

The three dimensional (3D) model of conventional pallet racking systems were prepared using the finite element program ANSYS and free vibration modal analysis carried out on conventional pallet racks with the 18 types of column sections developed along with semi-rigid connection. The stiffness of the connector was tested using the conventional cantilever method and also using a double cantilever method. Non-linear finite element analysis of both the tests was carried out. From the experimental study on connection and finite element modal analysis, a simple analytical model that captures the seismic behavior of storage racks in their down aisle direction is proposed. The model is aimed at developing simplified equation for the fundamental period of storage racks in their down aisle direction. A parametric study was carried out to find out fundamental mode shape and time period. Finite element method is used for the accuracy and appropriateness of cold-formed steel frame.     

Investigation of high strength steel connections with several bolts in double shear

A series of 26 tests on tension splices with three or four bolts positioned in the direction of bearing force are presented. Steel grade S690 was used for the fabrication of connection plates. The tests were also numerically simulated to obtain the distribution of forces between bolts. Tests on similar connections made of high strength steel were gathered from the literature. These tests were also numerically simulated. The numerical results agreed with experimental data very well, and were used to evaluate the bearing resistance formula according to EN 1993-1-8.     

Numerical investigation of net section failure in stainless steel bolted connections

Despite fundamental differences in the mechanical behaviour of stainless steel and carbon steel, design provisions for stainless steel connections in current standards essentially follow the rules for carbon steel with some limited modifications. For the case of net section capacity, the design rules from EN 1993-1-3 for cold-formed carbon steel have been adopted for stainless steel connections in EN 1993-1-4 and the SCI/Euro Inox Design Manual without any modification. In this paper, an investigation into the behaviour of stainless steel connections failing by net section rupture has been conducted. Numerical models for austenitic and ferritic stainless steel have been developed and validated against existing test results. The validated models were subsequently used to perform parametric studies to investigate the main parameters affecting the net section rupture of bolted connections; these include edge distance e₂ and bolt configuration. By studying the stress distribution along the net section for different edge distances and bolt arrangements, it was found that the ductility of stainless steel is sufficient to ensure extensive redistribution of stresses prior to fracture. Hence, a revised design equation (based on that given in EN 1993-1-3) for net section capacity of stainless steel connections has been proposed and its reliability demonstrated by means of statistical analysis.     

Effect of longitudinal stress gradient on the ultimate strength of thin plates

When thin-walled sections are subjected to a moment gradient, the plates that comprise the section are themselves subjected to a longitudinal stress gradient. This paper analyzes the effect of longitudinal stress gradient on the ultimate strength of thin plates. Two types of thin plates are investigated: (1) plates simply supported on all four edges; and (2) plates simply supported on three edges, and with one longitudinal edge free. These two cases illustrate the influence of longitudinal stress gradient on stiffened and unstiffened elements of cold-formed steel sections, respectively. Nonlinear finite element analysis (ABAQUS) was performed to determine the ultimate strength of thin plates under a longitudinal stress gradient. The results indicate that the longitudinal stress gradient increases the strength of both types of thin plates, but has significantly more influence on unstiffened elements than stiffened elements. The beneficial effect of longitudinal stress gradients can be accounted for in design by using a plate buckling coefficient modified to account for the longitudinal stress gradient, an example of the impact of this change on a common cold-formed steel channel is provided.     

Q460高强钢螺栓连接承载性能试验研究

通过对20个Q460高强钢螺栓连接的静力拉伸试验,研究高强钢材料强度和螺栓布置方式对连接承载力和变形的影响。根据力平衡和变形协调条件建立方程,理论分析高强度钢材螺栓连接的受力性能,考察相关规范的适用性。结果表明：螺栓横向布置时,试件的承载力和变形随间距增大而增大;边距由1.5d0增大到2d0,端距由2d0增大到2.5d0时,试件极限承载力仅提高了0.78%和2.37%,说明达到标准构造取值后,边距和端距增大对连接的承载力影响甚微。螺栓纵向布置时,试件的承载力仅随边距增大呈线性增大趋势。钢板承压强度设计值取1.26fu,对于Q460高强度钢材其取值偏小。为国产高强度钢材螺栓连接的设计理论和方法提供了科学依据。