Gusset Joints Research Articles

Shape optimization for non-linear buckling load of aluminum alloy reticulated shells with gusset joints

Abstract Non-linear stability plays an essential role in the design of reticulated shell structures. In order to improve the buckling strength of aluminum alloy spherical shells with gusset joints, this paper proposes a shape optimization method to maximize the non-linear buckling load using a genetic algorithm. The control points of a cubic spline are chosen as the design variables defining the height of the surface. In the non-linear buckling analysis, a linear combination of the symmetric and antisymmetric buckling modes is used as the imperfection mode, and an initial eccentricity is introduced for each member to consider the disadvantageous effect caused by the interaction between the flexural-torsional buckling and global buckling. It is verified in the numerical examples that the proposed method can increase the non-linear buckling load maintaining the smoothness of the surface, while the conventional approach of minimizing the total strain energy is not effective for improving the buckling strength. Finally, the design tables of the parameters of the optimized cubic spline curve are obtained through the parametric analysis considering various load factors and height-to-span ratios, and are verified to be practical and useful under different height of the section, number of rings and support condition.

관벽에 작용하는 전단력의 영향을 고려한 거셋트 플레이트-강관 접합부의 극한강도

관벽에 작용하는 전단력의 영향을 고려한 거셋트 플레이트-강관 접합부의 극한강도

Discussion on the Hot-Spot and Notch Stress Based Fatigue Assessment Methods Based on Test Results

The focus of the current paper is the investigation of different local stress calculation methods for fatigue design. To evaluate the accuracy and applicability of the hot-spot and effective notch stress (ENS) fatigue assessment methods an experimental and numerical research program is carried out at the BME Department of Structural Engineering, in Hungary. Two types of structural details are tested using 32 test specimens, a cruciform and a gusset plate type joint. The test results and the accompanying numerical calculation results are statistically evaluated and compared. Analysing the results of the fatigue tests and numerical calculations, it is concluded, that both the hot-spot and the ENS method could be used for fatigue design of the cruciform joints according to the recommendation of the IIW (Hobbacher in Recommendations for fatigue design, Springer, Paris, 2004). However, the rules of the ENS method needs improvement, if used for the design of gusset plate type joint. According to the current results, the ENS method can be adjusted to make applicable for the gusset plate joints as well, recommendation for that is presented in the current paper.

Fatigue Properties of Cruciform and Flange-gusset Joints Using Normal and High Strength Steels

The objective of this paper is to investigate and compare the fatigue behavior of Normal Strength Steel (NSS) and High Strength Steel (HSS) welded specimens (cruciform and flange gusset joints). Numerous specimens were tested in the framework of the research project. The experimental S-N curves of the test specimens are determined and analyzed by mathematical statistics to consider the uncertainties and scatter of test results. Statistical analysis of the S-N curves showed that the fatigue behavior of as-welded flange gusset joints is identical in the cases of HSS and NSS specimens, which means that there is no difference in the fatigue lifetime depending on the steel grade. However, the as-welded HSS cruciform joints can be more favorable and their fatigue lifetime is longer than the specimens made from NSS, if the stress range is below 100 MPa. The current study shows that the fatigue behavior of as-welded HSS details depends on the geometry of the investigated specimens and its fatigue lifetime can be larger in the small stress range region than for NSS specimens.

Experimental and numerical studies on ductile-fracture-controlled ultimate resistance of bars in aluminum alloy gusset joints under monotonic tensile loading

Aluminum alloy gusset (AAG) joints have been applied extensively in single-layer latticed shells. This paper investigates the resistance of the aluminum alloy bar (AL bar) in AAG joints under monotonic tensile loading. The main failure mode is the fracture of the I-shaped AL bar, accompanied by local buckling of the web. The fracture modes of the flanges differ: block tensile–shear fracture in the small plate (SP) group, whereas net-section fracture in the big plate (BP) group. Compared with traditional simulation, the simulation which considers the fracture can yield a load-elongation curve with a declining stage so that the ultimate resistance can be obtained straightforward. This simulation is based on the modified Mohr–Coulomb (MMC) fracture criterion with damage-induced softening, which is achieved by VUHARD and VUSDFLD subroutines implemented into ABAQUS/Explicit. The parameters in this criterion are calibrated on smooth plate specimen tests. The results from the finite element models are in excellent agreement with the experimental results in terms of the web buckling, fracture path, and ultimate resistance governed by the crack initiation and succeeding propagation. This simulation, particularly the fracture model and its detailed calibration procedures, have a broad prospect of applications for evaluating the resistance of aluminum components that are governed by various ductile fracture modes under monotonic loadings, such as the rupture of bolt connections and block tearing of AAG joint plates.

Influence of cyclic loading on the relaxation behavior of compressive residual stress induced by UIT

Fatigue strength of welded joints is improved by inducing compressive residual stress at weld toes. The ultrasonic impact treatment (UIT) is regarded as an effective method for inducing compressive residual stress at weld toes. However, excessive loads that cause plastic deformation at weld toes relieve the induced compressive residual stress. In addition, stress fluctuation affects the relaxation of residual stress even it is smaller than the yield strength. The relaxation of compressive residual stress decreases the fatigue strength improvement. Therefore, in order to evaluate the fatigue strength of welded joints enhanced by UIT, it is necessary to quantify the relaxation of local residual stresses at weld toes under cyclic loading. In this study, we measured a residual stress at the UIT groove using the X-ray diffraction method with a small-diameter collimator and an irradiation angle that was corrected based on the shape effect of the UIT groove, and we investigated its relaxation behavior under cyclic loading. In addition, we estimated the fatigue test results of the out-of-plane gusset joints improved by UIT using the modified Goodman diagram considering the relaxation of residual stress.

Prediction of Bending Fatigue Life of Cracked Out-of-Plane Gusset Joint Repaired by CFRP Plates

Carbon fiber reinforced polymer (CFRP), plates bonding repair method is one of the simple repair methods for cracked steel structures. In this study, the influence of width of CFRP plates on bending fatigue life of out-of-plane gusset joint strengthened with CFRP plates was investigated from the experimental and numerical point of view. In the bending fatigue test of cracked out-of-plane gusset joint strengthened with CFRP plates, the effect of width of CFRP plates on crack growth life was clarified experimentally. Namely, it was revealed that the crack growth life becomes larger with increasing the width of CFRP plates. In the numerical approach, the stress intensity factor (SIF) at the surface point of a semi-elliptical surface crack was estimated based on the linear fracture mechanics. Furthermore, the extended fatigue life of cracked out-of-plane gusset joint strengthened with CFRP plates was evaluated by using the estimated SIF at the surface point and the empirical formula of the aspect ratio of semi-elliptical crack. As the results of numerical analysis, the estimated fatigue life of the specimen strengthened with CFRP plates showed the good agreement with the test results.

Repair effect of installation of pre-tensioned CFRP strips on fatigue cracks initiated at out-of-plane welded gusset joints

Repair effect of installation of pre-tensioned CFRP strips on fatigue cracks initiated at out-of-plane welded gusset joints

Experimental study on hysteretic behavior of aluminum alloy gusset joints

This paper presents the hysteretic behavior of aluminum alloy gusset (AAG) joints by means of experimental study. Eight AAG joint specimens are tested under cyclic load. Initially, the test program is introduced, and the test phenomena and failure modes are demonstrated. Subsequently, the hysteresis curves, skeleton curves of the specimens are plotted and discussed. The experimental results reveal that there are two kinds of failure modes of AAG joints under cyclic load. The deformation process and mechanical behavior under cyclic load can be summarized into four stages and five phases, respectively. Finally, based on the hysteresis curves and skeleton curves, the deformation ability, energy dissipation capacity, bearing capacity and stiffness degradation of the AAG joint specimens are evaluated, and the following conclusions can be drawn: (1) due to the existence of the gap between the bolt hole and the bolt shank, AAG joint specimens experienced bolt slipping during the experiment, hence the hysteresis loops of the AAG joint specimens are not very plump; (2) judged by the load-displacement hysteresis curves, the AAG joint has good deformation ability but poor overall energy dissipation capacity, which can be further improved; (3) the moment-relative rotation hysteresis curves are plumper than the load-displacement hysteresis curves, indicating that the joint zone has better energy dissipation capacity than the whole specimen; (4) with the increase of the thickness of the gusset plate, the AAG joint performs better hysteretic behavior including bearing capacity, deformation ability and energy dissipation capacity; (5) all of the specimen performed stiffness degradation under cyclic loading.

The in-plane effective length of members in aluminum alloy reticulated shell with gusset joints

This paper presents an analytical research on the in-plane stability of members in single-layer reticulated latticed shells with aluminum alloy gusset (AAG) joints. The influence of two kinds of actual boundary conditions are considered, namely, the stiffness of the AAG joint (k1) and restraint of adjacent members (k2). In order to explore the influence of k1, an experimental program including 5 member specimens with AAG joints is introduced, and finite element (FE) models are established and verified. Based on the test and FE results, the effective length of the specimens are obtained. Subsequently, theoretical analysis is conducted to investigate the effect of k2, with accounting for the stiffness reduction caused by axial compressive force. Finally, the effective length factors of members in reticulated shell with AAG joints are derived and tabulated. Numerical examples are presented to illustrate the necessity of considering the influence of k1 and k2, and verify the good accuracy of the given effective length factors.

Study on out-of-plane flexural behavior of aluminum alloy gusset joints at elevated temperatures

Aluminum alloy gusset (AAG) joint is the most widely applied joint system in aluminum alloy reticulated shells, and the elevated-temperature mechanical behavior of joints have serious influence on the safety of structures. This paper investigated the out-of-plane flexural behavior of AAG joint by means of experimental and numerical analysis, and theoretical formulae of its bearing capacity and bending stiffness were derived. Firstly, elevated-temperature experiments on 9 AAG joints were conducted in a special-shaped oven. The test results revealed that: (1) the failure modes of thin-plate AAG joints at temperatures under 300°C are block tearing and local buckling of the gusset plate, which remain the same as those at room temperature; (2) when the gusset plate is thick enough (usually as thick or thicker than the flange of the member), the joint zone will not collapse under 300°C; (3) the initial stiffness approximately remains unvaried, while the ultimate flexural bearing capacity drops with the elevation of temperature. Subsequently, finite element (FE) models using ABAQUS were established and verified by the test results. It is confirmed that the FE models can accurately describe the mechanical performance of the AAG joints at elevated temperatures. Based on the simplified FE model, a parametric study was carried out, considering various aluminum alloy brands, thickness of the gusset plate, radius of the center region of the gusset plate and different temperatures. Finally, the block tearing resistance, the local buckling resistance, and parameters of four-linear bending stiffness model of the FE models were presented, and the theoretical formulae were derived using statistical regression technology. The theoretical formulae were verified to be accurate enough against the experimental and FE results, to estimate the bearing capacity and the nonlinear bending stiffness of AAG joints at elevated temperatures under 300°C, which can serve for practical engineering.

Experimental investigation on bending and shear performance of two-way aluminum alloy gusset joints

Two-way aluminum alloy gusset joints (AAGJs) are considered to be employed in cable-stiffened aluminum alloy single-layer reticulated shell structures meshed with quadrilateral grids. In this study, a series of experiments on six AAGJs with and without shear connectors were conducted to investigate their semi-rigid behavior. Two joints were subjected to pure bending moments and others to shear loads, then their corresponding failure modes were investigated which were mainly beam rupture, beam web buckling, and bolt failure. The moment-rotation curves, shear load-rotation curves, and strain-load curves were also obtained, indicating that AAGJs are typical semi-rigid joints. Shear connectors can optimize the load transferring path and improve ductility under bending moment while enhancing shear performance significantly. A simplified theoretical AAGJ model was also established and parameterized according to the experimental results.

Numerical analysis of aluminium alloy gusset joints subjected to bending moment and axial force

A test series was carried out and reported in a companion paper on the semi-rigid behaviour of aluminium alloy gusset (AAG) joints subjected to bending moment and axial force. This paper presented the results of an extensive numerical analysis program devoted to the investigation of the bending behaviour of AAG joints. The analysis was developed by means of finite element (FE) models implemented in the non-linear code ABAQUS. The procedure was accurately calibrated on the basis of the available experimental results. It is indicated that the FE models could be used effectively to describe the mechanical performance of AAG joints, including the failure modes, deformation process and bending moment-rotation curves. Furthermore, the shear connector, the thick plate and the advanced contact of bolts and bolt holes could improve the bending behaviour of AAG joints. According to the deformation process of AAG joints, a four-line model was proposed to simulate the bending moment-rotation relationship. To develop a further understanding, the effects of the member height, axial force, bolt pretension force, bolt gap and material nonlinearity on the bending behaviour of AAG joints were investigated.

09.09: Experimental fatigue analysis of high strength steel structures

ABSTRACTThere are contradictional information in the previous studies regarding the relationship between the fatigue strength and the yield strength in case of steel structures. Several previous test result show that the fatigue strength of as‐welded specimens do not depend on the yield strength of the base material. However, several studies show that the fatigue detail class of HSS structure can be higher than for structures made form NSS material for the same structural detail. Collecting the previous fatigue test results of cruciform and flange gusset structural details the effect of the yield strength on the fatigue behaviour is studied. Additional laboratory test program with 32 test specimens is performed to investigate the fatigue behaviour of structural details typically used in bridges produced from HSS and NSS material. For cruciform welded joints the test results show clear correlation between the yield strength and the fatigue life time. For flange gusset joints this relationship cannot be observed. In addition, post weld treatment of the flange gusset plate joint is studied. Using the results of the fatigue tests the fatigue lifetime increase applying the grinding type post‐weld treatment is evaluated.

Experimental and numerical studies on single-layer reticulated shells with aluminium alloy gusset joints

Single-layer reticulated shells with aluminium alloy gusset (AAG) joints have a significant application prospect in spatial structures. To investigate their buckling behaviour, a single-layer reticulated shell with AAG joints subjected to a concentrated load at central joint was tested. The tested shell was a K6 shell with 5 rings, 8m span and 0.5m height. Its failure mode, buckling behaviour, internal force distribution of members, stress distribution of plates and joint stiffness were discussed. Finite element (FE) method implemented in the non-linear code ANSYS was adopted for the further investigation of single-layer reticulated shells with AAG joints. The FE procedure was accurately calibrated on the basis of the available experimental results. To develop a deep understanding, parameter studies considering the influence of joint bending behaviour on the buckling behaviour of single-layer reticulated shells were conducted.

Elasto-plastic stability of single-layer reticulated shells with aluminium alloy gusset joints

The single-layer reticulated shell with aluminium alloy gusset (AAG) joints is an innovative space structure system, and has been widely used in the building engineering. According to the bending behaviour of AAG joints obtained from the theoretical formulae, the finite element (FE) models of K6 AAG joint shells were established in the ANSYS program. The buckling performance of K6 shells with semi-rigid and rigid joints was discussed. It is indicated that the semi-rigid behaviour of AAG joints had a significant effect on the buckling performance of K6 shells. To develop a further understanding, parametric studies were performed, varying the span-to-thickness ratio, height-to-span ratio, ring, member section, joint bending behaviour, joint stiffness model, material property, load distribution, support condition and initial geometric imperfection. It is found that the effects of these parameters on the elasto-plastic stability of K6 shells with rigid and AAG joints were different obviously. At last, to predict the elasto-plastic buckling load of AAG joint shells, theoretical formulae were proposed on the basis of the FE results of more than 8000 shell models.

Extending fatigue life of out-of-plane gusset joint by bonding CFRP plates under bending moment

Carbon fiber reinforced plastic, CFRP, plates bonding method is one of the new repair methods for fatigue cracks. In this method, propagation of fatigue crack will be delay because of the suppression of crack opening by crack bridging and stress reduction by composite effect of bonding CFRP plates. In this study, to clarify the effect of bonding CFRP plates on fatigue life extension, bending fatigue tests were carried out. First, fatigue tests on the specimens in as-welded condition were conducted until fatigue crack propagated to 10mm away from the weld toe. Then, fatigue crack was covered by CFRP plates and the specimens were re-tested until fatigue crack penetrated through the base plate. As the results of bending fatigue tests, the fatigue test data of the specimens repaired by bonding CFRP plates showed much longer fatigue life compared with that in as-welded condition, under stress ratio, R=0 and -infinity

散逸エネルギ測定に基づくガセット溶接継手に対する破壊箇所予測

散逸エネルギ測定に基づくガセット溶接継手に対する破壊箇所予測

Application of the Component Method to Aluminum Alloy Gusset Joints

The stiffness of aluminium alloy gusset (AAG) joints plays a key role in the global buckling behaviour of single-layer reticulated shells. In this paper, the bending stiffness of AAG joints is mainly analysed by using the component method. Based on the M-φ curves obtained from a previous experimental program, a four-linear mathematical model which is used to evaluate the bending stiffness behaviour of AAG joints is proposed. To calculate the four-linear mathematical model, the deformation mechanism of AAG joints is discussed and the component model for the joint bending stiffness is developed. According to theoretical derivations and extensive finite element simulations, the formulae to estimate the whole range bending stiffness of AAG joints are presented. Finally, the applicability of the theoretical formulae is verified by comparing the theoretical results with the experimental results.

Block tearing and local buckling of aluminum alloy gusset joint plates

Aluminum Alloy Gusset (AAG) joints widely used in the single-layer latticed shells have a significant application prospect in spatial structures. Unfortunately, studies on the resistance of AAG joints are insufficient, leading to a lack of applicative design methods for this joint system. This paper is devoted to investigate the resistance of AAG joint plates. Firstly, tests on fourteen AAG joint specimens are carried out to explore their collapse modes. Experimental phenomena show that the main collapse modes of AAG joint plates include the block tearing of top plates and the local buckling of bottom plates. Secondly, Finite Element (FE) simulations to investigate the mechanical behavior of AAG joints are performed by means of the non-linear FE code ABAQUS. Thirdly, formulae for predicting the block tearing resistance and the local buckling resistance of AAG joint plates are proposed, which are based on theoretical analyses. Fourthly, test results are of great help in the determination of parameters k and α which are adopted to modify the block tearing resistance and the local buckling resistance respectively. Finally, a comparison of test results verifies that theoretical formulae are applicable. In addition, in order to avoid the block tearing and the local buckling of AAG joint plates, convenient design criteria are provided.