Load Bearing Capacity Of Joints Research Articles

Research on residual behavior of tensile stiffened welded hollow spherical joints after exposure to fire

Space grid structures are subject to fire like other building structures, but they rarely collapse as a whole after exposure to fire. The welded hollow spherical joints are the main joint types of space grid structures. It is particularly critical to accurately identify the mechanical behavior of welded hollow spherical joints after exposure to fire to confirm whether the grid structure needs reinforcement or demolition for reconstruction. Therefore, the mechanical behavior of tensile stiffened welded hollow spherical joints after exposure to fire without load was studied by experiment. The failure modes of stiffened welded hollow spherical joints after exposure to fire are pull-out failures and oblique splitting pull failures. The initial axial stiffness of stiffened welded hollow spherical joints declines with the increase of exposure temperature, and the cooling method has little effect on it. When the exposure temperature is low, the cooling method has no impact on the load-bearing capacity of the joint. The load-bearing capacity of the air-cooling joints decreases linearly with the progress of exposure temperature, while the water-cooling joints present an opposite trend. The ductility of the air-cooling joints increases rapidly with the growth of exposure temperature, while the water-cooling joints fluctuate up and down. The strain of the tensile stiffened welded hollow spherical joints closely relates to its location. The numerical model of the joint after exposure to fire without load and with load was established, and the model was verified against experimental results. Through the numerical simulation, a method for calculating the residual mechanical behavior of stiffened welded hollow spherical joints after exposure to fire without load and with load was presented.

Finite element data-driven deep learning-based tensile failure analysis of precast bridge slab joint

The joint is a critical component that facilitates force transmission across precast bridge slabs while maintaining structural integrity. Finite Element Analysis (FEA) is commonly used to examine the mechanical properties and load-bearing capacity of joints with different configurations. However, the repetitive process of “modeling-meshing-computing” consumes substantial manpower, time, and expertise. This study proposes an approach consisting of three key steps: (1) predicting strain distributions, (2) determining failure modes, and (3) analyzing interpretability of predicted results. Specifically, DeepLabv3+ is used to map the Finite Element (FE) model to strain distributions. A binary classification model based on VGG-16 predicts the failure state of the specimen. Interpretability analysis, using Gradient-weighted Class Activation Mapping (Grad-CAM), provides insights into the neural network’s decision-making process. The optimized models achieve a Mean Intersection over Union (MIoU) of 0.5691 for strain distribution prediction on the cross-sectional surface and 0.6424 on the front surface. The failure detection model achieves an F1 score of 0.992 in determining failure states. The interpretability results align well with fracture mechanics theory, enhancing confidence in the model’s predictions. This method serves as a surrogate to reduce the workload of finite element analyses, facilitating strain analysis and failure detection.

Ductile Fracture Analysis of Welded Hollow Spherical Joints Subjecting Axial Forces with Micromechanical Fracture Models

Two micromechanical fracture models, void growth model (VGM) and stress modified critical strain (SMCS) model, were adopted to distinguish the failure mechanism of welded hollow spherical (WHS) joints under axial load based on FE analysis. Ductile fracture was successfully predicted for WHS joints under axial tension. The predicted fracture location is at the weld toe between WHS joints and circular hollow section members, which is consistent with corresponding test results. The predicted fracture load is lower than the peak load on the load–displacement curve, which indicates that the failure mechanism of WHS joints under axial tension is fracture due to inadequate strength and the fracture load should be taken as the ultimate load bearing capacity of the joints. A simplified SMCS model was proposed and verified for ductile fracture prediction of WHS joints under axial tension. Micromechanical fracture analysis was also conducted on WHS joints under axial compression. It was obtained by both VGM and SMCS model that no fracture would occur before the load reached its peak value, the reason of which was discussed by tracing the variation of the equivalent plastic stain and stress triaxiality at the potential location of fracture. Therefore, the failure mechanism of WHS joints under axial compression is losing stability with the depression of the sphere cap and the peak load on the load–displacement curve should be taken as the ultimate load bearing capacity of WHS joints.

A new physical simulation tool to predict the interface of dissimilar aluminum to steel welds performed by friction melt bonding

Optimization of the intermetallic layer thickness and the suppression of interfacial defects are key elements to improve the load bearing capacity of dissimilar joints. However, till date we do not have a systematic tool to investigate the dissimilar joints and the intermetallic properties produced by a welding condition. Friction Melt Bonding (FMB) is a recently developed technique for joining dissimilar metals that also does not exempt to these challenges. The FMB of DP980 and Al6061-T6 was investigated using a new physical simulation tool, based on Gleeble thermo-mechanical simulator, to understand the effect of individual parameter on the intermetallic formation. The proposed method demonstrates its capability in reproducing the intermetallic characteristics, including the thickness of intermetallic bonding layer, the morphology and texture of its constituents (Fe2Al5 and Fe4Al13), as well as their nanohardness and reduced modulus. The advantages of physical simulation tool can enable novel developing routes for the development of dissimilar metal joining processes and facilitate to reach the requiring load bearing capacity of the joints.

Effect of FRP parameters in strengthening the tubular joint for offshore structures

This paper presents the strengthening of tubular joint by wrapping Carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP). In this study, total number of layers, stacking sequence and length of wrapping are the different parameters involved when fiber reinforced polymers (FRP) composites are used for strengthening. For this, parameters where varied and results were compared with the reference joint. The best stacking sequence was identified which has the highest value in ultimate load with lesser deflections. For determining the best stacking sequence, numerical investigation was performed on CFRP composites; length of wrapping and number of layers were fixed. Later, the studies were focused on CFRP and GFRP strengthened joint by varying the total number of layers and length of wrapping. An attempt was done to propose a parametric equation from multiple regression analysis, which can be used for CFRP strengthened joints. Hashin failure criteria was used to check the failure of composites. Results revealed that FRP was having a greater influence in the load bearing capacity of joints, and in reducing the deflections and stresses of joint under axial compressive loads. It was also seen that, CFRP was far better than GFRP in reducing the stresses and deflection.

Tests of Joints in AAC Masonry Walls

Abstract The paper presents the results of the Authors’ tests on the joints in AAC masonry walls. The shape of the tested element and the test stand were fitted innovatively based on the Authors’ own experience as well as on the literature overview and numerical analysis. Cracking morphology and mode of failure were investigated. The relationship between the load and displacement for different types of joins was compared. The obtained results were also compared to the results obtained on the reference model, which was a model with a traditional masonry bond. In the remaining testing elements, the connection was realized with the use of steel connectors. Various mechanisms of cracking and failure have been observed as well as the behaviour and load-bearing capacity of joints were different. The obtained results encourage to further analyses focused on detailing the joints and application of new methods in the construction of the joints.

Effect of welding residual stresses on local behavior of rectangular hollow section joints/Einfluss der Schweißeigenspannungen auf die Tragfähigkeit von Rechteck-Hohlprofil-KnotenTeil 2: Parameterstudien

Welding residual stresses that occur in tubular joints after the welding process affect their structural behavior. To ensure that these stresses do not negatively act on the load-bearing capacity of joints, their influence should be carefully investigated. This paper represents the second part of a study that numerically evaluates the structural behavior of rectangular hollow section T joints taking into account welding residual stresses. The finite element model developed in Part 1 is now used to evaluate their effect on the resistance and initial stiffness of tubular joints. The conducted parametric analyses show that welding residual stresses have a positive influence of 1–19 % on the plastic resistance of tubular joints and insignificantly reduce their initial stiffness. At the same time, the behavior of the considered joints is found not to depend on the welding sequence.

全焊接组合梁–柱节点承载力试验研究

为了研究全焊接组合梁–柱节点的承载力，通过两个中跨全焊接组合梁–柱节点在单调静力作用下和低周往复荷载作用下的破坏试验，获得了节点承载性能、滞回性能和破坏模式。由试验结果可看出：节点主要的破坏模式为钢梁下翼缘及腹板局部屈曲和混凝土压溃。本文将介绍主要试验结果，为后续试验研究提供依据。 An experimental research on load bearing capacity of joints for composite beam to column was carried out. Two specimens were tested under monotonic static loading and cyclic loading, and the load bearing capacity, cyclic performance and failure mode were derived from the test results. It can be concluded that the major failure mode of the joints is the local buckling of the lower steel beam flange and the crush of the compressed concrete. The experimental results can provide some reference for the following research and experiments.

Experimental Evaluation of Joints using Thin Steel Angles for Wood Structures

The load-bearing capacity of joints using thin steel elements for wood buildings was considered. Six variants of a specific type of joint consisting of two wood elements in a ceiling structure joined by steel angles were experimentally tested. These variants differed in utilization of nails as well as screws (of various lengths) for wood. Another observed factor was the percentage of holes filled in the angles. In this work the percentage of holes filled means how many of the holes in the steel angles were filled by nails/screws. The evaluation characteristic was the maximum loading force at the breaking point. Based on the results, a set of recommendations for designing a specific type of joint with steel angles was formulated. The results showed that during loading of the joints, tensile stresses occur in the direction perpendicular to the fibers, which causes a failure of the wood parts of the joints.

Study of metal timber join by Acoustic Emission method

Actual behaviour and general load carrying capacity of timber structures depends primarily on the load bearing capacity of joints. The present paper deals with slotted-plate steel-to-timber joints. In addition, innovative measuring methods were used to determine the strength of the metal-wood-metal structure. One of them was the acoustic emission method, which belongs to the group of non-destructive testing methods. It is to be noted that the acoustic emission method responds to the defect generation much sooner than the visual or any other method. The time-frequency analysis can play a central role in the signal analysis.