Hollow Spherical Joints Research Articles

Failure Pressure of Welded Hollow Spherical Joints Containing Grooving Corrosion Defects and Wall Reduction

Failure Pressure of Welded Hollow Spherical Joints Containing Grooving Corrosion Defects and Wall Reduction

Probability distribution model of the bending capacity for WHSJ with multiple randomly pitting corrosion

Welded hollow spherical joints (WHSJs) are commonly used joints in reticulated shell structures. Corrosion that occurs on the surface of WHSJs can considerably reduce the bending capacity of WHSJs. Randomness, including random location and size, is the nature of corrosion. Random size is indicated by random planar size and random thickness. The corrosion of steel structures is always a multiple random problem. A series of nonlinear numerical analysis is conducted in this work to investigate the probabilistic distribution of bending capacity of WHSJs. The objectives of this work are to investigate the influence of corrosion parameters on bending capacity and construct a probabilistic distribution model of the bending capacity of WHSJs with multiple randomly pitting corrosion. The method to determine the probabilistic model of WHSJs in actual condition is also discussed. This work can serve as a basis for the stochastic analysis of integral structures connected by WHSJs with randomly located corrosion.

Mechanical performance of welded hollow spherical joints with H-beams after elevated temperatures

Welded hollow spherical joints with H-beam (H-WHSJ), as a new connection pattern in space lattice structures, have been applied in practical engineering. This study aims to investigate the residual mechanical properties of H-WHSJ after loading in elevated-temperature environments and provide an important basis to evaluate the performance of space lattice structures after the occurrence of fire. The effects of temperature history, plastic residual deformation, sizes of WHSJ and H-beam, type of steel, and stiffening rib arrangement on the residual mechanical performance of H-WHSJs after exposure to elevated temperatures are determined via axial compression test by using 28 specimens and finite element (FE) parametric study. The major conclusions are as follows. (1) The residual characteristics of H-WHSJ after elevated temperature are rarely affected by temperature history, but mainly determined by the residual deformation at elevated temperature when the temperature is lower than 700 °C. (2) Plastic residual deformation can considerably reduce the residual bearing capacity (Nu,p) of the loaded H-WHSJ. In particular, Nu,p decreases by approximately 20% when the residual deformation is 6% of the hollow sphere diameter. (3) The formula to calculate the residual bearing capacity of H-WHSJ after loading in elevated-temperature environments has been proposed, and its prediction are in good agreement with the test and FE results.

Influence of compression force on the probability distribution of moment capacity for WHSJs with randomly located corrosion

Welded hollow spherical joints (WHSJs) are commonly used in reticulated shell structures. Corrosion on the surfaces of WHSJs can drastically reduce their loading capacity. WHSJs in reticulated shell structures are constantly subjected to compression force and moment. Compression force may affect the probability distribution of the moment capacity of WHSJs with randomly distributed corrosion. A large number of stochastic FE analyses were conducted in this work to investigate the influence of compression force on the probabilistic distribution of the bending capacity of WHSJs. The objectives of this work were to investigate the influence of compression force on bending capacity and to construct a probabilistic distribution model of bending capacity that considers the influence of compression force. The proposed method was validated and determined to have high accuracy in predicting the probabilistic distribution of the bending capacity of WHSJs in a complex force state.

Axial compression properties of welded hollow spherical joints with H-beams under high temperature

Space frames are mostly steel structures whose material and mechanical properties are largely affected by the high temperature of fire such that the bearing capacity of the structure deteriorates. Welded hollow spherical joints, as the most widely used form of joints in space frames, are the key factors affecting structural stress. Thus, the resistance to fire of such joints must be further studied. In this paper, the mechanical properties of welded hollow spherical joints (abbreviated WHSJ) with H-beam under elevated temperature are investigated through experiment and finite element analysis. Axial compression tests at 300 °C, 500 °C, and 700 °C are used to analyze the failure modes of the joints under axial compression at high temperatures. The experiments obtained load–displacement curves, yield and ultimate bearing capacities, ductility, and initial axial stiffness. Furthermore, results are used to validate the finite element model. Through parametric analysis of temperature, steel grade, ribbed or non-ribbed, diameter, wall thickness, and H-beam section, the present study proposes formulas for designing joints with ultimate bearing capacity and initial axial stiffness to withstand high temperatures.

Ultimate bearing behavior of H-beam welded hollow spheres under eccentric compression

An H-beam welded hollow spherical joint is a new kind of spatial grid structure. In this study, the eccentric-loaded behavior of H-beam welded hollow spherical joints was studied, and the influential law of material strength, joint size, and stiffening rib on its mechanical properties was analyzed through experimental research and numerical simulation. Parametric analyses were conducted to study the eccentric-loaded behavior of H-beam welded hollow spherical joints subjected to pure bending or the combined action of axial force and bending moment using a finite element model verified through experiments. The calculation formula of the bending bearing capacity of the joints and the axial force-bending moment curve were also obtained. Finally, the design rule for eccentric compression was proposed and verified through test results.

Influence of Corrosion Location on Compression Capacity of WHSJs

AbstractThe welded hollow spherical joint (WHSJ) is one of the most commonly used joints in reticulated shell structures. Corrosion at the surface of WHSJs has significantly different influences on...

Residual behaviour of welded hollow spherical joints under corrosion and de-rusting

This paper presents an experimental study of welded hollow spherical joints (WHSJs) under corrosion and de-rusting conditions. First, two scanning tests (3D scanning and scanning electron microscopy (SEM)) and a weight loss test were conducted on the same batch of steel used to manufacture the joints to investigate the corrosion morphology and development of the WHSJs under the same corrosion conditions. Subsequently, axial compression and tensile tests on eight corroded WHSJ specimens without anticorrosive coating (including two reference specimens for comparison) were conducted, and the relevant mechanical properties, such as the failure mode, load-displacement relationship, initial stiffness, bearing capacity, and strain distribution were studied. The results showed that the corrosion morphology of the WHSJs consisted mainly of uniform corrosion with slight pitting corrosion; the corrosion depth exhibited a lognormal distribution, and the initial axial stiffness, yield load, and ultimate load of the WHSJs were influenced by the corrosion and different de-rusting methods. After 100 days of accelerated corrosion tests (equivalent to 20 years in the corrosive environment of Qingdao), the compressive ultimate load decreased by 8.433%, and the tensile ultimate load decreased by 7.235%. Finally, a practical corrosion evaluation method with the statistical distribution and corrosion damage kinetics was established and validated.

基于盲孔法的焊接空心球节点网架中无缝钢管表面残余应力的测试研究

基于盲孔法的焊接空心球节点网架中无缝钢管表面残余应力的测试研究

Compressive strength of corroded special-shaped welded hollow spherical joints based on numerical simulation

Special-shaped welded hollow spherical joints (WHSJ) are increasingly used in several important spatial grid structures. The corrosion of WHSJ is inevitable and can eventually threaten structural safety. There is no research or comparison on the compressive strength of corroded special-shaped WHSJ. Therefore, through the simulation and analysis of the corrosion depth, corrosion mode, corrosion size, joint size, and steel material, the compressive strength of three types of special-shaped WHSJ after corrosion was studied, and the corresponding evaluation method for compressive strength was established. Results indicated that the loss of wall thickness (Tc/T) and the ratio of grooving corrosion (2Wc/D) were the key factors affecting the compressive strength of the special-shaped WHSJ after corrosion. The effect of corrosion on the bearing capacity was related to the size ratio (d/D). WHSJ connected by the H-beam were most affected by corrosion; the failure mode was basically buckling failure, but punching failure might occur in the H-beam WHSJ. The results obtained could form the basis for the selection of the WHSJ shapes and the evaluation of the bearing capacity of the space grid structure with special-shaped WHSJ after corrosion.

Study on compressive bearing capacity and axial stiffness of welded hollow spherical joints with H-shaped steel member

To study the compressive bearing capacity and stiffness of welded hollow spherical joints with H-shaped steel member(WHS-HSM joints), axial compression test was conducted on eight specimens of WHS-HSM joints. By verifying the correctness of the numerical model, the parametric analyses were done considering the following factors, such as the welded hollow sphere diameter (D), the wall thickness of the welded hollow sphere (t), and the height (h) and width (b) of the H-shaped steel member(HSM). The calculation methods of the compressive capacity and axial stiffness of WHS-HSM were proposed. The results show that the failure mode of the joints under axial compressive load is the hollow sphere’s concave failure starting from the flange edge of H-beam. Under axial compressive load, the joints show good ductility. The bearing capacity and initial axial stiffness of the joints are positively related with the wall thickness of the welded hollow sphere (t), the section height(h) and width(b) of HSM, but are negatively correlated with the diameter(D) of the welded hollow sphere. The formulas for calculating the compressive bearing capacity and initial axial stiffness proposed in this paper have high accuracy.

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.

Post-fire axial compression properties of welded hollow spherical joints

Fire disaster-induced collapse rarely occurs for space grid structures because of their high redundancy and their fire protection design. Consequently, with reasonable evaluation and repair, most space grid structures after fire can still be used. The post-fire axial compression properties of welded hollow spherical joints, which have been commonly used in space grid structures, were studied through experimental and numerical analyses. Then, the influence of factors such as material mechanical properties, loading condition and plastic residual deformation on the post-fire mechanical properties were analyzed. A calculation formula was presented to evaluate the post-fire bearing capacity of welded hollow spherical joints.

Load capacity of corroded welded hollow spherical joints subjected to bending moment and axial force

Welded hollow spherical joints (WHSJs) have been extensively used in space lattice structures. Corrosion is inevitable in the service life of WHSJs, and it can significantly reduce their load capacity and seriously threaten their structural safety. A series of nonlinear numerical analyses was conducted to investigate the moment and axial force interaction for corroded WHSJs. The moment-rotation surface of corroded WHSJs subjected to axial force was derived. The influence of the location, size, and thickness of corrosion of WHSJs on their compressive capacity were revealed in this study. Two types of corroded shapes were investigated. Results indicate that the geometrical parameters exert a significant influence on the moment and axial force interaction. An analytical equation has been proposed to quantify the influence of axial force on the bending stiffness and moment capacity of corroded WHSJs.

Mechanical behavior of welded hollow spherical joints with diameter exceeding 1.0 m

The welded hollow spherical joint (WHSJ) with diameter greater than 1.0 m is commonly employed in long-span tubular transmission towers. It has a relatively higher ratio of diameter to thickness compared to traditional spherical joints, since the larger thickness leads to difficulties in fabricating a spherical joint with a diameter of more than 1.0 meter, and will also lead to deterioration of mechanical properties of materials. Therefore, longitudinal and transverse stiffeners are usually set inside to avoid local buckling and improve bearing capacity. In this study, experimental tests and finite element (FE) analyses of full-scale WHSJs with a diameter of 1400 mm under the multi-axial load are conducted. The results indicate that all specimens have similar failure modes, namely the indentation of the hollow sphere near the main tube, and the failure of the longitudinal stiffeners at the same position. In addition, the setup of longitudinal stiffeners would obviously improve the ultimate bearing capacity (UBC) of WHSJ. After the validity of the FE model is verified, the parametric study is carried out. The results indicate that the UBC of stiffened WHSJ can be approximated by the sum of the resistances of the corresponding unstiffened WHSJ and the stiffeners. Accordingly, design equations are proposed for stiffened WHSJs with diameter greater than 1.0 m. The results obtained by proposed equations are compared with that obtained by tests and FE analyses. They are basically in good agreement, which shows the validity of the equations.

Experimental Study on Constant-Amplitude Fatigue Performance of Weld Toe in Steel Tube of Welded Hollow Spherical Joints in Grid Structures

The grid structure with welded hollow spherical joints (WHSJs) is widely used in industrial buildings with suspended cranes. Cyclic loadings generated by the suspended cranes could result in the fatigue failure of WHSJs. However, a corresponding fatigue design method has not been established. This paper presents an experimental study on the fatigue performance of the weld toe in the steel tube of WHSJs under axial force. Stress distribution on the joint’s surface was obtained by the static load test. By using the MTS fatigue testing machine, a constant-amplitude fatigue test was performed on the full-scale joint specimens. Twenty effective test data were obtained and fitted to a fatigue S-N curve by the least squares method. The corresponding fatigue design method for allowable stress amplitude was established. The mechanism of fatigue failure at the joint was investigated through microscopic analysis using scanning electron microscopy. The results of this paper can be potentially used as a basis for revising specifications and to promote the practical application of grid structures with WHSJs.

Probability distribution of the compression capacity of welded hollow spherical joints with randomly located corrosion

Welded hollow spherical joints (WHSJs) are commonly used joints in reticulated shell structures. Corrosion that occurs on the surface of WHSJs can considerably reduce the compression capacity of WHSJs with randomly distributed corrosion. Randomly located corrosion is a typical corrosion type on steel structures. However, the influence of randomly located corrosion on the loading capacity of WHSJs has not yet been quantified. This work aims to construct a probabilistic distribution model of the compression capacity of WHSJs with randomly located corrosion and to establish the relationship between such model and the specified corrosion (including corroded thickness Tc, corrosion diameter Dc, and corrosion number n) and geometric parameters (including the thickness T and diameter D of the spherical body). The influences of the corrosion and geometric parameters on the random distribution of compression capacity were first analyzed. Then, the probabilistic distribution model of the compression capacity of WHSJs with randomly located corrosion was established. The analytical method presented in this study achieved high accuracy in predicting the probabilistic distribution model of compression capacity with specified Tc/T, n, and Dc.

Behavior of eccentrically loaded welded hollow spherical joints after elevated-temperature exposure

Welded hollow spherical joint is an extremely widely used connection pattern in space lattice structures. Understanding the behavior of the welded hollow spherical joint after elevated-temperature exposure is critical for the fire damage assessment of the entire space lattice structures. In this study, both experimental and numerical studies were conducted to reveal the mechanical behavior of eccentrically loaded welded hollow spherical joints subjected to eccentric loads after cooling from three elevated temperatures up to 1000°C, wherein two different methods were considered, namely, air and water cooling. Associate mechanical performance, such as load versus longitudinal displacement and load versus steel tube rotation responses, initial stiffness, load-bearing capacities, and strain development, were obtained and further analyzed. The results showed that the behavior of welded hollow spherical joints began to change when the exposure temperatures exceeded 600°C, with obvious reductions in both stiffness and strength. In addition, the influences of different cooling methods were significant. The joints cooled by water generally presented higher load-bearing capacities than those cooled by air. Furthermore, three-dimensional finite element analysis was conducted via ABAQUS software. After validating the finite element model against experimental results, parametric studies were performed and a practical formula was proposed to calculate the load-bearing capacity of welded hollow spherical joints subjected to eccentric load after elevated-temperature exposure.

Compressive Capacity of Corroded Welded Hollow Spherical Joints

AbstractWelded hollow spherical joints (WHSJs) are widely used in reticulated shell structures. WHSJs inevitably experience corrosion in their service life that significantly reduces their loading ...

Ultimate tensile and compressive performances of welded hollow spherical joints with H-beam

Welded hollow spherical joints with H-beam are a new type of spatial grid structural joints. Experiments and numerical simulation were conducted to investigate the axial tensile and axial compressive performances of the welded hollow spherical joints with H-beam. The influences of material strength, size of joint, and stiffening rib on the mechanical properties, were analyzed. The formulas were proposed to calculate the bearing capacity under axial tension and compression. The major conclusions are as follows: (1) Welded hollow spherical joints with H-beam developed strength fracture under axial tensile load, and hollow spheres developed buckling failure under axial compressive load. The failure mode was related to the strength of the material. (2) Proper arrangement of stiffening ribs can increase bearing capacity of welded hollow spherical joints with H-beam. The improvement coefficients were 1.1 under axial tension and 1.4 under axial compression. (3) The compression bearing capacity of welded hollow spherical joints with H-beam increased with the increase in height and flange width of H-beam, as well as wall thickness of the hollow spheres, but it decreased with the increase in diameter of hollow spheres. (4) The formula used to calculate tensile bearing capacity of welded hollow spherical joints with H-beam was proposed according to the punching shear model. (5) The design formula of compressive bearing capacity of welded hollow spherical joint with H-beam was obtained through the linear regression of abundant numerical simulation data.