Cast Steel Joints Research Articles

Reliability-based capacity safety factor for G20Mn5 cast steel joints

Cast steel joints have complex geometries and great load-carrying capacity, and hence their resistances are commonly determined through FE simulations. Considering the significant variability in the material mechanical properties (that in fracture strains, in particular) and the model uncertainty inevitably involved in the FE analysis, a large safety factor (γR) should be adopted for the FE simulation-based design of cast steel joints. However, the γR-values specified by the current design specifications, e.g. the Chinese standard CECS 235: 2008 in which γR = 3.0, are deemed to be overly conservative. This paper examined the structural reliability of G20Mn5 cast steel joints to provide a rational γR-value for the practical joint design. The above-mentioned uncertainty of the material and geometric properties as well as the model uncertainty related to FE simulations are evaluated, and Monte Carlo simulations were conducted on nine representative joints to obtain the statistical characteristics of cast steel joints’ ultimate resistance, allowing for both failure modes of material fracture and instability caused by large-scale yielding. FORM was adopted to calculate the reliability index β for the assumed γR-values and different loading scenarios, and the recommended values for γR under target reliability indices are proposed. For snow load-dominant and wind load-dominant load combinations, the recommended γR corresponding to β = 4.2 are 2.29 and 2.16, respectively, and the recommended γR corresponding to β = 3.7 are 2.01 and 1.90, respectively.

Experimental investigation and simulation analysis of cast-steel joints under vertical pressure

The joint made of cast steel is frequently utilized within a treelike column structure to ensure a smooth transition. It is of great significance in ensuring the overall structural safety, but currently, the mechanical property and bearing capacity of this type of joint cannot be fully understood. This study investigates the load characteristics of three-forked cast steel joints through concrete experiments, finite element analysis, and regression method formula derivation, filling the gap in mechanical properties and calculation formulas of forked cast steel joints. Initially, a comprehensive model of the cast-steel joint, sourced from a practical engineering, underwent vertical load testing. Detailed scrutiny of stress distribution and vertical displacement of the tested joint was conducted based on the experimental outcomes. Subsequently, a finite element model of the tested joint was constructed using SolidWorks and subjected to analysis via ANSYS. The numerical findings were juxtaposed with experimental data and extrapolated to encompass other parametric scenarios. Ultimately, a regression analysis method was employed to derive a calculation formula for the load-carrying capacity of branch-bearing cast-steel joints. The regression analysis method can accurately obtain the load-bearing capacity calculation formula for tree-shaped joint models and can be extended to determine corresponding branch and main pipe dimensions, as well as the deviation angle between branches and the main pipe, under known load conditions. This improves design efficiency and accuracy. Comparative analysis reveals a substantial concurrence among experimental, finite element analysis, and formula-based predictive outcomes. The maximum error between experimental results and those obtained from finite element analysis is 9.02%. The maximum error between the results calculated using the load-bearing capacity formula derived from regression methods and those from finite element analysis is only 1.9%.

Monte Carlo simulation of grain growth in heat-affected zone during welding process of cast steel joint and optimization of welding process

Monte Carlo simulation of grain growth in heat-affected zone during welding process of cast steel joint and optimization of welding process

Research on the Seismic Performance-Based Design of Cast Steel Joints Based on the Capacity Spectrum Method

Research on the Seismic Performance-Based Design of Cast Steel Joints Based on the Capacity Spectrum Method

Research on the Design Method of Compressive Bearing Capacity of Y-Type Cast Steel Joints

Research on the Design Method of Compressive Bearing Capacity of Y-Type Cast Steel Joints

Study on failure modes and calculation method of the cast steel joint with branches in treelike structure

The treelike structure links members and transfers loads via its solitary cast steel joint with branches. Therefore, the joint’s bearing capacity significantly affects the treelike structure’s stability, security, and economics. This paper utilized experimental verification and numerical modeling to examine the mechanical behavior of cast-steel joints with branches in the treelike structure under various loading conditions. Then, researchers investigated the failure process and mechanism of joints, and the three most common failure modes were outlined. Furthermore, the researchers proposed the bearing capacity calculation formula based on the common failure modes. The results show that the three common failure modes of the cast-steel joints with branches under different loading conditions are the failure in the joint core area under the axial load, the failure in the main pipe compression side under eccentric load, and the failure in the compression side of the single branch pipe root when the single branch pipe is under the uneven load. The suggested empirical calculation method can serve as a reference point for similar engineering practices design.

Optimization and experimental research on treelike joints based on generative design and powder bed fusion

Optimization and intelligent construction are of particular interest and important to improve the traditional design and manufacturing methods of cast steel joints. The optimal design, intelligent construction, and experimental research of treelike joints are conducted is this study based on generative design and laser power bed fusion (L-PBF) technology. First, the principle of generative design is comprehensively discussed in accordance of the Audze space-filling criteria. This method is applied to the optimal design of the treelike cast steel joint for Jinming Campus Museum of Henan University. Second, static behaviors of the generative design joints are compared with those of other joints obtained via parametric design through ANSYS version 2022R1 (64-bit) software. Finally, instead of traditional casting, all joints are produced using the L-PBF technology, and the manufactured 316L stainless steel joints are subjected to experimental research and finite element analysis. Results showed the minimum mass, optimal static behaviors, and evenly distributed stress of the generative design joint, thereby indicating that the generative design can effectively optimize treelike cast steel joints. The failure mode of 316Lstainless steel joints obtained via the L-PBF technology is similar to that of traditional cast steel joints but with higher yield load and ultimate bearing capacity. Therefore, employing the generative design and L-PBF technology in the optimization and intelligent construction of cast steel joints is effective and feasible.

Seismic behavior of prefabricated steel multi-ribbed composite walls connected with cast steel joints

In order to research the failure mechanism and seismic behavior of prefabricated steel multi-ribbed composite wall (PSMCW) with cast steel joints, quasi-static tests were carried out on three PSMCW specimens and one prefabricated multi-ribbed composite wall (PMCW). Specimens under low cycle reciprocating load were contrastively analyzed on damage processes, failure patterns, hysteretic characteristics as well as shear, deformation and energy dissipation capacities and stiffness and strength degradation by changing their cast steel joints and aspect ratio. The results demonstrates that PSMCWs connected with cast steel joints showed a typical shear failure pattern and the cast steel joints (which had high reliability) had not been damaged. The shear and energy dissipation capacities and stiffness of PSMCW were improved compared with those of PMCW, but their deformation capacity remained largely consistent. Numerical simulation was conducted by ABAQUS software, and the numerical results were in good agreement with test data. On this basis, PSMCWs were further analyzed with different parameters. Finally, the calculation methods of shear strengths of PSMCWs were given.

Analyzing of bolted joints for connecting rectangular hollow sections in reticulated shells

ABSTRACT This paper investigates a novel joint method for connecting rectangular hollow section (RHS) members in reticulated shells. It is proposed to overcome the problem of connecting rectangular tubes using the traditional joint (cast steel joint) under dead and snow load. A case study is a structure in the eastern region of Turkey that was built on August 20, 2019. This museum-style structure is 40 meters long and 20 meters wide, with an oval shape. In the middle of the building, five tree-shaped columns were used. ANSYS is used to create a refined 3D solid model of the RHS joint. The moment-rotation results show that the proposed RHS joint (plate steel joint) for connecting rectangular hollow section members can be considered a semi-rigid connection and preferred due to its lower cost and weight. Moreover, the dissipated energy capacity has been raised by approximately 3.22 times when the plate steel type model has been used instead of the cast steel type. The stress ratios indicate that the connection stress in the Cast steel type model is lower than the stress in the Plate steel type model. As a result, the Cast steel type model is determined to be incredibly safe and more rigid than plate steel. Furthermore, since the resulting stress rates are lower than those of S355 steel, both models (cast and plate steel type models) can be used for connecting RHS.

Cyclic constitutive models for G20Mn5QT cast steel at low temperatures

Cyclic constitutive model for G20Mn5QT cast steel is essential to simulate the hysteretic behaviour of cast steel joints. In consideration of cast steel joints exposing to low temperature environments, understanding of the effect of the drop of temperature on the cyclic behaviour of the material is preferred. Cyclic loading tests were then conducted on 12 smooth round bar specimens for G20Mn5QT cast steel at 20 °C, −20 °C, −40 °C and −60 °C. Cyclic stress-strain curves were obtained and variations of the peak stress, flow stress and backstress during cyclic loadings were calculated. The cyclic hardening behaviour of G20Mn5QT cast steel was discussed for the four temperature levels. It was found that the isotropic strengthening capacity of G20Mn5QT cast steel decreases with the drop of temperature, while the kinematic hardening behaviour of the material is not sensitive to temperature variations. Parameters in the Voce-Chaboche model were calibrated and validated based on the results of these tests for G20Mn5QT cast steel at the four temperature levels. By specifying the range of values for some parameters, the accuracy of the Voce-Chaboche models was improved in the simulation of the cyclic loading tests.

Evaluation of welded cast steel joint fatigue data using structural stress methods

Understanding the weld-root-based fatigue failure of welded cast steel joints is critical, and the fatigue stress parameter corresponding to the S-N curve for the fatigue-derived design of welded cast steel joints still needs to be addressed. In this paper, we compared three widely used fatigue stress parameters, namely, the structural hot spot stress, the traction stress, and the 1-mm stress, for the analysis of different types of welded cast steel joints under various loading conditions. The results indicate that: (1) the structural hot spot stress calculated through linear extrapolation is close to the traction stress proposed by Dong (2001) but is easier to compute; (2) the 1-mm stress performs slightly better in correlating the fatigue data of different joint geometries and loading conditions, but its calculation requires more effort; and (3) finally, the equivalent hot spot stress parameter is proposed for fatigue design and data-based analysis of welded cast steel joints as it balances computational efficiency and data correction accuracy. Two S-N curves corresponding to the equivalent hot spot stress and the 1-mm stress are provided for the fatigue-based life evaluation of welded cast steel joints.

Application of Cast Steel Joint in large-Span Steel Structure

Cast steel node is a new type of structure joint developed with the application of large-span steel structure. The stress distribution is discussed of cast steel nodes under three-dimension load by FEM, in the space grid structure of a hangar. By the measurement, the stress on the surface of the cast steel node under the design load is obtained. Combined with the test on-the-spot and computation, the result proves FEM result.

A simplified approach to estimate the fatigue life of full-scale welded cast steel thin-walled tubular structures

Cast steel joints (CSJ) are widely used in complex tubular structures to connect different parts of structures. This paper presents a simplified approach for efficient fatigue life estimation of full-scale welded cast steel structures. The proposed approach is applied to analyze a set of fatigue data of a full-scale CSJ thin-walled tubular truss structure. The results indicate that the fatigue lives estimated based on the simplified approach compare well with the experimental data. It is also shown that the simplified approach is much more efficient than the classical three-dimensional finite element-based method.

Additive Manufacturing and Mechanical Performance of Trifurcated Steel Joints for Architecturally Exposed Steel Structures.

Additive Manufacturing (AM) technology has unique advantages in producing complex joints in architecturally exposed steel structures. This article focuses on the process of manufacturing and investigating the mechanical properties of a reduced scale model of a trifurcated joint using Selective Laser Melting (SLM) method and mechanical tests, respectively. The orthogonal test method was used to optimize the main AM process parameters. Then the trifurcated steel joint was printed using the optimal process parameters and treated by solid solution and aging treatment. To investigate the mechanical performance of the printed joint, an axial compression test and complimentary finite element analyses were carried out. Failure processes and failure mechanisms of the trifurcated steel joint were discussed in detail. The research results show that the preferred process parameters for printing 316L stainless steel powder are: scanning power 150 W, scanning speed 700 mm/s, and scanning pitch 0.09 mm. Using these AM parameters, trifurcated steel joints with good surface quality, geometrical accuracy and tensile strength are obtained after heat treatment. Our mechanical tests and Finite element analyses results indicate that the failure mechanism in the AM trifurcated joint are similar to those of cast steel joints. Based on these results, we conclude that the AM technology serves as a promising new way for the fabrication of joints with complex geometries.

Traction structural stress analysis of fatigue behaviors of girth butt weld within welded cast steel joints

Due to its good mechanical properties, aesthetic and structural advantages, welded cast steel joints are widely utilized in engineering applications. The fatigue failure mode of girth butt weld between the cast steel node and the connecting steel tubular member was not well characterized. In this paper, fatigue tests of typical types of welded cast steel joints with different welding details were conducted. Fatigue failure mode and nominal S–N curves obtained from these tests were compared with that of an additional type of welded joint obtained from the literature. Then the equivalent structural stress parameter was selected to analyze the fatigue performance of the welded cast steel joint. The following conclusions can be drawn: (1) The traction structural stress concentration factor is higher at the weld root than at the weld toe for all five types of welding details, so the crack initiates at the weld root, which is consistent with test results; (2) Different lab-testing setups have an effect on the fatigue life of welded cast steel joints, and the traction structural stress can capture this test condition effect efficiently; (3) All fatigue data of 5 different test conditions fall within the 99% confidence interval of the master S–N curve. Furthermore, the scatter band of fatigue data processed by the traction structural stress method, is smaller than that processed through the nominal stress method. This suggests that the traction structural stress method is more suitable for the fatigue design for welded cast steel joints.

Casting simulation of cast steel joint based on Pro-CAST

The casting process is usually divided into five steps of melting, molding, casting, heat treatment and testing. This paper focuses on the two stages of casting and quality inspection of a casting process for a cast steel joint in actual engineering. Studies have shown that the sharp change or improper arrangement of the sections of cast steel joints will make certain areas more likely to produce defects than other areas, and these areas are often complex stress locations when they are in service, which leads to “risk-on-risk”. So both structural design and process design should pay attention to these issues. The analysis results show that ultrasonic flaw detection can detect casting defects but cannot be quasi-deterministic. The setting of riser and cold iron plays a key role in casting quality. The design of riser has a great influence on the generation and distribution of casting defects.

Numerical Simulation Analysis of the Cast-Steel Joint in a Tree-Like Column Structure

The cast-steel joint is often used in a tree-like column structure to achieve smooth transition. Its performance is critical to ensure the whole structural safety. In this paper, the load bearing behavior of a cast-steel joint with three branches is investigated. First, a finite element model of the test joint was established by SolidWorks and analyzed by ANSYS considering the geometric and material nonlinearity. Then, the calculation formula for load-carrying capacity of the cast-steel joint with branches was deduced by the method of regression analysis, which is used for estimating the geometric parameters and load-carrying capacity at the stage of preliminary design of the cast-steel joint. Comparison analysis shows that there is a good agreement between the experimental result, the FEM result, and the prediction result from formula.

Application of Cast Steel Joint in Steel Structure Project of Big-Span Space

Cast steel node is a new type of structure joint developed with the application of large-span steel space structure. The stress distribution is discussed of cast steel nodes under three-dimension load by the use of FEM, in the space grid structure of maintenance hall. By the measurement, the stress on the surface of the cast steel node under design load is obtained. Combined with the test on-the-spot and computation, the result proves FEM result.

Bearing capacity of the cast-steel joint with branches under eccentric load

Bearing capacity of cast-steel joint with branches in a tree-like column structure is important when adopted, since failure of the joint will surely lead to the collapse of its whole superstructure. In this paper, by using the means of numerical simulation and experimental verification, mechanical behavior of three-branch cast-steel joints in the tree-like column structure under eccentric load was studied. A typical full-scale cast-steel joint with three branches was first tested under eccentric loads. Numerical analysis of the cast-steel joint with three branches under eccentric load was then carried out through ANSYS and SolidWorks. Failure mechanisms of this kind of joint were analyzed and the main failure mode was summarized. Finally, the formula for predicting load-carrying capacity of the cast-steel joint with branches under eccentric forces was proposed. The results showed that the failure mode of the joint under eccentric load is the buckling failure at the end of the compression side of the main pipe, and the formula based on the main failure mode is applicable in engineering and building designs.

Experimental investigation of the residual mechanical properties of cast steels after exposure to elevated temperature

Cast steel is extensively used in civil engineering, especially for complex joints in spatial steel structures. Provided that local or global structural collapse of structures that incorporate cast steel structural elements and joints does not occur during or immediately after a fire event, the post-heating residual behavior of the steel castings in steel structures must be accurately characterized to estimate the remaining structural capacity and resulting safety. An experimental investigation was undertaken to explore the post-heating residual mechanical properties of two widely used structural cast steels, namely G20Mn5N and G20Mn5QT. Tensile coupon tests were performed on specimens after exposure to one of 13 preselected maximum temperatures (up to 1000°C). Both air cooling and water cooling methods were considered, and residual mechanical properties, such as stress–strain curves, elastic modulus, yield strength, ultimate strength, and fracture strains were obtained for both types of cast steel. Additional tests were undertaken to investigate the effects of cyclic heating and cooling. The mechanical properties of both cast steels began to change after exposure to temperatures exceeding approximately 700°C. With increasing exposure temperatures, up to 1000°C, G20Mn5N showed maximum variations of approximately 28.6%, 14.8%, and 57% in yield strength, ultimate strength, and fracture strains, respectively; while the corresponding variations for G20Mn5QT were less severe at 16.8%, 7.6%, and 45%, respectively. The influence of different cooling methods was considerable, particularly when the exposure temperature exceeded 700–750°C, whereas the effects of cyclic heating and cooling appeared to be insignificant. Predictive empirical equations to evaluate the post-heating mechanical properties of the two cast steels studied herein are proposed for both air and water cooling.