The high-strength bolted end plate connection is widely used in the construction industry with its green environmental protection and excellent seismic performance. The joints of the joints are semi-rigid, the force performance is extremely complicated, and the experimental research cost is relatively high, and the cycle is very long. Therefore, the establishment of an efficient numerical model is of great significance for evaluating the force performance of high-strength bolt end plates. In this paper, the influence of different material models on the rotation performance of the joint is studied by numerical simulation, and the bending moment-rotation curve is obtained. The numerical simulation and the experimental results are in good agreement, so as to provide a reference for the design and application of this kind of joint.
Steel structure beam-column high-strength bolt extension end plate connection is a typical semi-rigid connection. Under load, the rotation performance of the semi-rigid connection is an important mechanical performance, and the bending moment-angle curve is an important characterization of the rotation performance of the connection node, which is reasonable the material constitutive model can accurately describe the most realistic rotation performance of the beam-column node. Experimental research cannot reflect the changes in the internal force of the structure during the test, and often only the final phenomenon of the test can be seen. However, the finite element analysis can clearly reflect the force situation inside the structure at any time during the test.
Krishnamurthy first conducted finite element analysis on the end plate connection nodes, studied the end plate connection without stiffening ribs and two rows of four bolts in the tension zone, and proposed a design method [
The analysis found that the simplification of the material model will affect the accuracy of the simulation results, especially the nodal bending moment curve. At present, the European norm EC3 [
This paper compares the ideal elastoplastic, three-line and four-line material models through numerical simulation and analyzes that the four-line material model can simulate the bending moment curve at the node most accurately.
In order to verify the accuracy of the model, this paper selects the experimental model of Dr. Shi Gang from Tsinghua University. The beams and columns are all welded H-shaped steels. The beam cross-section dimensions are both 300 mm × 200 mm × 8 mm × 12 mm, and the column cross-section dimensions are both 300 mm × 250 mm × 8 mm × 12 mm. The column flange is locally thickened within 100 mm of the upper and lower extension edges of the end plate, and the thickness is the same as that of the end plate. The geometric model shown in
For each part of the test piece, solid45 elements are used. The contact between the end plate and the column flange and the contact between the nut and the column flange are considered to create a three-dimensional contact pair for simulation. The three-dimensional eight-node surface-surface contact element CONTA174 and the three-dimensional Simulation of the target unit TARGE170. The high-strength bolt generates a three-dimensional pre-tightening unit PRETS179 through the PSMESH command to apply pre-tension [
In this paper, all the grids of the beam-column model are divided into hexahedral grids by sweeping. In order to save calculation time, the size of the mesh refinement at the node domain is 4 * 4 * 4, and the rest of the grid is 4 * 10 * 12. The meshing of the end plates and bolts is shown in
Material parameters are obtained by static tensile test. The tensile test piece is a rectangular specimen, which is then processed into a material test piece according to the “Metal Tensile Test Specimen” (GB6397-86), and the loading is carried out in accordance with the “Metal Tensile Test Method” (GB228-87). The material properties of steel are measured, including yield strength f y , yield strain ε y , yield plateau strain ε ′ y , tensile strength f u , ultimate strain ε u and elastic modulus E are shown in
The steel used in this paper is all Q345 structural steel, and its stress-strain relationship takes into account the ideal elastoplastic model of the material. The three-line follow-up strengthening model and the four-line follow-up strengthening model are shown in
According to the product quality assurance data, the stress-strain relationship of high-strength bolts (including bolt heads, bolt rods and nuts) adopts a trilinear model [
| Specimen number | Specimen thickness | Yield Strength f y (MPa) | Yield strain ε y | modulus of elasticity E (MPa) | tensile strength f u (MPa) | Ultimate strain ε u |
|---|---|---|---|---|---|---|
| C8-1 | 8 | 376.5 | 0.00197 | 189,789 | 592.6 | 0.144 |
| C8-2 | 8 | 379.6 | 0.00194 | 190,243 | 586.4 | 0.137 |
| C8-3 | 8 | 388.2 | 0.00199 | 191,877 | 589.3 | 0.156 |
| C20-1 | 20 | 358.9 | 0.00177 | 201,898 | 559.5 | 0.099 |
| C20-2 | 20 | 365.8 | 0.00179 | 203,270 | 556.4 | 0.076 |
| C20-3 | 20 | 363.4 | 0.00179 | 202,425 | 557.1 | 0.085 |
| average value | - | 372.1 | 0.00188 | 196,583 | 573.5 | 0.11 |
| f y (MPa) | ε y | E (MPa) | ε ′ y | f u (MPa) | ε u | |
| Ideal elastoplastic model | 372.1 | 0.00188 | 196,583 | / | / | / |
| Three-line model | 372.1 | 0.00188 | 196,583 | / | 573.5 | 0.11 |
| Four linear model | 372.1 | 0.00188 | 196,583 | 0.13 | 573.5 | 0.11 |
| Stress (MPa) | 995 | 1160 | 1160 |
|---|---|---|---|
| Strain | 0.00483 | 0.136 | 0.15 |
All materials are isotropic, and the Poisson’s ratio is 0.3. The yield criterion adopts the von Mises yield criterion. After the material yields, the flow theory and the follow-up strengthening criterion are adopted. The anti-slip coefficient of the friction surface of the end plate is 0.44 [
The GUI is used to create contact pairs through the contact wizard. This article considers three contact pairs, respectively, the first pair of contacts are nut and column flange, the second pair of contacts are nut and end plate, and the third pair of contacts are end plate and column flange. According to the principle of selecting the contact surface and the target surface, in the first pair of contact, the column flange is set as the target surface, and the surface of the nut and the column flange is set as the contact surface; the second pair of contact middle end plate surface is set as the target surface, and the screw The contact surface between the cap and the end plate is set as the contact surface; the third pair of contact center column flange and the end plate contact surface is set as the target surface, and the end plate and the column flange contact surface are set as the contact surface.
The pre-tension of the high-strength bolt is applied in the generated three-dimensional pre-tension unit PRETS179 through the SLOAD command. The pre-tension takes the standard design value, that is, M24 takes 225 kN. The boundary condition of the test piece is considered as the fixed constraint of the left and right ends of the column. The analysis and calculation process is divided into three load steps: the first step is to load the bolt with pretension; the second step is to lock the displacement generated by the bolt pretension in the first step; The third step is to impose a forced displacement load on the beam end according to the test situation. The first and second steps adopt small deformation static analysis, and the third step adopts large deformation static analysis, that is, considering the second-order effect, automatic time steps are used in all three load steps [
It can be seen from
Through the comparison of
ideal elastoplastic model and the three-line material model are very different from the experimental curve, which is sufficient to explain the yield of the steel. The platform cannot be ignored when the material model is simplified.
From the perspective of the overall deformation of the nodes in
The simulation data in this paper is compared and analyzed with Shi Gang’s experiment from multiple angles, including four aspects: bending moment angle curve, bending moment shear angle curve, bending moment gap angle curve,
and loading force displacement curve to verify the four-line material model. The reliability of the finite element model is shown in Figures 11-14.
Through the above analysis, it can be seen that regardless of the initial rigidity, ultimate bending moment, or bending moment-angle curve of the semi-rigid connection of the overhanging end plate, the results obtained by ANSYS are in good agreement with the results obtained by the test, which is to further analyze the joint rotation capacity Impact provides a solid foundation and feasibility.
The prestress distribution of bolts after the completion of the first two loading steps of ANSYS simulation is shown in
contact part between the two rows of bolts on the left and the end plate during the load application process is subjected to compressive stress under the action of the bending deformation of the end plate. And the von mise stress on the inner side of the rod adjacent to this part is the largest.
This paper uses ANSYS finite element analysis software to simulate and analyze the beam-column joint test, and get the following conclusions:
1) The contact parts of the first and second rows of tension bolts and the end plate at the node domain are subjected to compressive stress under the action of bending and deformation of the end plate, and the inner side of the screw adjacent to this part bears the greatest stress.
2) Through the comparative analysis of the ideal elastoplastic material model, the three-line material model and the four-line material constitutive model, it can be obtained that the four-line material model can better simulate the rotation performance of the node, which is accurate for future finite element analysis. Sex provides a strong guarantee.
3) In the next step, the finite element model established in this paper can be used to perform a large number of finite element parameter analysis on end plate connection nodes of different structures to obtain an accurate and comprehensive understanding of its force characteristics, so as to establish a complete analysis model and design method.
The author declares no conflicts of interest regarding the publication of this paper.
Lang, X. (2021) Numerical Model Research on Rotational Performance of Beam-Column High-Strength Bolt Extension End-Plate Connection Node. Open Journal of Modelling and Simulation, 9, 231-245. https://doi.org/10.4236/ojmsi.2021.93015