Evaluation method for seismic resistance of thin-walled steel structures Gao Qiongxian, Wang Haiying (Kunming University of Science and Technology, Kunming, Yunnan, Kunming, Yunnan, push over analysis) and failure criteria based on ductility formula of short column, a simple and practical evaluation method is proposed.
0 Introduction Under the action of rare earthquakes, the seismic structure will enter the elastoplastic state. In order to meet the seismic requirements of the structure under the action of large earthquakes, it is necessary to study the elastoplastic deformation of the structure. Therefore, structural elastoplastic analysis has become one of the seismic design important part. At present, structural elastoplastic analysis mainly includes dynamic elastoplastic analysis and static elastoplastic analysis. Dynamic elastoplastic analysis is the most reliable method for elastoplastic time history analysis. However, this method is complicated in technology, large in calculation workload, and cumbersome in result processing, and the response of the same structure obtained by selecting different seismic waves is very different. Therefore, its application in practical engineering is limited. Relatively speaking, static elastoplastic analysis (push over analysis) is a simplified method for calculating nonlinear seismic response of structures. It has strong practicability and has been widely used at home and abroad in recent years.
In recent years, the thin-walled steel structure has achieved rapid development. However, the damage of steel structures in previous earthquakes shows that under strong earthquakes, such steel structures are prone to damage due to local or global compression and buckling. Therefore, the evaluation of the seismic resistance of thin-walled steel structures under earthquake action has become a Issues to be solved urgently. Research in this area in China is almost blank. It is very difficult to consider this buckling in practical applications, because reliability and simplicity must be considered at the same time. A large number of experiments and numerical analysis show that the critical local buckling of thin-walled steel structures mainly occurs in the flange part of the member in the effective failure range, and the maximum seismic resistance of the structure is determined by the bearing capacity of this part. By determining the effective failure range, a simplified method for evaluating the seismic resistance of thin-walled steel structures is proposed by applying the formula of short column ductility that can simulate local buckling characteristics.
1 Method overview The specific steps of this method are: 1) According to the layout and load of the structure, establish an analysis model (as shown in Figure 1). If it is a multi-degree-of-freedom system, the seismic response is mainly controlled by the first mode The multi-degree-of-freedom system is equivalent to a single-degree-of-freedom system.
In the Journal of Kunming University of Science and Technology (Science and Technology Edition), b is the width of the box-shaped cross section, h is the height of the box-shaped cross section, A is the cross-sectional area, M is the plastic moment of the cross-section to the Z axis.
2 Criteria for failure When the average compressive strain E of the box-shaped compression flange is equal to the compressive strain E at failure, the structure reaches the limit state. In the literature, the performance of box-section short columns with vertical stiffeners under compression and bending has been extensively studied, and an empirical formula for failure strain has been obtained: where P is the axial force and P is the yield Is the axial pressure R the width-to-thickness ratio of the flange?
The aspect ratio of the stiffener.
In the literature, the standard empirical formula for failure expressed in terms of top displacement is given based on experimental analysis: where the peak displacement of the corresponding structure when the load after yielding is 95 peak load is taken.
In the frame structure, there are more than one part that reaches the critical flexion state (see Figure 1), and every part should be checked. In thin-walled steel structures, excessive deformation occurs locally, which may cause unexpected stress redistribution. Therefore, when performing static elastoplastic analysis, the periodical and horizontal loads on the structure after plastic hinges should be applied Calculate and control carefully.
3 Case analysis To prove the practicability and rationality of this evaluation method, this paper uses a single-layer rigid frame (shown in Figure 1) for example analysis and comparison with experimental data of the same frame structure under repeated cyclic loading.
The structure of this example is a single-layer frame. The cross-sections of beams and columns are box-shaped with stiffeners and have the same size. Times. The geometric dimensions are: layer height 5 m, span 4 m, b = h = 500 mm, t = 0.276. When performing static elasto-plastic analysis, the horizontal load on the top of the structure is calculated according to the seismic response spectrum and loaded step by step Loop analysis until destruction. The experiment is a periodic repeated loading test, and the vertical application of a constant load P = 0.1 Py. The mechanical properties of the materials used are shown in Table 1.
In this analysis, the mechanical properties of the material are taken into account, due to local compression and buckling, cracks in the column foot, and fatigue of the column with a small slenderness ratio due to fatigue caused by cyclic loading. The maximum strength after the peak is 90 The displacement is used as the basis for evaluating ductility.
During the test, the buckling first appeared on the flange at the column foot when the maximum horizontal load was approached. First, there was only local buckling on the flange plate between the stiffeners, and then there was compression on the entire flange plate. Flex. The buckling of the column and the buckling of the beam are not simultaneous.
The structure comparison between the static elastoplastic analysis and the periodic loading test is shown in Figure 4. The dotted line is the periodic loading test curve, and the thick dashed line is the outer envelope line. The thick solid line is the static elastoplastic analysis result. Among them, point a is the point where the buckling of the column foot flange begins to appear during static elastoplastic analysis. Point b is the maximum load point of the periodic load test. Point c is the failure reference point y used in static elastoplastic analysis. The static elastoplastic analysis method of steel structure considering local compression and buckling is very close to the test results.
4 Conclusion At present, the elastoplastic analysis of the structure has become an important part of the seismic design of the structure. Due to the complexity of the elastoplastic dynamic method, its practical application is limited. Static elastoplastic analysis (push over analysis) as a simplified method for evaluating the seismic resistance of structures is feasible at this stage. Under the strong earthquake action, the steel structure is easy to be damaged due to local or overall compression and buckling. This damage mainly occurs in the flange part, and determines the bearing capacity and ductility of the steel structure. For the convenience and practicability of practical application, local buckling is not easy to consider in the static elastoplastic analysis. Therefore, based on the failure standard empirical formula of the steel structure short column, the local buckling is all consider. Computational analysis and experiments show that this method is reasonable and effective.
Ye Liaoyuan, Pan Wen. Principle and calculation example of static elastoplastic analysis (push over) of structure [J]. Journal of Building Structures, 2000, (1) Yang Pu, Li Yingmin, Wang Yayong, etc. Improvement of static elastoplastic analysis (push over) method of structure [J]. Journal of Building Structures, 2000, Gao Qiongxian, Wang Haiying: Evaluation method of seismic resistance of thin-walled steel structures
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