The Pushover Analysis of R.C frames Based on SAP2000 Jing Li 1, a, Xinghua Yu 2,b

Transcription

1 Advanced Materials Research Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland The Pushover Analysis of R.C frames Based on SAP2000 Jing Li 1, a, Xinghua Yu 2,b 1 No.1 Zhongshan North Road, Longhu Town, Xinzheng City, Henan Province, China 2 No.1 Zhongshan North Road, Longhu Town, Xinzheng City, Henan Province, China a zz_lijing@126.com, b yuxinghua9810@yahoo.com.cn Keywords: R.C frames; Pushover analysis; Pushover Abstract: The pushover analysis had been done for a R.C frame model, vertex displacement,base shear, appear order and development situation of plastic hinges of the model had been get in different steps of pushover analysis, The pictures of basal shear-vertex displacement and response spectrum displacement-accelerated speed had been studied. The analysis results show that,the R.C frame model correspond with the seismic design principle of stronger column weaker beam,and meet the seismic requirements of the first stage and the calculating resistance to collapse of the second stage. 1. The analysis method of Static elastic-plastic Pushover Pushover methods are widely applied to assess the performance, based on the existing structure and design of the structure at home and abroad in recent years. Static nonlinear he analysis of the structural analysis model distribution patterns along the structural height required for a gradual increase in the lateral force or lateral displacement under the action until the structural model of the control point of the process until the target displacement or structural overturning[1]. 1.1 The basic principles of Pushover analysis Pushover method is the one used to predict earthquakes caused by the force and deformation demand. The basic principle is: Impose some kind of distribution pattern (such as uniform loads, inverted triangular load) analog seismic level of the lateral force of the inertial force, and gradually monotonic increase in the structural analysis model, until the structure to achieve the desired state (as institutions, excessive displacement of the limit or to reach the target displacement), and then assess the performance of the structure. The deductive method can be used for seismic evaluation and strengthening of buildings, and seismic design and performance evaluation of the new structure. In essence, Pushover method is a static analysis method, which uses two-dimensional or three-dimensional model to replace the original structure, the lateral edge of the level of analog seismic inertia force imposed on the model in some way, and increase gradually and monotonously, if the component is to coming into being cracking or Yield, then modify its stiffness, until the structure to achieve the desired state (as a plastic bodies or reach the target displacement).in this analysis, to get the structure base shear and the entire process curve of with the top floor displacement. Although the lateral distribution of power is a kind of static load, but can be approximated to reflect the structure under the earthquake effect the dynamic response of a moment in the whole process of analysis. Relatively active for designers to grasp the structure of the lateral load, the plastic hinge location, the plastic hinge reaches its ultimate rotation capacity corresponding feature point displacement and base of the total shear, which can control the extent of structural damage. 1.2 The implementation steps of Pushover analysis[2] (1) Prepare to structure data including establishing structure model, the physical constants of component and restoring force model and so on. All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-04/03/16,19:57:34)

2 Advanced Materials Research Vols (2) Computing architecture of the internal forces in the vertical loads(superimposed with the internal forces in the horizontal force components under the force of a certain level of internal forces, to determine whether the component cracking or yield); (3) The centroid of each layer in the structure, the load is applied along a certain level of height distribution. The size of the horizontal force is applied according to the following principles: After the superposition of the horizontal forces generated by internal forces and step (2) the calculation of internal forces, so that one or a number of component cracking or yield; (4) Cracking or yield components, and modify its stiffness, and then apply a load to another or group of component cracking or yield; (5) Repeated (3)(4)step, until the structure of vertex displacement is large enough or the plastic hinge is more than enough to achieve the desired destruction of limit state. (6)Draw basis shear-top displacement curve, that is, to derive curves. 2. Reinforced concrete frame structure nonlinear static analysis 2.1 Reinforced concrete frame structure KJ-1 In this paper, the reinforced concrete frame prototype for one or two industrial plants, the size of the frame column grid is 6m 6m storey is 5.1m, design framework for the cross section and reinforcement, according to 9 degree earthquake intensity PKPM Software. And then using 1:3 scale model, designed, produced a framework of test specimen, No. KJ- 1, the test model and the reinforcement shown in Figure 1. Fig.1 Details of the KJ KJ-1 Pushover analysis of the implementation steps Sap2000 software Pushover Analysis of Frame Structure KJ-1.First Grave vertical load (load +0.5 live load) analysis, and then based on the result of this analysis, the derivation of horizontal load. During the derivation of horizontal load analysis, the second lateral load pattern is adopted by the Structure loading, that is, Inverted triangular load pattern. Also, according to the specifications that default PM3 hinge and PMM hinge are adopted respectively when defining the plastic hinges of beams and columns. 2.3 The nonlinear static analysis results for KJ-1 structure model (1)The structure of the base shear top displacement for KJ-1 Table 1list the KJ-1 structural model in different Pushover analysis steps corresponding vertex displacement, base shear and plastic hinge order and development. Figure2, Figure3 are the base shear by the pushover analysis-vertex lateral map and the response spectrum of displacement-acceleration diagram of KJ-1.

3 814 Advances in Industrial and Civil Engineering Tab.1 The analysis results of Pushover for KJ-1 steps Topdisplacement(mm) Base shear(kn) The formation and development of plastic hinge Beam appear plastic hinge on both ends The below of left column appears the plastic hinge The below of right column appears the plastic hinge, being form of agency All plastic hinge into immediate use phase The bottom hinge of the two columns to enter the safety life stage The below of left column reaching the ultimate bearing capacity The below of left column failure Fig.2 The picture of basal shear-vertex displacement Fig.3 The picture of response spectrum displacement-accelerated speed It can be seen from Table 1, when the Pushover carried out to the first step, Beam appear first plastic hinge on both ends, indicating to the elastic limit state, at this time corresponding to the base shear 18.28KN greater than the maximum lever of more than 9 degrees earthquake seismic force 10.7KN, and 7 degrees rare earthquake class Ⅱ site, two-group calculation of horizontal seismic forces 16.73KN description of the structure of the framework to fully meet the preliminary seismic design requirements. Table 1 and Figure 2 shows the Maximum base shear of the structure comes to 21.32KN, close to horizontal seismic force 24.1KN of 7 degrees (0.3g) severe earthquake calculated by two group of class III site, corresponding to the vertices of the maximum horizontal displacement increased to 19.6mm, less than the maximum plasticity displacement between floors limits [3] : [θp]h=1700/50=34mm, base shear lateral curve shows obvious turning point. When to achieve the maximum base shear, the response spectrum acceleration corresponded by figure 3 is 11.84m/ s 2, far more than the maximum acceleration 1.4 m/s 2 of 9 degrees frequent earthquake and design basic acceleration 4.0 m/s 2 of 9 degrees seismic fortification intensity. To sum up, the frame structure KJ-1 designed by the current seismic code meets frequent earthquake seismic requirements in the first stage and second stage anti-collapse of the checking and less than maximum plasticity displacement between floor limits. (2) The formation and development of plasticity of the KJ-1 model The plastic hinge formation and development in a different class Pushover analysis for KJ-1 model is as shown in Figure 4. Figure 4(a) is the plastic hinge state under the first level horizontal loading (Horizontal loading to right), it can be seen that Frame beams form plastic hinge first on both ends under the first level horizontal loading, according with the seismic design principles of the strong column weak bean ; corresponding to the horizontal displacement of 2.3mm. The first inconspicuous turning point is in KJ-1 Basel shear-vertex lateral figure of the figure 2. Add to the second load, the bottom of the left column appears plastic hinge (figure4 (b)). Add to the third load, the bottom of the right column appearing plastic hinge at the bottom of the right column (figure4 (c)), but the agency of

4 Advanced Materials Research Vols framework does not reach the ultimate bearing capacity, and a significant turning point appears in KJ-1 Basel shear -vertex lateral figure in figure 2. When add to the fourth load, all plastic hinges from the beams and columns get into immediate use session (figure 4 (d) the color of plastic hinge is blue). Add to the fifth load, the bottom hinges of the two columns (plastic hinge color is green) get into the life safety session firstly. Napping to the fifth step from the third step, basal shear increases less, and the vertex displacement increases greatly. When napping to the fifth step, the plastic hinge of the bottom of left column gets into the limit working state, plastic hinge color of yellow, framework to achieve maximum capacity(figure4(e)). Fig.4 The development of plastic hinge during the Pushover analysis of different levels The above analysis results show that for the framework structure KJ-1, the order of appearance of plastic hinge under the effects of earthquake is: beam and the bottom of column. Complying with the seismic design principles of strong column weak bean, but in the last the destruction of KJ-1 is in the plastic hinge in the bottom of left column. Of course, historical damage indicates that the reinforced concrete frame structure can not design to make the entire structure to form the desired beam hinge failure mechanism. However, the energy dissipation mechanism of the framework structure tends to reasonable and ideal by adjusting the design. 3. The conclusion (1) The results of The Pushover calculation show that the order of appearance of plastic hinge of KJ-1 under the effects of earthquake is: beam and the bottom of column. Complying with the seismic design principles of strong column weak bean. (2)The results of The Pushover calculation show that the frame structure KJ-1 designed by the current seismic code meets frequent earthquake seismic requirements in the first stage and second stage anti-collapse of the checking. (3)The results of The Pushover calculation show that the destruction of the frame structure KJ-1 is in the plastic hinge in the bottom of left column. The reinforced concrete frame structure does not form the desired beam hinge failure mechanism. References [1]Civil King Software Technology Ltd., China Institute of Building Standard Design and Research. The Chinese Version User Manual of SAP2000 [M]. 2006,China Communications Press, In Chinese. [2] Xinling Wang. Theoretical and Experimental Studies on New Chevron Bracing Compound Structures [D]. Doctoral Dissertation of Southeast University.2006, In Chinese. [3] GB Code for seismic design of buildings [S], In Chinese.

5 Advances in Industrial and Civil Engineering / The Pushover Analysis of R.C Frames Based on SAP /