Vol-7, Special Issue-Number4-June, 2016, pp615-621 http://www.bipublication.com
Research Article
Comparing Seismic Parameters of SSW and Concentrically Braced Steel
Frames (CBF) by ABAQUS Software
*Ali Banazadeh and Ahmad Maleki
Civil Engineering- Seism,
Islamic Azad University,
Maragheh Branch, Maragheh, Iran.
*alibanazadeh1362@yahoo.com.
ABSTRACT
Due to the need of retrofitting on most structures existing in earthquake-prone zones, the use of systems resistant against lateral loads with high capacity of energy absorption and high formability is necessary. In the present study, two samples of lateral loading systems including a SSW and Concentrically Braced Steel Frames (CBF) are compared and investigated. Both samples are modelled in ABAQUS software and compared with experimental results in order that the efficiency of numerical modeling can be investigated. The results of analysis indicated that while the weight of both systems are equal, the SSWhave higher final loading capacity and energy dissipation capacity than the Concentrically Braced Steel Frames (CBF). The use of the results of modeling, the stability of hysteretic curves and more uniform distribution of stress in peripheral elements are among other advantages of SSW compared to Concentrically Braced Steel Frames (CBF). By considering the experimental results of numerical micro-models, it can be concluded that the use of SSW can have better results in reducing the seismic response of structures.
Keywords: SSW, Concentrically Braced Steel Frames (CBF), energy absorption, formability, cyclic behavior.
1. INTRODUCTION
Regarding the fact that 90% of Iran Country is located on seismic belt, the necessity of using an appropriate structural system should be considered by engineers. There are different resistant structural systems among which flexural frames, bracers, and concrete and SSW can be referred to. With a brief review of damages imposed on structures in recent earthquakes, it can be identified that steel structures have better performance and are more economical than other structures due to formability of their materials as well as capability in energy absorption.
Therefore, regarding the mentioned issues, such a research is needed for investigating structural resistant systems for coping with lateral forces and seismic forces. To do so, the present study is to
investigate two structural resistant systems of CBF and SSW as well as the replacement of SSW with Concentrically Braced Steel Frames (CBF). Therefore, in the present research with modeling the behavior of the SSW using ABAQUS software andverification of it, the results obtained from the modeling middle-level and high-level steel structures are used. The results obtained form these studies reveals the possibility or impossibility of replacement of concentrically braced frames with SSW. Positivity of this method can help appropriate seismic behavior of structures and economical nature of projects. 2. Review of literature
Park in 2008 [1]in Korea. The results of experiments indicated that energy absorption of SSW is much higher than braced and flexural frames, and formability of SSW and flexural frames is equal, while tolerable shear force and stiffness of SSW is much higher than those of flexural frames. In addition, the results of experiments indicated that braced frames have much lower flexibility than SSW and their tolerable force is lower than SSW (figure 1).
Figure 1 changes of curves sheathing samples of SSW
and flexural braced frames [1]
Zahedi and Mahtab in 2008 [2], by retrofitting a ten-story structure with weak flexural frames with two methods, compared two lateral loading systems of SSW and X braces in such a way that with a series of try and error operations, the flexural frame was retrofitted by these two systems and according to rehabilitation codes and was controlled using nonlinear static method. Finally, comparing the degree of the shear absorbed by shear walls and braces, it was
observed that the share of the shear absorbed by the frame in the model resisted by the shear wall is more outstanding; therefore, the existing frame is optimally used (figure 2).
In addition, the amount of consumed steel in SSW is about 30% less than X braces. If plates with at least 3mm thickness are used, the amount of consumed steel is about 15% less than X braces. Moreover, in retrofitting with the SSW, the magnitude of operations degradation and improvement is less.
Figure 2 changes of rate of shear absorbed by frames and SSW (right)- rate of shear absorbed by frames and braces (left) [2]
In recent years, the Finite Element Method has been considered as a powerful instrument for analysing structures. In the present research, to confirm the Finite Element Method of SSW, sample 1 of the experimented SSW was modelled
by Mofid et al. [4] under cyclic loading. Details of features of beams, columns, stiffeners, and experimented steel plates are indicated in figure 3 and mechanical features of their materials are shown in table 1.
Figure 3 geometry and location of the SSW, unit in terms of mm [4] Table 1 features of used materials [4]
To compare the results and verify them, in figure 4, the stress contour on the model is deformed and in the final step and also in figure 5, the final state of the sample in the laboratory is shown. Regarding the figures, it is clear that deformation of steel plates in the numerical analysis has an acceptable experimentally similarity.
Data of the shear-deformation curve of the above figure is transmitted to the numerical analysis of the Excel software and compared with the sheath of the shear-deformation curve of the experimental sample as indicated in figure 6. As indicated in the figure, the basic shear-displacement obtained from the numerical analysis has relatively higher shear force and displacement than the experimental model. This is due to idealization of materials and interaction between connected components and also loading conditions. In numerical models, by cyclic loading, overlap of curves is acceptable and supplies the accuracy of numerical modelling.
Figure 5 comparing basic shear-displacement of experimental and numerical models
Therefore, regarding the accuracy of motioned stimulation, in the next section, the modelled SSW with trapezoidal corrugated plates, in same loading conditions and different loading conditions, was evaluated and the results obtained from different conditions were reported.
4. Investigation of the possibility replacing concentrically braced frames with SSW
Figure 7 comparing basic shear-displacement with sheathing curve of CBFs
Regarding figure 7, it is observed that the most optimal and resistant CBF is V-Braced CBF and the weakest one is K-Braced CBF. In addition, SSW and V-Braced CBF are modeled for reinforcing three-story frames with equal weight and under same seismic loading in ABAQUS software.
5. Comparing behaviors of modeled three-story frames with reinforcing the SSW and V-Braced CBF
In this section, SSW and V-Braced CBFs are used for reinforcing three-story frames with equal weight and are modeled under equal seismic loading in ABAQUS software. The results are in forms of hysteretic charts according to figure 8 in order that verification of displacement of CBFs with SSW in more stories can be investigated.
Figure 8: comparing 3-story hysteretic curve in two states of SSW and V-Braced CBF As figure 8 observed, the maximum force of SSW
or final resistance in SSW in three stories with 381 KN and V-Braced CBF equal as 274 KN.
Regarding the fact that the final resistance of SSW of a story is 21% higher than that of the V-Braced CBF, it is clear that the more the number of stories, the ratio of final resistance and energy dissipation by the SSW system are higher than CBF. Consequently, in case of using SSW in high buildings, the possibility of too displacement of floors and construction of plastic hinges is available and the use of the SSW system can result in lighter than s systems and economic nature of projects better than CBF.
6. CONCLUSION
1. Verification of numerical and experimental results indicated that ABAQUS software can model most behavioural features and modes of CBF and SWW in one story and multi-story frames under seismic loading.
2. With regard to modelling and analysing SWW and V-Braced CBF for reinforcing three-story frame with same weight and under same seismic loading in ABAQUS software it was clarified that the more the number of stories, the ratio of final resistance and energy dissipation by the SSW system are higher than CBF. Consequently, in case of using SSW in high buildings, the possibility of too displacement of floors and construction of plastic hinges is available and the use of the SSW system can result in lighter than structured systems and economic nature of projects better than CBF.
3. The results indicated that under the same conductions in SWW, like border frames, beam to column connections and thickness of plates, in both one and three-story models, firstly SWW surrenders and then beam to column connections surrender in such a way that the surrender point is diffused I the point of beam to column connections.
4. SWWs have more uniform distribution than CBFs on peripheral elements and prevent from the concentrating of stress at the place of bracings connection arrows.
5. Using the results of modelling, stability of hysteretic curves and more uniform distribution of stress in peripheral elements are among other advantages of SWWs compared to CBFs.
REFERENCES
1. Choi, I.N. and Park, H.G. (2008), “Ductility and Energy Dissipation Capacity of Shear – Dominated Steel Plate Walls”, Journal of Structural Engineering, ASCE, Vol. 134, No. 9.
2. Zahedi, M. and Mahtab, M. (2008). Reinforcing metal structures using SWWs. The third national conference on improvement and reinforcement of Iran. Tabriz. National Centre for Reinforcing Structures. University of Tabriz.
3. Irani, F. and Yamini, A. (2010). Comparing SWWs with flexural frame systems and X-Braced CBF in terms of supplying safety of structures during utilization. The second conference on immunization of structures. Tehran. Iran.
