Keywords: masonry, mixed structure, infilled frame, finite element, strengthening.

Investigations show that about 80% of structures in Iran are masonry structures. In some of these structures, known as mixed structures, there are steel frames in the middle region. Evidence from past earthquakes has shown that these structures are more vulnerable than common masonry buildings, when an earthquake occurred [1,2,3,4].

Further investigations have shown that, their vulnerability results from the lack of required wall and different seismic behavior between steel frames and masonry walls. This would cause different seismic modes in buildings and would cause the collapse of the buildings [5,6,7]. Researchers have suggested various methods for rehabilitation of these structures. One of these is to use masonry infilled walls in existing steel frames [8].

The authors have conducted research on the effect of added masonry infill for existing steel frames in mixed structures under cycling loading [9]. In this investigation, we employed the finite element method considering the nonlinear behaviour of materials. Two methods of finite element modeling are common in the modelling of masonry walls: micro modelling and macro modelling. Although micro modelling is more accurate, it needs complex and intensive calculations. In order to make the research less time consuming and less expensive we used the macro modelling method. Studies have demonstrated that with appropriate assumptions for homogenizing materials, results would have an acceptable accuracy. In order to certificate the modeling, an experimental specimen investigated by Mosalam et al. [10], is modelled in a similar procedure. The results show a good agreement.

In this research, the behavior of steel frames under cyclic load was investigated. Then the effect of adding masonry infilled with different thicknesses and strengths was investigated. Results show that adding infilled walls increases the stiffness and energy damping capacity of the system. Then the effect of the opening and its location was investigated. Also, the effect of shotcrete performance and adding reinforcing steel mesh was studied and desirable behaviour was found. This paper introduces this investigation and its results.

1

A. Naderzadeh, "The Kobe, Japan Earthquake of 17 January, 1995 and Lessons for Iran", center for Earthquake studies of Tehran (CEST), 1995.

2

A.A. Moinfar, A. Naderzade, "An immediate and preliminary report on the Manjil-Iran Earthquake of 20 June 1990", BHRC, Tehran, Iran, July 1990.

3

H. Shekib, H. Baiat, "Behavior Evaluation of Structures of Ghaenat Earthquake Stricken Region", Natural Disaster Reduction, Tehran, Iran, 1997.

4

M. Foroughi, "A Report on Bam Earthquake", the University of Yazd, Yazd, Iran, 2003.

5

M. Wakabayashi, "design of earthquake - resistant building", 1986.

6

M. Foroughi, "Structural Investigation on Common Masonry Buildings", the University of Yazd, Yazd, Iran, 2004.

7

M. Foroughi, "Investigation on Mixed Constructions- named semi skeleton- in Iran", the International Congress of Civil Engineering, Tarbiat Modarres University, Tehran, Iran, 2006.

8

H. Azizi Bondarabadi, "Analysis of the seismic behavior of brick wall retrofitted with steel mesh and concrete overlay", Department of civil Engineering, Tarbiat Modarres University, Iran, 2007.

9

S.M. Aghaie Meybodi, "Investigation on Influence of use of Infilled Frame in Rehabilitation of Masonry Buildings with Centric Steel Frame", MSc thesis, directed by M. Foroughi, Dept. of Engineering, Yazd University, Iran, 2009.

10

K.M. Mosalam, R.N. White, P. Gergely, "Seismic evaluation of frames With infill walls using quasi-static experiments", Technical Report NCEER- 97-0019, National Center for Earthquake Engineering Research, State Univ. of N.Y. at Buffalo, 1997.

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