Document Type : Research Note
Authors
1
Dept. of Civil Engineering Kharazmi University
2
Dept. of Civil Engineering University of Science and Culture
Abstract
Tunnel form construction is a new method in industrialized construction that could be broadly used in mass construction projects, thereby decreasing construction time and having appropriate performance against lateral forces. Reduction of material consumption and, therefore, decrease in expense, are the advantages of this method. This leads structural designers to choose tunnel form systems because of limited natural and financial resources in their countries. Nevertheless, lack of sufficient guidelines and codes for structural design and construction are among the defects of tunnel form concrete buildings. Moreover, the modular shape of this system creates some restrictions in architectural design. Tunnel form concrete structures are not often mentioned and discussed in present codes, especially Iranian codes. Thus, the seismic behavior of this structural system, designed and constructed with present codes, is the main query of this study.In this study, eighteen tunnel form concrete structures, as representatives of low- to medium-rise structures (6 different plans with 6, 9 \& 12 stories), were structurally analyzed and designed. Section properties, such as thickness, reinforcement ratio and boundary element length of shear walls, were calculated, and essential parameters of the seismic behavior of structures, such as ductility, overstrength, base shear ratio, roof drift and response modification factor, have been derived.It was determined that the first mode shape of tunnel form structures has a high probability of being torsion. In low rise structures, the codes minimum design requirements, compared to calculative design needs, are dominant in the structural design of shear wall sections and the overstrength factor is relatively high. Thus, the tunnel form system is not economically justifiable for low-rise buildings. The failure mode in tunnel form structures could be failure in steel or concrete. In cases where the length in one direction in the plan is high, the failure is more probably in concrete. In low-rise structures, energy absorption is realized by verstrength, but in high-rise structures, it is realized by ductility. Increase in the number of parallel shear walls has no effect on the strength and base shear ratio of tunnel form structures.
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