Keywords: masonry, finite element, dynamic analysis, wood floors, concrete slabs, diaphragms.

Stone masonry buildings are particularly vulnerable under seismic loads. An important factor in the selection of the intervention method is the effect of the mechanical behavior of each intervention method under static and dynamic loads [1]. From the literature it is known that the construction of stiff in-plane roofs/floors play an important role in the horizontal load resistance, since the total lateral stiffness is dramatically decreased due to the diaphragm flexibility [2,3].

As restoration techniques, the construction of horizontal reinforced concrete beams at the floor levels, or the replacement of the old wooden floors with reinforced concrete slabs, are widely used. A detailed investigation on the influence of floor rigidity on the seismic behavior of stone-masonry buildings, were done by the finite element analysis of a simple two-story stone-masonry building. The models are based on the research of Tomazevic [4,5,6]. The North-South component of earthquake in Montenegro, 15/04/1979, from the recording at Petrovac was considered as the seismic load.

When horizontal reinforced concrete beams at the floor levels in parallel with the timber floor or concrete slabs, were considered, the plastic strains were reduced to the ground floor. Concrete slabs especially caused the development of higher strains, near the base and the openings. The horizontal diaphragm increased in comparison with the timber floor, something that relates to the reduction of maximum displacements and plastic strains to special areas, which are critical for structural safety.

The general result that the replacement of wooden floors with reinforced concrete slabs, leads to a significant influence on mass and stiffness of the structure is a notable parameter that must be taken into account when this restoration technique is selected, since additional reinforcement could be required within the masonry where overstressing develops after the restoration. Also the changes to the dynamic characteristics affect the dynamic behavior of the structure under different seismic loads.

1

B.P. Leftheris, M.E. Stavroulaki, A.C. Sapounaki, G.E. Stavroulakis, "Computational Mechanics for Heritage Structures", WIT press, Boston, 2006.

2

S-C. Kim, D.W. White, "Nonlinear analysis of a one-story low-rise masonry building with a flexible diaphragm subjected to seismic excitation", Engineering Structures 26, 2053-2067, 2004. doi:10.1016/j.engstruct.2004.06.008

3

D.F. Peralta, J.M. Bracci, M-B.D. Hueste, "Seismic Behavior of Wood Diaphragms in Pre-1950s Unreinforced Masonry Buildings", Journal of Structural Engineering, 13(12), 2040-2050, 2004. doi:10.1061/(ASCE)0733-9445(2004)130:12(2040)

4

M. Tomazevic, T. Velechovsky, "Some aspects of testing small-scale masonry building models on simple earthquake simulators", Earthquake Engineering and Structural Dynamics, 21, 945-963, 1992. doi:10.1002/eqe.4290211102

5

M. Tomazevic, M. Lutman, P. Weiss, "Seismic upgrading of old brick-masonry urban houses: Tying of walls with steel ties", Earthquake Spectra, 12, 599-622, 1996. doi:10.1193/1.1585898

6

M. Tomazevic, "Dynamic modeling of masonry buildings: storey mechanism model as a simple alternative", Earthquake Engineering and Structural Dynamics, 15, 731-749, 1987. doi:10.1002/eqe.4290150606

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