Seismic Performance of Unreinforced Masonry Building with Flexible Floor Diaphragm

Abstract

Un-reinforced brick masonry has been the popular mode of the construction from centuries in Nepal. Past earthquake in Nepal had shown evidence of large damages in URM building. In the mid of the 19th century, during the Rana regime, the big palaces were constructed by un-reinforced brick masonry with timber floor. These building were constructed without seismic consideration and for the residence use only. Today, most of these buildings are used by the different Governmental and non-governmental offices in their daily use. Since, many of theses buildings are over 100 years and possess the heritage value. Preservation of these buildings from future earthquake is very essential for their future use and also preserve to coming generation. Before analyzing the actual buildings, a fictitious building having a simple plane of 6 m by 3 m is studied in detail, in order to reflect the characteristic of the unreinforced masonry (URM) structure. The finite element method is adopted for a number of parametric analyses to determine the response of the fictitious building in terms of displacement, like:(a) the effect of the wall thickness, (b) the effect of the floor rigidity (c) the effect of opening (d) the effect of number of stories and, (e) the effect of the lateral load distribution on different floor condition. The preliminary conclusions are used for the analysis of the real building, Shital Niwas, as a case study. Due to the complexity of modeling and analysis of the whole building, only the North wing of the building is taken for the study. The performance of the building is investigated in terms of the displacement response. It is found that the outer wall of the building is collapsed due to the excessive out-of-plane deformation. The loosely connected timber floor with masonry wall, long and unsupported URM wall, which extends throughout the height and length of the building, large sizes of the room which makes the cross wall further apart are main drawback of the existing form of the building. The conclusion obtained by the analysis of the North wing of the building can be generalized with the whole building configuration.