Seismic vulnerability assessment of reinforced concrete buildings built according to the mandatory rules of thumb of Nepal National Building Code NBC205:1994

Abstract

It is not practical to enforce professional design for all small buildings constructed all over Nepal. Therefore, Mandatory Rules of Thumb (MRT) are provided in the Nepal Building Code (NBC) for reinforced concrete buildings not exceeding simple criteria regarding height, configuration, number of storey and floor area. Given the high seismicity of Nepal the main focus of this thesis is to carry out seismic vulnerability assessment of simple buildings erected according to the MRT. A representative sample building model was designed according to MRT NBC205 (1994) and analysed using nonlinear methods of analysis with and without infill walls. Pushover analyses are carried out according to Eurocode 8 for identifying the main structural behaviour of the considered frames, and Incremental nonlinear dynamic analyses are carried out to determine the seismic safety of the buildings. Fragility curves are therefore derived for the bare frame, and for two infilled frames, the one with and the other without infills at the ground level (partial infill frame). The fragility curves have been established for three limit state; Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevension (CP) limit states with respect to 1st mode period spectral acceleration Sa(T1). Moreover, the mean collapse capacity has also been calculated for all those three models. It has been observed that the structural performance of both the bare frame and partially infill frame is significantly affected by P-delta effects, whereas these are basically negligible in case of uniformly infill frame. The obtained fragility curves allows to assess the probability of exceeding the above limit states for each of the building constructed according to MRT NBC205 (1994), providing several damage scenarios depending on the expected seismic intensity. On the basis of the obtained outcomes, an upgrade of MRT NBC205:1994 is given in order to guarantee greater strength and capacity. In detail, a larger column section is proposed for the considered building models.