Effects of beam configuration on dynamic properties and seismic performances of multi-storey frame building models

The present study aims at comparing the dynamic properties and seismic performances offered by reinforced concrete frame structures characterised by different beams distribution. Multi-storey regular frame buildings are considered as reference structures. Different models are then developed according to various layout of the beams (x-direction is the longitudinal direction, whilst y-direction is the transversal one): (1) beams placed along the x-direction at the odd storeys and placed along the y-direction at the even storeys; (2) beams placed along the y-direction at the odd storeys and placed along the x-direction at the even storeys; (3) and (4) alternating beams every two storeys; (5) beams placed along the x-direction at all storeys; (6) beams placed along the y-direction at all storeys; (7) complete three-dimensional frame with beams placed along both the x- and the y-direction at all storeys. In all models, smaller perimeter beams are placed along the direction orthogonal to the one of the main beams. Modal analysis has been conducted to evaluate the influence of beams distribution on the period of vibration. Response spectrum and time-history dynamic analyses have been carried out to assess the effects of beams distribution on the base shear and base bending moments, top-storey displacements, interstorey displacements and floor accelerations. On the contrary of what could be expected, the results indicate that structures with beams alternating every storey do not behave unfavorably with respect to the complete three-dimensional frames. In more detail, two effects may be clearly recognized: one associated to the period and one associated to the static scheme. The former acting basically on the base shear; the latter acting mainly on the base bending moment. The understanding of the influence of beams distribution on frame structures is useful when dealing with seismic vulnerability assessment of existing buildings and design of new buildings.