Global structural analysis of central cores supported tall buildings compared with FEM
The focus of this article is to present an approximate method of calculation based on the equivalent column theory. This approximate method of calculation may be successfully applied in the case of tall buildings. Knowing the geometrical and stiffness characteristics of the structure, applying the equivalent column theory may determined: the displacements in both directions, the rotation of the structure, critical load, shear forces, bending moments for each resisting element and the torsional moment of the structure. The results obtained using the approximate calculation method will be compared with the results obtained using an exact calculation based on F.E.M.: Autodesk Robot Structural Analysis and ANSYS 12.1.
Role of inclination in the seismic vulnerability of bell towers: FE models and simplified approaches
The role played by inclination in both the load carrying capacity and seismic assessment of masonry bell towers is investigated through the results obtained from different analyses on three case studies. The Italian Code for the built heritage is not explicit about the influence of inclination on the seismic assessment of towers, leaving to practitioners the task to properly consider it, potentially leading to both an overestimation of the capacity and an underestimation of the horizontal actions. The case studies investigated in this paper are three leaning masonry bell towers, all exhibiting a quite meaningful inclination and all located in Emilia-Romagna region (Italy), recently (2012) stricken by a moderate/high intensity seismic sequence. This study compares the procedure provided by the Italian Code with the finite element (FE) results obtained through non-linear static analyses and proposes a modification of the Italian code simplified mechanical model (SMM), which explicitly accounts for the actual inclination of the towers within a cantilever beam approach. The FE results show that inclination may considerably reduce the load carrying capacity, increasing the seismic vulnerability of the structures. The SMM approach proposed properly takes into account the role played by inclination, always providing results on the safe side with respect to FEM.
Torsional vibration and stability of wind-excited tall buildings with eccentricity
Abstract This paper describes an experimental investigation in wind tunnel of torsional vibration and stability of a tall square cross-section building with eccentricity between building elastic and geometric centres. 1:400 scale wind models of natural wind flow over open country and city centre terrains were deve3oped in the wind tunnel. The eccentric building model was tested by using an aeroelastic test rig designed for pure torsional vibration. The probability distribution of torsional peak response, aerodynamic damping and excitation spectrum were examined to determine torsional excitation and response characteristics. It was found that with a 10% geometric eccentricity ratio the tall square building was susceptible to torsional vibration. There was also a significant increase in the maximum mean response. For the open country terrain unstable torsional vibration due to vortex shedding was observed in which lock-in type large amplitude twist angular displacement occurred. Increase in turbulence associated with the city terrain, however, effectively mitigated torsional lock-in excitation.