EXPERIMENTAL AND NUMERICAL SEISMIC RESPONSE OF MULTI-STOREY POST-TENSIONED TIMBER FRAMED BUILDINGS WITH SUPPLEMENTAL DAMPING SYSTEMS

This doctoral project aims to contribute to advancement of the research in the field of innovative and resilient timber buildings with high seismic performance and minimum environmental impact in a green and sustainable way. Recent seismic events have raised questions about the adequacy of the current seismic design in code provisions. In modern seismic codes, the performance objectives are expressed in terms of life safety of the occupants and according to capacity design rules a certain damage level of structures is accepted under strong earthquakes. The resultant seismic damages are often difficult and financially prohibitive to repair. In order to significantly reduce structural and non-structural damage and avoid high economic loss, in the last decades research studies focused on the development of low damage design and technologies. In this thesis, seismic design and performance of multi-storey post-tensioned timber framed buildings with different dissipative systems have been investigated in order to develop new low-damage construction systems for high seismic areas. An extensive experimental campaign was performed at the structural laboratory of the University of Basilicata (Italy), in collaboration with the University of Canterbury (New Zealand), considering a three-dimensional, two-third scale, three-storey, post-tensioned glulam timber frame building. Different testing configurations were considered: i) the bare timber frame with post-tensioning only at the beam-column connections (free rocking); ii) the post-tensioned timber frame with dissipative devices at the beam-column and column-foundation connections (dissipative rocking); and iii) the post-tensioned timber frame with dissipative bracing systems at all storey (dissipative bracing). The seismic response of test specimen was investigated through unidirectional shaking table tests under consecutive ground motions at increasing PGA intensities, while the cyclic behaviour of hysteretic dampers was characterized by means of quasi-static tests. In particular, the testing configuration with dissipative bracing, which had not been previously implemented in post-tensioned glulam timber structures, has been deeply investigated in this research. The estimation of equivalent viscous damping has been proposed in order to optimize the displacement-based design procedure for sizing the hysteretic dissipative devices of the bracing systems. The experimental seismic response of the braced model is evaluated in terms of global and local behaviour and nonlinear numerical analysis have been carried out within two different FEM software (Sap 2000 and OpenSees). The comparison of the results obtained from all configurations demonstrated that the dissipative bracing system improved the seismic performance of post-tensioned timber buildings reducing inter-storey drift with full re-centring capability. During all seismic tests no damages were observed to structural elements, only localized breakage of external replaceable devices occurred during the test with strongest earthquake. More than one hundred inelastic cycles were experimentally recorded from dynamic tests before the failure of devices. The reliability of quasi-static testing procedures proposed by current seismic and guidelines codes for type tests and factory production control tests was also investigated. The number of cycles estimated from shaking table tests and non-linear dynamic analyses shows a decreasing trend with the increase of ductility demand in line with American standards testing requirements.