Isolation system for precast concrete buildings (numerical modeling and structural response)

Student: Luca Marinini
Supervisors: Prof Roberto Nascimbene, Prof Paolo Riva

ABSTRACT

The recent development of Italian and European standards had a deep influence on precast structures design, with the introduction of dedicated chapters for static and seismic actions. The importance of connections is explicitly recognized, and the possibility of using energy dissipating connections is offered, with the support of experimental tests on representative specimens.

A new type of hysteretic isolator was designed, in order to meet the code requirement of reliability (mechanical connection) and in the same time to provide good dissipation properties and economic efficiency; isolators have to be positioned between columns and cap beams or between cap beam and roof beam (in this work only this second interaction is investigated) to isolate the superstructure, emulating a concept similar to bridge deck isolation. During the normal life of the structure, thermal deformations of the superstructure are allowed with low frictional resistance, while in case of earthquake, the higher displacement level activates the energy dissipation mechanism, which consists of two bronze elements (washers), prestressed by high resistance bolts, sliding on a steel plate. After the earthquake, the system can be retrofit by replacing the two bronze elements, without any business interruption for the building.

Since this is a new device, experimental investigations are required to characterize the behavior of the components and to verify the stability of the hysteretic loop of the assembly. For this scope, a frame test was designed and applied to a traction/compression machine installed in the laboratory of the Università  degli Studi di Bergamo.

An analytical study is performed with the Finite Element Program Midas Gen with two main targets: implement the experimental results in a simple numerical model suitable for performing non-linear analyses and compare the seismic response of precast structures designed according to EC8, with standard and hysteretic connections.

Finally, the Direct Displacement Based Design (DDBD) procedure is applied to the design of a representative precast structure, with standard and hysteretic connections, and the results are compared with those obtained with the Force Based Design (FBD) procedure.

You may download a digital version of this MSc dissertation here.