Seismic displacement-based designans assesment of bridges

Research focus

The Peer review has evaluated this group as Average

The focus of thise group is the definition and application of displacement-based approach for the seismic design and assessment of reinforced concrete bridges. In particular this research aims for applying and developing the Direct Displacement-Based Design (DDBD), proposed by Priestley and Calvi, in the case of multi-span R.C. bridge structures. The procedure is based on the Substitute Structure approach, proposed by Gulkan and Sozen, and allows to obtain the base shear from a given target displacement and the level of ductility: in this way a structure is designed to achieve, rather than be bounded by, a given performance limit state under a given seismic intensity. This methodology seems to be very promising, but it needs a deep investigation: the main challenges facing the extension of the DDBD approach to complex structural forms lie in the determination of the “substitute structure” characteristics, the determination of the design displacement, and distribution of the design base shear force throughout the structure. Moreover an extensive application to different types of bridges could be useful to evaluate its overall efficacy and to lay the foundation for a future generation of seismic codes. Indeed the final goal of this research is the definition of principles and rules to develop a model code for the design and assessment of R.C. bridges. One of the crucial point in this work is the validation of the DDBD procedure. It is accomplished comparing the expected behaviour with the effective structural response, obtained running inelastic time-history analyses (ITHA). Hence it is very important that the inelastic model be able to describe correctly the structural behaviour, in particular for what concern the damping capacity. A preliminary experimental study has been performed at the EUCentre laboratory (Pavia) to investigate whether the elastic damping, representing damping in the initial stages of response and specified as a percentage of critical damping, has to be related to the initial or tangent stiffness. Two identical SDOF hollow-section cantilever bridge piers were constructed. The first test was carried out under static cyclic displacement-controlled excitation and allowed to calibrate the numerical model. The second unit was tested on a shake table using an accelerogram based on the 1984 Morgan Hill record. This test was numerically reproduced considering the two damping models. The comparison between the experimental and numerical results provided compelling support for the use of tangentstiffness elastic damping.

Departments

Dipartimento di Ingegneria Strutturale (DIS)

Professors

Assistant Professors
Lorenza Petrini