Design of a dynamic and pseudo-dynamic testing facility

Student: Paola Ceresa
Supervisor: Dr. Alberto Pavese

Abstract

In this thesis the design of new testing facilities of the European Centre for Training and Research (EUCENTRE), Pavia, Italy, is developed. In particular, the design of the high performance uniaxial shaking table as well as the two reaction walls and the strong floor is described. As an introduction, an overview of the main existing dynamic and pseudo-dynamic testing facilities of Italy, Europe and USA is given. Moreover, the main dynamic and pseudo-dynamic testing techniques are briefly reviewed. The performance characteristics of the EUCENTRE facilities are also given, based on the definition of local needs and constraints that conditioned the final requirements.

The complete design of the shaking table is described, going through the many steps that lead to the final configuration. The shaking table project has been developed defining its structural and mechanical arrangement in order to have a stiff but quite light platform. The stiffness of the table and the bearings have to be very high in order to reach frequency responses out of the fundamental ones of the test structures. The design of the hydrostatic bearings that allow the one-degree-of-freedom motion of the shaking table is given, as result of in-depth investigation of deformations induced by loads on both bearings and sliding guides. The stiffness, number and locations of the hydrostatic bearings are derived from the results of several finite element non-linear analyses, performed with test specimens as (1:2) and (1:3) scaled bridge piers, as well as the combinations of the maximum design loads. The EUCENTRE platform is built within a concrete seismic block made of heavily reinforced concrete in order to have a very stiff reaction structure with frequency response above the operating range of the shaking table. The amount of mass is designed to be several times (more than 20) the specimen-table mass in order to reduce the forces, velocities and displacements to the surrounding soil and the adjoining structures. The soil conditions lead the reaction mass to rest directly on the supporting soil, without any isolation damping and isolation system.

The EUCENTRE pseudo-dynamic testing (PsD) facility is designed to test full-scale structure like bridge piers, multi-storey reinforced concrete and/or masonry buildings. Precast technology is chosen in order to avoid the deformations and the irregularities of the reaction surfaces due to possible concrete shrinkage. Post-tensioning cables as well as reinforcement bars are designed to absorb the tension forces due to the overturning moments during experimental tests. The material and construction technology are chosen in order to create a non-deformable testing apparatus. The dimensions, the geometrical characteristics of walls and floor, and the amount and location of post-tensioning cables have been calibrated with parametric analyses: bridge piers were considered as test specimens. The displacement and stress distributions due to the maximum applicable loads are evaluated.

The testing equipment made by the actuators for the shaking table and the PsD apparatus is presented underlying the design performances. The piping system, the oil flow, the pump and accumulator numbers are briefly described, as well as the dimensions and locations of the pipelines for outflow, return and drainage.

Finally, the interaction between the surrounding soil and the facility is studied, computing the vertical settlement due to the design static loads. A preliminary evaluation of the liquefaction potential and soil densification under cyclic loading is given, based on the study of the dynamic interaction due to the shaking table’s resultant motion transmitted to the soil.

This work has been, or is about to be, published as a ROSE Research Report, for which reason a copy of it is not available for download, but can rather be obtained from IUSS Press.