Luís Guerreiro

Seismic Tests and Numerical Modeling of a Rolling-ball Isolation System

For the seismic isolation of light structures, the use of laminated rubber bearings is neither economical nor, for most cases, technically suited. For the isolation of this type of structure a new system, consisting of steel balls rolling on rubber tracks, has been developed at TARRC (Tun Abdul Razak Research Centre). This article presents the results of experimental tests carried out for the characterization of the behavior of this new device. A numerical model is also proposed that can be used to assess the seismic response of structures with this isolation system. Comparison of the predictions of the numerical model with the experimental data shows that the model is adequate to perform the correct assessment of the seismic response of isolated structures. The results of the experimental campaign of shaking-table tests, as well as the numerical simulations, show that there is an effective reduction of the acceleration levels induced in the isolated structures.

Shaking Table Tests of a Structure Equipped with Superelastic Dampers

The energy dissipation capacity of the NiTi alloy was evaluated as part of a series of shake table tests. A superelastic damper was developed to take advantage of the hysteretic energy dissipation associated with this type of shape memory alloy. Each device was tested at different intensity levels. A vertical steel cantilever with 600 kg mass on top was subjected to a series of ground motions with different spectral characteristics. The dampers were placed as part of a tie system, restraining the horizontal movement of the top mass. The devices showed stable hysteretic behavior allowing for energy dissipation.

Seismic Vulnerability Assessment of a RC Pedestrian Crossing

ABSTRACT The paper addresses the seismic vulnerability assessment of a multi-span footbridge, prone to span unseating due to shorter seat lengths. The structure is representative of a series of pedestrian crossings located in the Southern part of Portugal, a region with a relevant seismicity. A probabilistic approach allows considering the variability of the seismic action and uncertainties in the definition of the material properties and/or structural behavior. Based on incremental dynamic analyses and corresponding fragility curves, it is shown that, for code compliance design acceleration, there is a significant probability that the structure will only suffer minor damage.

Characterization of Timber Masonry Walls with Dynamic Tests

Most of the Lisbon 18th century timber-framed masonry “Pombalino” buildings currently need seismic rehabilitation due to: (i) natural degradation with aging; (ii) need for adaptation to new serviceability requirements, generally involving higher loads and consequent structural changes; (iii) former interventions with elimination or damage of structural elements, affecting seismic resistance and (iv) noncompliance with the present seismic codes. The research presented in this paper aimed at experimentally evaluating the seismic vulnerability of the “Pombalino” buildings and at proposing a strengthening technique to reduce it by reinforcing their timber framed “Frontal” walls. The experimental program was based on extensive dynamic testing on prototype representative of the current characteristic of “Frontal” walls. The results of the dynamic tests carried out in the LNEC 3D shaking table are presented regarding the two types of tests performed: (a) seismic tests, in which the seismic action was applied with increasing amplitude in the direction of the walls; (b) dynamic identification tests, aiming at evaluating the decrease of the mechanical properties of the models. A comparison of the performance of the non-strengthened and strengthened tested prototypes is also presented.