Narrow Results

The overturning resistance of structures base-isolated using laminated rubber bearings (LRBs) is crucial to the stability of the structure due to the poor tensile performance of LRBs. Pounding occurs between the structure and moat wall, which can result in a reduction of the overturning resistance of the structure. This study aims to investigate the overturning resistance of a structure base-isolated by LRBs considering pounding against the moat wall based on numerical simulations. The influence of the gap size, pounding stiffness, and the horizontal stiffness of the isolation storey on the overturning resistance of the isolated structure was evaluated through parameter studies. The results indicate that poundings between the structure and moat wall result in short but large pounding forces. Pounding forces would amplify acceleration, inter-storey drifts of the isolated structure, and significantly increase the risk of overturning of the isolated structure. Increasing the gap ratio can improve the seismic performance of the structure. Larger pounding stiffness leads to greater pounding forces generated by the structure, and the risk of overturning of the structure increases. The coefficient of overturning resistance initially decreases, and then increases, as the stiffness of the isolation storey increases.

Most current seismic codes recommend a minimum separation between adjacent structures to avoid pounding during severe earthquakes. Those recommendations are based on displacements of adjacent structures estimated using the equivalent static analysis. They usually overestimate the necessary separation between high-rise structures because the equivalent static analysis neglects the response phase difference of the adjacent structures. On the other hand, they might underestimate the necessary separation of low-rise structures because they neglect the inevitable ground motion spatial variations. This paper calculates the minimum required separation between adjacent structures subjected to spatially varying ground excitations. Adjacent structures are modelled as two single-degree-of-freedom (SDOF) oscillators with multiple supports. A linear and a trilinear stiffness degrading hysteretic model for reinforced concrete frame structures are used to represent the material behaviours of structures. Spatial ground motion input is stochastically simulated. The simulated spatial ground motion time histories are compatible with the Newmark and Hall design spectrum individually and with an empirical coherency function between each other. Numerical results are calculated and presented in terms of the various parameters that affect the structural response. Comparisons are made between the numerical results and the current seismic code recommendations. The primary objective of this paper is to study the effect of ground motion spatial variations on the relative displacements of adjacent structures rather than to present the advancement of analytical procedures.

Seismic induced pounding damage to bridge structures was repeatedly observed in many previous major earthquakes. To avoid this adverse effect, extensive research efforts have been made by many researchers. This paper presents a state-of-the-art review in this field. It includes a brief review of the numerical modeling of bridge structures and impact models, numerical simulation of pounding responses between different components of bridge structures, experimental investigations, and pounding mitigation methods.

In this paper, the seismic collapse probability of base-isolated reinforced concrete buildings considering pounding with a moat wall and financial loss estimation is studied. For this purpose, three-dimensional finite element models of a code-compliant 10-story base-isolated shear wall-frame (BI-SWF) building and a 10-story base-isolated moment resisting frame (BI-MRF) building are used. Results indicate that the BI-MRF building has a greater probability of collapse compared to that of the BI-SWF building, the probability of collapse in 50 years for the BI-MRF building is 1.3 times greater than that of the BI-SWF building for both no pounding and pounding cases. The probability of collapse increases when pounding is considered, which results in a smaller value of the collapse margin ratio compared to no pounding case for both the buildings. The financial losses resulting from damage to the BI-MRF and BI-SWF buildings under design earthquake (DE) and risk-targeted maximum considered earthquake (MCE_R) levels are calculated for the no pounding case, since there was no pounding under DE-level and very few instances of pounding under MCE_R-level. Calculation of financial losses due to damage to structural and nonstructural components, service equipment and downtime shows that the BI-SWF building results in larger repair costs and downtime cost compared to the BI-MRF building.

Pounding of adjacent buildings or parts of buildings due to earthquake shaking is often implicated as a significant source of damage. The majority of theoretical studies of pounding have focused on determination of the minimum separation required to prevent pounding. While this is useful for design of new structures, a great many existing structures are not sufficiently separated to preclude pounding. For these existing structures it is clearly useful to have a measure of the expected level of damage that may occur in future earthquakes. This paper attempts to assess the effects of pounding from measured earthquake records. The concept of Maximum Impact Velocity Spectrum (MIV) is introduced. The MIV records the envelope of the maximum impact velocity obtained during the earthquake for all separation distances as a function of the structure's natural period. Several measured earthquake records are considered and some surprising results are obtained.