Seismic isolation is considered an effective solution to protect buildings and reduce seismic losses. However, the reliability level achieved by code-conforming base-isolated structures can be not uniform due to different design choices allowed by the codes. Moreover, the seismic response of such structures is affected by the variability of dynamic properties of isolation bearings due to behavioural or environmental effects. For elastomeric bearings made by High Damping Rubber (HDR), the main behavioural effect is the dependence of the shear response on the strain amplitude, the strain rate, but also on the previous strain history (known as repeated cycling or Mullins or scragging effect). The shear response of elastomeric bearings is also influenced by environmental conditions, such as temperature and long-term environmental actions (ageing). Currently, some of the behavioural effects are included in advanced numerical models, however, current seismic codes allow to use a simplified approach based on less accurate models in conjunction with property modification factors (called λ-factors in the European context) defined for both behavioural and environmental effects. These factors, although quite used are based on old and limited data, especially for HDR bearings. For this reason, in the first part of the paper a statistical analysis of a large set of material tests carried out according to EN 15129 is illustrated. Experimental data include low and high damping rubber compounds currently used for elastomeric bearings with shear modulus ranging from 0.4MPa to 1.3MPa. The response variability in terms of equivalent linear properties is analysed for each behavioural effect and environmental condition. Based on the experimental results, new λ−factors for stiffness and damping are proposed and compared with those suggested by the code prescriptions. In the last part of the paper some preliminary considerations are made on the influence of such variability on the reliability of base-isolation structures.
EFFECT OF THE VARIABILITY OF DYNAMIC PROPERTIES OF ELASTOMERIC BEARINGS ON THE SEISMIC RELIABILITY
F. Micozzi;L. Gioiella;Andrea Dall’Asta
2024-01-01
Abstract
Seismic isolation is considered an effective solution to protect buildings and reduce seismic losses. However, the reliability level achieved by code-conforming base-isolated structures can be not uniform due to different design choices allowed by the codes. Moreover, the seismic response of such structures is affected by the variability of dynamic properties of isolation bearings due to behavioural or environmental effects. For elastomeric bearings made by High Damping Rubber (HDR), the main behavioural effect is the dependence of the shear response on the strain amplitude, the strain rate, but also on the previous strain history (known as repeated cycling or Mullins or scragging effect). The shear response of elastomeric bearings is also influenced by environmental conditions, such as temperature and long-term environmental actions (ageing). Currently, some of the behavioural effects are included in advanced numerical models, however, current seismic codes allow to use a simplified approach based on less accurate models in conjunction with property modification factors (called λ-factors in the European context) defined for both behavioural and environmental effects. These factors, although quite used are based on old and limited data, especially for HDR bearings. For this reason, in the first part of the paper a statistical analysis of a large set of material tests carried out according to EN 15129 is illustrated. Experimental data include low and high damping rubber compounds currently used for elastomeric bearings with shear modulus ranging from 0.4MPa to 1.3MPa. The response variability in terms of equivalent linear properties is analysed for each behavioural effect and environmental condition. Based on the experimental results, new λ−factors for stiffness and damping are proposed and compared with those suggested by the code prescriptions. In the last part of the paper some preliminary considerations are made on the influence of such variability on the reliability of base-isolation structures.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
