Reduction of Structural Damage by Nonlinear Soil Response

Abstract

Following the 1994 Northridge earthquake, the areas with a high density of reported breaks in water pipes in typical residential areas in San Fernando Valley and in Los Angeles often did not coincide with the areas having a high density of severely damaged (red-tagged) buildings. As the former is an indicator of large strains and nonlinear soil response, this observation suggests that the damage to buildings in some areas may have been smaller than expected because the soil dissipated part of the energy of the ground motion by nonlinear response. This paper presents an attempt to quantify this relationship between the density of red-tagged buildings, N (per km 2), and the severity of shaking (via peak horizontal ground velocity, v max , or modified Mercalli intensity, I MM), including the density of breaks in water pipes, n (per km 2), as a variable specifying the level of strain in the soil. Approximate empirical relationships for N = f(v max , n) and N = f(I MM , n) are presented. The trends in the data indicate that, for v max in the range from ϳ35 to ϳ125 cm/s, the rate of growth of N versus v max tends to decrease at sites with large strain in the soil (i.e., large n). For v max beyond ϳ150 cm/s, the beneficial effects of nonlinear soil response seem to fade out, as large differential motions associated with soil failure begin to contribute to the damage of structures. Assuming fairly uniform density and quality of building stock and of water pipes in the areas studied, the derived relationships are then used to map v max and I MM in San Fernando Valley and in Los Angeles. The resulting maps are more detailed than what could be obtained from the density of strong motion stations and of sites with reports on felt intensity.

Seismic isolation using granulated tire–soil mixtures for less‐developed regions: experimental validation

“…The rubber–soil layer, which is underneath the foundation, can provide seismic isolation for the superstructure, similar to base isolators. This base‐isolation effect of RSM is partly due to the in situ nonlinear soil response, as described by Trifunac, who reported that the energy‐absorption effect of soil nonlinearity could provide a powerful, convenient, and low‐cost ‘base‐isolation and energy‐dissipating system’ . On the other hand, rocking of the foundation can provide further energy dissipation in the subsoil.…”

Detection thresholds in structural health monitoring

“…8), but no major damage to the interior longitudinal (B and C) frames was observed. In the vicinity of the building, the peak strain factor was as follows: horizontal $ 10 À 2.6 and vertical $ 10 À 3.2 [133,134,122]. The (refined) estimate of Modified Mercalli intensity at the site was VIII [119,120].…”

A note on predetermined earthquake damage scenarios for structural health monitoring

“…The M L = 6.4 Northridge earthquake of January 17, 1994 severely damaged the building, but its possible further damage was probably reduced by nonlinear response of the soils in the area surrounding the building . The structural damage was extensive in the exterior north (D) (Figure (a), top) and south (A) frames that were designed to take most of the lateral load in the longitudinal (E–W) direction.…”