Small-Strain Stress-Strain Properties of Expanded Polystyrene Geofoam

Abstract

The small-strain stress-strain properties of expanded polystyrene (EPS) geofoam with densities of about 20 kg/m 3 and 30 kg/m 3 were evaluated by laboratory unconˆned compression tests on specimens of 75 mm in diameter and 150 mm in height. Two series of tests were conducted, which were continuous monotonic loading (ML) tests and ML tests intervened by sustained creep loading and minute cycles of unload and reload. Relatively small vertical and horizontal strains were locally measured by means of a pair of local deformation transducers (LDTs) and a set of three clip gauges, respectively. The paramount importance of measuring local strains in compression tests on EPS to reliably evaluate its stress-strain properties, in particular those at relatively small strains, is demonstrated. The initial modulus, E0, and Poisson's ratio, n0, were evaluated from initial stress-strain relations at small strains obtained by these ML tests. The tangent parameters, Etan and ntan, were also evaluated from the ML stress-strain behaviour. The equivalent parameters, Eeq and neq, were evaluated from the stress-strain behaviour during minute cycles of unload and reload. The stress-strain behaviour is essentially linear only at small strains, and it becomes highly non-linear and a signiˆcant drop of stiŠness occurs as observed in the overall stress-strain behaviour. The Poisson's ratio for inelastic deformation is found to be negative.

Integral abutment bridges: Investigation of seismic soil‐structure interaction effects by shaking table testing

“…A value of E i ranging between 3.6 and 6.3 kPa was found for the PU. Similar relationships, available in literature for EPS geofoam, provide the Young's modulus, E i in the range 4.5‐10 kPa for ρ i = 20 kg/m 3 66 …”

Rate Effects on the Stress-Strain Behaviour of Eps Geofoam

“…The largest lateral strain measurable with CGs was about -1.5z. In the present study, this limit was never reached until the end of the respective tests due to a very low Poisson's ratio at large strains of EPS geofoam (Abdelrahman et al, 2008). Therefore, changes in the cross-sectional area of the specimen evaluated based on the lateral strains measured with CGs were actually very small.…”

“…Therefore, the stress and externally measured strain relation exhibits apparently softer behaviour with a decrease in the specimen size (e.g., Hazarika, 2006). This apparent size eŠect due to the bedding error is pointed out by Abdelrahman et al (2008) and this eŠect may become negligible in full-scale cases in theˆeld. In the present study, it is assumed that the relationships between the vertical stress and the locally measured vertical strain, both averaged for the whole specimen, are material properties, independent of specimen size.…”

“…Specimens: As the details of the test method are reported in the companion paper (Abdelrahman et al, 2008), only a brief summary is herein presented. Two types of EPS geofoam having diŠerent densities (19.3 and 28.0 kg/m 3 ), termed D-20 and D-30, were used.…”