Performance Properties of Geogrids - Reinforced Soil Engineering: Advances in Research and Practice - page 22

4 DESIGN STRENGTH

As outlined by Jewell (1990a), soil reinforcement designs have separate
requirements for maximum allowable strength and for stiffness or maximum
allowable deformation of the structure. Both criteria must be checked for the
entire lifetime of the structure and are based on the creep and stress-rupture
behavior of the geogrid (Figs. 2- 4 ). More than 15 years ago, Voskamp (1986)
proposed calculating the maximum allowable strength (today defined as design
strength) from the general equation

P all ¼ð P char ½ t ; T Þ=ð f m ·f e ·f d Þ ð 1 Þ

where

P all is the allowable design strength for the design life time, t.
P char is the characteristic tensile strength for the design lifetime t, and
design temperature T.

f m is the partial factor for extrapolation and accuracy of test data.

f e is the partial factor for environmental aspects.

f d is the partial factor for mechanical damage (Fig. 5) .

For tensile rupture failure, a similar formulation has been embodied in BS
8006 (1996):

T d ¼ T c = f m ð 2 Þ

Figure 2 Stress-rupture line, Fortrac. (From BBA, 1997).