Lifetime-Oriented Structural Design Concepts- P12: At the beginning of 1996, the Cooperative Research Center SFB 398 financially supported by the German Science Foundation (DFG) was started at Ruhr-University Bochum (RUB). A scientists group representing the fields of structural engineering, structural mechanics, soil mechanics, material science, and numerical mathematics introduced a research program on “lifetimeoriented design concepts on the basis of damage and deterioration aspects”. | 288 3 Deterioration of Materials and Structures the drained thermo-mechanical coupling tensor A Au - 3at uMB Ced 1at and the drained tensor A Au S B respectively 321 . Identification of Coupling Coefficients According to 321 the poroelastic hygro-mechanical coefficients b and M can be determined by relating differential stress and differential strain quantities defined on the meso-level to respective homogenised quantities on the macrolevel. The so-obtained tangential Biot coefficient is determined as b Si 1 fiK Ks _ which includes the expression b Sl suggested by 211 for the special case of poroelastic materials with incompressible matrix behaviour. An expression for the Biot modulus M fiM is obtained as Si b S 1 -1 Sipffi dSi fiSt see 705 493 for a similar formulation. For cementitious materials expression can be replaced by dSi _ dpi In the special case of a fully saturated material St 1 yields the classical relation 211 493 -1 M - P b-fi M Si 1 -1 Si 1 Kffi Ks The coefficients related to damage phenomena A and s are identified by exploiting the symmetry relations that are connected to the existence of a macroscopic potential. Using the Maxwell symmetries the drained tensor A can be expressed as 533 A C e Sidpil C latT pi and the coupling coefficient H is obtained as _ MSlK i H K 2 s Pl ep e M fi 1 M 0. Modelling 289 Effective Stresses The concept of effective stress 281 791 is a generally accepted approach in soil mechanics for the determination of stresses in the skeleton of fully saturated soils. In addition to the original proposal of 791 several alternative suggestions for the definition of effective stresses exist taking the compressibility of the matrix material or the porosity into account see . 123 587 128 . Based on the relevance of the concept of effective stress for the analysis of fully saturated soils this concept has also been adapted for the description of .
