GGU-RETAIN: Structural system
The structural analysis required to determine the state variables (displacement, moment, shear force and normal force) is not carried out by means of a continuous beam analysis, as is usual in retaining wall applications, but by means of a rod construction module, which treats the retaining wall and any anchors and struts as a single structural system. For inclined anchors in particular, the interactions between the anchor and the retaining wall can thus be correctly processed in a single computation. In a system with one anchor and one strut, for example, the following schematic would represent the governing structural system:
In addition, a vertical load can be defined for a strut and, if necessary, a rigid connection to the retaining wall be taken into consideration. For anchors and struts, the axial rigidity must be specified so that its influence on the action effects can be correctly recorded. The rod construction module can also compute using 2nd order theory. This means that buckling length investigations for struts, for example, can be dispensed with.
The theoretical principles of the rod construction module can be traced back to an article by Duddeck/Ahrens (Betonkalender 1976 (Concrete Calendar), Volume 2). Basically, this is a finite element method based on the displacement method.
Using FEM produces equation systems in which the number of unknown quantities is a function of the number of rods. The solution to the equation system is acquired in GGU-RETAIN using Cholesky's method, which is also employed in other GGU programs and is highly stable numerically. Nor have there been any numerical difficulties reported from other GGU applications.