A computer-implemented method of B-rep processing for performing structural simulation of a mechanical part including obtaining a first B-rep is described. The first B-rep forms a solid representing the mechanical part. The method further comprises providing a predetermined thickness threshold. The method further comprises constructing, based on the first B-rep, a second B-rep. The second B-rep forms a non-manifold object representing the mechanical part. The constructing comprises identifying one or more thin regions of the first B-rep. Each thin region has a thickness smaller than the predetermined thickness threshold. The constructing further comprises computing, for each identified thin region, a respective mid-surface of the identified thin region. The constructing further comprises replacing the identified thin region by the respective mid-surface.