The ideal tensile test in transition metal disilicides MoSi2 and WSi2 with a C11b structure is simulated by ab initio electronic structure calculations using the full-potential linearized augmented plane wave method. The theoretical tensile strength for [001] loading is determined for both disilicides and compared with that of other materials. A full relaxation of all external and one internal structural parameter is performed, and the influence of each relaxation process on energetics and strength of materials studied is investigated. Differences in the behavior of various interatomic bonds including tension-compression asymmetry are analyzed and their origin in connection with the changes of the internal structural parameter is traced. For comparison, the response of bonds in MoSi and CoSi with B2 structure to the [001] loading is also studied.