Mechanical properties of electrorheological suspensions are studied with computer simulations using a point-dipole model. The behaviour of these fluids is compared under constant-rate compressive and shear straining. The mechanisms of local deformations in single chains under straining are discussed. Also structures which have been grown before straining under the influence of electric field have been studied. In these structures the ratios of compression and shearing were found to have a significant effect on the corresponding yield stresses. The tensile yield stress was found to be about an order of magnitude larger than the sheared yield stress.