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The synchrotron SIS300 is a core component of the FAIR facility, which is under development at GSI. The high intensities of proton and heavy ion beams require the synchrotron to be ramped in a few seconds. In particular, the bending dipole magnets have to be pulsed from the injection magnetic field of 1.5 T up to the maximum field of 4.5 T at the rate of 1 T/s. The fast field ramp together with the particular characteristic to be geometrically curved (the sagitta is 114 mm) make these dipoles critical from design and construction point of views. Aside from the thermal ac losses, the mechanical fatigue is one of the main issues of these 7.8-m long magnets having cos-theta shaped coils with a 100-mm bore. Just the large number of magnetic cycles (10 7 ) oriented the mechanical design to the involvement of stiff structures working at a relatively low stress level with respect to the elastic limits. To this aim, the coils are mechanically supported by 3-mm thick laminated stainless steel collars, assembled through keys, and 1-mm thick iron yoke laminations kept together through large stainless steel C-shaped clamps. The mechanical behavior of these challenging dipoles has been studied in detail through several 2 and 3-D finite-element (FE) analyses. In order to assess the soundness of the mechanical analysis, a series of mechanical studies were performed on stacking samples and single poles under compression, comparing FE computations with the results of the mechanical tests. Finally, the collaring of short models was performed and the measured deformations were compared with expectations.