Abstract: The pressure relief support structure comprises a sheet-like flexible cover and a mechanical apparatus under the cover. The mechanical apparatus consists essentially of a frame, an endless belt assembly of tapered rollers, a pair of spaced track members for support of an upper stretch of the belt assembly, and means for moving the belt assembly to cause its tapered rollers to move in sequence along the upper stretch. Preferably, the tapered rollers are segmented into frusto-conical sections independently rotatable with respect to each other; and in addition, the track members are preferably contoured to allow a depression of at least a part of the upper stretch of the belt assembly.