A sieve support structure including an elongate first rail, an elongate second rail, and rigid elongate compression members pivotally connected to and extending between the first and second rails at longitudinally spaced locations therealong, wherein the rails and the compression members form a rail assembly having a predetermined shape bounding a correspondingly shaped space, the rail assembly being configured for supporting a sieve of a cleaning system in at least substantially covering relation to the space, the structure including elongate tension members extending generally diagonally through the space and having opposite end portions connected to the first and second rails and being tensioned so as to simultaneously urge the rails against the compression members so as to apply a compression force thereagainst for retaining the rail assembly in the predetermined shape in opposition to forces urging the assembly from the shape.