A shelf is connected to risers that are interference fit together to achieve a clamping effect between the shelves and the risers. Each shelf may comprise a plastic shelf portion and at least one reinforcement portion secured to the plastic shelf portion to reinforce the plastic shelf portion along its length. In one embodiment a plurality of metal bars are used as the reinforcement portion having a tapered end. The reinforcement portions may be inserted into channels formed in the plastic shelve portions and secured to the shelf portions using an interference fit.