A tank assembly includes an elongated plastic tubular pipe structure and at least one end wall or internal bulkhead wall attached to the plastic tubular pipe structure. The end wall or internal bulkhead wall is a composite unit formed by a plastic sheet member sized to cover a cross-sectional area defined by the tubular pipe structure and a composite reinforcement strip bonded to the plastic sheet member. The composite reinforcement strip includes an elongated plastic base portion having a plurality of spaced apart ribs extending from a first side thereof and lengthwise therealong, each rib comprising an elongated metal reinforcement encased in plastic, the plastic base portion having a second side abutting against a surface of the plastic sheet member. Other structures can be reinforced using composite strips that are electrofusion welded to one or more walls of the structure.