Large composite structures are produced using a vacuum assisted resin transfer molding process incorporating a resin distribution network. The structure includes cores each having a main feeder groove or channel therein. A resin distribution network is provided adjacent the core surface in fluid communication with the feeder groove. In a first embodiment, the resin distribution network comprises a plurality of microgrooves formed in each core surface. In a second embodiment, the resin distribution network comprises a separate distribution medium surrounding each core. Each core and associated resin distribution network is covered with a fiber material. The dry lay-up is placed against a mold and encapsulated in a vacuum bag. Uncured resin is fed under vacuum directly into the main feeder groove in each core via a fitting through the bag. The resin flows from the main feeder groove through the resin distribution network and outwardly into the fiber material and is allowed to cure. The resin distribution network forms an integral part of the finished structure. The fiber material with cured resin between adjacent cores may comprise various structural members.