A tank for containing compressed air for supplying the air to one or more pneumatically-operated components, devices, or systems of a heavy-duty vehicle such as a tractor-trailer or straight truck, also serves as part of the structure of the frame or subframe of the vehicle. The frame or subframe includes a pair of spaced-apart, parallel, elongated and longitudinally extending main members. One or more of the tanks also serve as interconnecting cross members of the frame or subframe structure. Each tank/cross member generally extends between and is perpendicular to the main members and is secured to the main members and/or suspension hangers and/or the air springs to form a rigid, integrated frame or subframe structure having reduced weight, yet which is capable of reacting the loads imparted to the structure by the axle/suspension system during operation of the vehicle.