A dual-use ladder and bridge modular system preferably includes tubes, gussets, flanges, and/or joints. In a preferred embodiment, the tubes, gussets, flanges, and/or joints are made of carbon fiber. A method connects and disconnects modular carbon fiber ladder segments. Another method creates a lightweight carbon-fiber beam with exceptionally high stiffness and strength using a combination of carbon-fiber braid material, uni-directional cloth, and pultruded carbon-fiber strips. A carbon fiber ladder segment and tube connectors are also disclosed.