A portal crane for roads and bridges comprises a base, an outer
barrel is fixedly mounted on the base, a plurality of coaxial inner barrels are rotatably mounted in the outer
barrel, the inner diameters of the inner barrels are gradually increased from inside to outside, strip-shaped through grooves are formed in the bottom sides of the inner barrels and the bottom side of the outer
barrel respectively, and one side of the periphery of the inner barrel on the innermost side is fixedly connected with one end of a steel
wire rope. A nut is installed on the periphery of the reciprocating lead screw in a threaded fit mode, the sleeve is fixedly connected with the nut, a driving device capable of driving the inner barrels to rotate is arranged on the base, and when one inner barrel rotates, the inner barrel inside the inner barrel synchronously rotates along with the inner barrel, and the inner barrel outside the inner barrel is static. The device is simple in structure and ingenious in conception, multiple
layers of steel wire ropes are wound on different inner barrels,
extrusion and abrasion between the steel wire ropes are reduced, the service life of the steel wire ropes is prolonged, the steel wire ropes are wound on the inner barrels with different diameters, the steel
wire rope winding and unwinding speed is adjusted, the market requirement can be met, and the device is suitable for popularization.