As one of the bridge construction machinery, its boom is a box beam, which is cantilevered forward, and its front end is equipped with a folding column (composed of left and right legs). The crane can drive into the bridge position under no-load condition, and then straighten the front column and support it on the front pier. When the erected beam (or whole beam) moves along the boom, the boom is close to the simply supported beam state. When erecting the bridge, the machine can drive into the bridge site under the no-load state by itself. First, the beam pieces must be transferred from the railway flat car to the special beam transport car by using the special gantry crane, then the beam transport car and the rear end of the bridge erecting machine shall be aligned, and the beam pieces shall be lifted by the two beam trolleys running on the arm of the bridge erecting machine, and then move along the arm to reach the bridge site to drop the beam. In order to adapt to curved bridge erection, the crane boom can swing slightly in the horizontal plane. The method for placing beam pieces is the same as that used for double cantilever bridge erecting machine (moving beam or track). The advantages of this machine are: the counterweight is canceled, the locomotive is no longer required to push, the bridge head switch is not required to feed the beam, the mechanization degree is improved, and the safety performance is improved. Shengli type bridge erecting machine with a lifting capacity of 130 tons belongs to this category.
One of the bridge construction machinery, this type was used earlier in the Soviet Union. When it was introduced in 1948, steel plate beams were used for both front and rear arms, with lifting weights of 45 tons and 80 tons. In the 1950s, the double arm was changed into a frame, and the lifting capacity was developed to 130 tons. This type of bridge erecting machine cannot be pushed by itself and needs to be pushed by locomotive. The forearm is used to lift the beam, and the rear arm is used to lift the counterweight. The front and rear arms cannot swing in the horizontal plane. When erecting a bridge, it is often necessary to use a special 80t flat car to transport the beam pieces under the hook of the fore arm of the bridge erecting machine (called "beam feeding") before lifting; In order to facilitate shunting operation, it is necessary to lay turnout at bridge head every time. After the girder is lifted by the bridge erecting machine, the axle load increases, while the new embankment at the bridgehead is relatively soft. Therefore, reinforcement measures must be taken for the section where the girder is lifted by the bridge erecting machine, such as using heavy vehicles to press the track and inserting sleepers.