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An Introduction to Single-Girder and Double-Cantilever Bridge-Erecting Machines
One type of bridge construction machinery features a box-girder boom that cantilevers forward, with a foldable vertical support at the front end consisting of left and right legs. The machine can self-propel onto the bridge under no-load conditions, then upright the front support and brace it against the abutment. As the girder segment (or entire girder) is moved along the lifting boom, the boom effectively behaves like a simply supported beam. During bridge erection, the machine can self-propel onto the bridge while still unladen. First, a dedicated gantry crane must transfer the girder from the railway flatcar to a specialized girder transporter. Subsequently, the girder transporter will… Bridge erector Back-end alignment is achieved by using two girder-lifting trolleys that run along the crane’s boom to lift the transverse girders. The girders are then moved along the boom and placed onto the bridge deck. To accommodate curved bridges, the crane’s boom can be slightly swung in the horizontal plane. The girder positioning method is the same as that used on double-boom bridge erectors—either by shifting the girder or by shifting the girder carriage. The advantages of this type of machine include the elimination of counterweights, the absence of the need for a locomotive to push the unit, the elimination of the requirement for a bridge-head turnout when delivering girders, an increased level of mechanization, and enhanced safety performance. The 130-ton Shengli bridge erector falls into this category.
A type of bridge-building machinery that was used in the early Soviet period. When it was first introduced in 1948, its front and rear booms were made of steel plate girders, with lifting capacities of 45 tons and 80 tons, respectively. By the 1950s, the booms had been redesigned as trusses, and the lifting capacity was increased to 130 tons.
This type of bridge-launching gantry cannot move under its own power and requires a locomotive to push it. The front boom is used to lift the girder, while the rear boom is used to lift counterweights; neither the front nor the rear boom is permitted to swing in the horizontal plane. During bridge erection, a dedicated 80-ton trolley is often employed to transport the girder beneath the front-boom hook of the gantry—this operation is known as “girder delivery”—before the girder is lifted into place. To facilitate shunting operations, each branch line must be laid out at the bridge abutment. After the gantry lifts the girder, the axle load increases, whereas the newly constructed embankment at the bridge abutment is relatively soft. Consequently, reinforcement measures must be implemented along the gantry’s travel section during girder-lifting operations, such as heavy-vehicle compaction and the insertion of sleepers.
Keywords:
Bridge erector
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