路桥门式起重机主要用于桥梁建设，工作速度慢，由门架、卷扬机小车、大车运行机构、司机室和电气控制系统组成。

门架为桁架结构，具有结构轻、抗风力强等优点。包括主梁、上端梁、支腿、下端梁、走行台车及走台栏杆等。主梁采用三角桁架结构，上面铺设有轨道，供小车沿主梁方向作横向移动。支腿采用箱形或钢管两种形式。  

   Boad-bridge gantry crane is mainly used for bridge construction which is worked at a low rate. It is composed of gantry, windlass crab, trolley travelling mechanism, cab and electric control system.

The gantry, of a truss structure and having advantages of light structure, strong wind resistance and so on, is composed of girder, upper end girder, leg, lower end girder, travelling trolley and platform railing. The girder is of a triangular truss structure, on which laid rails for crane crab to transversely move along the main girder. The legs are of a box structure or steel tube structure.