对已有结构的加固,有时会遇到采用预应力加固法,如对屋架,屋面梁这类跨度较大结构的加固处理.因此,加固钢筋需作冷拉处理.现在常用的预应力钢筋冷拉装置有二种,即机械式冷拉装置和液压拉伸机装置.前者由混凝土基础、测力计,滑轮组及卷扬机组成,设备多、占地大,需要一定数量的混凝土.后者设备较为昂贵,为专用设备.这两种设备适合于预制厂使用,用于制作钢筋混凝土预应力预制构件. For the reinforcement of existing structures, sometimes the use of prestressed reinforcement methods, such as the truss, roof beams such as the reinforcement of large span structure. Therefore, the reinforcement needs to be cold-drawn steel. Now commonly used prestressed steel cold There are two kinds of pull devices: mechanical cold drawing device and hydraulic tension device. The former consists of concrete foundation, dynamometer, pulley block and winch. It has many equipments and covers a large area and requires a certain amount of concrete. The latter equipment is relatively Expensive, for special equipment. These two kinds of equipment are suitable for use in prefabricated factories and used to make reinforced concrete prestressed prefabricated components.