桁架 桁架的英文 英语翻译 truss 拓展翻译 桁架塔derrick tower桁joist桁板flitch桁端yardarm桁梁牵条girder stay横桁crossyard横旋转刀架facting arm后架after-frame护架cage滑动扶架slide rest滑动架slide rest滑动轴架tail stock画架easel话器架cradle话器架电键cradle switch环构架hoop truss环形支架ring support惠特曼氏支架Whitman's frame混凝土管架concrete pipe rack活动框架movable frame