Erecting long, vertical precast concrete members with one crane and two operating lines

摘要

Erect on of long, vertical precast concrete members from their as-delivered horizontal position to their vertical position in the structure involves devising handling procedures that protect the safety of the erection personnel while preventing the precast concrete member from cracking during the tilting procedure. The author investigates the most commonly used procedures, three-point and four-point rolling-block lifting systems, and identifies a common instability condition that causes sudden, uncontrolled rolling of the members as they are being tilted toward their vertical position. Methods are devised to detect in any member the potential for such instability, lo establish safe location of lifting devices and minimum lengths of crane slings to prevent this condition from occurring, and to analyze and control tensile stresses from causing cracking of long precast concrete wall panels as they are lifted from their horizontal position, rigged for the tilting operation.