Safe working load of strand lifting eyes for precast concrete construction

Abstract

In the precast concrete industry, it is common to install lifting eyes within the slab to use them for lifting and transporting the precast concrete elements. For instance, the shallow precast pre-stressed solid concrete slab units are required to be lifted usually the next day after manufacturing and stored in a precast yard before being delivered to site. Normally, a set of four lifting eyes are located in the corners of each slab. These lifting eyes consist of strands that have been bent into loops and cast within the slabs or beams. It is economical to use strands because short, off-cut lengths have little or no value in production and are normally wasted. Currently, limited guidelines and standards for the design and installation of these lifting eyes exist. Additionally, the safe working load of such unstressed strand lifting eyes are rarely studied in the extant literature. Therefore, in this research an experimental plan was developed to investigate the safe working load of lifting eyes used in typical commercial precast slab units. A series of tests were conducted on several shallow precast concrete slabs with different concrete strength and lifting eye design embedded in the slabs. For each testing scenario, several lifting eyes were loaded to failure to obtain the lower fifth percentile safe working load. The results obtained from different testing scenarios are then evaluated and compared. The findings provide a valuable insight on the behavior and safe working load of lifting eyes applicable to the precast concrete industry.