Most major suppliers of threaded lifting inserts give recommendations for reinforcement to be included to ensure that the inserts function properly.  The purpose of this reinforcement is simply to ensure that the tension forces are transferred into the body of the precast element and do not allow the insert to pull out under load.

These recommendations are generally based on simple or idealised conditions, and it is up to the designer to decide what reinforcement detail to adopt in other, more unusual  instances.  The following guidance is based on a selection of common inserts and some frequently used situations.  The list is far from exhaustive though, and common sense and engineering judgement is required to ensure safe lifting in all conditions.

The reinforcement is an integral part of the lifting system and it cannot be emphasised enough that correct detailing of the reinforcement is essential to ensure that failures do not occur.
This failure, in a very thin panel, was due to the reinforcement being too far from the top of the insert, allowing movement to take place.

Socket lifter

This is probably the most simple and commonly used lifting insert.  It is primarily used for vertical (or near vertical) lifting.  It has a hole near the base to take a reinforcement bar.  Manufacturers normally recommend that an opened-out ‘U’ bar is used for vertical lifting.  It is normally bad practice to use a simple straight bar through the hole.  Such a bar would be in bending rather than in tension and would have a very limited capacity.  A possible exception to this is to incorporate numerous hairpin bars around the straight bar so as to prevent movement.

When the bar is inserted, it is important that there is no gap between the bar and the socket.  Any gap is likely to be subject to local crushing under load, and the socket could (partially) pull out.  To ensure that bars are kept in place, sockets have a plastic ‘plug’ inside.  This plug should be firmly pressed down the inside of the socket to sit on the bar.  The bar should be long enough to take loads well into the body of the unit, and ideally lap onto other reinforcement.