Rapid Lift:

Rapid Lift is a range of lifting inserts especially made for precast concrete.   The load range is from 0.7t up to 26t, and there are several types, including simple spread anchor, erection anchor, flat foot anchor, and double-ended anchor.   It is a well established system and allows quick attachment and release using a compatible ring clutch.  The insert is held in place by a rubber former that creates a half-round recess.  This recess accepts the ring clutch, which engages into a hole in the insert.  The main advantage of this method is speed.  It is also possible to release the clutch remotely by attaching Bowden cables.

This type of system has been available for many years, and during that time it has been copied extensively by other manufacturers.  Due, in part, to the simplicity of the insert, they can be made with unsophisticated equipment.  It is important therefore to ensure that inserts and ring clutches are manufactured to an appropriate standard of quality, with the relevant test certification being available.  Ring clutches and inserts from different manufacturers should not be used with each other.

Threaded inserts:

Threaded systems are probably the most widely used method of lifting.  The system consists of a cast-in insert having a female thread like a socket.  This is used with a lifting attachment having a male thread.
It is possible to obtain systems that use a normal ISO metric thread.  However, the vast majority of systems use a special thread called ‘Rd’ (short for round).  This is a slightly different thread profile to a metric  ‘M’ thread.  The result is that, whilst an M thread can be screwed into an Rd socket, it is not possible to screw an Rd thread into an M socket.  The purpose of this is to prevent a lifting head or loop being screwed into a fixing socket on a precast element and imposing heavier loads than expected.  In addition, the fixing socket may be in a location that would not accept the higher load.   

The simplest type of threaded insert is a barrel insert.  This is intended for simple vertical lifting and is not normally used for turning units.  The load range is from 5 kN (Rd12) up to 125 kN (Rd52).  These capacities are for axial lifting.  The capacity in shear is 50% of the axial capacity.  The sockets have a hole near the base, through which a reinforcing bar is inserted.  Manufacturers give guidance on the size and shape of bar.

Where units are shallow, such as a slab, a shorter version of socket may be used.  This type is called a ‘plate’ or flat steel anchor.  It has a plate welded to the base, which compensates for the loss of depth of the cone of resistance by increasing the width.  The load range is as the barrel socket.  However, the shear capacity is the same as the tensile capacity. The reinforcement required sits on top of the plate and manufacturers give guidance.