Inserts cast into precast concrete are used for handling the unit or for connecting it to the structure. Erection inserts vary depending on the member's use in the structure, the size and shape of the member, and the manufacturer's preference. The location of the lifting device can affect ease of erection and connection of the precast concrete unit to the structure. Lifting points should be compatibile with the method of shipping and be placed so that the structure does not interfere with rigging and crane lines.
Many lifting devices are devised from prestressing strand or aircraft cable loops that project from the concrete. When strand lift loops are used as a lifting device, a short piece of loooped strand usually is shoved into the concrete to the required depth after the concrete has been screeded. Manufactured inserts also are available for use with precast concrete. Threaded inserts are the most common type of hardware connection. In order to achieve optimum capacity, they must be aligned perpendicularly to the bearing surface. Lifting devices may fail for a number of reasons, including insufficient bolt thread engagement, improper sling angle, worn threads, and low concrete strength.
Temporary lifting and handling devices should be placed to minimize patching after use. When temporary lifting and handling devices are located in finished edges or exposed surfaces, bolt or insert holes must be recessed, filled, and patched.
Wedge inserts are usually made of malleable iron with an integral anchoring device. Wedge inserts allow for 1 inch linear field adjustments. However, the position and fit of the bolt within the inserts can determine its strength. In general, wedge inserts usually are used only for light wind and gravity loads.
Mindful placing of hardware to required tolerances is important because bearing surfaces of panels and matching hardware on the structure must be parallel to achieve the optimum bearing or load transfer.