How are Columns Lifted?

In many conditions, columns are architecturally exposed which prevents installation of steel yoke plates and screws into the side faces of the column. A column must lifted upright and into place which leaves the installer and rigging engineer with few options in deciding where the "picking points" should be located. Whatever is chosen must meet a variety of criteria, including but not limited to; screw geometry requirements, withdrawal governing, suitability for end-grain etc.

Column weights are not usually too heavy and can be lifted and supported by a single 1/2" (112mm) diameter screw in withdrawal with a transport anchor. Withdrawal in end-grain will always be weak as a result of several factors through deign codes and our own testing that must be applied; pulling a screw out of the end grain has multiple possible failure modes. Withdrawal is best when the threads are penetrating many layers of wood grain, but in a parallel to grain application (i.e. end-grain install) the threads really to not have much to "hold on to". Table 1.1 from the Fastener Catalogue shows that a pure withdrawal application in end grain (0 degree to the grain) would use an angle to grain reduction factor, Rα, of 0.3.

Additionally, using screwed in yokes at the end grain of a column for lifting leads to an awkward removal process. Columns are usually the first elements to be installed, meaning that the only way for construction crews to remove the screws attaching yokes for re-use on the next set of columns to be lifted is the move a scissor lift to each column location to remove 4 screws (or other piece of machinery that lets workers work from heights) while also requiring a height taller than the column. Crane time is extremely expensive to rent, and a yoke with screw application for rigging is not a time sensitive solution. For this reason we almost always suggest a Transport Anchor which can easily be slid on and off in a time-efficient manner - while also generally providing sufficient capacity for column lifts. A second screw and transport anchor is added as a failsafe, with the second screw at a 45 degree incline in the end grain.

When columns are simply too heavy for a 1/2" Kombi: the longest thread length we have for Kombi LT and the Standard Kombi is 5 3/4", which translates into 510 lbs of resistance in end-grain with a safety factor of 5 for a single screw.

Columns not at the roof level will be larger since they have to take the gravity load of the floors above them, thankfully, these columns also often come with the column-column connection installed (as seen below) which may be used as the picking point for rigging. The engineer/wood fabricator still need to confirm capacity and safety factor.