4.5 RAISING STEEL BUILDING RIGID FRAMES

The intermediate or interior frames nearest the bearing endwall are usually erected first. This bay usually contains the optional diagonal bracing. The proper completion and plumbing of this first bay, as will be discussed later, is extremely important to the successful completion of the Steel building.

Although several methods are used to erect general steel rigid frames, it has been found most satisfactory to erect the columns first, tie them together with the girts and tighten the anchor bolts*. On small spans and short eave heights, columns can often be set in place by hand without the use of hoisting equipment. Temporary bracing should always be installed as soon as sections are lifted in place.

* The anchor bolt tension may need to be adjusted to seat the rafter.

After the columns have been erected, the ground assembled rafter is hoisted into place and connected to the columns. The size of the rafter which can be safely handled depends on the equipment available and the experience of the erection foreman. Generally as many connections as possible are made on the ground.

The flange brace should be bolted to the rafter prior to raising in order to save time. The hoisting equipment should never be released from the rafter until the frame is adequately braced, so it cannot buckle or tip in the longitudinal direction of the building.

NOTE:
Stay well in the clear of loads being moved by any type of lifting equipment. Safety first!

A second method, when equipment is limited, (while not recommended) is illustrated below. After the column is erected, the first rafter section, with the lifting cable around the balance point, is raised into position and bolted to the column. Then, when the free end of the rafter is supported by any safe method (such as an adequate wood frame, or a metal scaffold, properly braced, and of satisfactory capacity ) the lifting cable can be released. The procedure is then repeated until the entire frame is in place and bolted together at the ridge.

Still a third method for erecting general steel rigid frames with limited equipment adopts the same support procedure described previously, but differs in that the sidewall column and the first rafter section are bolted together on the ground and raised into position in one lift. The lifting cable is again attached at the balance point (about the quarter point of the rafter in this case). When the column is secured by the anchor bolts and the free end supported, the process is repeated with the frame bolted together at the ridge.

NOTE:

Stay well in the clear of loads being moved by any type of lifting equipment or supported.

When the rafters consist of several steel building roof beams, as in the case of wide buildings, a safe procedure of raising by sections and supporting the free end must be followed, regardless of the type of equipment available. In most instances the work proceeds from outside columns inward toward the peak until the entire frame is bolted into place.

The same general procedures of erection apply to either clear span or multiple span frames. In the case of the latter, the support for rafter sections during erection is generally supplied by the interior columns, themselves, making temporary supports unnecessary.

Two words of caution concerning the erection of rigid frames are in order. The first is that rigid frames, especially free ends or cantilevered sections should never be left “for the day” in an unsupported, unbraced or unguyed condition. Such practice has resulted in the total loss of considerable amounts of erected steel because of wind. The second word of caution pertains to the additional care required in the erection of multiple span frames compared to clear span frames.Steel Building Frames with interior columns, because of closer supports, have much lighter sections. They are much more apt to buckle during erection than clear span frames, and consequently require greater care in rigging and handling.

Lifting Cables and Spreader Bars >>