Joist Pre-installation

When joists arrive at the job site, frequently on a flatbed truck, they are usually ready to be installed. No forming, pouring, curing or stripping is required and their erection procedure is relatively simple and fast. However, they should be inspected for physical damage before becoming unchained or unstrapped. From there, they should be unloaded by bundles with either a crane or forklift. While waiting to be installed, they should be removed from job-site traffic routes, and stored and secured in the same orientation they were shipped.

We make sure the  steel joist manufacturer will supply the contractor with a set of project joist placement plans. “These plans will have a ‘Field Use’ label, which signifies that the installation (erection) of the steel joists be governed by these plans,”  “The plans will show joist piece marks, joist location, joist orientation and bridging layout. A metal identification tag is placed on one end of the joist and will identify the joist mark with the project placement plan. The joist end with the metal tag is called the ‘tag end’ of the joist. It is important that the joist tag end is placed at the column line or wall exactly as indicated on the plan. When the joists are delivered to the job site, joist bundles are tagged with labels that identify each joist within that bundle. These can be used for staging the unloading of the joists at or close to the area where they will be installed. For larger jobs, or at job sites with limited access, the contractor will want the job delivered in sequences, which reduces the number of joists to a specific area.”

According AMP Welding And fabrication, when joists cannot be delivered as a single piece, they can be delivered in several pieces, with the pieces spliced together in the field. Follow the manufacturer’s instructions to ensure matching pieces are joined, proper bolts are used and any required bolt tensioning is incorporated. Attention must be paid to the joist installation process at all times to avoid accidents through careless handling during unloading, storing and erecting. Dropping of joists is unacceptable. “Have a pre-erection meeting with those who will unload, handle and erect the joists,”

Steel joists and accessories

Steel joists and accessories must be installed plumb, square and true to line. Do not install them on any support structure unless the structure is stabilized and readied. Only then, can joists be placed and securely anchored, per established regulations and approved shop drawings. To elevate the joists, hoisting cables must be attached at appropriate joist panel points and these panel point locations must be selected to minimize erection stresses. Longer joists may require spreader bars, multiple hoisting cables or multiple cranes to safely handle the joist. Cranes lift the joists onto the steel frame where steelworkers place the joists at their specified locations.

“The size of crane will depend on the size and weight of the joists to be installed,” says Pugh. “Groups or bundles of smaller joists can be lifted into place together, whereas a single larger joist may require an additional crane. Field-bolted splice joists may require additional cranes to put the pieces together on the ground before installation.” Once joists are elevated and landed on a structure, a steel worker connects their bearing ends to the structural steel by bolting, but more frequently, welding. Joists must be welded to the supporting steel framework in accordance with SJI specifications for the type of joist used. Comply with American Welding Society requirements and procedures, and contract documents for the welding, appearance and quality of welds, and the methods used in correcting welding work. Field welding must not damage the joists.

The Importance of Bridging

Joist bridging is a critical part of the installation process. Bridging braces the joists against unanticipated horizontal movement during installation and restrains the joist chords from out-of-plane or lateral movement under loading. Bridging secures the steel joists in the proper position as shown on the joist placement plans. Bridging is spaced depending on joist span and chord size. When two pieces of bridging are attached to the steel joist by a common bolt, the nut that secures the first piece of bridging must not be removed from the bolt for the attachment of the second piece. Bridging attachments must not protrude above the top chord of the steel joists. Where bottom chord bearing joists are utilized, a row of diagonal bridging must be provided near the support(s).

“Bridging can be horizontal, diagonal or a combination,” says Charles. “Most roof applications also require additional bridging to resist uplift forces. In some instances, joists and bridging can be ‘panelized’ on the ground. This method involves a grouping of joists with bridging in place assembled with workers on the ground, then lifted into place onto the supporting structure and properly attached.”

ALvon says there are three main types of bridging: horizontal bridging that attaches (typically welded) to the top and bottom chords of the joist; X-welded bridging that provides a more rigid connection between the joists; and erection bridging is X-bridging bolted to the top and bottom chords of the joists. Alvon Portis  says that what is unique about metal building joists is that the bridging configuration is often specialized to accommodate standing seam roofs.

“If erection bridging is required it shall be installed before the hoisting cable is released, and shall be bolted per the instruction on the erection plan in order to tie the joists back to the tie off point to maintain stability,” s “All other bridging can be installed after the joists have been erected, but prior to any loads being placed on the joists. A long slender joist with small chords may require bolted cross erection bridging for stability whereas a shorter stiffer joist may not require this erection bridging. Non Parallel chord joist profiles can also lead to instability and therefore require erection bridging.”

Before anyone is allowed on the steel joist, both ends of joists at columns (or joists designated as column joists) must be attached to its supports. When a bolted seat connection is used for erection purposes, as a minimum, the bolts must be snug tightened. The snug tight condition is defined as the tightness that exists when all plies of a joint are in firm contact. This shall be attained by a few impacts of an impact wrench or the full effort of an employee using an ordinary spud wrench. Steel joists must not be used as anchorage points for a fall-arrest system unless written approval to do so is obtained from a qualified person.

“Once the joists have been installed, the bridging provides lateral resistance for the joists under loading,” says Pugh. “Bridging at the bottom chord will provide lateral stability under wind loads, and bridging at the top chord will provide lateral stability if the deck does not do so, typically with standing seam roof systems. If the attachment of metal deck or panels to the joist top chord provides that stability, then the top chord bridging serves no purpose under loading.”

Joist Post Installation

Once the bridging is attached, the steel workers can use the joists as working platforms for construction by attaching the metal deck and panels to the joists. “Whether used in floor or roof construction, the installation process is basically the same, with the final system consisting of steel joists and decking ready for a concrete slab or roofing membrane attachment,” says Pugh. Once fully installed, repair damaged galvanized coatings on exposed joist surfaces with galvanized repair paint according to ASTM A780 and the manufacturer’s instructions. Clean, prepare and prime (or reprime) field connections, rust sports and abraded surfaces of prime-painted joists, accessories, bearing plates and abutting structural steel.