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Long-Span Metal Truss Installation

Mcn  Prod Feature  Apr17 1 Low Rez

Safely and securely install 60-foot-plus, long-span metal trusses

Long-span metal trusses are 60 feet or greater in length. A long-span truss can pose a risk to installers because the dimensions and weight of the truss itself can create instability, buckling and collapse of the truss if it is not handled, installed and braced properly. Long-span trusses can be installed safely and efficiently, but they require more detailed safety and handling measures than short-span trusses.

Long-span metal trusses are being used more frequently today. Mike Noonan, vice president of marketing at Cascade Manufacturing Co., Cascade, Iowa, says this is because design professionals have come to value the ability to design structures that are larger in size and more residential in appearance. "When the code requires the use of non-combustible materials in a particular project, cold-formed steel is a natural choice," he adds. "As a result, longer span trusses are becoming more common. Do not refrain from this type of construction, but become more proficient in it."


Before Starting

Research and know the established and approved industry documents that address installing long-span metal trusses. The Cold-Formed Steel Council (CFSC) furnishes documents that address the proper handling, installing and bracing of long-span metal trusses. "These documents are not project specific but rather a guideline of best practices for proper handling and bracing," Noonan says. "These documents should be furnished on every project. The engineer of record is generally responsible for identifying project specific bracing relative to the structure." Section 42211.3.3 of the International Building Code (IBC) 2015 discusses long-span, cold-formed steel trusses.

According to The Cold-Formed Steel Building Component Safety Information (CFSBCSI) book, "Guide to Good Practice for Handling, Installing, Restraining & Bracing of Cold-Formed Steel Trusses," truss installation can be dangerous if proper precautions are not taken. Long-span truss installation requires, above all, careful planning and communication among the contractor involved with the erection/installation, the installation crew and the crane operator.

Depending on the experience of the contractor, it is strongly recommended that a meeting be held with all on-site individuals. It should include all those involved in the lifting/hoisting, installing, restraining and bracing operations to review the provisions of CFSBCSI, the truss design drawings, the construction documents, the truss placement diagram (if/when required by the contract), OSHA job-site lifting and fall protection requirements, the erection and installation plan (if provided) and sitespecific conditions.


Long-span Truss Arrival

When long-span metal trusses arrive on a job site, confirm the trusses are accurate according to the approved designs. Noonan feels that, ideally, longspan metal truss delivery should be coordinated with the superintendent on-site to have them arrive shortly before installation to avoid them being in the way of other trades.

"Long-span, cold-formed steel trusses require additional clear space around the job site for storage and staging prior to installation," says Mike Pellock, PE, executive vice president of Aegis Metal Framing, a division of MiTek, Chesterfield, Mo. "Because they are long, it can be a challenge with many job sites to find this area with access to and in close proximity of the building. Trusses should never be dragged. Always use a crane to move them."

Long-span trusses can be built and shipped in two pieces due to shipping constraints. When they are either too long or too tall to ship in one piece, there is an added step in putting the two pieces together. "You need a suitable location at the job site to join the truss halves together," says Maribeth Rizzuto, director of education and sustainable construction of the Steel Framing Alliance and managing director, Cold-Formed Steel Engineers Institute. "And, the installer will need to take the extra time and manpower into consideration when submitting a bid on the project, as well as the overall timeframe requirements for project completion."

Pellock says a jigging system is required to ensure all trusses are spliced the same to ensure consistent profiles. "When trusses are built in two pieces because of height limitations, a base truss and cap truss are supplied," he adds. "The base truss will require additional bracing of the top chord that supports the cap truss. A series of lateral and diagonal restraint bracing will need to be applied to the flat portion of the base truss top chord."

When dealing with long-span trusses, Serge Dussault, PE, vice president of Canam Structures, a division of Canam Group Inc., in St-Gédéon, Québec, Canada, recommends to always shop assemble the largest truss pieces possible to reduce the work to be performed on the job site. "To determine the pieces, we have to take into consideration the site logistic and make sure that we can safely get the pieces to the location where they will be unloaded," he says. "Because of the large pieces that we may have to deal with, we always want to minimize the handling on the field and bring the pieces close to the area where they will be erected."

The field connection of the long-span truss halves needs to be clearly detailed to the field installers. Also, "The method of truss installation needs to be taken into account," stresses Jacob Thompson, PE, SE, senior engineer, Alpine TrusSteel, Orlando, Fla. "Depending on whether the trusses are connected together on the ground and then raised into place, or the two truss halves are temporarily shored in place before the trusses are connected, will make a difference on the installation procedure. The CFSBCSI booklet discusses field splices in the 'Field Assembly & Other Special Conditions' section of the document."


Handling and Bracing

A long-span metal truss is flexible and special attention must be taken during its handling to avoid damage or injury. A long-span metal truss can bend out of plane if not handled correctly. "When lifting a truss, use more than one connection point," says Thompson. "Spread the connection out through multiple points along the truss using a spreader bar." Dussault believes that because long-span trusses are slender and unstable during erection, pick points have to be carefully planned and engineered. "The best way is for the designer to recognize that the trusses will have to go through different stages of construction before they are put to service," he says. "We have had very good results when working directly with consultants to incorporate construction steps in the design of long-span trusses."

Pellock stresses that long-span trusses always require a spreader bar or other member to aid in hoisting them into place. "The spreader bar provides multiple lift points positioned to avoid bending or twisting of the truss," he says. "Additional workers may be needed to guide the truss as it is lifted into place. Improper use of, or failure to use, a spreader bar when lifting the truss in place will very often lead to damage of the chord and web members from bending or twisting. Follow the guidelines of the CFSBCSI for spreader bar selection and sizing."

The correct amount, position and attachment of installation bracing is needed for all truss installations to keep the trusses in a vertical position until the permanent restraint bracing is applied. Inadequate bracing during installation is the most common reason for truss collapse and potential injuries.

Danny Feazell of Roanoke, Va., a cold-formed steel contractor and installer with more than 40 years of experience in construction, says the IBC requires a qualified registered (contracted by the owner) design professional design the temporary and permanent bracing. "Installers must follow the guidance," he adds.

Thompson believes assigning the design of the bracing should help eliminate the confusion of who's responsible and not be forgotten. "Longspan trusses are also to have a special inspection to ensure the bracing is installed correctly," he adds. "The nature of long-span trusses is to be more unstable until it is properly braced," says Pellock. "Special attention to provide the required rows of lateral restraint and diagonal bracing is critical for long-span truss installation safety."

Feazell stresses that installers must confirm they have correctly temporarily braced the longspan metal truss in a vertical position before they climb on or unhook the spreader bar. "Attention to details including proper count and placement of fasteners is critical," he says. "As an example: did the truss manufacturer or engineer require hold down clips on both sides of the truss at each end or just one side of the truss at each end? Before it is sheathed, it should be permanently braced as specified by the design professional."

Neglecting to use multiple connection points when lifting trusses, or neglecting to use temporary bracing with both lateral and diagonal braces at required intervals, are indeed the most common mistakes made when installing long-span trusses. Thompson believes working with a crew who is educated or experienced in the installation of long-span trusses should help avoid these mistakes. And, as mentioned earlier, good preplanning is a must for long-span metal installation. "Long-span trusses are very different from other trusses and by doing the planning in advance you will avoid errors and save yourself a lot of time on the job site," Rizzuto says.


Sidebar: Long-span Metal Truss Safety Factors

• Erection, installation and safety plan
• Secure storage on flat surface
• Correct use of spreader bar and crane
• Proper installation of lateral and diagonal restraint bracing
• Secure truss to bearing connection
Information provided by Aegis Metal Framing