Long-Span Metal Truss Installation
Safely and securely install 60-foot-plus, long-span metal
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."
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
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
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
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
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
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
Sidebar: Long-span Metal Truss Safety
• Erection, installation and safety plan
• Secure storage on flat surface
• Correct use of spreader bar and crane
• Proper installation of lateral and diagonal restraint
• Secure truss to bearing connection
Information provided by Aegis Metal Framing