Course Sponsor AEGIS Metal Framing Jayna Altman Jayna Altman 14515 N Outer 40 Drive Suite110 Chesterfield, MO 63017 Light Gauge Steel Trusses 314-851-2234 E-mail [email protected]The Specification, Design Manufacturing and Installation of Light Gauge Steel Trusses Web www.aegismetalframing.com Installation of Light Gauge Steel Trusses Course Number AMF05A AMF05A Please note: you will need to complete the conclusion quiz online at ronblank.com to receive credit An AIA Continuing Education Program Credit for this course is 1 AIA/CES HSW Learning Unit
Please note: you will need to complete the conclusion quiz online at ronblank.com to receive credit
An AIA Continuing Education ProgramCredit for this course is 1 AIA/CES HSW Learning Unit
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U C l ti f thi th D i P f i l ill b Upon Completion of this course the Design Professional will be able to:
• Explain why Light Gauge Steel Trusses are a Good Alternative • Explain why Light Gauge Steel Trusses are a Good Alternative Solution
• Explain applications for Proprietary LGST• List and describe Case Studies• List and describe Case Studies• Specify LGST• Describe the design process for Factory-built LGST• Explain: Fabrication Packaging Shipping & Installation of Explain: Fabrication, Packaging, Shipping, & Installation of
Factory-built LGST• Compare and contrast an LGST proposals and explain what
makes a complete truss systemmakes a complete truss system
Why Light Gauge Steel Trusses?y g g
Wh t l d id ti l t l Wherever steep sloped, residential-style roofs are desired…
ANDANDNon-combustibility is mandated…
The IDEAL solution is...
Light Gauge Steel Trussesg g
The Advantages
Advantages Are:
g
Advantages Are:
1. 100% non-combustible2. Long clear-span capabilitiesg p p
A. LGSTs can typically span 80+ feet, depending on loading criteria.
B. Obviously, spans will vary greatly between snowy regions such g gas New England and warmer climates like Texas.
3. Limitless roof and ceiling profiles--just like wood trussesA. Engineers hate to hear this, but with the computer software
available today, designs can be more dynamic than ever.4. Lightweight
A. LGSTs are typically half the weight of wood trusses due to their hi h t th t i ht tihigh strength to weight ratio.
B. This is an advantage for long spans and heavy concentrated loads since the trusses are not having to work double duty to
t th l ll th l d b i li dsupport themselves as well as the loads being applied.
The Advantages
5 Pre-engineered and pre-fabricated by truss professionals
g
5. Pre engineered and pre fabricated by truss professionalsA. Proprietary trusses are designed by experts, and sealed by
veterans in the light gauge truss business.6. Eliminate attic sprinkling systems6. Eliminate attic sprinkling systems
A. Often sprinklers can be downsized or even eliminated when the roof structure is built from completely non-combustible materials. There is nothing to burn!g
7. Compatible with almost any decking/roofing systemA. There are fastening methods that can effectively handle
connections to everything from plywood and metal deck to unique materials like Structural Insulated Panels or SIPs.
8. Relieves design firms of costly, time consuming roof design work--frees them up for more productive endeavorsA. Because the design software handles the engineering, sizing
of materials and calculation of loads, architects and engineers can simply specify that LGSTs be used, provide the b i d i it i d fil Th t d i t k basic design criteria and profiles. The truss designer can take it from there.
LGST are an ideal substitute for…
Bar Joists
Red IronConcrete
Fire Retardant Retardant Wood
Almost any Configuration is Possible…y g
Radius forms
Bow string trusses
Scissor trusses
Almost any Configuration is Possible…
The LGST Marketplace
The Market Today- Commercial/Institutional
I t d ’ k t th b t j t t t k d t f
y /
• In today’s market, the best projects to take advantage of LGSTs are commercial and institutional projects. These are typically large projects in diverse market segments.
• Sloped roofs are in the architectural favor allowing the water • Sloped roofs are in the architectural favor, allowing the water to drain from the roof area and reducing the chance for leaks.
• Tighter code enforcements are requiring that more and more structures be built with non-combustible building productsstructures be built with non-combustible building products.
• LGSTs are popular in high growth segments, areas that are seeing larger than normal construction growth.
• Although proprietary LGSTs have been in use for more than 10 Although proprietary LGSTs have been in use for more than 10 years, and C-stud trusses have been used for 30+ years, they are still considered “Up and Coming” in the design community. Certain markets have begun to embrace the features and gbenefits of LGSTs. Others still view them as new or do not know about them at all. There is still a lot of education to be done.
Applications
Applicationspp
There are many types of structures that are a natural fit with LGSTs…
We will look at a few of the most common i iapplications…
Assisted Living
These structures are a growing
g
g gmarket as our population ages. The combination of noncombustible structures and the desire for a “Residential Look” bode well for LGSTs.
Educational
Primary and secondary Primary and secondary schools as well as dorms and university buildings all present a great opportunity for sloped a great opportunity for sloped roofs that need non-combustible structures. In addition to new construction addition to new construction, covering over flat roofs of 30 year old schools are a great option that save lots of option that save lots of money for school budgets. We will look at a case study further into the course that illustrates the opportunities for old school roofs to be changed dramatically.
Offices
Office construction is another growing opportunity for LGSTs. Again, codes require non-combustible construction. In addition, in some areas codes require office buildings to complement the surrounding architectural landscape, which may reflect residential design.
Correctional
U f t t f i t Unfortunate for society, but good for business, Correctional Facilities are another growing are another growing segment for LGSTs.
Banks/Financial
M i h d h t k ith t it i i fl !
/
Money is hard enough to keep without it going up in flames!
Non combustible materials are a must for financial institutions. Some U.S. suburban banks tend to have more of a residential look as well.
Sports/Recreational
With th i f
p /
With the increase of new stadiums for professional teams as well as the new trend of minor league trend of minor league sports complexes, this segment is also growing.
Light Industrialg
Light Industrial is another Light Industrial is another opportunity to apply the look of residential roofs to warehouse fronts and office warehouse fronts and office spaces that are part of warehouses.
Hospitality
D it th d d f th k t h it lit h ld
p y
Despite the ups and downs of the market, hospitality should always be a growing and changing industry. LGSTs provide great solutions for two building methods; as the complete roof system and by providing mansard framing to conceal air system and by providing mansard framing to conceal air handling and other mechanical devices placed on the roof.
Retail/Mansards/
When residential construction goes on the rise, strip shopping center construction often follows. LGSTs are often used to frame out these structures.
Other Building Types May Include…
Th t
g yp y
• Theaters• Military Housing• DormitoriesDormitories• Stadiums• Water Treatment Facilities• Fire Stations• Libraries
d • and so on…….
Case Studies
Case 1
Project Nursing Home of Eunice Project- Nursing Home of Eunice, Eunice, LA
70 000 ft i t d li i f ilit• 70,000 sq. ft. assisted living facility• Light gauge framing specified for
non-combustibility • Normally contractor would have • Normally, contractor would have
“stick framed” with studs• LGST fabricator designed and
produced more than 1 500 trussesproduced more than 1,500 trusses• By utilizing pre-fabricated trusses, the
contractor estimated they saved 24 man-months versus conventional man months versus conventional framing. There were a lot of savings realized, not to mention the benefits in scheduling!in scheduling!
Case 2
Project Villa Marie Asstd Living Project- Villa Marie Asstd. Living, Livonia, MI
• Five buildings totaling 35,000 ft2
• 20 year old Fire retardant wood roof trusses and plywood decking literally f lli t t b ki i falling apart--trusses breaking, sagging, decking crumbling
• Insurance company required complete l t d i f i ti replacement and or covering of existing
roof• LGST fabricator stepped in with several
innovative solutionsinnovative solutions• The utility building trusses and deck were
torn off in sections and Ultra-Span trusses installed The wood overhangs remained installed. The wood overhangs remained and were attached to steel trusses
Case 2
• The four residential units proved to be more challenging. The mechanical and electrical systems were running THROUGH th t t ! I d f • Light gauge scissors trusses
were designed to fit over the existing roof and take over
the truss system! In order for the wood trusses to be pulled, all the mechanicals would have to be pulled and the g
the load handling responsibilities. Light gauge trusses were placed over the
have to be pulled and the residents relocated during the entire process
top of the old truss system, eliminating the need to (1) remove the mechanical and electrical systems, and (2) the residents were able to remain in their homes, eliminating a l t f t ( d ) f lot of stress (and expense) for everyone!
Case 3
P j t H d T E i S h lProject- Howard T. Ennis School
• 30+ year old flat roof leaking like a sievesieve
• Additionally, school board wanted to conceal new rooftop AC units
• LGST designed at 6’ centers with • LGST designed at 6 centers with built-in mechanical space
• Single row of stub columns installed along centerline of buildingalong centerline of building
• Roof penetrations reduced from hundreds to only 50
• Entire re-roof completed in two pweeks with no class interruption
Specifying Light GaugeSpecifying Light GaugeTruss Systems
Critical Elements of a Comprehensive LGST S ifi ti
LGST hi hl i d b ildi t With t
LGST Specification
LGSTs are highly engineered building components. Without proper design, quality control, and precautions, serious problems can arise. In order to ensure that a quality product is provided, factory built trusses should be used instead of field assembledfactory-built trusses should be used instead of field assembled.
The following examples illustrate the difference between factory verses field assembly You be the judge Which fabrication verses field assembly. You be the judge. Which fabrication method would you prefer for your project?
Which is More Precise?
Field vs. FactoryField vs. Factory
ThisThis
Versus This!
Critical Elements of a Comprehensive LGST S ifi ti
I dditi t b i f t b ilt l t i i
LGST Specification
In addition to being factory-built, complete engineering and technical support is a must. All truss-to-truss, truss-to-bearing connections, and system bracing specifications must be provided by the truss supplier. Including specs for 100% mill certified steel and UL® classifications when required. These elements are critical. They must be q yspecified and enforced or someone will likely attempt shortcuts.
Cost Effective LGST Assemblies
Another benefit to specifying LGST from a proprietary supplier is the availability of UL rated t bli A bli truss assemblies. Assemblies from proprietary suppliers are able to achieve 1-2 hour ratings
ith l l f with only one layer of gypsum, compared to wood truss assemblies that must use two layers of boardlayers of board.
Typical Commercial Assembly
1 h ith l LGST t bl t
yp y
1 hour + with only one layer of Type C pitched truss with insulation on top chord
LGST systems are able to achieve the UL ratings while maintaining the typical commercial
56
top chord typical commercial practice of 48 inches on center.
3
4
1
7 8
Design of Factory-built LGST
Designing Factory-built LGST
Alth h i t t t th d
g g y
Although proprietary truss systems are a new method relative to other framing systems like red iron and bar joist, they are modeled after the wood truss industry, a strong forty-year history with a proven track record of quality and cost effectiveness. That tradition, combined with best of breed design software, makes for a very powerful tool. g y pTruss design software allows fabricators to design with speed, agility, and accuracy. Modifications can be made quickly. Full estimating capabilities allow for realistic made quickly. Full estimating capabilities allow for realistic budgets and fine tuned estimates. CAM and management tools are also a reality with truss design softwaresoftware.
There are three main steps to designing a complete truss system: Layout, a complete truss system: Layout, Design, and Cost Estimating. Most proprietary systems provide these three elements to the truss fabricator. It is the job of the fabricator to input the building information into the software.
Designing Factory-built LGST
Th f ll i i t i l f bli l bid t k
g g y
The following process is typical for publicly bid truss work:
Once the bid for trusses is awarded, engineering drawings are electronically submitted to the full service truss supplier the electronically submitted to the full-service truss supplier, the drawings are reviewed and sealed. Connections, bracing, and other special services may also be requested. At that point, the sealed component drawings are returned to the fabricator sealed component drawings are returned to the fabricator, (typically multiple copies), in less than 48 hours. Submittals are then made to the architect, contractor, and project engineer for approvalfor approval.
Parameters Effecting LGST Cost
Design Features Impacting Truss Cost
Roof pitch and heel height are two of the Truss Cost vs. Span
6" Heel Height, Variable Roof Pitch
g p g
most critical elements that can effect the cost of a truss system. Based on these graphs which have been developed over
5.50
6.50
7.50
8.50
ost,
$ pe
r sq
ft
2:12
3:12
a period of several years, you can see that as span increases, steeper slopes are able to keep the costs lower. Also, i i th h l h i ht ll f
1.50
2.50
3.50
4.50
Trus
s M
ater
ial C
o
4:12
5:12
6:12
increasing the heel height allows for a more efficient and therefore more cost effective design.
20 30 40 50 60 70
Span, f t
Truss Cost vs. Span10" Heel Height, Variable Roof Pitch
5.005.50
ft
2.503.003.504.004.505.00
ss C
ost,
$ pe
r sq 2:12
3:12
4:12
5:12
6:12
1.502.00
20 30 40 50 60 70
Span, f t
Tru 6:12
Design Features Impacting Truss Cost
Regarding truss spacing in most cases, 48 i h t i i th t t
Truss Cost vs. SpacingVariable Pitch 10" Heel 40 ft Span
g p g
48 inch truss spacing is the most cost effective, especially when designing truss systems with slopes less than 3 on 12 The length of o erhang can also
Variable Pitch, 10 Heel, 40 ft Span
3 00
3.50
4.00
per s
q ft
2:12
3:12 12. The length of overhang can also play a role in the cost of the truss system. As overhangs reach 3 feet, the cost of the each truss increases 1 50
2.00
2.50
3.00
Trus
s C
ost,
$ p 3:12
4:12
5:12
6:12
the cost of the each truss increases dramatically.
1.502 4 6
Truss Spacing, f t
Truss Cost vs. Overhang SizeVariable Pitch, 10" Heel, 20 ft SpanVariable Pitch, 10 Heel, 20 ft Span
3 804.204.605.005.40
per s
q ft
2:12
3:12
1 401.802.202.603.003.403.80
Trus
s C
ost,
$ p
4:12
5:12
6:12
1.400 1 2 3 4 5
Overhang Length, f t
Design Features Impacting Truss Cost
Concerning the debate of h th t t dd i t l
Truss Cost vs. SpanVariable Pitch, No Interior Bearings
g p g
whether or not to add internal bearings, one can see that the cost of adding one bearing can more than pay for itself
g
5.00
5.50
6.00
per s
q ft
2:12
3:12p ycomparing the overall cost of the truss system. For instance, a truss with a clear span of 70 feet and slope of 5 on 12 will 2 50
3.00
3.50
4.00
4.50
Trus
s C
ost,
$ p 3:12
4:12
5:12
6:12
feet and slope of 5 on 12 will cost approximately $4.60.
2.5050 60 70
Span, f t
Truss Cost vs. SpanVariable Pitch, One Interior BearingVariable Pitch, One Interior Bearing
2.702.903.103.30
per s
q ft
2:12
3:12
By adding one internal bearing, the cost of the same truss drops to less than $2 50! That’s quite a savings
1.701.902.102.302.50
Trus
s C
ost,
$ p 3:12
4:12
5:12
6:12
$2.50! That s quite a savings. Just because LGSTs can span 80+ feet, it isn’t always the best option.
1.5050 60 70
Span, f t
Design Features Impacting Truss Cost
Long overhangs can add Truss Material Cost vs. Wind Speed4:12 Pitch, 40 ft Span, No Overhang
g p g
g gsubstantial costs, especially in high wind load zones. It is interesting to note that in either case, the Main
3 5
4
4.5
er s
q ft
Wind Force design method is less costly than designing using components and cladding.2.5
3
3.5
Trus
s C
ost,
$ pe
MWFRS
C&C
2110 130 150
Wind Speed, mph
Truss Material Cost vs. Wind Speed4:12 Pitch, 40 ft Span, 3 ft Overhang
5
5.5
6
6.5t,
$ pe
r sq
ft
2 5
3
3.5
4
4.5
russ
Mat
eria
l Cos MWFRS
C&C
2
2.5
110 130 150
Wind Speed, mph
Tr
Design Features Impacting Truss Cost
Minor changes in profile can also cut costs while making very
g p g
Minor changes in profile can also cut costs while making very little change to the overall design of the structure. Looking at this example, the truss on the left provides the same interior slope, yet saves $165 per truss because of the elevated heel and slope, yet saves $165 per truss because of the elevated heel and slightly higher exterior slope. By adding some space within the truss, loads are able to be distributed much more efficiently. This truss also performs much better, allowing the building much less p g gdeflection in all directions.
Truss Cost = $583.00 Truss Cost = $748.00
Environmental Benefits of LGST
L.E.E.D. Certification with LGST
Li ht t l t ll t d t f t d Light gauge steel trusses are excellent products for use toward achieving certification through green building rating programs such as LEED. Because light gauge steel products are up to 100% recycled and recyclable, they help to increase the chance of receiving Material and Resource Credits. The number and category of credits that steel trusses helps in contributing to varies depending on the structure of the rating system being applied. Another potential area of contribution include regional material production and fabrication in relation g pto the jobsite depending on location. Other sustainable advantages could be realized through the use of steel trusses, but must be decided by the design team or green rating but must be decided by the design team or green rating system expert.
Fabrication
Fabrication Guidelines
Now we are going to go into more depth about the advantages Now we are going to go into more depth about the advantages of factory fabricated LGSTs. Trusses can be built and staged in conjunction with the schedule of the rest of the project. Trusses can be delivered in stages as they are needed for erection. g yFactory built trusses can be built to exact design parameters. Because of the factory setting, supervisors can manage and control multiple projects within the factory, contrasted to an occasional jobsite visit to check quality of work. In addition, those who are building trusses are truly “Truss Professionals.” It’s what they do. They aren’t building trusses one day and hanging drywall the next. Jig assemblies are utilized in factories to be sure that the last truss in a run matches all other trusses in the same run. Quality is further enhanced due to a controlled environment. On the j b it lit li lt f “Th El t ” Sh t t jobsite, quality may slip as a result of “The Elements.” Shortcuts may be used when temperatures drop or when rain starts to fall. There are also services being developed that can provide third party quality guidelinesparty quality guidelines.
Assembly Methods for LGST
Uni-Strut jigs
y
Laser set-upUni Strut jigs
G t T blGantry Tables
Plywood TablesPlywood Tables
Shipping
LGST Shipping Basics
Trusses are typically shipped on flat bed trailers Typically 48 to
pp g
Trusses are typically shipped on flat bed trailers. Typically 48 to 50 foot maximum length and 8 to 10 foot maximum width without permits and escorts. Trusses up to 80 feet long and 20 feet tall can be shipped with special accommodations. feet tall can be shipped with special accommodations. However, “piggy backing” & split trusses are more common. Some fabricators will ship vertically with a low trailer when possible. Wood truss “roll off” trailers can be used when trusses pare adequately protected from damage. Coordination between fabricator and job site for proper sequencing is vital.
LGST Shipping Techniquespp g q
These photos illustrate several examples of trusses shipped correctly.
Hoisting and Installation
Installation Fundamentals
Hoisting and installation are critical elements to the success of Hoisting and installation are critical elements to the success of LGSTs. With proper precautions taken, installation should be smooth and uneventful.
Installation Fundamentals
O t f th t One great resource for the truss industry is “The Field Installation Guild for Cold-Formed Steel Roof Trusses ” This document is Trusses. This document is available through the LGSEA, a division of the Steel Framing Alliance Alliance. www.steelframingalliance.comIt is a great resource for many elements of truss installation, such as permanent truss bracing.
Hoisting
N t t b i thi i h th k t f l i t ll ti
g
Next to bracing, this is perhaps the key to successful installation.There are so many ways to do it wrong, and only a couple of ways to do it right.
This is how NOT to do it This is how NOT to do it...
Hoistingg
THERIGHT WAY
A spreader bar and…
WAY
A i d LGST I t llAn experienced LGST Installer
Pre-assemblies
bli th d ti t id h Pre-assemblies are another good option to consider when planning the truss install. Depending on available space, this option makes a lot of sense, allowing workers to stay close to the
d i t d f ki f fi t i O th t ground instead of working from five stories up. Once the trusses are erected, braced and sometimes decked, the entire roof is lifted (or flown) into place. This also allows crane time to be reduced from weeks to days or even hours! Another great way reduced from weeks to days or even hours! Another great way to save money.
A Great Idea for…
• Tall buildingsg• Unusual site conditions• Job sites with ample space• When crane time is costly• When time is of the essence
Comparing LGST Proposals
Comparing Proposals
Th i id ti b f i h
p g p
These various considerations can become very confusing when the truss customer has to compare and contrast five to ten different truss packages. Each truss supplier will provide different elements at different prices and many will leave out certain elements at different prices and many will leave out certain pieces of the package. Come bid day, it becomes very challenging to determine the best package deal.
Comparing Proposals
With the growth in the specification of LGST’s there has been a
p g p
With the growth in the specification of LGST s, there has been a proliferation in the number of truss fabricators
• Barriers to entry are lowBarriers to entry are low non-capital intensive limited real estate requirements low skilled labor
I t i i / hit t till ll i j b it In certain areas, engineers/architects still allowing job site fabrication
• Third party software available for simple truss analysis• Absence of industry standardsAbsence of industry standards• The result can be multiple bids on same project
A recent large project in TN attracted 12 truss bids
Comparing Proposals
With t ti l
p g p
With so many potential truss bidders, how is one to choose?one to choose?
Comparing Proposals
The answer is to understand
p g p
The answer is to understand what elements make up a complete truss systemp y
Make sure you & Make sure you are not comparingapples to oranges
&pp g
Comparing Proposals
A l t LGST S t t i l d
p g p
A complete LGST System must include...
• Properly designed trusses• Truss to truss connections• Truss-to-truss connections• Truss-to-structure connections• Installation bracing• Permanent bracingPermanent bracing• Let’s look at each item in more detail….
Properly Designed Trusses
Properly Designed Trusses
Aft h t i d i d tl th t t b
p y g
After each truss is designed correctly, the system must be designed to work as a whole.
Engineering DrawingEngineering DrawingJob Name
Quantity of trusses
Number of pliesJob Name
Quantity of trusses Number of plies
There are a lot of elements that go into a correctly designed truss.g g gg g gTruss ID
Quantity of trusses
Truss Dimensions
Truss ID
Number of plies
I di t
Truss Dimensions
Overall truss
Number of screws required at each connection
Truss slope
Indicates lateral web
brace locations
Overall truss height
Truss slope
Indicates lateral web
brace locations Number of
screws required at each connectiontruss
heightconnection
Heel Truss Loading
connection
Heel Height
HeightTruss Loading Deflection Information
Truss Spacing Applicable
code Combined
Fastener Values
D fl ti I f
Truss weight
Combined Stress Index
Applicable code
Truss Spacing
Fastener Values
code
Steel sections
Combined Stress Index
Bracing Requirements
Deflection Info
Steel sectionsBracing Requirements
Truss Reactions
Truss Reactions
Bracing Requirements
Individual member forces
Individual member forces
forces
Truss-to-Truss Connections
Truss-to-Truss C ti
These connections are
Connections
• These connections are critical to the proper functioning of the truss systemsystem
• Connections must safely transfer all loads into girder trussesgirder trusses
• They must resist uplift as necessary
• You must insist that the You must insist that the truss designer provide for these connections (ANSI TPI 95)( )
If a LGST provider declines to provide these connections DO NOT connections, DO NOT ACCEPT THE PROPOSAL!
Trust-to-Structure Connections
Truss-to-Structure Connections
M k ifi ti t t l l hi h t h Make sure specifications state clearly which party has responsibility for design and provision of these critical connections! If the bid does not discuss this element, chances are high that it will not be a part of the truss package will not be a part of the truss package.
Insist that all truss suppliers provide all truss-to-structure connections connections.
Truss-to-Structure C tiConnections
h iti l t th • These are critical to the proper functioning of the truss system
• Resisting upliftA h t t t t• Anchors trusses to structure
• Designer must account for bearing surface, attachment techniques and existing field techniques, and existing field conditions
• “Standard” details useful, but “Special” details become Special details become critical, especially in high wind zones
• Typically designed by truss Typically designed by truss engineer
Truss Bracing
The Cardinal Rules of Truss Bracing
E ll i t t t th t th l i th t b i
g
Equally important to the trusses themselves is the truss bracing, both installation and permanent.
• Rule # 1• Rule # 1 ALL truss systems require bracing--PERIOD!!
• Rule #2• Rule #2 Failure to adhere to Rule #1 is the primary reason for truss
collapses (typically during installation)
• Rule #3 Disputing Rules #1 and #2 displays an absence of
knowledge of how truss systems functiong y
The Cardinal Rules of Truss Bracing
lt t f O
g
Resultants for NOTfollowing Rule #2
Trusses that had insufficient insufficient bracing
Types of Truss Bracing
I t ll ti B i
yp g
• Installation Bracing Lack of installation bracing is the reason for virtually all
roof collapses during construction Sometimes referred to as “temporary” or “erection” Sometimes referred to as temporary or erection
bracing
• Permanent Bracing• Permanent Bracing Provides for web bracing, shear diaphragm transfer,
and overall roof system stability Sometimes referred to as “Wind Bracing” Sometimes referred to as Wind Bracing
Installation Bracing
I t ll ti b i i j t th i li b i th t k
g
Installation bracing is just as the name implies, bracing that keeps the trusses in place during installation. There are three parts to it, top chord bracing, bottom chord bracing, and web bracing. Each is critical to the system In addition diagonals must also be Each is critical to the system. In addition, diagonals must also be used in each location. It is said that without diagonal braces, all the trusses simply fall the same direction. Don’t forget the diagonals! Some “temporary” or installation bracing may actually diagonals! Some temporary or installation bracing may actually remain in the system and serve as permanent bracing.
Guidelines published by LGSEA
• Ground bracing• Top chord bracing
Keeps chords in lineB h d f b kli Braces chords from buckling
• Bottom chord bracing Keeps chords in line
• Web plane bracingp gHelp stabilize the entire system prior to decking
Field Installation Guide for Cold-Formed Steel Trusses
The Field Installation Guide for Cold-Formed Steel Trusses, provided by the Light Gauge Steel Engineers
i i iAssociation, goes into great detail about the bracing required for ttrusses.
Permanent Bracing
P t b i i th t hi h i i l ft th
g
Permanent bracing is that which remains in place after the trusses are erected. This bracing is designed to keep the trusses in plane as loads are applied, preventing the chance for out of plane buckling Again don’t forget the diagonals!plane buckling. Again, don t forget the diagonals!
Permanent Bracing
P t B i
g
Permanent Bracing• Top Chord
Typically direct applied deck Could be purlins 24” o.c.
Bottom Chord Can be rigid ceiling directly appliedg g y pp 24” o.c. purlins with drywall Drop ceilings will require user defined spacing for lateral
bracingg Typically 6’ to 8’ o.c.
Don’t forget the diagonal bracing! Web Plane Web Plane
Lateral Bracing Be sure webs line up--otherwise, T-bracing will be
requiredrequired Diagonals are essential
Who has responsibility for Permanent B i D i ?
B f th i t f h t j t th b t
Bracing Design?
Because of the unique nature of each truss project, the best way to assure that the bracing is handled correctly is to provide a permanent bracing design. According to typical protocol, this responsibility falls on the Engineer of Record They know the responsibility falls on the Engineer of Record. They know the overall building design and understand how the building components are to be integrated. However, because of the various structural properties and unfamiliarity he or she may have various structural properties and unfamiliarity he or she may have with proprietary LGSTs, the job may be best addressed by the truss engineer. Regardless of who provides it, be sure the specification calls for itspecification calls for it.
Bracing Details
Th f ll i l f i d b i d i
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The following are examples of an engineered bracing design. One shows the permanent web bracing required, the other is a sheet of additional details that must be a part of the bracing layoutlayout.
Bracing Designg g
Bracing Designg g
The Future forThe Future forLight Gauge Steel Trusses
What Will Drive the Use of LGST
I i l t i t fi d• Increasingly stringent fire codes• Building designers love the features & benefits• More cost effective than traditional materials• Ever improving software fabrication techniques and • Ever improving software, fabrication techniques, and
accessories• Architects and engineers looking for ways to get the job done
faster and more effectivelyfaster and more effectively• The trend for pre-fabricated components continues to increase
In Conclusion…
Specifiers and contractors can separate apples from Specifiers and contractors can separate apples from oranges by…
• Clearly defining which party is responsible for which • Clearly defining which party is responsible for which portion of the truss system—Put it in the specification
Don’t forget to identify responsibility for other ancillary items such as:items such as:Shear blocking and transfer framing, bent metal
for deck support, fascia material, and over-framing• Doing a little homework on prospective truss providersDoing a little homework on prospective truss providers• Understanding truss nomenclature• Thoroughly evaluating proposals and bids
Don’t just grab the lowest number and run with itj g• Being cautious of the term “Value Engineering”• Communicating!!!
In Conclusion…
C b iblFor Non-CombustibleCommercial/Institutional Construction...
Light Gauge Steel Trusses are a great alternative...
Summaryy
Th D i P f i l h ld b bl tThe Design Professional should now be able to:
• Explain why Light Gauge Steel Trusses are a Good Alternative SolutionSolution
• Explain applications for Proprietary LGST• List and describe Case Studies• Specify LGST• Specify LGST• Describe the design process for Factory-built LGST• Explain: Fabrication, Packaging, Shipping, & Installation of
Factory-built LGSTFactory built LGST• Compare and contrast an LGST proposals and explain what
makes a complete truss system
Links to more information about LGST
Li ht G St l E i A i ti (LGSEA) • Light Gauge Steel Engineers Association (LGSEA): www.lgsea.com
