Rm 5 Eikenberry - Understanding Restraint Rod Systems ... · Understanding Restraint Rod Systems Shear Wall Overturning vs. Wind Uplift and how to design them properly Alicia Eikenberry,
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
WELCOME!
Welcome! We will begin in a few minutes.
Pl d b i d d i h b lPlease drop a business card or name card in the bowlby the sign in table for today’s drawing.
Copyright Materialspy g
This presentation is protected by US and International Copyright laws ReproductionInternational Copyright laws. Reproduction,
distribution, display and use of the presentation without written permission of the speaker is
The “Wood Products Council” is a Registered Provider with TheAmerican Institute of Architects Continuing Education Systems(AIA/CES). Credit(s) earned on completion of this program will bereported to AIA/CES for AIA members Certificates of Completion forreported to AIA/CES for AIA members. Certificates of Completion forboth AIA members and non AIA members are available upon request.
This program is registered with AIA/CES for continuing professionaleducation. As such, it does not include content that may be deemedor construed to be an approval or endorsement by the AIA of anymaterial of construction or any method or manner of handling, using,distributing, or dealing in any material or product.distributing, or dealing in any material or product.
Questions related to specific materials, methods, and services will beaddressed at the conclusion of this presentation.pThis course offers 1LU/HSW Credit.
Learning Objectives
Upon completing this course, you will be equipped to:
• Explain and contrast the differences between wind uplift andshear wall overturning restraint rod systems.g y
• Account for AC391 acceptance criteria in restraint rod systemdesign.
• Evaluate performance differences between all floors tied offand skipped floor shear wall overturning restraint rod
tsystems.
• Evaluate 3 different design specification methods and selectan appropriate method for any projectan appropriate method for any project.
Restraint Rod Systems
A Brief History
• Over 20 year history in the marketplace.• Address both uplift and overturning
restraint.• Evolved from early system of connectors
(metal ties,brackets or screws) to today’s systemof rods andcouplers.
• Shrinkage compensation devicesintroduced in 1998introduced in 1998.
Restraint Rod Systems
A Brief History
• “Engineering judgment” was the earlydesign guidance.
• Today uplift systems: guided by ICCy p y g yAcceptance criteria AC391 and AC316(shrinkage compensation devices).
• Today overturning systems:– designed by EOR with
manufacturer’s design input.– Guided by code reports and
id li (NDS ASTM AISC St lguidelines (NDS, ASTM, AISC SteelConstruction Manual, ACI, and IBC).
Overturning (Lateral)When a building weight cannotWhen a building weight cannotstabilize a structure under a lateralforce, it causes the structure to rotateoff its foundation.
U lift (V ti l)Uplift (Vertical)As wind flows over the roof the windcreates a strong lifting effect, muchg g ,like that of air flowing over an airplanewing.Diff t F Diff t S tDifferent Forces = Different Systems
Evaluation Reports, issued prior toA C i i b iany Acceptance Criteria being
developed for rod systems.
Newer Evaluation Reports include anew “design” section requiring thedesigner to evaluate top plateb di d fl i d h dbending, deflection, and other woodcomponent performance.
Caveat Emptor… trust but verify….Be sure your manufacturer hasevaluated the performance of thewood system, not just the rod system.
And!!
There is some additional help….
In June 2010 ICC ES passed and made effectiveIn June 2010, ICC ES passed and made effectiveAcceptance Criteria 391 for continuous rod tie down
systems for uplift.
This standard establishes the minimum levels ofperformance to meet the code’s intent.
ICC-ES AC391: CRTR and CRTS
ICC ES AC391 establishes guidelines for the evaluation of either:
ContinuousRod Tie-Down System (CRTS)
[includes•The steel componentscomprising continuous rod tiedown runs (CRTR) only.
[includes
CRTR]
•The entire continuous rod tiedown systems (CRTS), whichincludes CRTR and the light
ContinuousRod Tie-includes CRTR and the light
framed wood structure used toresist wind uplift.
Rod Tie-Down Run
(CRTR)
Specific Design Requirements of AC391
Section 1 2Section 1.2Limited to resisting roof
wind uplift in woodlight framedlight framedconstruction.
Excluded from AC391:Excluded from AC391:shear wall overturningsystems or use in coldformed steel framing.g
What’s NOT in the Code?
The building code does not define the requirements forthe wood structural system the rod system is installedwithin such as:within, such as:
• Deflection limit for top plate flat bending
• Top plate rotation
• Rod elongation
• Wood plate crushing
• Wood shrinkage• Wood shrinkage
• Bearing plates
• Anchorage capacity
But…. AC391 does establish guidelines forl i f h d f h devaluation of the wood frame system the rod
system must perform in.
Design Guidance for Wind Systems
Some manufacturers define the winduplift restraint rod components (CRTR)uplift restraint rod components (CRTR),but leave the “system” components(CRTS) design to the engineer.
Who is responsible for the design ofthe wood structural system…..
CRTR
?CRTR
CRTS? CRTS
Restraint Rod Systems forRestraint Rod Systems for Shear Wall Overturning
Overturning Restraint Rod System – System Load Path
Observe how forcesl h h denter, travel through, and
exit the shear walloverturning restraintg
system.
Overturning Restraint Rod System – System Load Path
Lateral forces are appliedt h llto shear walls.
Overturning Restraint Rod System – System Load Path
Sheathing fastenerstransfer loads into
posts, creating upwardcompression on woodcompression on woodplates and blocking as
Tied offIncremental uplift at each level istransferred directly into the
6- 2x46- 2x4
tiedown system at that level,reducing lumber/rod/plate sizes. Skipped Tied off
Rod Elongation
Skipped system: elongation accumulates at the base, damaging shearfastening, weakening system.Tied off system: elongation distributed between floors, lessening impact.
Rodl ti
divided
elongationaccumulatesat base
Tied Off SystemSkipped Floor System
Design Example
Skipped Floor System 27 k
F3=4kT3=27k
C3=13+10+4=27k 23 k
F2=10kT =27kT2=27k
C2=13+10=23k
13.5 k 13.5 k
13 k
F1=13kT1=27kC1=13k
27 k
Post axial load uplift side
Detail A
Testing Tells No Lies
Tyrell Gilb Lab Test3 Story Skipped Floory pp
Click to playvideo
Notice stud andsheathing shear failure
Design Example
All Floors Tied Off System4 k
Uplift forces
F3=4kT3=4kC =4k
14 k
10 kC3=4k
F2=10kT =10+4=14k
2 k
13 k
2 k
13 k
T2=10+4=14kC2=10k
2 k
4 k27 k
2 kF1=13k
T1=13+10+4=27kC1=13k
Detail C1
Post axial load uplift side
Detail B
Testing Tells No Lies
Tyrell Gilb Lab Test3 Story All Tied Off3 Story All Tied Off
Click to playvideo
Wood Solutions Fair Field Test
Today’s Audience Participation Question???“Are the principles of ‘All Tied Off’ support systems even loadAre the principles of All Tied Off support systems, even load
distribution, multiple points of restraint, and lateral load restraintsufficient to prevent overturning in today’s world?”
We’re going to demonstrate this principle before your very eyesg g p p y y yand let you be the judge.
Construction Stability
Skipped floor system: unstable until allSkipped floor system: unstable until allfloors are complete. Susceptible to midconstruction collapse in seismic or high
i d twind event.
Tied off system: restraint installed as eachTied off system: restraint installed as eachlevel complete, minimizing risk.
Frequency of Restraints
When no redundancy ….. One fails, all fail.
RedundancyNo Redundancy
All-Floors-Tied-Off
Accommodatesshrinkage at eachfloor independently: Lower overall cost:
Greater systemredundancy and isconsistent with typical
Reduced drift:consistent with typicaldesign load path:
Forces in the elements getsmaller as they move up thestructure:
Skipped-Floor vs. All Floors Tied-Off Summary Where does design guidance come from?
What is in the Building Code for Overturning Systems?
All parts of an overturning restraint rod except the optional take up devices.
T l t
Part of System Defined By:
Top platecapacity
NDS Supp. Tables 4A & 4B
ASTM A36 bearing stress of the plate in bendingSteel bearingplates/nuts
ASTM A36 – bearing stress of the plate in bending.AISC Steel Construction Manual Table 7 20 for heavy hexnut sizes
Steel rodcapacity
AISC Steel Construction manual, 13th Ed.
What is in the Building Code for Overturning Systems?
All parts of an overturning restraint rod except the optional take up devices.
Shear wall driftSection 4.1.3 of the AWC Special Design Provisions forWind and Seismic.
Designing and Specifying Sh W ll O t i R t i tShear Wall Overturning Restraint
Rod Systems
Manufacturer Solutions
• Multiple manufacturers design shearwall overturning restraint rod systems.
• Product solutions should addressoverturning as well as shrinkage thatoccurs at each level of a multi storystructure.
• Shrinkage compensation (take up)g p ( p)devices are one way to addressshrinkage.
• Manufacturers differentiate themselvesManufacturers differentiate themselveswith design services or product andinstallation enhancements such as colorcoded rod ends and bearing plates
Take up devicescoded rod ends and bearing plates.
Take up devices
Specification Methods
Design Professional Responsibilities
• Determine project loading and performance requirements.
• Determine best solution to meet requirements (overturning restraintrod vs. conventional holdowns and strapping.
• Stipulate (specify) these requirements on the design documents.• Review proposed solutions and shop drawings for conformance top p p g
specs and design intent.
Specification Methods
Design Review Checklist for Overturning Restraint Rod Systems
• Run type design vs. structural requirementsyp g q
• Rod manufacturer component capacity check
– Rods/steel strength and mill certs
– Bearing plate size and capacity
– Shrinkage compensation devices for compression and tension
• AC 316 compliance• AC 316 compliance
• Movement/shrinkage check including maximum rod elongation andmaximum deflection per floor
• Tension rod location check
• Drawing and calculation review
(See Design Review Checklist Handout)(See Design Review Checklist Handout)
Specification Methods
Design Considerations
Areas of concern????
– Performance of the wood structural system, not just the rodsystem
– Cost based decisions that effect product qualityProduct substitution…Grade stamps and mill certificationsplease?
– Deferred submittal…..Friend of Foe?
Specification Methods
Specification methods for overturning restraint rod systems
1. Send loads to manufacturers who optimize the runs.
a) Software analysis
b) Engineering calculations
2. Provide loads and generic specifications on drawings, thenf fsubmit to manufacturer for optimization.
3. Specify catalog runs from a product catalog.
Manufacturer can optimize runs during design review processManufacturer can optimize runs during design review process
Installation drawings and calculations typically provided for EORreview. (See sample submission set)
Conclusion
Summary
• There are two types of restraint rod systems; one for wind uplift and onefor shear wall overturning.
• Significant performance differences exist between overturning skippedfloor systems and all floors tied off systemsfloor systems, and all floors tied off systems.
• Testing rod systems for uplift has shown that by not accounting for thewood structure in designs, system performance is compromised.
• For overturning systems, manufacturer’s have a number of ways to assistthe EOR in the design and selection of the system.
Course Completion
Simpson Strong TieSimpson Strong Tie
What are your Questions?y
This concludes the American Institute of ArchitectsContinuing Education Systems course
For a library of Simpson Strong Tiey p gAIA CES courses, visit