moment resisting frames - part2
TRANSCRIPT
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Strategies for Improved Performance of Moment
Connections:
WELDING
Required minimum toughness for weld metal:
Required CVN forall welds in SFRS:20 ft.-lbs at 00 F
Required CVN forDemand Criticalwelds:40 ft.-lbs at 700 F
ANSI/AISC 341-10 Section A3.4
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WELDING
Improved practices for backing bars and weld tabs
Typical improved practice:
Remove bottom flange backing bar
Seal weld top flange backing bar
Remove weld tabs at top and bottom flange welds
Greater emphasis on quality and quality control (AISCSeismic Provisions Chapter J)
Strategies for Improved Performance of Moment
Connections:
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Typical Pre-Northridge
Bottom Flange Weld
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Improved POST-Northridge Bottom Flange Weld
Weld tabs andrunoff regions
removed; ground
smooth
Back-up bar removed; root visually
inspected, defects removed; smallreinforcing fillet weld placed at
bottom of groove weld
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Typical Pre-Northridge
Top Flange Weld
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Improved POST-
Northridge Top
Flange Weld
Weld tabs and
runoff regions
removed;
ground
smooth
Back-up bar left in place; smallfillet weld placed between bar
and column face
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Strategies for Improved Performance of Moment
Connections:Materials (Structural Steel)
Introduction of expected yield stress into designcodes
Fy = minimum specified yield strength
Ry = 1.5 for ASTM A36 (hot-rolled shapes and bars)= 1.1 for A572 Gr. 50 and A992
Expected Yield Stress = Ry Fy
ANSI/AISC 341-10 Table A3.1
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Strategies for Improved Performance of Moment
Connections:
Materials (Structural Steel)
Introduction of ASTM A992 steel for wide flangeshapes
ASTM A992
Minimum Fy = 50 ksi
Maximum Fy = 65 ksi
Minimum Fu = 65 ksi
Maximum Fy / Fu = 0.85
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Pre-Northridge
Improved
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Strategies for Improved Performance of Moment
Connections:
Connection Design
Development of Improved Connection Designsand Design Procedures
Reinforced Connections
Proprietary Connections
Reduced Beam Section (Dogbone)Connections
Other SAC Investigated Connections
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Reinforced Connection
Cover-Plated
Connection
Cover plates fillet welded
to beam flanges, thencombinedbeam flange
and cover plate groove
welded to face of column
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Cover-Plated Connection
Improvedperformance in
general, but
costly to
construct
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Cover-Plated Connection About 2/3 of specimensdeveloped total plasticrotation of 0.03 radwithout brittle fracture
(strong panel zone) Others, panel zone
yielding dominatedresponse
2 specimens with boltedwebs failed in brittlemanner (< 0.02 radplastic rotation)
Brittle fracture inspecimen for whichwelding procedure notenforced
Failure in specimen withLONG cover plate
Not sufficiently
reliable?
Susceptible to sameproblems of weld
quality and through-
thickness behavior of
column flange?
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Reinforced Connection
Flange Rib
Connection
Like cover-plated connection,
connection is stronger than
beam, plastic hinge formation
forced away from face of
column
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Flange RibConnection
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Lee, C.H. et al. (2005) Experimental Study of Cyclic Seismic Behavior of
Steel Moment Connections Reinforced with Ribs, Journal of Structural
Engineering, Vol. 131, No. 1, January 1, 2005
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Reinforced Connection
Haunched
Connection
May be at bottom flange or
both top and bottom flanges
Initially tested as four pre-Northridge connections
repaired with bottom
triangular T-shaped haunches
H h d C ti
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Haunched Connections
Generally good
performance inlaboratory
Costly to construct
Not included asprequalified for newbuildings in FEMA350
Recommended SeismicDesign Criteria for NewSteel Moment-FrameBuildings(2000) More on FEMA 350 later
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Reduced Beam
Section (RBS)
Also called Dogbone
connection; less costly, simplerthan reinforced connections
Forces hinge formation to
occur within reduced section
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RBS has become one of the most common moment
connection details used in current practice.
(More details later )
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Proprietary Connection
Side Plate
Connection
Beam flanges NOT directly
welded to column flanges;
forces transferred through sideplates.
http://www.sideplate.com/
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Connections Investigated Through
SAC-FEMA Research Program
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Reduced Beam
Section (RBS)
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WeldedUnreinforced
Flange - Bolted
Web (WUF-B)
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Welded
Unreinforced
Flange - Welded
Web (WUF-W)
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Free Flange
Connection
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Bolted Unstiffened
End Plate
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Bolted Stiffened
End Plate
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Bolted Flange
Plate
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Double Split Tee
Typically treated
as a partially-
restrainedconnection
(effects of
connection
flexibility must
be included inoverall frame
analysis).
R lt f SAC FEMA R h P
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Results of SAC-FEMA Research Program
Recommended Seismic Design Criteria
for Steel Moment Frames FEMA 350Recommended Seismic Design Criteria for New Steel Moment-
Frame Buildings
FEMA 351Recommended Seismic Evaluation and Upgrade Criteria for
Existing Welded Steel Moment-Frame Buildings
FEMA 352Recommended Postearthquake Evaluation and Repair Criteria
for Welded Steel Moment-Frame Buildings
FEMA 353Recommended Specifications and Quality Assurance
Guidelines for Steel Moment-Frame Construction for Seismic
Applications
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FEMA 350
Nine momentconnection details just
shownprequalifiedconnections
Recommended designprocedures, limits of
usage (e.g., OMF only,W36 beams andshallower, flange
thickness limits, webconnection, etc.)
Not a standard; butstill a valuable
reference
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New standardReplaced FEMA 350
Prequalifiedrigorousprogram of testing, analytical
evaluation and review by theconnection prequalificationreview panel (CPRP).
Reduced Beam Section(RBS)
Bolted Stiffened andUnstiffened Extended EndPlate
ANSI/AISC 358-05
Connection Prequalification
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Connection Prequalification
AISC Connection Prequalification
Review Panel ANSI/AISC 341-10 Chapter K
Connections shall be prequalified based on
test data satisfying Section K1.3, supportedby analytical studies and design models.The combined body of evidence must besufficient to assure that the connection can
supply the required story drift angle forSMF and IMF systems . on a consistentand reliable basis within the specified limitsof prequalification.
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ANSI/AISC 358-10
Proprietary Connections
Reduced Beam Section (RBS)
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Reduced Beam Section (RBS)
Bolted Unstiffened Extended End Plate (BUEEP)
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Bolted Unstiffened Extended End Plate (BUEEP)
Bolted Stiffened Extended End Plate (BSEEP)
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Welded Unreinforced Flange Welded
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Welded Unreinforced FlangeWelded
Web (WUF-W)
Kaiser Bolted Bracket (KBB)
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Kaiser Bolted Bracket (KBB)
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Steel Connections: Proprietary or Public Domain? by P. Cordova & R.
Hamburger, Modern Steel Construction, October 2011
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Experimental Evaluation of Kaiser
Bolted Bracket Steel Moment-Resisting Connections
Scott M. Adan and William Gibb
AISC Engineering Journal 2009
http://www.steelcastconnections.com/
ConXtech ConXL moment connection
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ConXtech ConXL moment connection
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http://dcm-designs.com/steel-prefabricated-moment-frame/
This innovative
connection system
enables beams to besimply lowered and locked
onto square columns in
the field, resulting in a
dimensionally accuratestructural chassis. The
system is often referred to
as a full-scale erector set.
http://www.conxtech.com
/conx-system/
VIDEO CLIP
Connections in process of prequalification
http://www.conxtech.com/conx-videos/introduction-to-conxtech/http://www.conxtech.com/conx-videos/introduction-to-conxtech/ -
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Connections in process of prequalification
Double Tee
Simpson Strong Frame SENSE TSC
Side Plate
SOM Pin Fuse Joint
Double Tee
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Double Tee
http://www.aisc.org/uploadedcontent/2012NASCCSessions/N11/
Simpson Strong Frame (Yield Link)
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Simpson Strong Frame (Yield Link)
http://www.aisc.org/uploadedcontent/2012NASCCSessions/N11/
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SidePlate
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SidePlate
http://www.aisc.org/uploadedcontent/2012NASCCSessions/N11/
SOM Pin Fuse Joint
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SOM Pin Fuse Joint
Steel Connections: Proprietary or Public Domain? by P. Cordova & R.
Hamburger, Modern Steel Construction, October 2011
SOM Pin Fuse Joint
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SOM Pin Fuse Joint
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http://www.som.com/content.cfm/pin_fuse_joint
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A number of
experiments havebeen conducted
with specimens
with weak panel
zones
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Very weak panel
zone; localizedkinks cause
strain
concentrations,
ultimately leadingto fracture in
vicinity of beam
flange groove
welds.
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Same specimen
as previous slide.
Connection failed
at moment well
below Mp
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"kink" at corners
of panel zone
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-1200
-800
-400
0
400
800
1200
-0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08
Panel Zone g (rad)
PanelZoneShe
arForce(kips)
Composite RBS Specimen with
Weak Panel Zone
g
Observations on Panel Zone Behavior
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Very high ductility is possible.
Localized deformations (kinking) at cornersof panel zone may increase likelihood offracture in vicinity of beam flange groovewelds.
Current AISC Seismic Provisions permitslimited yielding in panel zone (SpecificationJ10.6 for available strength)
Further research needed to better defineacceptable level of panel zone yielding