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TRANSCRIPT
Moment Frames: Design and Detailingper AISC 341 and 358
By Matthew J. Mester, PE, SE
SidePlate Systems, Inc.
SE University, June, 2017 www.LearnWithSEU.com
Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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Learning Objectives
Identify how drift can be controlled in moment framesDifferentiate between R=3, OMF, IMF, and SMF lateral systemsIdentify when to use AISC 358 prequalified connections in moment frames
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Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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What code is required in your jurisdiction?
Lateral Analysis/Choosing your Code
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What code is required in your jurisdiction?
Lateral Analysis/Choosing your Code
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What code is required in your jurisdiction?ASCE 7-05, IBC 2006 or IBC 2009, AISC 360-05, AISC 341-05, AISC 358-05
ASCE 7-10, IBC 2012 or IBC 2015, AISC 360-10, AISC 341-10, AISC 358-10 including Supplements 1&2
Future codes: ASCE 7-16, IBC 2018, AISC 360-16, AISC 341-16, AISC 358-16 including Supplements
Lateral Analysis/Choosing your Code
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What is important in Moment Frame Design?
Drift?, Strength?, Ductility?
Lateral Analysis
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Columns
BeamsVerticalForce
LateralForce
Beam/ColumnConnection
Typically, DRIFT will govern the design of moment frames, not STRENGTH, but must check bothWhat governs drift in Moment Frames?
Rotation of beamsRotation of columns
Base conditionsDeformation of panel zones
To limit drift, you can increase beams, columns, or panel zone thickness…BUT you will have the most success with increasing BEAM size
Lateral Analysis
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Drift Limits for Wind ProvisionsWhat is required? Is it the Law?
IBC 1604.3 Serviceability: “Structural Systems shall have adequate stiffness to limit deflections and lateral drift.”ASCE 7-10 §1.3.2 Serviceability: “Structural systems, and members thereof, shall be designed to have adequate stiffness to limit deflections, lateral drift, vibration, or any other deformations that adversely affect the intended use and performance of buildings and other structures.”
Lateral Analysis for Wind Loads
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What is required? Is it the Law?ASCE 7-10 §C1.3.2 Commentary Appendix C –Serviceability Considerations (non-mandatory): “Serviceability limit states involve the perceptions and expectations of the owner or user and are a contractual matter between the owner or user and the designer or builder. It is for these reasons, and because the benefits are often difficult to define or quantify, that serviceability limit states for the most part are not included within the model United States Building Codes.”
Lateral Analysis for Wind Loads
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How do you select drift limits?AISC Design Guide 3 – Serviceability Design Considerations for Steel Buildings by West & Fisher
H/400, H/500, H/600 for frames with spandrel supported cladding depending on type of exterior system using a 10-year wind MRI
Lateral Analysis for Wind Loads
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How do you select drift limits?“Serviceability Limit States Under Wind Loads” by Lawrence G. Griffis, EJ AISC, v30, 1993 Q1
H/400 for steel frames (H=story height and total height)H/400 corresponds to 1/4” in 8’ (the damage threshold limit for gypsum wallboard), or 3/8” in 12’ which corresponds to standard soft joint thickness in brick veneer construction.
Lateral Analysis for Wind Loads
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Wind Speed Maps in ASCE 7-10 Commentary, App C
Lateral Analysis for Wind Loads
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Drift Limits for Seismic Provisions (ASCE 7 Table 12.12-1)
Maximum drift based on ASCE 7 provisions
Lateral Analysis for Seismic Loads
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d xex
CI
The R Factor in Moment Frame Design
ASCE 7 Design Coefficients (ASCE 7 Table 12.2-1)
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Seismic Design Principles
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Response Spectrum of MRFs
Reduction in Response Spectrum based on type of system used and its R factor
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Design Ground Motions
0
0.2
0.4
0.6
0.8
1
1.2
0 0.5 1 1.5 2 2.5 3
Period, T
Res
pons
e Ac
cele
ratio
n, g
Poll Question
The element to increase in size to most efficiently help you control drift in a moment frame is:
The Type of Weld Used in a ConnectionBeamsContinuity PlatesDoubler Plates
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Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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R=3 Moment Frame Systems
Not required to be designed for seismic resistanceTypically wind governed structureMembers (beams, columns, connections) designed for the LRFD or ASD load combinations in the building code LRFD ASD
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R=3 Moment Frame Systems
When are they allowedSeismic Design Category A, B, and C with no limits on heightStill must check some of the seismic requirements in Chapter 12 of ASCE 7
Overstrength Factor = 3Deflection amplification Factor = 3
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R=3 Moment Frame Systems
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R=3 Moment Frame Systems
Use of AISC 360 for design of beams, columns, and connection elementsConnections designed for LRFD or ASD load combinationsTypically, EORs will delegate the connection design to fabricators with their in-house/connection design engineerEORs need to show/give design loads on drawings and indicate which force level shears and moments are shown
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Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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R=3.5 OMFs
When are they allowedSDC A, B, C with no restrictions
ASCE 7-10, Section 12.2.5.6Limitations on SDC D, E, and F: Allowed for lighter buildings Typically allowed up to 65 feet in height, but weight no more than 20 psf for floors and walls tributary to OMFMostly single story frames unless under 35 feetPermitted in light frame construction up to 35 feet where floor/roof load does not exceed 35 psf and wall load does not exceed 20 psf
Overstrength Factor = 3Deflection amplification Factor = 3
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R=3.5 OMFs
Provides minimal inelastic deformation capabilitiesNo width-thickness ratios of members beyond what is required in AISC 360No protected zones on beamNo strong column-weak beam requirementsNo lateral bracing requirements except as required to meet AISC 360Must use Demand Critical Welds between beam flange and column where applicableConnection may be fully restrained(FR) or partially restrained (PR)
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R=3.5 OMFs
FR Connection must be designed for: Flexural strength of 1.1*Ry*Mp
Shear load of maximum moment from connection, Ev = 2[1.1*Ry*Mp]/Lcf
OR maximum flexural & shear load that can be delivered to the system based on strength of column/foundation upliftPanel zone requirements of Section J10.6 of AISC 360Continuity plate requirements of Sections J10.1-10.3 of AISC 360
PR Connections must be designed for minimum of:50%*Mp of beam for flexural strengthShear strength similar to FR OMF connection
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R=3.5 OMFs
When would you use an OMF in practice?Local code requires its use over R=3 systemEngineer wants to specify over IMF to avoid requirements in AISC 341At a connection where capacity of beam is required by code (ie. BRBF beam to column connection)Engineer wants control over lateral joint design/does not want to specify moments and shears at all lateral jointsLight gage/residential structure or small enclosed mechanical room at top of a building
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R=3.5 OMFs
Example of what an OMF looks like in practice
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Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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R=4.5 IMFs
When are they allowedASCE 7-10, Section 12.2.5.7
Limitations on SDC D: 35 feet in height or lighter buildingLimitations on SDC E, and F: lighter buildings Typically allowed up to 65 feet in height, but weight no more than 20 psf for floors and walls tributary to IMFMay be multi story frames in certain situationsPermitted in light frame buildings up to 35 feet where floor load does not exceed 35 psf and wall load does not exceed 20 psf
Overstrength Factor = 3Deflection amplification Factor = 4
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R=4.5 IMFs
Provides limited inelastic deformation capabilitiesMembers must meet moderately ductile requirements within AISC 341Protected Zone requirements exist on beam/connectionNo strong column-weak beam requirementsLateral bracing requirements exist…~100*ry of moment frame beam for fy = 50ksi for moderately ductile beamsMust use Demand Critical Welds for:
Between beam flange and column where applicableColumn splice groove weldsWelds between column and base plate
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R=4.5 IMFs
Connection must be able to sustain story drift angle of 0.02 radians and flexural resistance must be 0.80*Mp at the 2% radiansRequired shear strength of connection:
Ev = 2[1.1*Ry*Mp]/Lh
Connections within AISC 358 may be used to justify conformance to performance requirementsPanel zone requirements similar to OMFs, Section J10.6 of AISC 360Continuity plates must follow requirements of SMF section
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R=4.5 IMFs
When would you use an IMF in practice?Local code mandates a minimum R valueSDC D with building no taller than 35 feet, BUT do not want to or cannot achieve SCWB, lateral bracing, provisions of AISC 341Short spans with Deep Beams, connections each have a span/depth ratio found in AISC 358Want to specify a connection on your drawings and get a small break in design spectrum, R=3.5 vs R=4.5Not very common…
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R=4.5 IMFs
Example of what an IMF looks like in practice
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Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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R=8 SMFs
When are they allowedAlways allowed…but can you get drift to work in your moment frame?
ASCE 7-10, No Limits on any height buildings
Overstrength Factor = 3Deflection amplification Factor = 5.5
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R=8 SMFs
Provides significant inelastic deformation capabilitiesMembers must meet highly ductile requirements within AISC 341Protected Zone requirements exist on beam/connectionStrong column-weak beam requirements existLateral bracing requirements exist…~50*ry of moment frame beam for fy = 50ksi for highly ductile beamsMust use Demand Critical Welds for:
Between beam flange and column where applicableColumn splice groove weldsWelds between column and base plate
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R=8 SMFs
Strong Column Weak Beam Requirements…why?
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Plastichinges
Deformed frame shape
Undeformedframe
L’
L
h
Drift angle -
Plastichinges
Deformed frame shape
Undeformedframe
L’
L
h
Drift angle -
R=8 SMFs
Connection must be able to sustain story drift angle of 0.04 radians and flexural resistance must be 0.80*Mp at the 4% radiansRequired shear strength of connection:
Ev = 2[1.1*Ry*Mp]/Lh
Connections within AISC 358 may be used to justify conformance to performance requirementsPanel zone requirements thickness based on t>(dz+wz)/90, doubler plates typically requiredColumn bracing requirements in AISC 341
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Comparison of OMF vs IMF vs SMF
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OMF IMF SMF Deformation Capabilities Minimal Limited Significant Story Drift Angle None specified 0.02 radians 0.04 radians
Connection Flexural Strength 1.1RyMp
Performance confirmed by testing per AISC 341, ChK; connection achieves
80%Mp at story drift angle = 0.02 radians
Performance confirmed by testing per AISC
341, Ch K; connection achieves 80%Mp at
story drift angle = 0.04 radians
Connection Shear Strength
V for load combination including overstrength plus shear from application of Emh = 2[1.1RyMp]/Lcf
V for load combination including overstrength plus shear from application of
Emh = 2[1.1RyMp]/Lh
V for load combination including overstrength
plus shear from application of Emh =
2[1.1RyMp]/Lh
Panel Zone Strength AISC 360, J10.6 AISC 360, J10.6 AISC 360, J10.6
Equations J10-11 & J10-12
Panel Zone Thickness AISC 360, J10.6 as required
AISC 360, J10.6 as required t>(dz+wz)/90
Comparison of OMF vs IMF vs SMF
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OMF IMF SMF
Continuity Plates As required by AISC 341, Section E1.6b
Match tested or AISC 358, Section 2.4.4 and E3.6f
Match tested or AISC 358, Section 2.4.4
and E3.6f
Beam-Column Proportions No requirements No requirements M*pc/ M*pb > 1.0
Width-Thickness Limitations AISC 360 AISC 341 Section D1.1, Moderately Ductile Member
AISC 341 Section D1.1, Highly Ductile
Member
Stability Bracing of Beams AISC 360 Bracing per AISC 341 for Moderately Ductile Member
Bracing per AISC 341 for Highly
Ductile Member
Column Splices AISC 360 AISC 341 Section D2.5 and E2.6g
AISC 341 Section D2.5 and E3.6g
Protected Zones Not required Yes, as governed by connection in AISC 358
Yes, as governed by connection in AISC
358
Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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Connection Design Principles & Failures
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Mu
VuT OR CV
T OR C
%Vu
%Vu
Connection Design Principles & Failures
Typical Failures in Moment Frame Connections
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Connection Design Failures
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Weld Element
Stresses
Through Thickness Column Flange Pull-Out
Column
Flange Stress Distribution
Beam Flange
Web Fracture due to Weak Panel Zone
Abrupt “divot” pull-outcolumn flange base metal
Brittle weld fracture due topeaked triaxial strains
Sudden column web fracture due to inherently weak panel zone
Divot ‘pull-out’ of column flange base metal
Brittle failure of girder flange weld of girder-to-column
weld connection
Beam-to-column weld failure propagates into column flange and web
Connection Design Principles
SAC: SEAOC, ATC, CUREELed to FEMA project after 1994 Northridge EarthquakeSeries of guides, FEMA 350-353 developed as a guide to use moment frame connections in buildingsEventually, AISC 358 published in 2005 with first set of prequalified connectionsCPRP, Connection Prequalification Review Panel in charge of reviewing and adding connections to AISC 358
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Connection Testing to Justify Performance
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-0.05 0.0 0.05-15
-10
-5
0
5
10
15
Total Plastic Rotation (rad.)
Mom
ent a
t Col
umn
Face
(x10
00 k
ip-in
)
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
M/M
pn
Topics
Moment Frame Design PrinciplesR=3 Moment Frame SystemsR=3.5 Ordinary Moment Frame SystemsR=4.5 Intermediate Moment Frame SystemsR=8 Special Moment Frame SystemsConnection Design PrinciplesConnection Types in AISC 358
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Connection Types in AISC 358-05
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Number of Connections in AISC 358-053 connections totalIncluded: Reduced Beam Section (RBS), Bolted Unstiffened Extended End Plate, Bolted Stiffened Extended End Plate
Supplement Number 1 to AISC 358-053 additional connectionsIncluded: Bolted Flange Plate(BFP), Welded Unreinforced Flange-Welded Web(WUF-W), Kaiser Bolted Bracket (KBB)****First Proprietary Connection introduced
Connection Types in AISC 358-05
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Number of Connections in AISC 358-056 total connections
Connection Types in AISC 358-10
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Total number ofConnections in AISC 358
8Includes: Original six +
SidePlate** & ConXtech**(**Proprietary Conns)
Connection Types Added to AISC 358-10
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Common Connection Types in AISC 358
Reduced Beam Section (RBS)
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RBS Connection
Reduced Beam Section (RBS) Examples
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RBS Connection Limits
Beam limitsW36x Max, 300 lb/ft Max, bf = 1.75” Max
Span to depth7 or greater for SMF, 5 or greater for IMF
Column limitsW36x Max, Built Up or Rolled Shape, No Limit on Weight
Protected Zone = Face of Column to Edge of Reduced Beam Section CutReduced Beam Section Cut shall have surface roughness of 500 -in or better
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Common Connection Types in AISC 358
Welded Unreinforced Flange, Welded Web (WUF-W)
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Connection Types in AISC 358, WUF-W
Beam limitsW36x Max, 150 lb/ft Max, bf = 1” Max
Span to depth7 or greater for SMF, 5 or greater for IMF
Column limitsW36x Max, Built Up or Rolled Shape, No Limit on Weight
Protected Zone = Face of Column to One Beam DepthWeld access hole shall be per AWS D1.8
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WUF-W Connection
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Connection Types AISC 358 Summary
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Type of Connection SMF Span/Depth IMF Span/Depth
Reduced Beam Section (RBS) 7 5
Bolted Unstiffened Extended End-Plate 7 5
Bolted Stiffened Extended End-Plate 7 5
Bolted Flange Plate (BFP) 9 7
Welded Unreinforced Flange-Welded Web (WUF-W) 7 5
Kaiser Bolted Bracket (KBB) 9 9
ConXtech 7 5
SidePlate 4.5 3
Simpson Strong-Tie Strong Frame No Limits No Limits
Double Tee 9 9
Connection Types AISC 358 Summary
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Type of Connection Beam Depth Limit Beam Weight
Limit Beam tbf Beam Width
Req. Reduced Beam Section (RBS) W36x 300 lb/ft 1.75" None
Bolted Unstiffened Extended End-Plate Table 6.1, AISC 358 None 1" None
Bolted Stiffened Extended End-Plate Table 6.1, AISC 358 None 0.75" None
Bolted Flange Plate (BFP) W36x 150 lb/ft 1" None
Welded Unreinforced Flange-Welded Web (WUF-W) W36x 150 lb/ft 1" None
Kaiser Bolted Bracket (KBB) W33x 130 lb/ft 1" 6" to 10" min
based on type of bracket
ConXtech W18x-W30x 132 lb/ft 1" 12" Max
SidePlate W40x** 302 lb/ft** 2.5" Typically 1.5-2" less than column
Simpson Strong-Tie Strong Frame W16x None 0.40" None
Double Tee W24x 55 lb/ft 0.625" None
Connection Types AISC 358 Summary
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Type of Connection Column Depth
Limit Column Weight
Limit Column
tbf Reduced Beam Section (RBS) W36x None None
Bolted Unstiffened Extended End-Plate W36x None None
Bolted Stiffened Extended End-Plate W36x None None
Bolted Flange Plate (BFP) W36x None None
Welded Unreinforced Flange-Welded Web (WUF-W) W36x None None
Kaiser Bolted Bracket (KBB) W36x None None
ConXtech HSS 16x16 or 16"
Built Up Box Column
None 3/8" Min
SidePlate W44x None None
Simpson Strong-Tie Strong Frame W18x None None
Double Tee W36x None None
Connection Types AISC 358 Summary
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Type of Connection Protected Zone Length First Lateral Brace
Reduced Beam Section (RBS) dbeam to end of RBS cut Near RBS cut, no greater than d/2 away
Bolted Unstiffened Extended End-Plate Lesser Of: dbeam OR 3*bf from face of column Per AISC 341
Bolted Stiffened Extended End-Plate Lesser Of: dbeam OR 3*bf from face of column Per AISC 341
Bolted Flange Plate (BFP) Plates and bolted flanges of beam + dbeam
No greater than 1.5dbeam away from face of column
Welded Unreinforced Flange-Welded Web (WUF-W) dbeam from face of column Between dbeam and 1.5dbeam
away from face of column
Kaiser Bolted Bracket (KBB) Plates and bolted flanges of beam + dbeam
Between dbeam and 1.5dbeam away from face of column
ConXtech dbeam to end of RBS cut Per AISC 341
SidePlate 0.833*dbeam past SidePlate** Per AISC 341 past end of SidePlate
Simpson Strong-Tie Strong Frame Yield Links, Shear Plate, and
portion of beam in contact with them
AISC 360
Double Tee Plates and bolted flanges of beam + dbeam
Between dbeam and 1.5dbeam away from farthest bolt
Poll Question
Which of the following is not prescribed in AISC 358 connections:
Protected Zone RequirementsRotation Capacity of ConnectionWhich Connection an Architect will like the mostSize limitation on beams and columns
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Learning Objectives
Identify how drift can be controlled in moment framesDifferentiate between R=3, OMF, IMF, and SMF lateral systemsIdentify when to use AISC 358 prequalified connections in moment frames
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Moment Frames: Design and Detailingper AISC 341 and 358
By Matthew J. Mester, PE, SE
SidePlate Systems, Inc.
SE University, June, 2017 www.LearnWithSEU.com
CHALLENGE QUESTION:
Which type of Moment Frame System is the answer to this session’s Challenge Question?
A. R=3 Moment Frame SystemsB. R=3.5 Ordinary Moment Frame SystemsC. R=4.5 Intermediate Moment Frame SystemsD. R=8 Special Moment Frame Systems
Please circle the answer that is announced so that you can use the information to complete your quiz for PDH.