Learning Objectives. Topics. Moment Frames: Design and Detailing per AISC 341 and 358. Topics. Lateral Analysis/Choosing your Code

Transcription

1 Topics Moment Frames: Design and Detailing per AISC 341 and 358 By Matthew J. Mester, PE, SE SidePlate Systems, Inc. SE University, June, Learning Objectives Topics Identify how drift can be controlled in moment frames Differentiate between R=3, OMF, IMF, and SMF lateral systems Identify when to use AISC 358 prequalified connections in moment frames 3 4 Lateral Analysis/Choosing your Code Lateral Analysis/Choosing your Code What code is required in your jurisdiction? What code is required in your jurisdiction? 5 6

2 Lateral Analysis/Choosing your Code Lateral Analysis What code is required in your jurisdiction? ASCE 7-05, IBC 2006 or IBC 2009, AISC , AISC , AISC What is important in Moment Frame Design? Beams Vertical Force ASCE 7-10, IBC 2012 or IBC 2015, AISC , AISC , AISC including Supplements 1&2 Future codes: ASCE 7-16, IBC 2018, AISC , AISC , AISC including Supplements Columns Beam/ Column Connection Drift?, Strength?, Ductility? Lateral Force 7 8 Lateral Analysis Lateral Analysis for Wind Loads Typically, DRIFT will govern the design of moment frames, not STRENGTH, but must check both What governs drift in Moment Frames? Rotation of beams Rotation of columns Base conditions Deformation 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 9 Drift Limits for Wind Provisions What is required? Is it the Law? IBC Serviceability: Structural Systems shall have adequate stiffness to limit deflections and lateral drift. ASCE 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. 10 Lateral Analysis for Wind Loads Lateral Analysis for Wind Loads 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. 11 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 12

3 Lateral Analysis for Wind Loads Lateral Analysis for Wind Loads 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. Wind Speed Maps in ASCE 7-10 Commentary, App C Lateral Analysis for Seismic Loads The R Factor in Moment Frame Design Drift Limits for Seismic Provisions (ASCE 7 Table ) ASCE 7 Design Coefficients (ASCE 7 Table ) x C d I xe Maximum drift based on ASCE 7 provisions Seismic Design Principles Response Spectrum of MRFs Reduction in Response Spectrum based on type of system used and its R factor Design Ground Motions 1.2 Response Acceleration, g Period, T 17 18

4 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 Connection Beams Continuity Plates Doubler Plates Topics R=3 Moment Frame Systems R=3 Moment Frame Systems Not required to be designed for seismic resistance Typically wind governed structure Members (beams, columns, connections) designed for the LRFD or ASD load combinations in the building code LRFD ASD When are they allowed Seismic Design Category A, B, and C with no limits on height Still must check some of the seismic requirements in Chapter 12 of ASCE 7 Overstrength Factor = 3 Deflection amplification Factor = R=3 Moment Frame Systems R=3 Moment Frame Systems Use of AISC 360 for design of beams, columns, and connection elements Connections designed for LRFD or ASD load combinations Typically, EORs will delegate the connection design to fabricators with their in-house/connection design engineer EORs need to show/give design loads on drawings and indicate which force level shears and moments are shown 23 24

5 Topics R=3.5 OMFs 25 When are they allowed SDC A, B, C with no restrictions ASCE 7-10, Section Limitations 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 OMF Mostly single story frames unless under 35 feet Permitted 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 = 3 Deflection amplification Factor = 3 26 R=3.5 OMFs R=3.5 OMFs Provides minimal inelastic deformation capabilities No width-thickness ratios of members beyond what is required in AISC 360 No protected zones on beam No strong column-weak beam requirements No lateral bracing requirements except as required to meet AISC 360 Must use Demand Critical Welds between beam flange and column where applicable Connection may be fully restrained(fr) or partially restrained (PR) 27 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 uplift Panel zone requirements of Section J10.6 of AISC 360 Continuity plate requirements of Sections J of AISC 360 PR Connections must be designed for minimum of: 50%*Mp of beam for flexural strength Shear strength similar to FR OMF connection 28 R=3.5 OMFs R=3.5 OMFs When would you use an OMF in practice? Local code requires its use over R=3 system Engineer wants to specify over IMF to avoid requirements in AISC 341 At 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 joints Light gage/residential structure or small enclosed mechanical room at top of a building Example of what an OMF looks like in practice 29 30

6 Topics R=4.5 IMFs When are they allowed ASCE 7-10, Section Limitations on SDC D: 35 feet in height or lighter building Limitations 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 IMF May be multi story frames in certain situations Permitted 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 = 3 Deflection amplification Factor = R=4.5 IMFs R=4.5 IMFs Provides limited inelastic deformation capabilities Members must meet moderately ductile requirements within AISC 341 Protected Zone requirements exist on beam/connection No strong column-weak beam requirements Lateral bracing requirements exist ~100*ry of moment frame beam for fy = 50ksi for moderately ductile beams Must use Demand Critical Welds for: Between beam flange and column where applicable Column splice groove welds Welds between column and base plate 33 Connection must be able to sustain story drift angle of 0.02 radians and flexural resistance must be 0.80*Mp at the 2% radians Required shear strength of connection: Ev = 2[1.1*Ry*Mp]/Lh Connections within AISC 358 may be used to justify conformance to performance requirements Panel zone requirements similar to OMFs, Section J10.6 of AISC 360 Continuity plates must follow requirements of SMF section 34 R=4.5 IMFs R=4.5 IMFs When would you use an IMF in practice? Local code mandates a minimum R value SDC D with building no taller than 35 feet, BUT do not want to or cannot achieve SCWB, lateral bracing, provisions of AISC 341 Short spans with Deep Beams, connections each have a span/depth ratio found in AISC 358 Want to specify a connection on your drawings and get a small break in design spectrum, R=3.5 vs R=4.5 Not very common Example of what an IMF looks like in practice 35 36

7 Topics R=8 SMFs When are they allowed Always allowed but can you get drift to work in your moment frame? ASCE 7-10, No Limits on any height buildings Overstrength Factor = 3 Deflection amplification Factor = R=8 SMFs R=8 SMFs Provides significant inelastic deformation capabilities Members must meet highly ductile requirements within AISC 341 Protected Zone requirements exist on beam/connection Strong column-weak beam requirements exist Lateral bracing requirements exist ~50*ry of moment frame beam for fy = 50ksi for highly ductile beams Must use Demand Critical Welds for: Between beam flange and column where applicable Column splice groove welds Welds between column and base plate 39 Strong Column Weak Beam Requirements why? Undeformed frame h Deformed frame shape Plastic hinges Drift angle - L L 40 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% radians Required shear strength of connection: Ev = 2[1.1*Ry*Mp]/Lh Connections within AISC 358 may be used to justify conformance to performance requirements Panel zone requirements thickness based on t>(dz+wz)/90, doubler plates typically required Column bracing requirements in AISC Comparison of OMF vs IMF vs SMF OMF IMF SMF Deformation Capabilities Minimal Limited Significant Story Drift Angle None specified 0.02 radians 0.04 radians Connection Flexural Strength Connection Shear Strength 1.1RyMp V for load combination including overstrength plus shear from application of Emh = 2[1.1RyMp]/Lcf Performance confirmed Performance confirmed by by testing per AISC testing per AISC 341, Ch 341, Ch K; connection K; connection achieves achieves 80%Mp at 80%Mp at story drift angle story drift angle = 0.04 = 0.02 radians radians 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 Panel Zone Thickness AISC 360, J10.6 as required AISC 360, J10.6 as required V for load combination including overstrength plus shear from application of Emh = 2[1.1RyMp]/Lh AISC 360, J10.6 Equations J10-11 & J10-12 t>(dz+wz)/90 42

8 Comparison of OMF vs IMF vs SMF Continuity Plates OMF IMF SMF As required by AISC 341, Section E1.6b Match tested or AISC 358, Section and E3.6f Match tested or AISC 358, Section and E3.6f Beam-Column Proportions No requirements No requirements M*pc/ M*pb > 1.0 Width-Thickness Limitations AISC 360 Stability Bracing of Beams AISC 360 Column Splices AISC 360 Protected Zones Not required AISC 341 Section AISC 341 Section D1.1, D1.1, Highly Ductile Moderately Ductile Member Member Bracing per AISC 341 for Moderately Ductile Member AISC 341 Section D2.5 and E2.6g Yes, as governed by connection in AISC 358 Bracing per AISC 341 for Highly Ductile Member AISC 341 Section D2.5 and E3.6g Yes, as governed by connection in AISC 358 Topics Connection Design Principles & Failures Connection Design Principles & Failures T OR C %Vu V u Typical Failures in Moment Frame Connections M u T OR C %Vu Connection Design Failures Through Thickness Column Flange Pull-Out Abrupt divot pull-out column flange base metal Divot pull-out of column flange base metal Weld Element Stresses Column Flange Stress Distribution Beam Flange Brittle weld fracture due to peaked triaxial strains Brittle failure of girder flange weld of girder-to-column weld connection Web Fracture due to Weak Panel Zone Sudden column web fracture due to inherently weak panel zone Beam-to-column weld failure propagates into column flange and web 47 Connection Design Principles SAC: SEAOC, ATC, CUREE Led to FEMA project after 1994 Northridge Earthquake Series of guides, FEMA developed as a guide to use moment frame connections in buildings Eventually, AISC 358 published in 2005 with first set of prequalified connections CPRP, Connection Prequalification Review Panel in charge of reviewing and adding connections to AISC

9 Moment at Column Face (x1000 kip-in) Connection Testing to Justify Performance Total Plastic Rotation (rad.) M/Mpn Topics Connection Types in AISC Connection Types in AISC Number of Connections in AISC connections total Included: Reduced Beam Section (RBS), Bolted Unstiffened Extended End Plate, Bolted Stiffened Extended End Plate Supplement Number 1 to AISC additional connections Included: Bolted Flange Plate(BFP), Welded Unreinforced Flange-Welded Web(WUF-W), Kaiser Bolted Bracket (KBB)** **First Proprietary Connection introduced Number of Connections in AISC total connections Connection Types in AISC Connection Types Added to AISC Total number of Connections in AISC Includes: Original six + SidePlate** & ConXtech** (**Proprietary Conns) 53 54

10 Common Connection Types in AISC 358 Reduced Beam Section (RBS) RBS Connection Reduced Beam Section (RBS) Examples RBS Connection Limits Beam limits W36x Max, 300 lb/ft Max, bf = 1.75 Max Span to depth 7 or greater for SMF, 5 or greater for IMF Column limits W36x Max, Built Up or Rolled Shape, No Limit on Weight Protected Zone = Face of Column to Edge of Reduced Beam Section Cut Reduced Beam Section Cut shall have surface roughness of 500 -in or better Common Connection Types in AISC 358 Welded Unreinforced Flange, Welded Web (WUF-W) Connection Types in AISC 358, WUF-W WUF-W Connection Beam limits W36x Max, 150 lb/ft Max, bf = 1 Max Span to depth 7 or greater for SMF, 5 or greater for IMF Column limits W36x Max, Built Up or Rolled Shape, No Limit on Weight Protected Zone = Face of Column to One Beam Depth Weld access hole shall be per AWS D

11 Connection Types AISC 358 Summary 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 Simpson Strong-Tie Strong Frame No Limits No Limits Double Tee Connection Types AISC 358 Summary 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 62 Connection Types AISC 358 Summary Column Depth Column Weight Column Type of Connection Limit Limit 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 None 3/8" Min Column SidePlate W44x None None Simpson Strong-Tie Strong Frame W18x None None Double Tee W36x None None 63 Connection Types AISC 358 Summary 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 No greater than 1.5dbeam + dbeam away from face of column Welded Unreinforced Flange-Welded Web (WUF-W) Kaiser Bolted Bracket (KBB) dbeam from face of column Plates and bolted flanges of beam + dbeam Between dbeam and 1.5dbeam away from face of column Between dbeam and 1.5dbeam away from face of column ConXtech dbeam to end of RBS cut Per AISC 341 SidePlate Simpson Strong-Tie Strong Frame Double Tee 0.833*dbeam past SidePlate** Yield Links, Shear Plate, and portion of beam in contact with them Plates and bolted flanges of beam + dbeam Per AISC 341 past end of SidePlate AISC 360 Between dbeam and 1.5dbeam away from farthest bolt 64 Poll Question Which of the following is not prescribed in AISC 358 connections: Protected Zone Requirements Rotation Capacity of Connection Which Connection an Architect will like the most Size limitation on beams and columns Learning Objectives Identify how drift can be controlled in moment frames Differentiate between R=3, OMF, IMF, and SMF lateral systems Identify when to use AISC 358 prequalified connections in moment frames 65 66

12 CHALLENGE QUESTION: Moment Frames: Design and Detailing per AISC 341 and 358 By Matthew J. Mester, PE, SE SidePlate Systems, Inc. Which type of Moment Frame System is the answer to this session s Challenge Question? A. R=3 Moment Frame Systems B. R=3.5 Ordinary Moment Frame Systems C. R=4.5 Intermediate Moment Frame Systems D. R=8 Special Moment Frame Systems SE University, June, Please circle the answer that is announced so that you can use the information to complete your quiz for PDH.