Application of Steel Braced Frames for Areas with Moderate Seismic Risks

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1 Application of Steel Braced Frames for Areas with Moderate Seismic Risks Sutat Leelataviwat, Ph.D. Head of Civil Engineering Department King Mongkut s University of Technology Thonburi Nattapat Wongpakdee Ph.D. Candidate King Mongkut s University of Technology Thonburi Anek Siripanitchgorn Engineering Institute of Thailand King Mongkut s University of Technology Thonburi (KMUTT)

2 STEEL FRAMES CBF (Single Diagonal) CBF (Inverted V) Moment Frame Concentrically Braced Frame Eccentrically Braced Frame (EBF)

3 EBF Frame in Chiang Rai, Thailand

4 Number of Schools in Seismic Area 2 Province #Schools #Students Chiangmai Mae Hongson Nan Prae Phayao Lumpoon Lumpang Tak Kanchanaburi Chiangrai ,548 Total 4,492 1,191,263

5 Seismic Hazard of Thailand Earthquake Activities Areas near Fault Lines (North and West of Thailand) Areas with Seismic Hazard from Long Distant Earthquake (Bangkok and Surrounding Areas) Ref: Department of Public Work Seismic Design Standard 1302 (2011)

6 Wat Chedi Luang of Chiand Mai Damaged by an Earthquake in 1545AD.

7 M5+ Earthquakes Recorded in Thailand Date Location Magnitude 13 May Feb April Sep Dec Dec Dec 1996 Nan Provinve Tak Province Kanchanaburi Province Phan, Chiang Rai Phare Prao, Chiang Rai Thai-Myanmar Border (Chiang Rai) , 5.9, May 2007 Lao March 2011 Myanmar 6.8

8 Seismic Hazard of Bangkok

9 Soil Amplification of Ground Motions + Resonant Amplification of Building Responses = Risk from Distant Earthquakes km Bangkok

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12 2007 Ministerial Regulation Requires Seismic Design for Public Buildings and Buildings 15 m or Higher Located in 1) Areas Near Known Faults, and 2) Areas with High Risk Due to Long-Distant Earthquake

13 May 2014 M6.3 Mae Lao Earthquake

14 ShakeCast Map of M6.3 Mae Lao, Chiang Rai Province, 5 th May 2014 Chiang Rai Mae Lao Mae Suai Epicenter Mw 6.2 Strike, Dip, Rake 68, 88, 5 7 km focal depth 30 cm average displacement Approx. Affected Area 15 x15 km 2 No. of Buildings Damaged No. of Red-Tagged Buildings 400 No. of Death 1 Phan (Ornthammarath 2014)

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16 Lessons from Mae Lao Earthquake Lack of Lateral Strength and Poor Configuration are the Primary Causes of Collapse Accidental Torsional and Soft Story are the Primary Causes of Collapse Effects of Nonstructural Element (Masonry Infill Walls)

17 Lack of Lateral Strength and Nonductile Reinforcement Details Low Transverse Reinforcement High Longitudinal Reinforcement Construction Joints Lap-Splice in Potential Plastic Hinge Region Non-Uniform Flexural Capacity Non-Uniform Shear Capacity No Joint Reinforcement Discontinuous Positive Beam Reinforcements Short Embedment Length into Columns

18 4-Story RC School Building

19 Shear Failure in Columns Above Infilled Wall

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22 Damage to Infill Wall Panels

23 Infill Wall Around Stair Case 3 Story School

24 Infill Severely Damaged Columns Plan View Damage in First Story Columns

25 Failure Mode: Lap-splice Failure Near Infill Wall Middle of Building Right-Most Column

26 WALL-FRAME INTERACTION

27 WALL-FRAME INTERACTION

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29 VULNERABILITY FACTORS FOR A TYPICAL SMALL- OR MEDIUM-SIZED BUILDING Infill Wall-Frame Interaction Soft/Weak First Story Torsional Irregularity Non-seismic Detailing & Lack of Lateral Strength Analysis Model Public Perception of Damage to Infill Panels

30 WALL-FRAME INTERACTION

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32 Design Case Study: EBF Frame in Chiang Rai, Thailand

33 Why Steel EBF? Steel EBF Offers Excellent Stiffness and Ductility In the Event of Extreme Loading Beyond the Design Level, Steel Structures can be Repaired More Quickly

34 Source:

35 Steel Moment Frame No Obstruction in the Bays High Ductility High Redundancy Flexible

36 Flexible Frame may result in the damage of infill wall

37 Reduced Beam Section Welded Unreinforced Flange - Bolted Web

38 STEEL BRACE FRAMES Single Diagonal Inverted V- Bracing V- Bracing High Stiffness Reduces Damage to Non- Structural Elements Source: AISC X- Bracing High Lateral Strength

39 Inelastic Response of CBFs under Earthquake Loading Tension Brace: Yields (ductile) Compression Brace: Buckles (nonductile) Columns and beams: remain essentially elastic Source: AISC

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41 Eccentrically Braced Frame e Link

42 Eccentrically Braced Frame High Stiffness Reduces Damage to Non- Structural Elements High Lateral Strength High Ductility

43 Source: Chao (2005)

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49 Designed with Overstrength to Remain Elastic

50 EBFs are distributed around the perimeter to reduce torsional response

51 Design Issues with EBF for Moderate Force V e = S a xw Seismic Zones R Value Depends on the Ductility of the System (R = 3 to 8) V e /R YIELDING Deformation

52 Seismic Design Per Thai Standard (DPW1302) Spectral Acceleration Importance Factor V Sa( T ) V R I W Design Base Shear Response Modification Factor R = 8 For EBF High R Value May Result in Very Low Required Lateral Strength!

53 ISSUES WITH CURRENT ELASTIC DESIGN METHOD High R Value may result in very low required frame lateral strength Reserve strength beyond elastic limit is neither quantified nor utilized explicitly The inelastic deformation is not directly computed making it difficult to limit the deformation of the structure to a target level

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55 Source: Haselton and Deierlein 2008

56 Performance-Based Plastic Design The Target Deformation of the Structure is first selected Frame and member strengths are calculated using plastic analysis corresponding to the target deformation PBPD method has been applied to the design of steel BRBF, EBF, STMF, and CBF, and has been validated by nonlinear

57 Introduction to PBPD

58 Force Distribution at Target Drift

59 Pushover Analysis

60 Next Step

61 Next Step

62 Summary Steel structures (EBF) provide efficient and effective solution for moderate seismic hazard In moderate zone, code based design must be carried out with care New Technology in design and framing system are required