Gene Stevens - J. R. Harris & Company 1

Transcription

1 SEAC Existing Structures Committee Examining Issues of Existing Structures: IEBC I know what to do! Why do I need such a complex Code? Mostly, it is a simple question of - when is it necessary to structurally assess, strengthen or repair an existing structure and what provisions do I use for loads & strengths? Guidance: IEBC 2015, Model Code ACI used w/ IEBC for Conc. This committee s mission is to assist you w/ improving safety, performance & durability [codes] Gene Stevens - J. R. Harris & Company 1

2 Why do I need a code? Primary Answer is SAFETY Inconsistencies in Eng. Fractured P.T. Wires work & the I know what to do w/ the don t tell me what to do has resulted in failure rates for repairs that are inordinately high $$$. Has prompted codes for existing buildings to improve safety, performance & durability. Complexity comes from variability in conditions to address Gene Stevens - J. R. Harris & Company 2

3 ACI, Concrete International May 2017, Page 71 As an Example: LDP R/C Bldg. Mid 60 s design: Floor members do not meet ACI stirrup spacing exceeds d/2 yada yada and to compound these issues the floor Live load is being increased due to a change in use. Load ( ) vs. Strength This article explains how you use the original building code with the new live loads. No, NO, NO! This is mostly wrong. Per IEBC ( & 1007) & ACI (A.9.1) must use the current bldg. code June CI will clarify the issue of which code to use when loads change vs. a change in use or occupancy. If you do not know which code to use - Ask a committee member or use the current bldg. code Gene Stevens - J. R. Harris & Company 3

4 Esteem Members of SEAC/ESC with me include: Jerry Maly Principal with WJE, & a member of the NCSEA Existing Building Committee Guidance on IEBC compliance methods Donald Harvey Associate VP of Atkinson-Noland & Associates, Expert in Masonry Masonry provisions of IEBC & fill in some of the gaps Dale Statler Engineer with WJE since 2011 IEBC s provisions for roof diaphragm evaluation in regions of high wind most of Colorado Gene Stevens - J. R. Harris & Company 4

5 The IEBC application SOLUTIONS FOR THE BUILT WORLD & case studies Jerry Maly, PE

6 1927 Solutions for the Built World Page 6

7 1927 UBC: Percent-Rule Triggers & Major vs. Minor Work Requirements dependent on Cost of Work vs. Bldg. Value Cost > 50% of Building Value & 12 Month Rule - entire bldg. must meet requirements for new construction. Cost > 25% of Building Value but < 50% & 12 Month Rule - Only affected portions must meet requirements for new bldgs. Minor Work: Cost < 25% of Building Value & 12 Month Rule - use same materials, nothing needs to meet new bldg. req mts. Solutions for the Built World Page 7

8 The Grandfathering Clause Buildings in existence at the time of the adoption of the current code may have their existing use or occupancy continued, if such use or occupancy was legal at the time of the adoption of this Code, provided such continued use is not dangerous to life. Solutions for the Built World Page 8

9 3 Model Codes ICBO Uniform BC BOCA National BC All 3 had similar cost-to-value based provisions for Existing Buildings SBCC Standard BC Leon, R. & Rossberg, J. (2012) Evolution and Future of Building Codes in the USA, Structural Engineering International (SEI), International Association for Bridge and Structural Engineering (IABSE), May 2012 Solutions for the Built World Page 9

10 1979 UBC Percent-rule triggers had come to be seen as obstacles to the re-use of existing buildings and were largely eliminated. New approach: Upgrade only what is affected Don t make the building less safe Solutions for the Built World Page 10

11 1994 ICBO Uniform BC BOCA National BC Solutions for the Built World Page 11

12 2000 IBC 1 st Edition UNIFORM BUILDING CODE CONTRIBUTIONS Upgrade only what is affected, and do not make less safe. Change Occupancy comply w/ code for new buildings unless change is to less hazardous use. Solutions for the Built World Page 12

13 2000 IBC 1 st Edition STANDARD BUILDING CODE CONTRIBUTIONS Accessibility for persons with physical disabilities. Solutions for the Built World Page 13

14 2000 IBC 1 st Edition NATIONAL BUILDING CODE CONTRIBUTIONS The intent of this section is to set forth part of an alternative criteria for rehabilitation of existing buildings, with sufficient latitude to achieve an acceptable degree of safety without requiring full and rigid compliance with Chapters 2 through 33 of the code. Solutions for the Built World Page 14

15 2000 IBC 1 st Edition Chapter 34 Existing Buildings NATIONAL BUILDING CODE CONTRIBUTIONS 3409 Compliance Alternatives Solutions for the Built World Page 15

16 YIKES! Where did those #?\#*~/! code provisions come from?? P.E. Solutions for the Built World Page 16

17 2015 IEBC 3 Compliance Methods 1. Prescriptive Method - Chapter 4 2. Work Area Method - Chapters 5 through Performance Method - Chapter 14 Solutions for the Built World Page 17

18 2015 IEBC 3 Compliance Methods 1. Prescriptive Method - Chapter 4 Similar to 1997 UBC Chapter 34 and the primary compliance method in 2012 IBC Chapter 34: Work Area Method - Chapters 5 through 13 Separate chapters for repairs, alterations, additions, changes in occupancy, historic bldgs. Structurally...identical to the Prescriptive Method 3. Performance Method Chapter 14 Identical to Compliance Alternative Method in 2012 IBC, Chapter 34: 3412 Solutions for the Built World Page 18

19 2015 IEBC 3 Compliance Methods 1. Prescriptive Method - Chapter 4 Similar to 1997 UBC Chapter 34 and the primary compliance method in 2012 IBC Chapter 34: Work Area Method - Chapters 5 through 13 Separate chapters for repairs, alterations, additions, changes in occupancy, historic bldgs. Structurally...identical to the Prescriptive Method 3. Performance Method Chapter 14 Identical to Compliance Alternative Method in 2012 IBC, Chapter 34: 3412 Solutions for the Built World Page 19

20 2015 IEBC 3 Compliance Methods 1. Prescriptive Method - Chapter 4 Similar to 1997 UBC Chapter 34 and the primary compliance method in 2012 IBC Chapter 34: Work Area Method - Chapters 5 through 13 Separate chapters for repairs, alterations, additions, changes in occupancy, historic bldgs. Structurally...identical to the Prescriptive Method 3. Performance Method Chapter 14 Identical to Compliance Alternative Method in 2012 IBC, Chapter 34: 3412 Solutions for the Built World Page 20

21 2015 IEBC REPAIRS: Prescriptive and Work Area Methods Substantial Structural Damage Damage < SSD... restore to pre-damaged state Damage > SSD... Structural evaluation is triggered, and scope of structural repairs dependent on outcome Solutions for the Built World Page 21

22 2015 IEBC REPAIRS: Prescriptive and Work Area Methods Substantial Structural Damage 1. The vertical elements of the structure s LFRS 2. Vertical components of the gravity loadcarrying system Solutions for the Built World Page 22

23 2015 IEBC ALTERATIONS: Prescriptive and Work Area Structural Upgrade Triggers... When re-roofing or alterations exceed certain % of the roof or aggregate areas of a building, respectively, and the building is in certain SDCs, bracing req d for URM walls and parapets Solutions for the Built World Page 23

24 2015 IEBC ALTERATIONS: Prescriptive and Work Area Structural Upgrade Triggers... When reroofing > 50% of a roof diaphragm, and building is located where V ult > 115 mph or is in a special wind region, roof diaphragms and roof diaphragm connections to roof framing and walls must be evaluated Solutions for the Built World Page 24

25 WHAT DOES IT MEAN FOR EXISTING BUILDINGS TO MEET CURRENT CODE? It DOES NOT mean that the existing building complies with the current code requirements for new structures, including Chapter 16. In the context of structural work pertaining to repairs, alterations, and changes of occupancy, meeting current code means the existing building satisfies the code provisions that control such work. Solutions for the Built World Page 25

26 IEBC - Masonry May Meeting PE Structural Engineers Association of Colorado e: New York: Boulder: International Existing Building Code - Masonry SEAC General Meeting May 18, 2017 Atkinson-Noland & Associates

27 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 2 Quick Review of Code Organization Chapters Subjects 1-2 Administrative Requirements and Definitions 3 Compliance Methods 4 Prescriptive Compliance Method for Existing Buildings 5-13 Work Area Compliance Method for Existing Buildings 14 Performance Compliance Method for Existing Buildings 15 Construction Safeguards 16 Referenced Standards Appendix A1 (A2 Concrete and Reinf. Masonry, A3&A4 Wood) Appendix B Guidelines for Seismic Strengthening Provisions for Unreinforced Masonry Bearing Wall Buildings Supplementary Accessibility Requirements for Existing Buildings Atkinson-Noland & Associates

28 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 3 IEBC Masonry Provisions - Historic Historic Building Exception PRESCRIPTIVE The provisions that require improvement relative to a building s existing condition shall not be mandatory for historic buildings (listed exception: life safety hazards) Historic Building Inclusion W.A.M historic buildings shall comply with applicable provisions of this code for the type of work being performed. (similar in ) Huh? Atkinson-Noland & Associates

29 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 4 IEBC Masonry Provisions Code does not include chapters for various materials Special provisions for masonry diaphragm attachments and parapet bracing. Most masonry content in Chapter/Appendix A1: Seismic Strengthening Provisions for Unreinforced Masonry Bearing Wall Buildings. (ALL METHODS, Chapter 3) Appendix A1 has pass/fail tests for existing masonry in order to QUALIFY for use of the Appendix. Atkinson-Noland & Associates

30 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 5 IEBC Masonry Provisions Appendix A1 establishes a series of prescriptive requirements for masonry if the Appendix is to be used: 10% minimum FULL (not diagonal) headers (relatively restrictive) Shear Test a.k.a. Shove Test minimum value Alternative procedures for testing masonry Splitting Tensile Test 8 core Sawn Sample Diagonal Test for splitting tensile Estimation of f m from Unit Strength Tables for modern masonry only. Anchor Tests A , 10% of Existing and 5% of New (except through-wall) A &4 Location and Number of Tests (Shove Tests): Represent all conditions 1 or 2 per Shear Wall but no fewer than one per 1,500 sq. ft. of wall or eight (8) tests Atkinson-Noland & Associates

31 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 6 IEBC Masonry Provisions If minimum values not met 100% Repoint or REPLACE! Minimum Values to Qualify : Property Shear Strength Splitting Tensile Strength Compressive Strength (Unit Strength Method) Tension Minimum Value 30 psi (80% of tests must exceed this value) 50 psi 1000 psi Zero (A108.4) Masonry Compression (A108.3): Where any increase in dead plus live compression stress occurs, the compressive stress in unreinforced masonry shall not exceed 300 pounds per square inch. (Allowable?) Table A1-E Anchor Values: DO NOT USE FOR HISTORIC MASONRY! (However, encourages use of through bolts. Yeah!) Atkinson-Noland & Associates

32 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 7 Actual Masonry Properties - Background Shear Testing Shear Strength Index Flatjack Testing Compression Bond Wrench Testing Flexural Bond Strength Splitting Tensile? Atkinson-Noland & Associates

33 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 8 Actual Masonry Properties In-Plane Shear Shear Testing Shear Strength Index ASTM C1531 Standard Test Methods for In Situ Measurement of Masonry Mortar Joint Shear Strength Index Index because test values include frictional component. Atkinson-Noland & Associates

34 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 9 Actual Masonry Properties - Compression Flatjack Testing Compression ASTM C1197 Standard Test Method for In Situ Measurement of Masonry Deformability Properties Using the Flatjack Method Determine stiffness, strength, in place Atkinson-Noland & Associates

35 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 10 Actual Masonry Properties Flexure Bond Wrench Testing Flexural Bond Strength ASTM C1072 Standard Test Methods for Measurement of Masonry Flexural Bond Strength (sort of ) Adapted for field use. Atkinson-Noland & Associates

36 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 11 Actual Masonry Properties ANA database of values Compiled over the last 10 years Hundreds of projects, but ONLY COLORADO projects considered for this presentation Examples of Test Locations: Rossonian Hotel Kacey Furniture Building Buffalo Rose (Golden) Kirkland Studio/Museum Atkinson-Noland & Associates

37 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 12 Actual Masonry Properties In-Plane Shear Shear Jack Testing Remember: IEBC requires 80% of tests to exceed 30 psi for Appendix A1. Historic Clay Brick Low High Average Standard of Deviation Value 9 psi 171 psi 54 psi 28 psi Coefficient of Variation 53 % CMU Test Results: 205 psi (MSJC ~150 psi for fʹm 1500 psi) Modern Brick Test Results: 230 psi Atkinson-Noland & Associates

38 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 13 Actual Masonry Properties - Compression Flatjack Testing Vast majority are common brick backup (softer) IEBC Appendix A psi minimum Unit Strength Method Historic Clay Brick Low High Average Value 120 psi 840 psi 401 psi Standard of Deviation 197 psi Coefficient of Variation 49 % (Relatively) Modern Brick: 2420 psi Stone with Lime Mortar: 230 psi (limited tests) Atkinson-Noland & Associates

39 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 14 Actual Masonry Properties Flexure Bond Wrench Testing Flexural Bond Strength (Historic Data Only) Very limited Colorado Data: 6 psi average National Data: 8 psi average No Code Values for softer than Type N Zero is conservative, but some bond strength is usually present. Atkinson-Noland & Associates

40 IEBC - Masonry May Meeting Structural Engineers Association of Colorado 15 Summary IEBC Provisions Appendix A1 Minimum Values are MARGINAL (at best) for historic structures in Colorado We cannot ASSUME Appendix A1 is relevant Therefore, not much guidance (other than 100% repointing or reconstruction) Actual (Measured) Masonry Properties Historic fʹm: 401 psi Modern fʹm: 2420 psi Historic Shear: ~54 psi (average) Historic Modulus of Rupture: 6psi Atkinson-Noland & Associates

41 IEBC 2015 SOLUTIONS FOR THE BUILT WORLD Diaphragm evaluations for reroofing in high wind regions and a case study Segment Outline Provision language History & Background What it means in CO Case Study Conclusions Dale Statler, PE

42 What it Says:.. Scary seismic problem Scary wind problem??? Solutions for the Built World Page 2

43 The Beginning (2003): Where it Came From: Now (2015): Always in Work Area Method New to Prescriptive Method in 2015 (Section 403.8) IEBC Commentary: Accessible for evaluation Is it? Solutions for the Built World Page 3

44 Want a new roof? Diaphragm Evaluation What it Means: MWFRS C&C Have drawings? Field Investigation Doesn t meet 75% of code? Strengthen Solutions for the Built World Page 4

45 Where it Applies: Fort Collins Boulder Denver Colorado Springs V ULT < 115 MPH V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 5

46 Case Study Intro: Fort Collins Boulder Denver Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 6

47 Case Study: Original 1934 Building: Fort Collins Wood-framed Straight-sheathed lumber Boulder diaphragm Masonry bearing/shear Denver walls Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 7

48 Case Study: 1948 Addition: Fort Collins Steel bar joist framing Straight-sheathed lumber Boulder diaphragm Masonry bearing/shear Denver walls Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 8

49 Case Study: 1965 Addition: Open-web steel joists Steel deck roof diaphragm Masonry bearing/shear walls Fort Collins Boulder Denver Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 9

50 Case Study: 1986 Addition: Wood/steel truss-joist framing Plywood diaphragm Masonry bearing/shear walls Fort Collins Boulder Denver Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 10

51 Case Study: Latest Addition: Wood/steel truss-joist framing Plywood diaphragm Masonry bearing/shear walls Fort Collins Boulder Denver Colorado Springs V ULT > 115 MPH Special Wind Region Solutions for the Built World Page 11

52 Conclusions Roof replacement cost increased by $100,000 (for a building with a long & successful history of performance) A wise or just expenditure of resources? Existing Building Committee Opinion An extraordinary burden on building owners No commensurate extraordinary hazard in Colorado Pursuing initiatives for: Code change Local and/or state amendments Solutions for the Built World Page 12

53 IEBC Assessment Criteria IEBC implies equations - strength design 1. Demand: Factored load combinations based on probability of occurrence over time [say 50 yrs.] w/c.v. (V U ). Ex. - Snows from SEAC 2. Member Capacity: mean strength with strength reduction factors based on statistical probabilities with coefficient of variation (V R ). Ex. - MM nn Steel Corbel Added to (E) Concrete Column for External P.T. reinforcement Gene Stevens of J. R. Harris & Company 13

54 Reliability Analysis for Demand to Capacity ratios foundation for LRFD 1980 s See - ASCE 7-10 ββ UU ln( ss RRmm ) VV 2 2 RR + VV UU Reliability index J. R. Harris & Company

55 Reliability as it relates to D/C D/C estimates of structural reliability (β) or probability of failure (P F ) Examples for Sudden Failure w/ Progressive Damage from ASCE 7-10: D/C = 1.0: β = 3.5: P F = 0.023% in 50 yrs.: baseline from ASCE 7-10, Table C.1.3.1a D/C = 1.05: β = 3.11: P F = 0.082% in 50 yrs.: 3.5± x baseline D/C = 1.1: β = 2.75: P F = 0.3% in 50 yrs. 10± x baseline D/C = 1.25: β = 1.73: P F = 4% in 50 yrs. 200± x baseline D/C = 1.33: β = 1.24: P F = 11% in 50 yrs. 500± x baseline [D/C = 1.5 defined in ACI as IEBC s Significant risk of Collapse ] J. R. Harris & Company 15

56 Baseline - Probability of failure 0.023% in 50 years (1 in 4,500) 1.33 Probability of failure 4% in 50 years (1 in 25) 1.25 Probability of failure 11% in 50 years (1 in 9) 16

57 Colorado Engineers are to provide the Quality of Work Expected to comply with Standard of Care Colorado s Bylaws {3.1.4} require engineers use Generally Accepted Standards and for their Work Product to be Safe. IEBC no Ref. to FRP Repairs use CO laws What is currently Safe, may not remain Safe without appropriate Repairs Fractured P.T. reinforcement Gene Stevens of J. R. Harris & Company 17

58 In Concrete Structures, detailing of the existing reinforcement need not be per ACI , if: - Seismic design Cat. A, B, or C and deterioration is addressed - The repaired structure shall have capacity demand of either original or current bldg. code. - No unsafe conditions - The structure has demonstrated historical structural reliability. External P.T. reinforcement - repairs [30 years or more via Canada s bldg. code.] ACI , Gene Stevens of J. R. Harris & Company 18

59 High Wind Regions & Diaphragm Evaluation - Look for SEAC/ESC to recommend that IEBC, sections & be revised or deleted for Colorado. - Request that you direct questions or items that you see need to be revised or explained in the IEBC to one of the members of the SEAC/ESC. External P.T. reinforcement - repairs Gene Stevens of J. R. Harris & Company 19