Ductile Fuses for HSS Seismic Bracing of Low-rise Buildings

Transcription

1 Ductile Fuses for HSS Seismic Bracing of Low-rise Buildings P P Peter Timler - CISC/Sandwell Helmut Prion - UBC a CISC - Ecole Polytechnique UBC Collaborative Project

2 Outline of Presentation Code Changes and Designer s Concerns Background to Pilot Research Program Phase I Testing - Ecole Polytechnique Phase II Testing - UBC Phase III Testing - Ecole Polytechnique Conclusions and Recommendations

3 Code Changes and Designer s Concerns Since release of CSA/S braced connections are to be designed for A g F y unless EOR can show otherwise. Has created hardship for designers, particularly in the low-rise building industry, where R=2 force modification factor and HSS bracing are commonly applied.

4 Code Changes and Designer s Concerns - Cont. Brace end connection forces (R=2 case) increases from 1.33(T f or C f ) to A g F y. For typical applications of HSS bracing this means force increases between 2 and 10 times those experienced in designs using S16.1-M89. Results from the gross disparity between the C r and the T u for the optimized HSS section selected.

5 V 3.7m T T = C m 4.6m NOTES: LOCATION - VANCOUVER Za = 4 Zv = 4 v = 0.20 SF = 3.0 I = 1.0 Ve = vs IFW = 0.20(1.0)(3.0)W = 0.6W Ve = Ve U U = 0.6 R = 0.6(0.6)W R = 0.36W R THEREFORE: FOR SBF; R = 1.5, V = 0.24W NDFB; R = 2.0, V = 0.18W DBF; R = 3.0, V = 0.12W SET W = 1500 kn ASSUME BOLTED CONNECTIONS FOR DEMONSTRATION PURPOSES

6 Prototypical Example Summary Case Frame Type R Value Applied Force V (kn) Brace Size Class C - 350W Mass (kg/m) Bolts for Connection S S16.1-M89 1 SBF HSS 127x127x * 6* 2 NDBF HSS 102x102x DBF HSS 127x127x8.0 * Based on local industry state of practice prior to S16.1-M89

7 Code Changes and Designer s Concerns - Cont. Have the code writers made a mistake, or do we as designers have to change our way of thinking? For code compliance, options available are: demonstrate lower resistance is adequate; shift design strategy; reduce disparity between C r and T u.

8 Code Changes and Designer s Option 1) Concerns - Cont. From Clauses & :» unless the engineer/designer can show a lower resistance is adequate. Implies dynamic time/history analysis is required to substantiate lower force levels for connection design. Not a practical method for most structures, however.

9 Code Changes and Designer s Option 2) Concerns - Cont. Shift design strategy from ductile performance of brace (R=2 or 3) to strength based (R=1.5). Forces in braces limited to the capacity of other weak links within the developed load path. Strategy has been developed by SECBC with assistance from CISC. Draft guidelines have been submitted to the S Technical Committee on Steel Structures for review and comment.

10 Code Changes and Designer s Option 2) - Cont. Concerns - Cont. Proposed interim solution/guidelines for local designers until:» further research completed;» easier analysis techniques developed for commercial use;» modified philosophies warrant new design procedures.

11 Code Changes and Designer s Options 3) & 4) Lower T u : Concerns - Cont.» material removal near brace ends for reduced cross sectional area;» incorporate controlled yield plate fuses within the brace. Increase C r :» utilize composite performance capabilities of HSS.

12 Background to Pilot Research Program Spawned by interest received by the SSEF from local designers regarding testing. Also from requests of local designers on performance expectations of proposed connections intended for current building integration. Concerns were developing that untested solutions may be innocently incorporated into designs.

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14 Background to Pilot Research Program - Cont. Funding obtained from: APEGBC, DSE, SECBC, VSEG (CSCE), VISEG (CSCE), EERF (UBC), CWB, Herold Engineering NSERC NRC IRAP Grant Program Fabricators:Les Constructions Beauce-Atlas, Canron, XL Iron Works, Empire Iron Works, Solid Rock Steel. Geo. Third & Son, and Agra Coast

15 Background to Pilot Research Program - Cont. Process of developing the research program allowed the participation of local consultants to assist in the development of potential details. Ecole Polytechnique and UBC were selected as collaborating universities because of their past experience in the testing of CBF s and of their involvement in earthquake engineering research with steel.

16 Background to Pilot Research Program - Cont. Phase I - full scale tests of an industry proposed detail and subsequent modifications. Phase II - development of a suite of alternate details for strain characteristics/ductility/limitations investigation. Phase III - full scale tests of the most promising details.

17 Phase I - Ecole Polytechnique Full-Scale Testing of Prototype Brace Fuse Detail Robert Tremblay Nebil Bouatay

18 Phase I PINNED JOINT (typ.) 900 kn ACTUATOR (typ.) 2 C15 x W 12 x W 12 x 106 ANCHOR PLATE (typ.) 4877 PINNED JOINT (typ.)

19 Specimen B / y ATC-24

20 Specimen B1

21 Specimen B1

22 Specimen B V / Vy / y

23 Specimens B2 & B3

24 Specimens B2 & B3

25 Specimen B2

26 Specimen B2

27 Specimen B V / Vy / y

28 Specimen B V / Vy / y

29 Phase II - UBC Pilot Testing of Fuse Details for HSS Bracing Members Helmut Prion Mahmoud Rezai Peter Timler

30 A HSS Class C 190 mm A: 125 mm B: 175 mm 55 mm A SECTION A-A 1250 mm Opening on four sides to be control cut to produce as smooth a finish as possible (no grinding).

31 Fracture across the corner leg yielding along the fuse length

32 Axial Load (kn) Axial Displacement (mm)

33 190 mm A B: 175 mm A: 125 mm 50 mm HSS Class C Wood blocking inside 25 mm 55 mm A HSS SECTION A-A Opening on four sides to be control cut to produce as smooth a finish as possible (no grinding) mm 3 This End Only

34 LVDT LVDT

35 Slight global out-of-plane buckling of the specimen Formation of ripples along the fuse detail resulted in jamming effect. Fracture across the corner leg

36 Axial Load (kn) Axial Displacement (mm)

37 A HSS Class C 200 mm B: 175 mm A: 125 mm 152 mm 20 mm PL 22 mm slot 55 mm 5 A 1250 mm SECTION A-A Opening on two sides to be control cut to produce as smooth a finish as possible (no grinding).

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40 Axial Load (kn) Axial Displacement (mm)

41 A HSS Class C 240 mm 40 mm 40 mm 20 mm 20 mm CL A SECTION A-A 30 mm DIA Typ mm Same hole pattern on all four sides.

42 Compression yielding (oval shape of circular holes) Opening up of a tear during tension loading

43 Inelastic local buckling initiated global instability

44 Axial Load (kn) Axial Displacement (mm)

45 LVDT Steel jacketing around the fuse detail Gap LVDT

46 Axial Load (kn) Axial Displacement (mm)

47 HSS Class C No weld to PL A over this length. 25 mm A 25 mm No weld to PL A over this length. HSS Class C 250 mm 50 mm 100 mm 50 mm 150 mm PL A 5 End PL 10 3 A 1250 mm 5 Typ. PL PL SECTION A-A 5 See elevation for discontinuity. No weld of end PL this location, Typ.

48 Global out-of-plane buckling of the specimen Yielding was mainly concentrated around the 25 mm unsupported length of the fuse detail.

49 Axial Load (kn) Axial Displacement (mm)

50 HSS Class C A PL mm 135 mm 150 mm B A HSS Class C 15 mm L mm 65 mm 38 L B 1250 mm R = 144 mm Typ. 175 mm 175 mm 5 30 mm Typ. L cut the outstanding leg to fit inside HSS. 51 mm 90 mm PL mm φ for M16 bolt. 220 mm SECTION A-A 69 mm, Typ. 18 mm φ slot hole for M16 bolt. SECTION B-B

51 Global and local out-of-plane buckling of the specimen

52 Axial Load (kn) Axial Displacement (mm)

53 HSS Class C 5 A Typ. HSS Class C 60 mm x* mm 60 mm Typ. 5 5 mm no weld Typ. Straps for the 3rd specimen only 25 mm 100 mm 6 mm all four sides. A 1250 mm L all four sides SECTION A-A Straps on all four sides specimen 7C only. * Specimen 7A: x = 75 mm Specimen 7B: x = 50 mm Specimen 7C: x = 75 mm with straps in the middle

54 Uniform yielding along the angles Local bending (ripples) at connection detail

55 Local twisting and bending of the angles under compression loading Fracture across the angle section at the end of testing

56 Axial Load (kn) Axial Displacement (mm)

57 Yielding along the angles Twisting and bending of the angles under compression loading

58 Global out-of-plane buckling of the angles under compression loading Fracture across the angle section at the end of testing

59 Specimen failed in tension Axial Load (kn) Axial Displacement (mm)

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62 Specimen failed in tension Axial Load (kn) Axial Displacement (mm)

63 Phase III - Ecole Polytechnique Full scale testing of frames with selected fuse details Robert Tremblay Nebil Bouatay

64 Phase III PINNED JOINT (typ.) 900 kn ACTUATOR (typ.) 2 C15 x W 12 x 106 W 12 x 106 FUSE DETAIL ANCHOR PLATE (typ.) 4877 PINNED JOINT (typ.)

65 Specimens B4 & B5 HSS 127x127x9.5 X 375 L. (EXT. SLEEVE) HSS 102x102x4.8 (BRACE) HSS 89x89x8.0 FULL LENGTH (INT. SLEEVE) 55 X 175 ELLIPTIC HOLE TO BE CONTROL FLAME CUT ON FOUR SIDES HSS 127x127x9.5 X 700 L. (EXT. SLEEVE) HSS 102x102x4.8 (BRACE) HSS 89x89x8.0 FULL LENGTH (INT. SLEEVE) 55 X 350 ELLIPTIC HOLE TO BE CONTROL FLAME CUT ON FOUR SIDES

66 Specimens B4 & B5

67 Specimen B4

68 Specimen B V/Vy / y

69 Specimen B5 Protocols 6 4 ATC-24 / y ATC-24 4 SEISMIC / y

70 Specimen B5 Failure Mode

71 Specimen B5-A (ATC-24) V/Vy / y

72 Specimen B5-B (Seismic) V/Vy / y

73 Specimen B6 HSS 102x102x4.8 WITH 175 L. GAP (BRACE) HSS 89x89x8.0 x 375 L. (INT. SLEEVE) 4 L25x25x5 x 325L. WITH 3 25x100x6 STRAPS ON FOUR SIDES

74 Specimen B6

75 Specimen B6

76 Specimen B V/Vy / y

77 Specimen B7 13 mmgusset PLATE WITH 100 x 400 L. FUSE SLOTTED HOLE 2 (BRACE)

78 Specimen B7

79 Specimen B7

80 Specimen B7-A (ATC-24) V/Vy / y

81 Specimen B7-B (Seismic) V/Vy / y

82 6 Fracture 4 2 B7-A Life / y 0-2 B4 B6 B5-A B5-A -4 B B7-B / y B5-B Partial fracture Com plete fracture

83 Conclusions Ductile brace fuse detail for steel CBFs is a very effective means of reducing the demand on non ductile elements and achieving a high level of seismic response. More research is required to: i) ) improve the proposed systems and, ii) ) develop a model to predict the fracture life of brace fuse systems.

84 The next steps.. Refine fuse details Analytical studies of braced frames Dynamic analysis of frames with different brace configurations subjected to real earthquake input Determination of displacement demand and appropriate R-factors Shake table tests of braced frames Verification of analytical models