Assessment of the Seismic Response of Concentrically-Braced Steel Frames

Transcription

1 COMMISSION OF THE EUROPEAN COMMUNITIES FP7- INFRASTRUCTURES-28-1 SP4-Capacities S E R I E S SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Assessment of the Seismic Response of Concentrically-Braced Steel Frames TA Project Team Brian Broderick, Alan Hunt (Trinity College Dublin) Philippe Mongabure, Alain LeMaoult (CEA Saclay) Jamie Goggins, Suhaib Salawdeh, Gerard O Reilly (NUI Galway) Darko Beg, Primoz Moze, Franc Sinur (University of Ljubljana) Ahmed Elghazouli (Imperial College London), Andre Plumier (U Liege)

2 Concentrically Braced Frames Seismic Design Tension only or tension-compression based design A Elastic loading B Tension yielding C Elastic buckling D Straightening Shortening Brace Configurations D Tens. Axial Force B A Elongation Non-dimensional member slenderness: Af N, 5 A y / cr Hollow cross-section bracing members: crosssection slenderness: b/t; d/t Comp. C Cyclic Brace Response

3 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Low cycle fatigue fracture of hollow section brace members Higher slenderness Lower slenderness Displacement ductility predictions: Cyclic testing: brace fracture following global and local buckling (Tremblay) (Goggins et al) (Nip et al)

4 Gusset plate connection behaviour Brace buckling Gusset plate buckling Conventional Design Leads to large, thick gusset plates: R yt,gusset >> R yt,brace Elliptical Clearance Proposal (Roeder, Lehman) Facilitates more compact and thinner gusset plates such that R yt,gusset > R yt,brace Balanced Design R yt,gusset = R yt,brace

5 TA Project BRACED: Objectives Investigate under realistic earthquake loading and response conditions some key characteristics of CBFs with hollow section brace members and gusset plate connections: Influence of low cycle fatigue on ductility capacity of brace members evaluation of prediction equations for m D Influence of gusset plate connections designs on ultimate response: conventional and balanced design approaches connection to beam and column or beam only Influence of brace size and connection design on stiffness and damping in elastic range evolution of stiffness and damping with response level Obtain experimental data for the validation of numerical models OpenSees and Abacus

6 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Experimental Design Multiple experiments performed on one test frame. Brace-connection test specimens changed between experiments. Specimens with different brace cross section dimensions and connection details. Uniaxial earthquake excitation. Three levels of seismic loading: elastic (~5% / 5) post-yield/buckling (~1% / 5) ultimate (~2% / 5) Test Frame Model CBF Test Specimens (Brace Member and Connections) Repeat low level white noise excitation to measure stiffness and damping at different damage levels Brace fracture at ultimate response level.

7 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES BRACED Test Frame CB CA

8 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Experimental Programme Test ID Brace Size d/t Connection Type Gusset Plate Design 1.S1-CA-G1 8 x 8 x Beam & Column Conventional.28 2.S3-CA-G1 8 x 4 x Beam & Column Conventional.35 3.S4-CA-G1 6 x 6 x Beam & Column Conventional.36 4.S2-CA-G1 1 x 5 x Beam & Column Conventional.23 5.S1-CA-G2 8 x 8 x Beam & Column Balanced.73 6.S2-CA-G2 1 x 5 x Beam & Column Balanced.68 7.S3-CA-G2 8 x 4 x Beam & Column Balanced.62 8.S1-CB-G1 8 x 8 x Beam Only Conventional.27 9.S2-CB-G1 1 x 5 x Beam Only Conventional.24 1.S4-CB-G2 6 x 6 x Beam Only Balanced S2-CB-G2 1 x 5 x Beam Only Balanced S3-CB-G2 8 x 4 x Beam Only Balanced.62

9 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Braced Test Frame

10 Acceleration [g] Acceleration [g] Earthquake Record & Scaling Table accx vs Time (Run37) Test ID Brace Size AxTab Area (mm 2 ) Yield Strg (N/mm 2 ) 2%/5 pga (g) 1%/5 pga (g) 5%/5 pga (g) 1.S1-CA-G1 8 x 8 x S3-CA-G1 8 x 4 x S4-CA-G1 6 x 6 x S2-CA-G1 1 x 5 x S1-CA-G2 8 x 8 x S2-CA-G2 1 x 5 x S3-CA-G2 8 x 4 x S1-CB-G1 8 x 8 x S2-CB-G1 1 x 5 x S4-CB-G2 6 x 6 x S2-CB-G2 1 x 5 x S3-CB-G2 8 x 4 x Table accx vs Time (Run41) Elastic 5%/5 Ultimate 2%/5 AxTab

11 Videos S1-CA-G1 1% / 5 (pga =.35g) Front view Side view S2-CA-G1 2% / 5 (pga =.57g) Front view S3-CA-G1 2% / 5 (pga =.5g) Front view Side view

12 Base Shear [kn] Base Shear [kn] S2-CA-G1 Brace Axial Force [kn] Brace Axial Force [kn] S2-CA-G1 DXB Drift [mm] DXB Drift [mm].2.15 pga =.21g pga =.64g Roof Drift vs Time (Run65) Roof Drift vs Time (Run69) 1.5 DXB Drift 1 DXB Drift drift v time Brace Axial Force vs Time (Run65) Brace Axial Force vs Time (Run69) 1 FbracedL FbracedR 3 FbracedL FbracedR brace forces v time Base Shear (Brace) vs. Relative Disp (Run65) Base Shear (Brace) vs. Relative Disp (Run69) VbBr VbBr base shear v drift Relative DXB Displacement [mm] Relative DXB Displacement [mm]

13 Base Shear [kn] Base Shear [kn] S1-CA-G2 Brace Axial Force [kn] Brace Axial Force [kn] S2-CA-G1 DXB Drift [mm] DXB Drift [mm] pga =.77g Roof Drift vs Time (Run82) pga =.64g Roof Drift vs Time (Run69) 1.5 DXB Drift 1.5 DXB Drift drift v time Brace Axial Force vs Time (Run82) Brace Axial Force vs Time (Run69) 3 FbracedL FbracedR 3 FbracedL FbracedR brace forces v time Base Shear (Brace) vs. Relative Disp (Run82) Base Shear (Brace) vs. Relative Disp (Run69) 2 VbBr 2 VbBr base shear v drift Relative DXB Displacement [mm] Relative DXB Displacement [mm]

14 Brace and Connection Deformations

15 nat frequency (Hz) nat frequency (Hz) Damping (%) Initial natural frequency and damping S1 S2 S3 S4 CA-G1 CA-G2 CB-G1 CB-G Change in natural frequency with response amplitude 5 1.S1-CA-G1 2.S3-CA-G1 5.S1-CA-G2 4 7.S3-CA-G2 8.S1-CB-G1 3.S4-CA-G max drift (%) in prior test max drift (%) in prior test

16 Max Drift (%) Comparison of maximum response Conventional Gusset Design 8x8 8x4 6x6 1x5 8 x 8 x 3 braces pga (g)

17 SEISMIC ENGINEERING RESEARCH INFRASTRUCTURES FOR EUROPEAN SYNERGIES Transnational Access The BRACED Project Team