Experimental Testing of Vulnerable Concentric Braced Frames PI: STEVE MAHIN GRADUATE STUDENT RESEARCHER: BARB SIMPSON UC BERKELEY

Transcription

1 Experimental Testing of Vulnerable Concentric Braced Frames PI: STEVE MAHIN GRADUATE STUDENT RESEARCHER: BARB SIMPSON UC BERKELEY

2 Outline 1. Brief Introductory Background 2. Project Scope 3. Baseline Experimental Test at UC Berkeley 4. Possible Future Tests & Projects

3 Project Scope UNKNOWN VULNERABILITY OF OLDER BRACED FRAMES. Two Mains Goals: 1. Evaluation 2. Improvement & Retrofit Prior to 1988: Very few seismic regulations Braced frame gained popularity Seismic provisions introduced only gradually International Collaboration: University of Washington National Taiwan University Source: NCBF Damage during 1994 Northridge. (Rai and Goel 2003)

4 Sa (g) Design Spectra Design Response Spectra Period (sec) 1982 UBC (Rw = 8; K = 1) ASCE 7-10 (R = 6 SCBF)

5 Fell, Kanvinde, Deierlein (2010) Stanford Sen (2013) NCREE Test NCBF-INV-1 Test Summary Width-to-Thickness Local buckling can significantly reduce the member s capacity,, causing a premature loss in member strength. HSS rectangular sections have been shown to exhibit only a limited inelastic deformation capacity under cyclic loading

6 Weak Beam T C T 0.3C Pre-Buckling Load T C Post-Buckling Load T 0. 3C Uang, UBC/EERC-86, US-Japan Cooperative Research

7 Connection Detail NCBF SCBF W/ FOLD LINE

8 Experimental Testing ADVANCING THE BUILDING CODE Problems with ASCE 41: Requires analytical models to evaluate existing NCBF s No data to verify these models. No clear failure Hierarchy Outcomes of this project: Simple & effective retrofits Enhance engineer s and owner s ability to assess existing structures Collaborative network to foster more informed decisions about the safety of these structures Source: University of Washington & National Taiwan University Summary Report

9 TEST Setup

10 NCBF-B-1: Baseline Study

11 NCBF Design W10x54 W10x54 W10x54 W10x54 W14x53 W14x53

12 General Results

13 1st Story Shear [kips] Base Shear [kips] 2nd Story Shear [kips] Base Shear v. Roof Drift 2nd Story Shear v. Story Drift Ratio East Brace Fractures -0.9% -300 Reload +0.34% West Brace Fractures +0.9% Story Drift Ratio [%] 1st Story Shear v. Story Drift Ratio Roof Drift [%] Story Drift Ratio [%]

14 Fracture of West Brace

15

16 NCBF-B-2 CFT Braces

17 UC Berkeley NCBF-B Hollow: λhd = 0.55 (E/Fy) = 13.8

18 UC Berkeley NCBF-B & CFT: λhd = 1.4 (E/Fy) = 35.1

19 Global Views

20 Base Shear [kips] Base Shear [kips] 600 Base Shear v. Roof Drift Ratio 600 Base Shear v. Roof Drift Ratio West Brace Fractures +0.9% East Brace Fractures -0.9% East Brace Fractures -0.75% Roof Drift Ratio [%] NCBF-B Roof Drift Ratio [%] NCBF-B-2

21 Story Shear [kips] Base Shear [kips] Story Shear [kips] 600 Base Shear v. Roof Drift Ratio 600 2nd Story Story Drift Ratio [%] 1st Story Roof Drift Ratio [%] Story Drift Ratio [%]

22 Fracture of East Brace

23 1F Beam Displacement

24

25 Vertical Displacement [in.] Vertical Displacement [in.] 5 2nd Floor Beam 0-5 Pseudo-time 5 1st Floor Beam 0-5 Pseudo-time

26 East Weak Axis Column

27 East 1 st Floor Shear Tab

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30 NCBF-B-3SB Strongback retrofit

31 Strongback (SB) Concept

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33 Kinematic relationships

34 Base Shear [kips] Base Shear [kips] 600 NCBF-B-3SB Prior to loss of BRB NCBF-B-3SB After loss of BRB , F Shear Tab Failure Reload BRB satisfies AISC BRB Failure Roof Drift Ratio [%] BRB Failure F Shear Tab Failure Reload Test End 0 2 Roof Drift Ratio [%] 4

35 Base Shear [kips] 600 Story Shear [kips] Story Shear [kips] 2nd Story BRB Satisfies AISC Story Drift Ratio [%] 1st Story NCBF-B-3SB NCBF-B NCBF-B Roof Drift Ratio [%] Story Drift Ratio [%]

36 BRB Rupture

37 Beam Plastic Hinge

38 Welded Shear Tab Failures

39 Future Work Further Analytical studies assessing the qualities of each system Further calibration between experimental and numerical models Create a framework for applications of the SB system into professional practice Assess performance of SB system Quantification of effectiveness of mast Numerical models considering the frame s response spectrum and dynamic characteristics Further optimization and refinement of the SB design concept

40 Thank You. ANY QUESTIONS? Source: Example of build SB system in Berkeley