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Dynamic Tests of Field Specimens

Dynamic Tests of Field Specimens. Puneet Agarwal, Asli Kurtulus, Farn-Yuh Menq, and Sharon Wood Department of Civil Engineering University of Texas at Austin. Test Specimens. 6'-0". 3'-0". 6'-3". 6'-3". Bent 2. Bent 1. Terminology. Longitudinal Response of Bridge. Transverse Response

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Dynamic Tests of Field Specimens

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  1. Dynamic Tests of Field Specimens Puneet Agarwal, Asli Kurtulus,Farn-Yuh Menq, and Sharon Wood Department of Civil Engineering University of Texas at Austin

  2. Test Specimens 6'-0" 3'-0" 6'-3" 6'-3" Bent 2 Bent 1

  3. Terminology Longitudinal Response of Bridge Transverse Response of Bridge

  4. Scope of Presentation • Response of Bent 2 (short bent) is summarized. • Types of dynamic excitation: • Structural excitation using modal hammer • Ground excitation using T-Rex • Structural excitation using Thumper • Linear and nonlinear response was observed.

  5. Austin Weather 120 6 Daily High Temperature 100 5 80 4 Daily Low Temperature 60 3 Temperature, degree F Rainfall Since 1 June 2005, in. Dates of Tests 40 2 20 1 Cumulative Rainfall 0 0 6/1/2005 6/8/2005 6/15/2005 6/22/2005 6/29/2005 7/6/2005 7/13/2005 7/20/2005 7/27/2005 8/3/2005

  6. Instrumentation • Bent Cap • Two, 3D accelerometers • Two sets of three geophones • Columns • Strain gages • 1D accelerometers at three levels • Shafts • Strain gages • Two sets of three geophones in each shaft • Soil • One set of three geophones at ground surface

  7. Modal Hammer • Essentially free-vibration response. • Very low levels of excitation. • Accelerometers and geophones captured response. • Strain gages exhibited only noise.

  8. Modal Hammer f = 16.6 Hz  = 6.1% 0.1 0.05 Longitudinal Acceleration (g) 0 -0.05 -0.1 0 0.5 1 1.5 Time (sec)

  9. Modal Hammer Longitudinal Response 1.0 0.9 f = 16.6 Hz 0.8 0.7 0.6 Power Density 0.5 0.4 0.3 0.2 0.1 0.0 0 10 20 30 40 50 Frequency (Hz)

  10. Harmonic Excitation • Stepped Sine • Sufficient cycles to achieve steady-state response at each frequency increment. • Duration of tests ranged from 2 to 10 minutes. • Chirp • Duration of tests ranged from 10 to 30 seconds. • Fixed Sine • Excitation at natural frequency observed during stepped sine tests.

  11. T-Rex – Position 3

  12. T-Rex – Longitudinal Excitation Stepped Sine: 20-10 Hz 0.8 0.6 0.4 0.2 Longitudinal acceleration (g) 0 -0.2 -0.4 -0.6 -0.8 0 50 100 150 200 Time (sec) T-Rex is 25.3 ft from Bent 2 (Position 3)

  13. T-Rex – Longitudinal Excitation Stepped Sine: 20-10 Hz 0.8 0.6 0.4 0.2 Transverse acceleration (g) 0 -0.2 -0.4 -0.6 -0.8 0 50 100 150 200 Time (sec) T-Rex is 25.3 ft from Bent 2 (Position 3)

  14. T-Rex – Stepped Sine (20 – 10 Hz) Longitudinal Response 1.0 0.9 f = 14.6 Hz 0.8 0.7 0.6 Power Density 0.5 0.4 0.3 0.2 0.1 0.0 5 10 15 20 25 Frequency (Hz) T-Rex is 25.3 ft from Bent 2 (Position 3)

  15. N S W T-Rex – Fixed Sine (15 Hz) Longitudinal Response of Column 2N 4 2 0 N W E -2 Distance from Ground Surface (ft) S -4 -6 Direction ofMotion -8 -10 -20 -15 -10 -5 0 5 10 15 Range of Measured Strains (microstrain) T-Rex is 25.3 ft from Bent 2 (Position 3)

  16. Thumper – Longitudinal Excitation

  17. Thumper – Longitudinal Excitation Stepped Sine: 20-5 Hz 30% of Peak Force 0.5 Longitudinal acceleration (g) 0 -0.5 0 20 40 60 80 100 120 140 160 Time (sec)

  18. Thumper – Stepped Sine Longitudinal Response 30% of Peak Force 1.0 0.8 f = 12.6 Hz 0.6 Power Density 0.4 0.2 0 5 10 15 20 25 Frequency (Hz)

  19. Longitudinal Response Transverse Response Frequency Response 35 30.0 30 25 23.0 20.5 20 Predominant Frequency, Hz 16.6 14.6 15 12.6 10 5 0 Thumper Modal Hammer T-Rex

  20. Thumper – Longitudinal Excitation Stepped Sine: 12-5 Hz 80% of Peak Force 1.5 1.0 0.5 0 Longitudinal acceleration (g) -0.5 -1.0 -1.5 0 100 200 300 400 500 Time (sec)

  21. Thumper – Stepped Sine Longitudinal Response 80% of Peak Force 1.0 f varies during test 0.8 0.6 Power Density 0.4 0.2 0 5 6 7 8 9 10 11 12 Frequency (Hz)

  22. Longitudinal Response 20 Range of Nonlinear Response 16.6 15 12.6 11.7 – 12.0 10.9 8.2 – 9.5 10 Predominant Frequency, Hz 7.6 – 8.2 5 0 Modal Hammer 30% 60% 80% 100% Modal Hammer % of Peak Force using Thumper

  23. Thumper – Longitudinal Excitation Gaps were observed at the shaft/soil interface.

  24. S E W Thumper – Fixed Sine (9.5 Hz) Longitudinal Response of Column 2N 4 2 0 N W E -2 Distance from Ground Surface (ft) S -4 -6 Direction ofMotion -8 -80 -60 -40 -20 0 20 40 60 80 Range of Measured Strains (microstrain) 70% of Peak Force

  25. Summary • Only a cursory review of the data has been completed. • Both bents experienced nonlinear response when excited using Thumper. • Soil gapping was observed. • Extent of concrete cracking is not known. • Static pull-over tests will be conducted after thorough review of the data. • Response of top 6 to 12 in. of soil is sensitive to moisture content.

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