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Stop criteria for proof load tests verified with field and laboratory testing of the Ruytenschildt Bridge

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As the existing bridge stock is aging, improved assessment methods such as proof load testing become increasingly important. Proof load testing involves large loads, and as such the risk for the structure and personnel can be significant. To capture the structural response, extensive measurements are applied to proof load tests. Stop criteria, based on the measured quantities, are used to identify when further loading in a proof load test is not permitted. For proof load testing of buildings, stop criteria are available in existing codes. For bridges, recently stop criteria based on laboratory tests on beams reinforced with plain bars have been proposed. Subsequently, improved stop criteria were developed based on theoretical considerations for bending moment and shear. The stop criteria from the codes and the proposed stop criteria are compared to the results from field testing to collapse on the Ruytenschildt Bridge, and to the results from laboratory tests on beams sawn from the Ruytenschildt Bridge. This comparison shows that only a small change to the stop criteria derived from laboratory testing is necessary. The experimental evidence strengthens the recommendation for using the proposed stop criteria in proof load tests on bridges for bending moment, whereas further testing to confirm the stop criteria for shear is necessary.

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Stop criteria for proof load tests verified with field and laboratory testing of the Ruytenschildt Bridge

  1. 1. Challenge the future Delft University of Technology Stop criteria for proof load tests verified with testing of the Ruytenschildt Bridge Eva Lantsoght, Yuguang Yang, Cor van der Veen, Dick Hordijk, Ane de Boer
  2. 2. 2 Overview • Introduction to proof load testing • Ruytenschildt Bridge testing: field and laboratory • Analysis of stop criteria • Summary & Conclusions Slab shear experiments, TU Delft
  3. 3. 3 Why load testing? Bridges from 60s and 70s The Hague in 1959 Increased live loads common heavy and long truck (600 kN) End of service life + larger loads
  4. 4. 4 Proof load testing • Target load – other research topic • Stop criteria: • Further loading not permitted • Failure near • Irreversible damage near • Safe for bending moment AND shear? MSc Thesis W. Vos
  5. 5. 5 Existing Guidelines for proof loading • Europe: DAfStB Richtlinie • Stop criteria • Concrete strain • Steel strain • Crack width and residual crack width • Residual deflection • For flexure • For buildings
  6. 6. 6 Existing Guidelines for proof loading • North America: • Buildings: ACI 437.2M-13 • Bridges: Manual of Bridge Rating Through Load Testing (1998) • ACI 437.2M-13 stop criteria: • Residual deflection • Permanency ratio • Deviation from Linearity Index
  7. 7. 7 Ruytenschildt Bridge (1) • Existing reinforced concrete slab bridge (1962) • Test to failure in two spans • 4 concentrated load – one tandem • Cyclic loading protocol • Failure only achieved in span 2 • Failure test: analyse stop criteria and determine margin of safety
  8. 8. 8 Ruytenschildt Bridge (2) Existing bridge Partial demolition and building new bridge
  9. 9. 9 Test results Span 1 • Maximum load 3049 kN • Maximum available load for span 1 • Flexural cracks • No failure • Order additional load for test 2!
  10. 10. 10 Test results Span 2 • Maximum load 3991 kN • Large flexural cracks • Flexural failure • yielding of reinforcement • Settlement of bridge pier with 1.5cm • Elastic recovery to 8mm
  11. 11. 11 Ruytenschildt Bridge (3)
  12. 12. 12 Beams from Ruytenschildt Bridge • Beams from Ruytenschildt Bridge • Cyclic loading protocol • Tests: Failure in shear and flexure • Measurements: • Lasers: deflection of beam • LVDTs: crack opening • Acoustic emission sensors • Analyze stop criteria and determine margin of safety Beams RSB01 after failure (Yang, 2015) Yang, Y. (2015). "Experimental Studies on the Structural Behaviours of Beams from Ruytenschildt Bridge," Stevin Report 25.5-15-09, Delft University of Technology, Delft, 76 pp. Beams RSB02B after failure (Yang, 2015)
  13. 13. 13 Comparison between stop criteria and field test – German guideline Criterion Plim (kN) Span 1 Plim (kN) Span 2 Strain 2719 3028 Increase in crack width >Pu >Pu Residual crack width 481 418 Residual deformation (measured) 408 221 Residual deformation (zero) 474 3156 • Strain stop criterion: OK • Increase in crack width: not exceeded • Residual crack width and residual deformation: exceeded at first load level (extremely conservative)
  14. 14. 14 Comparison between stop criteria and field test – ACI 437.2M-13 Criterion Plim (kN) Span 1 Plim (kN) Span 2 IDL, loading branch 1438 418 / 3156 IDL, unloading branch 1923 418 / 2657 Ipr 481 444 Residual deformation (measured) 780 3738 Residual deformation (zero) >Pu 3738 • Not very suitable when other loading protocol is used than what is prescribed by ACI 437.2M-13 • Residual deformation after 24 hours: not practical for bridge testing
  15. 15. 15 Comparison between stop criteria and field test – TU Delft proposal Criterion Plim (kN) Span 1 Plim (kN) Span 2 Concrete strain 2719 3028 Maximum crack width >Pu >Pu Residual crack width >Pu >Pu Stiffness reduction (5%), loading branch 481 444 Stiffness reduction (5%), unloading branch 481 1492 Stiffness reduction (25%), loading branch 1923 3159 Stiffness reduction (25%), loading branch 1949 3159 Deformation profiles – longitudinal 1900 2600 Deformation profiles - transverse 1900 2600 • Based on this analysis: replace stiffness reduction (5% in original proposal, now use 25%)
  16. 16. 16 Comparison between stop criteria and field test – TU Delft proposal • Stiffness is determined based on loading and unloading branch • Use deflection plots to check repeatability and linearity
  17. 17. 17 Comparison between stop criteria and lab test – German guideline Criterion Plim (kN) RSB01F Plim (kN) RSB02A Plim (kN) RSB02B Plim (kN) RSB03F Plim (kN) RSB03A Strain 150 196 219 319 585 Increase in crack width 274 Pu >Pu Pu >Pu Residual crack width 77 76 74 147 >Pu Residual deformation (measured) 49 226 74 147 196 Residual deformation (zero) 49 Pu 74 147 Pu • Recommended: use strain stop criterion • Other stop criteria: sometimes exceeded at very low load level
  18. 18. 18 Comparison between stop criteria and lab test – ACI 437.2M-13 Criterion Plim (kN) RSB01F Plim (kN) RSB02A Plim (kN) RSB02B Plim (kN) RSB03F Plim (kN) RSB03A IDL, loading 77 175 > Pu 293 390 IDL, unloading 77 175 >Pu 244 391 Ipr 75 126 125 293 196 Residual deformation (measured) 49 Pu 74 147 Pu Residual deformation (zero) 50 Pu 74 Pu Pu • Loading protocol should be same as in ACI 437.2M-13 • Requires force-controlled testing • Residual deformation: large scatter
  19. 19. 19 Comparison between stop criteria and lab test – TU Delft proposal Criterion Plim (kN) RSB01F Plim (kN) RSB02A Plim (kN) RSB02B Plim (kN) RSB03F Plim (kN) RSB03A Concrete strain 150 196 219 319 585 Max. crack width 274 > Pu > Pu Pu > Pu Res. crack width 150 226 416 Pu > Pu ΔEI (25%), L, laser 3 77 175 - - 391 ΔEI (25%), UL, laser 3 103 175 - - 391 ΔEI (25%), L, laser 6 274 Pu > Pu 244 Pu Stiffness reduction (25%), UL, laser 6 150 >Pu > Pu 244 391 Def. prof. – horizontal, N 150 225 175 Pu - Def. prof. – horizontal, S - > Pu 175 342 - Def. prof. – vertical 150 225 175 342 391
  20. 20. 20 Comparison between stop criteria and lab test – TU Delft proposal • Different results for lasers 3 and 6 because beam was not sawn straight • “-” required sensor output not measured • Ignore crack width smaller than 0.05 mm • RSB01F: strong fluctuation of stiffness, possibly torsional distress due to beam not being straight, stop criterion (stiffness) exceeded at 28% of Pu • RSB02A: stop criterion (stiffness) exceeded at 47% of Pu • RSB02B: stop criterion (deformation profiles) exceeded at 42% of Pu • RSB03F: stop criterion (stiffness) exceeded at 41% of Pu • RSB03A: stop criterion (displacement profiles) exceeded at 57% of Pu
  21. 21. 21 Recommended stop criteria • Validation of stop criteria for bending moment • Not enough data for shear • Field test: exceeded at 60 – 70% of max load • Lab test: exceeded at 40 – 60% of max load (RSB01F neglected)
  22. 22. 22 Summary & Conclusions • Ruytenschildt Bridge • Existing slab bridge scheduled for replacement • Testing in 2 spans, failure in span 2 • Beams sawn and tested in lab • Stop criteria • When exceeded: margin of safety • Comparison to German guideline and ACI 437.2M-13 • Comparison to TU Delft proposal • OK for bending moment • More experiments necessary for shear
  23. 23. 23 Contact: Eva Lantsoght E.O.L.Lantsoght@tudelft.nl // elantsoght@usfq.edu.ec +31(0)152787449

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