Defining loading criteria for proof loading
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Defining loading criteria for proof loading
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As the bridge stock in The Netherlands and Europe is ageing, various methods to analyse existing bridges are being studied. Proof loading of bridges is an option to study the capacity when crucial information about the structure is lacking. This information could be related to the material (for example, the effect of alkali-silica reaction on the structural capacity) as well as to the structural system (for example, the effect of restraints at the supports or transverse redistribution capacity). When it is decided to proof load a bridge, the question arises which maximum load should be attained during the experiment to approve the capacity of the bridge, and which criteria, based on the measurements during the test, would indicate that the proof loading needs to be aborted before reaching the maximum desired load (the so-called stop criteria). To define the required loading criteria, a review of the literature has been made, finite element models of existing viaducts have been made, and on these viaducts, proof loading tests have been carried out. These bridges were heavily instrumented, with a goal of learning as much as possible about the structural behaviour during proof loading. As a result of the analysis and experiments, recommendations are given for proof loading of bridges with respect to the required maximum load and the stop criteria. These recommendations are important, since they form the basis of a guideline for proof loading of existing concrete bridges that is under development in The Netherlands.
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Defining loading criteria for proof loading
- Challenge the future Delft University of Technology Defining loading criteria for proof loading Rutger Koekkoek, Eva Lantsoght, Yuguang Yang, Ane de Boer, Dick Hordijk of existing reinforced concrete bridges
- 2 Overview • Introduction • Why proof loading? • Stop criteria? • Overview of existing guidelines • Past proof load tests by TU Delft • Recommendations • Preparation of proof load tests • Execution of proof load tests • Summary and conclusions Slab shear experiments, TU Delft
- 3 Why load testing? (1) 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 Why load testing? (2)
- 5 Stop criteria • Safety philosophy • Stop criteria: • Further loading not permitted • Failure near • Irreversible damage near MSc Thesis W. Vos
- 6 Proof load testing of bridges • Apply predetermined load to bridge • Information lacking • Damage due to ASR, … • Proof load testing • Immediate approval of bridge • Recalculate updated β
- 7 Existing Guidelines for proof loading • Europe: DAfStB Richtlinie • Stop criteria • Concrete strain • Steel strain • Crack width and residual crack width (new & existing cracks) • Residual deflection • For flexure • Structures with large existing cracking?
- 8 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
- 9 Research need • Guideline for proof loading of existing bridges for the Netherlands • Flexure + shear • Stop criteria?
- 10 TU Delft Proof Load Tests • Proof load tests: • Heidijk 2007 • Medemblik 2009 • Vlijmen-Oost 2013 • Halvemaans Bridge 2014 • Ruytenschildt Bridge 2014 • Viaduct in the Zijlweg 2015 • Viaduct De Beek 2015 Load test to failure of Ruytenschildt Bridge, summer 2014
- 11 Preparation steps (1) • Determination of dimensions • Live load: EN 1991-2:2003 • RBK load levels • Different β • Different load factors • In FEM model • mx over 3 m • v over 4d
- 12 Preparation steps (2) • Critical position • Bending moment: largest moment • Shear: 2.5d from support • Required proof load • Same shear or bending moment as with load combination • Value → considered safety level
- 13 Execution steps • Cyclic loading scheme • Acoustic emission measurements • Check linearity and reproducibility of measurements • Check residual deformations • Stop criteria • Evaluated during tests • Research in progress • Criteria for shear failure need to be developed
- 14 Summary and conclusions • Proof loading to approve existing bridges • Existing guidelines: • Only flexure • Cracked structures? • Determination of maximum proof load • LFEA • Different safety levels • Execution • Cyclic loading protocol • Safely applying large loads Viaduct Zijlweg, tested in summer 2015
- 15 Contact: Eva Lantsoght E.O.L.Lantsoght@tudelft.nl // elantsoght@usfq.edu.ec +31(0)152787449