Proof loading of existing bridges is an option to study the capacity when crucial information about the structure is lacking. To define the loading criteria for proof load testing, 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, to learn as much as possible about the structural behaviour during proof loading. Additional laboratory experiments have been used to develop controlled loading protocols, and to identify which stop criteria can be used for which case. 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 have resulted in a guideline for proof loading of existing reinforced concrete slab bridges for The Netherlands.

1. Recommendations for proof load testing of
reinforced concrete slab bridges
Eva O.L. Lantsoght1,2, Cor van der Veen2, Ane de Boer3, Dick Hordijk2
1 Politécnico, Universidad San Francisco de Quito, Quito, Ecuador
2 Concrete Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology, The Netherlands
3 Rijkswaterstaat, Ministry of Infrastructure and the Environment, The Netherlands
Proof load testing in the Netherlands
To explore the possibility of using proof load testing for the assessment of existing
bridges, a number of pilot proof load tests on shear- and flexure-critical bridges, with
and without material degradation, were carried out [2].
What is proof load testing?
In a proof load test, a load representative of the factored live load is applied to the
bridge. If the structure can withstand the applied load without signs of distress, it is
experimentally shown that the bridge fulfills the loading requirements.
Why proof load testing?
Existing bridges often do not rate sufficiently for the current live load models [1].
When uncertainties with regard to material degradation or the structural system
are large, proof load testing can be used.
Fig. 1: Load application methods
(a)
Assessment after proof load test
Direct result
Post-processing
of data for report
Execution of proof load test
Loading protocol Stop criteria
Preparation of proof load test
Target proof load Load position
• Live load: NEN-EN 1991-2:2003 [3]
• Different load levels, depending on different
safety levels
• Using a linear finite element model: find load
and load configuration that results in the same
sectional shear or sectional moment as
Eurocode live loads
• For bending moment based on moving the live
load to find the position that results in the
highest section moment
• For shear (RC slab bridges): 2.5d from the face
of the support
Fig. 2: Moving the live load to find the critical
position
Fig. 3: Recommended loading protocol
Existing flexural cracks?
Uncracked Cracked
Flexure
εc < 0.8 ‰ – εc0
wmax ≤ 0.5 mm
wres ≤ 0.1 mm
wres < 0.3wmax
ΔEI ≤ 25 %
Deformation profiles
Load-deflection graph
εc < 0.8 ‰ – εc0
wmax ≤ 0.5 mm
wres ≤ 0.1 mm
wres < 0.2wmax
ΔEI ≤ 5 %
Deformation profiles
Load-deflection graph
Shear
εc < 0.8 ‰ – εc0
wmax ≤ 0.3 mm
ΔEI ≤ 5 %
Deformation profiles
Load-deflection graph
εc < 0.8 ‰ – εc0
ΔEI ≤ 5 %
Deformation profiles
Load-deflection graph
• Cyclic loading protocol: check linearity and
reproducibility of the measurements
• First load level: check all sensors
• Second load level: Serviceability Limit State
• Interim level
• Target load level as determined with linear finite
element analysis
• After Serviceability Limit State: small steps for
safe loading
• Constant loading speed: 3 kN/s – 10 kN/s
• Baseline load level to keep jacks and
instrumentation activated
• Stop criteria based on ACI 437.2M-13 [4] and
DAfStB [5]
• Analysis of beams tested in the lab [6] and
verification of pilot proof load tests [7]
• Note: limited data of lab tests on shear
• Future work: improvement of stop criteria for
shear and verify with experiments on slabs
References
[1] Lantsoght EOL, van der Veen C, de Boer A, Walraven JC (2013) Recommendations for the Shear Assessment of Reinforced Concrete Slab Bridges from
Experiments. Structural Engineering International, Vol. 23, Nr. 4, pp. 418-426
[2] Lantsoght EOL, Van der Veen C, De Boer A, Hordijk DA (in press) Proof load testing of reinforced concrete slab bridges in the Netherlands. Structural
Concrete.
[3] CEN, Eurocode 1: Actions on structures - Part 2: Traffic loads on bridges, NEN-EN 1991-2:2003. 2003, Comité Européen de Normalisation: Brussels,
Belgium. p. 168.
[4] ACI Committee 437, Code Requirements for Load Testing of Existing Concrete Structures (ACI 437.2M-13) and Commentary 2013: Farmington Hills,
MA. p. 24.
[5] Deutscher Ausschuss für Stahlbeton, DAfStb-Guideline: Load tests on concrete structures (in German). 2000, Deutscher Ausschuss fur Stahlbeton,. p. 7.
[6] Lantsoght EOL, Yang Y, van der Veen C, de Boer A, Hordijk DA (2017) Beam experiments on acceptance criteria for bridge load tests. ACI Structural
Journal Vol. 114, Nr. 4, pp. 1031-1041.
[7] Lantsoght, E., Verification of stop critera for proof load tests. 2017, Delft University of Technology: Delft. p. 40.
Table 1: Overview of stop criteria
Fig. 5: Beam test and
instrumentation used
for verification of stop
criteria
• Correction of measurements for deflection of
support
• Correction of measurements for effects of
temperature and humidity
Fig. 4: Envelope of load-
deflection graph for pilot
proof load test De Beek:
(a) bending moment; (b)
shear