Beam experiments to investigate loading protocol and stop criteria for load testing

Beam Experiments to Investigate Loading Protocol and Stop Criteria for Load Testing

Eva O.L. Lantsoght1,2, Yuguang Yang2, Dick Hordijk2

1 Politécnico, Universidad San Francisco de Quito, Quito, Ecuador2 Concrete Structures, Faculty of Civil Engineering and Geosciences, Delft University of Technology, The Netherlands

Proof load testing research: field testing

Laboratory testing: beams

Results

Proof load testing in the NetherlandsTo 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].

Open questions after pilot testsWhich stop criteria should we use? Stop criteria [3, 4] are criteria based on the structural response measurements. If a criterion is exceeded, the test needs to be terminated. Further load could cause irreversible damage or collapse.Which loading protocol should we use? How many load cycles per load level? At which loading speed?

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] Deutscher Ausschuss für Stahlbeton (2000) DAfStb-Guideline: Load tests on concrete structures. Deutscher Ausschuss für Stahlbeton.[4] ACI Committee 437 (2013) Code Requirements for Load Testing of Existing Concrete Structures (ACI 437.2M-13) and Commentary Farmington Hills, MA.

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 sufficient 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. 4: Vertical deformation of a beam test

Fig. 2: Loading protocol followed for proof load test on viaduct De Beek

Fig. 1: Load application methods: (a) loading vehicle; (b) steel spreader beam with

counterweights

Fig. 5: Beam with instrumentation: grid of LVDTs, lasers for vertical displacement, AE sensors

UNCRACKED CRACKEDFlexural failure

εc < 0.8 ‰ – εc0

wmax ≤ 0.5 mmwres ≤ 0.1 mmwres < 0.3wmax

Stiffness reduction ≤ 25 %Deformation profilesLoad-displacement graph

εc < 0.8 ‰ – εc0

wmax ≤ 0.5 mmwres ≤ 0.1 mmwres < 0.2wmax


Shear failure

εc < 0.8 ‰ – εc0

wmax ≤ 0.3 mmStiffness reduction ≤ 5 %Deformation profilesLoad-displacement graph

εc < 0.8 ‰ – εc0


Table 2: Overview of recommended stop criteria based on beam tests

Current practice• Codes: German

guideline [3] and ACI 437.2M-13 [4]

• Stop criteria for flexure, not shear

• Developed for buildings

Loadingprotocol

Cyclic: repeatability and linearity

Load levels: check linearity, check measurements

Target proof load as maximum load level

Parameters• Loading speed• Number of load cycles• Rest time at peak• Rest time at baseline

load• Safe approach to higher

load level

TestNo.

Shear span(mm)

Effective depth(mm)

Shear capacity

(kN)

Bending capacity

(kN)

Tested capacit

y(kN)

Failure mode

P804A1 3000 755 273 199 207 FP804A2 2500 755 219 248 232 SP804B1 2500 755 219 248 196 SP502A2 1000 465 150 154 150 F

Table 1: Overview of tested beams

Fig. 6: Recommended loading protocol

RecommendationsStop criteria depending on failure mode,See Table 2.Four load levels, see Fig. 6: lowest level tocheck functioning of sensors, serviceabilitylimit state, interim level, target proof load

Fig. 3: Stiffness reduction with load cycles

(a)