Cor van der Veen

Shear in One-Way Slabs under Concentrated Load Close to Support

One-way slabs under concentrated loads are generally designed for shear by checking the beam shear resistance and the punching shear resistance over an effective width. Only a small number of test data regarding the shear resistance of one-way slabs subjected to concentrated loads is currently available. To be able to better evaluate the shear resistance of one-way slabs, a series of experiments was carried out on continuous one-way slabs (5 m x 2.5 m x 0.3 m [16.4 ft x 8.2 ft x 11.8 in.]) subjected to concentrated loads close to the supports, in which the load position, transverse reinforcement ratio, and concrete strength were varied. The test results are compared with code provisions and a method developed by Regan. The results show a different behavior in shear for slabs under concentrated loads than for beams.

One-Way Slabs Subjected to Combination of Loads Failing in Shear

SUMMARY AND CONCLUSIONS For the assessment of existing solid slab bridges subjected to dead loads and live loads, it is necessary to analyze the combination of the shear stresses from concentrated and distributed loads. A first series of experiments on the shear capacity of slabs only considered concentrated loads close to supports. Recommendations for the effective width in shear resulted from these tests.The current series of experiments studied the combination of loads. The hypothesis of superposition of concentrated loads over their respective effective width and distributed loads over the full slab width was tested. A unique series of 26 experiments on eight slabs subjected to a combination of a concentrated load close to the support and a line load was conducted. It was found that the hypothesis of superposition is valid and conservative. Typically, larger shear capacities were found for the case of combined loading.The influence of the distance between the concentrated load and the support and the shear capacity was confirmed for the case of combined loading. Slabs supported by a line of elastomeric bearings showed a less brittle failure mode than slabs supported by a line of steel bearings. There is no experimental evidence for treating direct load transfer differ -ently depending on the support material (as prescribed by NEN-EN 1992-1-1:2005).Experiments were carried out with the concentrated load close to the simple and continuous support. A slightly larger shear capacity was found at the continuous support. This increase was smaller than predicted by α

Collapse test and moment capacity of the Ruytenschildt reinforced concrete slab bridge

Abstract A large number of existing reinforced concrete solid slab bridges in the Netherlands are found to be insufficient for shear upon assessment. However, research has shown additional sources of capacity in slab bridges, increasing their total capacity and possibly changing their failure mode. Previous testing was limited to half-scale slab specimens cast in the laboratory. To study the full structural behaviour of slab bridges, testing to failure of a bridge is necessary. Research on load testing is carried out in order to develop load testing guidelines. In August 2014, a bridge was tested in two spans. The bridge was load tested, and additional cycles until yielding occurred in the reinforcement were added to the experiment. Though calculations with current design provisions showed that the bridge could fail in shear, the field test showed failure in flexure before shear. The unity check for flexure was determined. The experiment shows that the methods for rating of existing reinforced concrete slab bridges are conservative.

Probabilistic prediction of the failure mode of the Ruytenschildt Bridge

In the Netherlands, the shear capacity of a large number of existing reinforced concrete solid slab bridges is subject to discussion, as initial assessments indicated that their capacity was insufficient. In certain cases, the deterministic value of the moment capacity is larger than the deterministic value of the shear capacity. However, when the variability of the material properties, and of the capacity models themselves are factored in, a probability of a certain failure mode can be calculated. Here, a method is introduced to calculate the chance that a cross-section fails in shear before it fails in bending. The method that is derived here is applied to the Ruytenschildt Bridge. This case study is a reinforced concrete solid slab bridges that was tested to failure in two spans during the summer of 2014. The relative probability of failure in shear of the bridge was determined. The predictions indicated a smaller probability of a shear failure than of a bending moment failure. In the first tested span, failure was not reached, but indications of flexural distress were observed. In the second span, a flexural failure was achieved, in line with the probabilistic predictions. The presented method can be used in the assessment of existing bridges to determine which failure mode is most probable, taking into account the variability of materials and capacity models.

Case study on aggregate interlock capacity for the shear assessment of cracked reinforced-concrete bridge cross sections

AbstractA 55-year-old bridge showed large cracking in the approach bridge caused by restraint of deformation and support settlement. After repair, it was uncertain at which crack width the traffic loads on the bridge should be further restricted. The shear capacity was calculated by counting on the aggregate interlock capacity of a supposedly fully cracked cross section. An aggregate interlock relationship between shear capacity and crack width based on an unreinforced section was used to find the maximum allowable crack width. Limits for crack widths at which load restrictions should be imposed were found. The large structural capacity of the cracked concrete section shows that the residual bearing resistance based on the aggregate interlock capacity of reinforced concrete slab bridges with existing cracks is higher than expected. This expected capacity could be calculated with the inclined cracking load from the code provisions. The procedure outlined in this paper can thus be used for the shear assessm...

Pilot Proof-Load Test on Viaduct De Beek: Case Study

For existing bridges, proof-load testing can be a suitable assessment method. This paper addresses the evaluation of a posted reinforced concrete slab bridge over a highway through proof-load testing, detailing the preparation, execution, and analysis of the test. As the target proof-load and the required measurements for proof-load testing currently are not well-defined in the existing codes, this pilot case was used to develop and evaluate proposed recommendations for proof-load testing for a future guideline on proof-load testing for the Netherlands. Moreover, the pilot proof-load test is used to study the feasibility of proof-load testing for both shear and flexure

Experiments on Punching Shear Behavior of Prestressed Concrete Bridge Decks

In the Netherlands, most of the bridges were built more than 50 years ago and it is essential for bridge authorities to find out if these bridges are still safe for modern traffic loads for which they were not designed initially. Experiments on a 1:2 scale were carried out in the laboratory of the Delft University of Technology (TU Delft) to investigate the bearing capacity of bridge decks with varying levels of transverse prestressing subjected to concentrated wheel loads. All the tests showed failure in punching shear. It was found that, as a result of compressive membrane action (CMA) by virtue of lateral restraint effects, in combination with the transverse prestressing, the punching shear resistance of the decks was much larger than predicted by most international codes that do not consider the effect of CMA. It appears to be worthwhile to regard CMA when assessing the bearing resistance of existing bridges to avoid unnecessary strengthening measures.

An Experimental Study on the Transition of Failure Between Flexural and Shear for RC Beams

The paper presents a large experimental research program carried out at Delft University of Technology supported by the Dutch Ministry of Infrastructure and the Environment. The research evaluates the shear capacity of RC beam/slab strips at transition of the failure modes between flexural and shear (defined as v bd ). With 106 tests, the values of v bd were obtained for specimens with 7 different configurations covering the variables that are usually found in the existing solid bridge deck slabs. The results are compared with the related expressions suggested by several available design provisions. Suggestions are made to further improve these expressions.

Extended Strip Model for Slabs Subjected to a Combination of Loads

Reinforced concrete slab bridges are assessed for a combination of loads that include self-weight, superimposed loads, and distributed and concentrated live loads. The shear capacity of reinforced concrete slabs subjected to a combination of loads is thus an important topic for the assessment of existing bridges. Currently, a plastic model exists for the assessment of reinforced concrete solid slabs subjected to a concentrated load: the Extended Strip Model, based on the Strip Model for concentric punching shear. To apply this model to slabs subjected to a combination of loads, the model needs to be adapted based on theoretical principles. The results are then compared with the results from experiments on half-scale slab bridges subjected to a combination of a concentrated load close to the support and a line load. The result of this comparison is that the proposed method is suitable to find a safe estimate of the maximum concentrated load on the slab. The implication of this development is that an improved tool is available to estimate the maximum load of a truck that can be placed on a reinforced concrete bridge, thus improving the current assessment.

Determination of Loading Protocol and Stop Criteria for Proof Loading with Beam Tests

Proof loading of existing bridges is an interesting option when insufficient information about a bridge is available. To safely carry out a proof loading test, high loads are placed on the bridge. To avoid permanent damage to the structure, a controlled loading protocol needs to be described, and the measurements need to be closely monitored to identify the onset of distress. The criteria from existing codes and guidelines to evaluate the measurements, called stop criteria, are not universally applicable. To develop recommendations for proof loading of reinforced concrete solid slab bridges, beam experiments were analysed. The beams were heavily instrumented to evaluate the existing stop criteria, and possibly develop new stop criteria. The result of these experiments is the development of a standard loading protocol for the proof loading of reinforced concrete slab bridges. Recommendations for the use of the stop criteria are also formulated. These insights are used to develop a new guideline for the proof loading of reinforced concrete slab bridges in the Netherlands.