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. Previous testing was limited to half-scale slab specimens cast in the laboratory. To study the full structural behavior of slab bridges, testing to failure of a bridge is necessary. In August 2014, a bridge was tested to failure in two spans. Afterwards, beams were sawn out of the bridge for experimental work in the laboratory and further study. Though calculations with current design provisions showed that the bridge could fail in shear, the field test showed failure in flexure before shear. The experiments on the beams study the transition from flexural to shear failure and the influence of the type of reinforcement on the capacity. The experimental results were compared to predictions of the capacity for the bridge slab and the sawn beams. These comparisons show that the current methods for rating of existing reinforced concrete slab bridges, leading to a sharper assessment, are conservative. It was also found that the application of plain bars instead of deformed bars does not increase the shear capacity of beams. @en

Proof load tests of bridges can be very useful for structures with a lack of information, or for structures of which the effect of material degradation is difficult to assess. Contrary to diagnostic load testing, proof load testing is not well-defined in current standards in terms of required load and analysis of measurements. The risk related to the high loads used in proof load testing requires standardisation for these tests. The paper highlights important considerations for proof load testing that may lead to the development of guidelines in the Netherlands, by illustrating a pilot study on the viaduct Zijlweg in the Netherlands. This reinforced concrete bridge rates too low in shear. Topics of interest are the required load that the bridge has to withstand to be approved by the load test and the interpretation of the measurements during the test to avoid permanent damage to the structure. These measurements were compared to the stop criteria from existing codes for buildings, to examine if recommendations for the use with bridges can be formulated. The final result of the test on this case study is that the capacity of the viaduct is proven to be sufficient for shear and bending moment.@en

Most Dutch bridges were constructed around the middle of the twentieth century and considering the fact that traffic has increased exponentially since, it is important to find out if these bridges are still safe for use. Experiments on a 1:2 scale were carried out in the laboratory of the Delft University of Technology to investigate the bearing capacity of transversely prestressed concrete bridge decks subjected to concentrated wheel loads. All the tests showed failure in punching shear at loads much higher than expected from the current codes. This paper presents the results of the experimental parametric study including the effect of the transverse prestressing level (TPL), location of the load, number of loads, size of the loading area (wheel print/loading plate), and influence of previous damage to the deck slab panel, on the bearing capacity.@en

In Anbetracht steigender Verkehrslasten und geringer angesetzter Tragfähigkeiten in den vor Kurzem eingeführten Eurocodes steht in den Niederlanden die Querkrafttragfähigkeit vieler bestehender Brücken mit Stahlbetonmassivdecke zur Debatte. In den Normvorschriften werden jedoch günstige Wirkungsmechanismen, wie die Querkraftverteilung in den Platten, nicht berücksichtigt. Man benötigte Forschungsergebnisse, um das Verhalten von Stahlbetonplatten unter Einzellasten in der Nähe von Auflagern zu verstehen. Für diese Studie wurden Versuche an Platten und Balken durchgeführt. Sie zeigten, dass Platten unter konzentrierter Querkraftbelastung eine größere Tragfähigkeit haben als Balken. Das bedeutet, dass für Plattenbrücken ein höherer Belastungswert angesetzt werden kann, sodass weniger Brücken als bisher vermutet einer weiteren Prüfung bedürfen. @en

Proof load testing can be a suitable method to show that a bridge can carry the required loads from the code without distress. This paper addresses the preparation, execution, and analysis of a proof load test on a four-span reinforced concrete solid slab bridge, viaduct de Beek. The bridge has one lane in each direction, but was restricted to a single lane, since an assessment showed that the capacity is not sufficient to allow both lanes. For this proof load test, the bridge was heavily equipped with sensors, so that early signs of distress can be seen. The difficulty in this test was that, for safety reasons, only the first span could be tested, but that the lowest ratings were found in the second span. A direct approval of the viaduct by proof loading was thus not possible, and an analysis was necessary after the field test. The result of this analysis is that only by allowing 6.7% of plastic redistribution in the second span, sufficient capacity can be demonstrated.@en

Assessment of the capacity of the existing infrastructures has become more relevant in the recent years. With regard to the concrete bridges, the shear capacity of a large amount of existing concrete slab bridges reinforced with plain (smooth) bars are of concern. However, it was argued that the shear formula that is currently adapted in the design codes are not fully calibrated by experiments on members with plain bars. The arguments are based on several experimental results found in literature from the 60s. At that time, the size effect on shear capacity of members without shear reinforcement was not widely recognized yet. Thus, the specimens applied in these experiments were mostly of small depth (d = 300 mm). In those experiments a significant improvement of the shear capacity was obtained in members reinforced by plain bars. The conclusions derived in those tests have to be further evaluated with specimens that represent realistic dimensions and other configurations of the slab bridge of concern. To serve that purpose, a series of shear tests have been carried out at the Stevin Lab in Delft University of Technology recently. A number of shear tests have been carried out on specimens reinforced by plain bars with low yielding strength. The heights of the specimens are 300 mm, 500 mm and 800 mm. The test results are compared with results of peer specimens with normal deformed bars with the same configurations (dimensions, concrete strength and reinforcement ratio). The experimental results are reported in this paper. @en

As the bridge stock in the Netherlands and Europe is ageing, various methods to analyze existing bridges are being studied. Proof load testing of bridges is an option to experimentally demonstrate that a given bridge can carry the prescribed live loads. Based on extensive research on proof load testing of reinforced concrete slab bridges carried out in the Netherlands, recommendations for proof load testing of reinforced concrete slab bridges were developed. The recommendations for the preparation, execution, and post-processing of a proof load test are summarized in this paper. The novelty of the recommendations is that proof load testing for shear is studied, and that a proposal for stop criteria for shear and bending moment has been formulated. Further research on the shear behavior is necessary, after which the recommendations will be converted in guidelines for the industry.@en

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. @en

Loading protocols and acceptance criteria are available in the literature for load tests on buildings. For bridges, proof load tests are interesting when crucial information about the structure is missing, or when the uncertainties about the structural response are large. The acceptance criteria can then be applied to evaluate if further loading is acceptable, or could lead to permanent damage to the structure. To develop loading protocols and acceptance criteria for proof loading of reinforced concrete bridges, beam experiments were analyzed. In these experiments, different loading speeds, constant load level times, numbers of loading cycles, and required number of load levels were evaluated. The result of these experiments is the development of a standard loading protocol for the proof loading of reinforced concrete bridges. Based on these limited test results, recommendations for acceptance criteria are also proposed. @en

Existing reinforced concrete solid slab bridges in the Netherlands are re-assessed for shear based on a Unity Check: the ratio of the shear stress caused by the applied loads to the shear capacity of the concrete cross-section. The governing shear stress resulting from the self-weight, weight of the wearing surface, distributed and concentrated live loads, can be determined with a simplified spreadsheet-based method, the Quick Scan (Level of Assessment I) as well as with a linear finite element model (Level of Assessment II). When a finite element model is used, a distribution of shear stresses over the width of the slab bridge is automatically found. To compare the governing shear stress caused by the loads to the shear capacity, it is necessary to determine over which width the peak shear stress from the finite element model can be distributed. To answer this question, a finite element model is compared to an experiment. The experiment consists of a continuous, reinforced concrete slab subjected to a single concentrated load close to the support. Seven bearings equipped with load cells that measure the reaction force profile along the width of the slab are used to compare to the stress profile obtained from the finite element model. From this analysis, it is found that the peak shear stress in a linear finite element model can be distributed over 4dl with dl the effective depth to the longitudinal reinforcement of the slab. The comparison of measured reaction force profiles over the support to the stress profile from a finite element model results in a research-based distribution width that replaces the rules of thumb that were used until now.@en

Proof load testing is part of the engineering practice, and can be particularly useful for the rating of existing bridges. This paper addresses how reliability-based concepts can be used in combination with proof load testing, and discusses how this approach differs from the current practice for proof load testing. Whereas the calculation methods for determining the updated reliability index after a proof load test are available in the literature, this approach is now used to determine the proof load magnitude required to demonstrate a certain reliability level in a bridge, the viaduct De Beek. To determine the required proof load magnitude, the known integrals of the limit state function are solved. The method is applied to a case of a bridge that was proof load tested in the Netherlands, viaduct De Beek. The data of this bridge are used to determine the required proof load magnitude to fulfill a given reliability index. A sensitivity study is carried out to identify the effect of the assumptions with regard to the coefficient of variation on the resistance and load effects. The result of this approach is that large loads are necessary in proof load testing if a reliability index needs to be proven in a proof load test. In the current practice of proof load testing with vehicles, it can typically only be demonstrated that a certain vehicle type can cross the bridge safely. The results in this paper provide a new insight on the required proof load magnitudes to show that the reliability index of the tested bridge is sufficient. However, consensus on the coefficients of variation that need to be used on the resistance and load effects, is still missing, which significantly affects the results for the required proof load magnitudes.@en

Load testing of bridges is a practice that is as old as their construction. In the past, load testing gave the traveling public a feeling that a newly opened bridge is safe. Nowadays, the bridge stock in many countries is aging, and load testing is used for the assessment of existing bridges. This paper aims at giving an overview of the current state-of-the-art with regard to load testing of concrete bridges. The work is based on an extensive literature review, dealing with diagnostic and proof load testing, and looking at the current areas of research. Additional available information about load testing of steel, timber, and masonry bridges, buildings, and collapse testing is briefly cited. For the implementation of load testing to the aging bridge stock on a large scale, efficiency in procedures is required. The areas requiring future research are identified, based on the available body of knowledge.@en

Existing bridges with large uncertainties can be assessed with a proof load test. In a proof load test, a load representative of the factored live load is applied to the bridge at the critical position. If the bridge can carry this load without distress, the proof load test shows experimentally that the bridge fulfills the requirements of the code. Because large loads are applied during proof load tests, the structure or element that is tested needs to be carefully monitored during the test. The monitored structural responses are interpreted in terms of stop criteria. Existing stop criteria for flexure in reinforced concrete can be extended with theoretical considerations. These proposed stop criteria are then verified with experimental results: reinforced concrete beams failing in flexure and tested in the laboratory, a collapse test on an existing reinforced concrete slab bridge that reached flexural distress, and the pilot proof load tests that were carried out in the Netherlands and in which no distress was observed. The tests in which failure was obtained are used to evaluate the margin of safety provided by the proposed stop criteria. The available pilot proof load tests are analyzed to see if the proposed stop criteria are not overly conservative. The result of this comparison is that the stop criteria are never exceeded. Therefore, the proposed stop criteria can be used for proof load tests for the failure mode of bending moment in reinforced concrete structures.@en

As the bridge stock in The Netherlands and Europe is ageing, various methods to analyse existing bridges are bemg 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 structiu-al 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 diuing the experiment to approve the capacity of tiie bridge, and which criteria, based on the measiurements 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 defme the requked loading criteria, a review of the literature has been made, finite element models of existing viaducts have been made, and on tiiese viaducts, proof loading tests have been carried out. These bridges were heavily instrumented, with a goal of leaming 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. @en

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. @en

Most methods for the design and analysis of reinforced concrete slabs for punching are based on experiments on slab-column connections, reflecting the situation in building slabs. Slab-column connections with unbalanced moments have also been studied in the past. Experiments indicate that the accuracy of models for asymmetrically loaded slabs is lower than for symmetrically loaded slabs. In this paper, the difference in accuracy between test predictions for symmetrically and asymmetrically loaded slabs is tackled. A plastic model, the Extended Strip Model, is proposed. The results of maximum loads according to this model are compared to experimental results of symmetrically and asymmetrically loaded slabs. The comparison between the proposed Extended Strip Model and the experimental results shows that the model has a consistent performance for both symmetrically and asymmetrically loaded slabs. Moreover, the model has as an advantage that it combines the failure modes of flexure, shear and punching. The proposed model can be used for the analysis of slabs. In particular, it can be used for the assessment of existing slab bridges subjected to concentrated live loads.@en

In August 2014, the Ruytenschildt Bridge, a reinforced concrete solid slab bridge (reinforced with plain bars) in the Friesland province in the Netherlands was tested until failure. One of the goals of proof loading and testing this bridge to failure, was to study the failure mode of existing slab bridges. The combination of smaller shear capacities as prescribed by the Eurocode in combination with the heavier live load models, has raised concerns with regard to a number of existing slab bridges in the Netherlands. As the shear capacity of existing bridges is under study, the results of testing an actual slab bridge until failure are used to compare to the results of testing half-scale slab specimens in the laboratory, and the conclusions resulting from those experiments. In this paper, the results of the predictions based on the first order of approximation rating procedure from the Netherlands for shear, the Quick Scan method, as well as based on predictions of the failure mode and the average predicted capacity are compared to the experimental results. The predictions show a possibility of shear failure in the second span of the bridge. The experiment showed that both spans of the bridge failed in flexure. The observed failure mode is important, as some of the results indicate that the solid slab bridges, currently under discussion with regard to their shear capacity, fail in flexure in reality. Flexural failure is considered a ductile failure compared to the brittle failure mode in case of a shear failure. @en

This paper presents an experimental research program aiming at assessing the current code provisions of vmin. A large test series was carried out, by varying the reinforcement ratio and loading conditions, the minimum average shear stress that can cause shear failure of a specimen with different depth, concrete strength is determined. The three test series cover two types of concrete mixtures and a moderate structure depth range. In addition, the Eurocode and ModelCode 2010 provisions on vmin are discussed. They are compared with the test results. Recommendations on the present code expression are given.@en

When designing a concrete structure, a structural engineer often assumes that it is initially free of stresses and cracks. Serviceability limit state analyses are therefore often carried out only taking into account the structure’s self weight and the other imposed loads. As a result, initial tensile stresses and (internal) cracking that can arise from, e.g., partially restrained shrinkage is not accounted for. This might imply that service life predictions can be too optimistic since micro-cracks can promote the penetration of chlorides, with the result of an accelerated corrosion of the reinforcement. The impact of restraint can be at both the structural level (plane sections must remain plane) and the material level (concrete is a non-homogenous material from components having different shrinkage behaviour and stiffness). In this contribution the results of the numerical analysis of eigenstresses and micro-cracking due to the shrinkage of the cement paste in concrete are highlighted. The two-dimensional Delft beam lattice model (BLM) is used to simulate concrete on meso-level as a three-phase material. Stress relaxation in the cement paste is calculated with the activation energy method. For the comparison of the calculated micro-cracking the results of laboratory tests on concrete are used by which the chloride penetration is measured under different restraint conditions with different levels of micro-cracking. The results of the numerical analyses with BLM specimens showed that micro-cracking can increase the diffusion coefficient of (uncracked) concrete with a factor 1.2–1.6, depending on the magnitude of stress relaxation. The residual tensile eigenstresses in concrete reduces due to micro-cracking and stress relaxation till values in the order of 0.5–1.0 MPa which are not taken into account in global calculations and can speed up (unexpected) cracking in the concrete.@en

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.@en