Recommendations for the Shear Assessment of Reinforced Concrete Slab Bridges from Experiments

Abstract

Upon assessment of existing reinforced concrete short-span solid slab bridges according to the recently implemented Eurocodes that include more conservative shear capacity provisions and heavier axle loads, a number of these structures were found to be shear-critical. The results from recent experimental research on the shear capacity of slabs indicate that slabs benefit from transverse load distribution. Recommendations for the assessment of solid slab bridges in shear are developed on the basis of these experiments. A load spreading method for the concentrated loads is proposed and the applicability of superposition of loading is studied. The resulting most unfavourable position for the design trucks is provided and implemented in the so-called Dutch "Quick Scan" method (QS-EC2). Cases of existing bridges are studied with the previously used QS-VBC as well as with the QS-EC2 that includes the recommendations. As a result of the assumed transverse load distribution, the shear stress to be considered at the support based on the recommendations becomes smaller.Keywords: effective width; live loads; load distribution; reinforced concrete; slab bridges; shear.The shear capacity as prescribed by NEN 6720 3 and NEN-EN 1992-1-1 2 is determined from a statistical analysis of experiments on relatively small, heavily reinforced concrete beams loaded in four-point bending.6 When these expressions are applied to determine the shear capacity of a slab under a concentrated load, the contribution of the surrounding material, which is activated through transverse load distribution, is not taken into account. Moreover, the effective width in shear for slabs under a concentrated load needs to be determined. In practice, the effective width is based on a load spreading method:1. from the centre of the load towards the face of the support as used in Dutch practice (Fig. 1a), resulting in b eff1 ; or 2. from the far side of the load towards the face of the support as used in French practice 7 (Fig. 1b), resulting in b eff2 .To quantify the enhancement due to transverse load distribution in slabs under a concentrated load in shear, a comprehensive series of experiments was carried out. [8][9][10] In a first series of experiments, 18 slabs and 12 slab strips were tested under a concentrated load near the support. In a second series, eight additional slabs were tested under a combination of a concentrated load near the support and a line load. These experiments form the basis for new recommendations for the shear assessment of slab bridges. In sections Experiments and Recommendations, the link between these experiments and the recommendations is discussed.The large number of solid slab bridges that are identified as shear-critical require a systematic approach. In a preliminary general assessment, the database of slab bridges was screened in order to identify the particular bridges that require a more detailed analysis. For this purpose, a fast, simple and conservative tool is required: the "Quick Scan" method (QS-EC2). The fi...

Database of wide concrete members failing in shear

“…With the change from using national codes to Eurocodes, the shear capacity of a large number of slab bridges in the Netherlands is subject to discussion (Lantsoght et al, 2013). As compared with the previously used national codes, NEN-EN 1992-1-1:2005(CEN, 2005 predicts a smaller shear capacity and at the same time NEN-EN 1991-2:2003(CEN, 2003 uses heavier live load models.…”

Using Eurocodes and Aashto for assessing shear in slab bridges

“…To take into account the higher shear capacities of slabs, an additional enhancement factor reducing the contribution of concentrated loads to the total shear force was proposed (Lantsoght et al, 2013a); this factor is equal to 1·25 (as a 5% lower bound of the ratio of the tested to predicted values for loads close to supports). The enhancement factor and the reduction factor β = a v /2d l can be combined into β new = a v /2·5d l …”

“…The goal of the first round of assessments is to determine which particular bridges require a more detailed analysis; for this, a fast, simple and conservative tool is required (e.g. the quick scan method (Lantsoght et al, 2013a)). The quick scan is a spreadsheet-based method, similar to extended hand calculations (Vergoossen et al, 2013).…”

Beam Experiments on Acceptance Criteria for Bridge Load Tests

“…In the Netherlands, a large number of reinforced concrete bridges that were built in the decades 2 following the second World War are reaching the end of their originally devised service life 3 (Lantsoght et al, 2013). These bridges were designed for lower live loads than the currently 4 governing live loads (CEN, 2003) and were designed according to codes that allowed higher shear 5 capacities than according to the current provisions from Eurocode 2 (CEN, 2005).…”