Applying Experimental Results to the Shear Assessment Method for Solid Slab Bridges Eva O.L. Lantsoght 1 , Cor van der Veen 2 , Joost Walraven 3 and Ane de Boer 4 1 PhD Candidate, Delft University of Technology 2 Associate Professor, Delft University of Technology 3 Emeritus Professor, Delft University of Technology 4 Senior Advisor, Dutch Ministry of Infrastructure and the Environment Abstract: The combination of increased live loads and a more conservative shear capacity in the recently implemented Eurocodes, resulted in a large number of existing solid slab bridges in the Netherlands being shear-critical upon assessment. However, an enhancement of the shear capacity can occur in slabs under concentrated wheel loads due to transverse load redistribution. To quantify this effect, a comprehensive series of experiments on slabs and slabs strips under a concentrated load near to the support and under a combination of a concentrated and a line load was carried out. The experiments show the difference in behaviour for slabs, carrying the load in a two-dimensional way, as compared to beams in shear. The results from the laboratory research are used to develop recommendations, that are easily used in combination with the codes. These recommendations are implemented in a spreadsheet-based first-level assessment tool, the Quick Scan method. The assessment with this tool of selected cases of existing solid slab bridges shows that applying the experimental results into the assessment practice leads to an improved selection ability of the Quick Scan method. Keywords: slabs, shear, bridge assessment, effective width, experiments. 1. Introduction A large number of the existing bridges in the Netherlands are short-span solid slab bridges without shear reinforcement that were built during the expansion of the road network in the decades after the second World War. Within the current bridge stock, 60% of the structures have been built before 1975. Upon assessment according to the governing codes, these bridges are found not fulfil the criteria for shear. There are two reasons for this observation: 1. the prescribed live loads have increased, and 2. the shear provisions have become more conservative (shear was not checked according to codes used prior to 1974). In the recently implemented Eurocode that determines the loads on bridges, NEN-EN 1991-2:2003 (1), larger concentrated loads at smaller axle distances and with a smaller number of axles (2 instead of 3) are used in Load Model 1 for the design truck loads. The shear provisions in the Eurocode for concrete design NEN-EN 1992-1-1:2005 (2) are more conservative than the provisions of the previously used national Dutch code NEN 6720:1995 (3), especially for deep cross-sections and for lightly reinforced cross-sections. However, when shear-critical slab bridges are inspected, no signs of distress are observed (4). Experiments on decommissioned slab bridges indicated that this bridge type possesses a high residual capacity that can be a multiple of the original design capacity (5-7). The shear provisions from NEN-EN 1992-1-1:2005 (5-7) are based on a statistical analysis of a large number of experiments on (mostly) heavily reinforced, small concrete beams in four-point bending. Slabs subjected to a concentrated load close to the support will have a larger shear capacity as a result of the action of transverse load redistribution. When the shear capacity of a one-way slab subjected to a concentrated load is to be determined, not the full element width can be used as done for beams. A certain effective width in shear carries the load at the support. The effective width in shear is determined based on local practice and rules of thumb. In Dutch practice, horizontal load spreading is assumed under a 45° angle from the center of the load towards the support (Fig. 1a). In French practice (2), load spreading is assumed under a 45° angle from the far corners of the loading plate towards the support (Fig. 1b). The fib Model Code 2010 (8) advises a similar load spreading method to determine the effective width, but uses a 60 o angle for simply supported elements (Fig. 1c).