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Abstract
1- Introduction
2- Strut-and-tie method
3- Use of Strut-and-Tie methods for the assessment of RC Half-Joints
4- Experimental program
5- STM predictions of load carrying capacity
6- Conclusions
References
Abstract
A reinforced concrete half-joint bridge consists of suspended span dapped-end beams or a full-width deck supported on the nibs of abutments or adjacent beams. The design of their disturbed regions is traditionally performed by means of strut-and-tie modelling. The design provisions found in standards and codes can be used for the assessment of existing structures with minor adjustments. However, current documents provide limited guidance on the incorporation of deterioration aspects such as corrosion, insufficient anchorage lengths, and crack formation. Experiments performed on 12 half-joint beams demonstrated the effects of single defects, but synergistic effects were also found to exist and might lead to much higher reductions than expected from the sum of individual defects. These results were compared to different strut-and-tie models (STMs) and the application of STMs to achieve the highest lower bound estimate of the load carrying capacity is discussed. For the beams studied in the current work, the predictions based on codes and standards, combined with appropriate methods to incorporate deterioration effects, led to safe load bearing capacity estimates. However, the developed STMs seem to be, in some instances, unable to pick up alternative load paths that develop as soon as the capacity of a certain tie is reached. Hence the actual capacities might be higher than what is obtained from the STM calculations.
Introduction
With increasing traffic volumes and load demands in an era of limited resources, there is a pressing need for the accurate strength assessment of aging infrastructure. When assessing the load carrying capacity of existing bridges, the influence of factors including deterioration and previous repair works are often disregarded since current code provisions or guidelines do not provide sufficient guidance. However, the de la Concorde Overpass collapse in 2006 [1], killing 5 people, emphasises the importance of proper inspections, maintenance, and adequate assessment techniques. Reinforced concrete half-joints, such as de la Concorde Overpass, provide specific challenges with respect to their assessment. A half-joint bridge consists of suspended span dapped-end beams or a full-width deck supported on the nibs of abutments or adjacent beams (Fig. 1). Advantages of this type of bridge detailing are the suitability for precast construction [2] and a reduced construction depth with a level running surface along the bridge deck and the support spans. Disadvantages are the vulnerability of the structures to deterioration at the nib due to seepage of chloride-rich water through the expansion joints and the existence of large regions that are not easily accessible for inspection or repair. Common issues raised during half-joint bridge assessments are [3]: • Deterioration of the concrete and/or reinforcement • Inconsistencies between the as-built and as-designed internal steel reinforcement • Non-compliance of half-joints with current code provisions Deterioration processes, such as carbonation, chloride ingress, and freeze-thaw cycles, mean that the mechanical properties of the concrete and steel will alter over the lifetime of a reinforced concrete half-joint. The extent to which these processes affect the compressive strength, tensile strength and modulus of elasticity of the concrete can be significant.