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- Eurocode shear design of coarse recycled aggregate concrete: reliability analysis and partial factor calibrationPublication . Pacheco, João; Brito, Jorge de; Chastre, Carlos; Evangelista, LuisThis paper contributes to the definition of design clauses for coarse recycled aggregate concrete. One of the main reasons for scepticism towards recycled aggregate concrete is the perceived notion that the heterogeneity of recycled aggregates may increase the uncertainty of the behaviour of concrete. Therefore, the paper uses structural reliability concepts to propose partial factors for recycled aggregate concrete's design for shear failure. The paper builds upon a previous publication by the authors, in which the model uncertainty of recycled aggregate concrete elements designed for shear, with and without shear reinforcement, was compared with that of natural aggregate concrete elements. In that paper, the statistics of the model uncertainty for recycled aggregate concrete shear design were indeed found to be less favourable than those of natural aggregate concrete. Therefore, a partial factor for recycled aggregate concrete design is needed to ensure safety. This paper presents partial factors calibrated with explicit reliability analyses for different cases of design concerning beams (in the case of shear design of elements with shear reinforcement) and slabs (for the design of elements without shear reinforcement). For full incorporation of coarse recycled concrete aggregates and the design of elements without shear reinforcement, the calibrated partial factor reduces the design value of shear resistance by 10% (design with EN1992) or 15% (design with prEN1992) in comparison to natural aggregate concrete's design. For the shear design of elements with shear reinforcement, the partial factor decreases resistance by 5% but a sensitivity analysis showed that the reduction might be, under pessimistic expectations, of up to 20%.
- Bond of recycled coarse aggregate concrete: model uncertainty and reliability-based calibration of design equationsPublication . Pacheco, João; Brito, Jorge de; Chastre, Carlos; Evangelista, LuisThis paper concerns the design of lap splice lengths for ribbed steel reinforcement bars embedded in concrete produced with coarse recycled concrete aggregates. Recycled aggregates are weaker and typically lead to concrete with lower tensile strength. Both aspects change the model uncertainty of bond strength formulae and a major topic of the paper is the influence of recycled aggregates on the model uncertainty of the bond strength model of fib Bulletin 72. A stochastic model for this model uncertainty is developed from a meta-analysis. The model uncertainty, estimated from analogue specimens made with either natural aggregate concrete or recycled aggregate concrete, is compared and the incorporation of recycled aggregates was indeed found to have a detrimental influence on the model uncertainty. A partial factor for lap splice length design is calibrated through reliability analyses so that the probability of failure of the bond length design of recycled aggregate concrete is equivalent to that of natural aggregate concrete. Two design equations were studied: that of the fib Bulletin 72 and that of the D6 draft of the second generation of Eurocode 2.