Abstract. This paper presents a coupled observation and modelling strategy aiming at improving the understanding of processes triggering flash floods. This strategy is illustrated for the Mediterranean area using two French catchments (Gard and Ardèche) larger than 2000 km 2 . The approach is based on the monitoring of nested spatial scales: (1) the hillslope scale, where processes influencing the runoff generation and its concentration can be tackled; (2) the small to medium catchment scale (1-100 km 2 ), where the impact of the network structure and of the spatial variability of rainfall, landscape and initial soil moisture can be quantified; (3) the larger scale (100-1000 km 2 ), where the river routing and flooding processes become important. These observations are part of the HyMeX (HYdrological cycle in the Mediterranean EXperiment) enhanced observation period (EOP), which will last 4 years (2012)(2013)(2014)(2015). In terms of hydrological modelling, the objective is to set up regional-scale models, while addressing small and generally ungauged catchments, which represent the scale of interest for flood risk assessment. Topdown and bottom-up approaches are combined and the models are used as "hypothesis testing" tools by coupling model development with data analyses in order to incrementally evaluate the validity of model hypotheses. The paper first presents the rationale behind the experimental set-up and the instrumentation itself. Second, we discuss the associated modelling strategy. Results illustrate the potential of the approach in advancing our understanding of flash flood processes on various scales.

To quantify the safety margin of shear design provisions for ultrahigh performance fiber-reinforced concrete (UHPFRC), an experimental campaign has been performed. In a four-point bending configuration, shear tests have been conducted on 11 3-m long and 0.38-m high I-shaped girders with varied types of shear reinforcement (stirrups and/or fibers, or neither), combined with longitudinal prestressing or mild steel reinforcing bars. These shear tests have been analyzed in conjunction with a complete materials characterization. To identify the contribution of the fibers to the shear response, prisms have been extracted horizontally, vertically, at 30 and 45° in both undamaged ends of the beams to determine the effective orientation factor. Through this unique combination of data, detailed in the writers' paper, design provisions and models have been developed, as detailed in a companion paper

This paper deals with the experimental determination of the bond behaviour between ultra-high performance fiber-reinforced concrete (UHPFRC) and reinforcing bars (rebars). An experimental campaign has been carried out to assess the bond behaviour considering different rebar diameters, different embedment lengths and different concrete covers. A relationship between bond strength, compressive strength and rebar diameter has been drawn from the results of this campaign and results found in the literature. Thanks to an original instrumentation method using Fiber-Optic Sensor, the local constitutive law linking the local relative displacement between UHPFRC and rebar and the bond stress has been determined and compared with the law proposed by fib Model Code 2010.