Fracture Energy of Steel Fiber-Reinforced Concrete
Steel fiber-reinforced concrete (SFRC) is a cementitious material reinforced with discrete fibers. The energy absorption capacity is the main material property benefited by fiber reinforcement. Closed-loop servo-controlled equipment should be used to evaluate this property. The tests should be carried out using displacement control in order to obtain the postpeak force- displacement relationship (tensile strain-softening branch). To assess the fracture energy of SFRC, three-point bending tests were carried out using displacement control. Series of notched beams reinforced with 30, 60, and 90 kg/m3 of hooked-end steel fibers were tested. Besides the energy dissipated in fracturing the concrete, the energy determined from the force-displacement relationship can also include the energy absorbed during nonlinear behavior of concrete in compression. Ductile materials, such as concrete reinforced with a high content of fibers, develop large deflections before exhausting their energy absorption capacity. In these cases, the "fixed" points of the bar supporting the displacement transducer may not remain fixed, adding an extra deflection into the control displacement transducer and thus leading to incorrect evaluation of the fracture energy. These factors are analyzed in the present work in order to assess the suitability of the specimen dimensions and the test procedures for evaluating the fracture energy of SFRC.
Analysis of concrete slabs supported on soil
Resumen : A numerical model for material non-linear analysis of concrete slabs supported on soil is described in this work. In this model, the cracked concrete is regarded as cracks with concrete between cracks. The behaviour of the concrete between cracks is simulated by the conventional theory of plasticity. The behaviour of the cracks is defined by their constitutive laws using the concrete fracture properties. Smeared multifixed and rotating crack models are available in the model. Concrete can be reinforced with sets of smeared bars of different materials and geometric properties, as well as with discrete steel fibres. A tension-stiffening model that takes into account the concrete fracture properties and the reinforcement characteristics is used for the reinforced cracked concrete. Main effects of the fibre reinforcement are reproduced in the model, introducing the material fracture energy and a convenient softening law in the crack constitutive law, and using a new stress-strain relationship for the behaviour in compression. Soil supporting the concrete slab is simulated with springs perpendicular to the slab middle surface. The soil non-linear behaviour and the loss of contact between slab and soil are accounted for. Concrete slabs supported on soil are analysed with the model proposed. Safety of wire mesh reinforced concrete slabs and steel fibre reinforced concrete slabs is discussed. A comparison with conventional design methods is performed. The influences of the soil load bearing capacity, as well as the loss contact between soil and slab on the behaviour of slab-soil system are analysed.
An Optimization Approach to Occupant Safety and Fuel Economy in Vehicle Design
1. Abstract A major challenge in automotive design is the creation of safe vehicles with minimal environmental impact. This study presents a modeling framework for evaluating and optimizing body designs for improved occupant safety and fuel efficiency. Vehicle body mass is considered as the main link between safety and sustainability. The modeling framework includes frontal crash energy absorption, restraint system design and fuel economy. Preliminary results indicate a Pareto-optimal curve between safety and sustainability may exist when other factors are not taken into account. A more complete modeling framework that includes more sophisticated sustainability and safety metrics, cost and other market considerations, is suggested in order to support better design and regulatory decisions. 2. Keywords: Automotive body structures, fuel economy, occupant safety, optimal vehicle design, restraint systems