Failure tests on concrete bridges: Have we learnt the lessons?

Full-scale failure tests of bridges are important for improving understanding of bridges’ behaviour and refining assessment methods. However, such experiments are challenging, often expensive, and thus rare. This paper provides a review of failure tests on concrete bridges, focusing on lessons from them. In total, 40 tests to failure of 30 bridges have been identified. These include various types of bridges, with reinforced concrete or prestressed concrete superstructures, composed of slabs, girders and combinations thereof. Generally, the tests indicated that theoretical calculations of the load-carrying capacity based on methods traditionally used for design and assessment provide conservative estimates. It can also be concluded that almost a third of the experiments resulted in unexpected types of failures, mainly shear instead of flexure. In addition, differences between theoretical and tested capacities are often apparently due to inaccurate representation of geometry, boundary conditions and materials.     

New method for stress determination based on digital image correlation data

Accurate material characterisation of anisotropic yielding behaviour for modern sheet metal requires the testing under multiaxial stress conditions like in the shear test or plane strain test. While most approaches include time-consuming finite element simulations for evaluation of inhomogeneous stress distributions, this paper shows a new method to determine stress data based directly on digital image correlation data. This accurate and efficient semi-analytical method can be used in direct stress analysis or inverse material parameter identification schemes as well. The methodology will be described and exemplarily results of the plane strain test and the shear test will be discussed.     

Additive Manufacturing of Syntactic Foams: Part 1: Development,Properties, and Recycling Potential of Filaments

This work focuses on developing filaments of high-density polyethylene (HDPE) and their hollow particle-filled syntactic foams for commercial three-dimensional (3D) printers based on fused filament fabrication technology. Hollow fly-ash cenospheres were blended by 40 wt.% in a HDPE matrix to produce syntactic foam (HDPE40) filaments. Further, the recycling potential was studied by pelletizing the filaments again to extrude twice (2×) and three times (3×). The filaments were tensile tested at 10^?4 s^?1, 10^?3 s^?1, and 10^?2 s^?1 strain rates. HDPE40 filaments show an increasing trend in modulus and strength with the strain rate. Higher density and modulus were noticed for 2× filaments compared to 1× filaments because of the crushing of some cenospheres in the extrusion cycle. However, 2× and 3× filament densities are nearly the same, showing potential for recycling them. The filaments show better properties than the same materials processed by conventional injection molding. Micro-CT scans show a uniform dispersion of cenospheres in all filaments.     

Roboat III: An autonomous surface vessel for urban transportation

In this paper, we present our novel autonomous surface vessel platform, a full-scale Roboat for urban transportation. This 4-m-long Roboat is designed with six seats and can carry a payload of up to 1000 kg. Roboat has two main thrusters for cruising and two tunnel thrusters to accommodate docking and interconnectivity between Roboats. We build an adaptive nonlinear model predictive controller for trajectory tracking to account for payload changes while transporting passengers. We use a sparse directed graph to represent the canal topological map and then find the most time-efficient global path in a city-scale environment using the $A^{*}$ algorithm. We then employ a multiobjective algorithm's lexicographic search to generate an obstacle-free path using a point-cloud projected two-dimensional occupancy grid map. We also develop a docking mechanism to allow Roboat to “grasp” the docking station. Extensive experiments in Amsterdam waterways demonstrate that Roboat can (1) successfully track the optimal trajectories generated by the planner with varying numbers of passengers on board; (2) autonomously dock to the station without human intervention; (3) execute an autonomous water taxi task where it docks to pick up passengers, drive passengers to the destination while planning its path to avoid obstacles, and finally dock to drop off passengers.