Current topics on bridge engineering

Nowadays, design engineers are challenged more than ever to provide economic solutions that could be implemented within minimum time schedules, making an efficient use of the available resources. In addition, higher security levels against the possibility of an extreme event such as a terrorist attack could be in need.Bridges are key components of this country's infrastructure that when disrupted cause not only discomfort to users but also a big negative impact to the economy. About twenty five percent of the 500,000+ bridges exist in the United States suffer geometrical and/or structural deficiency. New construction techniques, connection details and better design procedures and tools are required to reduce this ratio and help in raising the quality of our highway system.One of the most time consuming tasks in a bridge project is the construction of the bridge's superstructure, which includes the concrete deck and its supporting girders. The use of precast full-depth concrete deck panels in combination with prestressed concrete girders could significantly improve the time schedule for this task while providing a better quality product. In this investigation, a connection system using 1-1/4" diameter steel double-headed studs is proposed to provide the composite behavior between the precast deck panels and the prestressed girders. Six specimens were tested under direct tension to test the capacity of the mechanical connectors to provide their full strength capacity in order to achieve the composite behavior. The performed tests showed that the new connection system provides the adequate capacity if additional reinforcement is placed next to the mechanical connectors. In addition to the experimental tests, non-linear finite element model simulations were performed to analyze in detail the failing mechanism of the connection and to validate the experimental results.Currently, prestressed concrete designs use high-strength materials and factored loads procedures achieving slender and lighter sections that could develop large deflections. Used to estimate long-term deflection, the "Precast Concrete Institute multiplier method" was developed for prestress concrete girders and has not been updated since 1977. A parametric investigation was performed to develop refined multipliers for different precast prestressed concrete girders considering different concrete strengths, two different codes and different time stages for the girders placement. A time-step method that considers the most recent advances in concrete such as creep, shrinkage and relaxation formulations was used to estimate the girders deflection at different stages and for comparison with the deflections obtained with the original multipliers method.Recent terrorist attacks to non-military structures and the openness of structures such as bridges increases and emphasizes the need to evaluate their vulnerability to extreme events such as impact loads and the need to include their effects into the design. In this research, analytical and experimental investigation was conducted to study the vulnerability of bridge girders under impact loads correlating the velocity at impact of a moving mass with the specific damage level caused by the impact. A displacement-based design procedure was modified to predict the velocity of a known mass that will cause a specific damage level in a reinforced concrete element. As part of the procedure, moment-curvature relations that consider the strain rate effects due to the impact and nonlinear load deformation relations were developed. In addition, a single degree of freedom system was used to develop nonlinear shock spectra that correlate the peak dynamic impact force with the peak force of an equivalent static linear system. To validate the procedure, nine reinforced concrete beams were tested under a lateral impact load for different damage levels. To estimate the impact velocities a pre-experimental Monte Carlo statistical simulation was also performed.