Post-Fire Assessment of Prestressed Concrete Bridges in Indiana

This project focused on evaluating the effects of fire-induced damage on concrete bridge elements, including prestressed concrete bridge girders. A series of controlled heating experiments, pool fire tests, material tests, and structural loading tests were conducted. Experimental results indicate that the portion of concrete subjected to temperatures higher than 400°C loses significant amounts of calcium hydroxide (CH). Decomposition of CH increases porosity and causes significant cracking. The portion of concrete exposed to temperatures higher than 400°C should be repaired or replaced. When subjected to ISO-834 standard fire heating, approximately 0.25 in. and 0.75 in. of concrete from the exposed surface are damaged after 40 minutes and 80 minutes of heating, respectively. Prestressed concrete girders exposed to about 50 minutes of hydrocarbon fire undergo superficial concrete material damage with loss of CH and extensive cracking and spalling extending to the depth of 0.75–1.0 in. from the exposed surface. These girders do not undergo significant reduction in flexural strength or shear strength. The reduction in the initial stiffness may be notable due to concrete cracking and spalling. Bridge inspectors can use these findings to infer the extent of material and structural damage to prestressed concrete bridge girders in the event of a fire and develop a post-fire assessment plan.

Re-using existing prefabricated prestressed concrete girders

<p>The future of bridge and overpass design is to be fully circular. To reach that goal many innovations in construction should be made. One of the first steps is to alter the mainly existing linear construction sequence. Therefore, Royal HaskoningDHV started the innovation of re-using prefabricated concrete girders for new overpasses and bridges. The economic and technical feasibility is researched as well as the impact on climate and emissions. To prove our concept, an overpass is deconstructed, and the 40-year-old prefabricated concrete girders are disassembled and put on transport, instead of crushing them to aggregate. In a temporary storage the girders are inspected, repaired, adapted and certified. So, they are fit for their future use in a new structure. Structural assessments, environmental impact and costs calculations are made for a case study. It is concluded that re-using prefabricated girders is technical and economical feasible, with a remaining lifespan of at least 100 year. Up to 44% of CO2-eq. emissions can be saved and even 61% of abiotic depletion (in Sb-eq.). The main obstacle is the unawareness at the different stakeholders that re- using these high-quality girders is possible and these girders can function for the next century.</p>

State-of-the-Art Review on Determining Prestress Losses in Prestressed Concrete Girders

Prestressing methods were used to realize long-span bridges in the last few decades. For their predictive maintenance, devices and dynamic nondestructive procedures for identifying prestress losses were mainly developed since serviceability and safety of Prestressed Concrete (PC) girders depend on the effective state of prestressing. In fact, substantial long term prestress losses can induce excessive deflections and cracking in large span PC bridge girders. However, old unsolved problematics as well as new challenges exist since a variation in prestress force does not significantly affect the vibration responses of such PC girders. As a result, this makes uncertain the use of natural frequencies as appropriate parameters for prestress loss determinations. Thus, amongst emerging techniques, static identification based on vertical deflections has preliminary proved to be a reliable method with the goal to become a dominant approach in the near future. In fact, measured vertical deflections take accurately and instantaneously into account the changes of structural geometry of PC girders due to prestressing losses on the equilibrium conditions, in turn caused by the combined effects of tendon relaxation, concrete creep and shrinkage, and parameters of real environment as, e.g., temperature and relative humidity. Given the current state of quantitative and principled methodologies, this paper represents a state-of-the-art review of some important research works on determining prestress losses conducted worldwide. The attention is principally focused on a static nondestructive method, and a comparison with dynamic ones is elaborated. Comments and recommendations are made at proper places, while concluding remarks including future studies and field developments are mentioned at the end of the paper.