Application of new technologies to structural safety
Because many engineering materials exhibit time and stress-path dependent properties and loads tend to be highly variable (e.g., traffic, wind, environmental), the calculations need to be performed within a probabilistic framework. In the design phase, loading conditions are overestimated and structural strength underestimated to cater for the inherent uncertainties associated with in-service conditions. While the cost of providing this enhanced level of safety may be marginal at the design stage, the same cannot be said for assessment, where over conservatism can lead to considerable unnecessary replacement or strengthening of existing structures and a misallocation of the limited available resources.
Indeed the greatest benefit may result from assessing an existing structure as much of the uncertainty contained in the mathematical models used during design can be removed using measurements. For this reason, emphasis is placed upon the rapid evolution of Structural Health Monitoring (SHM) technology and the urgent need for the next generation of experts, trained in these new techniques to assess structural safety accurately.
For example, when the bridge that collapsed in Minneapolis in 2007 was replaced by a new bridge, an early-warning system made up of 323 networked sensors was embedded in the structure (wire and fiber optic strain and displacement gauges, accelerometers, potentiometers, and corrosion sensors). These sensors monitor structural weakness such as corroded concrete or overly strained joints. The cost for all the electronics and technology was about $1 million, a small fraction of the bridge’s $234 million cost. This approach constitutes a model for the future direction of structures – they will incorporate more sensors and algorithms which will improve safety and prolong their lives, reducing demand for non-renewable resources. TRUSS is timely because it has the potential to make significant use of the newly available sensors for tuning advanced load, structural and material models that will facilitate a more accurate assessment of the safety associated to an existing structure or to a new design.