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Digital image correlation (DIC)-a photographic measurement technique that relies on pattern recognition to calculate displacements and strains-can provide unprecedented data on bridge behavior, strength, and overall condition. A major challenge in using DIC to measure full-field strains and displacements (as opposed to point tracking) in bridges is applying an appropriate stochastic pattern over the entire field of view as conventional strategies (e.g., spray paint) are time-intensive to apply. For steel bridges, in which members are treated with a protective multilayer paint coating, the pattern must also be applied without removing the protective coating system and be compatible with the coating system such that it follows the strain in the steel. This paper investigates pressure-activated adhesive tape as a strategy to rapidly apply a stochastic pattern for full-field monitoring of steel bridges. A stochastic pattern, designed for minimal noise in DIC measurements, can be generated electronically and printed on the tape prior to tape installation. This paper investigates tape as a pattern strategy by performing tensile tests on bare and coated steel samples. Measured DIC results using tape patterning are compared with readings from conventional instrumentation (i.e., strain gauges and extensometer) and DIC measurements using spray paint patterning, as well as finite element predictions. The results clearly indicate that the pressure-activated adhesive tape follows the strain in both bare and coated steel and affords a viable patterning approach to implement DIC in monitoring and assessing steel bridges.

With the recent American Association of State Highway and Transportation Officials bridge design code acceptance of cold bent fracture-critical and nonfracture-critical plates and the increasing use of cold bending by the bridge industry, there is a need to better understand and predict residual strains in cold bent steel. However, measuring residual strains is a challenging task since the bending process typically interferes with conventional instrumentation. This paper introduces three-dimensional Digital Image Correlation (DIC) as a new, non-destructive approach to measuring residual strains in cold bent steel that captures fullfield strain data with high accuracy. DIC was used to measure residual strains in 18 cold bent 12.7 mm thick ASTM A36 steel plates, bent using a press-brake to a constant radius of 102 mm with varying angles (10, 20, and 30 degrees) and plate widths (76.2 mm and 203 mm). The measured residual strains are compared to analytical predictions and both twoand three-dimensional finite element models. A parametric study, using the validated finite element models, is completed for additional widths (12.7 mm and 140 mm) and thicknesses (6.35 mm and 19.1 mm) to investigate the effect of these parameters on circumferential strains, contact pressure, strain state, and to make modeling recommendations. Results are used to develop a means of predicting peak residual strains based on the final plate dimensions-a useful quality control measure.

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