Digital Image Correlation Measurements during Gusset Plate Connection Testing to Structural Failure.

摘要

This report describes the use of three-dimensional (3D) digital image correlation to measure the shape, displacement, and in-plane strain fields, during testing of gusset plate structural connections. Twelve full-scale bridge gusset plate connections of various geometries and boundary conditions were tested at the the Federal Highway Administration (FHWA) Turner- Fairbank Highway Research Center (Ocel et al., 2012). These experiments are part of the verification of numerical models as part of the National Cooperative Highway Research Program (NCHRP) Project 12-84 Guidelines for the Load and Resistance Factor Design and Rating of Riveted and Bolted Gusset Plate Connections for Steel Bridges. The measurements described here are in regards to the tests performed to failure (i.e., maximum load carrying capacity of the connection). During each of the twelve tests to failure, a series (typically about 150) of image pairs were taken for subsequent digital image correlation analysis. Although all of the image pairs were processed, only a very small portion of the results are explicitly presented here. General access to the overall data set will be given to other researchers. Overall, the measurements showed reasonable uncertainties on the order of 175 m/m of maximum inplane shear strain, and the measured out of plane initial shapes of the plates typically matched qualitative inspections of the connections. In this report, the layout, calibration, and measurement procedure associated with the digital image correlation system are described in detail to aid in understanding of the results. The results shown here include a sample of the measured and derived variables for one experiment at two conditions, to inform the reader of the type of data that is available. The results also include an abbreviated set of results that show the evolution of the out of plane shape and maximum shear strain field at four points in loading from the initial condition to failure. These are very useful in visualizing the mechanisms (buckling and/or shear failure of the plate) that lead to eventual failure of the connection. The evolution of strain bands of maximum in-plane shear is seen quite clearly in many of the plates. These localized bands of deformation frequently extended from the bolt lines of one member to another member through the large open areas of the plate. Comparison between all of the plates at failure, in terms of the maximum in-plane strain fields, is also presented. This comparison helps delineate plates that failed after significant shearing versus the ones that failed with minimal or no shearing. The comparison also shows very clearly the effect of reduced thickness, which was used as an analog to section loss due to corrosion.