Rapid impact modal testing for bridge flexibility: towards objective evaluation of infrastructures

Current infrastructure condition evaluation by visual inspection is a subjective endeavor while maintenance, repair and retrofit are effective only when designed and implemented by engineers with extensive experience and heuristic knowledge. As experienced engineers retire and as available funds dwindle, infrastructure owners, managers, and operators face a loss of expertise as well as diminishing resources for preservation and renewal. In this research, an integrated analytical/experimental strategy and an associated experimental tool is proposed for an objective evaluation of bridge condition to supplement visual inspection. Termed as rapid modal analysis, this test technique aims at reducing both the time and personnel required to produce estimates of bridge flexibility at strategic coordinates using spatially truncated measurement grids.The reported research started with an overview of modal analysis by impact and through the process of applying modal analysis to bridges, limitations to its widespread application were identified including, time and personnel requirements, traffic control requirements, and scaling factor reliability. To address these limitations several mitigation strategies were identified, validated, and implemented to increase the applicability of modal analysis for evaluating large populations of bridges.The use of a spatially truncated measurement grid to evaluate bridge flexibility along a girder, diaphragm, or traffic lane was evaluated by examining the variability of flexibility estimates at a point using a full grid, truncated grid, and single point estimates of flexibility. It was found that reliable estimates of flexibility were possible using truncated measurement grids by integrating individual single input multiple output test setups. To overcome the identified problems in obtaining reliable scaling factors, the use of an analytical mass matrix for scaling of mode shapes was examined using several simulated impact tests subjected to extraneous noise sources. It was determined that the use of an analytical mass matrix for mode shape scaling is a reliable substitute for traditional scaling methods if accurate estimates of material properties are available.Ph.D., Structural Engineering -- Drexel University, 201