ABSTRACT
The aging U. S. infrastructure has given rise to well-founded concerns for existing bridge structures; the number of bridges which require repair and/or additional monitoring is approaching 200,000. Advanced methodologies are needed to: (a) provide field data which can be used to quantitatively measure global bridge parameters (e.g. stiffness) in support of bridge management, (b) locate and assess local damage in existing bridge structures, (c) determine the durability of repairs and (d) assess the degradation of relatively new structures so that repairs can be implemented.
Since a bridge management system combines management, engineering and economic inputs, it is essential that accurate data on the current condition of each bridge be available to help the decision-makers make timely decisions relative to bridge repair/replacement. Currently, much of the data available to bridge management is based almost entirely upon routine visual inspections; these inspections are both subjective and limited in ability to detect hidden deterioration or flaws (i.e. such as early corrosion of the steel reinforcement or cracks).
In recent years, a completely computer-based optical method which measures the full, three-dimensional displacements and surface strains and uses normal white light (e.g. sunlight, incandescent light) illumination has been developed. The method is based on stereo vision principles and uses two cameras to record images digitally and store them in a portable computer. The images are analyzed at the convenience of the user to obtain the surface deformations and/or 3-D displacements at points of interest. Due to the character of this method, it has many advantages over previous optical methods including: (a) ability to eliminate effects of most vibrations, (b) ability to interrogate large or small regions; the system can be configured so that data for either global or local structural response can be quantified and (c) ability to be converted to a portable field device without affecting accuracy of the measurements.
This paper presents some preliminary results from an on-going research project on the monitoring of the performance of bridge structures using the computer stereo vision method. The computer stereo vision method and a DCDT were used to measure the vertical displacements of the steel girder frame of a small scale bridge structure. The preliminary results show very good agreement between the displacements obtained by the two methods.
