With a Camera Measure, Monitor, and Document Bridges

Posted on Monday, July 31st, 2017

The process of monitoring the health of bridges demands reliable measurement techniques. Traditional methods of monitoring the conditions of bridges are disruptive and may cause inconvenience to users. In addition, the approaches are labor-intensive, and the results are usually less accurate. Considering that there are many transportation structures that require routine monitoring, it is a costly endeavor to measure them all. Photogrammetry allows professionals to obtain accurate three-dimensional descriptions of structures from photographs. As compared to traditional measurement methods, this technique produces more accurate results, and it is suitable for various civil engineering projects. Furthermore, the method is less expensive than most traditional techniques.

It is a standard practice for professionals to conduct feasibility studies before restoring a transportation structure. This involves measuring the structure and generating CAD models and drawings. In most cases, it is challenging to measure old structures. The task becomes even more challenging if the bridge is surrounded by vegetation, or if it is located in an inaccessible location. For many years, professionals have relied on  traditional measurement methods to monitor and assess the behavior of structures. These methods include hand measurements, field sketches, and LVDT technique. Traditional methods have many limitations, and they are applicable only under specific conditions.  Photogrammetry allows professionals to acquire measurements and generate accurate models of structures. Moreover, this  method has less limitations.

Surveying a Bridge Using Photogrammetry

Ely Bride

An image of a bridge with digitized details

Some of the difficulties that field experts encounter in bridge structure measurement include inaccessible terrain, unfavorable weather, and lack of suitable shot angles. Despite these challenges, accurate and reliable measurements are required to generate models. This paper on survey of Ely Bridge  describes use of photogrammetry for bridge surveying. A photogrammetric tool and a CAD software were used to generate a  3D finite element stress model. To start with, a camera was used to capture images of the structure. Using PhotoModeler, a scaled model of the bridge was generated. The scaled model was then exported to AutoCAD. The wire frame was used to generate a 3D finite element stress model required for structural analysis of the bridge.

Photogrammetry for Bridge Monitoring

The linear variable differential transducers (LVDTs) technique is commonly used for measuring the displacements of a bridge.  The method entails positioning LVDTs at specific points on the structure. In some cases, it is difficult to access the suitable points for LVDTs, and this makes the technique an unsuitable monitoring option for many civil engineering projects. The study described in this paper on bridge monitoring revealed that a high accuracy can be achieved using photogrammetry. The method is, therefore, a better option for monitoring great structures. Furthermore, this technique is less expensive as compared to LVDTs method.

Routine Inspection and Documentation of a Bridge

This paper on bridge inspection and documentation  explores two applications of close-range photogrammetry. The results obtained from the study revealed that photogrammetry can achieve a high level of accuracy. This impressive accuracy makes the method a suitable option for routine bridge inspection. In addition, the study revealed that photogrammetric method provides better orthophotos and surface models as compared to traditional techniques. It is, therefore, a better technique for documenting historic bridges. Another application of this method is described in this paper on measurement of Charles’ bridge. The construction of this bridge began in 1357. PhotoModeler, was used to document and assess the condition of this old bridge in Prague.

Conclusion

Traditional methods of measuring the structural behavior of bridges have many limitations. They are, therefore, unsuitable for many engineering projects. Various studies have revealed that the photogrammetric technique is capable of providing highly accurate measurements. It is, therefore, a suitable method for assessing the structural conditions of bridges. In addition, the technique allows experts to generate accurate orthophotos and three-dimensional models of bridges from photographs. This makes the method a better measurement option for documenting historic bridges.


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