Determination of linear deformations in joints of steel tension elements using image processing techniques

In this thesis, determination of deformation distribution in welded and bolted connections used in steel structures is studied by using digital image processing methods. It is known that material properties, connection quality and manufacturing methods are of primary importance for the connections affecting the behavior of steel structures. The possible difference in performance between a fabricated connection and its computer model under a defined load may pose important problems for structures during their service life. If the material properties and loading conditions applied to the connection could be modeled correctly, the behavior of the structure during its service life can be estimated accurately.Conventionally, the stress and strain distribution in connections is calculated using the finite elements method with assumed material properties and constitutive models. And connections are evaluated according to the deformation characteristics obtained from laboratory strength tests. However, there is no available method to measure the stress and strain distribution in connection components, local deformation zones and the stress-strain localizations caused by various manufacturing faults. The lack of such methods results in neglecting these important aspects during the design procedure. Because the conventional strain gages allow the measurement of deformation only at one point and direction for a specific time duration, it is not possible to determine a general characteristics of stress-strain distributions in connections after the laboratory performance tests.In this thesis, a new method is developed to measure deformation distribution of steel connections under tension tests. The method is based on analyzing digital images of connection specimens taken periodically during the laboratory tension test. By using this method, deformation distribution of steel connections can be calculated with an acceptable precision for the tested connections.It is believed that accurately determining the deformation behavior of steel connections and its components is very important for the evaluation of connection performance and deformation behavior in the engineering design problems.In this thesis, it is concluded that in comparison with the conventional deformation measurement methods, the digital image processing method which has obvious advantages against the conventional methods provides acceptable results for the deformation distribution of typical welded and bolted connections subjected to the tension test.Key Words: Steel structures, Steel connections, Image processing, Image acquisition, Image analysis.