Fotogrametryczny pomiar odkształceń termicznych mostów stalowych

Interest in natural thermal phenomena, which occur in bridges, has been lasting from the thirties. However, field measurements of real objects have been performed very seldom. Therefore experimental verification of theoretical works becomes very important. An attempt concerning such investigations was performed within the Research Project KBN (the Committee of Scientific Research) no 7 T07E 012 15 "Development of methodology of determination of thermal deformations of steel bridges" at the Institute of Road and Bridges of the Warsaw University of Technology. Analysis of climatic conditions in Poland allowed to select a region characterised by the extreme distribution of annual and daily temperatures. Such requirements were met by the area of the city of Przemyśl. Two bridges were selected for measurements and tests within this area: one plate girder road object with an integrated pier of 152.9 m expansion, and the second object, a railway flyover with an ortotropowym channel cut-walk of 20 m expansion. Measurements of temperatures and spatial deformations, made by means of electronic meters, with the use of a photogrammetric method, were performed in January and July of 1999 and 2000. A concept of differential measurements was assumed as an initial method for designing photogrammetric measurements. For that purpose photographs were taken from stable positions, with repeatable external orientation photogrammetric cameras. Due to considerable time intervals of successive registration, this condition was approximately met in practice. This allowed to perform observations according to the temporary stereogramme mode, for which only changes of external orientation of photographs, resulting from the method of restoration of positions and utilisation of the (JMK-IO low stability camera, were determined. Observations were performed by means of an analytical stereo-plotter. with the use of a specialised procedure of measurements performed according to the mode of temporary stereogrammes. Each of measured objects was registered by means of a net of coherent photographs, in order to allow equal determination of co-ordinates of investigated points. In practice, photogrammetric models, which describe particular geometric features of investigated bridges, were reconstructed with the accuracy of m_{x = my = mz = +/-2mm Values of deformations, determined by means of the photogrammetric method (with an exception of the component perpendicular to the axis of the investigated bridge) have met expectations of "road experts".}