sábado, 15 de marzo de 2014

Modern technology looking into ancient bridges (Galicia, Spain)

Bridges are considered quite prosaic engineering structures because quite simply they connect separated land and so improve economic and social development. In Spain, many of them still in service within the transport network are masonry arch bridges built in ancient times.
In addition to their age, the stability of these remaining bridges is under question due to the changing loading conditions; no longer horse and cart traffic, but large modern commercial vehicles. Therefore, they require periodic assessment of their condition and because some of these bridges are considered part of the cultural heritage of a region, the method of evaluation must be non-destructive to preserve their historical character.
The new methodology uses ground-penetrating radar supported by a detailed geometric survey performed through a terrestrial laser scanner and carried out by researchers at the University of Vigo. They are looking at around 85 ancient bridges in north-west Spain and the latest bridge one to be studied is Monforte de Lemos, in Lugo, according to the ‘Journal of Bridge Engineering’..
The results revealed a range of previously unknown data and hidden features, including the thickness of stones in the interior of the vault, as well as the presence of ancient arches and prior restorations. To assist in the interpretation, 3D modelling was used, where realistic models were built from the accurate geometry provided. The data obtained was then referenced with field data, which allowed for the identification of unknown structural details.
“As well as obtaining information like the thickness of the stones inside, the GPR has reported the existence of two hollow arches in this medieval bridge, hidden underground at one of the edges,” Dr. Mercedes Solla, one of the authors and current professor at the Defence Academy (Marín, Pontevedra), explains.
The GPR comprises an antenna that emits and receives short pulses, a control unit and a computer. The kit can be set up on a type of cart, in which the system is installed or even in a mobile survey vehicle to collect data along the road of the bridge.
“The information from this system is combined with the information provided by the LiDAR or terrestrial laser scanner, whose beam sweeps over the whole bridge and in a few minutes takes the XYZ coordinates of millions of points of the monument,” says Solla. The result is a point cloud, from which detailed plans and 3D models of the bridge can be obtained.
In some cases, such as in the Roman bridge of Segura, between the municipalities of Piedras Albas (Cáceres, Spain) and Segura (Portugal), this technology has also been used to detect the remains of a Renaissance engraving in one of the arches.
On another Roman bridge, in Lugo, researchers have identified restorations carried out over time, differentiating between areas where granite has been used (the waves of the radar spread faster) and other zones where schist is present, a material which has a lower conductivity. It has also been detected that the outline of the bridge sloped up to the centre with a high humpbacked appearance during the Middle Ages, although today it is level.
According to Solla, “all this information is of historic interest, but it is also useful to civil engineers so that they can plan conservation, improvement and restoration measures in these types of infrastructures”.
The researchers are currently working with a bridge survey vehicle that contains a mobile 3D laser scanner, a GPR, thermographic cameras and a surface ‘profilometer’. The initiative is part of a European project for the application of technologies for infrastructure management and inspection (known in Spanish as SITEGI).

Source: Past Horizons: http://www.pasthorizonspr.com/index.php/archives/03/2014/modern-technology-looking-into-ancient-bridges

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