PSI - Issue 64

Nicoletta Bianchini et al. / Procedia Structural Integrity 64 (2024) 352–359 Bianchini N., Sabra Z, Green K.. Wrigth, R. Structural Integrity Procedia 00 (2024) 000 – 000

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within the Borough of Waverley in Surrey, this bridge is characterized by a two-span sand and cobble solid spandrel arch design. An additional brickwork arch extension was incorporated at an unspecified date on the southern side. The absence of archive drawings complicates decision-making processes. Consequently, the reliance on in-situ investigations becomes imperative for understanding insights into the structure's history and making informed decisions regarding its maintenance and potential modifications. The bridge is a two-span sandstone solid spandrel arch with 0° skew and a square span of 2.63m and 2.55m to the east and west respectively (Fig. 1) a b

Fig. 1. Waverley Main Mill Bridge (a) Southern elevation view, (b) Northern elevation view.

2.1. Inspection and diagnosis From the latest general and principal inspections, the overall condition of the bridge was deemed ‘very poor’. This judgement was given based on some defects identified in all the elements including reduction of arch barrel (Fig. 2a), evidence of the formation of a plastic hinge at the midspan of the west rubble span (Fig. 2b), missing blocks at critical points in the arch rings (Fig. 2c), notably at the springings and quarter points. Evidence of minor arch barrel deformation was observed; however, it cannot be ascertained whether this was a construction defect or related to all the defects observed. a b c

Fig. 2. Waverley Mill defects: (a) thickness reduction, (b) plastic hinge, (c) missing bricks, (d) vegetation growth.

Considering these observations, a more in-depth investigation of the bridge's geometry and materials was necessary to accurately determine its load-carrying capacity. This involved conducting both non-destructive and minor destructive tests on-site. Furthermore, a thorough understanding of the structure's mechanical and structural characteristics is crucial for developing well-conceived repair strategies and implementing an effective monitoring system. Limit state analysis can be employed to assess the bridge's capacity using more realistic assumptions about the materials and structural behaviour. This approach helps to avoid underestimating or overestimating the bridge's true load-carrying capacity. Firstly, an aerial LiDAR survey has been performed to understand the existing deformations on the arch profile. Aerial LiDAR is an airborne version of terrestrial laser scanning and because the scanner is in the air, it is able to rapidly scan large or complex areas. It can collect 700,000 points per second with an average surface density of >700 points per square meter. Aerial LiDAR is ideal for continuous mapping and can produce 3D point clouds that cannot