38 X. Wei et al. Fig. 5.1 The Wilcott Bridge structures there is a need to experimentally determine them. This paper contributes to this goal by providing a rare insight into the dynamic features of suspension footbridge near to the village of Nesscliffe, Shropshire, UK (Google Earth co-ordinates 52ı 45054.8900 Nand 2ı 55004.6800W). The paper starts with a description of the FRP bridge in Sect. 5.2, followed by a description of the ambient-based modal testing in Sect. 5.3. Identified modal parameters are reported in Sect. 5.4 with conclusions from their evaluation made in Sect. 5.5. 5.2 Bridge Description The Wilcott Bridge, shown in Fig. 5.1, is a single span suspension footbridge over the Nesscliffe A5 bypass road. The bridge has a width of 2.1 m and a span of 51.3 m. It consists of a lightweight glass FRP deck, two pairs of steel pylons, two steel cables with a span of 57.89 m, and four steel backstays and 20 steel hangers (10 per side). The FRP deck is constructed from pultruded components of E-glass fibre embedded in an isophthalic polyester matrix, which are adhesively bonded together to form an integral box section. The pultruded construction system is known today as Composolite, and is supplied by the American pultruder Strongwell. Ballast is employed to increase the mass of the deck. The deck was built in three units of approximately equal length that are connected by bonded interlocking splice joints and was integrally connected to the foundation, without the need for movement joints. 5.3 Ambient Vibration Testing To provide a precise and reliable characterization for the dynamic characteristics of the Wilcott footbridge an ambient testing programme was conducted by the authors from the University of Warwick, UK, on 09 September 2016. Acceleration responses of the deck were measured under the natural excitation of wind and road traffic passing underneath the bridge on a main truck road. During data recording the bridge was closed to pedestrian traffic. To identify the first few modes of the bridge we used the measurement grid in Fig. 5.2, having 26 measurement stations on top of the deck. These measurement locations included anchoring points of each hanger, the mid-span points and supports at the two span ends. Vertical accelerations only were recorded on the North side, whilst both vertical and horizontal accelerations were acquired on the South side. Figure 5.3 shows the accelerometers at a location on the South side. The measurement campaign was divided into seven set-ups. In each set-up we had eight Honeywell accelerometers QA750 (of nominal sensitivity of 1300 mV/g). A lateral accelerometer and a vertical accelerometer at measurement station 55 were used as reference vibration sensors, whilst the other six accelerometers are the roving transducers.
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