Vibration serviceability of National Gallery Singapore skybridges

The National Gallery Singapore is a conversion by studioMilou architecture (Paris) of “two of Singapore’s most significant heritage buildings – the former Supreme Court and City Hall – into one major regional institution dedicated to modern and and contemporary visual arts”.
The conversion cost S$530 (about £250m) and the building (Figure 1) was opened to the public on November 24th 2015.

Full Scale Dynamics Ltd (FSDL) evaluated the vibration serviceability of the two sky bridges crossing the atrium between the two buildings (Figure 2). Antonino Quattrone and James Bassitt from the Vibration Engineering Section joined FSDL to collect data for the EPSRC research project ‘synchronisation in dynamic loading due to multiple pedestrians and occupants of vibration-sensitive structures’ (EP/I029567/1 and EP/I031031/1) .

The testing involved a range of pedestrian loading scenarios with up to 100 pedestrians (Figure 3), including contraflow and studying the perception of moving and standing pedestrians and the effect of music (by Daft Punk, Beastie Boys and Stardust). On the second day, with the building pre-opened to 12,000 members of the public, a group of dancers was engaged to check induced vibration levels.

The measurements used a set of small 12 wireless inertial measurement units, which also enabled indirect measurements of ground reaction forces. For example, Figure 5 shows vertical acceleration on the body of a single person jumping at half the bridge’s first natural frequency and Figure 6 shows the bridge’s response build up and free decay. These data allowed estimation of modal mass, damping ratio and natural frequency.

Jogging and sway ground reaction force measurement using instrumented treadmill

Civil and structural engineering students from the University of Exeter visited the University of Sheffield’s motion capture laboratory to collect data for their third year projects.

Josephine Benthall, Harry Coulthard, Imogen Duggan, Dominic Self, Volodymyr (Vlad) Osmlovych and James Walton visited the lab, based at the Department of Civil and Structural Engineering.

The aim was to characterise the forces generated by less usual pedestrian activities, and to assess the nature and level of forces that could be generated in a horizontal direction, by one person operating as a ‘vibrodyne’. Using a person as a shaker avoids problems with transporting heavy equipment and electrical power supplies. The figures show a selection of such activities.

UoS lab photo 1

Dominic walking on treadmill

UoS lab photo 2

Imogen jogging

UoS lab photo 3

James shifting weight fore-aft

UoS lab photo 4

Vlad “skipping” laterally

The forces generated by swaying are shown below. The spectrogram shows how lateral forces are generated at half the ‘footfall’ frequency and contain only odd harmonics.

UoS lab data 1

UoS lab data 2

UoS lab data 3

Student profile – Elmar Talibli, MSc in Structural Engineering

Elmar, from Azerbaijan, received a full scholarship from the Azeri Government to study at the University of Exeter.

IMG_6901

“Structural Engineering is very important globally, which is one of the reasons it appeals to me – when I finish, I would like to work in the UK for some years, as I feel this would give me excellent knowledge and experience, and ensure me considerable career opportunities when I return to my country.

“My main motivation for studying for the MSc at Exeter was the reputation of the Vibration Engineering team, and of the professors leading the course – Aleksander Pavic, James Brownjohn and Paul Reynolds are well-known in their field. As well as the Vibration Engineering Section, which is their research arm, they run a spin out company, Full Scale Dynamics, which has commercial links, not just in the UK, but all over the world.

“I also checked the rankings and discovered that Exeter is among the top 10 universities in the UK and one of the top 100 in the world. It is a very reputable university – the former Turkish president Abdullah Gül is an alumna.

“Exeter is a very good environment – it’s very green. It is only two and half hours to London by train, which is a small distance. The weather is also very good for the UK – Exeter is located in the South West, so it is warmer than some parts. However, it’s a popular place, with a large number of students – so I would encourage anyone accepted on a course here to find accommodation early!”

Walking test on a cable-stayed footbridge in Exeter

The forces imposed by pedestrians on structures are an important topic for civil engineering, and are an active area of research for VES. With the help of some undergraduate students, VES carried out some walking tests on a 110 metre long, single-tower cable-stayed footbridge (see Figure 1) to study the synchronisation among walking pedestrians on the bridge. Six volunteers (shown in Figure 2) were instrumented with wireless accelerometers, and each pedestrian had one accelerometer placed on their lower back and one accelerometer on their right foot.

Figure 1 Exeter footbridge         Figure 3 data acquisition system for wired sensors

The data from these sensors were used to estimate the forces exerted by the volunteers on the bridge which could then be used to simulate the response of the footbridge. To measure the bridge response, a set of 17 wired accelerometers was arranged along the deck; Figure 3 shows the data acquisition system for the wired sensors. Twenty walking tests were conducted, with different walking speeds or spatial arrangements. During some tests, a metronome was used to control one volunteer’s speed, while other tests involved unprompted walking. Figure 4 shows a 10-scecond time history of vertical acceleration in the bridge deck by wired sensor, and also the accelerations of one pedestrian during walking.

Figure 4 Time history of vertical accelerations        Figure 2 Six volunteers walking on the bridge