Church Street Bridge
Melbourne, Australia: Built in 1921, the Church Street Bridge is a three-span, seven-rib, reinforced concrete arch structure on piled foundations. It carries vehicular and tram traffic over a major arterial roadway and the Yarra River.
When an extra lane was added to the arterial, engineers determined that the arch that sspanned the roadway provided inadequate vertical clearance for traffic. The only solution was to replace the arch elements, and this had to be done without interrupting the flow of traffic over and under the bridge.
The replacement arch was designed to be 0.6 m higher at the crown and 1.2 m higher at either end, and this would result in a redistribution of the forces within the structure. It was expected that local stresses in the massive piers would be acceptable or kept within acceptable limits by the addition of reinforcement, so the major concern was the possible overloading of the foundation system of the North pier due to eccentric applied loads introduced by the new arch structure.
Consequently, kinematic relationships were developed to describe the behavior of the bridge, and the instrumentation plan was focused on monitoring changes in the geometrical arrangement of the elements of the bridge. The drawing shows the elements of the bridge and the behavior that would indicate movement of the North pier.
Infratech Systems & Services was commissioned to install and monitor the instrumentation system used on the project. Inclinations were measured using EL tiltmeters mounted on critical elements. Infratech's displacement transducers supplemented these readings. Temperatures were also recorded at a number of locations on the bridge. All sensors were then linked to an automatic data acquisition system, which collected readings each minute and calculated hourly averages. The system was also configured to trigger alarms if readings exceeded alarm thresholds. Data management and processing was conducted at Infratech's Brisbane office via modem link with the data loggers in Melbourne.
Monitoring started prior to commencement of construction activities to determine the initial behavior of the bridge, i.e, how the elements of the structure moved in response to diurnal temperature changes. The data reveal a good correlation between inclination of the arch and temperature. Figure 1 shows that changes in temperature are paralleled by changes in inclinometer of Element 5. Element 6 is essentially a mirror image of Element 5, which is consistent with expected behavior.
Figure 2 shows that the relationship between temperature and tilt is reasonably linear, which is also consistent with expected behavior. This baseline data would later be compared to data collected after construction was complete to verify that the modifications had not degraded the structural integrity of the bridge.
The prime contractors on the Church Street Bridge project were Hyder/CMP Joint Venture in conjunction with Transfield Obayashi Joint Venture (TOJV). Thanks to Mr. Tim Heldt of Infratech for providing this story. Infratech's head office is in Brisbane, Australia. (Tel: +61-7-3237-8100, Fax: +61-7-3237-8188)