Assessment of Highway Bridge Upgrading by Dynamic Testing and Finite-Element Model Updating

Abstract

The Land Transport Authority of Singapore has a continuing program of highway bridge upgrading for refurbishing and strengthening bridges to allow for increasing vehicle traffic and increasing axle loads. One subject of this program has been a short-span bridge taking a busy main road across a coastal inlet near a major port facility. Experiment-based structural assessments of the bridge were conducted before and after upgrading works including strengthening. Each assessment exercise comprised three separate components: ͑1͒ a strain and acceleration monitoring exercise lasting approximately one month; ͑2͒ a full-scale dynamic test carried out in a single day without closing the bridge; and ͑3͒ a finite-element model updating exercise to identify structural parameters and mechanisms. This paper presents the dynamic testing and the modal analysis used to identify the vibration properties and the quantification of the effectiveness of the upgrading through the subsequent model updating. Before and after upgrade, similar sets of vibration modes were identified, resembling those of an orthotropic plate with relatively weak transverse bending stiffness. Conversion of bearings from nominal simple supports to nominal full fixity was shown via model updating to be the principal cause of natural frequency increases of up to 50%. The utility of the combined experimental and analytical process in direct identification of structural properties has been proven, and the procedure can be applied to other structures and their capacity assessments.

Vibration-based monitoring of civil infrastructure: challenges and successes

“…Accelerometers represent only a fraction of the 1500 sensors on this bridge. (Wong, 2010) 30 Pioneer Bridge 18.2m span comprising precast pre-tensioned inverted T-beams supporting a RC slab Monitoring of dynamic strains over a period of several weeks before and after upgrading showed changes in extreme values of strain for given return periods, confirming effectiveness of upgrade (and that it was perhaps unnecessary) (Brownjohn et al, 2003) 31 Kalbaskraal Bridge 2x32m span wrought iron truss Dynamic testing and model updating followed by dynamic response monitoring characterised strain regime in order to predict fatigue life for a range of increased loading conditions. (Moyo, 2007) …”

Dynamic Testing of Alfred Zampa Memorial Bridge

“…Forced vibration tests are directly related to the application of classical experimental modal analysis (Ewins 2003), in which the bridge is usually excited by artificial means such as eccentric or linear inertial shakers (Halling et al 2001;Brownjohn et al 2003) or drop weights (Abdel Wahab and De Roeck 1998).…”

A bridge-monitoring tool based on bridge and vehicle accelerations

“…They point out that using a vehicle to excite the bridge often has the disadvantage of inducing vehicle vibrations into the bridge response but that for large bridges, ambient methods such as vehicle traffic are the only practical way to excite the bridge. Similarly, Brownjohn et al (2003) compare three different methods of excitation of a bridge (18 m simply supported span formed using inverted T beams) to extract its modal parameters: shaker testing, vehicle induced response and hammer testing. The best quality data is found to be obtained from forced vibration testing with the shaker, which is capable of providing a level of excitation sufficiently high without altering the bridge frequencies.…”