Martin Turek

In-Plane Shake-Table Testing of GFRP- Strengthened Concrete Masonry Walls

In-plane shake-table tests were performed on eight full-scale unreinforced concrete block walls. Three of the walls were left as plain unreinforced masonry and five were strengthened using glass-fiber-reinforced plastic (GFRP) strips in four different configurations. All walls were first subjected to design-level earthquake records to determine the improvement obtained from the addition of the GFRP. The walls were then subjected to extreme-level earthquake records to examine the ultimate failure modes and the effects of the various GFRP configurations on the response of the walls. It was observed that all strengthened specimens performed well during the design-level shaking, and three of the four GFRP configurations also performed well during the extreme-level shaking. The tests showed that the use of vertical GFRP strips alone is able to improve the in-plane performance of URM walls. The strips were also able to control the failure modes, and prevent collapse after severe damage, improving significantly the life safety performance of URM walls.

Model Updating of the Ironworkers Memorial Second Narrows Bridge, Vancouver, Canada

The Ironworkers Memorial Second Narrows Crossing is a critical transportation link in the Lower Mainland Region of British Columbia, Canada, which is a zone of high seismic risk. The IMSNC is being instrumented as part of a real time seismic and health monitoring system, which will also include many other bridges around the region. As part of the system, a finite element model has been developed and updated using previously obtained ambient vibration measurements. This paper focuses on updating of one approach truss section of the bridge. The model was updated in several steps using both manual and automated techniques. Updating included stiffness of a set of seismic isolators that were added to the bridge in a retrofit in the mid 1990’s. The complete updated set of models will be used in fatigue and damage studies as a part of the monitoring system.

Temperature and Traffic Load Effects on Modal Frequency for a Permanently Monitored Bridge

Many of the damage detection techniques available compare measured parameters of a structure in a known, reference state to an unknown, possibly damaged state. In the case where the measured parameters are the modal characteristics of the structure, it has been shown that these can be sensitive to changes other than damage, such as temperature. Therefore it is useful to install permanent monitoring systems that can track normal changes in measured modal characteristics. The Ironworkers Memorial Second Narrows Crossing, in Vancouver, Canada, had a permanent monitoring system installed in 2011. The purpose of the system is to monitor the response of the bridge during seismic and other potentially damaging events, and to perform long term performance monitoring. During an assessment of the modal parameters it was observed that there is a regular fluctuation in the measured frequencies, so a detailed study on a 17-day segment of continuous data was performed. Analysis was performed on both temperature data and acceleration amplitude (to represent traffic on the bridge). The modal fluctuations were very regular, with maximum at night and minimums in the day, which correlated well with the maximum traffic in the day and minimums at night. The temperature fluctuations coincided with daily changes but had a more variable pattern, which was not directly correlated to changes in frequency. It is also observed that the traffic load on the bridge amplifies the response of the first vertical mode seven and ten times during daytime weekdays and daytime weekends, respectively whereas the first torsional mode of the structure amplifies 5.5 and 4 times in daytime weekdays and weekends, respectively.

Structural Monitoring and Analysis of Bridges for Emergency Response

The British Columbia Ministry of Transportation and the University of British Columbia have implemented a program to instrument key structures to provide confirmation of seismic capacity, assist in focusing retrofit efforts, perform structural health evaluations and provide rapid damage assessment of those structures following a seismic event. The instrumentation system installed at each structure will automatically process and upload data to a central server via the Internet. The alert systems and public-access web pages can display real time seismic data from the structures and from the BC Strong Motion Network to provide input for assessments by the Ministry of non-instrumented bridges. These systems may also provide other agencies, emergency responders and engineers with situational awareness.

Vibration Testing of Bridge Stay Cables to Obtain Damping Values

This paper discusses a series of tests performed on a cable stayed bridge in British Columbia, Canada to obtain the cable damping properties. Free vibration tests were performed on selected cables, in two phases: one during a state of construction, with the cables at a load less than 100%, and the second after the cables were complete and at the final load, and with additional neoprene inserts at the deck end of the cable. In a comparison of 8 cables on a single tower, the typical results showed an increase in modal frequency and increase in damping value. Damping values typically ranged between 0.2 and 0.4%.

Dynamic Characteristics of Tall Buildings in Vancouver, Canada

This paper presents the results of a series of vibration tests conducted on tall reinforced concrete shear-wall buildings located in Downtown Vancouver, British Columbia, Canada. The buildings tested were the Sheraton Wall Centre, The City Tower building, The Heritage Court Tower and The Melville. Ambient vibration tests were performed on each building to obtain its dynamic characteristics. Overall vibration levels, mode shapes, modal frequencies and modal damping were determined. In addition, detailed ground measurements were taken on the Melville and the City Tower buildings to examine potential rocking behaviour and soil-structure interaction effects of the raft foundation. Interesting results of the study show that some lateral modes of vibration of the buildings include base rocking, even at low levels of vibration, and that modal coupling between the lower modes of vibration is significant. These findings indicate that the seismic response of these buildings during severe shaking may be different than that predicted during the design process.