Gamil Tadros

Long-term structural health monitoring of the Crowchild Trail Bridge

Steel-free deck design is a relatively new approach to bridge deck construction. Several steel-free deck bridges constructed in Canada exhibited satisfactory behaviour immediately after construction. However, the long-term health of many of these structures has not been investigated. Significant cracking has been observed in many of these structures after only a few years in service. Long-term structural health monitoring of these structures is key in determining their long-term performance and future adoption of this new technology. Structural health monitoring data were obtained from the steel-free deck of the Crowchild Trail Bridge during its first seven years in service. Field monitoring included ambient vibration tests, static and dynamic load tests, and deck crack mapping. Despite significant amounts of cracks in the concrete deck and barriers, the overall behaviour of the Crowchild Trail Bridge has remained satisfactory and consistent. Future steel-free deck designs should consider crack control to...

Monitoring of Hall's Harbor wharf

The Halls Harbour wharf in Nova Scotia is the first Canadian project to demonstrate the application of fibre reinforced polymer reinforcement, the steel-free concrete deck slab concept and fibre optic monitoring systems to structures in the marine environment. The extreme environmental exposure conditions make the site an excellent location for testing both material performance and sensing system durability. The early results of the monitoring program indicate that the innovative structure is meeting service level performance requirements. Long-term durability assessment is continuing and being complemented by controlled field and laboratory testing programs. Continuous remote monitoring of the fibre optic sensors is producing valuable reinforcement strain information for tracking structural response to ambient conditions. The fibre optic sensors themselves were found to be rugged enough to withstand the construction process and exposure environment; however, further work is required to achieve feasible field units for some types of fibre optic sensing instruments and associated equipment.

First application of second-generation steel-free deck slabs for bridge rehabilitation

The arching action in concrete deck slabs for girder bridges is utilized fully in steel-free deck slabs. These concrete slabs, requiring no tensile reinforcement, are confined longitudinally by making them composite with the girders, and transversely by external steel straps connecting the top flanges of external girders. Between 1995 and 1999, five steel-free deck slabs without any tensile reinforcement were cast on Canadian bridges. All these slabs developed fairly wide full-depth cracks roughly midway between the girders. While extensive fatigue testing done in the past three years has confirmed that the presence of even wide cracks does not pose any danger to the safety of the structures, wide cracks are generally not acceptable to bridge engineers. The developers of the steel-free deck slabs have now conceded that these slabs should be reinforced with a crack-control mesh of nominal glass fibre reinforced polymer (GFRP) bars. Steel-free deck slabs with crack-control meshes are being referred as the second generation slabs. With the help of testing on full-scale models, it has been found that deck slabs with GFRP bars have the best fatigue resistance and those with steel bars the worst.

Predicting deflections of a simply supported pre-stressed concrete girder subjected to static loads from observed strains

Deflections of structures, such as bridge girders, are often the most difficult to monitor. Strain measurement is relatively simple with the use of electronic strain gauges, fiber optic sensors, or other strain measuring devices. This paper investigates two different methods for predicting or monitoring the deflection of a simply-supported full-scale bridge girder subjected to a partially distributed uniform load using strain measurements. A full-scale pre-stressed concrete bridge girder was instrumented and tested under a static monotonic load in the linear elastic range. This paper highlights the experimentally measured deflections along the length of one half of the girder and compares them to theoretically predicted deflections and deflections predicted using numerical integration along with harmonic analysis of curvatures determined from theoretical and observed experimental strains. Experimental test results indicate that estimating deflections from observed strains is feasible within the linear-elastic range of such girders. The methods outlined for predicting deflections of full-scale pre-stressed concrete bridge girders from observed strains are a valuable tool for structural engineers and for the periodic and continuous monitoring of civil structures such as bridges.

Are Civil Structural Engineers “Risk Averse”? Can Civionics Help?

This paper discusses the reasons civil engineers have for being conservative in their design and argues that structural health monitoring will assist in providing data that could realistically be used to calibrate load and strength factors leading to more efficient and economical designs.

GFRP Reinforced Corrosion-Free Bridge Deck Slabs Based on ISIS Winnipeg Principles

In places where deicing salts are used to keep roads free of ice, the bridge components most prone to corrosion are concrete deck slabs, which can be made corrosion-free by replacing the steel reinforcement by bars made of fibre reinforced polymer (FRP). Recent experimental investigation has shown that only the transverse bars at the bottom of the deck slab confine the slab for full arching action. The rest of the reinforcement in the two assemblies only controls the widths of environmental and fatigue-induced cracks. An experimental fatigue study on full-scale models of deck slabs showed that slabs with steel bars have the poorest fatigue resistance and slabs with glass fibre reinforced polymer (GFRP) bars the best. ISIS Canada conducted field studies in 2005 to show that the GFRP is not attacked by alkaline reaction in concrete. Because of this finding the Canadian Bridge Highway Bridge Design Code (CSA S06–06) permits GFRP as a primary reinforcement.

METAL FORMS REPLACE REINFORCEMENT IN BRIDGE DECK SLABS

Publisher Summary Research has shown that the strengths of composite concrete deck slabs of girder bridges are governed by transverse confinement, which can be provided internally in the form of bottom transverse reinforcement, or externally by means of steel straps connected to the top flanges of the girders. It is generally believed that because of the lack of bond between concrete and the galvanized surface of the metal form, the form does not participate in the load carrying action of the slab. It is shown in this chapter that with simple modifications in design, the metal form can be made to confine the deck slab transversely; the modifications comprise the provision of transverse continuity in the metal form across the bridge width. Thus, all the tensile reinforcement in the slab can be removed, except that required for transverse negative moments induced by loads on the deck slab overhangs. A full-scale model is under construction to confirm the above hypothesis. In current designs, the metal forms cease to be useful after the casting and setting of the slab, because of which, the durability of the form is of little consequence to the safety of these slabs. The same is not the case in the proposed design. It is suggested by the chapter that the problem of metal form corrosion can be solved by one of three means such as using a fiber reinforced polymer form, providing bottom transverse reinforcement, which could take over after the form has corroded, or installing steel straps when the form begins to corrode.

Structural health monitoring of innovative bridge decks

The concept of steel-free deck slab is discussed along with six field applications in Canada. In particular, the phenomenon of cracking in deck slabs is discussed with reference to laboratory studies as well as field observations, both of which have shown that, notwithstanding the presence of cracks, the fatigue resistance of the steel- free deck slab is very high. The provision of a layer of nominal tensile reinforcement within the thickness of the steel-free deck slab, however, eliminates the unaesthetic wide cracks. Laboratory studies, currently underway, have shown that the technique of acoustic attenuation is very effective in tracking the growth of cracks in concrete deck slabs. The conventional sensors were not successful in this respect.