Aftab A. Mufti

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.

Synthetic Fiber-Reinforced Concrete Bridge Decks: Redefining Bridge Deck Design and Behavior

Researchers at the Technical University of Nova Scotia have pioneered the development of concrete slab on girder bridge decks totally devoid of all internal steel reinforcement. The decks are constructed of synthetic fiber-reinforced concrete on composite steel girders restrained by external steel straps. The discrete reinforcing fiber used is a collated fibrillated polypropylene fiber. The major benefit of this approach is the reduction of long-term maintenance costs and the increase in bridge deck lifespan. An overview of the concepts behind this technology, theoretical and experimental work that has been undertaken, and some the practical aspects of designing a fiber-reinforced concrete mix with high volume fractions of synthetic fiber are presented.

The Earthquake-Resistant Design of Critically-Important Concrete Structures

In the design of concrete bridges and buildings it is becoming increasingly common in countries around the world to use limit states design methods. These methods are based upon probability and statistics, and a very important part of such design methods is the concept of the safety index. In most design codes and specifications the intensity of the earthquake that must be included as one of the design loads is specified to be that intensity which has a stated probability of exceedance at the site concerned during the design life of the structure.