Bridge Structures

Rebar cages are the skeletons of reinforced concrete columns formed by connecting the longitudinal to the transverse reinforcement with tie wire connections. The collapse of several bridge rebar cages recently showed the need to establish guidelines to enhance the lateral stability of these temporary structures. The results of experimental and analytical studies on the stability of bridge column rebar cages are presented in this paper. An experimental investigation was conducted on two full-scale rebar cages to determine their lateral behavior and to calibrate nonlinear computational models. Using these calibrated models, the effects of various cage parameters on the lateral stability of rebar cages were investigated. Based on this investigation, it was concluded that the internal bracings provide the significant component of the cage lateral stiffness and strength. Guidelines to improve the lateral stability of column rebar cages are proposed.

The combination of dead load and live load is very important in design of bridge superstructure as, in practice, it controls the strength limit states. The basic set of load factors for the Strength I limit state is 1.25 for dead load and 1.75 for live load and dynamic load. For design cases when the dead load dominates, i.e. for Strength IV limit state, the dead load factor is 1.5. The acceptability criterion for load and resistance factors in the AASHTO LRFD Code is closeness to the target reliability index, which is assumed to be 3.5 for steel and concrete girder bridges. However, the reliability analysis performed for a full range of dead load to live load ratios indicates that when live load is about 10–20% of the total load, the reliability indices are about 3.0 which is lower than the target value of 3.5. This is an indication that the reliability level is insufficient and there is a need for increasing load factors. On the other hand, for dead load constituting about 100% of the total load (i.e. no live load), the reliability index is much higher than 3.5, which means that the load factor 1.5 can be reduced. Therefore, it is proposed to change the current Strength IV load factors to dead load of 1.4 and live load factor 1.4. The result is a more uniform reliability level for all combinations of dead load and live load. The results of reliability analysis are presented in graphs.

Most of the major cities in the United Arab Emirates (UAE) have witnessed a rapid growth rate in population during the past two decades, which was accompanied by the development of major transportation infrastructure. This fast growth of the infrastructure and the pressure of constructing more infrastructures in the UAE cities did not allow the local authorities to develop a suitable Bridge Management System (BMS) to maintain the nation's valuable asset at acceptable levels of safety and serviceability. This paper aims at developing a conceptual framework for a BMS that recognizes the local conditions and needs of the UAE. To achieve this objective, the paper provides a review of the BMS around the world and a summary of the local practices and experiences in this area. In addition, a proposed framework for the development of a comprehensive bridge management system for UAE and discussion of the main components of the proposed BMS are presented.

Thermal imaging can be used to image subsurface damage resulting from the corrosion of embedded reinforcing steel, which typically manifests as delaminations at or near the level of the reinforcing steel. Delaminations interrupt the heat transfer through the concrete, resulting in surface temperature variations that can be assessed using thermal cameras. This type of damage occurs in bridge decks, soffits, parapets, abutments and other concrete bridge components. This paper will discuss advances in the application of thermal imaging for the condition assessment of concrete bridge components, focusing on applications to the areas of the bridge not exposed to the radiant heating of the sun. Research results describing ambient temperature variations and inspection timing requirements for conducting thermal inspections are presented. Research exploring the effects of environmental parameters on the ability to image subsurface defects (delaminations) at different depths in concrete is also discussed.