End Zone Reinforcement for Pretensioned Concrete Girders
In this study, a literature review was conducted to establish the background of current specifications and to evaluate the applicability of various theories and methods for design of end zone reinforcement. Analytical methods reviewed in this paper include finite element analysis, strut- and-tie modeling, and the Gergely-Sozen equivalent beam method. Previous experimental work combined with work conducted as part of this study were used to correlate between various theoretical and experimental results. This paper illustrates that no single theoretical method adequately represents the complex behavior at the end of a pretensioned concrete member. A general semi-empirical design procedure is proposed here. It is based on theoretical behavior and experimental observation. Standard reinforcement details are given. The proposed procedure could result in reduction in the congestion of reinforcement while maintaining acceptable crack control at the member end. Application of the proposed procedure to highly pretensioned bridge girders is demonstrated.
Evaluation of Crack Control Methods for Deep Pretensioned Bridge Girder Ends
Deep pretensioned concrete bulb Tee girders exhibit cracking at the end regions during detensioning. These cracks, discourage engineers from using deep sections, or if considered severe may result in the rejection of the girders upon shipment from a producer. The durability of the members is of concern, particularly if corrosion agents reach strands through cracks. The industry uses various crack control methods chosen based on practical experience. The impact of these methods on controlling cracks has not been well quantified or compared. This paper describes an evaluation of the effectiveness of existing and proposed crack control methods. The girder ends were analyzed using nonlinear finite element analysis verified by test data. The effects of end zone reinforcement pattern, debonding of strands, strand cutting order, draped strand pattern, and lifting of the girder on cracks were examined. For each method, the reduction in the tensile strains associated with cracking is presented.
Ocean thermal energy conversion: The promise of a clean future
Due to the world's heavy dependence on fossil fuels for electricity, pollution and global warming is on the rise. However, numerous countries are still relying on diesel generators as their main source of energy. There is a lack of practical alternative energy source that can meet the global energy demand without posing any threat to the natural environment. Ocean Thermal Energy Conversion (OTEC) is a concept that has the potential to address this growing issue. It is basically a mechanism that exploits the temperature difference between warm surface seawater and cold deep ocean water, to produce electricity. Although OTEC has a low energy density, the thermal energy in the ocean is vastly abundant. OTEC development has been dormant for a long time since it was first proposed in 1881. However, it has now regained recognition worldwide as a realistic solution to our world energy issue. Instead of having a great potential for power generation, it also carries the ability to produce high value products from the large volume of Deep Sea Water (DSW) that can be released as byproducts of OTEC plant operation. These products can hold a very profitable place in industries such as pharmaceutical, food, cosmetics and mineral water production. Further research on ocean current and DSW properties can someday lead to the commercial used of OTEC. This paper is a review of the basic concept, present status and future prospects of OTEC around the world.