Littérature scientifique sur le sujet « PRETENSIONED AND POST TENSIONED GRIDERS »

The results of a study on the use of cathodic protection on prestressed and post-tensioned concrete bridge members are summarized. Previous laboratory tests to evaluate hydrogen embrittlement of high strength steel embedded in concrete have proven that cathodic protection will generate hydrogen on high-strength steel in concrete if the potential is more negative than the thermodynamic hydrogen evolution potential. The hydrogen generated will enter the steel and cause a loss in ductility that will adversely affect the steel's performance if a notch is present. Full-scale beams were constructed to further study those phenomena. Four pretensioned beams were constructed. In addition, two post-tensioned slabs were constructed to evaluate cathodic protection of anchorages and tendons encased in metal or plastic conduits. Cathodic protection currents were supplied by IR drop-free potential controlled rectifiers. Good potential control at control points was achieved by using externally mounted silver-silver chloride reference electrodes and a conductive gel bridge. However, inconsistent potential control occurred at locations other than at the control points. Later in the study, constant current power supplies were used on two of the beams. Hydrogen entering the steel as the result of corrosion appears to have masked the presence of hydrogen that might have been produced by cathodic protection. The analysis also revealed that there was corrosion of some pretensioned wires at crossings with interior steel reinforcing bars due to interference (stray current) caused by cathodic protection application. Analysis of the post-tensioned slabs indicated little effect of cathodic protection on tendons inside plastic or metal ducts from the application of cathodic protection. Beneficial effects were noted on anchor points where mortar was in contact with the metal.

In today’s world, there is a higher demand of roads and grade separated structures to avoid traffic congestion. Thus, a lot of elevated viaducts, flyovers and bridges are being constructed all over the world. The bridge superstructure is of various types and the type of superstructure to be adopted depends upon several factors. The most used superstructure type is beam slab system in which, generally, the beams are prestressed. Pre-Tensioned and Post Tensioned girders are the most used type of prestressed beams in beam slab bridges and the practice of Prestress I-Girder type bridges are gaining popularity in bridge engineering fraternity because of its structural efficiency, better stability, serviceability, elegance, economy, aesthetic appearance and shortened construction time. Parametric study has been done with different configurations in terms of span length and the number of girders to evaluate the total quantities of Pretensioned and Post Tensioned girders. Finally, the cost comparison between the two types of girders is done considering the concrete quantity, reinforcement and prestressing steel quantity. The scheme of launching and logistics involved are also considered for the cost comparison between the two types of girders. The theoretical comparison is also done in order to understand the differences in bending moment & shear force between Pretensioned and Post tensioned I- Girders. The design & analysis of prestressed concrete girders is carried out using IRC:112-2020 Concrete Road Bridges based on India Live Load as per IRC 6-2017. The IRC:112-2020 code is based on limit state design philosophy. Based on the comparative study done, it has been found that the Pretensioned girders are very economical and time efficient primarily because more than 5 to 7 girders can be prestressed at the same time using the same equipment. Further, there is no requirement of anchorages, sheathing and grouting. It has been found that Pretensioned Girders are more economical when compared to Post Tensioned Girders if the number of girders required in the project is more than 250 number of girders.