As part of my studies, I’ve been asked to design a prestressed concrete beam for a bridge. As part of this. Magnel Diagram The relationship between 1/Pi and e are linear and if plotted graphically, they provide a useful means of determining appropriate values of. Magnel diagram. From StructuralWiki. Jump to: navigation, search. Graphical method for design of prestressed concrete beams.
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Responses cara What is quasi permanent load? This form of construction is known as a Magnel Diagram.
Magnel Diagram Equations – Concrete Design – Eurocode Standards
Construct the Magnel diagram for the beam given in example The relationships can be plotted as shown in figure Alternatively, if the eccentricity is fixed, he diagram can be used to investigate the range of possible prestress force for the given eccentricity. If this proves to be critical then the section may have to be redesigned taking the quasi-permanent load condition as more critical than the characteristic load condition. A much more useful approach to design can he developed if the equations are treated graphically as follows.
Assume a maximum possible eccentricity of mm allowing for cover etc.
Values of minimum and maximum prestress force can be readily read from the diagram as can intermediate values where the range of diafram eccentricities for a chosen force can be easily determined. Get My Free Ebook.
Post a comment Name The line of maximum possible eccentricity is also plotted but, as it lies outside the zone bounded by the four inequalities, does not place any restriction on the possible solutions.
The Magnel diagram is a powerful design tool as it covers all possible solutions of the inequality equations and enables a range of prestress force and eccentricity values to be investigated.
In addition, it is possible to assume values of eccentricity for which there is no solution for the prestress force as the upper and lower limits could overlap. From he previous examples:.
Magnel diagram example
Hence the intersection of these two lines should be diabram as the maximum prestress force and. Take 30 per cent of the variable load contributing to the quasi-permanent load. These inequalities are plotted on the Magnel diagram in figure The intersection of the two lines at position A on the diagram corresponds to a value of Pi — kN.
For the previous example, using minimum preslress force of kN.
The lines marked 1 to 4 correspond to equations Concrete Stair Reinforcement Design. Note that in equation From the previous example:.
The Magnel diagram can now be used to investigate other possible solutions for the design prestressing force and eccentricity. Since this is greater than the upper limit already established from equation The additional line 5 shown on he diagram nagnel to a possible physical limitation of the maximum eccentricity allowing for the overall depth of section, cover to the prestressing tendons, provision of shear links and so on.
For different assumed values of eccentricity further limits on the prestress force can be determined in an identical manner although the calculations would be tedious and repetitive.
The calculation in example! Two separate figures are shown as it is possible for line I. Once a value of preslress force lying between the minimum and upper limit value is chosen, the compressive stress at the top of the section under the quasi-permanent loads should also be calculated and compared with the lesser allowable value of 0.