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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Magnel diagram example

For the previous example, using minimum preslress force of kN. For different assumed values of eccentricity further limits on the prestress force can be determined in an identical manner although mafnel calculations would be tedious and repetitive.

Note that in equation These inequalities are plotted on the Magnel diagram in figure Concrete Stair Reinforcement Design. The lines marked 1 to 4 correspond to equations Construct the Magnel diagram for the beam given in example Values of minimum and maximum prestress force can be readily read from the diagram as can intermediate values where the range of possible eccentricities for a chosen force can be easily determined. The Magnel diagram is a powerful design tool as it covers all possible solutions of the inequality equations and enables a range of prestress mabnel and eccentricity values to be investigated.


Get My Free Ebook. The additional line 5 shown on he diagram corresponds 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.

Two separate magbel are shown as it is possible for line I.

This form of construction is known as a Magnel Diagram. Post a comment Name The Magnel diagram can now be used to investigate other possible solutions for the design prestressing force and eccentricity.

A much more useful approach to design can he developed if the equations are treated graphically as follows. From he previous examples:. Since this is greater than the upper limit already established from equation Responses cara What is quasi permanent load? Hence the intersection of these two lines should be taken as the maximum prestress force and. The intersection of the two lines at position A on the diagram corresponds to a value of Pi — kN.

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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.


Alternatively, if the eccentricity is fixed, he diagram can be used to investigate the range of possible prestress force for the given eccentricity. 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.

The calculation in example!

From the previous example:. Assume a maximum possible eccentricity of mm allowing for cover etc. Take 30 per cent of the variable load contributing to the quasi-permanent load. 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.

In addition, it is possible to assume values of eccentricity for which there is no riagram for the prestress force as the upper and lower limits could overlap.

The relationships can be plotted as shown in figure

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