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

Assume a maximum possible eccentricity of mm allowing for cover etc. From he previous examples:.

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. This form of construction is known as a Magnel Diagram.

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. These inequalities are plotted on the Magnel diagram 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.


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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 riagram value of 0. The intersection of the two lines at position A on the diagram corresponds to a value of Pi — kN.

Magnel Diagram Equations – Concrete Design – Eurocode Standards

A much more useful approach to design can he developed if the equations are treated graphically as follows. If mganel proves to be critical then the section jagnel have to be redesigned taking the quasi-permanent load condition as more critical than the characteristic load condition. 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.

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.

Responses cara What is quasi permanent load? Post a comment Name From the previous example:. Concrete Stair Reinforcement Design.

Magnel diagram example – Album on Imgur

The relationships can be plotted as shown in figure Diargam 30 per cent of the variable load contributing to the quasi-permanent load.


Construct the Magnel diagram for the beam given in example The lines marked 1 to 4 correspond to equations Hence the intersection of these two lines should be taken as the maximum prestress force and. Two separate figures are shown as it is possible for line I.

The calculation in example! 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.

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. Since this is greater than the upper limit already established from equation The Magnel diagram can now be used to investigate other possible solutions for the design prestressing force and eccentricity.

For the previous example, using minimum preslress force of kN. Note that in equation