If the option Cracked section analysis, is activated the program will consider the decrease in slab stiffness on behalf of cracking. So a certain reinforcement direction takes positive and negative loads at the same time. It can sound strange that the reinforcements are used for both positive and negative moment in one direction at the same time, but if we are looking at a plate where the m xis positive and the m y is negative and the reinforcements have an angle of 45 degree to the x direction we could imagine that the bottom reinforcement bars make equilibrium to the m xand the top reinforcement bars make equilibrium to the m y. So the result will be four values in a certain point: two moment values for each reinforcement directions. The valid positive pair will be the design moment for bottom reinforcement the valid negative pair will be the design moments for the top reinforcement (positive means positive and zero values negative means negative and zero values). the crack tensor invariant is less than the internal forces invariant:.The possible design moment pairs of the cases:įrom the four cases the one is invalid where: Now the design forces will be chosen from four basic cases called a), b), ξ) and η).
In the first step we are taking a ξ-ϑ coordinate system and transform the internal forces into this system: α, β angle of global x direction and the ξ, η reinforcement directions,.For the calculation of the design forces we have given:
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