# Changes for page Concrete Design

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edited by IwonaBudny
on 2018/11/29 16:04
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 ... ... @@ -8,9 +8,7 @@ 8 8 9 9 = {{id name="Design forces"/}}Design forces = 10 10 11 -(% style="text-align: justify;" %) 12 12 13 - 14 14 The design forces are the forces that the reinforcements should be designed for in the reinforcement directions. The term design forces have meaning only in surface structures like plate, wall or 3D plate. In beam structures the design forces are equivalent to the internal forces. The necessary reinforcement calculations are based on the design forces. 15 15 16 16 (% style="text-align: justify;" %) ... ... @@ -37,12 +37,38 @@ 37 37 38 38 [[image:1543503517958-895.png||height="311" width="399"]] 39 39 38 +(% style="text-align: justify;" %) 39 +Now the design forces will be chosen from four basic cases called a), b), ξ) and η). The possible design moment pairs of the cases: 40 40 41 +a) case: 41 41 43 +[[image:1543503652914-266.png||height="91" width="351"]] 42 42 45 +b) case: 43 43 47 +[[image:1543503750827-594.png||height="100" width="350"]] 44 44 49 +ξ) case: 45 45 51 +[[image:1543503838340-661.png||height="87" width="165"]] 52 + 53 +η) case: 54 + 55 +[[image:1543503816725-369.png||height="88" width="336"]] 56 + 57 +From the four cases the one is invalid where: 58 + 59 +* the signs are different: **m,,ξ,,*m,,η,, < 0** 60 +* the crack tensor invariant is less than the internal forces invariant: 61 + 62 +[[image:1543503891591-532.png||height="75" width="316"]] 63 + 64 +(% style="text-align: justify;" %) 65 +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). 66 + 67 +(% style="text-align: justify;" %) 68 +So the result will be four values in a certain point: two moment values for each reinforcement directions. 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,,x,, **is 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,,x,, **and the top reinforcement bars make equilibrium to the **m,,y,,**. So a certain reinforcement direction takes positive and negative loads at the same time. 69 + 46 46 ((( 47 47 ---- 48 48 )))