 # Discrepancy observed in top stress due to live load

Question:

Deck slab continuity provided between girder.  Therefore, discrepancy observed in top stress due to live load by manual calculation and Midas calculation.

1)  Bending moment, Top stresses and Bottom stresses (My, Mz) due to live load for 70Rmax load case at node no.- 19 are tabulated below, 2) Sig-xx(Summation) of top stresses (Position 1) for My and Mz is 4.9 + 21.7 = 26.6 T/m2 and in Midas it shows – 20.8 T/m2. (fig. attached)

Same observation for node no. – 31.

Question 1: Bending moment, Top stresses and Bottom stresses (My, Mz) due to live load for 70Rmax load case at node no.- 19 are tabulated below?
Answer: Moving load results are envelope of results like MV max 70 R will give maximum stress at each point irrespective of stress at other points which means when max sig-xx (bending My) occurs, max of sig-xx(bending Mz) may not occur.
Secondly, as the top stress for My is negative. So, it's value can be obtained for MVmin 70R as shown below. Question 2: Sig-xx(Summation) of top stresses (Position 1) for My and Mz is 4.9 + 21.7 = 26.6 T/m2 and in Midas it shows – 20.8 T/m2.
Answer: As explained above, when sig-xx (My) is max, sig-xx(Mz) may not be max for moving load as it is envelope of results. Thus, they can't be added directly.
Secondly, sig-xx(summation) is axial stress at location 1 when the principal stress reaches maximum/minimum for a moving load case. But, this is not the case for static case where there is no envelopes formed. Eg. for Wind Load(ST) case, sig-xx(My) = -2.9 and sig-xx(Mz)= 3.6 and sig-xx(summation)=0.7 which is sum of (-2.9+3.6).
Moreover, if you need results for particular vehicle position, then it can be done by converting it to static load using moving load tracer.

Creation date: 5/27/2021 10:47 AM      Updated: 5/27/2021 12:09 PM