# Self Weight Problem with Composite Section

Question:
In the attached model, I have a concrete/steel composite section created using the “Section Property Calculator”. The self-weight reported by Midas Civil does not match the self-weight using an alternate program AND hand calculations:
From Hand Calculations:
Total Element Length = 820.641m
Area Concrete = 9.05181m2
Area Steel = 0.555m2
Density Concrete = 23.56kN/m3
Equivalent Density Steel = 198.6385kN/m3
Weight of Concrete Section = 820.641m x 9.05181m2 x 23.56kN/m3 = 175010.4kN
Weight of Steel Section = 820.641m x 0.555m2 x 198.6385kN/m3 = 90471.07kN
TOTAL WEIGHT = 175010.4kN + 90471.07kN = 265481.5kN (this value matches the alternate program result).
From Midas Civil:
SUMMATION OF REACTION FORCES PRINTOUT
Load FX (kN) FY (kN) FZ (kN)
Self Weight -0.000000 0.000000 249460.845077Although this is close to the hand calculation (94%), it should be 100%. Please advise.
Thank you

In your model, there is no construction stage. Due to this reason, total weight value from midas Civil does not match the value from hand calculation.
Without construction stage data, the program does not consider the construction stage and cannot distinguish the materials between part1 (concrete) & part2 (steel).
If you set the construction stage, the structural analysis is performed by steps and it has the same value from hand calculation.

Here are the steps for setting the construction stage.

1. Construction stages comprise of activation and deactivation commands for the structure group, boundary group, and load group.
Therefore, set the structure group, boundary group, and load group.

2. Create the construction stage 1.

3. Create the construction stage 2 to set the [Composite section For C.S].

4. Define the material for steel.

5. Set the Composite section For C.S.

6. Perform the analysis.

7. Select [stage2] to check the results tables.

8. To confirm the total weight value from midas Civil, select [Results > Results Tables > Reaction].

9. You can get the same value from hand calculation.

Thank you.

Q.
Hi Jlhong, I was suspecting that this was the case. This is a very preliminary model, so I was trying to just “play” around with it, and I thought that this would work.

Q.
Hi Jlhong, I am trying to change the part 1 to steel and part 2 to concrete in the “Sectional Property Calculator” but when I try to import it back to Midas Civil it gives me an error:
[Error] Section Stiffness value has(have) been incorrectly entered.
I have tried to do it several times, but I cannot get rid of the error. Please advise.

A.
Hi,

If you change the part 1 to steel and part 2 to concrete in the SPC, you also have to change the setting of Composite section For C.S ( No. 5 in the previous attachment ) in midas Civil.

[Part1: 4:Deck, Part2: 1:A53] → [Part1: 1:A53, Part2: 4:Deck]

I hope the answer is well understood.

Thank you.

Q.
Thank you for your response. I do realize that I would have to change the material properties correspondingly.
My question was another one. I have recreated the cross section in the Midas tool “Section Property Calculator” with the steel as part 1 and the deck as part 2. However, when I try to import it to Midas Civil, I get the error:
[Error] Section Stiffness value has(have) been incorrectly entered.
I cannot figure out why I am getting the error. Please adivse.

A.
Hi,

When you define the steel section in SPC, you have to first create the steel model with one line by putting the width information and then define the steel section with “Line” option from the “Part Type” fields.
However, when I checked your model, your steel section was modeled with two lines and defined with “Plane” option from the “Part Type” fields.
Please refer to the attached model.
Thank you.
Creation date: 10/12/2017 3:21 AM      Updated: 10/12/2017 1:02 PM