How the design positive moment is computed at the middle of the beam by ETABS 3

[adarpodracir]

Hi there,

I am analyzing and designing a 4-Story RC Building with ETABS 9.7.2. I have a question regarding how the design positive moment is computed at the middle of the beam by ETABS. For example, according to the "Concrete Design Information ACI 318-08/IBC 2009" window (shown below), the design positive moment is 105.647 kN-m for combo COMB2 and station location 4.00 m (middle). However, according to the "Diagram for Beam B174 at STORY1 (B40x60)" window, the factored positive moment is 88.237 kN-m for the same combo and station location. How this difference can be explained? I mean, in theory ETABS should be using 88.237 kN-m instead of 105.647 kN-m as the design positive moment. So, how ETABS is computing this value of 105.647 kN-m, anyway?

NOTE: COMB2 = 1.2*DEAD + 1.6*LIVE.

I have to say that everything is computed as expected, except the design positive moment at the middle of the beam. This applies for all of the beams defined in the model.

Thank you very much for your time and consideration, and for any comments you could give me.

 

[slickdeals]

This should be your answer

https://wiki.csiberkeley.com/display/kb/Pattern+live-load+factor

If you change PLLF to 0, the analysis/design moments should match.

It’s no trick to get the answers when you have all the data. The trick is to get the answers when you only have half the data and half that is wrong and you don’t know which half - LORD KELVIN

 

[adarpodracir]

Dear slickdeals,

Thank you very much for reply. Your solution solved my problem!!!