Moments in one way slabs

[Sally_Ameen]

Hello Everyone,

I have modeled the one-way slab below (3 m short span X 16 m long span) supported by 30x50 cm RC beams on the edge and loaded with 5KN/m2 (without self weight), I used shell model and meshing 30x30 cm.

I see that the moments in the long span (Mxx) is higher than the moment in the short span (Myy) (while I expect the opposite!!)

Can anyone advice me what I have done wrong with my modelling.

Thanks in advance...

Moments in direction of long span:

Mxx

Moments in direction of short span:

Myy

Sign convention in Robot Structural analysis:

Sign convention in Robot

[Krzysztof_Wasik]

HI @Sally_Ameen 

Share zipped model version for verification

[Sally_Ameen]

sorry I couldn't attach the file at first

[Krzysztof_Wasik · Accepted solution]

Hi @Sally_Ameen 

Results correspnd to slab deformation. Mxx is bigger due to bigger deformation between axes 1-2 and 2-3.. Defined beams are not stiff enough to prevent slab span from deformation.

You probably expect moment distribution corresponding to one way slab supported around perimeter. The moment for shorter span is bigger.

[Krzysztof_Wasik · Accepted solution]

Hi @Sally_Ameen 

You probably expect moment distribution corresponding to one way slab supported along longer edge

[Sally_Ameen]

Thank you Krzysztof, actually I was expecting that any slab having L-long/L-short >2 to behave as one-way slab (meaning: moment of short direction to be greater than moment of long direction)

[Sally_Ameen]

Sorry I didn't notice your attachment, yest this is exactly what I was expecting. did you make any change in the model?

[Krzysztof_Wasik · Accepted solution]

Hi @Sally_Ameen 

I have defined pinned supports along longer slab edges.

[Sally_Ameen]

It is clear thank you. One more question 🙂 why the moments at mid span is negative while I expect positive moment in mid span (is it just a sign convention in Robot)?

[Krzysztof_Wasik · Accepted solution]

Hi @Sally_Ameen 

This is sign convention. Tension in z- layer is caused by negative Mxx or Myy moments