Design concrete bridge slab for tension and bending

[tuscan72]

Hello all, I have to design a reinforced concrete slab using the Aashto, what is the correct approach to design the reinforcement in the slab to take into account both tension and bending?
I was thinking find the flexural resistance Mr=0.9*Mn (cl 5.7.3.2) then the tension resistance Pr=0.9*Pn (cl 5.7.6) and check that (M/Mr)+(P/Pr) < 1.

Any hints much appreciated.

Tom

 

[Lion06]

How exactly is the slab in tension AND bending?

 

[tuscan72]

the slab is in a top of an arch thus it behave like a tie, bending is coming from the live loads. The slab thickness is 325mm, concrete 50MPa, rc steel 420MPa, cover 50mm and factored forces P=1980KN/m, M=293KNm/m, apologies for the SI units but the bridge is in the Emirates and they using SI.

Tom

 

[Lion06]

I would think the tie would need to be at the bottom of the arch, not the top.

 

[tuscan72]

it's not a bow string arch bridge, it comprise 3 steel arches with the concrete slab on top, the slab is not prestressed and for its particular shape the deck is in tension, any hints for design the slab with tension and bending?

 

[Lion06]

Just create an interaction diagram for the slab as a section with the depth of the slab and width of 12". Then you can determine appropriate interaction for tension and bending. You will enter your interaction diagram with axial loads and moments per foot.
This would be similar to analyzing a column, except you have tension instead of compression. The interaction chart and procedure is the same, though.
If you don't feel like creating an interaction diagram, PCAColumn does it rather quickly.

 

[tuscan72]

many thanks.I downloaded the trial version of PCA but what is the code related to the AAshto LRFD? I can choose ACI 318-05, ACI 318-02, CSA A23.3-04, and CSA A23.3-94. Can I use also PCA slab? Does it do also crack analysis?

 

[Lion06]

Check AASHTO for a reference to ACI, but I would bet ACI 318-05. I don't know anything about PCA clab.

 

[tuscan72]

what software is available to control the crack width according to the Aashto cl 5.7.3.4?

 

[Lion06]

I don't use AASHTO, so I don't know what that reference is, but if it is similar to the crack control in ACI just do a quick check. It isn't a difficult calc to do by hand.