Calculating Loads for a 2m x 2m Concrete Tunnel with 4 Supports

[curious_iza]

Hi I have tried this question and am struggling to work it out;

A concrete concrete tunnel with 2m x 2m dimensions on the outside (in cross section) with a uniform wall thickness of 200mm, is used to support a live load of 4kN/m^2 on its top surface. The density of the concrete is 25kN/m^3. The structure has 4 supports.

a) Calculate the dead load (G) and live load (Q) along its length in kN/m.

b) Calculate the ultimate state design load in kN/m of the concrete tunnel by applying the appropriate load factors of 1.2 and 1.5.

Obviously I have do work...

1) I got the cross section of the area which worked out to be 4m^2...

2) I then worked out the 'hollow' part since the thickness is only 200mm I got the 'empty' area as (2 - 0.2 -0.2)^2 = 2.56.

3) I subtracted this to get the actual cross section of the concrete.

4) I then made the length of the beam = Lm. And using the cross section and the Lm length I multiplied the cross section by the length to get the volume. Since density was given I multiplied volume by density and got 36L kN/m.

5) I then divided by L to get the force per m...

I don't know if I did all above right ... if so how do I tackle this question!

Thankyou for your time.

Kind regards, Isabelle

 

[Dr.D]

What is there in your problem to give you a live load at all? Do you have some design spec that calls out a live load for you? Nothing you mentioned in the problem statement sounds like a live load at all. Something seems to be missing here.

 

[curious_iza]

Hi, they give the live load of the top layer (which is 4kN/m^2) ... I have attached the file with the exact question asked (If you would like a diagram). Thanks.

 

[Dr.D]

I was unable to open your pdf previously.

I'm not sure what "calculate the live load" means when it is given in the figure, but oh well ...

The dead load should simply be the total weigh per length.

 

[curious_iza]

Oh... hang on... I think I just figured it out - I looked at the wrong solutions. Typical. :D