1. Mar 28, 2009

### 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.

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 dunno if I did all above right ... if so how do I tackle this question!!!

Kind regards, Isabelle

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2. Mar 28, 2009

### 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.

3. Mar 28, 2009

### 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.

4. Mar 28, 2009

### 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 ...