# Homework Help: What weight gives 0.42kN/m²

1. Mar 13, 2015

### Darryl Meek

I am setting up a test and the brief is as follows;

1. Mount a post horizontally on to a wall.
2. Apply a load corresponding to 0.42kN/m² at the centre of the post.

What weight corresponds to 0.42kN/m²?

2. Mar 13, 2015

### Darryl Meek

1. The problem statement, all variables and given/known data
How do I determine what weight gives 0.42kN/m²?
I have been asked to set up a test for a product as follows;
a) mount a post horizontally on a wall
b) apply a load corresponding to 0.42kN/m² at the centre of the post.
What weight do I hang off of the post to give this load?
2. Relevant equations

3. The attempt at a solution

3. Mar 13, 2015

### nasu

It depends on what area will the weight push (or pull) on.
How do you apply such a load (pressure) at the center (a point)?

4. Mar 13, 2015

### SteamKing

Staff Emeritus
You have a force distributed over an area, something equivalent to a pressure.

It's not clear what kind of product you are testing. Applying this type of load to a post implies you are testing the post itself. Since this test apparently involves the use of a port which is cantilevered from a wall, you should check to connection of the post to the wall and the strength of the post itself, before mounting or hanging anything. Safety first.

I suggest you ask for further clarification from whoever asked to set up this test.

5. Mar 13, 2015

### Darryl Meek

Sorry! It was a bit vague. You're right, safety first. I assure you that this will be a safe test. The product is a Ø60 tube made from HDPE but has a polyurethane base. It measures 900mm long. The test is to hang the weight on the centre of the post for 120 seconds and then remove the load before measuring the temporary deflection of the post. I'm just not sure how to calculate the weight to hang at the half way point of the post in order to achieve 0.42kN/m²

6. Mar 13, 2015

### Darryl Meek

In addition, the test is specified in a British standard. BSI will not comment on the standards content. They just say it's down to interpretation.

7. Mar 13, 2015

### SteamKing

Staff Emeritus
Regardless of whether this figure is in a British Standard or whatever, this doesn't change the nature of the loading; it's still a force distributed over an area, something which difficult to achieve by simply hanging a weight on a tube. What are the details of how the weight is to be hung from the tube? Are you using hooks, a strap, what? Which British Standard are you trying to satisfy?

8. Mar 16, 2015

### Darryl Meek

The British Standard is BS EN12899-3:2007. Clause 7.4.1.1 states "Precondition three new delineator posts for at least 4 hours at a temperature of 23°C ±2°C. That shall be fixed horizontally in a base clamp so that the ground line is level with the top of the clamp. Apply a test load in the traffic direction corresponding to 0.42kN/m² (42kg) in the middle of the delineator post. After 120 seconds measure the temporary deflection at the top of the delineator post with the test load still applied.

Remove the test load and after 120 seconds measure the permanent deflection at the top of the delineator post.

Report the measured values of the temporary and permanent deflection as a percentage of the total height of the delineator above the ground line"

9. Mar 16, 2015

### Darryl Meek

OK. Here's my attempt.

Surface area of my post is 0.6318m²

0.6318m² is 6.318% of 1m²

If 1 kN/m² = 100 kg/m² then 0.42kN/m² = 42kg/m²

Therefore, 6.318% of 42kg = Application load for 0.6318m² surface area = 2.65kg

10. Mar 16, 2015

### SteamKing

Staff Emeritus
Except 0.6318 m2 is 63.18% of 1 m2 [you move the decimal point over two places to the right to convert to percentage.]

Is 0.6318 m2 supposed to be the surface area of your test post?

11. Mar 16, 2015

### Darryl Meek

Hi SteamKing,

Thank you for looking at this. This is my error, the area is 0.06318m².

12. Mar 16, 2015

### SteamKing

Staff Emeritus
From what I have been able to gather, the figure 0.42 kN/m2 from BS EN12899-3 is a wind loading, which is to be used to check the strength of "Delineator posts and retroreflectors", either during their design or their selection for use in road works.

Without being able to acquire a complete copy of this standard (it's more than US \$300), I think for your test, what is required is that you calculate the total windage area of the post and any reflectors or other items intended to be attached. By windage area, I mean total up the area of any and all flat surfaces (including the width x height of the post itself) and then multiply this windage area in m2 by the wind pressure of 0.42 kN/m2. This will give a total load for the post and its attachments in kN.

For instance, if your total windage area is 1.5 m2, then the test load will be 1.5 m2 x 0.42 kN/m2 = 0.63 kN = 630 N, or roughly 63 kg.

For your test, after mounting the post horizontally, then apply the load in kN [or kg] (which you calculated in the previous step) to the center of the post. Make the measurements of deflection as required by the standard.

I think if you have any detailed questions about this procedure, a civil engineer (CE) should be able to advise you in more detail (I don't know if you have a CE handy at your work).