Hey Reader

I remember being pretty happy with how little my beam was deflecting.

Until I realised I had forgotten about 90% of the load. Haha, true story.

I was looking through AS 1170.1 recently and found an old note I had made about the self-weight of a 110 mm brick wall.

It reminded me of one of my first beam designs, with a brick wall sitting on top.

I ran the numbers, checked the beam, and got almost no deflection. Something felt wrong, so I went back through the calculations.

Eventually I spotted the two words I had missed in the material weight table:

PER 10 mm

I had treated 0.19 kN/m² as the weight of the entire brick wall. It was actually the value for each 10 mm of wall thickness.

For a 3 m high wall, the difference is huge:

My original calculation:

0.19 × 3 = 0.57 kN/m

Corrected calculation:

2.09 × 3 = 6.27 kN/m

That is 11 times the load I had originally used.

Luckily, 0.57 kN/m sounded far too low for a brick wall, so I kept digging. But if the number had been a little higher, I might have missed it.

Here is a brick wall reference image I keep in our BengLab Second Brain that may help you as well:

I think the real lesson is to build a feel for loads, not just learn how to calculate them.

A few rough comparisons help me do a quick sense-check:

· 1 kN is roughly the weight of a person.

· 10 kN is roughly the weight of a small car.

· 1 kPa is roughly the weight of one person spread over every square metre.

So when I see a 40 kN connection force, I picture something like four small cars hanging off that connection. It makes me think twice.

Next time you read a load table, check the units, the thickness and whether the result actually makes physical sense. Those small checks can save a lot of trouble.

Cheers,
Gabe