Thursday, September 4, 2008

Pre-Engineered Frames

It is still very quiet in the construction sector. With the 15 cent decrease per liter in petrol price, I was hoping it will generate some activity. Unfortunately, I really cannot see any difference yet. Maybe its just too soon. Unfortunately, not everybody has the luxury of time, waiting for the economy to improve, as there are bills to be paid and mouths to feed. In the meantime, all we can do is wait, hope and pray…..(can also grumble and moan. Ha ha)

Heard people complaining that the prices of goods have not come down in tandem with the decrease in petrol prices. Hope the Government realize that its easy for prices to go up and so difficult to come down. In the future, I hope the next time we can elect leaders who well-versed in the workings of an economy. For example, I personally think, the former Prime Minister handled the economy very well.

My bank, just called to remind me of my monthly payment. My loan payment is due on the 15th every month, today is the 4th and they have already called me twice this month.! I sure wish they could be as efficient in their other activities. Like lending money to people who are in need instead of driving them to Ah Longs.


The only project I got lat week was an existing building, that the owners was thinking of adding another layer of roof on top of the existing layer. The reasons being, the present roof has rusted or something like that. The roof is supported by pre-engineered frames. Attached is a cross-section of the frame. Note: Pre-engineered frames are made up of tapered I-beams which supposedly tapers according to the magnitude of the Bending Moment at that particular section.

My task was to ascertain whether the present frames was strong enough to cater for the additional loads. As nobody has a copy of the old drawings and calculations, I had to re-analyzed the structure based on actual measurement of the existing steel frame etc.

I checked the frame at various locations (as the frame is tapered), had to work out the section properties at these locations. Then check biaxial bending at these points. To cut a long story short, the frame seems adequate.

Then I check the two interior columns (see above sketch) which were made up of UC254x254x 73kg/m. Note: the height/length of the column is 13.09m. The slenderness ratio in the y axis works out to be 202.98! The maximum allowed per the code is 180. Theoretically, the 2 interior columns failed.

I also checked the various connection joints, that too failed!

My client when informed of this ask “How come the structure is still standing?”

More on this in next entry. Do not want to bore people to much at one go.
Bye & happy engineering!

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