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.

MY PRESENT JOBS

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!

Steel Engineering - Deflection

Happy Belated Merdeka Day to all fellow Malaysians. This year’s celebration seems subdued and low-keyed compared to previous years. Considering the soaring prices of goods and rocketing inflation nowadays, this is to be expected. I hardly saw any cars decorated with mini flags this year and hardly any shops flying the National flag. Well all these “belt tightening” to cope with high price of goods and services can sure put a damper on everybody’s mood.

It was actually a double whammy for me this year. First, the escalating expenses together with the slowdown in business, and secondly, the news that a leader of the ruling party, allegedly labeling the Chinese as immigrants or squatters. Its a bit depressing, having been born here, grew up here, lived and worked here, and suddenly labeled a “squatter”.

Actually there is a third whammy. All I got from this year Budget is an increase in price of cigarettes, my one bad habit (although my wife will disagree that I have only 1 bad habit – ha! ha!)

Somebody once said, “Its easy to be A Malay hero, or a Chinese hero, or an Indian hero, but its difficult to be a Malaysian hero”. I guess its safe to conclude that Datuk Ahmad does not aspire to be a Malaysian hero.

The most disappointing aspect about the whole episode, is the Prime Minister’s response, which is akin to “Aiyo! Never mind-lah. I am sure he doesn’t mean it”. Wow, that’s that even close to a light slap on the wrist.

Some politicians are still playing the racial card, but despite their best (or worst) efforts, the people in Malaysia as a whole are still living and working in harmony. United we must be, to face the challenges and competition from other countries.

MY PRESENT JOBS

Attached with today’s blog, is a photo of a job in Nilai, which was completed recently. Note that when designing cantilever trusses, do remember to check for deflection and make sure the design meets the requirements as specified in the British code are complied with.

Below is an extract from BS5950 : Part 1 : 1985 on the deflections criteria there must be met. Note, imposed or service loads are just another word for Live Load. Live load is generally equals to 0.25 kN/m² for buildings in this country. (per Uniform Building Code, Laws of Malaysia).

BS 5950 : Part 1 : 1985

Structural use of steelwork in building

2.5.1 Deflection

The deflection under serviceability loads of a building or part should not impair the strength or efficiency of the structure or its components or cause damage to the finishings.

When checking for deflections the most adverse realistic combination and arrangement of serviceability loads should be assumed, and the structure maybe assumed to be elastic.

Table 5. Deflection limits other than for pitched roof portal frames.

(a) Deflection of beams due to unfactored imposed load.

Cantilevers	Length/180
Beam carrying plaster or other brittle finish	Span/360
All other beams	Span/200
Purlins and sheeting rails	See 4.12.2

(b) Horizontal deflection of columns in single-storey buildings

Tops of columns in single-storey buildings	Height/300
In each storey of a building with more than one storey	Height of storey under consideration/300

(c) Crane gantry girders

Vertical deflection due to static wheel loads	Span/600
Horizontal deflection (calculated on the top flange properties alone) due to crane surge	Span/500

NOTE 1. On low-pitched and flat roofs the possibility of ponding needs consideration.

NOTE 2. For limiting deflection in runway beams refer to BS 2853.