Thursday, 29 May 2008

Don't Assume, Design!

Third day at work, the job itself have progressed nicely from yesterday. Nice learning curve, smooth but enough to kept me on edge. Same problem to solve: design a lintel which will support the weight of the bricks above, instead this time a simply-supported reinforced concrete beam will be used. Very straight forward but a chance for me to experience an alternative design and different document set.

My support was amazing, very patience, confident and all-knowing, strict Muslim who prays five times a day, good honest bloke! I must have learnt more from him in one day than I have from my lecturer of the concrete module in a one month! Although there was this rather weird look in his eyes when I asked him about having to pray in the direction of Mecca. I think I saw the same look before when I have shown a slight interest in Islam to my friend who later tried to convert me. Oh well. I will never make a good Muslim. I drink, I smoke and quitting pork would mean I won't be able to eat half the food my parents cook.

The process was so much simpler compare to when I first learnt it. Same as the process in the steel lintel, there is a loading due to the Load Triangle plus any additional attachments within the Load Triangle and 50% attachment contribution from within the Interaction Zone. The moment and shear imposed can be deduced from the point load or UDL (wL^2)/8 wL/2. Decide on an appropriate design and then calculate to see if such configuration will satisfy the required moment and shear: Work out the effective depth (d), determine K and then K' based on the redistribution factor. Choose the correct equation to work out the moment capacity based on the two Ks relationship. The necessity of shear links can be determined by working out the shear resistance of the beam + bars. If shear links are required then another equation can be used.

It is important to note that:
1/ The links can not be placed at the end of the re-bars;
2/ Even though compressive bars are not needs, they are often added so shear links can be installed;
3/ Shear links are included for safety issue even though the values suggests otherwise (shear stress<0.5 shear resistance of reinforced beam).

The highlight of my day - My support: "You are a designer now, you don't assume, you design!"

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Wednesday, 28 May 2008

Lintel and Piss

Even though I have already done a summer placement and have worked in an engineering office before, I think today was the first time I have made a real contribution to a real living and breathing engineering project. The work I did last year was all statistical based, building computer model on existing pipe networks which have already been built and been in use for a long time. Grooming data and adding hydraulics elements into the model so analysis can be done over its efficient and defects. Today, was something special! I was assigned the task of designing a structural member which will be actually be a functional part of a building! Needless to say, it was something small, a lintel which goes across the top of an opening in brick wall to support the weight of the bricks above. It was still interesting none-the-less and gave me a great insight on how things are done.

The method itself was pretty straight forward. It is assumed that the only part of the wall exerting a load on the lintel is within an isosceles triangle of two 45 degrees corners. The length of the base would be assumed to be the opening in the brick wall plus a predefined value (e.g. the width of a brick or a value given by the lintel manufacturer) for both ends. The volume of the load triangle can then be deduced with the thickness of the wall (presumed to be the thickness of two bricks) and when multiplied with the density of the brick and mortar, the loading on the lintel is produced. With the engineering industry as developed as it is today, the dimension of the lintel can then be chosen from the manufacturers' brochure. Additional detailing might need to be produced for the concrete padding below the lintel, which will help dissipation the loading into the bricks below, but they are usually specified by the lintel manufacturers.

Also had my medical test today. Considering the abuse I have put my ears through during all those endless raves and concerts, I am please to report that my hearing is only slight off optimal. Eye-sight is normal with my glasses on and so was my bloody pressure. Although the nurse was a little concerned with my high heart-rate which she measured three times. Each and every time, they were over 100bpm! I guess a guilty conscience can have a huge effect on your pulse! All I need to do now is wait for the result for the alcohol and drug test. *dum dum dum!*

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