One thing often ignored by designers is: material handling. Figure 1 below is picture sent by my friend Rendra. It shows beams which were being transported by trailer truck. What’s wrong in Figure 1?
Fig. 1. Structural beams transported by trailer truck.
Structural joint is one of the most important things in steel construction. Unfortunately, it is often overlooked by engineers. Many engineers nowadays master the sophisticated engineering softwares but lack the feeling and intuition of an engineer.
The most important skill in structural design is the ability to visualize the stress flow in structures and how the structures behave under certain loads. Many engineers lose this art of engineering and rely heavily on finite element analysis, make themselves more an operator rather than a critical engineer.
The Tube Joints
Figure 1 below is a picture I took in my project 2 years ago. Take a good look. Can you tell me what is wrong in the picture? Does it ring the emergency alarm in your head?
Fig. 1. Tube joint.
The devil is in the details. This time we are dealing with a very simple and trivial aspect of steel structure: ribs. Figure 1 below shows wide-flange beams which are reinforced with ribs. This is part of my latest design called LIMOV STM-50T, a sling test machine with capacity of 50 ton pull. If you need any heavy-duty test machine, or anything serious, just ring us here at LIMOV, OK? It is the only engineering company that matters. Seriously. 😉
Fig. 1. Wide-flange beam reinforced with ribs.
Rib is used to hold the adjacent structural members in its position. It keeps web and flange of beam from buckling. What are web and flange? See Figure 2. When rib is used inside a closed-box structure, it is called diaphragm. Figure 3 shows a series of diaphragms inside a closed-box structure. It is one of my early designs and a bit silly from my present point of view. But this will be discussed some other time. This time we only focus on rib and why it matters.
Designer should be aware of how his design will be fabricated. Alongside doing design, I am also in charge of the whole construction process and procurement. My last experience with casting product was a bad one. Casting product is inferior in strength and, for certain geometry, is more expensive compared to other fabrication process. Of course there are many good casting product but they are usually more expensive and take additional process and treatment (forging, machining, case-hardening, etc.). Take a look at the following assembly in Figure 1: Wheel set (Wheel, shaft, bearing, and bearing housing).
Fig. 1. Wheel set: Wheel, shaft, bearing, and bearing housing.
A designer can simply draw a wheel set and assign certain required properties such as load capacity. But for the construction engineer, working out the design to reality is much more complicated. Take the wheel for example. This wheel is made of a series of high-quality process. Casting, forging, machining, and case hardening. We imported this wheel from the States and it is very expensive.
Note: On the soporific drug chloral hydrate, they drop off before they even get started. Read the article in NewScientist.com.
Engineering tips: stay away from drugs!
Spider Web: 110 Million-Year-Old Structural Design
About 2 months ago I read that scientists discovered a fossilized spider web complete with its entrapped prey in a chunck of amber in Spain. Here is the article from BBC News, Science/Nature section. The fossil dates back to 110 million years ago.
I also found out from an older article that 3 years ago a strand of spider silk was discovered in Lebanese amber. It is about 120 million year-old. Because it is only a single strand, it doesn’t give any information about how the ancient spider web looks like.
Fig. 1. 110 million-year-old fossilized spider web with entrapped prey.
Scientists had been arguing about how ancient spider web configuration looks like. The latest discovery, in which part of the web is well preserved, gives the answer to the question. The latest article said: “The fossil web appears to have been designed along the same lines as the round nets woven by modern spiders.” That means today spider web design has not changed for 110 million years. Why is this so special? Here I am trying to relate spider web to lightweight design and construction.
I found a very nice article in BBC News, Science/Nature section, about trap-jaw ants. The first paragraph said: “Trap-jaw ants bite with a force of over 300 times their own bodyweight…,” Grab your calculator, mate! If we assume a human averages 70 kg is designed by nature like ant, then the power of his jaw is:
Jaw clamping force = 300 x 70 kg = 21,000 kg.
If we assume an average city car fully loaded with fuel and passengers is about 1,500 kg, then the number of cars which can be lifted by a stroke of this jaw is:
Number of cars = 21,000 kg / 1,500 kg = 14 cars.
A really powerful lightweight structure created by nature :).
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