structural engineering - What approaches are there for demolishing a structure and how is an approach chosen?

From my office on the 21st floor of a building in Vancouver, BC two parking garages in the process of being demolished are visible. A third is just out of view a few more blocks away.One of these structures is being taken down by a team consisting of an excavator with a jackhammer, an excavator with a claw and a man holding a hose. The jackhammer punches holes in the cement, and the claw breaks it up and allows it to fall to the floor below.A couple of blocks away a different approach has been taken where it seems they are cutting the concrete ...Read more

structural engineering - Eiffel Bridge Design

In bridge design normally base supports are strong,fixed/rigid. Why did he choose thicker arch sections at middle above mid-river and narrow sections at abutment supports? If he chose a simply supported condition, then for what structural advantage?EDIT1:Could it be some combination of arch and beam design? Between arch abutments it spans 5 pillar span lengths.Treating main structure as a long span Beam bridge simply supported at ends bending moment at mid-span is maximum so midsection should be designed deeply trussed as done here. However do...Read more

structural engineering - Why skyscrapers don't sink into ground?

We shared Mechanics of materials with structural engineers back in college. I learned some basic concept about structural engineering, but besides the basic knowledge i don't know anything about structural engineering. If i recall correctly, an engineer found a way to distribute the weight of buildings over a wide area to reduce the stress, i think he managed to solve the problem of sinking buildings for the first time in Chicago, and up to this moment, his solution has been popular. If the area has a strong bedrock, manhattan for instance then...Read more

structural engineering - Need Help to Remove Sway from Steel Post + Glass Panels

I have spanned ~15' with 2x 10mm tempered glass panels. They're connected in the middle with a 1.5" x 1.5" 16-gauge, 316 stainless steel post filled with concrete. This post has a 316 base welded on and this is securely bolted to structure below the floor. My spans of 88" are well within the specs of both the glass and the glass clamps, per their respective manufacturers. You can see the setup in this photo:The "base" footer on the post is ornamental only (shown with the green arrow). I did not want to introduce any more holes into my wate...Read more

structural engineering - Why not build container ships from plastic?

This may sound crazy but bear with me. I was thinking about why cargo ships are built from such heavy material as steel, while smaller boats are often made of plastics. I know cargo ships carry a lot of weight and the sea can be rough. Those ships of course need to maintain structural integrity and such. But wouldn't it be possible to build a structure from steel, supported by the strength of the containers that fill the ship. And then build a thick hull around it made from a combination of plastics and compartments of some kind of foam (polyur...Read more

structural engineering - Is a 1/8" AR400F steel plate strong enough, for 4,000 lbs?

I have a Ford F350 cab & chassis and a gooseneck trailer. For the gooseneck hitch I want to use a steel plate.The steel plate will be BOLTED to the frame, above the rear axle And the gooseneck ball will be welded to the steel plate.The distance between the frames is about 34". So the plate Is going to be 34"long x 8" wide.The trailer is 16,000 lbs GVWR. And a maximum tongue weight of 4,000 lbs (at 25%)A regular A36 steel plate, 3/8" thick, will bend under load. (A36 mechanical properties: Brinell=112, Tensile=58,000 psi, Yield=36,000 psi)So...Read more

structural engineering - Why dig out and then fill in before building a large structure?

I work in the middle of London, in an area full of large office blocks. Across the road from my office they have started construction of a large building (10 stories plus). Over the last few weeks, diggers have dug a large (and vertical walled) hole. Lorries have taken the resulting dirt and old concrete away, leaving a very neat hole.In the last day or so, the lorries have returned with new dirt (or the old dirt crushed) and diggers have been putting it back in the hole (and compacting it).Why put the dirt back? Surely leaving the hole deeper ...Read more

structural engineering - Concrete formwork - best approach to counter uplift forces, for a freestanding pour?

I'm casting a 4m long triangular-profile reinforced gravity retaining wall against soil movement due to a 1 metre jump in ground level.The lateral forces and moments on the formwork have been easy to handle, but I'm trying to find a good approach to the vertical uplift hydrostatic force on small-scale/DIY formwork while concrete is poured, which is a general problem for which I can't seem to find a good solution.Details -I'm using a very fluid self-consolidating (SCC) mix since access for compaction would be hard once poured (slump-flow ~ 550mm...Read more

structural engineering - Cooling tower for nuclear power plants

Cooling towers for nuclear power plants often have the shape of a hyperboloid. At first glance, I thought that an obvious reason for this would be the smaller sectional area, meaning the tower would be less exposed to wind.However, I did a quick calculation, based on a cooling tower nearby. I modeled the cooling tower as a hyperboloid and calculated its volume and its sectional area. I then calculated the radius needed for a cylindrical tower with the same volume. Its sectional area was just 1.5% larger. By reducing its height from 150 to 145 m...Read more

structural engineering - what actually cause quench cracking ? non-uniform cooling or rapid cooling?

It’s well known that quenching most alloyed steels starting from AISI 4140 to high speed steels in water, brine , or sometimes oil will cause cracking and industry oil quenching sometimes replaced by molten salt, which considered better than oil in decreasing crack probability and this advantage attributed to uniform cooling provided by salt bath compared to other quenching mediums.cracks and distortions caused by water or brine quenching usually attributed to rapid cooling , but sometimes they attributed to non-uniform cooling c...Read more

structural engineering - How to measure the unbraced length of lateral torsional buckling for negative moment in a W-shape steel beam?

I have a W-shape steel beam that is fixed-fixed and the top flange is fully braced for lateral torsional buckling. The negative moment at the end controls the design and there is no lateral bracing for the bottom flange. What will be the unbraced length ($L_b$) for the bottom flange? Also, if I provide brace points at the points of moment inflection then what will $L_b$ be? In general, what is the rule for measuring $L_b$ for bottom flange under negative moment? If possible, please provide proof from AISC code....Read more