Loads: 3a. Wind Loads Images

Loads: 3a. Wind Loads Images

Loads: 3a. Wind Loads Images - Full TranscriptionSo let's look at some images of wind and what it does to buildings and other structures. There is another video that describes more in depth the concepts behind this. So let's look at this image here that is basically the IBC code gives us the wind speed in our geographic location. But it gives it in four different maps. This is based on what used to be called the importance factor. And the importance factor is basically now called the risk category. And what it is, as discussed in the other video, if we look in at Miami, for example, the Miami area, we see in this map 150 mile per hour wind. But then we see in this category, Miami at 170 versus this category, Miami at 180. versus Miami at a speed of 200 miles per hour. First of all, Miami-Dade is the basis of the IBC code because it's the worst case scenario. So anyway, this one is for occupancy category one versus two versus three versus four. So category four was essential facilities that need to do search and rescue and other very important things after a natural disaster. This applies to snow, wind, and seismic. Category three was essential facilities where people may take shelter or large occupancies of people can go in a natural disaster. and number one is agricultural facilities. Number two is whatever is not in one, three, or four. So we saw 170 mile an hour for agricultural facilities category one or risk category one. For risk category two, such as commercial facilities and residential, it is 180 miles an hour, 170, what was it? I can't remember. 170 miles an hour. So 150 for category one, 170 for category two, 180 for category three, which is basically for shelters and essential facilities that if they collapse a lot of people, there will be a lot of casualties. So you up the design a little bit. Category four is essential facilities. So we are going to get the wind speed from these maps. And we're going to square it. And we're going to multiply it by a certain factor. And this gives us pressure. So the pressure to begin with is based on the occupancy or risk category and the geographic location. So we took wind speed. We squared it. It's important to keep in mind that it is squared. You're not going to do any of this math, but you need to understand the relationships. So wind speed is squared, and then you get pressure. This one is in pounds per square foot of pressure. This one is miles per hour, and this factor adjusts the units. After we get this wind pressure, we adjust it for exposure. There was three categories, a B, C, and D. D was near water, B was urban, C was the airport. So if you're in an urban context, you reduce that wind pressure a little bit. If you're near water, you increase that a little bit. Then there was a topography issues, a hill, a ridge, an escarpment. And if you're building on the upper half, then you need to increase the pressure. Very good. So that's the big picture. And let's remember that everything is measured at the airport and exposure C with an anometer in the case of wind, with a seismograph in the case of earthquakes, et cetera. Very good. So moving on from this slide, just a reminder that the wind pressure is increasing with height on the windward direction. It is suction or leeward on the leeward side, and it is an uplift on a flat roof. And it depends on slope for the windward roof of a sloped roof. Whereas the two sides and the leeward roof will always be negative. But we have to keep in mind that wind is free to come any which way it wants. So all walls and all roofs have to be designed for positive and negative pressure based on what we find here. Accident. So this one is wrong because the leeward pressure is outward, negative, not positive. This one is wrong because the leeward pressure does not increase with height. The windward does. And this one is wrong because the flat roof has uplift, not positive pressure. So these are all from an exam I gave, and so I included this. So the ideal shape, of course, for wind is one without corners. That's a round, but please don't make all your buildings round. That would be ridiculous. We have to have corners. The gentler the corner, the easier the wind goes around the corner. The sharper it is, the harder it is. And there's all kinds of dynamics that happen with wind going around corners and vortex shedding and all that good stuff. Very good. So this is a picture of the John Hancock Tower in Boston from 1976. And all the white spots are basically plywood because it had a lot of issues. This building had a lot of issues. One, they were afraid it would overturn under certain wind conditions. And then this was the first use of this signature blue windows that were 500 pounds each. And they were four foot by 11. They wanted the largest size possible of glass and without the use of spandrel beams. So these were some of the issues that happened and what happened there was the caulking and the mastic between the two layers, the double layer glass got hard because of thermal stresses and then it was not functioning the way it was supposed to and was popping out. Another problem was the Trinity Church next door from H.H. Richardson that was on the historic register. It was a historic landmark and it started settling and there was a lawsuit, etc., etc. But we're interested in the wind effect on the building. Another example is the Texas Commerce Bank or J.P. Morgan Chase Bank in Houston. This was under Hurricane Ike in 2008, and it was all on the leeward side. There was a wind speed up because of buildings around this building that didn't exist when it was built. So they lost all their glass on the leeward side. So the curtain wall is in charge of everything wind. And we need a certain depth in the direction of load. Load is coming horizontally in the case of wind. So we're going to need depth. And in the case of the Rose Center for Earth and Space in New York by James Polchek, the depth is pretty significant. I think it's three feet. And this is a six-story curtain wall. And so these spider connections are tied to each other and with cables. And that is how a six-story curtain wall is resisting the wind load. There's a planetarium in the middle of this atrium. Images of damage from Hurricane Wilma of 2005 in Miami. All of you have seen a lot of damage from Hurricane Katrina, flooding, etc. And more recently, there is Hurricane Debbie and Barrow. I know that Barrow caused a lot of damage in Houston. I used to live in Houston. That's why I keep up with Houston the most. So my images are old, but I'm sure you've seen plenty of damage and are familiar with what's going on. Everything falls on the ground floor, and then you've got debris, and you've got glass and all kinds of things, and the police have to cordon off the area and the cleanup and all that good stuff. So more images from Hurricane Wilma, 2005, Miami. These students of mine sent them to me. That's why I'm using them. Once there is a breach of the envelope, everything you see on the inside will become a projectile that goes into the building next door. And this is a major catastrophe when the wind is inside the building, putting more positive pressure, breaking the door, going into the corridor. It becomes a real nightmare. Building components are most vulnerable. They include corners. They include anything that sticks out from the envelope. a steeple of a church or a fireplace or this domed piece that fell off in the wind, trees falling on structures, all of this damage because of wind. Clearly, flexible or tensile structures are going to be affected a lot. And during Hurricane Katrina in 2005, the New Orleans Superdome, which is probably not an essential facility such as a category four, a risk category four, but category three, which is substantial hazard to human life in the event of collapse. So the roof of, part of the roof of the Superdome in New Orleans, a fabric structure, part of it tore off. And now you have rain and wind and flooding inside the Superdome. So these structures specifically are subjected to flutter and easier to damage in the wind. Images from Tropical Storm Allison in Houston, 2001. that is the big thing is the flooding that comes after all the wind forces. So you can see I-10 over here with all the big rigs stranded totally. The water, the tropical storm Allison parked on top of the Gulf of Mexico and started dumping water on Houston forever. So if I remember, well, this is around a 20-foot clearance on I-59, and that is ridiculous the way it filled up because the soil in Houston is mostly clay, so the water has no place to go. It went in the underground pedestrian tunnels and flooded all the establishments there. More images from Hurricane Wilma in Miami. 2005 seems to have been a great year with this one and Katrina and others. The infrastructure, of course, suffers greatly. be it the power lines, the gas, the water supply, all of this stuff is very vulnerable. So let's look at pictures of this wind tunnel in South Carolina that was constructed by the home insurance industry. And besides being a tribute to fans, it is a crazy structure. It has these blades that can be adjusted to increase the wind speed or decrease it. And with all these fans, it's kind of crazy. Anyway, there is a Lazy Susan in the middle of this structure, and then they put structures on it, and then they turn the fans on and simulate a certain wind speed. And the point of this exercise is they have ties, tie downs on one structure. And they're trying to prove that the roof will not come off and the second floor will not fly off of the first floor because of these connectors, hurricane tie downs, basically. So structure A has them. Structure B does not have them. And then they blow the wind and you can see the damage on that structure that is not fortified. Very good. There's a lot more images. I'm just trying to keep this concise. Thanks.