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Ecclesiastes 3: 1-8
Taking the heart out of a concrete column... with a spoon
Today's post is more informative than the usual juicy tale of Engineering Exploits. I'm often asked fairly esoteric information, such as 'how long does it take to drill a core in concrete'. Well, believe it or not, I typically do not witness this sort of thing. I request the test, and read the result, but I don't go out there and witness it. So, here I got the chance to witness the process. I carefully recorded the following answers to your burning questions about drilling cores. How long does it take? From the driller parking the truck to driving away: it took 2 hours to drill 4 cores, each 6 inches deep  How big is the apparatus? See above picture... It's that big. How loud is it? You need earplugs if you are going to be within 20 feet, but it's not nearly so loud as a jackhammer.  What does the core look like? Well, kind of like a beer can made out of concrete. Until the lab cuts off the bottom, it's rough as shown in the picture. The driller actually drills the sides and then snaps off the bottom.  Is it as smooth as it looks? Yes. The inside of the hole, and the outside of the core are smoother than wood grain. And those, Ladies and Gentlemen, are the most common questions I get about cutting into the very heart of concrete structures. I look forward to hearing from you! |
Numbers 19: 11-15
11 “Whoever touches a human corpse will be unclean for seven days. 12 They must purify themselves with the water on the third day and on the seventh day; then they will be clean. But if they do not purify themselves on the third and seventh days, they will not be clean. 13 If they fail to purify themselves after touching a human corpse, they defile the Lord’s tabernacle. They must be cut off from Israel. Because the water of cleansing has not been sprinkled on them, they are unclean; their uncleanness remains on them. 14 “This is the law that applies when a person dies in a tent: Anyone who enters the tent and anyone who is in it will be unclean for seven days, 15 and every open container without a lid fastened on it will be unclean. |
Hey, but what about those Incan stacked walls?
When discussing stacked limestone retaining walls, I frequently get reminded about the Incan walls in South America. Those have stood for thousands of years, right? And, always willing to do research to provide a better product to a client, I looked into this topic. Unfortunately, for hopeful owners, the short answer is no. They haven't. Admittedly, they have stood for several hundred years longer than anything I've designed. However, upon further research, those lovely terraces come with some severe restrictions that differentiate them from today's typical use.  1- Maximum height is about 5ft. Here is a 7 year old walking up a typical 500 year old wall.  2- nothing heavier than a llama or two. Today's walls have to account for vehicles or houses behind them. Those items are much heavier than a llama. Even cows are too heavy.  3-Installation of a 3 layer drainage system and no clay or expansive material allowed at all. You can see from the graphic (located here- http://www.pbs.org/wgbh/nova/ancient/wright-inca-engineering.html-thank you Nova) that they didn't use onsite fill. They used a lot of hand labor sorting rocks to ensure that water did not build up behind the walls.  4- Finally, there can't be any slope directly behind the stacked walls. See how the ground at the top of the wall is flat? FYI: the top one is flat for some distance. I hope you've enjoyed a little trip down to South America to look at some historic walls. I know this was one of the more fun postings to write. Merry Christmas! - Outlier Engineering |
Luke 2 1-20
The Birth of Jesus2 In those days Caesar Augustus issued a decree that a census should be taken of the entire Roman world. 2 (This was the first census that took place while[a] Quirinius was governor of Syria.) 3 And everyone went to their own town to register. 4 So Joseph also went up from the town of Nazareth in Galilee to Judea, to Bethlehem the town of David, because he belonged to the house and line of David. 5 He went there to register with Mary, who was pledged to be married to him and was expecting a child. 6 While they were there, the time came for the baby to be born, 7 and she gave birth to her firstborn, a son. She wrapped him in cloths and placed him in a manger, because there was no guest room available for them. 8 And there were shepherds living out in the fields nearby, keeping watch over their flocks at night. 9 An angel of the Lord appeared to them, and the glory of the Lord shone around them, and they were terrified. 10 But the angel said to them, “Do not be afraid. I bring you good news that will cause great joy for all the people. 11 Today in the town of David a Savior has been born to you; he is the Messiah, the Lord. 12 This will be a sign to you: You will find a baby wrapped in cloths and lying in a manger.” 13 Suddenly a great company of the heavenly host appeared with the angel, praising God and saying, 14 “Glory to God in the highest heaven, 15 When the angels had left them and gone into heaven, the shepherds said to one another, “Let’s go to Bethlehem and see this thing that has happened, which the Lord has told us about.” 16 So they hurried off and found Mary and Joseph, and the baby, who was lying in the manger. 17 When they had seen him, they spread the word concerning what had been told them about this child, 18 and all who heard it were amazed at what the shepherds said to them. 19 But Mary treasured up all these things and pondered them in her heart. 20 The shepherds returned, glorifying and praising God for all the things they had heard and seen, which were just as they had been told. |
a stacked block wall, poorly installed
Outlier designs a lot of retaining walls. One of the popular requests is for stacked block limestone retaining walls. Right away, I tell people that these are not gravity walls. The limestone is heavy, yes, but after about 3 courses, it is not heavy enough. Typical designs for this include several layers of geotextile that act the same way straps do on an MSE wall. Here's the pretty side of a recent project:  As always, we try to entertain and educate so that you can avoid mistakes. So here's one of the mistakes caught during construction.  You can see that there are some gray pipes installed behind the wall. You may also see that the wall leans out just a bit. There is a batter on the wall, so it is not in imminent danger of collapse, but ...  You can see that on the other side of the wall, there is a lot of erosion. The installation of the pipes caused a low spot, which attracted water that then flowed along the outside of the pipe. It didn't take long for the soil in front of the wall to get soft from the water in front and behind it. The sharp-eyed among you would notice the that the geotextile must have been cut, the slope in front of the wall is ridiculously steep and the water flowing under the block must have reduced the bearing/resistance to sliding. During the reconstruction, we had several conversations about these topics. For this project, something else dictated that this portion of the wall had to be rebuilt, so I didn't have to break that news. The next build was much better. |
New Braunfels attraction
Just to clarify: this isn't an invitation, really. It's more of just bragging of one of the cool things New Braunfels has to offer.  |
Trees- Nature's lungs and home wreckers
We all want trees around our home or commercial property. They provide shade and are interesting to look at. However, as far as your foundation is concerned, trees nearby are dangerous. For our case, nearby can be defined as: within 1 times the mature height of the tree. Trees are giant sponges. As a tree grows and matures, it removes moisture from the soil around the roots. If the tree is mature, it has sucked all the water out of the soil contained in the root ball. To put a foundation near an existing tree, we usually recommend cutting roots and installing a root barrier between the foundation and the tree. Often this is a grade beam several feet deeper than required by design. If the foundation is close to the tree, and many roots are cut, the tree may not survive. If the tree dies after you have built the foundation, then the moisture removal will stop and the soil will re-hydrate, causing swelling. If you remove the tree and stump before construction, then the tree will stop sucking the water out of the soil. This means that the soil will re-hydrate and probably swell. This can be mitigated during construction by digging out the stump and moisture conditioning and compacting the soil that is used to fill the hole. Some get around the whole situation by installing pier and beam foundations which are easier to re-level as the tree goes through it's life cycle. Typically, the best solution depends on the size of your building and how closely construction will be monitored. Of course, how much you want that beautiful home wrecker counts, too! |
Proverbs 24:3-4
3 By wisdom a house is built, and through understanding it is established; 4 through knowledge its rooms are filled with rare and beautiful treasures. |
you get what you pay for- or, you pay for what you get
Mr. Anon decided he wanted to build a deck on the back of his house. He went to the local home improvement store (LHIS) where he was given some advice about how to connect the deck to the house and also shown this nifty new product for the footing.  see how the 4x4 fits right into the hole on top? Perfect, right? Just needs a flat, level surface and you're halfway there. But, no. See that advice from LHIS was free. And Mr. Anon had to rebuild the entire deck- including the attachment to the house. 1- the ledger attachment to the house is tightly controlled. For your edification, I posted below the part out of IRC 2015 for you to look at. As engineers, we are not about to go against such explicit building code. 2- things that are attached to the house are considered permanent. Permanent things need footers that are below the frost line or 18" deep minimum. You can see that this product does not meet that. 3- all load paths must be considered. As we all know, wind creates uplift, there is nothing in this product to keep the deck from blowing UP in a strong wind (then ripping off the house). Now, I'm not saying that you all need to call me to add on a deck to your house. Actually, the City says you all need to call me, but that's beside the point. The point is that home construction advice from LHIS is often worse than worthless. It is often damaging and costly to repair. Also in the interests of saving you money and time and frustration (because I have your best interests at heart) the IRC has joist tables for minimum joist sizes for a particular span. It also has suggested details for a lot of typical connections on a deck. Now that the heat of summer is waning, deck season is just getting started. Enjoy safely! *Outlier totally gets the irony of giving out free advice while enumerating the shortfalls of someone else's free advice. |
| Attachments:
2012 IRC Chapter 5 - Floors.pdf
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