All right, guys, I think the count's starting to level off a little bit, so we can go ahead and get started. Welcome to March's webinar for the Post-Tensioning Institute. My name is Kyle Boyd, and I'm the moderator of today's session. I'm also the chair of the Education Committee, EDC 130, and EDC 130 is a committee within the Post-Tensioning Institute that sponsors this monthly webinar. For those of you who are returning, great, we're glad to see you back. For those of you who it's your first time here, we do host this webinar every single month at the same exact time, so it's always the second Wednesday at 1 o'clock Eastern or 10 o'clock Pacific, every month on there. As you can see, today's topic is on the new ACI PTI Joint 320-25 code. This code is definitely a big progression and landmark for our industry, really builds on ACI 318 with additional information related to the post-tensioning and new advancements in design. There's been quite a few new advancements in PT design over the last several years. What you guys will see as jurisdictions adopt code cycles in the future, you'll start to see this code become referenced as the code to design PT for. The two speakers we have today, Carol and Don, are both very senior folks at ACI and PTI and are by far the most credible individuals we have to speak on the topic. Carol is a past chair of ACI PTI 320 and Don is a current chair. The committee 320 is the group that really authored this new joint code, and so you're hearing it from the two folks that were overseeing the committee. But before we go deeper into introducing the speakers and into this topic, we do always have to go through those classic housekeeping slides on there. The first one has to do with our webinar sponsor. We have a sponsor for each one of these webinars, it's Post Tech Manufacturing. They do cable systems, wedges, anchors, but what they have is a really, really neat tendon shear machine called the Minimax. I highly recommend you guys go to their website and check it out. You know, high quality cable shears are a much cleaner and nicer way compared to torching tendon tails in the field and all the melted plastic around for protection that you start to see in the mess there. So definitely go check out that Minimax on their website on there. So continuing education, we have two different types of continuing education. One's through RCEP, the other is we are AIA accredited. What you will do is if you are listening to this webinar and you stay on for the entire time, all you have to do is just stay on the webinar for the entire hour, you will get an email with that continuing education certificate from RCEP. We're seeing it takes a week to two weeks to process. So just give it a week to two weeks to see it in your inbox and it'll show up on there. But you will see that just staying on for the entire time. Copyright material. This is just our classic, hey, this is copyrighted material through the Post-Tensioning Institute. We do not distribute PDFs of the slides afterwards. However, the presentations are available online. So just go to the Post-Tensioning's website, you can watch this webinar, you can see all the slides on there. So the webinar protocol. All y'all are in listen-only mode. We can't hear you. We can't see you. If you have questions, ask them through the Q&A feature and we'll go through them at the very end of the presentation. If we run out of time going through them, we'll just reach out to you guys at the end with responses to the questions there on that. The webinar is being recorded. So if you do have to step away and you still want to get that continuing education credit, just log on, watch it. Or you can go and watch, we've done 13, 14 of these now. So you can go watch any of those 14, take a quiz at the end and get that credit. You only have to take the quiz if you do the online one. If you're doing it today, like I said earlier, you just got to stick on there for the entire hour. And you also have to be registered through your email. All right. So now that we got that out of the way, let's introduce the speakers. I say this every single month and March is no different. We continue to have powerhouse presenters who are truly the most knowledgeable and senior folks to speak on the topic. March, we have two great presenters. The first one's Carol Hayek. She's got a PhD from John Hopkins and she is the Chief Technical Officer at CCL International. She's very involved with the industry to the point where I'm not quite sure how she actually has time for a day job or vice versa. It sounds like she's just not sleeping. She lectures at universities for graduate level post-tensioning. She's a fellow at both ACI and PTI, and for those of you who aren't very active in these, a fellow means you've done way too much time and put in way too much effort, but you've done notable contributions to the industry. So she's a fellow for both ACI and PTI. She's the past chair of DC20 at PTI, and that's the main building design committee. That's really what sets the standards for building design from the Post-Tensioning Institute. And she's the past chair of ACI PTI 320, which is obviously the code we're talking about today. So being the past chairs of both the main building design and the new joint ACI PTI committee, and she sits on ACI 318, she's obviously one of the top two individuals to speak on today's topic. The second individual is Mr. Don Kline. Don's got a very well-respected engineering firm, Kline Engineering Consultants. They specialize in post-tensioning, construction engineering, you know, formwork shoring, reshores, all that stuff, and they've designed many landmark structures throughout the East Coast and in some central U.S. as well. They've done one very, very impressive structure that's an aquarium in Miami. It's won multiple awards and it's seen in several publications. I recommend you guys go to his website, check it out. It's a very, very impressive post-tensioning structure. There. Like him, Don's also very involved in the Post-Tensioning Institute and ACI. He's the past chair of the Technical Advisory Board, which we call TAB for short, and that's really made up of the most senior technical folks at the Post-Tensioning Institute, and they review stuff for correctness, technical correctness, content before it goes out the door. They're the last review of the most senior guys there. He was the chair of TAB. He sits on DC20 committee, which is one I mentioned earlier with Carol, and he's now the current chair of ACI PTI 320 committee, which once again, I keep saying this, but that's the group that's responsible for this post-tension code that we're talking about today. The list goes on and on for different ACI and PTI committees and chapters that Don's involved with. He's very, very involved with the industry. So with that, you guys are really going to hear it from the two individuals who oversaw the code itself on where we're headed with post-tensioning design and where the future is. So Carol, I'm going to hand it off to you and let you run with it. Thank you. I'm going to, there you go. All right. Thank you, Kyle. Thank you for a great introduction. And I think I told you this, I've watched some of the previous webinars. You should have been really a sportscaster. I don't know what you're doing in engineering. So thanks for the hype. I'm really excited to be here. I'm really excited to give a talk about the new ACI PTI 320. This is the first ever structural code focused on post-tension concrete. This took a lot of effort. I would say five years solid working on this code. So really plenty of effort from a lot of people that were involved. The webinar today, we will talk about the development and purpose of the code. We will talk about how the code is used and some of the relationship between 318.25 and 320.25, how the code structure came about and the organization of the code. And then I will hand it over to Don, who will talk about the new provisions that we have in 320, talk about the next code cycle, the 320.28 and 320.31. Now, 320 will be in sync with ACI 318 code cycle. So really the full cycle is 2031. But the goal is to have an interim code in 2028 that will touch on some changes that are for addressing PT and then discuss the code change proposal opportunities and close it off with questions. So, now let's get to really the topic of the day. This way, this is way back during COVID time. So, back in 2020, there was a memorandum of understanding that was signed between ACI and PTI really to start a post-tension structural concrete code. There was a lot of back and forth and once that memorandum was signed, there was a clear understanding for the purpose of the code needs to be and how that code will be managed, how the balloting process would work and so on. So, really the purpose of having the code was to build on ACI 318 by providing supplemental information specifically related to post-tensioning. Everything you would need to design a post-tensioning member will be in that new code that came to be ACI PTI 320. And the 25 is just to say that this is the 2025 code cycle. The code will be coordinated and developed concurrently with ACI 318. So, it will have the same years. Anytime we have a new 318 code, the intent is to have a 321 code. The intent is to have a 320 that accompany that. This triggered a tremendous effort to collaborate between PTI and ACI both as institute starting with the formation of the joint committee. And that committee was joined between members from ACI and members of PTI. So, we had people from both institute covering the committee and that committee needs to follow a code structure, meaning it has to comply, for example, with NC consensus based. Everything has to be balloted. Everything has to be passed through a consensus balloting format. The committee had to be balanced, meaning in terms of representation, we needed to have as many practitioners, so engineers, researchers, and so on, academics, so professors, and anybody teaching within concrete, and suppliers. So, whether you're on the supply chain or materials. So, we had to have equal representation from all these different groups. So, no one group can really influence the code. And then, obviously, it had to meet the code creation. So, the language that has to be used, it cannot be ambiguous, and so on. Tim, sorry, I wasn't able to move aside. The code is now available. We're happy to say that the code was published. But it is available only on the PLUS platform today. So, it's only available in a digital format. And you have on that platform, you're going to have 318, 319, 320, and 562. Just a quick note on 319. If you haven't heard, but that's the ACI PCI precast code. This was also concurrent with 320. There was a lot of coordination with 319 to make sure that both 320 and 319 kind of followed that same framework and same code cycle. The hard copy should be published anytime now. So, be on the lookout for the hard copy. Hopefully, it will be published soon. When we first started, I mean, there was a lot of things to really cover. We had to coordinate between PTI Technical Advisory Board, TAP, and that's the highest technical entity at PTI that oversees all the technical document and reviews the document. PTI created a task group dedicated to the 320 code. At the same time, there's ACI 318T, and that's the subcommittee under 318 main that covers post-tensioning provisions. And lastly, ACI Technical Advisory Committee, TAC, which oversees all the technical document of ACI. And here, I would like to really thank everybody that contributed to this effort. We couldn't have done it without you, the 320 committee members. Thanks a lot. TAP task group did a tremendous effort. And a big shout out to ACI staff, Andrea Shocker, who was both the chair of ACI 318T, a member of 320, and the chair of 319 code. So, she helped us stay in sync between all of us and really relay things to 318 main. And Trey Hamilton, who has been really instrumental in getting 320. He was the secretary of 320, coordinating everything for the committee. In terms of how everything moved from PTI to ACI, PTI task group was in charge of really developing the provisions and the code changes, and then go through a balloting process at TAP, and also that through a consensus-based process. And then once those were finalized, they would move to ACI 320, which we will have our own balloting process at 320. And then those ballots that were passed, we kind of kept going until we kind of had a full draft. Once we had the full draft, it went to TAC. And TAC would oversee the draft, send us their ballot and comments so we can address them and so on until we got to the public discussion period where things were posted for anybody really to post comments. And in the meantime, all the behind-the-scenes coordination with 318T to get to 318 main. So that effort, that coordination effort with 318 led to 318.25 adopting the 320 code. Watch out for this section. So that's in 318. If you haven't seen the 318.25 code, section 4.12.21 says this, it shall be permitted to design post-tension concrete members in accordance with ACI 320. So really that's our avenue to design according to the 320 code. Once IBC adopts 318.25, by reference, 320 will be applicable. So what is meant by post-tension concrete members? When can we use 320? When do we go to 318? What do we do from that end? So really post-tension concrete members, what we're talking about really are the member chapters, if you recall, defines all the different members. So from a PT perspective, we have the one-way beams and slabs, two-way PT slabs, and any other structural, sometimes we have columns, sometimes we have walls, but really most of the PT is in slabs. So let's say we have a building. The building will have columns, foundations, slabs, and so on. Most of the time, the slabs will have post-tensioning, but the columns and foundations are typically non-pre-stressed, right? This is where 318 comes to play. So we still have to go to 318 anyways to design the columns, foundation, and so on. But once we start zooming in on the slab and say, OK, I have a PT beam, then I could go to 320, because 320 will cover all the provisions that are required to be able to design a PT beam or a PT slab and so on. PT anchorage detail. So anything that you can think of that's specific to post-tensioning will be in 320, but also the provisions that are related to that. So you're able to design that beam without really keep switching back and forth between 318. So there will be some duplication during that process, and this is where everything started. So how do we move with the code? What format needs to be? What do we keep? What do we duplicate? What we take out? So there's a lot of back and forth, and first order of business was really to decide, OK, what the format of the code would look like. How will the code be? Which sections we need to have? So all of this, the committee brainstormed with PTI, with the PTI tab task group to figure out, OK, what we want to do and what we want that code to look like. What we came up with is really to keep the same sectioning as 318, almost the same table of content. If you would open 318 and open 320, they're almost identical. They're almost identical. So that's from the 320 plus platform. You can see if you know what 318 will look like, this is the table of content, and it's very similar. And that was intentional, not because we just wanted to take that. There was a lot of back and forth as to what would be easier from a user perspective. That's who we had in mind from the start. We want the code to be easy from a user perspective and not really what we think about at the committee level. What should be in, what should be out. So, for example, if you're a designer and you want to look at a two-way slab, you know what the sections need to cover. So all the sections that are relevant will be in 320. And if you have 318 next to you, you can actually compare and see if that section is applicable or not or what changes. So they're kind of seamless. And as the time goes, there will always be coordination for the section numbering between 318 and 320. Once we decided, okay, that's the format we want, next will be, okay, what do we want to keep in? What are we taking out? And what shell are we going to take? Because we have to make sure that 320 is consistent with 318.25, because that is the year for the code cycle. But when we started, there's no 318.25 yet. So we had to base it on the 318.19, keeping our mind that, okay, 318.25, once they do their own balloting with those changes, we'll have to come back to 320. So a lot of committee work just to cover some part, but we did use the 318.19, but then adopted the 318.25 changes. So the 320.25 is seamless with 318.25. Once we did that, now we have to narrow the scope and say, okay, is this specific or not? The way things happened, we had the format. We decided on what provisions to include or not to include. So this is the narrowing down to the specifics of PT. Balloted all the chapters, and then we addressed the code change proposals, and then at the end addressed the 318.25 changes. But there's some things that we kept in that formatting. So the user, again, don't lose track of what's in this code and not in this code to make it easy, and so people can realize what is the same as 318. If you see a provision, once the code is out and you get the hard copy, and even on the Plus platform, you're going to see an equal sign next to some provisions. Equal sign, that means it's exactly the same as 318. So whichever, whether it's 318 or 320, that's the same. There will be some provisions that will say ACI 318, and that was decided in terms of let's not duplicate everything in 318. So if you're looking at loads, for example, you're already designing the walls, the com, you're analyzing the building based on the load combinations. So the load combinations that are applicable to any concrete will not be in 320 because it's assumed that you are designing already a concrete structure. But for example, going back to that load, if you're looking at the secondary effects, the load factors for the secondary effect and secondary and so on will be in 320. So anything specific to PT again will be there. Out of scope, this was debated quite a bit. The term that we wanted to use initially was not applicable, but then the committee decided let's go with out of scope and leave it up to the design professional to design if this is to decide if this is not applicable or not. These are items, for example, deep foundations, a non prestressed element that really have nothing to do, it's not, it's a non prestressed member. So this is the stuff that you might see as out of scope, anything very specific to non prestressed. Pre-tensioning, for example, is out of scope. And lastly, it's the new code provisions. There are new code provisions in the code, and these also are planned to be in sync with 318. This is a table of content to give an example from 318.25. You see here, for example, the 318 code ends at A724 and then jumps to 873. In 320, you're going to see a new section, which is 8725. If you are designing a two-way slab, that way, you know, I can cover all this in 320. And 8725 is the provision on banded-banded. All this is in the scope, by the way. If you go to 320, go to the scope, go to the front matter, there's a lot of things that are explained as to what was the intent and how to read the code when you see all these different notations. So the banded-banded, that's a new provision. It will have its own. There will be sections in the code that are new. I would point out to some of them, the dual-banded, which is also, we're extremely excited to have this in the code. We're hoping this will change how we do tendon layout, or at least give the engineer a new option on how we can detail the tendon layout. There's also a provision on headed shear studs for anchored zone reinforcement, and this gives you an option if you don't want to use U-bar, for example, behind the anchor, you can use a stud. Shrinkage and temperature tendons, this is for one-way slab and beam for the tendons parallel to the beam. Another provision is the tensile stress at the anchor. So what is the maximum stress that we can allow at the anchor right after stressing? And the corner restraint, for example, this is when you have a restrained corner and the code, 318 code, will have you put diagonal bars. All of this, Don will be discussing in detail. I'm just going to start on the dual-banded, talk a little bit about the experimental results and that study that happened, and then give it to Don to discuss, begin a little bit further. So what is the dual-banded? The dual-banded really, there were some papers back in the days, but it did start seriously in 2016 to 2017. It started at PTI, DC20, the Building Design Committee. It happened I was the chair at the time, and there was a lot of interest into looking seriously at providing something new, something that has not been done in the industry before. And given the way 318 was written, it really would not allow us to use anything but a banded distributed, where we have to comply with the maximum of five feet and eight times the slab thickness in one direction. We wanted to have something that will allow us to use this, a banded-banded without anything in the middle, but that's the extreme case. This is, you can maybe eventually in new code cycles have completely take out the provisions on spacing and just allow you to do whatever you want. But just so you know that this dual-banded now is in the code. And if you're interested in getting more information, there's a lot to cover on this. This can take a whole session, which is not the topic of today. I encourage you to go to the PTI Academy on PTI website. This is part of this series, the educational series. August, in August 2024, there was a webinar with really very interesting exchange on between the people who were involved on the analytical side, experimental side, and from an application perspective, and the code, how it came to be. In this webinar, we will just briefly talk a little bit about how it came to be in the code. So back when we first started, there was an effort to look at it analytically first to see, does this make sense? Or is this like completely, you know, an idea that will never work? But again, if we go back in time, who would have thought the banded distributed would be in the code, right? I mean, this was, can you think about having, if you're coming from a reinforced concrete, well, you have to have the distributed rebar everywhere. And now suddenly, you're using a banded distributed. So at the time, it was revolutionary. The PT used to be installed like this, called the weave, where we have distribution in both direction. But you can imagine for the PT savvy on listening, you can imagine how difficult it is to build this. Early in the 70s, there was a huge testing done at UT Austin that looked at the banded distributed. And they experimented on it, everything passed, and then eventually it became, made its way to the code and became standards when everybody uses the banded uniform. Once from an analytical perspective, it made sense, there was interest to do an experiment. And this is where Dr. Karen Roberts-Wolman and her PhD student did an experimental work to compare the post-tension slab with banded uniform to abandoned banded and really compare apples to apples. And from that work, they had, they published a paper and congrats to Karen and Taye Ocho, because they won the 2024 ASCE TY Lynn Award for the best paper. And that award looks at work in pre-stress concrete in ACI, PCI, PTI, ASCE, so among all of this. So that was a great achievement to Karen and her student. The experimental study really started being looked at at PTI. How can we do this? So at the end, PTI co-sponsored that experimental study as part of a larger program. That program had other proprietary systems and hopefully those systems also will make their way into the code. But PTI's interest was really just to compare the banded uniform to the banded banded layout, compare apples to apples. So if we can prove that the banded banded is comparable from a performance perspective to the banded uniform, then surely it can make its way into the code, same as the banded uniform made it. So at the time, PTI set up also a task group with leading industry professionals to coordinate research with Virginia Tech. What are we testing? First, we needed the prototype. So how are we going to test all this? What should be the protocol for testing? What's the loading? What's the span? So all of this came out through also a consensus process. So we had this task group to come up with all the difference ins and outs of the research. And similarly, Virginia Tech independently did their own analysis to see if also it works. But once this was done, technically Virginia Tech took the lead. I mean, it was all done under Karen Mullman's umbrella. They kind of built those labs and PTI was just invited to go and witness the test. So really an impartial test that no one, that Virginia Tech controlled from A to Z. That testing involved having two slabs really alike, the banded uniform, starting from this prototype. So the prototype was really to mimic what was done at UT Austin back in the 70s. It had three spans in both directions and 30 feet each and nine inch. The testing was done on a third scale. Obviously, we cannot build, you know, a 90 feet specimen that will be a fortune and plus there will be no lab where we can do it. So everything was shrunk to a third scale. We had 10 feet between the spans and the slab was shrunk to three inches. These are pictures to give you an idea. And you can see everything had to be shrunk. The PT strands were shrunk, the chairs, everything. The rebar, everything was made to a third scale. What you see here on this first picture, this is the banded uniform. That's the bands and these are the uniform cables distributed in the other direction. And this was the banded-banded. Here are the cables in both directions concentrated at the column with basically nothing, no cable whatsoever within the panel. This is a picture that I love. This shows the specimen and shows the scale. I mean, it almost occupied the whole lab at Virginia Tech. These are the three spans. You can see them clearly here. These are the PT. The anchorages were also shrunk. Everything had to be made to a third scale. You can even see a deflection. This was during the test. You can see some deflection here in this span and in this span. Those blocks are the compensation load blocks for self-weight of the nine-inch slab. So when we use a third scale, we have to make sure we're still having all the applied self-weight. And then the superimposed dead load and live load were applied through the Wiffle trees. And finally, the results that we got from that experimental study, you could see here four lines. This is the service load reduced based on reduced live load. This is the unreduced, the factored load. And then what was the limit where we started seeing nonlinear behavior? This is the banded uniform specimen. This is the banded-banded. Really, I mean, they're very, very similar. Extremely same behavior. So up to the 100 PSF, really, there's no difference. I mean, almost the same. And if you can see here multiple lines, this is purely due to the fact that we had load cycling. So we apply load, then release the load, and then apply it again. We would get linear behavior up to 100 PSF. And that 100 PSF, to be clear, that's only the applied load. So kind of a superimposed dead and live. We have to add the self-weight, which already was existing, which was 112. So basically, that behavior was under a total load of 212 PSF. And you can see the nonlinear behavior. And this would be the failure load, 212, for the banded uniform, which is almost the same for the failure load for the banded-banded. With that, I'll give it to Don now. Don, go ahead, please. Okay, thank you, Carol. Good morning, good afternoon to everyone. Depending on where you are in the country, it's great to be here. I'm going to continue with a discussion of the banded-banded. Sometimes it's called banded-banded in the code, and then some people refer to it as dual-banded. But I'm going to just continue with this discussion and talk about the analytical study that was done. So prior to the experimental investigation that was done by Karen Roberts-Bullman at Virginia Tech, we did a lot of analytical work on these labs, doing a comparison between the banded-distributed and the banded-banded. And we wanted to make sure that the behavior would make sense, and it would make sense to go into the experimental analysis. This work was primarily done by Jonathan Hirsch with Bentley. He spent a lot of time looking at different spans, different slap thicknesses, different levels of P over A. And what you have on the left side here is just a plot of the pre-compression of the slab in the east-west direction for a banded-distributed. And on the right side, you have a pre-compression in the slab in the east-west direction for a banded-banded. And this is just an example of one of the things he checked, but he checked all sorts of parameters in the behavior of the slabs. And what you're seeing here, I'm not going to go into a lot of detail. If you want more information about the analytical comparison, you can go back and watch the webinar back in August of last year, and they go into a lot of detail. But here you can see that where you have the anchorages in the banded direction, you have concentrated compression, and then you have these triangular wedges where you have reduced compression. That makes sense when you have banded tendons. And in the north-south direction, if we look at the behavior in the north-south direction, in the distributed direction, of course, you have a more uniform distribution of compressive stresses, so you don't have those wedges, whereas you do with the banded-banded. That's to be expected. One thing you see here is that you do have a reduction in the pre-compression in the north-south direction, where you have these concentrated anchorage forces going in the east-west direction, and that's just due to the splitting forces you get from the anchorage zones. You have that in both the banded-banded and the banded-distributed. It's just in the banded-banded, you have it in both directions, which is to be expected. I guess the bottom line here is that the behavior of the banded-banded when it comes to pre-compression is very similar to the banded-distributed, with the exception that you have a similar pattern in both directions. This is a summary of the analytical study that was done, and what you have on the left here is the behaviors, and then in this column, we have the banded-distributed, and in this column, we have the banded-banded. I'm just going to take you through this real quickly. The maximum peak compressive stress at pre-stress transfer is 1,300 psi for banded-banded versus 1,600 psi for banded-distributed, so we're a little bit lower there. The peak tension stress in the top of the slab is 2,100 psi compared to 3,450 for the banded-distributed, so we're actually a little bit better here. One clarification, you may be wondering why is the tension stress so high when we're supposed to limit to 6 square root f prime c. We have to keep in mind that that 6 square root f prime c limit applies to the average of the entire design strip, and what we're showing here is the peak stress right over the column, and it's not uncommon to have very high tension stresses at that location, and that's why we have the top rebar in the slab in both directions to take care of that peak stress. And then the bottom tension stress in the banded-banded is 450 versus 650, so we're a little bit better there. The maximum peak service compression stress, 2,400 versus 3,000, again a little bit better for the banded-banded. The deflection, the elastic deflection, is exactly the same, half an inch, and then the cracked service deflection, and this takes into account cracked sections, and you can see they were actually a little bit better than the banded-distributed. Perflexure and shear strength were equivalent to or superior with the banded-banded, so in almost all cases we're equivalent to or superior to the banded-distributed. That's what we discovered from the analytical comparison. So what's the reason we want to pursue this code change? And Carol kind of hit on some of these reasons. We want to provide more flexibility to you, the design professional out there. We want to give you more options, more tools that you can use to design post-tension slabs. We want to eliminate the necessity for a maximum spacing limit for distributed tendons. So let's say you don't necessarily want to do a dual-banded system, but you want to have more flexibility so you can spread out your uniform tendons. So you are able to do that. You have the flexibility to not follow the eight times the slab thickness or five feet that was previously in the code. And you may want to do that if you have large openings in the slab, for example, where you just are not able to get the height spacing on the uniform tendons. We also want to reduce overall construction cycle and placement costs and reduce reinforcement congestion at mid-bays of the slab areas. And this, obviously, if you're eliminating the tendons from the middle of the bay, then you're eliminating congestion there. Other reasons is to provide owners with flexibility. A lot of owners want to have flexibility to create openings and penetrations in their slab in the future. I can't tell you how many times we get calls from contractors and owners, and they want to save money, right? So they call us and they say, can you convert this structure or this design from a conventionally reinforced structure into post-tensioning? And we'll go through the exercise and show them the savings. And a lot of times there's huge savings, and sometimes they opt to go that way. Sometimes they'll come back if it's a commercial owner or a hospital or a lab. For example, they may say, well, we love the savings, but we just do not want to have the tendons out in the middle of the bay because we want to have flexibility for openings and penetrations in the future. They want to be able to adapt the use in the future, especially for commercial space and hospitals. We see it all the time. And so we want to be able to provide you as the design professional options for that owner. We want to give them the best of both worlds where we can save them money by going to post-tension slabs and also provide the flexibility for them to be able to modify their structure in the future. So if we look at the code, how has the code actually changed? If we go to section 8723, we're all familiar with the current maximum spacing limit for the uniform tendons of 8 times the slab thickness and 5 feet. Now there's an exception that says except as permitted by 8.7.2.5 for banded-banded tendon layouts. If you go to that section, it says that you just need to provide a minimum amount of bonded reinforcement or rebar in the slab. And the spacing, the maximum spacing on that rebar is 3 times the slab thickness or 24 inches. And if you go further, the code in 8.6.2.4, the code prescribes the minimum amount of reinforcing steel that has to be provided in that area of the slab where there's no post-tensioning. So if you look at this schematic or this sketch here, you can see that you have banded tendons in both directions. And then you've got this area in the middle of the bay, this zone in the middle of the bay with no post-tensioning tendons. So if we take the gross area of that piece of concrete that doesn't have any post-tensioning in both directions, you need to provide a minimum area of steel of 0.1% of the gross area in both directions. And what that equates to, let's say you have an 8-inch thick slab, that would be a number 4 bar at 25 inches on center each way. Of course, we have to also abide by this spacing limitation. And so we would end up putting a mat of steel at the bottom of the slab in that bay, which would be number 4s at 24 inches on center both ways. And then we go to I'm sorry, 8.7.5.5.2. And it prescribes how long the minimum length of those bars. And it says that you have to have a minimum length of three quarters of the clear span between supports. And if you're in an end bay, you have to extend into the exterior support six inches. And that's all described in this nice schematic that's in the commentary in the code. The next provision I want to cover is, yeah, we're doing on time. We're doing good. Next provision I want to cover is headed shear reinforcement in anchorage zones for unbonded tendons, for post-tensioned slabs and unbonded, unbonded tendons and post-tensioned slabs. We're all familiar with the requirement that when you have groups of anchorages in a slab, if you have more than, if you have six or more anchorages bundled together in a slab, then you need to provide not just the two number four backup bars, but also you need to provide reinforcement in the general anchorage zone, which is basically hairpins, vertical hairpins in the anchorage zone. The new code in section 25.9.4.4.6 allows us to use for the first time to use stud rails or headed shear reinforcement. And basically what you have to do is you've got to provide one stud in between each anchorage vertical and also on the outside, one on the outside, on the top and bottom. And the length, the size of that stud has to be half an inch diameter or greater. And the length of that stud should be the slab thickness minus the cover top and bottom. And the placement of that stud would be anywhere between three eighths of the slab thickness to one half of the slab thickness from the bearing surface of the anchorage device to the headed stud. And that's it. So we have a new code provision that allows for the use of stud rails as backup reinforcement for groups of anchorages. The next code provision change that I'd like to cover has to do with shrinkage and temperature tendons. So we all know that we have to provide temperature and shrinkage tendons parallel with the beams in the slab between the beam flanges. The current language says that you have to have maximum spacing of these tendons at four and a half feet on center. And in some cases up to six feet on center if you provide mild steel reinforcement at the anchorages. And what happens is if you have tendons at four and a half feet on center, which is required by the previous code, then you have the possibility of having a P over A or a pre-compression in the slab that drops below 100 psi, especially in this triangular wedge between the beam webs. This can happen in relatively thin slabs as thin as six to seven inches thick. And so we wanted to correct that. We always want to have a pre-compression in the slab. And we're talking about one-way slabs here. We always want to have a pre-compression in the slab in the direction of the beam of at least 100 psi. So I see Boxy did a study using finite element and he published a paper in 2023 that was published in PTI journal. And it shows very clearly that if you place temperature tendons in accordance with the code, you could drop below 100 psi pre-compression in the slab. And so what we've done is we've corrected that by basically going back to old language in the code from the 2008 code. We've gone back to that. And basically what that says is it's relatively simple. You design your T-beam according to the way you normally do with an effective flange. In this case, the effective flange is eight times the slab thickness on both sides of the beam. And what you want to do is look at the area of the slab that falls between the effective flanges of the two adjacent beams. And you calculate the gross area of that piece of concrete. And you want to design that for 100 psi pre-compression. And then space out the tendons equally within that zone. And then when you have a slab, a one-way slab that is supported on a wall on one side, then of course you just simply extend that slab that you're pre-compressing with the temperature tendons, extend that all the way to the wall. You still have the maximum tendon spacing limitations in the code of four and a half or six feet. Six feet again is only applicable if you have mild reinforcing steel at the ends. And what I'll tell you is that with this new code language, it almost always governs that the 100 psi pre-compression in that part will tell you it will govern the number of tendons you need for temperature and shrinkage steel. It's rare that the four and a half feet spacing will govern. One more clarification on this is, as a designer of a T-beam, a post-tension T-beam, you do have the flexibility of changing the effective flange for your design. You can go as small as you want or as large as you want. The code does not tell you how much effective flange to use. I'll tell you in our practice, we always use 16T plus B or the eight times on both sides of the beam. But you have flexibility to change that. Some designers will even go as far as using the entire tributary width as the effective flange. And you're certainly able to do that according to code. But this provision says that for purposes of determining how many tendons you need for temperature tendons, you have to assume 16T plus B for the effective flange in terms of calculating this gross area. You can still use a bigger effective flange for your flexural calculations, but to determine the number of temperature tendons, you need to assume no greater than 16H plus B. Sorry, I'm going the wrong direction. The next code change that I want to discuss has to do with the tensile stress in the prestressing steel reinforcement in the anchorage. The way it's currently written is we have a maximum tensile stress in the strand at the anchorage during jacking of 0.94 times the Fpy, which is the yield stress of the strand, and 0.8 Fpu, which is the ultimate stress in the strand. So we cannot jack higher than 80% of ultimate. We know that. That's been the code for many years. That means for a half-inch strand, you're jacking at 33 kips. There's another provision that says you should not exceed or you shall not exceed 70% of Fpu in the strand at the anchorage immediately after stressing. That part of the code has been eliminated, excluded from 320. The reason for that is that anchorage devices and couplers are always designed to develop a minimum of 95% of the Fpu of the tendon. And so there's really no need to limit the stress in the strand to 70%. And as a practical matter, if you're stressing to 33 kips, and if you check the stress in the strand at the anchorage immediately after stressing, it's quite common that you'll be at 0.7, at 70%, or perhaps even slightly higher than that. So to eliminate any future ambiguity, we just eliminated this from the code because it's not necessary. The last code change I'm going to cover relates to corner restraint in two-way PT slabs. You all know that when you have a two-way slab, non-pre-stressed, and if the slab is supported in the corner by two walls, or if it's supported in the corner by two very stiff beams, then you have to provide corner restraint reinforcement to prevent cracking in the corner of the slab. If you go back to the older version of the code before 2014, this never was applicable to post-tension concrete two-way slabs. And I think it inadvertently was included in the reorganization of the code in 2014. And so we're just going back and correcting that oversight, and we're eliminating it from post-tension slabs. So in 320, if you go to section 8.7.3, it simply says out of scope, which means it's not applicable to post-tension slabs. And if you look at the commentary in 320, we also want to recognize this. The post-tension concrete slabs should be designed to mitigate restraint through detailing to allow movement. That is to say that we always want to design to minimize restraint or shortening and to eliminate any potential restraint cracks that could develop in a post-tension slab. So just looking at where we are today and where we're headed, ACI PTI 320 2025 code is now available on the ACI Plus platform, as Carol mentioned. It's available today if you want to go find it, and it will be coming up very soon in digital format and then printed format. We encourage you to get copies of this as soon as it's available. We have an upcoming ACI convention in Toronto. It's coming up in a couple of weeks, and that will be the commencement of the new ACI PTI 320 cycle. We've put together a new code committee. We'll be meeting in Toronto, and already the PTI tab has met, and there's already a backlog of new code change proposals that we've got on the list, probably close to 20. We're just focused on trying to make the post-tension code as comprehensive and as practical and as user-friendly as possible. We want to be able to help you guys when you're out designing these post-tension slabs. We aim to have another interim code in 2028, and then we're going to get on the regular cycle and have another code issued in 2031. Just as a little bit of background, Carol and the committee put a lot of time and effort into developing this code, and we would have liked to have gotten more changes in, but it was such a big effort to put this new code together. We weren't able to get as many code changes in as we wanted to, so we will focus more on that in the next code cycle. Finally, the PTI DC20 committee is updating their DC20.9, and the main goal there and focus there is to have a companion document to ACI PTI 320. I just want to close by saying a big shout out to Carol. You did a great job in the last cycle. Appreciate everything you did to get that through, and look forward to continuing the effort going forward. Thank you. All right. We've got a lot of questions, some code-related, some more about the technical changes in there. One that we've had in several different forms is, as future iterations come out, do you guys envision ever the material from 3.18 regarding post-tensioning to be deleted and only be in 3.20, or 3.20 to eventually only get merged into 3.18? How do you guys envision that as the year has gone? You want me to say that? All right. That's a tough question, but understandable. 3.18 is its own committee, and 3.20 is its own independent committee, but yes, the goal is basically to take the PT provisions out of 3.18, but that will depend on 3.18 and their balloting process, so it's also a consensus process, but there is a big effort, coordination effort, between the different committees, between 3.18, 3.19, 3.20, to make this seamless from a user's perspective, again, to try to simplify as much as possible. It might take a few cycles, just because it takes a village, really, after going through the process, to make a code, even to make a small change. Sometimes people don't realize the effort that goes behind to make even a small code change. I have to say, I didn't mention it's also fun, so if you would like to get involved, there was a picture with all the 3.20 code people, so, yeah, I mean, we do a lot of work, but we also have fun, so on the last one, we celebrated the end of 3.20 and handed it over to Don, so if you want to be involved, I'm just taking this opportunity to. PTI, I'm sure, would love more participation as well. Great. There's a lot of questions about dual bandit and the technical stuff, you know, we're about out of time, so I'm going to, we'll try and respond to those emails in email format. As Don and Carol both mentioned, there's a webinar that you can go watch. There's also a tech note that's been produced that you can download and read on there that gives a lot of information on there. There's questions, all the questions I'm seeing are things that have been considered when we went through the dual bandit stuff, and so there's definitely answers to that stuff out there. For Don and Carol, another question that's come up several times is what about slab on grounds? Is that considered at all in the 3.20 code? Is that different, and can you kind of give some logic behind the different, why it's different there? I would hand it over, I mean Don maybe, because that's a good, there's work being done on that aspect, and Don, as the chair of 3.20, probably would be dealing with that change proposal. Yes, slab on ground traditionally has been excluded from ACI 3.18. It's not covered by, it's not governed by ACI 3.18, and it's, they have referred to design of slab on grade, post-tension slab on grade to, they referred to the PTI documents for design of PT slab on ground. We, there is some, a little bit of confusion, or maybe a lot of confusion in the way the code, ACI 3.18 is currently written, where it says that if you, if loads are being transferred through the slab into the soil, then it needs to be governed by 3.18, and we want to clarify that. We're going to work hard to clarify that in the next code cycle, so stay tuned on that. Okay, a couple of the questions that we've gotten, these are more administrative level questions. There's been several about, will slides be provided? We talked about this at the beginning, but if you joined a little bit late, we do not provide PDFs of the slides. However, you can go online, you can watch this webinar. It's, it'll be uploaded online, same with the last 14 that we've done, so you can go on there, you can see the slides, you can hear the presenters again, so that's how you can get that content. Now, as far as the continuing education credits, PDHs, you will get, if you're logged in under your email, you will get an email with that PDH within a couple weeks. You should expect to see that from RCEP. So with that, like I said, the ones that we didn't get to, we'll definitely try and get some emails out and get those responded. Let's talk about the next three months and where we're going with that. So talking about slab-on-grounds, construction and maintenance of post-tension slab-on-grounds. This is one of our most requested topics is slab-on-grounds here, and so we're continuing on. We did, we've done several already, they're online, but April 9th, we're going to do construction and maintenance of post-tension slab-on-ground foundations, and then from there, we're going to go elevate, and we're going to talk about barrier cables. It's a two-part series. We're going to talk about barrier cable design, and then barrier cable construction and maintenance. A lot of studies that's been done on barrier cables in the last few years, and so great content coming up in those two presentations as well. So yep, we got three more months of stacked stuff coming your guys way. We look forward to seeing you guys here at the same exact time, second Wednesday of the month, one o'clock Eastern, ten o'clock Pacific. With that guys, enjoy the rest of your day.

Post-Tensioning Institute

ACI PTI Joint 320-25 code

post-tensioning design

Kyle Boyd

Carol Hayek

Don Kline

dual-banded tendon layouts

headed shear reinforcement

ACI Plus platform

PTI Academy