Sitecast Long Span - Consider

6m 57s

In this ARE 5.0 NCARB-approved Project Planning and Design Exam Prep course you will learn about the topics covered in the ARE 5.0 PPD exam division. A complete and comprehensive curriculum, this course will touch on each of the NCARB objectives for the ARE 5.0 Project Planning and Design Exam.

Instructor Mike Newman will discuss issues related to the generation or evaluation of design alternatives that synthesize environmental, cultural, behavioral, technical and economic issues.

When you are done with this course, you will have a thorough understanding of the content covered in the ARE 5.0 Project Planning and Design Exam including design concepts, sustainability/environmental design, universal design, and other forms of governing codes and regulations. 

So remember in the discussion of site cast versus precast in the discussion of prestressing versus post tensioning, all of that. There are different moments of that discussion happening at different points along the way of the conversation or along the way of the project. For our purposes, the point that we're in right now, in this exam, what we're talking about are the planning implications. So if we start talking about certain ideas about planning that would lead us towards site cast.

That would lead us towards prestressing. We talk about other issues about planning that might lead us towards precast and lead us towards prestressing. The question is, at this stage, what are the planning implications? At the next exam when we're more in the kinda CD set phase of the project, there we'll be talking about the specific details about how the topping wouldn't work, and what kind of reinforcing we would have within those systems.

We'd be getting more into the detailing of it, and the specifics of the fire ratings, and things along those lines. At this point, it's really a question of how does it impact planning, or how does planning impact it. So one example might be, let's say the question is sort of talking about an issue that says there's very little time in order to build this structure.

We really have to make sure that from the moment we have the ability to start the construction, to the time that the construction is finished, that we have to be able to get out exactly on time because, the school starts, or the football games start, whatever it is that's keeping our timeline very, very short, or could be just financial, could be the fact that the cost of the land is very, very high.

And so the bridge loans that it takes to just hold the land before a project is being able to be finished, is so expensive that we really want to speed up the construction process. So something like that, any of those kinds of reasons, that's gonna push us towards the precast, because the site cast is gonna take a lot of time. We have to build all that form work. You then have to set the concrete. The concrete takes at least a week to get the initial set in place, and then won't actually be fully set for 28 days.

So there's a bunch of build-in time just in kinda making each individual element work, whereas with the precast, all of that time can be done before the actual construction starts. We could be making these things well ahead of time, even delivering them to the location so that as soon as construction starts you're able to just start craning those things into place.

So from a site construction stand point, the timeline with the precast is gonna be very, very quick compared to the site cast, especially for a long span. With other choices it can become, it's a lot more variables with other choices. But with long span, the precast will absolutely be faster than the site cast. So you can imagine a question that sort of leads you into that scenario.

But then in the same way you could imagine a question that leads you towards the idea that, well time isn't really the issue, maybe a sort of specialness is the issue, or the fact that the elements want to change at each point. Maybe it's an arch that starts as a very deep arch but then becomes flatter, and flatter, and flatter as it goes along, or something, so that you have multiple different versions.

Well if I had precast, the advantage of precast is always gonna be in when I have the same thing going over and over again. I might have a couple of different versions, but I really wouldn't want to spend the money to make all the form work if each piece of form work has to be novel and different. For precast that's just not where the money is. It would be very difficult to do that. But with site cast, I'm creating the form work in place for each one, each time anyway, so it doesn't really matter if I'm changing it a little bit on each different beam for example.

So if the situation is calling for customization, well then site cast is gonna be the thing that drives the day. There's a whole series of these different issues that you can imagine are partly about the plan of the building, partly about the project delivery system, partly about the sort of general nature of the way a project's gonna move forward.

Does it need to move forward quickly? Does it need to move forward in a way that is very expressive? Does it need to be something that can tie into the systems in a particular way? You might, with site cast, be able to manipulate the site cast set up so that you can integrate systems a little bit more easily. The precasts are gonna be these repetitive elements that won't necessarily play nice with your utilities.

So the scenarios around these questions are the reasons that you're gonna lean one direction or another, in terms of the site cast-precast, post-tensioned versus prestressed. It's gonna be all about the kinda scenario around. Remember, a typical long span situation with site cast is probably post-tensioned in order to get that compression into the concrete.

But it could be prestressed, it's just probably not. With precast, the typical is gonna be prestressed 'cause it just makes sense with the form work to be able to do all that robust pulling with the tendons in the form work. That just makes sense to do that prestressed as opposed to post-tension. But it is sometimes done as post-tension, so it's not a super clean line, it's just that if there's no other information that's the way that you would imagine it.

So when we're talking about these things, for this exam, we're not really getting into the detail about the exact way that these things are fitting together. We're really just thinking about it from a sort of planning standpoint. Which way are we leaning? Which way makes sense given the scenario that's been given?

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From the course:
ARE 5.0 Project Planning & Design Exam Prep

Duration: 30h 57m

Author: Mike Newman