Precast Prestressed Concrete (Fall 2006) - Part 6


Uploaded by WafeekWahby on 31.01.2012

Transcript:
>> Ms. Marty McIntyre: Security is an issue,
there's a new FBI building in Chicago that was built
using pre-cast concrete and the US Air Force is doing
some blast resistant design testing with pre-cast.
So we are seeing more and more people looking for
ways of building secure buildings whether it be
for floods or hurricanes or attack.
Early consultation is a trend that my members really
like to see there.
They're starting to get involved in projects, usually
in the schematic design fazes when they like to get involved.
When they can talk to the architect and say,
'Yes, this'll make a good pre-cast project', or
'no, it's, it's not an ideal project for pre-cast'.
This is Soldier Field and it really represents the speed of
design and construction in a lot of ways in the teamwork that
people are looking for on some of these bigger projects.
It was pretty interesting to erect because you could
only erect it from inside the bowl of the field.
You couldn't do anything from around there was a roadside on
one area and there were parking decks on either side
so they really were limited so the cranes
were quite challenging on this project.
The pre-caster worked with the team and came up with some
solutions for some lightweight concrete on some of the larger
pieces of the pre-cast on the top of the bowl because the
crane just wasn't able to have that reach with some of the
heavier pieces of concrete.
They also had to do some finagling with the
steel erectors.
The steel erectors actually came in and used the cranes during
the daylight hours so from 6 a.m. to 6 p.m. the
steel erectors came in and then the pre-cast erectors came in
and I don't know how they drew the short end of the stick.
But they got to erect pre-cast all night.
so they actually had 24-hour erection going on,
in the project.
So, you know typically this would have been a
24-month schedule, with the parking decks and the stadium.
But because of the Bears playing schedule they had to
finish it in 18 months and they did it.
The contractor would have been fined
I guessed $5 million for any games that the
Bears were going to miss at the stadium so
they had real incentive to get it done on time.
The other portions of the this that were pre-cast were the
parking decks and they're pretty interesting parking decks as
well because they've got large planters on the
top of it that actually have trees inside the planters.
And then part of the parking deck is underground
so the loads, and oh, Soldier Field rests
on top of one of the parking decks too.
So the loads that they were taking were not typical parking
deck loads and it was pretty interesting project.
So they were originally designed as cast-in-place,
but cast-in-place couldn't meet the design schedule
or the construction schedule,
so it was a pretty interesting project as far as the speed of
construction in the way that the group had to really function as
a team to get it done in time.
Just a little bit about finishes and colors, there are a lot of
possibilities out there when you're talking about
architectural pre-cast and how are you going to finish a
building and what is it going to look like?
One of the things that you'll see at the architectural plant
is that you can finish it, finish the surface of pre-cast
product in different ways and get very different looks.
This is actually an example of just a
12-inch by 12-inch sample of concrete.
And it's been finished in three different ways.
On the far side is an acid-etch finish, and that uses
muriatic acid and a hot water wash and it just removes
the finest particles of the concrete to give you a kind of
a smooth limestone like finish.
In the center, they've sand-blasted it so you get
that kind of white halo-effect.
And they've also gone a little bit deeper so
you can see more of the aggregate.
In the section here you've got a chemical retarder,
that's actually a sugar-based retarder that stops the
concrete from curing on the surface.
So you stop the concrete from curing, you then use a
high pressure water wash and you can expose a lot
of the aggregate that way.
So you really can get very different looks that's all the
exact same mix of concrete.
What's, what they've changed is the way they finished it.
>> Male speaker: [unclear dialogue.]
>> Ms. McIntyre: Yes, and it's all going to vary
on the project and how many pieces you're finishing
that way and the sizes of the panels and how many panels
you have to move in the yard and things like that.
But also you know some of the pre-casters do more acid-etching
then sand-blasting and those really cost about the same.
Chemical retarders can cost a little bit more than those.
>> Male speaker: Do you wait until it
dries all of the way before you do that?
>> Ms. McIntyre: Typically, yeah,
you'll do it, you'll cure it overnight, take it out.
It might sit in the yard for a day or two and then
they'll go ahead and finish it that way.
So it's not like they're waiting weeks and weeks.
But sometimes they'll let it cure a couple days.
Any other questions?
One of the things that we've seen a lot of lately are these
insulated wall panels where they're adding insulation and
you can see this a DOW system where they've got these
connectors that are done out of a composite material.
Sometimes you'll also see connectors done out of steel.
But those will carry the cold temperature through.
So a lot of the people who were really concerned about the
thermal mass and not having cold spots in a wall panel will
use something more like this.
It is possible now to have insulation from top to bottom
and side to side in a project.
Pre-cast connections just talk about that when you're
connecting wall panels you really are going to have two
basic types of connections.
One is your gravity connector, and that's going to be
what defies gravity and holds it up on the wall.
Gravity connectors are, you're going to have at least one,
you might have two but you'll never have more than two
because you can't predict the loads.
If you have more than two so those are going to be on the
wall panel where they need to connect to the structure
so it's going to change in every wall panel.
The gravity connectors will be in a different place.
Then the wall panels will also have tie-back connections.
And the tie-back connections, you're always going to
have a minimum of four connections and then
sometimes you'll also have six connections.
I need a brighter location but you've got them located on the
corners here and then if you have a long panel
you'll also have them located mid-span.
So the structure of the building needs to have a place
where those tie-back connections can actually connect
or tie-back to the building.
This just shows you again in a building where are all the
connections going to be for it.
You've got your cast-in-place slab on grade on the bottom.
And then you've got wall panels and then if you look kind of
behind it you can see where all of the connections are
with your gravity connectors, your mid-span connectors,
your floor connectors, and that's on a steel piece.
And there it is again you can see all of the framing.
This is with steel framing.
Then if you've got like a wall panel, you're also going to have
it connect back a lot of times you'll have some kind of shim or
some kind of composite material that the connections
are actually going to rest on.
So you don 't have steel resting on steel.
The weld plates are going to be cast right into the pre-cast
panels and so the pre-caster was going to have working drawings
in the plant that really shows the guys where are all of the
steel needs to go, where all the connection panels go.
And then you can connect it to a steel building,
a cast-in-place building or a pre-cast building.
And those other, the partners to those steel plates
or the connection plates have to be ready on the building
where you need them.
Just another panel-to-beam connection system where
you've got the panels or the, sorry, the pieces embedded right
into the pre-cast and then bolted on.
Then sometimes you'll also have a pane-to-panel connection to
keep there fro being too much movement in between the panels.
And those are usually done with a threaded insert.
Typically you are going to have a joint in-between the panels.
It'll be caulked on those wall panel projects with
either a single line or double line of caulk.