Components of Concrete Structure
We’ve got a good one here today. What are the different parts of a concrete structure? Let’s jump in.
So, use of concrete has played at least some role in our built environment since the Romans in the 5th to 3rd Century BC. Concrete hardens quickly into a rigid form and is free from the internal strains that are problematic for structures that are only made of stone or brick.
Today, concrete is more consistent and homogeneous than those early versions of concrete in the Roman era.
We also use reinforcing steel within concrete, which gives that concrete tensile strength. That’s where the term reinforced concrete originates. Including reinforcing steel inside the concrete at specific locations prevents the concrete from pulling away from itself, and results in a much more effective structural material.
Essentially, wherever we want that tensile strength, that's where the steel goes. So, if you look along the lines of a beam, you're gonna see steel at the bottom and the top. The bottom is because that's where the beam is pulling apart. It's its tensile forces along the bottom of the beam. At the top, it's actually in compression and that reinforcing steel also helps us in compression, ‘cause it's actually stronger than concrete. That's why it's at the top and the bottom and those are the most important areas for that reinforcing steel.
Concrete has some advantages over wood, steel, and masonry.
It can be economical and it can be widely available. Concrete is only a combination of cement, water, and aggregate, which can be again relatively inexpensive compared to similar volumes of steel or stone.
Concrete can be cast on-site, and it can be cast into many different configurations. Complex shapes and configurations are made using formwork.
Compared to wood and steel, concrete is relatively resilient to water. It holds up better in submerged applications and does not corrode like steel does. You can assemble that formwork on-site, get exactly the shape you're looking for and voila, you have a very complex shape created from a very simple material.
Concrete also resists high temperatures. Bingo. This is a big one for us. It's more tolerant of very high temperatures and is used as one way that we can increase fire resistance of other materials like steel. You take a steel column; you encase it in concrete. Now you have the properties of the steel, but the fire resistive qualities of concrete. That pictures, especially fire resistance qualities here plays a big role in our fire protection paradigm.
Now the downsides to concrete include a significant amount of weight. This has a negative impact on tall structures as that weight of the building itself begins to require additional strength below it, which then increases the structural size below and we repeat the cycle again.
Concrete also can rupture at low temperatures. It can crack and it needs reinforcing in order to be effective for most applications.
COMMON CONCRETE STRUCTURES
In my personal experience, I found that concrete structures most often come about in commercial buildings that have either significant interior loads or have significant fire resistive needs, such as hospitals, stadiums, arenas, prisons, or multi-story manufacturing facilities.
There are a lot of descriptors and different types for concrete. There’s different casting methods, there are different reinforcing methods, there are different weights and densities for concrete, and there are many different forms that concrete can take. Today, we're keeping this at a pretty high level and just introducing some of these concepts. I don't want to get too far in the weeds because I don't think that's important as part of this series, but certainly when we get to suppression design, we're looking at hanging methods and the details become really important, we'll dive into it then.
HOW CONCRETE TAKES FORM
So how do concrete building structures take form?
Well, for buildings that use concrete primarily as its main structure, concrete will be used for floor slabs, joists, beams or girders, columns, load-bearing walls, and foundations.
Now despite being mostly concrete, some portions of the building may still use steel for its structure. Roof decks, for instance, may not need as much support as a floor level, it just doesn't have the same amount of load when you have big interior loads in the building. So, steel beams or lighter open-web steel joists might still support a roof deck that consists of a metal deck, insulation, and roofing materials.
But once we get below the roof level, concrete structures use a lot of the same terminology as other structures. We have floor slabs, which can take many different forms. These can be poured monolithically which is just a single pour. It can include supporting concrete members like joists (which have smaller spacing), larger beams (which are spaced further apart), or even poured separately as Concrete Tees. There are many different types of slabs.
Beyond the slab and the support for the slab, ultimately, joists or beams are gonna transfer their load to a girder, a column, or a load bearing wall.
If we have beams, the beams may be spaced so that they tie directly into a column. Concrete columns are often significantly larger in area than an equivalent steel column. Also, which can make things a little bit trickier for sprinkler layouts, concrete columns sometimes have a capital that’s up at the top of the column. If these are missed, these could create issues for sprinkler layouts. Capitals on a concrete column (that’s a lot of alliteration) were very common in concrete manufacturing and warehouse buildings over the last century plus.
After the column, we work our way down to a footing. If we have a load-bearing wall, say on the exterior, well that wall will tie into a foundation wall, which then goes and works its way down to a footing.
At a high level, concrete structures work well to serve commercial applications where we have heavy loads or we need some additional fire resistance properties. Many of the identification for different parts of the building is gonna be very similar to the other building types, only that concrete has a lot more flexibility in its final form and has many different ways that it can be configured. We’ll get into detail in different example applications when we go deeper into design for various building types.
In our next segment, we’ll cover heavy timber construction.
I’m Joe Meyer, this is MeyerFire University.
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