You may have seen buildings collapsing on their own base, whether it was intentional or a disastrous accident. This straight-line collapse seems independent from where the failure started, from the ground or the top. So, you may wonder if buildings are actually designed to fall straight down.
Buildings aren’t purposefully designed to fall straight down. Instead, it’s the physical laws of gravity at work and something that naturally would happen. Since buildings are hollow, each floor collapses on the floor underneath when they get destroyed, making the whole building fall vertically.
Keep on reading this article to see what leads a building to fall in a straight line. I’ll also cover cases when the building leans to the sides or doesn’t fall in a straight line.
The Mechanism of a Building’s Collapse
There are many different factors that can cause a building to collapse, including fires, earthquakes, and intended demolitions by demolition companies. You may have noticed that, no matter what the main contributing factor was, all buildings tend to collapse in a straight line.
You may wonder why a building doesn’t tilt to a side like a tree does when it falls. The fact is, there’s no natural force that can make a building collapse sideways.
To understand why you need to understand how gravity affects a building.
Unlike a tree or pole, a building is not a solid structure – instead, it’s hollow inside and made up of different units. So, it can’t support its own weight when it falls. Plus, it’s always working against gravity and its own weight to stay straight. That’s why when it falls, it quickly gives way to gravity and falls straight down.
Another thing determining the direction of a building’s collapse is the primary support structures. When a building collapses, it loses its primary support from the place it has been destroyed. For example, if a building gets destroyed from the ground floor, it loses its main support point on the ground, leading the next floor to collapse.
It starts a domino of destruction leading to the collapse of the entire building. It’s also known as pancake collapse and involves floors falling on top of each other, like the layers of a pancake.
Preventing Collapses is an Essential Factor in Designing Buildings
As mentioned earlier, buildings aren’t designed to fall straight down. Instead of thinking of how the building will collapse, design plans and policies are more interested in ensuring safety and preventing a collapse in the first place.
Building codes aim at building structures that don’t collapse when one part of the building gets destroyed. That’s what designers and builders have in mind when designing and constructing a building. They study different forces that can destroy a structure and strengthen it against these forces and destruction patterns.
They have to comply with the building codes to ensure ultimate safety and many other factors, such as accessibility and energy efficiency.
When Buildings Don’t Fall Straight Down
Now, you may wonder whether a building always falls straight down. The collapse angle depends on a wide range of factors: the cause of the collapse and the location of the point of support destroyed.
For example, in older buildings where the primary support for the entire structure is a vertical pole in the center, the building may not fall in a straight line because it cannot collapse on its own weight.
Another thing to remember is that although buildings tend to collapse in a straight line, they may lean toward certain sides at some points of collapse. But in the end, they give way, and gravity takes over.
As a result, there will be debris extending around the base of the building, where the collapse had started. That’s because gravity isn’t simply the only force at play here. At the same time, the part of the building that’s falling is being pulled by other forces from other structures attached to it.
Here are some situations where collapse isn’t in a straight line:
A major case in which the building may not collapse in a straight line is in controlled demolition performed by demolition companies. In such cases, the demolition experts need to consider the surrounding buildings and choose the best type of collapse to prevent damage to adjacent structures.
The main method to achieve a clean and safe demolition is using explosives to create an implosion. In this case, the building falls on its own base without leaning toward the adjacent buildings.
They can also make the building fall on a particular side, depending on the conditions. The main factor that determines the direction of demolition is removing the supporting point. So, if the experts want the building to collapse on its southern side, they plant the explosives on that side.
It’s like felling a tree using an ax. If you want the tree to fall on a particular side, you chop into the tree from that side and destroy its support structure.
Plus, they may have to perform the implosion at different times or over different days, and they will have to plant explosives based on these considerations. If the demolition is happening all at once, they may also choose to plant explosives on all sides of the building and explode them simultaneously, so the building loses support from all sides simultaneously.
Different Angles of Collapse for Walls
Buildings may fall in a straight line, but walls don’t always follow this pattern. There are three types of wall collapse:
- Outward/inward collapse. As the name suggests, it occurs when the wall leans in an outward or inward direction.
- Curtain-fall collapse. It resembles a curtain when it drops in a straight line. In this type of collapse, all the debris gathers at the base of the wall.
- 90-degree-angle collapse. This type of collapse involves the wall separating from the building and falling like a tree.
While a wall may collapse in these ways, regardless of how the first wall collapses, the whole building will follow it and go down in a pretty straight line.
Architects and builders don’t design buildings to fall straight. It’s gravity that pulls the building down after it has lost its support structure. If it’s a skyscraper, each floor that collapses becomes the lost support for the above floor, making it collapse, too.
If you plan to demolish a building and make it fall in a particular direction, you need to do it in a controlled way. Controlled demolition sometimes uses implosions and explosives to make the building collapse in the preferred direction.