Why buildings fall down (Multiple collapse reasons!)

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The backbone of any building is its foundation, structural grid, and materials used during construction. Overloading, temperature change, deterioration of materials, design flaws are some of the factors that affect a building’s life expectancy. They can be divided into internal and external forces. 

Buildings collapse due to natural disasters such as earthquakes, soil liquefaction, hurricanes, etc. However, they can also damage due to material deterioration, lack of maintenance or many overlooked construction details as early as the design and conceptual level. This is why care and attention must be given to proper design, prescribing of structural system and foundation, appropriate and specific to the site’s conditions.

Image from That Huge Building Collapse on HBO’s Vinyl? True Story. Mostly. (vulture.com)

The Internal Forces:

1. Foundation:

Foundation acts as a medium to transfer loads from the building to soil cautiously. It provides stability for the entire building. It can fail due to poor soil inspection, insufficient depth, reclaimed soil, highly corrosive soil, liquefaction, and lastly design error. 

When there is a movement of expansive and highly plastic soil under various portions of footings, it leads to foundation collapse. This soil movement might take the form of shrinkage, which produces settlement, or expansion, which generates heave.

Image from Partially overturned building in Adapazari, Turkey during the 1999… | Download Scientific Diagram (researchgate.net)

For example, say an old 2 storey building was bought and the owner wants to convert it into a 5 storey building. If the foundations aren’t replaced, the building is automatically overloaded, having a base that was only fit to carry less than half its weight. (1)

Another scenario would be having a site on a swampy area or marsh land. This would mean to build higher, you need to dig deeper. The foundations would cost more being of a more expensive technology and digging deep enough until a hard bedrock is reached.

2. Overloading Structural Elements:

These would be your beams, columns and floor/ceiling slab. Sometimes, the loads can be heavier than expected putting the entire grid in jeopardy. It can also be affected by inexperienced workers who reduce or increase the bar placement.

The structural joints, such as building corners or roof connection to structure, need to be dealt with carefully considering they are the weakest links.

For example,

The massive fire overstressed the steel columns of twin towers. It went through thermal expansion causing it to buckle and floors to fall like a domino. 

Another example,

An L-shaped building is tugged back and forth in an earthquake, causing the two components of the building to pull and push one another, eventually weakening the corner. This is why square buildings are considered structurally more sound and safe.

This is why structural systems in buildings are built with redundancies. Meaning if one system fails, the loads will transfer to another.

Image from How to Repair Cracks in Concrete Foundation Wall? – Valid Pick

3. Materials:

Concrete might last for a hundred years but it is prone to corrosion due to water infiltration and lack of concrete surrounding the reinforcement. The moisture can easily seep and increase the vulnerability of the building internally. The alkali–silica reaction, exposure to rain and snow can make concrete crack and expand. (2)

Using cheap materials is also another cause of structure failure.

There are instances wherein people cut costs on getting lower class materials to save money. It can be a technique, but should not degrade the specified class for structural or load bearing elements (your beams, columns, slabs).  (1)

Another reason for material failure is lack of building maintenance: repainting, filling up cracks, ridding of rust and water puddles. Especially for buildings by the seaside, salt is more corrosive to concrete, which is why a regular inspection and retouch of paint every 5 years help keep the building in good shape. (3)

External forces:

1. Natural Calamities:

Earthquake

Seismic waves induce ground shaking during an earthquake. If the strength of the seismic wave is large, the ground and structures may shake violently. It boosts landslides and soil liquefaction (when soil loses its strength and behaves like a liquid) putting excessive load on the foundation.

Building shock absorbers and seismic dampers are devices that can absorb and safely redirect strong vibrations for high rise buildings.

Storms or cyclones:

Strong wind loads due to cyclones or storms can put high pressure on the windward side. Uplift load, shear load, and Lateral load are three types of forces that affect the building. 

Uplift load creates a lifting effect on the roof because of high wind flow. 

A shear load is a horizontal wind pressure making a building bend from the windward side. Also known as racking. 

Lateral load is when there is horizontal pushing and pulling strain on walls that might cause a structure to slip off its base or topple.

Floods:

If the power of the water is particularly strong during the flood, it exerts a lot of pressure on the bottom portion of the building. If the structure was not intended for flood pressure, it might damage and produce foundation movement. As a result of the unequal strains caused by the flood’s increased pressures, the structure may collapse.

Prolonged submersion of the building in water also weakens the concrete and deteriorates exposed steel.

Fire:

This can happen within our home, our neighbor, or rapid spread of wildfire. Either way, it is a common occurrence that could significantly weaken the building structure. Be sure to check your local fire codes as these differ per climate and country.

2. Deterioration because of Age:

A building with quality materials and design can last up to eighty years. However, restricted contraction and expansion, faulty Damp proof courses, weak joints between materials, bad grade of materials, zero considerations of maintenance are the reasons for early deterioration. 

                      Buildings must have strength, ductility, and flexibility to last long. Natural calamities can’t be tamed down but they can be avoided by investing in teaching laborers, using proper materials, and designing a better resistance grid. 

How Do We Prevent This?

Damages Beyond The Site

In 1990, the summer capital of the Philippines, “Baguio” was hit with a 7.7 magnitude earthquake, causing several high end hotels to collapse. This is because many of them were too high for the soil bearing capacity, and the site being earthquake prone.

The damages of a building collapse is not limited to the site itself. 1,283 people died, 2,786 were wounded, and at least 321 went missing. The fallen building also destroyed 25,305 houses and partially 77,249 more. Not to mention any flying debris could have harmed people a fair distance away. (4)

Image from FAST FACTS: The 1990 Luzon earthquake (rappler.com)

Design Failure

One hotel in that Baguio disaster, the “Hyatt Terraces”, is speculated to have collapsed due to an “irregular diaphragm.” The earthquake may have triggered it, but the concept of heavier stories on top of smaller ones have made it catastrophic.

Many buildings can be susceptible to “soft story failure.” This is when your lowest floor at ground level is weaker than those above. If our ground floor has an open, pilotis on stilts look, or trying to give the illusion of a “floating volume”, take extra caution if you need to additionally brace your building.

It just follows the logic that the lowest floor cannot be lighter and yet carry all those heavy floors above it.

Image from Look at how apartments can collapse during an earthquake – Los Angeles Times (latimes.com)

Reinforcement  of your structural elements must be laid along the weaker or shorter side of the building. This way should your seismic waves come in any direction, your building has a greater chance of avoiding structural failure.

Hire the Professionals

It is uncommon for buildings to collapse so often. So the first and safest step is to hire your building professionals. Architects and engineers not only train for years, but they continue to cross-check each other throughout the building process. Also, professionals are held liable by law should the structure fail. This in itself gives great comfort and assurance that your building is likely safe.

Architects and engineers ensure all building, structural, fire and local codes are followed, which if we often see around us after an earthquake, most buildings around us are still standing. This is because a soil test was conducted by a geodetic engineer, allowing the architect to design the appropriate structural system and the civil engineer to specify the correct foundation and reinforcements. (5)

Second, these professionals will help link you to good builders and contractors. Some think “buildings collapse due to corruption and money.” As the construction industry needs a constant shell out of a big amount of cash, it is tempting to cut costs in material and code standards. (5)

Next, follow all these design professionals. That’s what you’re paying them for! Follow their exact specifications, do not skimp on cheaper alternatives. Also, you need a building team that will be strict in conducting testing strength of materials, which is stipulated by code but can be overlooked. This ensures you are using the quality material you purchased before using it on your building. (1)

This team should carry you to the end and oversee that concrete pouring and steel bar connections are done at the precise points of non-failure. Human error plays a big factor in building failure, which is why it pays to have a professional team check on one another.

Solution is in Designing Well.

Attention to detail and . It really takes a village to put up a good structure. There are several building professionals that go on behind the makings of a building. This is what makes constructing a high-rise so expensive, but at the same time code compliant and safe.

Hopefully the pointers above will give you a few tips on what to look out for and the most structurally sound building shapes (being a square and a circle).

I remember my architect professor telling me that. a quick know how or sign that a building is unstable and could collapse, is if there are ANY cracks on the columns or beams…. get out immediately!

References:

  1. *. (2016, May 5). Five reasons why buildings collapse. BBC News. Retrieved March 2022, from https://www.bbc.com/news/world-africa-36205324
  2. Papadopoulos, L. (2021, August 3). When and why do buildings fall apart? Interesting Engineering. Retrieved March 2022, from https://interestingengineering.com/video/when-and-why-do-buildings-fall-apart
  3. Woodward, A. (2021, July 3). 3 structural engineers explain why a building like the Surfside, Florida condo might suddenly collapse. Business Insider. Retrieved March 2022, from https://www.businessinsider.com/surfside-florida-building-collapse-causes-structural-engineers-2021-7
  4. Agoot, L. (2018, July 16). A story of unity, resilience: 28 years after the 1990 killer quake. Philippine News Agency. Retrieved March 2022, from https://www.pna.gov.ph/articles/1041379
  5. Akinbobola, L. (2016, December 13). 7 Steps to Prevent Building Collapse. Nigeria’s Building and Construction website. Retrieved March 2022, from https://buildersenquiry.com/7-steps-to-prevent-building-collapse/