Mi opinión sobre las columnas de 20x20

Summary

In this video, the speaker critiques the use of 20x20 cm columns in construction, especially in small homes. The speaker explains the mechanical properties of such columns, their limitations under stress, and the potential risks of using them in taller structures due to their susceptibility to buckling or 'pandeo.' Key issues include reduced resistance when the columns exceed recommended lengths and problems during construction, such as damaging the column during the installation of door frames. The speaker advises against using 20x20 columns for long spans and suggests larger columns like 25x25 or 20x30 for better stability and safety.

Takeaways

• 😀 The speaker discusses why they dislike 20x20 columns, which are common in small houses and areas with low load-bearing requirements.
• 😀 A 20x20 column consists of a square section (20x20 cm) reinforced with 4 steel bars, typically 10mm thick, although using 12mm bars is more compliant with standards.
• 😀 These columns, when built with hand-mixed or small-scale concrete, can withstand around 40 tons, but this resistance diminishes as the column becomes taller and more slender.
• 😀 Tall, slender columns are susceptible to buckling, a type of failure where the column bends under load, especially when the column exceeds 4 meters in length.
• 😀 A 20x20 column becomes weaker and more prone to failure when its length exceeds 3 meters, and this should be avoided in design.
• 😀 A 20x20 column in a central position can theoretically support up to 55 tons, but if the column is taller, its capacity is reduced, making it more vulnerable to failure.
• 😀 The effective length of a column needs to account for the depth below the foundation level, which can make the column longer than initially expected, further weakening it.
• 😀 The speaker highlights practical issues when constructing columns, such as the difficulty of installing wooden door frames, which sometimes requires chipping the concrete and reducing the column's strength.
• 😀 Mortar used to fill gaps around frames does not contribute to the structural strength of the column and can reduce its load-bearing capacity if significant amounts of the column are removed.
• 😀 The speaker advises never to skimp on column dimensions in construction. Even small increases, like 5 cm more in size, can significantly improve column durability and prevent future issues like compromised strength from damage or poor construction techniques.

Q & A

Why does the speaker dislike 20x20 columns?

The speaker dislikes 20x20 columns because they are prone to flexural failure (pandeo), especially as their length increases. The structural integrity of the column reduces significantly with longer lengths, leading to a much lower load resistance.

What is the resistance of a 20x20 column made from standard materials?

A 20x20 column, made from artisanal concrete and standard reinforcement (4 bars of 10mm steel), typically resists around 40 tons of load if it is relatively short.

What happens to the strength of a 20x20 column as its length increases?

As the length of a 20x20 column increases, its resistance decreases due to the effect of pandeo (buckling), which makes it more susceptible to failure under much lower loads than the standard 40 tons.

What is pandeo, and why is it a problem for 20x20 columns?

Pandeo (or buckling) is a type of failure due to excessive bending or flexure, which occurs when a column becomes too long and slender. For 20x20 columns, pandeo can cause failure under much lower loads, making them unsafe beyond certain lengths, typically above 3-4 meters.

How does the effective length of a column impact its resistance?

The effective length of a column is determined by the column's total length, including the buried part below the finished ground level. This increased length reduces the column's strength because the section that is most vulnerable to pandeo is longer.

What happens when a worker accidentally damages a 20x20 column while installing a door frame?

When a worker damages a 20x20 column by drilling or chiseling into it, the section of the column around the damage is weakened. If a significant portion is removed, the column’s strength can be reduced by half, potentially compromising the entire structure.

Why is mortar used to fill gaps in columns considered ineffective for maintaining strength?

Mortar, which is softer and less durable than concrete, does not contribute to the structural strength of the column. When used to fill gaps caused by chiseling, it reduces the column's capacity to resist loads, making the structure more prone to failure.

What are some practical recommendations for avoiding problems with 20x20 columns?

The speaker recommends not using 20x20 columns for lengths longer than 3 meters, and suggests using columns with larger dimensions (e.g., 25x25 or 20x30) for better stability. Additionally, avoiding column damage during construction and planning for potential alterations later is advised.

How does the use of wooden door frames affect the column's integrity during installation?

When wooden door frames are improperly installed, such as by nailing through the column without proper reinforcement, it can weaken the column’s structure. This creates gaps and voids that reduce the column’s strength, especially in columns as small as 20x20.

What are the issues with concrete segregation in column pouring, and how can it be avoided?

Concrete segregation occurs when the heavier aggregate separates from the cement paste during pouring, leading to inconsistent strength. This can be avoided by using proper pouring methods, ensuring the concrete fills the column uniformly without excessive drop, and vibrating the concrete to eliminate air pockets.