What You Need to Know About Weight Tolerance in TMT Steel Bars

In the modern construction industry, TMT steel bars are one of the most important structural elements. These materials are well known for their strength, durability, and weight tolerance capabilities.

TMT bars come in different grades, which makes them ideal for different types of construction, such as residential projects, commercial buildings, bridges, highways, and more. While the grade of TMT bars is linked to yield strength (Fe 415, Fe 500, Fe 550, and Fe 600), it is also interconnected with the weight tolerance.

So, when choosing TMT steel bars, buyers and builders should consider the weight tolerance of the material. But what is it and why is it so important? Is there any way to calculate the weight? Let’s find out:

An Overview of Weight Tolerance in TMT Bars

What is the weight tolerance for TMT steel bars?

Weight tolerance is basically the deviation between the nominal weight and the actual weight that is allowed. Generally, the tolerance should not exceed the standard set by the government authorities.

Thermo-Mechanically Treated bars play a major role in the load-bearing capacity of a structure. These bars act as reinforcement of concrete, which helps to withstand both vertical and lateral loads. Hence, the weight tolerance of TMT steel bars is very important. Not complying with the weight tolerance can end up weakening the structural integrity of the structure and increase risks.

BIS Standards for TMT Bar Weight Tolerance

During the manufacturing process, the theoretical weight of the TMT bars may vary from the actual weight. It is completely normal. The Bureau of Indian Standards (BIS) has shared a product manual for high-strength deformed steel bars also referred to as TMT bars.

The IS 1786:2008 and its annexures suggest that when comparing the mass (weight tolerance) based on size and density, the bars must lie within the permissible limit.

TMT bars are available in different diameters, from 8mm up to 50mm. While for smaller diameters a larger deviation of ±7 is allowed, as the diameter grows, the deviation becomes smaller.

It’s mostly because for thinner bars it can be difficult to maintain the accuracy. However, for larger diameter bars even a minor deviation can impact the structural load, thus requiring more precision.

How to calculate the weight of TMT bars?

The formula to calculate the theoretical weight is:

W = (D² x L )/162 (Kg/m)

Here,

D is the diameter of the bar in mm

&

L is the length of the bar in m

Here’s an example to help you understand better:

Suppose you’re buying 12 mm TMT bars that are 15 meters long. So the theoretical weight would be:

W = (D² x L )/162 (Kg/m)

Or,

W = (12² x 15)/162 = 13.33 Kg

Now, as per IS 1786, the permissible variation for a 12mm TMT bar is ±5%; hence, the tolerance is 13.33 x 5% = 0.6665 kg.

So, the actual permissible weight range is

Minimum Weight: 13.33 kg – 0.6665 kg = 12.6635 kg

Maximum Weight: 13.33 kg + 0.6665 kg = 13.9965 kg

What is the importance of weight tolerance of TMT steel bars?

During a construction project, engineers and contractors generally recommend certain TMT steel bars based on their thickness. Choosing the right size TMT bars is essential to increase the structural strength of the project. Structures like bridges, dams, or skyscrapers need to withstand high loads. If the foundation is not strengthened, these structures may end up collapsing.

A lower weight tolerance means higher accuracy during the manufacturing process, which can be beneficial. For example:

• Builders must adhere to regulatory requirements mentioned by BIS during construction. One of them being, the weight tolerance of the TMT bars. If the difference between the theoretical and real weight is more than the mentioned amount, then it can affect the build’s integrity.
• TMT steel bars are generally charged based on their weight, grade, size, and market demand. So, if the weight deviation is higher, it can lead to a discrepancy in the financial statement. Though a little deviation may not seem much, when purchasing in bulk, the price difference can be significant.

Wrap Up

TMT steel bars are the foundation of structural integrity. These bars are especially designed to endure earthquakes, fire hazards and don’t get rust easily. There are several unique properties that have made them a popular choice for builders of modern-day construction. However, when purchasing the bars, it is also important to check the weight tolerance of the TMT bars. If you are a first-time buyer, consult with an engineer or an expert to make the right decision.