What are ribs & lugs in reinforcement steel bars?-Functions of ribs & lugs.

 1. What are ribs & lugs in reinforcement bars?

The embossed pattern formed over the reinforcement bars is known as ribs or lugs in the construction field.

The ribs that are in the longitudinal direction are known as longitudinal ribs or simply ribs.

The embossed pattern in the transverse direction having an angular slope is known as transverse ribs or lugs.

The angularly spaced lugs provide a good interlocking bond with surrounding materials & enhance the anchorage between the steel & concrete.

2. Why are ribs & lugs present on steel bars?

In the earlier days, plain smooth bars were used as reinforcement steel in structural members. After several years, slight deflection & cracks were observed in such structures.

After doing research on this subject, bars are introduced having ribs & lugs over their surface to overcome such defects.

Ribs & lugs provide a good bond strength with concrete & prevent the slippage of the bar from concrete.

This enhanced anchorage in turn provides a longer lifespan for the structures. They prevent cracks formed due to structural deflection & help to construct stable structures.

3. How are ribs provided to TMT bars?

When the steel rods are red hot at around 550° Celsius, they are passed through a series of rollers having slots or rib-shaped depressions machined over them. The steel rods get pressed through these slots creating embossed patterns known as ribs.

4. Why do steel bars have different types of ribs?

The geometry of the rib pattern governs the two main properties of steel bars. They are, bending capability & bond formation with concrete. 

Spiral ribs crossing over the lugs provide a good bond formation but reduce the bending capacity of the rebar.

Again, the increase in the depth of the ribs leads to a decrease in the bending ability of the bars.

So, the bars are manufactured having different rib patterns to achieve the required yield strength & design norms.

5. What is the significance of lugs & ribs on TMT bars?

◆. Anchorage:

Lugs & ribs provide a good anchorage with concrete that creates a strong bond within the structural elements.

◆. Deflection cracks:

The strong interlocking bond between the steel & concrete avoids slippage between these two materials at the time of structural deflection. This helps to reduce the deflection cracks in the structural members.

◆. Stability:

Higher bonding strength minimizes construction failures, thereby providing a stable & safe structure.

◆. Tensile strength:

Ribs & lugs enhance the load-carrying ability of the structural members. The superior bonding between the steel & concrete help to achieve good tensile strength within the structure.

◆. Life span:

 The buildings & other constructed structures will have a longer lifespan due to the enhanced reliability & stability in construction. 

 ◆. Resistance to calamity:

The danger to life & properties due to natural calamities like earthquakes, floods, earth settlements, hurricanes, etc. will be minimized. The higher withstanding ability of the structures provides good resistance to such natural disasters.

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