The replacement of conventional CTD bars by TMT bars results in saving in terms of weight and thereby cost. However, the percentage savings will depend upon the type of structural member and grade of steel.

For CTD bars, design strength is 0.85 times fy corresponding to 0.002 strain as there is no definite yield point. The design strength is further lowered by dividing it by 1.15 and 1.1; the respective factors of safety for material (steel) and eccentricity. Therefore, strength equal to 0.67 fy 0.067x415=278.05 N/sq.mm only is utilized for CTD bars in axial compression.

In case of TMT grade steel by virtue of definite yield point, design strength in axial compression is 400 N/sq. mm. This design strength further divided by factors of 1.15 and 1.1, gives a strength of 400/1.15x1.1=316.2 N/sq.mm. in place of 278.05 N/sq.mm. corresponding to CTD bars. In other words, an additional strength of 38 N/sq.mm is available if CTD bars are replaced by TMT bars. This, in turn increases the load carrying capacity of a column of the given cross-section and concrete grade with TMT bars in lieu of CTD bars.

Similarly, there are savings of steel by weight in a doubly reinforced beam, as the definite yield point in TMT bars results in saving of compressed steel as compared to CTD bars.




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