IS 2502:1963 Bar Bending Basics: Formulas, Hook Allowances & Bend Deductions

## Introduction to IS 2502:1963 In Indian civil construction, the **Code of Practice for Bending and Fixing of Bars for Concrete Reinforcement (IS 2502:1963)** defines the standard methods for drafting Bar Bending Schedules (BBS) and determining accurate rebar cutting lengths. Accuracy in bar bending is critical: an error of even 20 mm on high-diameter steel (e.g., 25 mm or 32 mm) multiplied over thousands of beam and column bars causes severe rebar congestion, incorrect cover thickness, or massive steel wastage on site. --- ## 1. Rebar Unit Weight Formula ($D^2 / 162.28$) Standard thermo-mechanically treated (TMT) rebars conforming to **IS 1786:2008** (Fe 415, Fe 500, Fe 500D, Fe 550D) have a nominal density of $7,850 \text{ kg/m}^3$. The weight per linear meter is calculated using: $$W = \frac{D^2}{162.28} \text{ kg/m}$$ Where $D$ is the nominal bar diameter in millimeters. ### Standard Nominal Weights: - **8 mm:** $0.395 \text{ kg/m}$ - **10 mm:** $0.617 \text{ kg/m}$ - **12 mm:** $0.888 \text{ kg/m}$ - **16 mm:** $1.578 \text{ kg/m}$ - **20 mm:** $2.465 \text{ kg/m}$ - **25 mm:** $3.853 \text{ kg/m}$ - **32 mm:** $6.313 \text{ kg/m}$ --- ## 2. Standard Bend Deductions per IS 2502 When steel rebar is bent around a mandrel on a bar bending machine, the steel on the outer radius stretches. If a draftsman simply adds straight segment dimensions without deducting for steel elongation at bends, the fabricated bar will be significantly longer than designed. Per **IS 2502 Clause 4.3**, standard deductions are: - **$45^\circ$ Bend:** Deduct $1 \times d$ - **$90^\circ$ Bend:** Deduct $2 \times d$ - **$135^\circ$ Bend:** Deduct $3 \times d$ - **$180^\circ$ U-Hook:** Deduct $4 \times d$ *(Where $d$ is the nominal bar diameter).* --- ## 3. Hook Allowances for Stirrups & Ties (IS 13920 & IS 2502) For ductile detailing under earthquake conditions (IS 13920:2016), open $90^\circ$ stirrups are strictly prohibited in beams and columns. Stirrups must terminate in **$135^\circ$ seismic hooks**. - **$135^\circ$ Stirrup Hook Extension:** Minimum $9 \times d$ or $75 \text{ mm}$, whichever is greater. - **$180^\circ$ Standard Hook:** Hook length $= 9 \times d + \text{bend length}$. --- ## 4. Lap Length Guidelines (IS 456:2000 Clause 26.2.5.1) Where continuous bars exceed commercial rolling lengths (typically 12 meters): - In direct tension: Lap length $\ge 50 \times d$ or development length $L_d$. - In compression: Lap length $\ge 24 \times d$. - Staggering: No more than 50% of bars should be lapped at any single cross-section. --- ## Conclusion Automating these deterministic formulas eliminates manual clerical errors on construction sites. Infrava uses this exact mathematical model to convert CAD drawings directly into audit-ready schedules.