Dimensions and member. The concrete member is square or rectangular; only the stirrup is triangular. Enter overall concrete width W and depth D. For cover c to the stirrup’s outside envelope: X = W − 2c and Y = D − 2c. The apex is centred, so each equal sloping side S = √[(X/2)² + Y²]. Outside perimeter P = X + 2S. Cover is measured from the four concrete faces; no triangular concrete section or inradius offset is used. If drawing dimensions already specify the stirrup’s outside X/Y, add twice the cover to obtain the overall member inputs.

Adopted practical triangular length. L = outside triangular perimeter P + 2T − 12d. The reference convention uses four nominal 135° allowances: two bottom corner allowances and two hook allowances, each 3d. The apex closure has four bends total. The bottom corner turn angles are 180° minus the corresponding interior angles; they are not universally 135°. The fixed 12d deduction is an explicitly adopted practical estimating convention, not a verified exact IS triangular fabrication equation.

Fixed seismic preset. T = max(8d,75 mm) is the straight extension beyond each end curve. Actual inward hook orientation and anchorage require the approved BBS. No separate inside bend diameter is entered for this practical convention; actual bend radius is checked during fabrication, not inferred by this calculator.

Hook and bend basis. IS 2502:1963 clause 3.8 addresses at least 8d straight extension for stirrups/links. The retained IS 13920:2016 preset adopts max(8d,75 mm). The 3d allowances come from the adopted practical reference, not an IS-published deduction table. Do not add Table VIII allowances or separate developed bend arcs to this method. IS 2502 / IS 13920 — code book downloads

Scheduling & quantities. IS 2502:1963 clause 5.1.1 specifies the next greater whole 25 mm of the bending dimensions and allowances, not nearest-25 rounding. Scheduled length = ceil(calculated length ÷ 25) × 25; an exact multiple is unchanged. Table XI cutting tolerance is separate. Quantities and weights use this scheduled length. Wastage does not change the stirrup’s cutting length or count.

Display units. Lengths show mm, inches and feet, with the selected member unit first. Whole-unit display rounds fractions greater than .500 upward and exactly .500 downward. Feet use construction notation such as 5’2″ ft. Display rounding never changes the underlying geometry, cutting schedule or steel weight; calculation substitutions retain precision in mm.

Nominal mass. Standard diameters use IS 1786:2008 Table 1 masses: 6 mm = 0.222, 8 mm = 0.395, 10 mm = 0.617, 12 mm = 0.888, 16 mm = 1.58 kg/m. Other supported standard sizes use the same table. Nonstandard custom diameters use πd²/4 × 0.00785 kg/m, assuming steel density 7,850 kg/m³.

Scope. This estimate covers a triangular link with a centred apex in a square or rectangular concrete member, two lower corners and two hooked ends at the apex. It checks positive covered base/height and bar-thickness fit. It does not check bend-radius fit, tail clearance, longitudinal-bar engagement, structural confinement or additional closure overlap. Verify the approved BBS and a trial stirrup before batch cutting.

IS code books used in civil engineering — PDF downloads