Steel Resources

Beam Reinforcement Guide

Comprehensive guide to reinforcement detailing for RCC beams — tension and compression bars, minimum and maximum steel percentages, stirrup spacing and bent-up bar rules, clear cover requirements, IS 456:2000 and SP 34 clauses, worked examples, and a bar bending schedule walkthrough.

Last updated: June 22, 2026

Beam reinforcement is the most detailed aspect of residential RCC construction. A beam carries bending moment, shear force, and in seismic zones, cyclic reversed loading — each requiring a specific reinforcement arrangement governed by IS 456:2000, SP 34, and IS 13920:2016. Getting the bar sizes, spacing, cover, and hook details right determines whether the beam performs as designed or fails prematurely.

This guide explains every component of beam reinforcement — main tension and compression bars, stirrups, hanger bars, side face steel — with the IS code rules, worked examples, and the five detailing mistakes most commonly found on Indian residential construction sites.

Components of Beam Reinforcement

An RCC beam contains several reinforcement components, each serving a specific structural purpose. Understanding what each component does explains why the detailing rules in IS 456 and SP 34 are what they are.

Component	Location	Structural Function	Governing Clause
Main tension bars	Bottom zone	Carry the tensile force from bending moment	IS 456:2000 Cl. 26.5.1.1
Compression bars	Top zone (doubly reinforced beams)	Supplement concrete compressive capacity where depth is limited	IS 456:2000 Cl. 26.5.1.2
Hanger bars	Top zone (throughout length)	Hold stirrups; carry construction loads and minor hogging moments	SP 34 — minimum 2 bars
Stirrups (links)	Vertical loops at regular spacing	Carry shear force; confine concrete; prevent bar buckling	IS 456:2000 Cl. 26.5.1.5
Bent-up bars	Bottom bars cranked at ~45° near supports	Supplement shear resistance; provide top steel at supports	IS 456:2000 Cl. 40.4
Side face reinforcement	Side faces of deep beams (D > 750mm)	Control cracking in deep beam webs	IS 456:2000 Cl. 26.5.1.3

Simply Supported Beam

Maximum bending moment at mid-span → maximum bottom steel at centre
Zero moment at supports → bottom bars can be curtailed near supports
Maximum shear at supports → closely spaced stirrups near both ends
2 hanger bars at top throughout — hold stirrups and carry erection loads

Continuous Beam

Hogging (negative) moment at supports → top steel at supports
Sagging (positive) moment at mid-span → bottom steel at mid-span
High shear at supports → close stirrups; lighter at mid-span
Both top and bottom steel run through supports for moment redistribution

Effective Depth — The Critical Design Dimension

All beam design calculations use effective depth (d), not overall depth (D). Effective depth is measured from the extreme compression fibre (top face for a simply supported beam) to the centroid of the tension reinforcement at the bottom.

Effective Depth Formula:

d = D − clear cover − stirrup diameter − (main bar diameter ÷ 2)

Example: 450mm deep beam, 25mm cover, 8mm stirrups, 20mm main bars:

d = 450 − 25 − 8 − 10 = 407mm

For two layers of bars (add 25mm for bar + gap):

d = 450 − 25 − 8 − 20 − 12.5 = 384mm

Beam Size (b×D)	Breadth (mm)	Overall Depth (mm)	Typical Eff. Depth (mm)	Common Application
230 × 300	230	300	~250	Secondary/loft beams, short spans ≤ 3m
230 × 375	230	375	~320	Standard residential beam, spans 3–4m
230 × 450	230	450	~407	Most common residential beam, spans 4–5m
230 × 525	230	525	~482	Longer residential spans, 5–6m
230 × 600	230	600	~550	Heavy loads or spans 5–7m
300 × 600	300	600	~550	Commercial buildings, long spans
300 × 750	300	750	~690	Deep beams, transfer beams, large spans

When bars are placed in two layers (due to congestion), the effective depth is further reduced by the bar diameter plus the minimum 25mm gap between layers. Always recalculate d if two layers are needed — using the single-layer d value for a two-layer arrangement under-estimates the depth and over-estimates the moment capacity.

Main Reinforcement — Tension and Compression Bars

Minimum Steel — IS 456:2000 Clause 26.5.1.1

The minimum tension reinforcement prevents brittle failure at first cracking. Below this minimum, a beam cracks and collapses simultaneously — with no deflection warning. The formula is: A_s,min = (0.85 × b × d) ÷ f_y

Steel Grade	fy (N/mm²)	Min Steel %	Example (230×450mm, d=407mm)
Fe 250 (Mild Steel)	250	0.34%	For 230×450mm beam: 355 mm²
Fe 415 (HYSD)	415	0.205%	For 230×450mm beam: 213 mm²
Fe 500 (TMT)	500	0.17%	For 230×450mm beam: 176 mm²
Fe 550 (TMT)	550	0.155%	For 230×450mm beam: 161 mm²

Main Bar Size Reference

Bar Diameter	Cross-Sectional Area (mm²)	Typical Beam Application
10mm	78.5	Light secondary beams, lintels, nominal steel only
12mm	113.1	Secondary beams, short spans, distribution — minimum practical for main bars
16mm	201.1	Standard primary beams in residential construction
20mm	314.2	Most common main bar for residential primary beams
25mm	490.9	Heavy residential or light commercial beams — longer spans
28mm	615.8	Commercial beams with significant span or load
32mm	804.2	Long-span or heavily loaded commercial beams

The maximum steel percentage per IS 456:2000 Clause 26.5.1.1 is 4% of gross cross-sectional area for both tension and compression zones combined. Exceeding this limit makes the beam over-reinforced — concrete crushes before steel yields, giving no deflection warning before failure. In practice, keep steel ratio below 2.5% to allow adequate concrete placement around bars.

Bar Arrangement Rules

Rule	Requirement	IS Reference
Minimum clear distance between bars	Max of: bar diameter, 1.25× max aggregate size, 25mm	IS 456:2000 Cl. 26.3.1
Maximum bars in one layer	Limited by clear distance requirement above	SP 34
Minimum bars in beam (bottom)	2 bars (to provide symmetry and hold stirrups)	IS 456:2000 + SP 34
Minimum bars at top (hanger bars)	2 bars throughout span	SP 34 standard practice
Side face reinforcement (D > 750mm)	0.1% of web area, spaced ≤ 300mm each face	IS 456:2000 Cl. 26.5.1.3
Maximum curtailment beyond theoretical point	Extend bar by ≥ effective depth (d) beyond theory	IS 456:2000 Cl. 26.2.3

Stirrups — Shear Reinforcement

Stirrups carry the shear force that concrete alone cannot resist. They also confine the concrete core, prevent main bars from buckling outward, and tie the reinforcement cage together for handling and placement. Stirrup diameter is typically 6mm, 8mm, or 10mm; 8mm is the most common for standard residential beams.

Rule	Requirement	IS Reference
Maximum stirrup spacing — general zone	Least of: 0.75d or 300mm	IS 456:2000 Cl. 26.5.1.6
Maximum stirrup spacing — high shear zone	Least of: 0.5d or 200mm	IS 456:2000 Cl. 26.5.1.6
Stirrup spacing near supports (seismic — IS 13920)	d/4 for 2d from face of support; then 0.5d max	IS 13920:2016 Cl. 6.3.5
Minimum stirrup spacing	≥ maximum aggregate size + 5mm (concrete placement constraint)	IS 456 Cl. 26.3.2
Maximum stirrup spacing — deep beams (D > 750mm)	Side face bars at 300mm max; separate shear design	IS 456:2000 Cl. 26.5.1.3
Stirrup spacing at first bar from support	50mm from face of support (standard practice)	SP 34 detailing practice

The maximum stirrup spacing of 0.75d or 300mm is the upper limit for the general zone. Near supports where shear is high, spacing must be reduced based on the shear design — 0.75d may still be too wide if the applied shear exceeds the concrete shear capacity. Never use the maximum spacing throughout — always check the shear design for each zone.

Clear Cover Requirements — IS 456:2000

Clear cover is measured to the outer surface of the stirrup. The main bars sit inside the stirrups, so the actual cover to the main bars is cover + stirrup diameter. Cover protects reinforcement from corrosion, fire, and provides bond length. IS 456:2000 Table 16 specifies nominal cover by exposure condition.

Exposure Condition	Nominal Cover — Beams (mm)	Nominal Cover — Slabs (mm)	Nominal Cover — Columns (mm)
Mild (inside buildings, away from moisture)	20mm	25mm	25mm
Moderate (sheltered outdoor, humid interiors)	30mm	30mm	35mm
Severe (alternate wet/dry, coastal ≤ 50km)	45mm	45mm	50mm
Very Severe (coastal < 1km, chemical exposure)	50mm	50mm	55mm
Extreme (tidal, splash zone, aggressive ground)	75mm	75mm	75mm

Nominal cover includes construction tolerance. IS 456:2000 Clause 26.4.1 states that the tolerance on cover is ±10mm for members with d ≤ 200mm and ±15mm for members with d > 200mm. In practice, use concrete cover blocks (spacers) of the correct thickness at 600–800mm spacing to maintain cover during concrete placement.

Cover is measured to the outer face of the stirrup — not to the main bars. A 25mm cover to stirrup + 8mm stirrup = 33mm from the beam face to the centre of the main bar. Many site teams measure cover to the main bar face, under-specifying the actual cover to the stirrup and creating a corrosion risk on the outermost steel.

Seismic Detailing — IS 13920:2016

Buildings in seismic zones II through V (which covers most of India, including Hyderabad in Zone II and parts of Telangana in Zone III) must follow IS 13920:2016 ductile detailing requirements for RCC beams. These requirements are additional to IS 456:2000 — not a substitute.

Requirement	Rule	IS 13920:2016 Clause
Minimum top steel at any section	≥ 25% of maximum bottom steel anywhere in span	IS 13920:2016 Cl. 6.2.3
Minimum bottom steel at face of support	≥ 50% of top steel at face of support	IS 13920:2016 Cl. 6.2.3
Hoop (stirrup) spacing in plastic hinge zone	d/4 or 8× smallest bar diameter or 100mm (min)	IS 13920:2016 Cl. 6.3.5
Plastic hinge zone length	2× beam depth (2d) from face of support	IS 13920:2016 Cl. 6.3.5
Stirrup hook angle in seismic zones	135° hooks; not 90°	IS 13920:2016 Cl. 6.3.1
Maximum stirrup spacing outside hinge zone	d/2 throughout	IS 13920:2016 Cl. 6.3.5
Longitudinal bar splices	Not in plastic hinge zone (within 2d of support)	IS 13920:2016 Cl. 6.4

IS 13920 applies to all buildings in seismic zones II–V per IS 1893:2016 (Part 1), which is most of India. Hyderabad falls in Zone II — IS 13920 detailing applies. 135° hooks and hoop zones are not optional enhancements; they are code requirements. Non-compliance creates liability for the structural engineer and builder.

Worked Examples

Two complete examples showing how the IS 456 and IS 13920 rules translate into an actual reinforcement arrangement.

Example 1 — Simply Supported Residential Beam (4.5m Span)

India — Seismic Zone II

A 230mm × 450mm simply supported RCC beam spanning 4.5m (centre-to-centre of supports), supporting a 150mm slab with live load 3 kN/m². Concrete M20, steel Fe 500 TMT. Non-seismic zone.

Step	Formula / Value	Result
Effective depth	450 − 25 (cover) − 8 (stirrup) − 10 (half bar)	407mm
Minimum tension steel (Fe 500)	0.85 × 230 × 407 ÷ 500	159 mm² — minimum
Design moment (approximate)	From structural calculation	~85 kN·m (typical)
Area of steel required (typical design)	From design: ~3–4 nos. 20mm bars	~942–1257 mm²
Steel provided (3T20)	3 × 314.2	943 mm²
Hanger bars (top)	2T12 throughout	226 mm²
Stirrups — max spacing (0.75d)	0.75 × 407 = 305 → use 300mm	R8@300 in mid-zone
Stirrups — near support (0.5d)	0.5 × 407 = 203 → use 200mm	R8@200 for 1m from support

This is a structural illustration, not a design output — actual bar sizes and spacing must come from a structural engineer's design for the specific loading and span. Always verify minimum and maximum steel limits before finalising the reinforcement.

Example 2 — Continuous Beam at First Floor (Seismic Zone III)

India — Seismic Zone III

A 230mm × 500mm continuous beam, end span 5m, IS 13920 ductile detailing applies. Concrete M25, Fe 500 TMT.

Step	Formula / Value	Result
Effective depth	500 − 25 − 8 − 10	457mm
Bottom steel at mid-span (from design)	4T20 = 1257 mm²	1.09% steel ratio
Top steel at support (from design)	4T20 = 1257 mm² (or as designed)	Must be ≥ bottom steel per IS 13920
Min bottom steel at support face (IS 13920)	≥ 50% of top steel at support = 628 mm²	2T20 minimum at support
Hoop zone length from support	2d = 2 × 457 = 914mm → use 1000mm	1m each side of support
Stirrup spacing in hoop zone	d/4 = 114mm → use R8@100	R8@100 for 1m from support
Stirrup spacing outside hoop zone	d/2 = 228mm → use R8@200	R8@200 for rest of span
Stirrup hooks	135° hooks required	Standard 135° bend at both ends

IS 13920:2016 seismic detailing requires 135° hooks on stirrups (not 90°), tighter spacing in the plastic hinge zone (2d from support), and minimum top and bottom steel at every section. These requirements often govern over standard IS 456 design in seismic zones III, IV, and V.

Common Mistakes

Using Overall Depth Instead of Effective Depth in Design

The single most common beam reinforcement error. Structural calculations use effective depth (d), not overall depth (D). Effective depth is approximately D minus 40–50mm (cover + stirrup + half bar diameter). A beam designed at D = 450mm but intended to work at d = 407mm will be over-reinforced when d is used correctly — the bars will be placed lower than the assumed centroid. Always calculate d from the actual cover, stirrup size, and main bar size, and use d in all moment capacity and spacing calculations.

Placing 90° Stirrup Hooks in Seismic Zones

IS 13920:2016 explicitly requires 135° hooks on stirrups in beams in seismic zones II through V. A 90° hook opens under earthquake loading, releasing the stirrup grip on the main bars and causing sudden shear failure. On residential sites, 90° hooks are common because they are easier to form — but they are non-compliant in seismic zones. Inspect stirrup hook angles before concreting, not after. 135° hooks require an additional straight extension of 10 bar diameters beyond the hook bend.

Ignoring Minimum Clear Distance Between Bars

IS 456:2000 Clause 26.3.1 requires minimum clear distance between parallel bars to be the maximum of: the bar diameter, 1.25× the maximum aggregate size, or 25mm. For 20mm bars with 20mm aggregate, this means 25mm minimum clear gap between bars. Placing 4 bars of 20mm in a 230mm beam with 25mm cover each side and 8mm stirrups leaves: 230 − 50 (cover both sides) − 16 (stirrups both sides) − 80 (4 bars) = 84mm for 3 gaps — 28mm per gap. This passes for 20mm aggregate but is tight. Site teams often crowd bars together without this check, producing concrete voids around congested reinforcement.

Stopping Top Bars at the Support Face

Top bars in continuous beams carry negative bending moment that extends beyond the face of the support into the span. IS 456:2000 Clause 26.2.3 requires bars to be extended beyond the theoretical cut-off point by at least the effective depth (d) or 12 bar diameters, whichever is greater. Stopping top bars exactly at the support face leaves the beam unprotected against negative moment in the adjacent span and creates a weak zone at the beam-column junction — the most critical location in an earthquake-resistant frame.

Incorrect Stirrup Spacing Transition Without Marking

Many beam reinforcement schemes have two stirrup zones — close spacing near supports, wider spacing at mid-span. If the transition point is not clearly marked on the reinforcement cage before placing, the bar fixer may continue close-spaced stirrups throughout (wasting steel) or switch to wide spacing too early (leaving a high-shear zone under-reinforced). Mark the transition point on the bottom bars with paint or chalk before the cage is placed in the formwork.

Relevant Standards

Standard	Coverage
IS 456:2000	Plain and Reinforced Concrete — Sections 25 and 26 govern beam design, reinforcement limits, clear cover, stirrup spacing, side face reinforcement, and curtailment rules
IS 13920:2016	Ductile Detailing of Reinforced Concrete Structures — governs beam reinforcement in seismic zones: minimum top and bottom steel, hoop zone length, stirrup hook angles, and splice restrictions
SP 34:1987 (BIS)	Handbook on Concrete Reinforcement and Detailing — the primary practical detailing reference; provides standard drawings for beam-column junctions, curtailment, and stirrup arrangements
IS 1786:2008	High Strength Deformed Steel Bars and Wires — specification for Fe 415, Fe 500, Fe 550, and Fe 600 TMT bars; defines yield strength values used in minimum steel calculations
IS 875 (All Parts)	Code of Practice for Design Loads — governs the applied loads used in beam design calculations from which reinforcement requirements are derived
IS 2502:1963	Code of Practice for Bending and Fixing of Bars for Concrete Reinforcement — defines standard bend radii and hook lengths for stirrups and bent-up bars

Final Verdict

Beam reinforcement combines structural design (how much steel) with detailing (how it is arranged, spaced, and terminated). Both must be correct — the right quantity of steel placed incorrectly or without adequate cover is as unsafe as too little steel. The IS 456 and IS 13920 rules exist because each failure mode they address has caused real structural collapses.

Always use effective depth (d), not overall depth (D), in design and spacing calculations.
Verify minimum steel (IS 456 Cl. 26.5.1.1) and maximum steel (4% gross area) before finalising bar sizes.
Maintain minimum clear distance between bars — (bar diameter, 1.25× max aggregate size, 25mm) — to ensure concrete can flow between bars.
Measure clear cover to the outer face of the stirrup, and use concrete cover blocks at 600–800mm spacing to maintain cover during concreting.
In seismic zones, use 135° stirrup hooks, provide hoop zones (d/4 spacing) for 2d from support faces, and do not splice bars in the hoop zone.
Check the shear design to confirm stirrup spacing in the high-shear zone near supports — do not apply the maximum allowable spacing without checking the shear demand.

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Related calculators

Use these calculators when you need to turn this reference information into project quantities:

Beam Steel Calculator
Calculate main bars, stirrups, and total steel weight for RCC beams per IS 456:2000 and SP 34.
Slab Steel Calculator
Calculate main bars, distribution bars, and total steel for RCC slabs — one-way and two-way.
Column Steel Calculator
Estimate longitudinal bars, lateral ties, and total steel weight for RCC columns.
Footing Steel Calculator
Calculate reinforcement for isolated and combined footings with bar bending schedule output.
Concrete Calculator
Estimate total concrete volume and material quantities for slabs, beams, columns, and footings.

Related resources

Development Length Guide
Complete development length (Ld) reference for RCC construction per IS 456:2000 Table 65. Covers all bar diameters, steel grades (Fe 415, Fe 500, Fe 550), and concrete grades (M15 to M40) — with worked examples for beams, slabs, columns, and footings, plus anchorage, lap splice, and hook equivalence rules.
TMT Bar Weight Chart
Complete TMT bar weight chart for all standard diameters 6mm to 40mm per IS 1786:2008. Covers unit weight (kg/m), weight per 12m rod, total weight formulae, bundle quantities, bar bending schedule calculations, and IS 1786 mass tolerance limits.
RCC Slab Thickness Guide
Understand common RCC slab thickness values for residential rooms, roof slabs, larger spans, commercial floors, and industrial applications, including span guidance, standards, concrete volume, cover, reinforcement, and curing.
Concrete Cover Guide
Understand concrete cover thickness for RCC slabs, beams, columns, footings, water tanks, retaining walls, cover blocks, corrosion protection, fire resistance, and common site mistakes.
M20 Concrete Guide
Understand M20 concrete, including 20 MPa strength, 1:1.5:3 nominal mix ratio, common RCC applications, standards, curing, compaction, mistakes, and site checklist.
Concrete Mix Ratios Explained
Understand concrete mix ratios such as 1:2:4, 1:1.5:3, 1:3:6, 1:4:8, and 1:5:10, including grades, uses, water-cement ratio, curing, and cost.

FAQ

IS 456:2000 Clause 26.5.1.1 specifies that the minimum area of tension reinforcement in a beam must not be less than (0.85 × b × d) ÷ fy, where b is the breadth of the beam in mm, d is the effective depth in mm, and fy is the yield strength of the steel in N/mm². For Fe 500 TMT bars (fy = 500 N/mm²), this works out to approximately 0.17% of the gross cross-sectional area. For Fe 415, it is approximately 0.205%. This minimum prevents sudden brittle failure at first cracking — without minimum steel, a beam would crack and fail simultaneously with no warning. In practice, beam design almost always requires more steel than the minimum to carry the design bending moment.

IS 456:2000 Clause 26.5.1.1 limits the maximum area of tension and compression reinforcement in beams to 4% of the gross cross-sectional area. For a 230mm × 450mm beam, gross area is 103,500 mm² and maximum steel is 4,140 mm² — approximately 4 bars of 32mm or 6 bars of 28mm. Exceeding 4% makes the section over-reinforced, meaning concrete crushes before steel yields — a sudden brittle failure mode with no warning deflection. It also makes concrete placement extremely difficult with congested bars. In practice, beam steel ratios above 2.5–3% are unusual on standard residential projects and signal that the beam size is too small for the applied load.

IS 456:2000 Clause 26.5.1.6 requires that the maximum spacing of stirrups (shear reinforcement) must not exceed the least of: (a) 0.75 × effective depth (d) for vertical stirrups, (b) 300mm, and (c) the spacing calculated from the shear design. The minimum practical stirrup spacing is determined by concrete placement — stirrups cannot be closer than the maximum aggregate size plus 5mm bar clearance, which typically means a minimum spacing of about 75mm on site. In zones of high shear (near supports), stirrup spacing is typically d/4 to d/3. Near mid-span where shear is low, stirrups are spaced at 0.75d or 300mm — whichever is less.

IS 456:2000 Clause 26.4.1 and Table 16 specify nominal cover to reinforcement based on exposure condition. For mild exposure (most protected interior beams), the nominal cover is 20mm. For moderate exposure (exterior beams, near-coast areas), it is 30mm. For severe exposure (direct weather, marine environment), it is 45mm. For very severe and extreme exposure, 50mm and 75mm respectively. In practice, most Indian residential beams use 25mm clear cover as a practical default that exceeds the mild exposure requirement and provides a margin for construction tolerance. Clear cover is measured to the outer surface of the stirrup, not to the main bars — the main bars sit inside the stirrups.

IS 456:2000 and SP 34 require at least 2 bars at the top of a simply supported beam — these act as hanger bars to hold the stirrups in position and carry any negative moment at the supports. For a continuous beam, the top bars at the support carry the hogging (negative) bending moment and are sized by structural design — typically 50–100% of the bottom steel area at mid-span. The number and size of top bars depends on the moment demand. At minimum, 2 bars of 12mm or the same size as the bottom bars (whichever is larger) are placed at the top throughout the beam length. In earthquake-resistant design (IS 13920), top and bottom reinforcement at any section must not be less than one-quarter of the larger amount at either end.

A singly reinforced beam has steel only in the tension zone (bottom face for a simply supported beam). A doubly reinforced beam has steel in both tension and compression zones. Doubly reinforced beams are used when the beam depth is limited and the section cannot carry the full bending moment with tension steel alone — the compression steel supplements the concrete's compressive capacity. Doubly reinforced sections are also required by IS 13920 for earthquake-resistant ductile detailing, where minimum compression steel is specified regardless of structural need. The compression steel in a doubly reinforced beam must be laterally tied with links to prevent it from buckling outward under load — the same requirement as column longitudinal bars.

Bent-up bars are bottom tension bars that are cranked (bent) at an angle (usually 45°) near the supports and continued into the top of the beam. They serve dual purpose: they contribute to shear resistance in the inclined zone near the support, and they provide top steel at the support to carry negative bending moment in continuous beams. IS 456:2000 Clause 40.4 permits bent-up bars as part of the shear reinforcement design, but they must be used alongside stirrups — they cannot replace stirrups entirely. In modern ductile detailing practice (IS 13920 for seismic zones), bent-up bars are generally avoided because they create congestion and are difficult to inspect. Straight bars with separate top steel and vertical stirrups are preferred.

Effective depth (d) is the distance from the extreme compression fibre to the centroid of the tension reinforcement. For a simply supported beam, the extreme compression fibre is the top face and the tension reinforcement centroid is in the bottom zone. The formula is: d = D − clear cover − stirrup diameter − (main bar diameter ÷ 2), where D is the overall depth. Example: for a 450mm deep beam with 25mm clear cover, 8mm stirrups, and 20mm main bars: d = 450 − 25 − 8 − 10 = 407mm. The effective depth is what the structural design calculation uses — not the overall depth D. Using D instead of d in design calculations over-estimates the moment capacity, leading to under-reinforced sections.