Shear Wall Design
Boundary element check · shear design · P–M interaction · shear friction ACI 318-25 · EN 1992/1998 · IS 456/13920 · TSC 2018
Input Parameters
SI · mm kN MPa📚 Design Background — ACI 318-25 §18.10.6
ACI 318-25 §18.10.6.2 — Boundary Zone Trigger
Special boundary zones are required at the ends of special structural walls when the extreme fiber compressive stress under factored axial and flexural demands exceeds:
Ag = lw·bw, Ig = bw·lw³/12 (gross uncracked section). This elastic stress check is intentionally conservative — it triggers confinement when extreme-fiber crushing is plausible under the maximum credible demand, not when it is certain. The 0.2f'c threshold corresponds roughly to the onset of significant nonlinear compressive strain in the concrete.
When σmax ≤ 0.2f'c, no special boundary zones are required; however, minimum longitudinal and transverse reinforcement per §18.10.6.5 still applies across the full wall length. Both Pu and Mu correspond to the governing seismic load combination (LRFD E-combination with 1.0E) — not gravity alone.
Neutral Axis Depth & Required Zone Length — §18.10.6.4
The depth of the compression zone at the base cross-section determines how much of the wall end must be confined (displacement-based approach):
ρv is the uniformly distributed vertical web reinforcement ratio. The zone must encompass the portion of the compression block beyond the code-permitted extreme strain limit, with a minimum equal to the wall thickness:
For SDC A/B/C: lbe ≥ 200 mm. The boundary zone must extend vertically over the critical height hcr = max(lw, Hw/6) from the base and must be fully developed over the entire plastic hinge length.
Confinement Hoop Reinforcement — §18.7.5.4 via §18.10.6.4
Two conditions govern; the larger Ash requirement controls in each direction:
Ag,be = lbe·bw (gross zone area); Ach = (lbe−2cc)·(bw−2cc) (confined core area); bc = bw−2cc (core width in the direction checked). The (Ag/Ach−1) term rewards smaller cover — thicker cover demands more confinement steel.
Maximum hoop spacing — so depends on the lateral support spacing hx of longitudinal bars:
hx is the maximum centre-to-centre spacing of laterally restrained longitudinal bars around the perimeter of the confined zone. Adding intermediate cross-ties reduces hx and allows wider hoop spacing.
Input Parameters
SI · mm kN MPa📚 Design Background — EN 1998-1 §5.4.3.4 / §5.5.3.4
EN 1998-1 §5.4.3.4 / §5.5.3.4 — Boundary Zone Trigger
Confined boundary zones are required at wall ends when the normalised axial force exceeds the ductility-class-dependent threshold:
fcd = fck/γc = fck/1.5. A high axial ratio compresses the plastic hinge region, reducing maximum achievable curvature — confinement extends the usable compressive strain to maintain target curvature ductility factor μφ.
Length of confined end region (§5.5.3.4(3)):
The 1.5bw floor prevents overly narrow zones in thick walls. For DCL, only nominal detailing applies — no boundary zone calculation is required regardless of νd.
Critical Zone Height — EN 1998-1 §5.4.3.4(2)
Confined boundary zones are required only within this height from the wall base, where inelastic deformations concentrate:
The max(lw, Hw/6) floor ensures even short walls are confined over at least one wall length — the extent of the anticipated plastic hinge. The 2lw ceiling prevents unreasonably tall critical zones in very slender walls.
Above hcr, minimum web reinforcement (§5.4.3.2.2) and minimum boundary reinforcement per §5.4.3.2.2(3) still apply, but the confinement hoop calculation no longer governs.
Mechanical Volumetric Ratio — EN 1998-1 §5.5.3.4(4)
Required confinement intensity derived from the target curvature ductility and the axial demand. Two bounds apply; the larger governs:
εsy,d = fyk/(γs·Es) ≈ 0.00217 for fyk=500 MPa. bc/bo is the ratio of gross to confined boundary width — larger cover demands higher ωwd. The 0.12 floor ensures minimum confinement regardless of axial level.
Required hoop area per unit height (one direction at a time):
Ach = lc·bw; bc = bw−2cc. Max hoop spacing s ≤ min(bo/3, 125 mm, 6db,long) per §5.4.3.2.2(8).
Input Parameters
SI · mm kN MPa📚 Design Background — IS 13920:2016 §9.4
IS 13920:2016 §9.4.1 — Boundary Zone Trigger
Boundary zones are required at wall ends when the extreme fiber compressive stress under factored combined axial and flexural load exceeds the threshold (identical to ACI 318):
Ag = lw·bw, Ig = bw·lw³/12 (gross uncracked section). fck is the characteristic cylinder compressive strength. The elastic stress check is conservative — it triggers confinement when compressive fiber crushing becomes plausible under maximum demand.
Minimum boundary zone length (§9.4.2):
tw = bw is the wall thickness. Even when the trigger is not met, minimum reinforcement at wall ends per IS 13920 §9.3.1 still applies.
Confinement Reinforcement — IS 13920:2016 §9.4.4
Applied independently in each orthogonal direction. The (Ag/Ach−1) term accounts for the passive confining pressure needed when the cover spalls:
Ag,be = lbe·bw; Ach = (lbe−2cc)·(bw−2cc); bc = core dimension checked. Smaller cover and more closely spaced cross-ties reduce the (Ag/Ach−1) demand.
Maximum hoop spacing (§9.4.4):
Hoops must be closed with 135° seismic hooks. Where bw ≤ 200 mm, U-bars with cross-ties are acceptable per §9.4.5. The boundary zone must extend vertically over the full critical height per IS 13920 §9.4.3.
Input Parameters
SI · mm kN MPa📚 Design Background — TSC 2018 §7.6.6
TSC 2018 §7.6.6.1 — Unconditional Boundary Zone Requirement
Confined end zones are unconditionally required at both ends of every structural wall, regardless of axial load level. No stress or axial ratio trigger applies — a fundamental difference from ACI and IS, and a key reason why TSC-designed walls consistently achieve higher ductility.
Required length depends on position relative to the critical zone height hcr:
The significantly larger lbe within hcr (up to lw/5) reflects the high inelastic demand in the anticipated plastic hinge region. The boundary zone must be detailed consistently from foundation to hcr without interruption at floor levels.
TSC 2018 §7.6.5.2(b) — Confinement Volumetric Ratio
Wall boundary zone confinement is governed by a single minimum volumetric ratio. Unlike columns, the (Ag/Ach−1) term is explicitly excluded for walls:
Required hoop area in each orthogonal direction (bc = confined core width in direction checked). Hoop spacing limits (§7.6.5.2):
TSC requires at least one intermediate cross-tie when bw > 300 mm. Every longitudinal bar must be restrained at a corner of a hoop or cross-tie bend.
Input Parameters
SI · mm kN MPa📚 Design Background — ACI 318-25 §18.10.4
ACI 318-25 §18.10.4.1 — Nominal Shear Strength
Nominal shear strength of special structural walls, combining a concrete diagonal tension term with a horizontal steel contribution:
Acv = lw·bw is the gross wall web area. ρt = Ah/(bw·sh) is the horizontal reinforcement ratio. The concrete term αc·√f'c represents aggregate interlock and dowel action; the steel term ρt·fy is the contribution of horizontal bars.
Aspect-ratio coefficient αc — squat walls develop arch action, boosting concrete contribution; slender walls rely on the truss mechanism:
αc is linearly interpolated for 1.5 < hw/lw < 2.0. Use the story height for multi-story walls unless designed as a single cantilevered element.
Maximum Nominal Shear — ACI 318-25 §18.10.4.4
The diagonal compression strut can crush regardless of horizontal steel present:
If φ·Vn,max < Vu, the wall cross-section must be enlarged — no amount of reinforcement can prevent strut crushing. For a system of walls sharing lateral load (§18.10.4.3), the maximum applies collectively:
Capacity-design shear (§18.10.3) — for SDC D/E/F walls, Vu must be the larger of: (a) amplified elastic shear or (b) shear from probable flexural overstrength Mpr. Using elastic analysis shear directly is non-conservative.
Minimum Horizontal Reinforcement — ACI 318-25 §18.10.2.1
Ensures distributed diagonal cracking and prevents brittle shear failure after inclined crack formation:
Required even when Vu < φVc. Two curtains required (§18.10.2.2) when:
Vertical web reinforcement (§18.10.2.2): ρl ≥ 0.0025. For slender walls (hw/lw ≥ 2.0), ρl need not exceed ρt since vertical bars contribute negligibly to shear.
Input Parameters
SI · mm kN MPa📚 Design Background — EN 1992-1-1 §6.2 / EN 1998-1 §5.5.2.4
EN 1992-1-1 §6.2.3 — Variable-Angle Compression Field
Structural walls with shear reinforcement use the variable-angle compression field (truss) model. Inclined cracks are idealised as struts; horizontal bars are the tension ties. For the default θ = 45°:
Asw,prov/s = nh·π·dh²/(4·sh) is the horizontal steel area per unit wall height. fyd = fyk/1.15. EC2 for walls neglects the concrete tensile contribution — the diagonal crack is assumed to run fully across the section.
Inner lever arm z ≈ 0.9·d, where d = lw − cc (cc = 40 mm fixed). Design check: VRd,s ≥ VEd,d. Minimum horizontal reinforcement (§9.6.3): ρh ≥ 0.002 in each face; sh ≤ min(3bw, 400 mm). Bars must be hooked around the boundary zone vertical bars.
Strut Crushing Limit — EN 1992-1-1 §6.2.3
The diagonal compression strut must not crush before horizontal reinforcement yields:
ν1 = 0.6·(1 − fck/250) is the strength reduction factor for cracked concrete in shear (e.g. C25: ν1 = 0.54; C40: ν1 = 0.50). fcd = fck/1.5.
If VEd,d > VRd,max, a shallower truss angle (21.8° ≤ θ ≤ 45°) may be used:
For seismic walls, θ < 45° is discouraged because shear reversals under cyclic loading degrade the concrete contribution assumed by the shallower angle model.
EN 1998-1 §5.5.2.4 — Capacity-Design Shear
Ductile walls must be designed for a shear force greater than from linear analysis. Modal analysis underestimates actual shear due to: (i) flexural overstrength at the plastic hinge (MRd > MEd) and (ii) dynamic shear magnification from higher-mode vibrations.
For DCH walls (§5.5.2.4.1) — amplified design shear:
ε depends on MRd,base/MEd,base and fundamental period T1. For most DCH walls, ε ≈ 1.2 to 2.0 (EN 1998-1 Annex A provides the full formula).
For DCM walls: no amplification is required. The calculator uses the user-entered VEd,d as the final design shear — apply the ε factor externally before entering the value.
Input Parameters
SI · mm kN MPa📚 Design Background — IS 456:2000 §32.4 / IS 13920 §9.3
IS 456:2000 §32.4 — Concrete + Steel Shear Model
Shear resistance computed on the effective cross-section bw×d. The model superimposes concrete and horizontal steel contributions. Effective depth d = lw − cc.
τc is intentionally lower than the beam value because walls are subjected to reversed shear cycles under seismic loading. 0.87 = 1/γm is the IS 456 partial safety factor for steel.
Maximum Shear & Seismic Ductility — IS 456:2000 §32.4.2.1, IS 13920 §9.3
Diagonal concrete crushing upper bound regardless of horizontal steel:
If Vu > Vmax, the wall must be deepened or thickened. IS 13920:2016 §9.3 seismic minimum:
Two curtains required when hw/tw ≥ 16 or lw ≥ 600 mm (§9.3.2).
IS 13920:2016 §9.3.4 — Capacity-Design Shear
The design shear Vu shall not be less than the shear corresponding to the full plastic moment capacity at the wall base:
Mcap is the probable (overstrength) moment capacity computed using actual mean material strengths — not Mu from elastic analysis. This prevents brittle shear failure before the intended flexural plastic hinge forms.
Squat vs. slender walls (IS 13920 §2): slender walls (Hw/lw ≥ 2.0) are governed by diagonal tension. Squat walls (Hw/lw < 2.0) behave as deep beams and are additionally susceptible to horizontal sliding shear at construction joints — IS 13920 §9.5 provides separate sliding shear checks.
Input Parameters
SI · mm kN MPa📚 Design Background — TSC 2018 §7.6.5
TSC 2018 §7.6.5.3 — Design Shear Strength (TBDY Denklem 7.17)
The formula combines a concrete diagonal cracking term with horizontal steel contribution, both expressed using design strengths:
Aw = lw·bw is the gross wall web area. ρsh = Ah/(bw·sh) is the horizontal reinforcement ratio. The 0.65·fctd coefficient is derived from the TS 500 §8.1 cracking shear model. Design material strengths per TS 500 §2.1 (γc = 1.5, γs = 1.15). No additional φ factor applies — safety is embedded in the material partial factors.
Maximum Shear & Minimum Reinforcement — TBDY 2018 §7.6.5.3, §7.6.3.3
Diagonal strut crushing upper bound (√fck characteristic, not √fcd, consistent with TS 500 semi-empirical calibration):
If Ve > Vr,max, the wall cross-section must be enlarged — no amount of horizontal reinforcement can prevent strut crushing. Minimum web reinforcement (§7.6.3.3):
Both directions must be provided in two curtains for DTS 1–4 seismic zones. Horizontal bars must be hooked around the outermost vertical bars of the boundary zone per §7.3.5 to develop the full tensile force.
TSC 2018 §4.3.4 — Capacity-Design Shear Ve
For ductile structural walls the design shear must reflect the probable plastic mechanism at the wall base, amplified for higher-mode shear effects:
Mp,base is the probable flexural capacity computed with mean material strengths including strain hardening. Dv ≥ 1.0 is the dynamic shear magnification factor for higher-mode contributions (TBDY 2018 §4.3.4.5 defines Dv as a function of the number of storeys).
In DTS 1–2 zones, using Vanalysis directly typically underestimates Ve by 30–100%. Enter the completed capacity-design shear directly into the calculator.
Input Parameters
SI · mm kN MPa📚 Design Background — ACI 318-25 PMM Fiber Model
ACI 318-25 — P-M Interaction via Neutral Axis Sweep
The P-M interaction diagram is generated by sweeping the neutral axis depth c from 2lw (pure compression) to near zero (pure tension). At each c, equilibrium of the equivalent rectangular stress block with all fiber strips yields (Pn, Mn):
Stress block parameters: a = β1·c, β1 = 0.85 for f'c ≤ 28 MPa, reduced 0.05 per 7 MPa increment (min 0.65). Concrete ultimate strain εcu = 0.003. Each fiber strain: εs,i = εcu·(c − xi)/c. Steel stress: fs,i = max(min(εs,i·200 000, fy), −fy).
ACI 318-25 §21.2.2 — Strength Reduction Factor φ
The net tensile strain εt at the extreme tension reinforcement controls φ. Three zones apply:
For structural walls with seismic loading, ACI §18.10 uses φ = 0.75 for shear and φ = 0.65 for compression-controlled flexure. Pure axial compression upper bound: φPn,max = φ·0.80[0.85f'c(Ag − Ast) + fy·Ast] (tied column cap applies to walls with Ast > 1%).
ACI 318-25 §11.6 — Minimum Wall Reinforcement Ratios
Two curtains of reinforcement are required when the wall thickness exceeds 250 mm or when Vu > 2Acv√f'c (psi). Minimum ratios for both longitudinal and transverse directions:
Maximum longitudinal steel for compression members used as walls: Ast/Ag ≤ 0.08 (ACI §22.4.2.1). At lap splices, bars in boundary zones must be staggered and ties provided at s ≤ min(6db, 150 mm). For special structural walls (SDC D–F), boundary zone confinement per §18.10.6 supersedes these minimums wherever triggered.
Input Parameters
SI · mm kN MPa📚 Design Background — EN 1992-1-1 §6.1 Fiber Model
EN 1992-1-1 §6.1 — Parabola-Rectangle Stress Block
Fiber strip model sweeps neutral axis depth x from 2lw (pure compression) to near zero (pure tension). The parabola-rectangle stress block is used: peak design concrete stress fcd = αcc·fck/γc (αcc = 1.0 per EN NA; γc = 1.5). Steel: fsd = fyk/γs (γs = 1.15), elastic-perfectly-plastic. At each neutral axis position, integration over all fiber strips gives (NRd, MRd).
The design point (NEd, MEd) must lie within the interaction envelope. EC2 has no separate φ factor; strength reduction is embedded in the material partial factors γc and γs.
EN 1992-1-1 §3.1.7 Table 3.1 — Rectangular Stress Block Parameters
For fck ≤ 50 MPa the rectangular block parameters are constant:
For fck > 50 MPa the block becomes narrower and the peak stress reduces:
The effective rectangular block depth equals λ·x; its stress intensity equals η·fcd. For fck ≤ 50 MPa the block is equivalent to the 0.85f'c/β1 ACI formulation in practice, but the stress amplitude and depth parameters are derived independently from the parabolic model.
EN 1998-1 §5.4.3.2.2 — Minimum Web Reinforcement for Ductile Walls
EC2 §9.6 sets minimum vertical and horizontal web ratios at 0.2% each for non-seismic walls. For ductile walls (DCM and DCH), EN 1998-1 §5.4.3.2.2 raises both to:
Boundary elements (where provided) require additional confinement reinforcement per §5.4.3.4 (DCM) or §5.5.3.4 (DCH). The maximum longitudinal steel ratio at boundary elements is 4% per §5.4.3.2.2 to prevent bar buckling during cycling. Two curtains of reinforcement are mandatory for DCM/DCH walls with tw ≥ 200 mm.
Input Parameters
SI · mm kN MPa📚 Design Background — IS 456:2000 Annex B Fiber Model
IS 456:2000 Annex B — Parabolic-Rectangular Stress Block
IS 456:2000 Annex B prescribes a parabolic-rectangular stress block for the concrete in compression. Peak design concrete stress: fcc = 0.67fck/γm = 0.447fck (γm = 1.5). Design steel stress: fsd = 0.87fy. Neutral axis xu is swept from 2lw (pure axial compression) toward zero to trace the full interaction envelope.
Cc and ȳc are the resultant and centroid of the parabolic-rectangular block. IS 456 does not use a separate φ factor; all partial safety factors are incorporated in the material strengths 0.447fck and 0.87fy.
IS 456:2000 Annex B — Parabolic Block Geometry
The IS 456 stress block has a parabolic leading portion (ε0 to 0) followed by a rectangular tail to εcu:
Fiber strain at position xi from compression face: εs,i = εcu·(xu − xi)/xu. The stress-strain curve for steel per IS 1786:2008 is elastic up to 0.87fy, then perfectly plastic. The actual bilinear IS curve is used for Fe415 and Fe500; fy,design is capped at 500 MPa for seismic applications per IS 13920 §5.4.
IS 456:2000 Cl.32.5 & IS 13920:2016 §9 — Wall Reinforcement Limits
IS 456 Cl.32.5 sets minimum and maximum reinforcement ratios for RC walls used as vertical load-bearing members:
For seismic walls per IS 13920:2016 §9.1, two curtains of reinforcement are required when the wall thickness exceeds 200 mm or the factored shear stress exceeds 0.25√fck. Minimum distributed reinforcement in both directions: ρmin = 0.0025. Boundary zone steel (when triggered by §9.4.1) may increase the local compression steel well beyond these limits; only the non-boundary web zone is governed by the 4% cap.
Input Parameters
SI · mm kN MPa📚 Design Background — TSC 2018 §7.3 Fiber Model
TSC 2018 §7.3 — TS EN 1992-1-1 Material Models
TSC 2018 adopts TS EN 1992-1-1 material models. The parabola-rectangle concrete stress block is identical to Eurocode 2 for fck ≤ 50 MPa. Neutral axis sweep from 2lw (pure compression) to near zero (pure tension) generates the full NRd–MRd envelope.
Fiber strains and stresses follow the EN 1992-1-1 §6.1 approach. The design point (Nd, Md) from analysis must lie inside the interaction boundary. For walls in DTS 1 & 2, the design moment is further amplified by capacity design requirements (§7.3.7) before the PMM check.
TSC 2018 §7.3.7 — Amplified Design Moment for Ductile Walls
For ductile walls (DTS 1 & 2), TSC 2018 §7.3.7 requires that the design moment at the base section account for dynamic amplification due to higher-mode effects. The design moment Md is not taken less than:
Mcap,shear is the moment compatible with the amplified design shear Ve computed per §7.3.7.2. The intent is to ensure that wall sections above the base cannot develop a plastic hinge before the intended base hinge, preventing soft-story mechanisms. This amplification is unique to TSC; neither ACI nor IS mandate an equivalent procedure at the cross-section level.
TSC 2018 §7.6.2 — Web and Boundary Reinforcement Limits
Minimum distributed reinforcement ratios for the web of ductile walls (DTS 1 & 2), applied in both the horizontal and vertical directions:
Two curtains of reinforcement are mandatory for DTS 1 & 2 regardless of wall thickness. At boundary zones (always required per §7.6.6.1, no stress trigger), the longitudinal steel ratio must satisfy As,be ≥ 0.01·Abe and must not exceed 0.04·Abe to avoid bar buckling under cyclic compression. The maximum total wall steel ratio Asc/Ag ≤ 0.04 per TS EN 1992-1-1 §9.6.2.
Input Parameters
SI · mm kN MPa📚 Design Background — ACI 318-25 §22.9
ACI 318-25 §22.9.4.2 — Nominal Shear-Friction Strength
The shear-friction model assumes sliding along a pre-existing or potential crack plane. Reinforcement crossing the crack is stretched in tension; the resulting clamping force times the friction coefficient provides the shear resistance:
Nu,comp is the permanent compressive force perpendicular to the shear plane (positive when compression); a sustained tension reduces the effective clamping. The upper limit on Vn (§22.9.4.4) prevents the model from extrapolating beyond its experimental basis.
ACI 318-25 Table 22.9.4.2 — Friction Coefficient μ
Friction coefficient μ depends on the interface condition and whether normal-weight or lightweight concrete is used (λ = 1.0 for normal-weight, 0.75 for all-lightweight, 0.85 for sand-lightweight):
"Intentionally roughened" per ACI means exposed aggregate or raking to a full amplitude of at least 6 mm (¼ in) — a broom-finished surface does not qualify. At shear wall base joints, monolithic placement achieves μ = 1.4λ, giving the highest capacity for a given Avf.
ACI 318-25 §18.10.8 — Horizontal Reinforcement at Wall Base
For special structural walls (SDC D–F), ACI 318-25 §18.10.8 checks sliding shear at the base construction joint separately from diagonal tension. The seismic design shear Vu at the base comes from capacity design and may exceed the analysis value. Minimum cross-joint reinforcement:
The vertical bars in the wall web and boundary zones all count as Avf when they are fully developed on both sides of the joint. For high axial loads, the compression term Nu,comp is favorable; for walls subject to net tension under seismic load combinations, Nu reduces the clamping and must not be included as a compressive clamping force.
Input Parameters
SI · mm kN MPa📚 Design Background — EN 1992-1-1 §6.2.5
EN 1992-1-1 §6.2.5 — Design Shear Resistance at Interface
The Eurocode interface shear model combines three contributions: cohesion (c·fctd), friction on applied normal stress (μ·σn), and the steel clamping force resolved in the shear direction:
For perpendicular reinforcement (α = 90°): sin α = 1, cos α = 0. The rebar reinforcement ratio at the interface: ρ = Avf/Ai. σn is the design normal stress perpendicular to the interface — positive for compression (beneficial), negative for tension (reduces capacity). fctd = fctk,0.05/γc ≈ 0.35√fck/γc.
EN 1992-1-1 Table 6.2 — Interface Surface Classification
The cohesion coefficient c and friction coefficient μ are selected from Table 6.2 based on surface roughness class:
Shear wall base construction joints are typically classified as "rough" when the fresh concrete surface is raked before hardening to expose aggregate. Monolithic joints effectively achieve "indented" parameters. For seismic analysis, EN 1998-1 §5.4.3.4.2 requires that the design shear at the base be checked using the capacity-design shear VEd from §5.4.2.4.
EN 1992-1-1 §6.2.5(2) — Strut Crushing Upper Bound
The upper limit on VRdi prevents diagonal strut crushing regardless of the amount of transverse reinforcement provided:
The strength reduction factor ν accounts for cracked concrete carrying reduced compression — it reduces with increasing concrete grade since high-strength concrete is more brittle in the post-peak regime. fcd = fck/γc. When σn = 0 and α = 90°, the formula simplifies to the common two-term form: VRdi = (c·fctd + μ·ρ·fyd)·Ai.
Input Parameters
SI · mm kN MPa📚 Design Background — IS 456:2000 §17.6 Shear Friction
IS 456:2000 §17.6 — Shear Transfer at Construction Joints
IS 456:2000 §17.6 provides a shear-friction approach analogous to ACI 318. The design shear capacity at a construction joint is governed by the frictional resistance of reinforcement crossing the plane:
Both the friction limit and the concrete bearing limit must be satisfied; the lower governs. Unlike ACI and EC2, IS 456 does not explicitly include a normal compressive stress term — the friction coefficient selection implicitly accounts for the typical compression at the base of a wall.
IS 456:2000 §17.6 — Friction Coefficient μ by Surface Type
IS 456 §17.6 specifies friction coefficients based on how the construction joint surface was prepared:
The values for roughened and smooth surfaces are more conservative than ACI 318 (which uses 1.0λ and 0.6λ) because IS 456 does not include a separate cohesion term. All reinforcement — vertical bars in the web, boundary zone bars, and additional starter bars — that are properly anchored on both sides of the joint may be counted as Avf. Minimum Avf = 0.0015·Ac is recommended for seismic zones III–V per IS 13920 commentary.
IS 13920:2016 §9.5 — Shear at Wall Base for Seismic Zones III–V
For structural walls in seismic zones III, IV, and V, IS 13920:2016 §9.5 requires the base construction joint to be designed for the maximum probable shear force Vu,max consistent with the wall's plastic hinge capacity. The design shear at the joint is taken as:
This amplification is IS 13920's proxy for capacity design — it guards against plastic hinge formation above the base joint. The joint is detailed to prevent sliding during cyclic loading: vertical bars must be staggered at the joint level, and the concrete surface must be roughened before the next pour. The τmax = 0.2fck ≤ 3.5 MPa limit still applies to the amplified force.
Input Parameters
SI · mm kN MPa📚 Design Background — TSC 2018 / TS EN 1992-1-1 §6.2.5
TSC 2018 — TS EN 1992-1-1 §6.2.5 with Turkish National Annex
TSC 2018 adopts TS EN 1992-1-1 §6.2.5 for shear friction (interface shear transfer). Turkish National Annex values: γc = 1.5, γs = 1.15. Strut crushing reduction factor: ν = 0.6(1 − fck/250).
Derived material strengths: fcd = fck/1.5; fyd = fyk/1.15; fctd = fctk,0.05/γc (approximately 0.35√fck/1.5 per TS 500 §2.1).
TS EN 1992-1-1 Table 6.2 — c & μ for TSC Application
The cohesion and friction parameters from EN 1992-1-1 Table 6.2 apply unchanged under the Turkish National Annex:
For shear wall base joints in Turkish practice, roughening to ≥ 3 mm amplitude (c = 0.45, μ = 0.70) is the standard construction specification. The interface area Ai = lw·bw. All vertical reinforcement — web bars and boundary zone bars — that are properly lapped or spliced through the joint counts as Avf for the ρ·fyd term.
TSC 2018 §7.6.7.2 — Capacity Design Shear at Wall Base
For ductile walls in DTS 1 & 2, TSC 2018 §7.6.7.2 prescribes the amplified design shear force at the base joint. The capacity design shear Ve must be used for the interface shear check rather than the analysis shear Vd:
Rs depends on the building's ductility class and the ratio of overstrength to elastic demand; for typical DTS 1 walls Rs ranges from 1.5 to 2.0. The base joint must provide VRdi ≥ Ve/φ (φ implicit in material factors). This ensures that the joint remains elastic while the intended plastic hinge forms just above it.