Ledger Anchorage to Masonry/Concrete

Last updated 2026-09-13

Restored - masonry and non-cracked concrete. This calculator was withdrawn while its anchor capacity data was reviewed. It is available for Rawlplug R-KEM II (M8, M10, M12, M16) in solid brick or aerated concrete, whose resistances are transcribed from UKTA-0836-22/6108 (2022-05-31, British Board of Agrément), Annex C1 Table C1, and for R-KEM II (M10, M12, M16) in non-cracked concrete C20/25 to C35/45, computed to EN 1992-4:2018 from values transcribed from UKTA-0836-22/6131 (2022-07-14), Annexes B and C.

Concrete is non-cracked only. R-KEM II is approved for non-cracked concrete (ETA-21/0243 / UKTA-0836-22/6131); cracked concrete is outside the product approval and is not offered. Every concrete report opens with an "Assumptions and scope" block - read it before the resistances: the bond parameters are the C20/25 values applied without strength increase, the edge-distance input is the free edge above the ledger, and concrete edge failure in the direction of shear (EN 1992-4 §7.2.2.5) is not checked.

Every other anchor has been removed from the catalogue, not merely gated. Hilti HIT-RE 500 V4, Fischer FIS EM Plus, Rawlplug R-KEX II, Würth ASSY 3.0 Combi, Hilti HSA-R2, Hilti HIT-HY 270, Simpson SDS and Fischer FAZ II carried capacity values that could not be traced to any published approval. Through-bolts were removed separately: their steel shear was computable, but the mode that governs them - the wall crushing behind their far-face plate washer - is not checked, and checking it needs masonry unit strengths the approvals do not publish. Dense concrete block and hollow block are no longer offered as substrates, since nothing remains that has data for them.

A project saved with one of the removed anchors opens on a notice rather than a recalculated result - nothing is silently substituted.

If you issued a design with this calculator before the withdrawal, re-check it. The corrected masonry resistances are roughly 4× lower than the placeholder values they replaced.

The page below describes the module as built; the substrate and anchor coverage it lists is wider than what is currently available.

Not checked, and stated here because the report prints the figure: the assessment publishes a characteristic tension resistance N_Rk, which is reported for information only. This calculator computes no tension demand - the fixing is analysed for shear alone - so any uplift, eccentricity or restraint tension must be checked separately.

A timber ledger (wall plate or bearer) fixed horizontally to a masonry or concrete wall, carrying vertical shear from joists or rafters into the wall through post-installed fixings. The module designs the fixings and the timber local checks; it does not design the wall or the supported members.

Overview

  • What it does: designs shear-dominant ledger fixings to EC5 on the timber side and EN 1992-4 / ETA on the anchor side.
  • Fixing types supported: resin anchors, mechanical expansion anchors, structural screws, and through-bolts.
  • Substrate types: concrete (C20/25 to C35/45), dense concrete block, hollow concrete block, solid brick, and aircrete (AAC).
  • Load model: a line load V_Ed (kN/m) acts along the ledger and is distributed to the fixings as V_Ed,bolt = V_Ed × bolt centres / number of rows.

Calculation method

Two parallel check streams run for every design: the timber local checks (EC5) and the anchor resistance (EN 1992-4 in concrete, or the product ETA in masonry). The governing utilisation across both streams determines the result.

Timber side (EC5):

  • Shear at the fixing line - EC5 §6.1.7: tau_d = 1.5 × V_Ed,bolt / (b × h), compared against f_v,d = kmod × f_v,k / gamma_M.
  • Bearing perpendicular to grain - EC5 §6.1.5: sigma_c,90,d = V_Ed,bolt / (b × t_wall), compared against f_c,90,d = kmod × k_c,90 × f_c,90,k / gamma_M.

Anchor side:

  • Concrete substrate (non-cracked): EN 1992-4:2018. Steel shear V_Rk,s = k7 × V0_Rk,s with the assessment's tabulated V0_Rk,s (Table C2) and k7 = 1 (ductile). Concrete cone N_Rk,c per Formula (7.1) with all modification factors, k1 = 11.0; combined pull-out/bond N_Rk,p per Formula (7.13) from the assessment's τ_Rk,ucr and ψ0_sus (Table C1), with its own critical spacing s_cr,Np; pryout V_Rk,cp = k8 × min(N_Rk,c, N_Rk,p) per Formula (7.39c), k8 = 2 (Table C4). The governing anchor resistance is min(V_Rd,s, V_Rd,cp). Installation limits (h_ef band, s_min, c_min, h_min) per Table B1 are enforced.
  • Masonry substrate (block, brick, aircrete): the resistance is taken directly from the product ETA table. No formula derivation is applied.
  • Through-bolt: steel shear only, V_Rk,s = 0.5 × A_s × f_ub (EN 1993-1-8). The bolt bears on a far-face plate washer and passes through the full wall thickness.

Bolt length and embedment

Embedment h_ef is derived from the bolt length you specify, not typed directly - except for mechanical expansion anchors. What a length buys differs by fixing type, so each gets the relationship that is true for it:

  • Resin anchor: h_ef = L − b − (washer thickness + nut height). The catalogue length is the total stud length, so what remains behind the ledger is the embedment.
  • Structural screw: h_ef = L − b. The head bears directly on the ledger face, so no nut is deducted.
  • Mechanical expansion anchor: h_ef is entered directly. A wedge or sleeve anchor sets at its own designed depth; its length designation encodes the fixture thickness it can clamp, not the embedment, so a longer anchor of the same size embeds no deeper.
  • Through-bolt: no embedment is derived (the bolt passes through the wall). The length is instead checked for sufficiency: L must be at least b + wall thickness + washer + nut.

Because ETA tables are keyed on round embedments while bolts come in round lengths, a derived h_ef usually falls between published rows. The solver interpolates and says so in the report. Washer thickness is taken from ISO 7089 (nominal) and nut height from ISO 4032 (m max).

Spacing and edge distances

  • Bolt centres (horizontal, parallel to grain): minimum 6d for anchors (EN 1992-4 Table 4.1 installation minimum); 4d for through-bolts (EC5 Table 8.4 a1).
  • Row spacing (vertical, perpendicular to grain): minimum max(3d, 40 mm) (EC5 Table 8.4).
  • Edge distance: minimum taken from the product ETA / EN 1992-4.
  • Rows are positioned symmetrically about the ledger mid-depth. A row that fails its edge distance is excluded from the effective fixing count (n_eff) and shown red in the drawing.

Assumptions

  • Shear-dominant connection only. The applied load is taken as pure vertical shear distributed equally to all effective fixings.
  • Equal load distribution across rows (no row-stiffness variation).
  • Timber density rho_k is derived from the grade, never user input.
  • k_c,90 = 1.0 (conservative - no bearing enhancement).
  • Concrete: R-KEM II is approved for non-cracked concrete only (ETA-21/0243 / UKTA-0836-22/6131); the EN 1992-4 coefficients k1 = k3 = 11.0 for non-cracked concrete are fixed by that scope. Not valid where the concrete may be cracked under the design situation. (Concrete remains withdrawn.)
  • Where h_ef exceeds the maximum tabulated embedment, resistance is taken at the maximum tabulated value (conservative) with a note.
  • Anchor database values are seed data and must be verified against the current product ETA before use in design.

Limitations

  • Tension modes (pullout, concrete cone, splitting, blowout) are not checked. The connection must be genuinely shear-dominant.
  • No moment from load eccentricity is considered.
  • The wall itself (masonry compression or bending behind the fixing) is not checked.
  • A single load case only - no combinations.
  • Fire, seismic, and fatigue are not covered.
  • Masonry anchor resistance is only as good as the tabulated ETA value; no substrate-specific formula is applied.

Partial factors and settings

  • gamma_M,timber comes from the timber check (grade-dependent, as elsewhere in ConnForge).
  • gamma_M for anchors: steel and pryout factors per EN 1992-4 / the product ETA (e.g. gamma_M,s = 1.25, gamma_M,cp = 1.50 for concrete). These are product-specific and read from the database, not from the global settings panel.
  • Service class and load duration drive kmod, shared with the rest of ConnForge.

References

  • BS EN 1995-1-1:2004+A2:2014 - timber side (shear §6.1.7, bearing §6.1.5, spacing Table 8.4).
  • EN 1992-4:2018 - anchor design in non-cracked concrete (steel §7.2.2.3.1, cone §7.2.1.4, bond §7.2.1.6, pryout §7.2.2.4). Concrete edge failure §7.2.2.5 is not checked.
  • EN 1993-1-8 - bolt shear for through-bolts.
  • Product ETAs - anchor characteristic resistances in masonry.