Ledger Anchorage to Masonry/Concrete

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: the EN 1992-4 formula engine. Steel shear V_Rk,s = 0.5 × A_s × f_uk. Pryout V_Rk,cp = k × N_Rk,c, where N_Rk,c = 7.7 × sqrt(f_ck) × h_ef^1.5 (cracked concrete, k1 = 7.7) and k = 2.0 for h_ef >= 60 mm. The governing anchor resistance is min(V_Rd,s, V_Rd,cp).
  • 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.

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 pryout uses cracked-concrete parameters by default.
  • 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 concrete (steel shear §6.2.3, pryout §6.3.3).
  • EN 1993-1-8 — bolt shear for through-bolts.
  • Product ETAs — anchor characteristic resistances in masonry.