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.

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 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.