Grade selection fills the properties below (all editable — the project specification governs). Defaults follow the OVM circular anchorage — verify against the supplier catalogue.
yo,a — tendon centre to the right vertical face (measured horizontally); yo,c — tendon centre to the top horizontal face (measured vertically); yo,b — half the c/c spacing to the adjacent tendon (0 = none). nAnch — anchorages acting together in the calc. zone. Duct and plate sizes are supplier values — verify against the catalogue. Schematic indicative — the entered mm values govern.
Spiral zone 0.2·yo … 2·yo from the loaded face (governing plane); coil Ø taken as 2·ypo + 50 mm (CIRIA §6.2 minimum — a larger manufacturer value also complies); effective length (turns − 1) × pitch ≥ 1.8·yo; provided steel counts 2·(turns − 1) legs per spiral. The bursting ratios are checked in both principal planes — circular plates are treated as equivalent squares of the same bearing area (§3.3). Typical pitch 50–80 mm (some systems up to ~100 mm).
Spalling bars act in two directions at right angles to the applied force (CIRIA §3.5). λ = 1.0 for a single anchorage at the calc. zone, 1.5 for several (project workbook rule) — set by nAnch in section B; the spalling and root forces use the zone total Ptot = nAnch × Pk. d1 / d2 and the bar counts derive from the yo inputs, cover, stirrup Ø and spacing. This surface steel continues through the blister root into the adjacent member — the 0.04·Ptot root tension (project rule, workbook 3#) is verified with it. Deviation (lateral) reinforcement is in part E.
1 · Lateral reinforcement — deviation of the tendon at the anchorage
2 · Tie-bar — longitudinal reinforcement below the anchorage
1 · Lateral bars — β = real deviation angle at the anchorage; the bars resist Fr = 2·Ptot·sin(β/2) (standard deviation-force formula; CIRIA §5.1 for the requirement), spread over the deviation zone L_dev = yo,c / tan β, each spanning the full depth (covers excluded). 2 · Tie-bar — additional longitudinal reinforcement below the anchorage (0.2·Ptot, project rule), provided by the structure adjacent to the blister; the davit connection sets the count: one face ⌈b / s⌉, two faces ⌈(b + h) / s⌉. Blister-root tension (0.04·Ptot, parallel to the blister surface) — carried by the surface steel of part D; no separate bars required. See diagram below.
K — bursting reduction for anchorage groups (CIRIA §3.3): 1.0 single / perimeter, 1.5 spread in one direction, 2.0 in two directions. k — bearing limit factor (0.4·fcu typical). γ — design factor on forces (1.0). 0.87 / 0.001 — steel stress & strain limits of the bursting and spalling checks. Confirm against the project specification.
Eurocode engine currently covers materials and the partially loaded area (bearing) check to EN 1992-1-1 §6.7. Bursting/spalling checks for EC will be added in a later release — use the BS 5400 / CIRIA engine meanwhile.
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