921.1 Purpose & when to use

Quickly test clear gaps for HVM bollard arrays before detailing. Use during concept and set-out verification (232, 612).

Use the checker any time you are defining an HVM array or verifying clear-gap at pre-design, tender, and set-out. It translates spacing rules from 232 Spacing rules and the method in 322 Clear-Gap Calculations into a simple pass/fail. It accounts for site tolerances and deflection/permanent set, helping you defend spacing decisions in reviews and authority submissions.

Run it before you freeze layouts, and again just before pour/installation to confirm that set-out under 626 Datum & Alignment Checks still meets the target clear-gap rule. For UAE projects, keep a SIRA note in the record and link to SIRA Bollards (UAE) if approvals apply.

921.2 Inputs & field rules

Enter center-to-center, diameter, slope/curb deltas, tolerances, deflection/set allowances (322, 314). Works for crash rated bollard patterns.

Minimum inputs: array center-to-center spacing, bollard diameter (or sleeve OD), local slope/kerb height deltas, construction tolerances (from 315), and allowances for deflection/set per 314. In the field, follow 626 alignment checks and use a project gap gauge for go/no-go. For sloped ground or kerb transitions, the tool offsets head elevations to calculate the tightest instantaneous gap at capture height.

• Vehicle target: choose from the project’s test vehicles or local vehicle class envelope.
• Pattern: inline, staggered, or mixed—see 321 Array Patterns.

921.3 Method & assumptions

Calculates minimum instantaneous gap with tolerance stacking and terrain adjustments (322, 324). Assumes calibrated dimensions for HVM bollard heads.

The checker computes the controlling “pinch” by projecting adjacent head profiles and subtracting half-diameters, then applies tolerance stack-up from set-out, manufacturing, and reinstatement. It models crossfall and kerb steps to find the lowest effective gap along the capture height. Where 324 Corners & Islands apply, it checks corner throats and island noses.

Assumptions: circular heads/sleeves; calibrated OD; straight centreline between posts; no significant ovalization or base rotation in service. For mixed products, see 326 Mixed-Type Arrays and apply the most conservative head profile.

921.4 Outputs & interpretation

Pass/fail vs target vehicles; highlight near-door, corner, and island risks (232, 323–324). Guides crash rated bollard acceptance.

Outputs include: pass/fail against the selected clear-gap rule, minimum computed gap, a pass margin, and flags for near-door spacing, corner throat, and island noses. Use the pass margin to judge sensitivity to site drift and whether further detail per 322 is needed. For storefront/frontage arrays, cross-check with 323 Frontage/Door Protection.

921.5 Limits & edge cases

Mixed heights, non-circular sleeves, skewed layouts, paving drift (312, 629). Note when a detailed check is needed.

Not ideal for: non-circular or heavily ornamental sleeves; significant height variation; skewed rows; heavy reinstatement drift after paving (629). In these cases, switch to the detailed 322 method or add a projected-gap check near oblique approaches.

921.6 Validation & QA

Export gauges/checklist to ITP/SAT (714, 638). Keep HVM bollard evidence reproducible.

Record the checker version, inputs, and Page-ID in your ITP. For SAT/witnessing, attach the pass/fail statement and the site alignment & gap sheet; book witnesses per 638. Keep a reproducible chain via 938 Submission-Pack Guidance.

921.7 Save/Export & audit

PDF/CSV with Page-ID, date, inputs, and version (911, 115). Traceable for crash rated bollard reviews.

Use CSV for calculation snapshots and PDF for sign-off packs. Include Page-ID, date/time, vehicle target, ruleset, inputs, computed minimum gap, and pass margin. Name files per 911 File Index & Naming Rules and log the version scheme per 115 Versioning & Numbering. Attach to authority submittals under 435 Anti-Downgrade when equivalence is debated.

921.8 Related steps & links

Jump to arrays, corners, foundations (321–326, 324, 331–334). Close the loop for HVM bollard design.

Next steps often include refining the pattern in 321 Array Patterns, corner/island treatments in 324, and checking foundations under 330 Foundations & Loads (see 331–334). For documentation, align with 432 Design selection guide and 938 Submission-Pack Guidance.

921.9 Common pitfalls

Ignoring deflection, stacking wrong tolerances, not rechecking after reinstatement (314, 629). Avoid crash rated bollard disputes.

Typical failure modes: using nominal centre spacing without tolerance stacking; assuming zero residual set allowance; not revisiting gaps after paving and utility reinstatement (629). Always check near-door and corner throats where desire lines concentrate.

921 Spacing Checker — FAQ