What Happens After Structural Calculations Are Issued?

What you actually receive

It is worth reading the assumptions rather than only the beam schedule. They frequently contain the items that will need action later: 'foundation depth to be confirmed on excavation', 'existing joists assumed to span front to back', 'restraint to top flange assumed from new blockwork'.

• —A calculation package covering the elements designed, with loadings, analysis and the checks carried out
• —Sketches or drawings showing beam sizes, bearings, padstones, connections and any foundation requirements
• —Stated design assumptions and any items excluded or to be confirmed on site
• —Specification notes — steel grade, concrete grade, bolt sizes, fire and corrosion protection
• —A revision reference and date, so that everyone can confirm they are working to the current issue

Building control submission

The calculations are normally submitted to the building control body — a local authority or a registered building control approver — either with a full plans application or during a building notice job. Building control reviews them for compliance with Part A and may raise queries.

Queries are routine and are usually resolved by clarification, an additional check or a small revision. It is helpful to pass them straight to the engineer rather than answering them second-hand, because most relate to design intent rather than to arithmetic.

Pricing and tendering

Builders price from the drawings and calculations. Clear structural information reduces both the price and the number of provisional sums, because contractors do not need to protect themselves against ambiguity.

Two items are almost always provisional at tender stage: foundation depth, and whatever is discovered when the structure is opened up. Expect those to be confirmed after excavation and strip-out rather than at signing.

Ordering steel and materials

Steelwork is normally ordered by the contractor or fabricator directly from the calculations and drawings. A fabricator may prepare shop drawings, and it is good practice for the engineer to review them before fabrication begins.

Section substitutions are the most common cause of problems at this stage. A different section of similar depth may have different capacity, different restraint sensitivity and different reactions at the bearings. Substitutions should always be referred back to the engineer, in writing, before the steel is cut.

Construction and site queries

Once work starts, the structure that was assumed becomes the structure that is actually there. Joists span a different way, an old chimney breast turns out to have been removed, foundations are shallower than expected, or a beam cannot physically be brought into the room.

These are normal. They are resolved quickly when the engineer is contacted with a photograph and a dimension, and expensively when they are resolved on site without engineering input and revisited later.

• —Foundation depth or ground conditions differ from those assumed
• —The existing construction differs from what was inferred
• —Access prevents installing the specified member in one piece
• —A service, drain or duct clashes with the new structure
• —The client changes the layout, the opening width, or the intended use
• —The contractor proposes an alternative section, connection or sequence

Site inspections

Building control will inspect at defined stages — typically the excavation before concrete, the foundation, damp proof course, steelwork installation, and completion. These are compliance inspections and are not a substitute for design supervision.

Separately, an engineer may be appointed to inspect specific items: steelwork installation and bearings, reinforcement before a pour, or temporary works before a wall is removed. On larger projects this is formalised as periodic site inspection with written reports.

Changes during construction

Any change to load, span, opening width, use or support arrangement is a design change, however small it looks. Widening an opening by 300 mm, adding a roof light, changing to a heavier floor finish, or omitting the blockwork above a beam all alter the basis of the calculation.

Revised calculations are usually a small piece of work if raised at the time. Retrospective assessment after the work is built is invariably more expensive and occasionally leads to remedial work.

Completion and certification

• —Building control issues a completion certificate once satisfied that the work complies
• —The engineer may be asked to confirm that installed structural work accords with the design, where they have inspected it
• —Fabricators may provide CE or UKCA declarations of performance for structural steelwork
• —Concrete, materials and testing records may be required on larger projects
• —Any residual restrictions — permitted floor loading, for example — should be recorded and displayed

Keeping the records

Structural calculations have a long life. They are asked for on sale, remortgage, insurance renewal, and by the next engineer who alters the building in twenty years' time. Keeping them costs nothing; recreating them requires opening the building up again.

Store the calculations, drawings, building control approval and completion certificate together, digitally as well as on paper, and pass them on with the property.

Related guidance

• BES-TG-005What Information Does a Structural Engineer Need?Read →
• BES-TG-007Steel Beam Design ExplainedRead →
• BES-TG-008Temporary Works ExplainedRead →
• FAQHow long do structural calculations take?Read →
• FAQDo I need Building Regulations approval?Read →
• FAQCan BES work directly with my contractor?Read →