Structural
Engineering Design Criteria: What They Are, Why They Matter, and How We Set Them at AmtaarGC
Nov
1) Design standards & references
Your criteria should lock the code basis from day one (e.g., BS/EU/IBC), plus any specialist studies. On exemplar tall-building projects, teams referenced BS 6399 for loading, BS 8110 for concrete, BS 5950 for steel, UBC-97 for seismic, and a dedicated wind tunnel study for cladding and global actions. That mix ensured consistency from floor loads to façade drift checks.
At AmtaarGC (London), we typically set Eurocodes with UK National Annexes as primary, and explicitly note any legacy BS/UBC items retained for continuity—backed by project-specific studies where needed (wind, vibration, thermal movement).
2) Materials: grades, durability, and covers
Criteria documents don’t just say “concrete” or “steel”—they specify strength classes, exposure classes, and minimum covers by location so durability and fire performance are built in.
- Typical tall-building examples ranged from C32/40 slabs and walls up to C65/80 for transfer and outrigger zones, with covers adjusted to meet 2–3 hour fire ratings. Steel generally used S355 where strength governed and S275where stiffness or economy did.
On London jobs, we align mixes to BRE SD1 exposure, sulphate risk, and chloride limits; covers are then tuned to the project’s required fire period (often 90–120 minutes in residential/mixed-use, more at critical transfer lines).
3) Loads: dead, live, wind, seismic & more
Loads drive member sizes and reinforcement. Good criteria tabulate them clearly by use so everyone—QS, architect, MEP—can budget and coordinate.
- Illustrative imposed loads (kN/m²): offices 2.5; residential 2.0; corridors/stairs 4.0; gyms/refuge 5.0; plant rooms 10.0 (non-reducible). Balconies can reach 4.0 in residential. These documents also spell out concentrated loadsand balustrade line loads, ensuring no surprises at edges and thresholds.
- Wind: criteria should either cite the code method or a wind-tunnel report and then cap building sway (e.g., H/500) and interstorey drift (e.g., H/500 under wind).
- Seismic (when applicable): even for low-seismic regions, criteria fix the procedure (static/dynamic), R-factor, and mass definitions so diaphragms, cores and anchors are sized correctly.
- Thermal & shrinkage: inputs include design temperature range and humidity; criteria ask designers/contractors to model restraints, joints, and staged pours accordingly.
For London, we still document live-load reduction rules, vehicular/knife-edge loads at ramps, and heavy kitfootprints (lifts, generators) so the slab schedule matches the MEP reality.
4) Foundations & ground environment
The criteria should summarise ground profile, groundwater, earth pressures, and aggressive agents (sulphate, chlorides) so the right concrete class and waterproofing are specified.
- Example investigations logged layered sands, calcarenite, sandstone, and mudstone with GWL ≈ 2 m, and set DS-5 / AC-5 for buried concrete durability—crucial to get right before tender.
In London clay or mixed made ground, we fix the geotech design approach, platform levels, dewatering assumptions, and verify retaining wall at-rest/active/passive pressures—including surcharges from roads and cranes—inside the criteria itself.
5) Performance limits: serviceability you can live with
End-users don’t read rebar schedules—they feel deflection, drift, vibration and acceleration. Criteria make these measurable:
- Deflection limits: e.g., concrete members sized to BS span/depth limits targeting span/250 total and span/350 net after finishes, with PT slabs capped at span/360 and 20 mm for live load. Cladding support lines often have a stricter ±16 mm vertical/horizontal differential per floor.
- Lateral performance: tip drift H/500 under wind, storey drift H/500, and perceptible acceleration capped (e.g., 18 mg at 10-year wind).
- Vibration: office steelwork typically has a ≥ 4 Hz natural frequency target unless a detailed check demonstrates acceptability.
6) Load combinations & fire
Criteria fix ultimate combinations and γ-factors for dead, live, wind, earth/water, temperature, and (if relevant) seismic, so everyone designs and checks to the same envelope. They also set fire periods—often 2 hours for general slabs/beams and 3 hours at columns, core walls, and transfer lines—so covers, jackets, or spray protection can be coordinated early.
7) Detailed floor-by-floor loads (the QS goldmine)
The best criteria include room-by-room dead loads (finishes, services, raised floors, toppings, planters/soil, curtain wall weights) next to the imposed loads. That level of granularity lets the QS price accurately and helps the GC plan formwork and pump capacity.
How we use this at AmtaarGC
Our Engineering-as-a-Product model packages these criteria into each scope (foundations, frames, drainage, cladding), so when you “add to cart,” you’re buying a deliverable backed by clear code bases, load tables, and performance targets—not vague promises. It’s the simplest way to control risk, time, and cost from the first sketch to the final pour.
If you’d like, we can draft a bespoke design-criteria document for your scheme (London or GCC), aligned to Eurocodes, your planning conditions, and your contractor’s construction method