Real questions. Credentialled answers.
Ask the engineering problem you can't Google. Get answers from Fellows, chartered engineers and Master Trade professionals — with their verified credential on every response.
How do you estimate shaft friction for bored piles in London Clay when SPT data is sparse?
SolvedWorking on a 15-storey RC frame in Lambeth — the SI only has 4 boreholes across a 0.3ha footprint. Trying to decide between the empirical α-method or going full effective-stress. The clay is heavily overconsolidated at depth but I'm not confident in the s_u profile. How would you approach the undersampling?
2 answers·18·#geotechnical#piles#london-clayGraduate MEngCEng MICEDr. Sarah MitchellAI-reviewed ✓For overconsolidated London Clay the α-method is conservative at depth — once you're below ~6m the effective-stress (β) approach gives a better fit with the real shear-strength profile. With only 4 boreholes I'd anchor s_u to the Skempton plasticity correlation, then sanity-check against any SPT N-values you do have using s_u ≈ 4.5N. Crucially: don't average across the footprint — London Clay's s_u increases ~7-10 kPa/m, so a single design line will over-predict the shallow piles and under-predict the deep ones. Split the profile.
EC2 punching shear at internal columns of a PT flat slab — which load combination actually governs?
Solved9m × 8m grid, 280mm PT flat slab. I get different governing combinations depending on whether I use the basic or refined method for v_Ed. Is there a clean workflow people trust, or is it always case-by-case?
1 answers·31·#EC2#post-tensioned#punching-shearIEng MIStructEFIStructE FICEProf. Rachel WhitfieldAI-reviewed ✓Refined method (cl. 6.4.4) almost always governs at internal columns for PT slabs, because the prestress reduces v_Ed non-uniformly across the control perimeter. The thing people miss: the eccentricity factor β changes when spans are unequal — your 9/8 ratio is enough to push β above the 1.15 default. Compute β from the moment-transfer, don't take the code default. And remember the prestress secondary moments feed M_Ed at the column — include them or you'll under-read the shear.