Pile Tip Resistance
Calculate a pile's tip resistance, Q_p = q_p·A_p, from the tip stress (bearing capacity) q_p (kPa) and the tip cross-sectional area A_p (m²). Tip resistance is the share of pile capacity from the BEARING of its base on a strong soil or rock layer — the pile acts as a column compressing the soil under its tip, mobilizing that soil's bearing capacity (like a shallow foundation, but at depth). The tip stress q_p is the soil's unit bearing capacity at the tip elevation, estimated by bearing-capacity theories (Terzaghi, Meyerhof, Vesic for piles), SPT correlations (q_p = K·N, with K depending on soil and pile type) or the CPT (cone) test. Times the tip area, it gives the force the tip supports. Tip resistance dominates in piles reaching a firm layer (end-bearing piles), and then the pile is very stiff (settles little). Large-diameter piles (caissons) have large tip areas and mobilize high tip resistance. This share adds to the side resistance for the total capacity. Enter the tip stress and the tip area.
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Pile tip resistance
The tip resistance of a pile is Q_p = q_p·A_p, from the bearing stress at the tip q_p and the cross-sectional area of the tip A_p. It is the share of capacity that comes from the bearing of the pile base on a strong layer of soil or rock — the pile works as a column that compresses the soil beneath its tip, mobilising the bearing capacity of that soil (analogous to a shallow foundation, but at depth). The tip stress q_p is the unit bearing capacity of the soil at tip level, estimated from theory (Terzaghi, Meyerhof, Vesic for piles), from correlations with the SPT blow count (q_p = K·N) or from the CPT cone test. Multiplied by the tip area, it gives the force the base can carry. Tip resistance is dominant in piles that reach a firm layer (end-bearing piles), and in that case the pile is very stiff and settles little. Large-diameter piles (large bored piles, caissons) have a big base area and mobilise high tip resistance. This term adds to the skin resistance to give the total capacity. Enter the tip stress and the tip area.
Related Tools
Pile Bearing Capacity
Calculate a pile's ultimate bearing capacity, Q_ult = Q_p + Q_l, summing the point (tip) resistance Q_p (kN) and the side (skin friction) resistance Q_l (kN). The pile is the DEEP foundation element used when surface soil lacks capacity for the structure's loads — it transfers loads to deeper, stronger subsoil layers. This transfer occurs by TWO mechanisms acting at once: TIP resistance (the pile bears on a firm layer at its base, like a column, mobilizing the soil resistance under the tip) and SIDE resistance (friction and adhesion between the pile's lateral surface and surrounding soil, along its whole length). Their proportion defines the behavior: END-bearing piles (crossing soft soil to bear on rock or firm soil) work mainly by the tip; FLOATING or friction piles (driven in homogeneous soil, no firm layer) work mainly by side friction. The ultimate capacity, divided by a safety factor (typically 2), gives the design allowable load. Determining Q_p and Q_l — by theoretical formulas, SPT-based semi-empirical methods (Aoki-Velloso, Décourt-Quaresma) or load tests — is the central deep-foundation design calculation. Enter the tip resistance and the side resistance.
Pile Skin Resistance
Calculate a pile's side (friction) resistance, Q_l = f_s·A_s, from the average unit skin friction f_s (kPa) and the pile lateral surface area A_s (m², = π·D·L for a cylindrical pile). Side resistance is the share of pile capacity from FRICTION and ADHESION between the pile's lateral surface and the surrounding soil, along its whole buried length. As the pile tends to settle under load, the soil 'grips' its sides and resists — as a nail driven in wood resists pulling by face friction. The unit skin friction f_s depends on soil type (in clays, on undrained cohesion via the α method; in sands, on effective stress and friction via the β method), pile type (driven piles mobilize more friction than bored, displacing and compacting the soil) and surface roughness. Side resistance dominates in FLOATING (friction) piles, driven in soils without a firm bearing layer — they hang by friction. It is also the share mobilized FIRST under load (with small settlement), before the tip. This share adds to the tip resistance for the total capacity. Enter the unit skin friction and the side area.
Pile Allowable Load
Calculate a pile's allowable (working) load, Q_adm = Q_ult ÷ FS, from the ultimate bearing capacity Q_ult (kN) and the global safety factor FS. The allowable load is the maximum load that can be applied to the pile in service with adequate safety — obtained by dividing the ultimate capacity (the load that would cause FAILURE of the pile-soil system) by a safety factor covering uncertainties. The pile-foundation safety factor is typically HIGH (FS = 2.0-2.5 for ultimate capacity, higher if based only on theoretical formulas without a load test), reflecting the great uncertainty in determining soil capacity (unseen, heterogeneous and poorly known) and the severity of a foundation failure (which can collapse the whole structure). Codes often require different partial factors for tip and friction (which have different uncertainties), or limit-state methods. The allowable load sets how many piles are needed for the column loads: number of piles = column load ÷ allowable load. Load tests (measuring real field capacity) allow reducing the safety factor and optimizing design. Enter the ultimate capacity and the safety factor.
Pile Structural Stress
Calculate the structural compression stress in a pile shaft, σ = Q ÷ (π·D²/4), from the applied load Q (kN) and the pile diameter D (m); the result is in MPa. Besides the SOIL having capacity to support the pile (geotechnical capacity), the pile itself, as a STRUCTURAL element (concrete, steel or timber), must resist the load without failing or deforming excessively — this is the pile's STRUCTURAL check. The shaft compression stress is simply the load over the cross-sectional area. It must be below the pile material's allowable stress: codes limit cast-in-place pile concrete working stress to conservative values (typically 5-8 MPa, less than the concrete strength, due to subsurface execution uncertainties — blind concreting, possible defects, eccentricities). This check often GOVERNS the minimum pile diameter (the pile may have ample geotechnical capacity, but structural stress limits the load). Pile design is always the SMALLER of geotechnical (soil) and structural (material) capacity — both must be checked. Enter the applied load and the pile diameter.
Pile Capacity by Driving (Engineering News)
Estimate a driven pile's allowable load by the Engineering News Record dynamic driving formula, Q_adm = (W_r·h) ÷ (FS·(s + c)), from the hammer weight W_r (kN), the drop height h (m), the set s (permanent penetration per blow, m), a loss constant c (m, ≈ 0.0025 m for drop hammers) and the safety factor FS (≈ 6 in this formula). DYNAMIC driving formulas estimate a pile's capacity from observing how much it PENETRATES per hammer blow during driving — the principle is intuitive: the HARDER to drive (smaller penetration per blow, the 'set'), the GREATER the soil resistance and thus the pile capacity. The blow energy (weight × drop height) is equated to the penetration work (resistance × displacement), with losses. The 'set' (s) is measured in the field during driving (average penetration of the last blows), making these formulas a valuable, cheap EXECUTION CONTROL — driving continues until the set reaches the value matching the desired capacity. The Engineering News formula is the most classic (and conservative, with FS = 6). Modern high-strain dynamic monitoring (PDA, with CAPWAP analysis) replaces these empirical formulas far more accurately, but the set is still used daily on site. Enter the hammer weight, drop height, set, constant and safety factor.
Cold Room Heat Load
Compute the product cooling heat load in a cold room, Q = m·cp·ΔT, from the product mass, its specific heat and the desired temperature change. It is the sensible-heat portion to remove to lower the product temperature — one of the components of the room's total load (which also includes wall transmission, infiltration, lighting, motors and people). It defines the refrigerating capacity needed. Enter the mass, the specific heat and the ΔT.
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