Pick the design code and the bridge: AASHTO LRFD 3.8 (3-s gust PZ = 2.56×10−6 V²KZGCD, default), Eurocode EN 1991-1-4 (qp(z), cf,x from b/dtot), the Korean KDS 24 12 21 and Japanese JRA standard pressures (4.0 − 0.2·B/D), and IRC:6 (Table 12, Pz = 0.6 Vz²). Pressure, line load, span force, substructure, wind on live load and vertical wind — drawn to match.
Wind pressure and forces on a bridge by design code — AASHTO LRFD 3.8 (default), Eurocode EN 1991-1-4 §8.3, KDS 24 12 21 (Korea), JRA Specifications (Japan) and IRC:6 (India) — superstructure, substructure, wind on live load and vertical wind, with a drawing that follows the code you pick.
B = urban/suburban terrain, C = open country (default for most bridge sites), D = flat coastal exposure facing open water — the usual pick for sea crossings and corniche viaducts.
10-minute mean at 10 m in terrain II, from the National Annex wind map (cdir = cseason = 1 here). With traffic on the deck the recommended vb,0* is 23 m/s.
Terrain category: 0 open sea · I lakes, flat open · II open country, few obstacles · III suburban, villages · IV urban. Sets z0, zmin, kr.
The standard pressure table is written for V10 = 40 m/s (10-min mean at 10 m). Other values scale the table by (V10/40)² — a convenience, not the code's detailed method.
Standard pressures are the no-live-load values; with live load on the deck the table halves them.
Fig. 9 wind map zones 33 / 39 / 44 / 47 / 50 / 55 m/s. Table 12 hourly mean speeds Vz are tabulated for 33 m/s and scaled by Vb/33.
Gust factor G = 2.0 (spans up to 150 m). With live load the exposed depth gains the 3 m vehicle strip; no live load is combined above 36 m/s at deck level.
Girder + deck edge + barrier/parapet, the full solid strip the wind sees.
Table 8.1: dtot = d + parapet allowance, or d + 2 m (road) / 4 m (rail) with traffic, whichever is larger.
| Code | Wind speed basis | Pressure | Superstructure drag | Wind on traffic | Vertical |
|---|---|---|---|---|---|
| AASHTO LRFD 9th, 3.8 | 3-second gust V at 10 m (mph), exposure B/C/D, KZ power law | PZ = 2.56×10−6 V² KZ G CD (ksf) | CD 1.3 girders, 2.0 trusses, 1.6 substructure | WL = 1.46 kN/m (0.10 klf) at 1.8 m above deck | 0.96 kPa (0.020 ksf) upward, Strength III |
| Eurocode EN 1991-1-4 §8.3 | vb,0 10-min mean at 10 m, terrain 0–IV, cr(z) log law | qp(z) = (1 + 7 Iv)·½ρvm² | cf,x from b/dtot (2.4 → 1.3), cscd = 1 | dtot = d + 2 m (road) / 4 m (rail), reduced vb,0* (23 m/s) | cf,z = ±0.9 on plan area |
| KDS 24 12 21 (Korea) | Standard table for V10 = 40 m/s (10-min mean); detailed ½ρVD²CDG for wind-sensitive bridges | 4.0 − 0.2·B/D (1 ≤ B/D < 8), 2.4 (B/D ≥ 8), trusses 3.0 kN/m² | built into the table; piers 3.0 rect. / 1.5 round | table halved with live load on deck | — |
| JRA 道路橋示方書 (Japan) | Same standard table (40 m/s basis) | 4.0 − 0.2·B/D, 2.4, trusses 3.0 kN/m² | built in; 下部構造 3.0 角形 / 1.5 円形 | halved 活荷重載荷時 | — |
| IRC:6 §209 (India) | Hourly mean Vz by height (Table 12), basic 33–55 m/s map | Pz = 0.6 Vz² N/m², FT = Pz A1 G CD, G = 2.0 | CD by b/d (Fig. 10), piers Table 13 | exposed area + 3 m; none above 36 m/s | FV with CL = 0.75 |
Rule of thumb for a 3 m deep deck at 15 m in open country: AASHTO Strength III (185 km/h) gives about 2.4 kPa, EN with vb,0 = 26 m/s about 1.5–2.0 kPa, the KDS/JRA table 3.2 kPa at B/D = 4, IRC with Vb = 33 m/s about 0.5 kPa × G·CD ≈ 1.6 kPa — the speed definitions differ (3-s gust vs 10-min vs hourly mean), so never swap a speed between codes.
The 9th-edition rewrite replaced the old base-pressure tables with this ASCE-style gust formula, and the practical consequence is that height and exposure now matter as much as the wind map: the same girder at Z = 60 m in exposure D sees roughly double the pressure it does at 10 m in exposure C. Use the mid-height of the exposed strip for Z, not the deck level. The 185/129/113 km/h presets are the generic 115/80/70 mph values — Gulf projects typically specify 3-s gusts around 160–190 km/h, but always take V from the project design criteria, not a default. Remember what this tool is not: anything flexible — spans past ~150 m, tall slender piers during staging, cable-supported decks — falls under aeroelastic effects (3.8.3), where buffeting and vortex response are analysed, not looked up. Staging cases with bare girders before the deck often govern the substructure and are worth a separate run with the full exposed depth of the girder line. Switching codes: the Korean and Japanese standard tables are the quick answer for ordinary girder bridges (B/D decides everything), Eurocode and AASHTO reward a correct height and terrain, and IRC's hourly-mean basis looks low until the gust factor G = 2 and CD are applied — compare pressures only after both are in.
Wind on a bridge is treated as a static pressure on the projected area of each element, derived from a 3-second gust speed. The 9th edition of AASHTO LRFD replaced the older base pressures with a velocity-based formula:
| Term | Meaning | Values |
|---|---|---|
| V | 3-second gust design wind speed | Strength III 115 mph (51.4 m/s) · Strength V 80 mph · Service I 70 mph (Table 3.8.1.1.2-1); site-specific where the owner specifies |
| KZ | pressure exposure and elevation coefficient | from the exposure category (B urban / C open / D coastal) and the height of the element above ground or water; 1.0 at 10 m in exposure C, higher for taller piers |
| G | gust effect factor | 1.0 for rigid structures (most girder bridges); larger for wind-sensitive structures from a dynamic analysis |
| CD | drag coefficient | 1.3 I-girder and box superstructures · 2.0 trusses, columns and arches · 1.2 sound barriers (Table 3.8.1.2.1-2); a round column may justify a lower value from wind-engineering data |
Strength III, exposure C, girder superstructure 2.5 m deep plus a 1.0 m barrier: V = 115 mph, KZ = 1.0, G = 1.0, CD = 1.3 → PZ = 2.56×10⁻⁶ × 115² × 1.3 = 0.044 ksf = 2.11 kPa. On a 3.5 m exposed height the transverse line load is 2.11 × 3.5 ≈ 7.4 kN/m of bridge, applied at the centroid of the exposed area and carried to the bearings and piers. With skewed wind, AASHTO gives transverse and longitudinal components as fractions of PZ by skew angle (3.8.1.2.3); the 60° case usually governs the longitudinal loading of the piers.
Wind on live load (WL) — 1.46 kN/m at 1.8 m above the roadway, with Strength V and Service I. Vertical wind (3.8.2) — an upward pressure of 0.96 kPa (0.020 ksf) on the deck plan area, applied at the windward quarter point with Strength III only, which matters for light decks and uplift at bearings. Wind on the substructure — PZ with the column's own CD on its projected area, which for tall piers on wide piers can govern the pier design together with braking and temperature.
Footbridges use the same pressures on the full exposed height of the deck and railings, but the governing issue is often not static wind: slender pedestrian bridges need a check of pedestrian-induced vibration (the AASHTO guide asks for evaluation below 3.0 Hz vertical and 1.3 Hz lateral, where walking frequencies of 1.6–2.4 Hz can excite the deck) and, for long spans, vortex shedding and galloping of the deck — a dynamic assessment outside this calculator.
AASHTO LRFD 3.8.1.2 converts a 3-second gust wind speed V (mph) to a design pressure PZ = 2.56×10⁻⁶ V² Kz G CD in ksf, where Kz is the height-and-exposure coefficient, G the gust effect factor (1.0 for rigid structures) and CD the drag coefficient of the element (1.3 for I-girder and box superstructures, 2.0 for trusses, columns and arches in Table 3.8.1.2.1-2). The pressure acts on the projected exposed area of the superstructure and substructure.
What wind speeds are used for bridges?AASHTO LRFD 9th edition ties the speed to the limit state: 115 mph (51 m/s) for Strength III with no live load, 80 mph (36 m/s) for Strength V with live load, and 70 mph (31 m/s) for Service I, unless site-specific values are specified.
What is wind on live load?Wind on live load (WL) is a 1.46 kN/m (0.10 kip/ft) line load acting 1.8 m above the deck, representing wind on vehicles; it is applied with Strength V and Service I only, when traffic is on the bridge.
How is wind load applied to a pedestrian bridge?The AASHTO Guide Specifications for Pedestrian Bridges refer to LRFD 3.8 for pressures, with the full exposed height of the deck and railings taken as the projected area; slender footbridges also need a vibration check (pedestrian-induced and vortex shedding), which is a separate dynamic assessment.