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.
Ordinary short and medium spans use the fixed pressures of 4.10.2.1 (design wind speed VD = 40 m/s).
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) | Ordinary spans: fixed table for VD = 40 m/s; typhoon-prone medium / long spans: VD = 1.723(zD/zG)αV10, regional V10 30–50 m/s (10-min mean, 100-year) | 4.0 − 0.2·B/D (1 ≤ B/D < 8), 2.4 (B/D ≥ 8) kPa; or ½ρVD²CDGr | built into the table; trusses 2.4/√φ; piers 3.0 square / 1.5 round | 1.5 kN/m at 1.5 m above the deck, pressure not reduced | — |
| 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.
The design code switch at the top of the inputs drives the page's own code selector. Eurocode follows EN 1991-1-4: a 10-minute mean basic velocity vb = cdir·cseason·vb,0, a log-law profile and turbulence by terrain category 0 to IV, the peak pressure qp(z), and a force coefficient cf,x from the width-to-depth ratio b/dtot (2.4 for squat sections down to 1.3 for wide decks). The headline force is wind alone on the deck plus parapets; wind acting together with traffic is a separate row, with a 2 m traffic band in dtot and the reduced velocity vb,0* = 23 m/s. Vertical wind uses cf,z = ±0.9 at a quarter of the width and longitudinal wind 25 % or 50 % of the transverse force; the simplified C factor of Table 8.2 is shown as a cross-check. All factors are the recommended values (ρ 1.25 kg/m³, cscd = 1.0). KDS 24 12 21 gives ordinary short and medium spans fixed pressures for a 40 m/s design speed: girder bridges 4.0 − 0.2·B/D kPa (2.4 kPa from B/D = 8), trusses 2.4/√φ, piers 3.0 kPa square or 1.5 kPa round, and a separate 1.5 kN/m on traffic 1.5 m above the deck, with no reduction of the pressure under live load. Medium and long spans in typhoon-prone areas use p = ½ρVD²CDGr, with the design speed scaled from the regional basic speed by height and terrain and a gust factor from the turbulence of the site. Load factors come from KDS 24 12 11 (wind 1.40 at ULS III).
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 take their wind pressures from the AASHTO signs, luminaires and traffic signals specification, as the pedestrian guide directs, on the full exposed height of the deck, railings and fencing, 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. That dynamic assessment is outside this calculator; the footbridge section below has the details.
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 LRFD Guide Specifications for the Design of Pedestrian Bridges take wind pressures from the AASHTO signs, luminaires and traffic signals specification rather than LRFD 3.8, on the full exposed height of the deck, railings and any fencing or enclosure, plus a vertical uplift of 0.020 ksf on the deck width at the windward quarter point. Slender footbridges also need a vibration check (pedestrian-induced and vortex shedding), which is a separate dynamic assessment.
Footbridges are light and often slender, so wind can govern their bearings, piers and piles more than it does on a road bridge. The rules differ from the vehicular case in three ways: where the pressure comes from, what area it acts on, and the dynamic checks.
The AASHTO LRFD Guide Specifications for the Design of Pedestrian Bridges (2nd edition, 2009; the 2015 interim revisions did not change the wind clauses) do not point to LRFD Article 3.8. They take wind pressures from the AASHTO specification for structural supports for highway signs, luminaires and traffic signals (Articles 3.8 and 3.9), because footbridges can be flexible and may carry signs. In outline:
Two caveats are widely discussed. The signs specification works on a 100-year return period while AASHTO LRFD 8th and 9th editions moved vehicular bridges to 3-second gusts with a 700-year return period and a wind load factor of 1.0, so mixing the two can under-design unless the factors are reconciled. And for stiff decks (concrete slabs, composite girders, short timber spans) many designers and owners agree to use LRFD 3.8 directly. Agree the basis with the owner at the start.
Section 8 of EN 1991-1-4 applies the same peak velocity pressure qp(z) and force coefficient cf,x approach to footbridges. The traffic band of 2 m (road) or 4 m (rail) does not apply; dtot takes the deck plus the parapet allowance, so use the calculator's "No traffic case" with the right parapet option. Light, long footbridges also need the vortex shedding and galloping checks of Annex E. Pedestrian comfort is a serviceability check in EN 1990 Annex A2: it is required when the vertical frequency is below 5 Hz or the horizontal and torsional frequencies are below 2.5 Hz, with recommended maximum deck accelerations of 0.7 m/s² vertical, 0.2 m/s² horizontal in normal use and 0.4 m/s² for exceptional crowds.
Sources: WSDOT design memo 11-2009 on the LRFD pedestrian bridge guide; NCHRP 20-07(244) final report (draft guide specification); A. Gordon, Revisiting Wind Loads on Pedestrian Bridges, STRUCTURE magazine; Majowiecki, footbridge design vs dynamic performance (Eurocode comfort values).