Bridge Girder Designer

For a beam-and-slab bridge, compute the AASHTO LRFD live-load distribution factors (interior & exterior, moment & shear), the longitudinal stiffness K_g, apply the HL-93 load with dynamic allowance IM, and combine via Strength I to the factored girder moment — with a section diagram and optional capacity check.

⭐ Free to design · Balance … EP

⚠️ Educational tool — verify against AASHTO LRFD. The distribution-factor equations apply only within AASHTO's ranges of applicability (flagged below). The HL-93 truck moment is your input (from analysis or AASHTO tables); confirm load factors, IM and capacities against the current AASHTO LRFD Bridge Design Specifications.

① Deck geometry

Girder spacing S (m)

Span length L (m)

Slab thickness t_s (mm)

Number of girders N_b

Beam position to design

Exterior dist. d_e (m) (ext.)

Design lanes available

② Longitudinal stiffness K_g

K_g (mm⁴)

③ Load effects (optional — for the factored girder moment)

HL-93 truck moment / lane M_truck (kN·m)

Dynamic allowance IM

Lane load w (kN/m)

…or lane moment / lane M_lane (kN·m)

M_DC dead / girder (kN·m)

M_DW wearing / girder (kN·m)

Capacity φM_n / girder (kN·m) opt.

Load modifier η

🌉 Distribution factors & girder demand

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AASHTO LRFD live-load distribution

g_m · 1 lane

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g_m · 2+ lanes

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g_m governing

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g_v governing

—

K_g

—

Factored M_u

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Bridge Girder Designer

① Deck geometry

② Longitudinal stiffness Kg

③ Load effects (optional — for the factored girder moment)

🌉 Distribution factors & girder demand

Worked solution

② Longitudinal stiffness K_g