Runway Beam (Gantry Girder) Calculator

Calculate maximum vertical bending moments, horizontal surge, and shear forces for crane runway structures.

Read the Crane Runway Beam Guide

1. Crane Wheel Data

kN

Maximum vertical load on a single wheel when fully loaded trolley is at extreme end.

m

Center-to-center distance between wheels on the same rail track.

2. Building & Surge Data

m

Distance between the building columns supporting the runway beam.

kN

Sum of the Trolley/Crab dead weight PLUS the Safe Working Load (SWL). Used for horizontal surge calculation.

Design Forces

Vertical Bending (My)
--
kNm (Includes Impact Factor)
Lateral Surge Bending (Mx)
--
kNm
Max Shear Force (Vz)
--
kN (At supports)

Note on Deflection: For EOT Cranes, ensure the selected steel beam's vertical deflection does not exceed Span / 600 (or Span/1000 for high-speed automated cranes).

The Engineering Theory

Designing a crane runway beam is vastly different from designing a standard floor beam because the loads are moving, dynamic, and multidirectional.

1. Moving Loads (Influence Lines)

Unlike a static point load in the center, a crane has two wheels (or more) moving across the beam. The absolute maximum bending moment does not always occur when the wheels are perfectly centered. For a two-wheel crane, the maximum moment occurs under one wheel when the center of the beam is halfway between the center of gravity of the load system and that wheel. This calculator automatically uses moving-load calculus to find the absolute maximum moment.

2. Dynamic Impact Factors

When an operator suddenly jerks the hoist up, the cables stretch and bounce, sending a shockwave into the structure. Industry standards mandate a vertical impact factor (usually 25% extra, or 1.25x) to account for this dynamic amplification.

3. Horizontal Surge (Lateral Bending)

When the trolley (crab) brakes suddenly while traveling across the bridge, it creates a lateral "surge" force perpendicular to the runway rail. This is typically taken as 10% of the combined weight of the crab and the lifted load. The runway beam must be strong enough laterally (in its minor axis) to resist this bending moment, which is why gantry girders often require a surge channel welded to the top flange.