Live Load Moment Calculator

About Live Load Calculator
  • Live load calculator permits both imperial and metric unit systems.
  • Calculator offers options for HL-93, KGM45, and a manual selection of live load model. The live load calculator aims to find maximum live load moment under a choice of truck models.
  • Truck Loads consist of P1, P2 and P3 axle loads, and wllu uniform load per lane. The parameters x1 and x2 denote distance between axle loads, parameter xmax is used to locate the middle-axle’s distance from the left support.
  • Mid-span live load moment is calculated using span length and dynamic load allowance values for the given truck model. Dynamic load allowance is set 33% of static weight of truck model and is not applied to the uniform load per AASHTO-LRFD . Live load distribution factor is usually computed to determine the force effect for an individual girder. To calculate the distribution factor, area of girder (Ag), moment of inertia (Ig), girder depth(d), geometric center from bottom(yb), slab thickness(ts), girder spacing(s), and  modulus of elasticity of slab and girder(Es,Eg) should be known. Girder and slab properties can easily be determined from Concrete Girder Geometry Calculator.  It has been known that for the multilane bridges the distribution factor can be different based on the number of loaded lanes.
  • Default setting of the calculator is that the truck moves from the left support to the right. In case the direction of movement is reversed, for computations, values of P1 and P3 axle loads can be switched.
  • In the final step, maximum moment for the given live load model is calculated for one of the interior girders.
  • Please use “.” for decimal digits between numbers, for example girder depth is 1.5 meters.
  • Drawings are representative to show only truck loads.
  • Reference : Generalized Approach for Determining the Maximum Moment under HL-93 Loading on Simple Spans.
  • Thanks to author Steven Lowinger.