Analysis
The Analysis Command provides the means to request analysis for all defined load cases and view the results graphically and in report form.
Once the bridge model and loads are defined, the Analysis command provides tools to analyze for dead and live load and view the results graphically and in report form. Three analysis methods are currently supported: line girder, grillage and FEM. In line girder analysis members are analyzed using an influence line approach and live load is distributed using live load distribution factors. In Grillage analysis a 3D grillage model is automatically generated from the physical model and live load is applied to the influence surface. Main members are modeled as beam elements and have member properties associated as required for the different stages (e.g. non-composite, short-term composite (n=n) and long term composite (n=3n). The slab is modeled using transverse beam elements that take on the section properties of the segmented slab. Cross frames are modeled as Timoshenko beam elements that are created from the physical cross frame using the technique published in NCHRP Report 725. In FEM analisys, a 3D finite element model is also automatically generated from the physical model and live load is applied to the influence surface. Deck ang web(and bottom flanges of tub-girders) are modeled using plate elements, and flanges and cross frames are modeled using beam elements.
Vehicle loads can be placed on the influence surface as axle loads or wheel loads. In axle loading the individual wheel loads on each axle are summed to a single load that is assumed to act at the vehicle centerline when applied to the influence surface. In wheel loading each wheel load acts at its defined position on the axle when applied to the influence surface.
Live Load Distribution factors
Live load distribution factors are calculated for interior and exterior members (with the rigid frame option turned off) for both positive and negative moments.
- for negative moment regions, if the POI is within 0.25 * the distance from an interior support LEAP Bridge Steel uses the average of the span length where the POI exist and the span on the opposite side of the interior support;
- for positive moment and negative moment regions if the POI is outside 0.25 regions LEAP Bridge Steel uses the length L of the current span;
After calculation, these Live Load Distribution Factors are multiplied by the negative moments for negative bending area and for the positive moments for positive bending area.
The Live Load Distribution Factors dialog will have negative and positive values for Shear and Moment, One-Lane, Multi-Lane and for Fatigue as shown below:
