The Cross Frame/Diaphragm Definition command provides the means to define various cross frame and diaphragm configurations (CFDs). The CFD will appear in the graphic window as it is being defined. Once defined the CFDs are located on the bridge using the Cross Frame/Diaphragm Location command.

Cross Frames are used in LEAP Bridge Steel to more accurately describe the overall deck stiffness (in grillage analysis) and to determine flange lateral bending stresses that result from dead and live load analysis. The flange lateral bending stresses are used as required in the various code checks (e.g. Article 6.10.1.6). Additionally LEAP Bridge Steel will report individual cross frame member forces for each load combination and perform preliminary design for tension and compression (See Analysis and Design Sections).

Individual cross frame member forces are reported by load case in the Cross Frame Detailed Forces Analysis Report. Additionally individual cross frame members are checked for compression and tension in the Cross Frame Design Report. Only cross frame members for X, V and inverted V cross frame types are reported (strut member end moments and shears are only reported in the Cross Frame Forces report on the Analysis Menu).

When reviewing the Cross Frame Detailed forces report or the Cross Frame Design report, the individual members are reported for X, V and Inverted V configurations using the respective diagrams below:

LEAP Bridge Steel uses the methodologies developed in NCHRP Report 725 “Guidelines for Analysis Methods and Construction Engineering of Curved and Skewed Steel Girder bridges” to analyze cross frames in grillage models. The user is referred to Section 3.2.3 “Improved Equivalent Beam Cross-Frame Models” and Section 3.2.4 “Improved Calculation of I-Girder Flange Lateral Bending Stresses from 2D-Grid Analysis” as these specific methodologies are employed by LEAP Bridge Steel.

Cross Frame analysis results for dead load and live load are reported in the form of equivalent cross frame beam end moments and shears by load case in the Analysis -> Cross Frame Forces command. Additionally the individual cross frame member forces are reported in the Analysis -> Cross Frame Detailed Forces command.

The cross frame end moments are used to determine the flange lateral bending moments and stresses as described in Report 725, Section 3.2.4.