# Cross-frame X (w/o Top Chord) \[SIG]

## Location

**Girders:** Choose the two girders that are connected by the cross frame.

**Skew Angle:** A positive skew value rotates the cross frame in a clockwise direction, while a negative skew value rotates it in a counterclockwise direction. It is important to remember that the cross frames are positioned at the specified station along a line perpendicular to the PGL, which is then rotated according to the entered skew value.

![](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20230307-082638.png?api=v2)

**Station\[Start/End]:** Enter the station along the PGL. When dealing with curved girder bridges, collecting distance along the girder length can lead to different inputs for the right and left girder that are connected by cross frames, causing ambiguity. Therefore, collecting the station along the PGL is a more reliable solution to avoid such issues. Furthermore, since cross frames are typically continuous in the transverse direction, entering the same station for all cross frames ensures that their locations are consistent between each girder.

The same principle can be applied for skewed cross frames. If the user enters the same station and skew values for the cross frames between Girder 1-2, Girder 2-3, and Girder 3-4, it ensures continuity between the cross frames. It should also be noted that the cross frames are positioned along a line perpendicular to the PGL, which is rotated according to the entered skew value.

Inaccurate finite element models and disconnected nodes/elements in the cross frame can occur if the entered station values are not >= the girder start station or <= the girder end station. This can cause stability issues in the finite element model. To ensure correct station input, users should select the start/end options from the station input. This approach is especially recommended for cross frames located at the beginning or end of girders.

**Has Middle Gusset Plate? \[YES/NO]:** Choose "YES" if there is a gusset plate at the overlapping section of the X. The image below does not depict a gusset plate in the middle.A node will be generated at the conjunction of two diagonals if this parameter is defined with the option 'YES'.

![](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20230307-084614.png?api=v2)

**Chord Flipping Side \[Back Station/Ahead Station]:** This parameter controls the orientation of the cross-frame chords. When set to 'Back Station', the chords are oriented towards the back station direction. When set to 'Ahead Station', the chords are oriented towards the ahead station direction.

## Sections

Assign a section for the bottom, or diagonal chord, which can be imported from the AISC database by users. The section data will be utilized for the 3D model of the object and will directly influence the Finite Element Analysis (FEA) and Finite Element Model (FEM).

**Bottom Chord Section:** Assign a section for the bottom chord.

**Diagonal Chord Section:** Define a section for the diagonal chord.

**Bottom Chord Orientation Angle:** Specify an angle for the bottom chord to rotate around its longitudinal axis.

**Diagonal Chord Orientation Angle \[0/90/180/270]:** Specify a rotation angle around the longitudinal axis of the diagonal chord.

**Top Chord Section:** Section assigned for the top chord. Not used by Cross-frame X (w/o Top Chord) but present for consistency with cross-frame objects.

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**Top Chord Material:** Material assigned to the top chord.

**Bottom Chord Material:** Material assigned to the bottom chord.

**Diagonal Chord Material:** Material assigned to the diagonal chord(s).

![image-20241009-103118.png](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20241009-103118.png?api=v2)

## Gusset Plate

The parameters listed below are used for 3D representation. While gusset plates do not have finite element model (FEM) and do not provide additional stiffness to the elements, they can still be applied as weight loads and used for code checks, depending on user-defined settings and specifications. For visual representation of each parameter, refer to the figure below.

**Top Gusset Plate:** Gusset plates that exist under Superstructure > Connections can be assigned to the related column.

**Bottom Gusset Plate:** Gusset plates that exist under Superstructure > Connections can be assigned to the related column.

**Center Gusset Plate:** Gusset plates that exist under Superstructure > Connections can be assigned to the related column.

**Top Plate - Vert. Offset from Top of Web:** The location of the top gusset plate with respect to the top of the web along the vertical direction can be defined by this parameter. For visual representation, refer to the figure provided below.

**Top Plate - Horz. Offset from Edge of Web:** The location of the top gusset plate with respect to the edge of the web along the horizontal direction can be defined by this parameter. For visual representation, refer to the figure provided below.

**Bottom Plate - Vert. Offset from Bottom of Web:** The location of the bottom gusset plate with respect to the bottom of the web along the vertical direction can be defined by this parameter. For visual representation, refer to the figure provided below.

**Bottom Plate - Horz. Offset from Edge of Web:** The location of the bottom gusset plate with respect to the edge of the web along the horizontal direction can be defined by this parameter. For visual representation, refer to the figure provided below.

**Center Plate - Vert. Offset from Cross Frame Center:** The location of the center gusset plate with respect to the center of the cross frame along the vertical direction can be specified by this parameter. For visual representation, refer to the figure below.

**Center Plate - Horz. Offset from Center of Bay:** The center distance between two girders, or in other words, the bay, can be used to specify the horizontal location of the center gusset plate, where a positive value offsets the center gusset plate to the right, and negative values offset the gusset plate to the left when looking upstation along the PGL.

**Center Plate - Along Diagonal Chord \[No/Left Diagonal/Right Diagonal]:** Controls how the center (middle) gusset plate is aligned with the X diagonals at the intersection. Choose 'No' to keep the center plate aligned with the cross-frame axes (independent of the diagonals), 'Left Diagonal' to orient the plate along the left-hand diagonal chord, or 'Right Diagonal' to orient it along the right-hand diagonal chord, so the plate follows the chosen diagonal's direction at the crossing point. Defaults to 'No', and is only available when a Center Gusset Plate is assigned and the cross frame has a middle gusset plate (Has Middle Gusset Plate set to YES).

**Show Gusset Plate \[YES/NO]:** This parameter controls whether the gusset plates are displayed in the 3D view. When set to 'YES', the gusset plates will be visible in the 3D model. When set to 'NO', they will be hidden.

![image-20250130-154532.png](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20250130-154532.png?api=v2)

## Stiffener

The parameters listed below are used for 3D representation. While cross-frame stiffeners do not have finite element models (FEM) and do not provide additional stiffness to the elements, they can still be applied as weight loads, depending on user-defined settings and specifications.

**Stiffener Used \[YES/NO]:** If this parameter is set to 'YES,' the user can define additional parameters for stiffeners. If it is set to 'NO,' the other parameters will be marked as not applicable (N/A).

**Vertical Stiffener Thickness:** For visual representation of vertical stiffener thickness, refer to the figure below.

**Vertical Stiffener Width:** For visual representation of vertical stiffener width, refer to the figure below.

**Distance from Top of Web:** Clear distance between the top of the stiffener plate and the top of the girder web.

**Distance from Bottom of Web:** Clear distance between the bottom of the stiffener plate and the bottom of the girder web.

**Material:** The material definition for the stiffener can be made using this parameter. Materials can either be imported or assigned from previously defined ones.

**Vertical Clip Height:** The height of the vertical clip at the corners of the stiffener. This parameter defines the size of the corner clip in the vertical direction.

**Horizontal Clip Width:** The width of the horizontal clip at the corners of the stiffener. This parameter defines the size of the corner clip in the horizontal direction.

**Show Stiffener \[YES/NO]:** This parameter controls whether the stiffeners are displayed in the 3D view. When set to 'YES', the stiffeners will be visible in the 3D model. When set to 'NO', they will be hidden.

**Generate FEM \[YES/NO]:** This parameter controls whether the stiffeners are included in the Finite Element Model. When set to 'YES', the stiffeners will be modeled as structural elements. When set to 'NO', they will not be included in the FEM analysis.

![image-20241009-084826.png](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20241009-084826.png?api=v2)

## Geometry

These parameters are used for both computing the member end offset of cross frame truss elements in finite element analysis and 3D representation. For visual representation of each parameter, refer to the figures below.

**Dia. Chord- Top Vert. Dist. from Top of Web:**: This parameter specifies the vertical distance between the working point (WP) of the Diagonal Chord and the top of the web, along the top side of the web. The definition of this parameter only affects the 3D model.

**Dia. Chord- Top Horz. Dist. from Center of Web:**: This parameter specifies the horizontal distance between the working point (WP) of the Diagonal Chord and the center of the web, along the top side of the web. The definition of this parameter affects both the 3D model and FEM.

**Dia. Chord- Bot. Vert. Offset from WP of Bot. Chord**: This parameter specifies the vertical distance between the working point (WP) of the Diagonal Chord and the working point (WP) of the Bottom Chord. The definition of this parameter only affects the 3D model.

**Dia. Chord- Bot. Horz. Offset from WP of Bot. Chord**: This parameter specifies the horizontal distance between the working point (WP) of the Diagonal Chord and the working point (WP) of the Bottom Chord. The definition of this parameter affects both the 3D model and FEM.

**Dia. Chord- Top Inner Offset from WP**: This parameter specifies the inner offset distance of the Diagonal Chord’s working point along the top side of the chord. The definition of this parameter affects both the 3D model and FEM.

**Dia. Chord- Bot. Inner Offset from WP**: This parameter specifies the inner offset distance of the Diagonal Chord’s working point along the bottom side of the chord. The definition of this parameter affects both the 3D model and FEM.

**Bot. Chord- Vert. Dist. of WP from Bottom of Web:**: This parameter specifies the vertical distance between the working point (WP) of the Bottom Chord and the bottom of the web. The definition of this parameter affects both the 3D model and FEM.

**Bot. Chord- Horz. Distance of WP from Center of Web:**: This parameter specifies the horizontal distance between the working point (WP) of the Bottom Chord and the center of the web. The definition of this parameter affects both the 3D model and FEM.

**Bot. Chord- Inner Offset from WP**: This parameter specifies the inner offset distance of the Bottom Chord’s working point (WP), measured along the inner edge of the structure. The definition of this parameter affects both the 3D model and FEM.

![](https://openbrim.atlassian.net/wiki/download/attachments/2271805557/image-20230915-083158.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2271805557/image-20230915-083231.png?api=v2)

## FEA

For detailed explanations on axial rigidity coefficients, refer to the AASHTO excerpts below.

**Bottom Chord Axial Rigidity Coefficient:** This parameter specifies the axial rigidity coefficient of the bottom chord.

**Diagonal Chord Axial Rigidity Coefficient:** This parameter specifies the axial rigidity coefficient of the diagonal chord.

![image-20241105-085311.png](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20241105-085311.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20241105-085401.png?api=v2)

![](https://openbrim.atlassian.net/wiki/download/attachments/2123268097/image-20241105-085415.png?api=v2)


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