Model types available

For the example code on this page, ospgrillage is imported as og

import ospgrillage as og

Beam Elements Only - beam_only

This is the traditional modelling approach that is comprised of beam elements lay out in a grid pattern, with:

• longitudinal members representing composite sections along longitudinal direction (e.g. main beams);

• transverse members representing slabs or secondary beam sections.

This is the default model type if model_type keyword argument is not specified to create_grillage()

example_bridge = og.create_grillage(bridge_name="Super T grillage", long_dim=10, width=7, skew=-42,
                                num_long_grid=7, num_trans_grid=5, edge_beam_dist=1, mesh_type="Ortho")

More information of this model type can be found here.

Beam with Rigid Links - beam_link

This is a modified version of the traditional beam element model with the following features:

• Offsets (in x-z plane) for start and end nodes along direction of transverse members - using joint offset.

• Offsets (in vertical y direction) for start and end nodes of longitudinal members - again using joint offsets.

Figure 2 shows the details of the aforementioned model type. Figure 3 shows the model type created in a similar commercial software SPACEGASS.

Figure 2: Beam grillage with rigid links - idealization.

Figure 3: Beam grillage with rigid links model from SPACEGASS software.

To create this model, have create_grillage() keyword for model_type set to beam_link.

example_bridge = og.create_grillage(bridge_name="Modified bridge grillage", long_dim=10, width=7, skew=-12,
                                    num_long_grid=7, num_trans_grid=5, edge_beam_dist=1, mesh_type="Ortho",
                                    model_type="beam_link",
                                    beam_width=1, web_thick=0.02, centroid_dist_y=0.499)

The joint offsets are rigid links. Information can be found in OpenSeesPy’s geomtransf

Table 1 outlines the specific variables for beam link model.

Table: 1 Input arguments for shell hybrid model

Keyword argument	Description
beam_width	width of the beam/longitudinal members - this is needed for ospgrillage to define the offset distance in z direction
web_thick	thickness of web - this is needed for ospgrillage to define the offset distance in z direction
centroid_dist_y	distance in y direction to offset longitudinal members (exterior,interior main beams)

Note

As of release 0.1.0, OpenSeesPy visualization module ops_vis is unable to visualize the joint offsets.

Shell & Beam Elements - shell_beam

This is a more refined model using two element types - shell and beam elements - with the following features:

• Shell elements lay in grids to represent bridge decks.

• Beam elements modelled with an offset to the plane of shell elements to represent longitudinal beam sections.

• Beam elements linked to shell elements at two corresponding locations using constraint equations - OpenSeesPy’s rigidLink command

This model has advantageous in modelling slabs using shell elements which are well-suited to represent two-dimensional slab behaviour. Figure 4 shows the details and variables of the shell beam hybrid model.

Figure 4: Shell beam hybrid model idealization

When shell_beam() model type is selected, ospgrillage automatically determines the position of shell elements within the grillage plane. Users only have to define and assign the section of the shell element via create_section() and set_shell_member() respectively. Finally, to create this model, have create_grillage() keyword for model_type set to shell. In addition, users are required to define and assign shell elements. The following example code shows the steps to create the shell model type:

# create section of shell element
slab_shell_section = og.create_section(h=0.2) # h = thickness
# shell elements for slab
slab_shell = og.create_member(section=slab_shell_section, material=concrete)
# create grillage with shell model type
example_bridge = og.create_grillage(bridge_name="Shell grillage", long_dim=10, width=7, skew=0,
                                    num_long_grid=6, num_trans_grid=11, edge_beam_dist=1, mesh_type="Orth",
                                    model_type="shell_beam", max_mesh_size_z=0.5, offset_beam_y_dist=0.499,
                                    link_nodes_width=0.89)
# set shell members to shell elements
example_bridge.set_shell_members(slab_shell)

Table 2 outlines the specific variable for shell hybrid model.

Table: 2 Input arguments for shell hybrid model

Keyword argument	Description
max_mesh_size_z	max mesh size in z direction. ospgrillage automatically determines the mesh size in z direction based on this variable and spacing of link nodes
offset_beam_y_dist	distance between offset beams and grillage shell plane.
beam_width	this determines the width between link nodes - left and right links to offset beam elements - in global z direction