Plate Buckling

Creating a beam-to-beam steel joint and running its ULS design including the plate buckling check: Create a welded I-section column and an IPE 500 beam meeting at one node Activate the Steel Joints add-on and add two member cuts and a stiffener Apply a bending moment and define the ULS design situation and load combination Enable the buckling analysis in the ULS configuration Calculate the model and print the maximum plate design ratio Read back the buckling critical load factors for each mode shape Keywords: steel joint beam to beam member cut stiffener buckling analysis critical load factor design ratios

PythonC#

from math import inf

from dlubal.api import rfem, common
from dlubal.api.common.packing import wrap_value

# -------------------------------------------------------
# This example creates a beam-to-beam steel joint and runs its ULS design
# including the buckling design check of the joint.
#
# A welded I-section column (member 1) meets an IPE 500 beam (member 2) at
# node 2. The joint connects them with two member cuts and one stiffener. The
# buckling analysis is enabled in the ULS configuration, and both the design
# ratios and the buckling critical load factors are read back.
# -------------------------------------------------------

# Editable parameters (SI units)

BEAM_CROSS_SECTION = "IPE 500"
STEEL_GRADE = "S235"
STIFFENER_THICKNESS = 0.016

# Welded parametric I-section for member 1: h/b/t_w/t_f in metres -> "I 840/250/4/10/0/0/H"
COLUMN_SECTION_H = 0.84
COLUMN_SECTION_B = 0.25
COLUMN_SECTION_TW = 0.004
COLUMN_SECTION_TF = 0.01

def define_structure() -> list:
    """Define the base RFEM model (column + beam) used for the analysis."""

    return [
        # Materials
        rfem.structure_core.Material(
            no=1,
            name=STEEL_GRADE,
        ),

        # Cross-Sections
        rfem.structure_core.CrossSection(
            no=1,
            material=1,
            type=rfem.structure_core.CrossSection.TYPE_PARAMETRIC_THIN_WALLED,
            parametrization_type=rfem.structure_core.CrossSection.PARAMETRIZATION_TYPE_PARAMETRIC_THIN_WALLED__I_SECTION__I,
            h=COLUMN_SECTION_H,
            b=COLUMN_SECTION_B,
            t_w=COLUMN_SECTION_TW,
            t_f=COLUMN_SECTION_TF,
            r_1=0.0,
            r_2=0.0,
        ),
        rfem.structure_core.CrossSection(
            no=2,
            material=1,
            name=BEAM_CROSS_SECTION,
        ),

        # Nodes
        rfem.structure_core.Node(
            no=1,
            coordinate_1=0.0,
            coordinate_2=0.0,
            coordinate_3=0.0,
        ),
        rfem.structure_core.Node(
            no=2,
            coordinate_1=0.0,
            coordinate_2=0.0,
            coordinate_3=-1.35,
        ),
        rfem.structure_core.Node(
            no=3,
            coordinate_1=1.045,
            coordinate_2=0.0,
            coordinate_3=-1.35,
        ),

        # Lines
        rfem.structure_core.Line(
            no=1,
            definition_nodes=[1, 2],
        ),
        rfem.structure_core.Line(
            no=2,
            definition_nodes=[2, 3],
        ),

        # Members
        rfem.structure_core.Member(
            no=1,
            line=1,
            type=rfem.structure_core.Member.TYPE_BEAM,
            cross_section_start=1,
        ),
        rfem.structure_core.Member(
            no=2,
            line=2,
            type=rfem.structure_core.Member.TYPE_BEAM,
            cross_section_start=2,
        ),

        # Nodal Supports
        rfem.types_for_nodes.NodalSupport(
            no=1,
            nodes=[1],
            spring_x=inf,
            spring_y=inf,
            spring_z=inf,
            rotational_restraint_x=inf,
            rotational_restraint_y=inf,
            rotational_restraint_z=inf,
        ),
    ]

def define_loading() -> list:
    """Define a load case, the ULS design situation and one load combination."""

    return [
        rfem.loading.StaticAnalysisSettings(
            no=1,
        ),
        rfem.loading.LoadCase(
            no=1,
            name="Moment",
            static_analysis_settings=1,
            action_category=rfem.loading.LoadCase.ACTION_CATEGORY_PERMANENT_G,
            self_weight_active=False,
        ),
        rfem.loading.DesignSituation(
            no=1,
            name="ULS (STR/GEO) - Permanent and transient - Eq. 6.10",
            design_situation_type=rfem.loading.DesignSituation.DESIGN_SITUATION_TYPE_STR_PERMANENT_AND_TRANSIENT_6_10,
            active_for_steel_joints=True,
        ),
        rfem.loading.LoadCombination(
            no=1,
            design_situation=1,
            name="Moment",
            static_analysis_settings=1,
            items=rfem.loading.LoadCombination.ItemsTable(
                rows=[
                    rfem.loading.LoadCombination.ItemsRow(
                        no=1,
                        factor=1.0,
                        load_case=1,
                    ),
                ]
            ),
            combination_rule_str="LC1",
        ),
        # Bending moment about the global Y axis at the free beam end (node 3)
        rfem.loads.NodalLoad(
            no=1,
            nodes=[3],
            load_case=1,
            load_type=rfem.loads.NodalLoad.LOAD_TYPE_MOMENT,
            moment_magnitude=-239190,
            load_direction=rfem.loads.NodalLoad.LOAD_DIRECTION_GLOBAL_Y_OR_USER_DEFINED_V_TRUE_LENGTH,
        ),
    ]

def define_joint_members():
    """Define members assigned inside the Steel Joint add-on table."""

    return rfem.steel_joints_objects.SteelJoint.MembersTable(
        rows=[
            rfem.steel_joints_objects.SteelJoint.MembersRow(
                no=1,
                is_active=True,
                members_no=[1],
                status="Member 1",
                end_type=rfem.steel_joints_objects.SteelJoint.MembersRow.EndType.END_TYPE_MEMBER_ENDED,
                supported=True,
            ),
            rfem.steel_joints_objects.SteelJoint.MembersRow(
                no=2,
                is_active=True,
                members_no=[2],
                status="Member 2",
                end_type=rfem.steel_joints_objects.SteelJoint.MembersRow.EndType.END_TYPE_MEMBER_ENDED,
                supported=False,
            ),
        ]
    )

def define_joint_components():
    """Define top-level Steel Joint components and their RFEM setting keys.

    Only the user-defined components are created here (two member cuts that
    connect the members plus one stiffener). RFEM auto-generates the derived
    plates, plate cuts and welds from these.
    """

    joint_components = [
        (
            rfem.steel_joints_objects.SteelJoint.ComponentsRow.Type.TYPE_MEMBER_CUT,
            "Member Cut 1",
            [
                ("member_to_cut", "Member 1"),
                ("type_of_cut", 0),
                ("cut_by", "Member 2"),
                ("cutting_method", 0),
                ("cutting_plane", 1),
                ("direction", 0),
                ("offset", 0.0),
            ],
        ),
        (
            rfem.steel_joints_objects.SteelJoint.ComponentsRow.Type.TYPE_MEMBER_CUT,
            "Member Cut 2",
            [
                ("member_to_cut", "Member 2"),
                ("type_of_cut", 0),
                ("cut_by", "Member 1"),
                ("cutting_method", 0),
                ("cutting_plane", 0),
                ("direction", 0),
                ("offset", 0.0),
                ("weld_is_active_1", True),
                ("weld_is_active_2", True),
                ("weld_is_active_3", True),
                ("weld_type_1", 3),
                ("weld_type_2", 3),
                ("weld_type_3", 3),
            ],
        ),
        (
            rfem.steel_joints_objects.SteelJoint.ComponentsRow.Type.TYPE_STIFFENER,
            "Stiffener 1",
            [
                ("stiffened_member", "Member 1"),
                ("reference_member", "Member 2"),
                ("plate_material", 1),
                ("plate_thickness", STIFFENER_THICKNESS),
                ("plate_count", 2),
                ("position", 2),
                ("direction", 1),
                ("location_offset", "0.0000 0.0000"),
                ("side", 2),
                ("inclination", 0.0),
                ("width_offset", 0.0),
                ("height_offset", 0.0),
                ("chamfer", 0.0),
                ("weld_is_active_1", True),
                ("weld_is_active_2", True),
                ("weld_is_active_3", True),
                ("weld_type_1", 3),
                ("weld_type_2", 3),
                ("weld_type_3", 3),
            ],
        ),
    ]

    joint_component_rows = []

    for component_no, joint_component in enumerate(joint_components, start=1):
        component_type, component_name, component_settings = joint_component
        setting_rows = []

        for setting_no, setting in enumerate(component_settings, start=1):
            setting_key, setting_value = setting

            setting_rows.append(
                rfem.steel_joints_objects.SteelJoint.ComponentsRow.SettingsTableRow(
                    no=setting_no,
                    key=setting_key,
                    value=wrap_value(setting_value),
                )
            )

        joint_component_rows.append(
            rfem.steel_joints_objects.SteelJoint.ComponentsRow(
                no=component_no,
                is_active=True,
                type=component_type,
                name=component_name,
                settings=rfem.steel_joints_objects.SteelJoint.ComponentsRow.SettingsTable(
                    rows=setting_rows,
                ),
            )
        )

    return rfem.steel_joints_objects.SteelJoint.ComponentsTable(
        rows=joint_component_rows,
    )

def define_steel_joint() -> list:
    """Define the steel joint and its design configuration."""

    return [
        rfem.steel_joints_design_addon_objects.JointUlsConfiguration(
            no=1,
            name="ULS Configuration",
        ),
        rfem.steel_joints_objects.SteelJoint(
            no=1,
            nodes=[2],
            user_defined_name_enabled=True,
            name="Nodes : 2 | Created via API",
            comment="Created via API",
            to_design=True,
            ultimate_configuration=1,
            members=define_joint_members(),
            components=define_joint_components(),
        ),
    ]

# -------------------------------------------------------
# MAIN SCRIPT
# -------------------------------------------------------

with rfem.Application() as rfem_app:

    # Initialize model
    rfem_app.close_all_models(save_changes=False)
    rfem_app.create_model(name='steel_joint_buckling_analysis')

    # Activate the Steel Joints add-on
    base_data = rfem_app.get_base_data()
    base_data.addons.steel_joints_active = True
    rfem_app.set_base_data(base_data=base_data)
    rfem_app.delete_all_objects()

    # Create structure, loading and the steel joint
    rfem_app.create_object_list(
        define_structure() +
        define_loading() +
        define_steel_joint()
    )

    # Enable the buckling analysis in the ULS configuration
    # (a freshly created configuration has it switched off by default)
    settings_tree = rfem_app.get_object(
        obj=rfem.steel_joints_design_addon_objects.JointUlsConfiguration(no=1)
    ).settings_ec3

    common.tree_table.set_values_by_key(settings_tree, "perform_buckling_analysis", values=[True])

    rfem_app.update_object(
        obj=rfem.steel_joints_design_addon_objects.JointUlsConfiguration(
            no=1,
            settings_ec3=settings_tree,
        )
    )

    # Calculate the ULS design situation
    rfem_app.calculate_all(skip_warnings=True)

    # --- Steel joint design checks (max ratios) ---
    design_ratios_df: common.Table = rfem_app.get_results(
        results_type=rfem.results.ResultsType.STEEL_JOINTS_DESIGN_RATIOS,
    ).data

    plate_ratio = design_ratios_df.loc[
        design_ratios_df["design_check_type"] == "UL1000.00", "design_ratio"
    ].dropna().max()

    print("Steel joint design check summary (max ratios):")
    print(f"Plates (UL1000.00): {plate_ratio:.3f}")

    # --- Steel joint buckling analysis (critical load factors) ---
    # Only available when perform_buckling_analysis is enabled.
    # design_check_type ST2000.00 -> "Buckling analysis"; f = critical load factor.
    buckling_df: common.Table = rfem_app.get_results(
        results_type=rfem.results.ResultsType.STEEL_JOINTS_BUCKLING_DESIGN_RATIOS,
    ).data

    print("\nSteel joint buckling analysis (critical load factors):")
    for row in buckling_df.itertuples():
        print(f"Mode {row.mode_shape_no}: f = {row.critical_load_factor:.3f}")

    lowest_factor = buckling_df["critical_load_factor"].dropna().min()
    print(f"Lowest critical load factor: {lowest_factor:.3f}")