Plastic Hinge#

The SSD task task_plastic_hinge_small Plastic Hinge tasks aims to deliver a ready-to-use material model for concentrated plasticity hinge within a pushover workflow. Based on nonlinear a cross sectional analysis, the task offers direct computation of an idealised work laws accounting for the force-moment-moment (P-M-M) interaction.

Input#

Define the input settings for a calculation of an idealised plastic hinge based on an interactive on-the-fly computation of the sectional capacity.

Cross Section and Material Properties#

Cross Section#

Select a reinforced concrete, structural steel or composite cross section for the computation of the plastic hinge. The grey fields provide informative information for the previously calculated cross sections and materials.

Note

The cross sections or materials need to be recalculated before entering the plastic hinge task, if there are any subsequent changes to them.

Material State#

The material state defines the type of material law (ultimate or serviceability) and the corresponding safety factors. The corresponding material laws and safety factors are based on a selected material state that corresponds to a design state of a building code, with exception of the mean values that refers always to unfactored serviceability material laws.

Concrete / Reinforcement / Structural Steel#

Define the material characteristics that are required for the cross sectional analysis and plastic hinge computation.

Reference Material - Choose a material for which the limit strains will be assessed. The automatic selection option will evaluate all materials within the specified category (concrete, reinforcement, or structural steel) and will select the material that first reaches the specified ultimate strain.

Limit Strains - The provided yield and ultimate limit strains for concrete and reinforcement control the cross sectional analysis and idealisation of the plastic hinge (i.e. bilinearisation). The concrete is assumed to carry only compressive forces; therefore, only negative input values are permitted for the concrete strains. Assuming isotropic material law for the reinforcement, only positive values are permitted for the reinforcement strains. Input for the structural steel can be provided as positive values. However, both compressive and tensile strains of a structural steel material will be cross-checked against the specified limit strains.

Safety Factors - Per user preference, the material safety factors can be directly modified only for the purpouse of plastic hinge computation.

Plastic Hinge#

Generated Work Law#

Select the number and title of the generated plastic hinge work law to be exported for further use.

Control#

Specify the plastic hinge properties based on selected axial force levels.

Hinge Type - Six types of plastic hinge work law may be defined, depending on the interaction between the force and moments:

Type	Description
P-My-Mz	Hinge accounting for axial force - moment (y) - moment (z) interaction
P-My	Hinge accounting for axial force - moment (y) interaction
P-Mz	Hinge accounting for axial force - moment (z) interaction
My-Mz	Hinge accounting for moment (y) - moment (z) interaction (single axial force level)
My	Hinge for moment in y direction (single axial force level)
Mz	Hinge for moment in z direction (single axial force level)

Note

Multiple axial force levels may be added in the table only for the hinge types that consider axial force interaction (P-My-Mz, P-My, P-Mz)

Hinge Length - The plastic hinge length is a required input to translate the sectional force-deformation relation into element force-displacement relation. This value is usually defined in building codes.

My - Mz Interaction - Compute or enter manually the interaction exponent for the moment-moment interaction:

Manual Input - Enter an interaction exponent larger than 1 to account for the interaction. Setting the interaction exponent to 0 yields no interaction between the two moments.

Compute - Compute the average interaction exponent based on the axial force levels provided in the table. At least one normal force level should be selected.

Note

The My - Mz interaction is only relevant for hinge types that consider interaction between the two moments (P-My-Mz, My-Mz).

Idealisation - Type of idealisation of the moment-curvature relationship for the computation of the plastic hinge, with two methods available: Limit Strains or CALTRANS. For more information please check the FEABENCH manual.

Plastic Moment Amplification Factor - Idealised plastic moment is calculated from the curvature analysis as: M_yield + factor * (M_max – M_yield).

Hardening Factor - Controls the hardening of the idealised curve after reaching the Idealised plastic moment. Hardening slope is calculated as Hardening factor * Elastic slope of the idealised curve.

Material Type - Material type for the work laws of the plastic hinge.

Sectional Capacity#

On-the-fly computation of the ultimate sectional capacity based on the material State, safety factors and Ultimate or Yield Limit Strains in the material tab (independent of the plastic hinge type). The figure is intended to guide the selection of the axial force levels and it is interactive with the axial force table. Selecting particular levels in the table results in cutting planes on the PMM figure.

Performance Limits#

Performance categories, along with their associated criteria, can be utilized for the limit strain-based seismic assessment of plastic hinges.

Performance Categories#

The Performance Categories table lists all previously defined categories. Selecting a category will display its associated criteria in the lower Performance Criteria table. Each category defines an independent set of performance criteria, sorted according to their performance indices. During the analysis, each category will be evaluated separately for the specific plastic hinge.

Note

Performance categories and their associated criteria (label, title and the order of performance indices) can be defined by using the Plastic Hinge - Performance Categories task.

Performance Criteria#

Reference Material - Select a material for which the limit strains will be assessed. If you choose the option “All concrete/reinforcement/structural steel materials,” all materials of the corresponding type available in the cross-section will be evaluated. The material that reaches the specified limit strain first will be selected.

Compressive/Tensile Limit Strains - Threshold limit strain values define the performance criteria for the specified plastic hinge. When the specified value is obtained within the hinge during the pushover analysis, the corresponding criterion will be marked as reached and can be used to indicate its position on the performance evaluation curves. For more info about the performance evaluation checks see the Pushover Analysis - Bridge Piers task.

Note

The limit strains associated with the criteria, within the same category, need to be defined in a manner that corresponds to increasing damage levels.

Output#

Select the output text properties and plots for the report.