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Eigenvalue and RSA can be done using this section of the workflow.

Modal Parameters

Stage: Specify the stage for which eigenvalue and response spectrum analysis will be generated. The chosen stage will be used to determine the elements of a bridge to be considered for eigenvalue and RSA.

Number of Mode Shapes: The total vibration patterns extracted or used in the analysis can be specified using this parameter.

RSA Curves

Curve in Dir. 1: This parameter is used to set the response spectrum curve previously defined under the Dynamic Loads category with the Response Spectrum Curve object for Eigenvalue and RSA.

Scale in Dir. 1:This refers to the scaling factor applied to the response spectrum curve. The scaling factor adjusts the spectral values to account for specific conditions (e.g., the intensity of seismic loads or normalization requirements).

Curve in Dir. 2: This parameter is used to set the response spectrum curve previously defined under the Dynamic Loads category with the Response Spectrum Curve object for Eigenvalue and RSA.

Scale in Dir. 2: This refers to the scaling factor applied to the response spectrum curve. The scaling factor adjusts the spectral values to account for specific conditions (e.g., the intensity of seismic loads or normalization requirements).

Curve in Dir. 3: This parameter is used to set the response spectrum curve previously defined under the Dynamic Loads category with the Response Spectrum Curve object for Eigenvalue and RSA.

Scale in Dir. 3: This refers to the scaling factor applied to the response spectrum curve. The scaling factor adjusts the spectral values to account for specific conditions (e.g., the intensity of seismic loads or normalization requirements).

Dir. Angle[deg]:: This is the rotation angle (in degrees) of the principal axis used for the seismic response.When seismic forces act along an axis that isn’t perfectly aligned with the global axes (e.g., rotated by 30°), this parameter specifies that rotation angle to account for directional effects correctly.

RSA Combination

Damping Ratio: The damping ratio represents the energy dissipation in the system, expressed as a fraction of critical damping, and it can be specified using this parameter. It influences how quickly the oscillations from seismic loads decay.

Model Combination Method [CQC/SRSS]: The model computation method can be specified using this parameter.

• CQC (Complete Quadratic Combination): This method is used when modes are closely spaced or have significant modal coupling. It accounts for the correlation between modes.

• SRSS (Square Root of the Sum of the Squares): This method assumes modes are uncorrelated. It is suitable when the modal frequencies are sufficiently separated.

Spatial Combination Method [ABS/SRSS]: The spatial computation method can be specified using this parameter.

• ABS (Absolute Sum): This method sums the absolute values of responses from different directions. It is a conservative approach.

• SRSS (Square Root of the Sum of the Squares): This method combines responses from multiple directions, assuming they are independent. It provides a less conservative result than ABS.

Mass Source

Eigenvalue and RSA-related calculations consider the bridge elements constructed based on the Stage parameter of this object. However, for loads that are not generated by objectwise methods (such as roadway and stay-in-place formwork), this section can be utilized.

The loads defined under Loading > Loads >Static Loads and Element Loads can be assigned to the Mass Case parameters.

Mass Case 1: Specify a mass case (a previously defined static load or element load case).

Mass Case Factor 1: This factor is a multiplier applied to the mass defined in Mass Case 1. It adjusts the effective mass used in the analysis to reflect variations in loading conditions or design considerations.

Mass Case 2: Specify a mass case (a previously defined static load or element load case).

Mass Case Factor 2: This factor is a multiplier applied to the mass defined in Mass Case 2. It adjusts the effective mass used in the analysis to reflect variations in loading conditions or design considerations.

Mass Case 3: Specify a mass case (a previously defined static load or element load case).

Mass Case Factor 3: This factor is a multiplier applied to the mass defined in Mass Case 3. It adjusts the effective mass used in the analysis to reflect variations in loading conditions or design considerations.

Mass Case 4: Specify a mass case (a previously defined static load or element load case).

Mass Case Factor 4: This factor is a multiplier applied to the mass defined in Mass Case 4. It adjusts the effective mass used in the analysis to reflect variations in loading conditions or design considerations.

Mass Case 5: Specify a mass case (a previously defined static load or element load case).

Mass Case Factor 5: This factor is a multiplier applied to the mass defined in Mass Case 5. It adjusts the effective mass used in the analysis to reflect variations in loading conditions or design considerations.