Most of the analysis parameters are entered via the Main Dialog box window (Figure 1). The user can see all of the required entries for each analysis type.

Figure 1 : Main Dialog

The analysis type can be determined by making a number of major selections:

1. Problem Type: User makes selection on the type of analysis problem:

• Unidirectional vs. Bi-directional
• Single Analysis vs. Spectral Analysis                

2. General Dynamic Properties:

• Mass [Kip.s2/in]
• Damping [% of critical]
• P-Delta ratio, which is a positive number (between 0 and 1) defined as (P/L)/ K, where K is the gross stiffness of the system. This represents the stiffness reduction due to P-Δ.

3. Spectral (Period and Strength) Parameters

3a.  Period/Frequency range for spectral analysis. The user specifies:

• The first value in the range
• The last value in the range
• The total number of values in the range
• Type of value: Period vs. Frequency
• How the intermediate values are obtained: Linear vs. Logarithmic generation

3b.  Target Strength/Ductility range for nonlinear spectral analysis. The user specifies:

• The first value in the range
• The last value in the range
• The total number of values in the range
• Type of value: Absolute Strength [Kips], Normalized Strength (η), Constant R (Elastic Force/Yield Force), Ductility μ, or damage index. The normalized strength η (eta) is equal to: Absolute Strength / (Mass x PGA)
• How the intermediate values are obtained: Linear vs. Logarithmic generation
• It is also possible to type in a custom range that does not follow a particular pattern (linear or log)

4. Nonlinear Properties:

4a.  Hysteretic Model Type: The nonlinear hysteretic model to be used along with model specific parameters. More details are provided in each model's section:

1. Linear Elastic Model
2. Bilinear Plastic Model
3. Bilinear Plasticity Model with Bidirectional Coupling: The user can specify the interaction surface power value n.
4. Clough Bilinear Stiffness Degrading Model
5. Modified Clough Bilinear Stiffness Degrading Model
6. Origin-Oriented Bilinear Model
7. Peak-Oriented Bilinear Model
8. Bilinear Elastic Model
9. Bilinear Flag Model: The user can specify the parameter Rflag, which determines the height of the flag portion of the hysteretic curve.
10. Bilinear Slip Model

4b.  Strength and Stiffness Ratios:

• K2/K1 ratio, where K1 and K2 are the gross stiffnesses in directions 1 and 2 respectively
• Y2/Y1 ratio, where Y stands for Yield Strength (positive or negative)
• Yneg/Ypos ratio, where Yneg and Ypos are the positive and negative yield strengths respectively

4c.  Hysteretic Model Parameters: The user can specify the model properties individually for the two directions

• Stiffness K, the gross stiffness [Kips/in]
• Positive Yield Ypos [Kips]
• Negative Yield Yneg [Kips]
• Positive hardening ratio (Khpos/K), where Khpos is the hardening stiffness in the positive direction
• Negative hardening ratio (Khneg/K), where Khneg is the hardening stiffness in the negative direction

This dialog also has a few buttons that are:

1.        The "Define Ground Motions" Button : brings up the Earthquake Suite Dialog.

2.        The "Test Model" Button: Opens the Interactive Model Testing Dialog.

3.        The "Run Analysis" Button: This button invokes the analysis, and the display of the result window.

4.        The "Analysis Options" Button: Opens the Analysis Options Dialog.

5.        The "Help" Button: Opens Help for Bispec.

6.        The "Exit" Button: Quits Bispec.