In this exercise, you will learn how to define the effective seismic weight of the structure that will be considered to contribute to the seismic base shear.

The following load types are available for this purpose:

1. Self Weight

2. Joint Weight

3. Member Weight

4. Reference Loads

5. Floor Weights

Note: All masses should be entered as a positive value (or with a consistent sign), because it represents a direction-less magnitude of dynamically active mass.

1. Continue with the model from the previous exercise.

2. In the Add New: Seismic Definitions dialog, select the Reference Load item in the left pane.

3. In the Available Load Cases window, hold down the Ctrl key and highlight the following load cases: R1: DEAD LOAD and R2: LIVE. Then, click on the Single Right Arrow button to move the reference load cases to the Reference Load Definition window.

4. In the Reference Load Definition window, modify the factors for each load case as follows:

Reference Load Case R1: 1.0

Reference Load Case R2: 1.0

Click on the Add button. Then, click Close.

Apply the Seismic Loads

In this exercise, you will learn how to apply the code seismic loads to the model in the positive X and Z directions.

Direction and Factor: Establishes the direction of the seismic load and allows a linear multiplier on the load.

Multiplying Factor for Accidental Torsion Moment: If the ACCIDENTAL option is selected in the Seismic Load Definition, the program calculates the additional torsional moment. When this factor is set to 1.0, the default eccentricity of 5% is used to determine the moment arm.

Multiplying Factor for Natural Torsion Moment: Set this option to include the torsion arising due to static eccentricity which is the difference between the center of mass and the center of rigidity of a rigid floor diaphragm.

1. Continue with the model from the previous exercise.

2. In the Load & Definition dialog, expand the Load Cases Details group and review the seismic load cases:

3. In the Load & Definition dialog, highlight the 1: SEISMIC LOAD +X load case. Then, click Add...

4. In the Add New: Load Items dialog, select the Seismic Loads > Factor & Direction item in the left pane. Then, enter the following parameters:

Direction: X Direction

Factor: 1

Multiplying Factor for Accidental Torsion Moment: (unchecked) Click Add, followed by Close

5. In the Load & Definition dialog, highlight the 3: SEISMIC LOAD +Z load case. Then, click Add...

6. In the Add New: Load Items dialog, select the Seismic Loads > Factor & Direction item in the left pane. Then, enter the following parameters:

Direction: Z Direction

Factor: 1

Multiplying Factor for Accidental Torsion Moment: (unchecked) Click Add, followed by Close.

9. In the Quick Access Toolbar, click on the Save icon.

                                                                                         

                                                                                                   

QUIZ

1. What Load types are available to model Seismic Mass?

(A) Self Weight

(B) Joint Weight

(C) Member Weight

(D)All of the Above

2. In order to use the torsion arising due to Static Eccentricity you use which of the following?

(A) Direction and Factor

(B) Multiplying Factor for Accidental Torsion Moment

(C) Multiplying Factor for Natural Torsion Moment

(D) Safety Factor