Certain types of load case, including response-spectrum and time-history, allow users to specify the direction of applied acceleration load, as shown in Figure 1:
Figure 1 - Angle specification for time-history acceleration load
While other types of load case, including static, modal, and buckling, provide for acceleration load along global axes, users may still apply acceleration load in an arbitrary direction through one of the following approaches:
- Establish an equivalent system by applying scale factors to acceleration loads oriented along global axes. For example, a resultant acceleration load 45° from the global X axis is equivalent to a UX and UY component, each scaled to 0.7071.
- Calculate and apply acceleration loads directly to the joints of the structure, as done through the following process:
- Analyze the model, then display the assembled-joint-masses table using the 'Display' > 'Show Tables' > 'ANALYSIS RESULTS' > 'Joint Output' > 'Joint Masses' > 'Table: Assembled Joint Masses' option.
- Export this table to Excel, then, using joint mass, acceleration magnitude, and acceleration direction, calculate the acceleration-load global-axes components at each joint.
- Within a load case, apply the calculated acceleration loads using the 'Edit' > 'Interactive Database Editing' > 'MODEL DEFINITION' > 'Joint Assignments' > 'Joint Load Assignments' > 'Table: Joint Loads - Force' option. Users may export this table to Excel, edit, then import back to the analysis software.
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For certain types of load cases (such as Response Spectrum and Time History), the program allows you to specify a direction for the applied acceleration loads as shown in the figure below:
Other types of load cases (static, modal, and buckling) permit acceleration loads to be applied only in the global directions. However, you can still apply acceleration loads in arbitrary direction using one of the following approaches:
- Simply apply global accelerations loads with scale factors such that they add up to the acceleration in the desired direction. For example, to apply acceleration loads at and angle of 45° from the global X axis, you could apply acceleration load UX with a scale factor of 0.7071 and acceleration load UY with a scale factor of 0.7071.
- Alternatively, you can calculate and apply the acceleration loads directly to the joints of the structure as follows:
- Analyze your model and use "Display > Show Tables > ANALYSIS RESULTS > Joint Output > Joint Masses > Table: Assembled Joint Masses" menu command to display the table with assembled joint masses. Export the table to Excel
- Within the Excel file, calculate the directional components of acceleration loads to be applied to each joint, based on the joint mass, acceleration magnitude, and acceleration direction.
- Use "Edit > Interactive Database Editing > MODEL DEFINITION > Joint Assignments > Joint Load Assignments > Table: Joint Loads - Force" to apply the calculated acceleration loads in a load case. Again, you can export the table to Excel, edit the file and import the changes back to SAP2000.
See also
- Context help 'Applying acceleration loads'
- Interactive database editing