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:

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 a 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.

See Also

• Context Help for acceleration-load application
• Interactive database editing