Form: Define Load Patterns
Use the Define menu > Load Patterns command to access the Define Load Patterns form and add, modify, or delete load patterns. Click there for more information about load patterns.Click there for more information about load patterns.
Loads represent actions upon the structures, such as force, pressure, support settlement, thermal effects, ground acceleration, and others. A spatial distribution of loads upon the structure is called a load pattern. An unlimited number of load patterns can be defined in SAP2000. Typically, separate load patterns would be defined for dead load, live load, wind load, snow load, thermal loads, and so on. Loads that need to vary independently, for design purposes or because of how they are applied to the structure, should be defined as a separate load pattern. SAP2000 uses the type of load to create design load combinations automatically.
Load patterns can include automated loads, such as self weight or code-specified wind or earthquake lateral force distributions. For all other loads on the structure, specific load values must be assigned to objects as part of a load pattern (see the topics in the Menus/Assign - Joint Loads, Frame Loads, Cable Loads, Tendon Loads, Area Loads, Solid Loads and Link/Support Loads books of this Help for more information about assigning loads). The load values assigned to an object specify the type of load (e.g., force, displacement, temperature, and so forth), its magnitude, and its direction (if applicable). Different loads can be assigned to different objects as part of a single load pattern. Each object can be subjected to multiple load patterns.
The Define Load Patterns form also displays when the + (plus symbol) is clicked on any of the forms used to assign loads; see the topics in the Assign - Area Loads, Frame Loads, Cable Loads, Tendon Loads, Joint Loads, Link/Support Loads and Solids Loads books of this Help.
Note: To calculate any response of the structure resulting from the load patterns, you must define and run load cases that specify how the load patterns are to be applied (e.g., statically, dynamically) and how the structure is to be analyzed (e.g., linearly, nonlinearly). The same load pattern can be applied differently in different load cases.
Tip: Every time a new load pattern is defined, the program automatically creates a corresponding linear static analysis case of the same name that applies the load. For a new model, the program creates a default load case called DEAD that applies the self weight of the structure. The corresponding linear static analysis case is also called DEAD.
Click the Define menu > Load Patterns command to access the Define Load Patterns form. The form has the following edit boxes and drop-down lists.
Load Pattern Name edit box. Type a unique name for the load pattern in this edit box. The previously assigned load pattern names will appear in the display list below this edit box. Note that each load pattern and load combination must have a unique name. Also, the word Mode is reserved and can not be used for either a load pattern name or a load combination name.
Type drop-down list. Choose the type of the load pattern for design. The program uses these values when automatically creating design load combinations for the design postprocessor. The factors used in the design load combinations are different for the various types of loads. The choices for load pattern types are extensive and are assumed to be basically self explanatory with the following brief explanations.
Use the OTHER option if the design load is not to be included in the design load combination automatically created by the program..
The SUPER DEAD option is superimposed dead load.
The REDUCE LIVE option is Reducible Live Load; a live load that is specified as reducible is reduced automatically by the program for use in the design postprocessors.
Self-Weight Multiplier edit box. This is a scale factor that multiplies the weight of the structure and applies it as a force in the gravity direction (negative global Z direction). The self-weight of the structure is determined by multiplying the weight per unit volume of each object that has structural properties times the volume of the object. The weight per unit volume is specified in the material properties. Use the Self-Weight Multiplier edit box to specify what portion of the self-weight is to be applied to any load pattern. A self-weight multiplier of 1 means to include the full self-weight of the structure in the load pattern. A self-weight multiplier of 0.5 means to include half of the self-weight of the structure in the load pattern. Normally a self-weight multiplier of 1 should be specified in one load pattern only, usually the dead load pattern, with all other load patterns having a self-weight multipliers of zero. Note that if a self-weight multiplier of 1 is included in two different load patterns, and then those two load patterns are combined in the same load combination, the results for the load combination are based on an analysis where double the self-weight of the building has been applied as a load.
Auto Lateral Load Pattern drop-down list. The Auto Lateral Load Pattern drop-down list becomes active when the load pattern type is specified as Quake, Wave or Wind.
Choose None from the drop-down list to not use the automatic loads and instead assign loads using the commands available on the Assign menu.
Choose one of the codes from the drop-down list to specify that code-compliant loads be created automatically for the load pattern. Another form will appear that can be used to review and as necessary specify the appropriate parameters for the automatic pattern. (See the Modify Lateral Pattern bullet below for hyperlinks to topics addressing those forms.)
Use the buttons in the Click To area of the form to complete the actions described below:
Add New Load Pattern button.
Type the name of the load pattern in the Load Pattern Name edit box.
Select a load pattern type from the Type drop-down list.
If appropriate, type a self-weight multiplier in the Self-Weight Multiplier edit box. (See the Self-Weight Multiplier text above for cautions related to applying self weight.)
If the load Type specified is Quake, Wave or Wind, select an option from the Auto Lateral Pattern drop-down list.
Click the Add New Load Pattern button. If the load pattern type specified is Quake, Wave or Wind, note the text for the Modify Lateral Load Pattern button.
Modify Load Pattern button.
Highlight the existing load pattern in the Load Patterns area. Note that the data associated with that load pattern appears in the edit boxes and drop-down lists at the top of the Load Patterns area.
Modify any of the data in the Load Patterns area for the load pattern.
Click the Modify Load Pattern button.
Note: If nothing happens when the Modify Load Pattern button is clicked, the load pattern is an automatic load pattern. As described in the Note below, highlight the load pattern and the click the Modify Lateral Load Pattern button.
Modify Lateral Load Pattern button.
If a new pattern is being defined with a load Type of Quake, Wave or Wind and a code (i.e., automatic pattern) has been selected in the Auto Lateral Load Pattern drop-down list, first click the Add New Load Pattern button, then click the Modify Lateral Load Pattern button to access a form specific to wave, wind or seismic loading. Use the form to specify parameters consistent with the code selected in the Auto Lateral Load Pattern drop-down list. For example, if the load type is Quake and NEHRP 97 is selected in the Auto Lateral Load Pattern drop-down list, the form that appears is the NEHRP 97 Seismic Loading form. The options available on that form relate to code requirements. Thus, fill in parameters on the form as appropriate. Then click the OK button to complete the operation and return to the Define Load Patterns form.
Note: After a code specific pattern has been defined as described here, highlight it in the list of patterns and click the Modify Lateral Load Pattern button to redisplay the form if any additional changes are needed.
If a new pattern is being defined with a Type of Moving Live, first click the Add New Load Pattern button to specify the load pattern, then highlight that pattern and click the Modify Moving Live Load button to access the Multi Step Live Load Pattern Generation form. Use that form to refine the path loading for a moving load analysis. Note that a path and a vehicle(s) must be defined before the live load can be defined.
Delete Load Pattern button.
Note that when a static load pattern is deleted, all of the loads that have been assigned to the model as a part of that static load pattern also are deleted.
Highlight the existing load pattern in the Load Patterns area. Note that the data associated with that load pattern appears in the edit boxes and drop-down lists at the top of the Load Patterns area.
Click the Delete Load Pattern button.
Show Load Pattern Notes button. Click this button to access the Load Pattern Notes form. Use that form to add load pattern notes to the model file. Type the notes directly into the form. Any previously entered Notes will be displayed when the form is accessed.
After a load pattern has been defined, assign loads to the objects as part of that load pattern by selecting the objects to be loaded and using the appropriate command from the Assign menu.
Example: Definition of load patterns is demonstrated in Problem A (Quake), Problem B (Quake), Problem C (Live), Problem E (Quake), Problem H (Live), Problem I (Live), Problem J (Live), Problem K (Live, Quake), Problem O (Live), Problem P (Other-Axial), Problem U (Live), Problem V (Dead with 0 Self Weight), and Problem W (Dead with 0 Self Weight).