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{info} This page is devoted to *frequently asked questions* (FAQ) related to [constraints|kb:Constraint]. {info} \\ {on-this-page} h2. What is the difference between a line constraint and an edge constraint? *Answer:* Line and edge constraint both refer to the same modeling feature except that _line_ constraint is terminology specific to [ETABS|etabs:Home], while _edge_ constraint is used in [SAP2000|sap2000:home]. h2. What are the advantages and disadvantages between using rigid links and body constraints? *Extended Question:* I am using the [bridgeBridge modelerModeler|Bridge Modeler] to model an offset rocker bearing. A combination of link objects seems to simulate the connection between girder and pier systems. Is there an explanation for the difference between links and body constraints? *Answer:* Application of either rigid links or body constraints is suitable for modeling a rigid connection. A comparison of these modeling techniques is described as follows: Advantages of using *links:* * [Links|kb:Link] are clearly shown in the model, which may assist review. * Internal forces are obtained for links, which is not the case for body constraints. * Link stiffness may be modified, if necessary, to match that of the component being modeled. [Joints|kb:Joint] constrained using body constraints are always fully fixed. Advantages of using *body constraints:* * Using body constraints reduces the number of degrees of freedom (DOF) in the model, which speeds numerical solution. {hidden-content} *Related Incident:* * 29317 {hidden-content} h2. Why are numerical problems reported for diaphragm constraints? *Answer:* Please see the [diaphragmDiaphragm constraint|kb:Diaphragm constraint] article for response. h2. Why do edge constraints have displacement discontinuity? *Answer:* Please see the [lineLine (edge) constraint|kb:Line (edge) constraint] article for response. {hidden-content} *When would a body constraint be applied with only some DOF constrained?* *Answer:* {open-question} {hidden-content} {hidden-content} *What behaviors occur when only some DOF are constrained?* *Answer:* {open-question} {hidden-content} {hidden-content} *Is there an example of how constraint coupling may cause numerical instability?* *Answer:* {open-question} {hidden-content} |
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