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*Geometric nonlinearity*, also known as P-delta effect, becomes critical is when gravity loadloads actsact on the adisplaced structuralconfiguration systemof whicha hasstructure, displacedincreasing laterally.the Secondaryinternal momentsforces areon thenelements inducedand whichconnections. contributeOf significantlyparticular toconcern structuralare behavior.column Itbending isstresses importantinduced toby accountsecondary formoments P-deltawhich effectincrease duringwith nonlinearlateral analysisdisplacement. ItThis doesn'tbehavior increaseis computationalillustrated timein verythe much,figure andon isthe accurateright.
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driftGeometric levelsnonlinearity upis toalso 10%.known as Large deformation analysis is another*P-delta effect*. Two sources of P-delta effect exist, exceptincluding thatthe itfollowing istypes:
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by the upper-case delta symbol. This type of geometric nonlinearity is assessed on the local level where equilibrium about column deformation is considered. This however* *P-δ* - also known as Large-Displacement effect, is associated with local deformation. Equilibrium conditions are evaluated using displacement relative to element chord. This behavior only becomes significant at unreasonably large displacement values or in especially slender columns or at unreasonably large displacements. Further, it increases. So long as a structure adheres to the slenderness requirements pertinent to earthquake engineering, it is not advisable to model P-δ since it may significantly increase computational time significantlywithout providing the benefit of useful information. An easier way to model capture Large-Displacement effect is to subdivide critical elements into multiple segments, which transfers behavior into P-Δ effect.

* *P-Δ* - also known as Gravity Load-Deformation effect, is associated with story drift, and is measured between member ends. Unlike P-δ, this type of P-delta effect _is_ critical to model additional nodes along a column length, which transfers the behavior (large displacement effect) into P-triangle.

 nonlinear modeling and analysis. As indicated intuitively by the figures below, gravity loading _will_ significantly influence structural response when the global system displaces laterally. P-Δ may contribute to loss of lateral resistance, ratcheting of residual deformations, and dynamic instability. In that laterally-displaced gravity loading magnifies internal forces, effective lateral stiffness decreases, reducing strength capacity in all phases of the force-deformation relationship. To consider P-Δ effect directly, gravity load should be present during nonlinear analysis. Application will cause minimal increase to computational time, and will remain accurate for drift levels up to 10%. 

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{table-plus:enableSorting=false|align=right|borderColor=white|title='Figure 2 - Multi-story P-Delta, 3D'}


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