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[GEN/Result]The Difference Between Local and UCS in Plate Force Options and How to Use Them in Practice

Question

What is the difference between Local and UCS in the Plate Force Option and how can it be utilized in practice?

 

Answer

In the Plate Force Option, "Local" refers to the unit force per unit width with respect to the element's local coordinates, as shown in Image-1. On the other hand, "UCS" represents the unit force per unit width along the user-defined UCS axis.

Here's how these concepts are practically applied

(a) Element Coordinates for Rectangular Elements

(b) Element Coordinates for Triangular Elements

[Image-1] Element Coordinates for Plate Elements

In cases where the shape of the slab is not rectangular but has a ladder-like configuration, as illustrated in Image-3, the Local x-axis of each element can vary from one element to another. Particularly when triangular elements are used or when an automatic mesh is generated, if the coordinates of each element differ, the UCS option can be employed to verify the force in the desired direction.
Typically, even when a specific slab has a ladder-like shape, if adjacent slabs align with the global coordinates, it's advisable to use the UCS option to confirm the forces, ensuring that the rebars of the slab aligns with the global coordinates.

[Image-2] Slabs under Concentrated Load

[Image-3] Element Coordinate System of Plate Element

Secondly, in the "Response Spectrum Load Cases > Modal Combination Control" section, select one mode at a time to create load cases for a total of nine load conditions, as shown in Image-5, labeled R1 to R9. Additionally, generate an Rall load case to consider all modes collectively for comparison with the SRSS (Square Root of the Sum of Squares) results of individual modes.

(a) When Plate Force Option is Local

(b) When Plate Force Option is UCS

[Image-4] Bending Moment per unit Width of the Slab (Mxx)

[Image-5] Consider only the first mode for R1 in the Response Spectrum Load Case

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