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This page contains frequently asked questions related to *[links|kb:link]*. {on-this-page} h1. General FAQ {anchor:changing-length} h2. Does changing the length of the link element have impact on the results? Changing the length of a [link element|Link] has no effect on the stiffness values, since they are based on the total force or moment. The only effect is the generation of a moment due shear acting over the length. Likewise, changing the length location of the shear deformation (defined by specifying a distance from J end) may change the response as this parameter has impact on the internal link deformations. Please note that the link deformations occur at a single location specified by "Shear Distance from End J" on the link definition form. Please refer to the {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc:CSI Analysis Reference Manual] (The Link/Support Element > Section Internal Deformations, page 238) for the equations used to calculate link deformations. h2. Which link property is the most suitable to model shear behavior of reinforced concrete? Multi-linear plastic link property with pivot hysteresis type would be most suited to model the shear behavior of reinforced concrete members. h2. Should I use hinge or link? _See_ _["Comparison of hinges and links"|Hinge and link comparison]_ _page._ h2. Link Directional Properties There are the following three main options when you define link directional properties: * You leave the Direction unchecked (as is the case for U1 in the screenshot below) - then the link will not contribute any stiffness for the given direction. * You check the Direction and Fixed (as is the case for U2 in the screenshot below) - in this case, the link will not experience any deformation in the given direction. In other words, it will behave as being infinitely stiff for the given direction. * You check Direction and NonLinear (as shown for U3 in the screenshot below) - then the link will contribute stiffness specified when you click the "Modify/Show ..." button below the Properties heading. !Link_directional_properties.png! h2. How should I calculate the link stiffness values? There are various types of links available in the program and you can define their force deformation relationship (for axial, major and minor shear, torsion, major and minor pure bending DOFs) to represent the behavior of the structural component (such as bearing, isolator, soil spring, etc.) that is being modeled by the link. Please review CSI Analysis Reference Manual, chapter "The Link/Support Element - Basic", sections "Internal Deformations" and "Link/Support Properties" for additional details on link internal deformations, force-deformation relationship and link internal forces. You may also find it useful to review the [doc:Derivation of link equations] page. h2. How can I plot force-displacement hysteresis curve for isolator? *Extended Question:* How do I get output force-displacement hysteresis curve for isolator? I was trying to see under Display/Show plot function but I couldn’t figure it out force vs. displacement only I found time vs. displacement. *Answer:* _[See plotting link hysteresis curve page.|Plotting link hysteresis]_ h2. What are the units for link effective damping? For all link properties, the damping input is the actual damping in units of Force-Sec/Length (i.e. Force/Velocity)page is devoted to frequently asked questions (FAQ) related to links. |
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Modeling
Does changing link length affect results?
Answer: The only difference which results from changing link length is an additional moment which results from shear acting over the increased length. Likewise, the specification of length location for shear deformation may change link response because this parameter correlates with internal link deformation. Please note that link deformation occurs at a single location specified on the Link Definition menu by the value Shear Distance from End J. The equations used to calculate link deformation are available in the CSI Analysis Reference Manual (The Link/Support Element > Section Internal Deformations, page 238). Changing link length does not affect link stiffness since this value is based on the total force or moment.
Which link property is most suitable for modeling reinforced-concrete shear behavior?
Answer: The multi-linear plastic-link property, with pivot hysteresis type, would be most suitable for modeling the shear behavior of reinforced-concrete members.
Should I use a hinge or a link?
Answer: For response, please see the Hinge and link comparison article.
How is friction modeled between two surfaces?
Answer: We recommend using nonlinear link/support elements to model friction behavior between two surfaces. The friction isolator is best for SAP2000 models, and the Isolator 2 is best for ETABS models.
Use engineering judgement when deciding upon linear and nonlinear stiffness properties.
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Formulation
What are the Link Directional Properties?
Answer: Three options are available when defining Link Directional Properties. Their descriptions are given as follows:
- Leave the Direction option unchecked, as shown in Figure 1 with U1. This will keep the link from contributing stiffness to the direction specified.
- Select the Direction and Fixed option, as shown with U2. In this case, the link will not experience any deformation in the direction specified because relatively large stiffness will be applied to that component.
- Select the Direction and Nonlinear option, as shown with U3. Here, the link will contribute the stiffness specified when Modify/Show is selected from below the Properties heading.
Figure 1 - Link directional properties
How is link stiffness calculated?
Answer: For the various link objects available, force-deformation relationships may be defined along each degree-of-freedom (DOF), including axial, torsional, major and minor shear, and major and minor bending. These properties may be specified to simulate the behavior desired of bearings, isolators, soil springs, and other structural components modeled using link objects.
The CSI Analysis Reference Manual (The Link/Support Element - Basic > Internal Deformations and Link/Support Properties, pages 238 and 240) provides additional details on force-deformation relationships and internal link deformation and forces. The Derivation of link equations article may also be useful.
Reporting
How can I plot force-displacement hysteresis for isolators?
Answer: For response, please see the Plotting link hysteresis article.
What are the units for link effective damping?
Answer: For all link properties, damping input is actual damping, given in units of Force-Second/Length, or Force/Velocity.