'Linked' Microstran Model

Hi there,

I am trying to model a steel portal frame. It is 3 bays high and 2 bays wide.

On-site the beams are going to have a moment end plate connection to the columns and the columns will be a continuous member from top to bottom.

When I go to check capacities of members I get very different results depending on if I linked or not linked the entire structure. I believe I should link the columns, but not the beams?

Is someone able to provide an explanation as to what linking does and when to use, or not use it?

I have read that you link members if the member is continuous beyond a node and does not have a twist restraint. But if we go into the element to enter in restraints, we can add lateral restraint, but not a twist restraint. Say we use fly bracing at knees so we can get lateral and twist restraint, we should use a non linked model?

Any guidance or discussion on this, would be hugely appreciated.

Thank you

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  • Generally speaking, you would initialized members as "linked" if collectively they form a design member, if you initialized members as "unlinked", then each analytical member in Microstran would be one design member.

    Use the Initialize Design Members > Not Linked command if you want each selected analysis member to be a design member. Twist restraint is then assumed at each end of each analysis member. If this twist restraint does not exist unlinked initialization is not valid and you may obtain unconservative results (For example, truss with unsupported chord.)

    In Microstran, every design member that is not a cantilever has twist restraint at each end. Interior nodes that do not have twist restraint make it necessary to link analysis members together forming a design member. On initialization, no twist restraint is assumed at intermediate nodes in linked members.
    You can add restraints in the Steel Restraint Dialogue.

    The restraints implicit with Linked vs Unlinked becomes apparent when you view the restraint data. To illustrate this, you can view the restraints prior to design by going to View-->Virtual Reality, try this for both Linked scenario as well as Unlinked scenario.

    You want to ensure that the restraints presented in these views, are indeed the intended physical restraints.

    For example, if you have a linked design column that spans many levels, then Virtual Reality view will show that it is completely unrestrained all along its length. But each level will provide restraint to the column, thus dramatically increase its design capacity. Design Restraints such as Column Buckling Restraint and Flange Restraint can be added by going to the Restraint Dialogue which can be accessed by going through the dialogues via Design-->Design Data-->Input/Edit.
    For further reference, Chapter 16 of The Microstran Manual also goes through this process in detail.
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  • Generally speaking, you would initialized members as "linked" if collectively they form a design member, if you initialized members as "unlinked", then each analytical member in Microstran would be one design member.

    Use the Initialize Design Members > Not Linked command if you want each selected analysis member to be a design member. Twist restraint is then assumed at each end of each analysis member. If this twist restraint does not exist unlinked initialization is not valid and you may obtain unconservative results (For example, truss with unsupported chord.)

    In Microstran, every design member that is not a cantilever has twist restraint at each end. Interior nodes that do not have twist restraint make it necessary to link analysis members together forming a design member. On initialization, no twist restraint is assumed at intermediate nodes in linked members.
    You can add restraints in the Steel Restraint Dialogue.

    The restraints implicit with Linked vs Unlinked becomes apparent when you view the restraint data. To illustrate this, you can view the restraints prior to design by going to View-->Virtual Reality, try this for both Linked scenario as well as Unlinked scenario.

    You want to ensure that the restraints presented in these views, are indeed the intended physical restraints.

    For example, if you have a linked design column that spans many levels, then Virtual Reality view will show that it is completely unrestrained all along its length. But each level will provide restraint to the column, thus dramatically increase its design capacity. Design Restraints such as Column Buckling Restraint and Flange Restraint can be added by going to the Restraint Dialogue which can be accessed by going through the dialogues via Design-->Design Data-->Input/Edit.
    For further reference, Chapter 16 of The Microstran Manual also goes through this process in detail.
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