Elongation

The value in the given in the Displacement column in the Design Properties table of the in the Hold-down database refers to refers to to the displacement of the hold-down due to

• elongation of the anchor bolt
• elongation of the bracket body
• slippage of fasteners connecting bracket to the studs.

The program divides the hold-down force by the capacity, then multiplies this ratio by the published displacement at maximum capacity.

Use Displacement at Maximum Capacity

The hold-down database allows you to specify that for particular hold-downs displacements always be evaluated at maximum capacity, rather than the applied hold-down force. This option is not recommended, and will be removed from the program. Refer to Hold-down Options for more details.

For the time being, if you select this option the displacement at capacity will be used. This will affect load distribution to shear lines using the rigid diaphragm method and within shear lines using to stiffness analysis, for which the effect may be conservative or non-conservative. .

Additional bolt length

In some cases, elongation of the anchor bolt is added to the displacement value from the hold-down database. This happens when

• The published displacement or elongation is for an anchor bolt which is shorter than the one input in Structure input view for the level the hold-down is on. The elongation for the additional length is calculated.

This elongation is

PL / AE,

where

• A is the bolt cross-sectional area
• E is the steel modulus = 29000000 psi
• P is the hold-down force at that location, derived from the shear force used for deflection analysis.
• L is the additional bolt length. For double bracket hold-downs, the published length is doubled before being compared to the actual anchor bolt length.