Elongation and Displacement

Refers to the elongation in tension of the hold-down brackets or straps plus anchor bolt elongation.

Database value

For those hold-downs with separate elongation and slippage (see , the hold-down database contains the strength-level elongation that occurs at the maximum capacity. For those hold-downs for combined slippage, the overall strength-level displacement at maximum capacity comes from the database.

Method of Determining Displacement

For each hold-down type in the database, you can specify the method used for determining displacement or elongation.

Displacement/Elongation at Maximum Capacity

With this method, the published displacement at maximum capacity is used regardless of the shear wall force. This ensures conservative storey drift calculations when Assembly Displacement (see above) is used as the data source, but may be overly conservative for other choices. This choice also affects load distribution to and within shear lines using to stiffness analysis, for which the effect may be conservative or non-conservative.

Displacement/Elongation at Actual Force

If this method is chosen, then the program divides hold-down force by the capacity, then multiplies this ratio by the strength-level displacement/elongation.

When Assembly Displacement is used as the data source, the assumption of linear may not bet correct, due to the non-linear effects of fastener slippage. This would yield non-conservative results for storey drift determination. However, the choice also affects load distribution to and within shear lines using stiffness analysis, for which the effect may be conservative or non-conservative. Note that full assembly displacement is the only method available in the Canadian version.

Additional bolt length

In some cases, separate elongation of the anchor bolt is added to the database deflection. 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. Note that in this case, for double bracket hold-downs, the published length is doubled before being compared to the actual length in the program.

The elongation of the length L of bolt that is to be analyzed is PL/AE, where A is the bolt cross-sectional area, E is the steel modulus = 29000000 psi and P is the strength level hold-down force at that location.