Hold-down Types and Properties

Important Note – These are descriptions to changes implemented in WoodWorks Shearwalls for version 9 and may not reflect current behavior.

1. Hold-down Assembly

   The hold-downs in shearwalls connect the wall end studs on an upper level to either the corresponding stud on a lower level or anchored to the foundation. Continuous tie rod systems extending over multiple building levels are not included in this version of Shearwalls.

   1. Vertical Connection

      Hold-downs include either an anchor bolt or threaded rod which connects upper and lower brackets or straps, or a continuous strap extending from upper to lower level.

   2. Horizontal Fasteners

      The connection from bracket or strap to the upper and lower studs is made via bolts or nails.

   3. Single or double bracket

      Hold-downs are designated as being either single-bracket or double bracket, indicating that the hold-down has a bracket or strap on one floor or both. By default, hold-downs on the ground level are single-bracket, and upper-level hold-downs are double-bracket. The data in the hold-down database are published for one bracket only and are doubled when the hold-down is designated as double bracket in the Shearwalls program.

   4. Shrinkage Compensating Device

      You can designate that the hold-down includes a mechanical device to adjust for the shrinkage of the perpendicular-to-grain wood between the extreme hold-down fasteners, so that such shrinkage is not included in the calculations for shearwall deflection.

2. Displacement and Capacity Sources

   Different hold-downs are designated in Shearwalls for the following different means of publishing displacement and capacity values. There are three possible sources of vertical hold-down displacement that affects shearwall deflection:

   • anchor bolt elongation,
   • bracket or strap elongation,
   • slippage of horizontal bolts or nails.

   Similarly, the capacity of the hold-down takes into account the possible failure in tension of the bracket or strap, the anchor bolt in tension, and the connection of the horizontal fasteners to the wood studs.

   The published data may include all or just some of these sources. For displacement, sources that are not included are calculated separately by Shearwalls. For capacity, sources that are not included are neglected by Shearwalls, with an appropriate warning message.

   The hold-down types corresponding to displacement/capacity data source are

   1. Assembly Displacement/Capacity

      Displacement values refer to entire hold-down – bracket or strap, anchor bolt, and horizontal fasteners. Capacity takes into account tensile capacity of brackets and straps, and wood-connection capacity of horizontal fasteners. Anchor bolt displacement applies to a maximum length, elongation of portion greater than that length is analysed separately.

   2. Separate Slippage/Connection Capacity, Combined Elongation/Tensile Capacity

      Displacement values refer to the elongation of the brackets or straps plus the anchor bolt, to a maximum length. Elongation past the maximum length is analysed separately. Capacities include only the tensile capacity of the brackets and anchor bolt. Slippage of fasteners is calculated by Shearwalls, and wood connection capacity of the horizontal fasteners is not considered.

   3. Separate Slippage/Connection Capacity,, Separate Elongation/Tensile Capacity

      Displacement values refer to the elongation of the brackets or straps only. The entire anchor bolt length is analysed separately. Capacities include only the tensile capacity of the brackets. Wood connection design of the horizontal fasteners is not included, and capacity of anchor bolt is not considered.

   4. Method of Determining Displacement

      Hold-downs are designated according to the method we use for determining the vertical displacement under loading, as follows.

   5. Displacement at Actual Force

      With this method, ratio of the ASD capacity of the hold-down to the maximum ASD capacity is multiplied by strength-level displacement to give the displacement used for deflection analysis and storey drift. When Assembly Displacement (see above) 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 shearlines using stiffness analysis, for which the effect may be conservative or non-conservative.

   6. Displacement at Maximum Capacity

      With this method, the published displacement at maximum capacity is used regardless of the shearwall 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 shearlines using to stiffness analysis, for which the effect may be conservative or non-conservative.