Uplift anchorage for perforated shear wall ends with the 2009 code

[cyeates]

With the transition to the 2009 code, the ICC refers the engineer to NDS SDPWS for design of shear walls. I had a question about one section in particular. In the 2006 IBC, 2305.3.8.2.4 refers to a "minimum tension chord uplift force, T". The ICC instructs the engineer to provide anchorage capable of resisting this tension. Because this was a minimum tension, the engineer had to call out hold-downs even if the dead load stablizing moments were sufficient to resist overturning.

However, NDS SDPWS does not make reference to uplift anchorage at perforated shear wall ends. In 4.3.6.4.2, it talks about the bottom plates being anchored for a uniform uplift force, t, which is equal to the unit shear force, vmax. 4.3.6.1.2 shows how to calculate the tension and compression in the chords of perforated shear walls. However, this section does not refer to the tension calculated as a minimum tension. If the dead load stabilizing moments are sufficient to resist overturning, do I not need to call out hold-downs at the ends of perforated shear wall segments? 4.3.6.4.2.1 (Uplift Achorage for Perforated Shear Walls) is given in addition to the requirements of 4.3.6.4.2.

Let me know what you guys think.

 

[woodman88]

The equation for T in my SDPWS 2008 section 4.3.6.1.2 is the same as the T in my IBC 2003 section 2305.3.7.2.4. Did the equation for T change in the IBC 2006? If not than you still have to hold the shear wall down for the T whether it is called out as a minimum (as in the IBC 2003) or not (as in the SDPWS 2008).

Garth Dreger PE
AZ Phoenix area

 

[WillisV]

Yes, you need hold-downs at the ends of all perforating segments. Perforated shear wall method is an emperical method and the minimum "T" should be provided per SDPWS Section 4.3.6.1.2.

 

[jpj3]

The 2006 IBC requires hold-downs only if the dead load moment is not sufficient to prevent uplift due to overturning moments on the wall (IBC section 2305.3.7), except in the case of perforated shear wall (PSW) ends: the code requires hold-downs sufficient to resist a "minimum" uplift force per Equation 23-3 (IBC section 2305.3.8.2.4).

This minimum uplift force requirement, however, has been removed from the 2009 IBC. Instead, the code requires the uplift force to be determined using Equation 4.3-5 of the 2005 SDPWS and only requires hold-downs when the dead load moment is not sufficient to prevent uplift (SDPWS section 4.3.6.4.2).

Unlike the 2006 IBC, the 2005 SDPWS / 2009 IBC allows the tension force at PSW ends to be reduced due to the effect of gravity loads, as stated in SDPWS section 4.3.6.4.4 (see also section commentary). Example No. 37 of the 2005 Structural Wood Design Solved Example Problems demonstrates the calculation of a reduced PSW hold-downs force due to the wall weight (page 442).

 

[jpj3]

*The post incorrectly references the 2005 SDPWS. The post should reference the 2008 SDPWS for the 2009 IBC. The content of the equation and sections referenced, however, is correct.

 

[abusementpark]

Yes, you need hold-downs at the ends of all perforating segments. Perforated shear wall method is an emperical method and the minimum "T" should be provided per SDPWS Section 4.3.6.1.2.

I thought the whole point of the perforated shear wall methods was to eliminate the need for hold downs at intermediate segments. I thought it was based on only provided hold downs at each end of the perforated shear wall.

??????

 

[DaveAtkins]

Yes, that is correct. When you use the perforated shear wall method, the entire length of wall becomes one wall with perforations, and holddowns are only needed at each end, not at every opening.

DaveAtkins

 

[WillisV]

agreed "segment" was a very bad word to use - I was trying to say you needed to meet the minimum uplift force for hold downs at the end of the perforated wall (not each segment). Though you do have to check the compression force for each segment within the perforated wall.