Anchor bolt spacing of wood to concrete 3

[Cayroo]

I am trying to find a current table that gives the allowable shear per anchor bolt with multiple bolts under shear walls in the wood to concrete contection. It used to the called out in an old UBC and is not even listed in the NSD. Beyer's book gives a formula and tells you to use the multiple bolt factor in the sill plate but it doesn't tell you where it comes from, the NSD has wood to wood table, wood to steel, but no wood to concrete. Woodworks uses the value of 1.0 in its program, is this correct? I would appreciate your help on this engineering problem. Thanks, Cayroo

 

[DaveAtkins]

I typically use a capacity of 912# per bolt for the connection of a 2X sill plate made of S-P-F to concrete. This is for 1/2" diameter bolts. This came from the 1997 NDS, and it includes the 1.6 duration of load factor for wind, and is, of course, for loading parallel to grain.

DaveAtkins

 

[RARWOOD]

Section 8.2. of the 1997 N.D.S. contains provisions for the calculation of wood-to-concrete connections. Table 8.2E provideds bolt values for single shear wood to concrete connections.

The 2001 & 2005 N.D.S. appear to have dropped the provisions for wood to concrete connections. I do not know why that was done, however I think it would be appropriate to apply the 97 provisions.

You could also go to the American Wood Council web site. AWC has a connection link which quickly provideds bolt values for a wide range of wood connections including wood to concrete.

 

[UcfSE]

Check 2001 NDS - Table 11E: BOLTS: Design Values (Z) for Single Shear (two member) Connections for Sawn Lumber of SCL to concrete.

 

[RARWOOD]

UcfSE

Thank you for the information. The same table is in the 2005 NDS. I guess I did not look through the 2001 NDS enough.

 

[Cayroo]

Thanks for all the help. The specific values I am looking for is the Z' or the Cg value for the reduction for multiple bolts in a wood member. I contacted the APA and the AWA and both do not take a reduction for multiple bolts in a sill plate or use the value of Cg as 1.0. If anyone knows of another value I should be using, please let me know. Thanks, Cayroo

 

[DaveAtkins]

I don't use the group action factor for this condition, either--I have always believed that the group action factor is for bolts that are closely spaced in a single connection. I look at sill plate anchor bolts as a series of separate connections.

DaveAtkins

 

[Cayroo]

The APA and the AWA both use 1.0 for the Cg factor of repetitive bolts in a wood member. This seems at first to be too high. Does anyone have more information or edification on this. Thanks to all who answered this posting. Cayroo

 

[RARWOOD]

The group action Cg was added to the NDS to account for the fact that when you have multiple fasteners in a row the one closest to the joint will carry a higher proportion of the load.

A general example of the application of Cg is when you have a tension splice in the bottom chord of a gable truss. For example assume you use two rows of 3/4" dia. bolts with 4 bolts per row to transfer the tension out of the bottom chord into two steel side plates. The first two bolts in the wood will carry more load than the last two bolts.

Assume the bolt value is 3500 lb per bolt with out the group action factor your connection capacity is 28,000 lbs. Because of the non-linear distribution of load to the bolts you apply a group action factor to the bolt value resulting in a capacity less than 28,000

The above application is different than the use of bolts to secure a bottom plate to the foundation wall. Assume that anchor bolts 12" o.c. are used to transfer the shear out of the shear wall panel.

The wall shear is a per foot load. It is transferred out of the wall sheathing by nails into the bottom plate so the bottom plate is loaded along its full length. You don't have all the load transfered into the plate then into the anchor bolts. In stead you have load transfered into the plate all the way along its length. The anchor bolts are then receiving load load directly. In a case like the above the use of the group action factor does not really apply.

On the end of the shear walls when you are designing hold downs for the tension chord you would apply the Cg gactor.

 

[UcfSE]

I agree with RARSWC.

 

[Cayroo]

Thanks to all your responses, especially RARSWC for explaining some logic about the issue. Cayroo