Stainless steel screws, aluminum plate and wood

[RARWOOD]

I have an application which requires the attachment of aluminum members in single shear, or possible double shear, to cedar timbers which are unseasoned. The attachment may be made with stainless steel screws or bolts.

Does anyone know how to calculate the allowable load values for the fasteners strength in the wood?

 

[SlideRuleEra]

I still prefer to use the "Pre-1991" method that is outlined in "Wood as an Engineering Material", free .pdf download at

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm

The calculations are rational and give realistic values.
See Chapter 7, page 7-10

http://www.SlideRuleEra.net

 

[SlideRuleEra]

...forgot to address the unseasoned wood. For screws, I apply the same 25% reduction discussed (for nails) on page 7-7. Note the statement that follows suggesting rechecking the joint after drying.

http://www.SlideRuleEra.net

 

[RARWOOD]

Looking at the "Wood Handbook", I would understand that you are saying you would use fastener values from the 1986 N.D.S.
I am I correct?

From my copy of the "Wood Handbook", revised in 1987, my understanding is that the method of calculating fastner values is based on the wood properties not the fastner and side plate properties?

I have never liked the "Post-1991" methods for calculating fastener values. There are too many variables in the equations, so when you arrive at a number you have no good way to judge if it is correct. When in doubt I compare my calculated "Post-1991" value with the "Pre-1991" value.

One major reason I don't like the "Post-1991" method, is that it allows you to calculated values for A325 bolts used in wood connections. I think the A325 bolts are too stiff to use in wood connections, and I have my doubts that the "Post-1991" methods are appropriate for use with A325 bolts.

What do you think?

 

[SlideRuleEra]

RARSWC - I have seen some of your other posts and know that you are both well informed and experienced. Totally agree with your positions on the above methods and materials. I have confidence in the "Pre-1991" approach - it has passed the "test of time", in my opinion. My 1974 hard copy of "Wood Handbook" has the exact same equations, tables, etc. An engineer, who knows what they are doing (with wood), can make wise use of the "Pre-1991" method. Often wonder why it was changed.

http://www.SlideRuleEra.net

 

[RARWOOD]

SliedRuleEra-Thank you for the compliment. I've learned a lot from your responses which also indicate that you have many years of experience. I wonder how many engineers today even know what a slide rule is, or how to use one. When I pull my old one out, about all I can do, is multiply.

It is my understanding that the "Pre-1991" bolt values were based on testing that was done on small diameter bolts loaded in compressdion. The results were then extrapolated for larger diameter bolts. The "Commentary" on the 1991 NDS indicated that the methods used to develop bolt values remained unchanged fromm 1944 through the 1986 NDS.

I believe the current method is based on research and testing that was done in Europe. I believe that when the 1991 NDS was developed the European Yield Model was considered the most accurate method at that time.

Beyond what I stated above, I don't really know much about the new method. I am familair with some of the questions that were raised about the old method. One objection was that the older testing didn't accurately represent tension loading.

Also there were questions raised about the reliablity of the published design values for larger diameter bolts. In the past the use of 1 1/4" or 1 1/2" diameter bolts were not that uncommon. The company I work for in the past, before my time, had a failure on a project that used large diameter bolts. Based on some in house testing after that the company didn't feel the values published for the larger diameter bolts, was reliable.

The 1991 and later NDS, do not contain procedures to calculate bolt values or 1" diameter, leaving it up to the designer to establish those values. I should mention that AITC did conduct research on bolts larger than 1" diameter and concluded that the bolt vales were reliable. However they did indicate that because of difficulty in fabricating holes for larger diameter bolts and other factors, that the use of larger diameter bolts should be discouraged