1997 UBC Chapter 23 "Mode III or IV" ? 1

[TomHubbell]

In the 1997 UBC, Chapter 23, Section 2316.2, Table 2.3.2 has two footnotes which address using load duration factor Cd greater than 1.33. However, the footnotes refer to "... connections exhibiting Mode III or IV behaviour..." which I cannot find any reference to within the UBC. I believe these are failure modes of some type but need additional info to determine their applicability.

Can someone point me in the right direction regarding "Mode III or IV" literature?

Thanks

Tom Hubbell

 

[JAE]

I found the "definitions" to MODEs of failure in the fourth edition of the AITC manual.

Basically, they are as follows:

Mode Im - Bearing yield of wood from dowels (i.e. bolts, nails, lag screws, etc) bearing on the main member

Mode Is - Bearing yield of wood bearing on the secondary members

Mode II - Yielding of the wood due to pivoting of the dowel and crushing near the face of the members.

Mode IIIm - Yielding occurs in the dowel with bending at one plastic hinge point per shear plane (single shear only)

Mode IIIs - Yielding occurs in the dowel with bending at one plastic hinge point per shear plane in secondary members (single and double shear conditions)

Mode IV - Yielding occurs in the dowel with 2 plastic hinge points per shear plane.

When you use the NDS, there are tables of bolt or lag screw capacities that are simply the controlling result of the different Mode capacity formulae. The NDS also includes these formulae for your use in programs or spreadsheets if desired. Basically, Modes III and IV involve dowel yielding while Modes I and II involve failure of the wood.

 

[TomHubbell]

Thanks for the very swift reply!

Tom

 

[TomHubbell]

Okay, found it.

The various modes are shown and explained in the NDS-1997, Appendix I, p164.

Thanks again for the info.

Tom