A Beginner's Guide to the Steel Construction Manual, 14th ed. Chapter 5 - Welded Connections © 2006, 2007, 2008, 2009, 2011 T. Bartlett Quimby
 Introduction to Welding Finding Forces in Welded Connections Effective Areas of Base Metal Strength Limit State Designing Welds Chapter Summary Example Problems Homework Problems References Report Errors or Make Suggestions Purchase Hard Copy

Section 5.7

Weld Summary

Last Revised: 11/04/2014

Strength Limit States:

All strength limit states take the form:

 LRFD ASD Ru < ftRn Ra < Rn/Wt Req'd Rn = Ru/ft < Rn Req'd Rn = Ra Wt < Rn Ru / (ftRn)  < 1.00 Ra / (Rn/Wt) < 1.00

Which is:  FORCE on a weld < STRENGTH of a weld

The STRENGTH of a weld is computed by:

The nominal capacity of the weld, Rn = minimum[Strength of Weld, Strength of Base Metal]

 Limit State Specification Nominal Capacity, Rn Typical Design Variables f W Weld Tensile Rupture, Shear Rupture, and Yielding J2.4 FwAwFw from SCM Table J2.5 te, Lw, Electrode, Weld Layout SCM Table J2.5 SCM Table J2.5 Base Metal J2.4 or J4 FBMABMFBM from SCM Table J2.5 or SCM Section J4 Lw, Weld Layout SCM Table J2.5 or SCM J4 SCM Table J2.5 or SCM J4

The FORCE on a weld is computed by:

Forces Concentric with the Bolt Group at the Faying Surface:

• All welds are assumed to be equally stressed.  The force per unit length equals the stress times a unit length.

Eccentricity in the Plane of the Faying Surface:

• Elastic Vector Method:  See SCM pg 8-12.  Computes shear in the weld.  Direct method that is conservative and has an inconsistent factor of safety.
• Instantaneous Center of Rotation Method:  See SCM pg 8-9.  Computes the relationship between the applied load and the shear load in the worst case weld segment.  Iterative method that is more consistent with test results and not as conservative as the Elastic Method.

Eccentricity out of the Plane of the Faying Surface:

• See SCM pg 8-14.  Basic mechanics (Mc/I) using the compression contact area to find the tension in the worst case weld segment.  If the shear is concentric with the bolt group it causes equal stress in plane in all the welds otherwise use either the elastic vector or IC method to find the distribution of in-plane stress.