New AISC Seismic Design Provisions (and they include my research)

If you have taken Steel Design, then you are certainly familiar with the AISC Steel Construction Manual.  While this Manual provides a wealth of knowledge related to the design of steel structures, because of the complexity of designing earthquake resistant steel structures, there is an entirely separate document for this purpose, referred to as the AISC Seismic Provisions.  I received notice today that the 2016 version of the AISC Seismic Provisions just became available for free download from AISC at www.aisc.org/2016SP.

I am especially excited to share this announcement with you because the research I conducted over the course of four years in the PhD program at UC Davis has been incorporated into these Seismic Provisions.  Here is a brief summary of my research and it's outcomes:

Since the 1994 Northridge Earthquake, column splices in intermediate and special steel moment resisting frames have been required to be complete joint penetration (CJP) welds, meaning the full surface between adjoining columns must be fused with weld material.  While CJP welds are stronger than partial joint penetration (PJP) welds, they are more costly to construct in terms of both materials and labor.

Complete Joint Penetration Welded Column Splice

Partial Joint Penetration Welded Column Splice

Following five full scale experiments on column splices conducted by Dr. Sean Shaw that demonstrated PJP welds with 82 - 95% of the adjoining surfaces fused were capable of remaining intact for loading well past the yield stress of the columns they were connecting, I conducted an analytical study in which I modeled 25 different splice geometries in a finite element analysis software known as ABAQUS.  My analyses used fracture mechanics principles to predict the stress in the column flanges that would cause fracture of the PJP column splice.  From this, I was able to generalize the conditions under which PJP welded column splices could be safely used.  If these conditions, as summarized in Section E3.6g of the 2016 Seismic Provisions, are met for a column splice, then the AISC Seismic Provision permits the use of a PJP welded connection.

This change may come as a shock to some structural engineers, as the industry has been weary of PJP welds following the fractures observed during the 1994 Northridge earthquake.  However, it is important to point out a number of items:

• The observed fractures in the Northridge Earthquake occurred in beam-to-column connections, not column splices. 
• Column splices are expected to experience far lower stress demands than beam to column connections.
• Improvements in material toughness and detailing requirements have been made since the Northridge Earthquake.
• The weld penetrations (% of surface fused) required for PJP welds in the new provisions is significantly higher than was used in pre-Northridge PJP splices.
• This change is supported by both full-scale physical experiments and finite element analyses that indicate the ability of the PJP welded column splices to exhibit ductile performance, developing the full yield stress of the column prior to fracture. 

For more information about my research, I refer you to the three publications that are cited as references in the 2016 Seismic Provisions.  Other major contributors to this research included Dr. Amit Kanvinde and Dr. Carmine Galasso.  Ongoing research (to be discussed in a future post) investigates the effect of a column splice fracture on the overall structural performance of a steel moment frame.