For years, the standard practice within the U.S. steel construction market, excluding the West Coast, has been for fabricators to design member connections. This gives the fabricator better control of the process by designing connections that best fit their particular machinery and shop standards. But the practice is ineffective and risky for all parties involved in todays litigious and claims-oriented environment.
As structural engineer of record (SER) on some very large and complex steel buildings, we have found that it is best for the SER to design the connections and present them in the construction documents. The larger and more complex the structure, the more imperative this process becomes.
On the West Coast, seismic requirements dictate design, making the SER not only better suited, but also required to design member connections. Due to the evolution and the eventual unification of the model building codes, all buildings must now be designed to meet at least moderate seismic standards.
Detailing requirements also have dramatically increased. If you factor in the use of todays computerized three-dimensional analysis and design tools, where the number of load combinations has gone from four or five to 40 or 50, it is increasingly unrealistic for fabricators to design the connections.
Under current standards the SER presents member shapes, sizes and design forces on the construction documents. The fabricator then designs the connection and submits the details to the architect and SER for review and approval.
But the submittal often is rejected due to improper design criteria, a disagreement in design methodology, spatial conflicts or aesthetics. On complex projects, this process can repeat itself several times. Only after the connection designs are agreed upon can actual shop drawings begin.
When the SER designs the connection, it takes slightly longer to produce the construction document, but the time is more than made up during the submittal preparation and review process. The overall benefit can be weeks to several months, depending on size and complexity of the project.
The SER often designates member sizes based on their internal forces, blindly delegating the connection design to the fabricator. But the configuration of a connection can actually control what member shape and orientation should be chosen. Meanwhile, the originally designed shape has been purchased and the fabricator is stuck either designing an expensive connection between inappropriately chosen members, or changing the member size or shape and absorbing the cost of the materials. This scenario often results in material and/or delay claims.
When the SER provides member design forces in the construction documents, the maximum forces in a joint are often chosen from as many as 50 different load cases. This means that the maximum forces given to the fabricator might not result in equilibrium.
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This makes design of common members very difficult or impossible. Also, structural engineers often place notes on their drawings such as, "design connections for 90% of the tensile or moment capacity." This often results in unnecessarily costly, over-designed connections, particularly for bolted connections.
Many fabricators design connections in a solely utilitarian manner, using the simplest analysis and design techniques. Members often appear bulky and severely compromise aesthetics of exposed steel.
When choosing your structural engineer, find out what the engineers policy is on steel connection design, allow a little extra design time and pay to properly perform these tasks. The rewards of a faster project, decreased material and delay claims and greater peace of mind will be well worth it. m
Ronald M. Jezerinac Jr. is vice president of Bliss & Nyitray Inc., a Fort Lauderdale, Fla.-based consulting engineer. He can be contacted at
r-jezerinac@www.bniengineers.com.
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