The slab-column connections are not part of the lateral system. Though the slab-column connections only take gravity loads, they still have to move with the building as it sways, Shield says.

Quake Conditions

In a quake, the connection must be ductile enough to hold the gravity load. "For seismic zones, strength is not the main thing," Shield says. The issue is whether there is enough shear reinforcement to allow sway and still hold the gravity load, she adds.

Parra and Shield are basing their concern regarding the code on results from four tests, to date, on slab-column specimens, which they say are designed to code (ENR 8/29 p. 13). In the first test, in 2007, the specimen had an orthogonal stud rail layout, but the rails did not emanate from column corners. The next two specimens, tested in December 2010 and March 2011 had three lines of stud rails emanating from each face of the column and perpendicular to the column faces, with two of the lines near the column corners. One specimen had tighter stud spacing than the other.

A test in July used an orthogonal layout with added diagonal lines of shear studs radiating from the corners of the column, at 45-degree angles. This specimen performed much better than the others, says Parra.

Ghali says recent tests conducted in Brazil show that the shear-stud reinforcement is equally effective when arranged orthogonally or radially. But a radial layout makes it much more difficult to install the slab's flexural reinforcement, which is set orthogonally.

Regarding the 2007 test, Ghali maintains that the test setup, measurements and analysis of the results were faulty. He says the slab's steel-mesh flexural reinforcement and the shear reinforcement were "well below the amounts required by the code."

Ghali adds that even though the specimen did not satisfy the code, it resisted loads well above the values predicted by code equations. "This clearly shows that the code is conservative. Slabs designed according to the code having stud-shear reinforcement are safe, and [the assertion of] premature failure is not substantiated," says Ghali, who maintains that Parra has not provided enough information on subsequent tests for a technical assessment.

Neil Hammill, a professional engineer and president of the Studrail division of Decon USA Inc., which is the original manufacturer of the studs-on-a-rail invention, licensed to Decon by Ghali and Dilger, says that Decon alone has supplied Studrails to tens of thousands of buildings since 1988. "I'm not aware of any failures," he adds.

Hammill maintains that, among other factors, Parra's original test specimen "did not comply with the code" because the stud rails used, which were not supplied by Decon, were not placed flush against the column faces at the column corners. There were not enough stud rails, they were not placed in the correct location, and the stud spacing was too large for the loads being transferred, says Hammill.

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