Behold a Seismic Fastener Test Database

Jul 31, 2017 · News
Shahab Torabian, Ph.D.

NBM Technologies has recently tested a wide variety of steel sidelap and deck-to-frame fasteners as part of an effort for advancing the seismic design of big-box buildings. A database of steel deck fasteners, now in progress, will provide invaluable fundamental information to industry and academia. For the first time, anyone will have what they need to study big-box buildings at very fine levels down to the fasteners, which the behavior of the whole building strongly derives from.

Fastener image.

A powder-actuated fastener. Credit: NBM Technologies.

Screw, power-actuated, welded, and punched fasteners comprise the different types of steel fasteners on the market. All of them contort in various specific ways when subjected to the ground motions of an earthquake. At Johns Hopkins University’s Thin-walled Structures Laboratory, NBM researchers subjected these to a specially-designed testing rig to find the constituent force-deformation properties and hysteric data each would exhibit in an earthquake’s back-and-forth, nonlinear forces.

Seismic data enables advanced analysis

This data coming out of this rig is immediately applicable to individual fastener design: already, a number of fastener manufacturers are working with NBM to discover how their fastener products respond to cyclic forces. Anyone involved in roofing or fastener products for the big-box building type could benefit from this analysis. Thinking ahead, engineers that pursue full-scale system modeling would find a seismic fastener test database useful for any steel-deck design.

Until very recent work by NBM, no seismic model had achieved successful collapse for the big-box building type, also known as RWFD (rigid wall flexible diaphragm). Missing was data on the physical behavior of each fastener, which are the first structural components to fail during an earthquake for this building type. In 2015, a FEMA report called on the steel industry to provide this data.

Truss to column connection for a steel-decked RWFD building.

Hundreds of fasteners stitch together the steel deck diaphragm (grey with stripes, pictured) of a building. Credit: NBM Technologies.

NBM has done so, collecting data on over 30 different fastener types that a successful full-scale system analysis for one big-box building has validated for each. The model exhibited the collapse profile observed for the big-box building type in real earthquakes. This project, now in Phase II, is funded by the American Iron and Steel Institute, Steel Deck Institute, and Steel Joist Institute.

A rare rig delivers

Rigs capable of imparting fastener-level cyclic loadings are not found in dedicated construction laboratories because of the high cost of their actuators and because the design of test details that replicate in-situ fastener performance requires unique experience and insight.

Seismic testing rig for fasteners, image.

NBM’s custom rig accommodates cyclical testing of steel fasteners. Credit: NBM Technologies.

NBM’s goal is to create a full database of nonproprietary steel fasteners’ seismic test results for partners in academia and industry without their own access to this equipment. For those interested in proprietary fasteners, custom testing programs are also available now. The NBM rig is open for cyclical testing of fasteners, accommodating forces up to a maximum of 10 kips per fastener, and shear deformation up to three inches. Though originally designed for 1.5-inch B-decks, it can test other types of cold-formed steel decks with minor adjustments.

Alone or combined with NBM’s strengths in complex, computationally-intensive full-scale system modeling, these opportunities to conduct seismic testing of fasteners offer a clear path to more resilient designs and optimized engineered structures.