Tech Briefs

Analyses and laboratory tests measure steel stud behavior in wall systems subject to blast loads.

Construction trends have brought about an increase in the use of cold-formed steel studs in Air Force facilities. These steel stud walls have significant potential for mitigating large blast events. The current state of steel stud research, however, has not addressed all the variables that can influence the behavior of typical wall systems. As a result, there is a research gap that exists in the blast-resistant design of conventional steel stud wall systems.

This Simulation of Load-Tree Specimens with idealized connections shows a close-up view of local buckling and yielding of material that occurs at the critical mid-span region of uniformly loaded studs.

This work includes the development of detailed finite element analyses and a series of laboratory tests to measure fundamental aspects of steel stud behavior, including connection response. Primary factors in the selection of steel stud wall systems are performance under blast loads, system cost, ease of construction, and availability of materials.

To characterize the response of steel stud walls it is important to recognize the wide range of construction practices that exist. Steel stud walls can be used as load-bearing components or non-load-bearing components, and a variety of exterior finishes and internal sheathing may be used. To meet the objectives of the current project, it is desirable to utilize wall construction techniques that use readily available materials so that costs are kept to a minimum. Accordingly, the test program aims to characterize how standard, cold-formed, steel stud walls, using common sheathing materials such as drywall, oriented strand board (OSB), or stucco, utilizing conventional structural connections and potentially proprietary connection devices, perform under blast loads.

Three component-level experiments have been devised: 1) Tensile Membrane Action (TMA), 2) Bending and Prying Action (BPA), and 3) Crippling and Crushing Action (CCA). TMA is for exploring the axial-tensile capacity of the steel-stud-to-track connection. Steel studs are placed back-to-back for symmetry, and then attached by various screw configurations to the track. Connection designs have been developed for achieving the full capacity of the steel stud; however, the aim of the TMA experiments is to explore the spectrum between full capacity and the single conventional screw installation. Using this setup, 73 samples were tested in an MTS load frame under quasistatic loading (0.5" per minute) to record each scenario’s load versus deflection response. The specimens included combinations of various track and stud thicknesses with different screw diameters and quantities.

The BPA series examines the identical test matrix as the TMA series, but subjects the samples to rotation and shear through a cantilever loading condition. The objective is to investigate rotational capacity of the stud in the track. The track is assumed to be held rigidly to the support with the focus of the testing to determine the degree of rotation at which the track and stud disconnect. Similarly to the TMA series, 73 samples were tested under displacement control at a loading rate of 0.5" per minute. An additional nine samples were examined at varying rates up to 2.0" per minute.

The purpose of the CCA test series is to evaluate the shear or crippling capacity of the studs inside the track channel. It is hypothesized that studs with deep webs and/or thin gauge sections have additional absorption capabilities not mathematically accounted for in current blast design procedures. Current procedures focus only on the flexural absorption of the steel stud and use the shear or connection capacity as a limit state. The experiment utilizes an MTS load frame under displacement control and is patterned similarly to a four-point bending experiment.

Computer-based simulations using detailed finite element models are a major component of this work. Because of the complicated failure mechanisms observed in past blast tests on steel stud walls, it is important to understand the role played by individual components in controlling the overall behavior of a typical wall assembly. Simulation models to date have been able to capture the local buckling and yielding of material that occurs at the critical mid-span region of uniformly loaded studs. While the general trend in response agrees well with observations from similar tests in the past, detailed data are needed to validate the predictions of the finite element models.

This work was done by Bryan Bewick of the Air Force Research Laboratory, John Hoemann of the U.S. Army Engineer Research & Development Center, and Eric Williamson of the University of Texas at Austin. For more information, download the Technical Support Package (free white paper) at www.defensetechbriefs.com/tsp under the Physical Sciences category. AFRL-0162

This Brief includes a Technical Support Package (TSP).

Performance of Steel Stud Walls Subjected to Blast Loads (reference AFRL-0162) is currently available for download from the TSP library.

Please Login at the top of the page to download.