Cyclic Seismic Behavior of Concrete-filled Steel Deck Diaphragms

Abstract

Earthquake disasters in the United States account for $6.1 billion of economic losses each year, much of which is directly linked to infrastructure damage. These natural disasters are unpredictable and represent one of the most difficult design problems regarding constructing resilient infrastructure. Structural floor and roof diaphragms act as the horizontal portion of the lateral force resisting system (LFRS), distributing the seismically derived inertial loads out from the heavy concrete slabs to the vertical LFRS. Concrete-filled steel deck diaphragms are ubiquitously used in steel construction worldwide due to the ease of construction and cost-effective use of material. This report first presents a series of concrete-filled steel deck push-out tests that explores the effect of cyclic loading on the strength of steel headed stud anchors. The effect that cyclic loading has on structural performance is explored across different concrete densities, steel headed stud anchor placements and groupings, steel deck orientations, and edge conditions. As compared to prior tests, the push-out tests conducted in this work included four rows of studs along the length rather than the typical two rows, and an ability to impose cyclic loading. This provided novel insight into force flows, failure mechanisms, and load distribution between studs and stud groups. Most of the specimens also used lightweight concrete, as is common in high seismic zones.Secondly, this report describes a full-scale experimental concrete-filled steel deck diaphragm specimen which explored the cyclic behavior and capacity of this structural system. This experiment builds on previously reported experimental studies. This specimen demonstrated force distribution and flows in an indeterminant floor system and captured realistic boundary conditions and construction practices that affect the performance of this system in building structures. The results showed that concrete-filled steel deck diaphragms fail as expected and may have significant overstrength. Furthermore, a finite element framework is presented that can simulate cyclic fracture through the use of a high-fidelity steel material model. This framework was used and validated against nine experimental push-out specimens tested and documented as part of this research. The simulation capacity provides an avenue to further investigate this structural system through simulated parametric study.