Vasdravellis, Karavasilis, and Uy, 2014
High strength and stainless steel web hourglass shaped pins (WHPs) were tested under monotonic and cyclic loading conditions until failure, and laboratory data were used to compose a numerical model of a prototype building using WHP connections. The study concluded that stainless steel was more effective at energy dissipation than high strength steel, and that the WHPs offered a stable hysteretic response for use as a replaceable energy dissipating component.
System Concept
Web hourglass shaped pins (WHPs) were designed to supply a replaceable energy dissipation component to beam-to-column connections in the event of seismic loading. The WHPs were made of either high performance or stainless steel and were shaped as a cylindrical rod in which there were two indents that were shaped like hourglasses. Under loading, strain was concentrated into the two indented portions of the pins because of the lower cross sectional area, thus fracture occurred at these locations.
The WHPs were designed for use in a six story steel frame prototype building in which two different configurations of small and large WHPs were used for the beam to column connections. The hourglass portion of the WHPs are to be placed between the pinned connections to the beams and columns, such that the members make contact with the larger diameter portion of the pins. The WHPs are intended to deform at the point of lowest cross sectional area under seismic loading, but to remain ductile for high loads up until fracture, under which conditions they can be easily replaced with minimal downtime and cost.
Experimental Study, Results and Discussion
Monotonic loading was performed on the stainless steel and high strength steel WHPs. The WHPs were loaded as they would be in a beam to column connection, and the maximum stress and strain of the WHPs were reported. The WHPs exhibited ductile behavior and were able to sustain high loads prior to fracture.
Cyclic loading was also performed on each WHP. The cyclic loading conditions exhibited stable hysteretic behavior of the WHPs and a maximum shear force amplitude high enough to sustain a maximum considered earthquake (MCE). Likewise, it was observed that stainless steel had a higher energy dissipation capacity due to its ability to remain ductile under higher loads than the high strength steel.
The results from the experimental procedure were used to conduct a numerical analysis of WHPs under seismic conditions. A void growth model (VGM) and a stress modified critical strain model (SMCS) were computed. Using the parameters experimentally determined for the WHPs of different materials, the VGM indicated that the WHPs are unlikely to fail under monotonic loading up to the MCE, while cyclic loading indicated fracture at locations that were not observed in the experimental testing, which is likely due to further modifications being needed for the cyclic VGM, though the load applications aligned with the experimental study. Overall, the WHPs offer stable and replaceable connections, but further research is needed to confirm their applicability for beam-to-column connections under three dimensional seismic conditions.
Reference
Vasdravellis, G., Karavasilis, T.L., and Uy, B. (2014). “Design Rules, Experimental Evaluation, and Fracture Models for High-Strength and Stainless-Steel Hourglass Shape Energy Dissipation Devices” Journal of Structural Engineering, 140, 11. pp. 10.