Non-linear performance of topology optimized orthotropic bare steel deck diaphragms

The objective of this paper is to compare the elasto-plastic response of traditional and optimized roof diaphragm designs under lateral loads. The seismic building design depends on the floor and roof diaphragms can transfer lateral loads to the vertical lateral force resisting systems and ensure continued global stability of the structure during seismic events. Diaphragms have traditionally been designed to remain elastic, but researchers have observed that diaphragms experience inelastic deformations in earthquakes. Work in a recent paper used topology optimization to design bare steel deck diaphragms by optimizing the deck selection and deck orientations assuming linear elastic behavior. The optimized designs as well as traditional designed diaphragms are subjected to a non-linear pushover analysis assuming the deck plasticization is solely governed by shear deformations and reduction in shear stiffness. It was found that the optimized designs outperform typical deck designs in terms of ultimate bearing capacity and energy dissipation despite being optimized with respect to linear stiffness alone. It is hoped that these findings will encourage further research into the design of diaphragm decks that are both stiffer and more stable under plastic deformations. This work is part of a larger initiative (steeli.org) that aims to better understand and optimize the role of diaphragms in the seismic response of steel buildings.The authors gratefully acknowledge the financial support funded by the American Iron and Steel Institute, the American Institute of Steel Construction, the Steel Deck Institute, the Metal Building Manufacturers Association, the Steel Joist Institute and the US National Science Foundation through grant CMMI-1562821. And support from the National Aeronautics and Space Administration (NASA) under Grant No. 80NSSC18K0428. Also, the ideas and contributions from collaborators in the Steel Diaphragm Innovation Initiative (SDII) effort are acknowledged. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation or other sponsors

Seismic Performance and Topology Optimization of Building Diaphragms

This dissertation investigates the seismic performance of steel deck diaphragms through the effects of rigid and flexible diaphragms on the seismic response, the diaphragm and wall interactions, and the improvements to the diaphragm design using topology optimization. The diaphragm is part of the lateral force resisting system (LFRS), which consists of two main components: the vertical LFRS, i.e., braced frames, shear walls, etc., and the horizontal LFRS, i.e., the diaphragm. With the use of mass-spring models, the diaphragm and wall interactions can be studied, therefore, mass-spring models of a single-story building model and multi-story building models were developed that include a degree of freedom for the diaphragm and two degrees of freedom for the vertical LFRS for each story. The seismic response was studied through a parametric study that considered variations of the diaphragm and wall stiffnesses, mass distribution in the model, and different levels of inelasticity in both the vertical and horizontal LFRS. It was observed that the force demands in both walls and diaphragm(s) depend on the diaphragm and wall stiffness, mass distribution, and the inelasticity levels. Secondly, dynamic amplification occurred in the diaphragm force demands when diaphragm and wall periods are similar. Thirdly, diaphragm forces are observed to be reduced by reducing the capacity of both horizontal and vertical LFRS. Finally, large ductility demands arise in the component of the LFRS with the larger inelasticity level. Three diaphragm examples are optimized for minimum compliance and then modified for a more constructible design. The elastic and inelastic behaviors of modified optimized diaphragm designs were compared to designs using traditional diaphragm design methods. Findings include that the modified designs have stiffer responses in the elastic and inelastic range compared to the traditional diaphragm designs. Furthermore, the modified designs reached a higher capacity at failure and had a better ability to redistribute stresses after initial yield, resulting in a higher amount of dissipated energy through plastic deformations

Seismic Performance and Topology Optimization of Building Diaphragms

This dissertation investigates the seismic performance of steel deck diaphragms through the effects of rigid and flexible diaphragms on the seismic response, the diaphragm and wall interactions, and the improvements to the diaphragm design using topology optimization. The diaphragm is part of the lateral force resisting system (LFRS), which consists of two main components: the vertical LFRS, i.e., braced frames, shear walls, etc., and the horizontal LFRS, i.e., the diaphragm. With the use of mass-spring models, the diaphragm and wall interactions can be studied, therefore, mass-spring models of a single-story building model and multi-story building models were developed that include a degree of freedom for the diaphragm and two degrees of freedom for the vertical LFRS for each story. The seismic response was studied through a parametric study that considered variations of the diaphragm and wall stiffnesses, mass distribution in the model, and different levels of inelasticity in both the vertical and horizontal LFRS. It was observed that the force demands in both walls and diaphragm(s) depend on the diaphragm and wall stiffness, mass distribution, and the inelasticity levels. Secondly, dynamic amplification occurred in the diaphragm force demands when diaphragm and wall periods are similar. Thirdly, diaphragm forces are observed to be reduced by reducing the capacity of both horizontal and vertical LFRS. Finally, large ductility demands arise in the component of the LFRS with the larger inelasticity level. Three diaphragm examples are optimized for minimum compliance and then modified for a more constructible design. The elastic and inelastic behaviors of modified optimized diaphragm designs were compared to designs using traditional diaphragm design methods. Findings include that the modified designs have stiffer responses in the elastic and inelastic range compared to the traditional diaphragm designs. Furthermore, the modified designs reached a higher capacity at failure and had a better ability to redistribute stresses after initial yield, resulting in a higher amount of dissipated energy through plastic deformations

One-to-one coupling of glacial climate variability in Greenland and Antarctica

Precise knowledge of the phase relationship between climate changes in the two hemispheres is a key for understanding the Earth's climate dynamics. For the last glacial period, ice core studies1, 2 have revealed strong coupling of the largest millennial-scale warm events in Antarctica with the longest Dansgaard–Oeschger events in Greenland3, 4, 5 through the Atlantic meridional overturning circulation6, 7, 8. It has been unclear, however, whether the shorter Dansgaard–Oeschger events have counterparts in the shorter and less prominent Antarctic temperature variations, and whether these events are linked by the same mechanism. Here we present a glacial climate record derived from an ice core from Dronning Maud Land, Antarctica, which represents South Atlantic climate at a resolution comparable with the Greenland ice core records. After methane synchronization with an ice core from North Greenland9, the oxygen isotope record from the Dronning Maud Land ice core shows a one-to-one coupling between all Antarctic warm events and Greenland Dansgaard–Oeschger events by the bipolar seesaw6. The amplitude of the Antarctic warm events is found to be linearly dependent on the duration of the concurrent stadial in the North, suggesting that they all result from a similar reduction in the meridional overturning circulation