NONLINEAR FASTENER-BASED MODELING OF COLD-FORMED STEEL SHEAR WALLS UNDER LATERAL LOADS

As cold-formed steel (CFS) has increasingly been used in low- and mid-rise construction across United States, it becomes necessary to capture and evaluate its lateral response in both, sub-system/member level and system level. The main lateral resisting system in cold-formed steel construction is shear walls; shear walls are the focus of this work. In particular, the present study aims to shed light on the response of wood sheathed coldformed steel (CFS) shear walls exposed to earthquake events through nonlinear high fidelity fastener-based modeling. The numerical approach is fastener-oriented including nonlinear experimental-determined connector elements for steel-to-sheathing connections, orthotropic oriented strand board (OSB) modeling for sheathing material, contact implementation and linear spring hold-down simulation for preventing uplift. The numerical results are compared and validated by a previous experimental study, assessing the efficiency of fastener-based modeling to capture the peak load and displacement, the failure mechanisms and the overall structural behavior of sheathed cold-formed steel shear walls. Furthermore, cold-formed steel to sheathing shear fastener response is computationally examined and validated by a previous experimental work. The main goal of this work is to introduce a robust computational tool capable of demonstrating how wood sheathed cold-formed steel framed shear walls behave during a lateral load event with potential use in any cold-formed steel screw-fastened connection system, such as diaphragms and in any fastener-based cold-formed steel full building simulation

Harnessing the Mechanics of Thin-Walled Metallic Structures: from Plate-Lattice Materials to Cold-Formed Steel Shear Walls

Thin-walled structures have received a lot of interest during the last years due to their light weight, cost efficiency, and ease in fabrication and transportation, along with their high strength and stiffness. This dissertation focuses on the mechanical performance of thin-walled metallic structures from cold-formed steel shear walls and connections (PART I) to plate-lattice architected materials (PART II) via computational, experimental, and probabilistic methods. Cold-formed steel (CFS) shear walls subjected to seismic loads is the focus of PART I of this dissertation. An innovative three-dimensional shell finite element model of oriented strand board (OSB) sheathed CFS shear walls is introduced and benchmarked by nine different experimental studies. Particular attention is given to the fastener behavior since they are governed by significant inherent variability and they represent a dominant failure mechanism in CFS shear walls. Shear fastener behavior is experimentally determined and introduced into the finite element approach. To further address the connection variability, an extensive parametric analysis accompanied by Monte Carlo simulations are conducted. Design recommendations for higher capacity sheathings (fiber cement board (FCB) and steel-gypsum (SG) composite board) that are not currently enabled in design specifications are also introduced. Architected plate-lattice materials subjected to uniaxial compression is the focus of PART II of this dissertation. Architected materials are structures whose mechanical performance is governed by their geometry rather than their constituent material. Plate-lattices are composed of plates along the planes of crystalline structures. They represent the stiffest and strongest existing materials, since they can reach the Hashin-Shtrikman and the Suquet upper bounds. The stability and imperfection sensitivity of plate-lattices are evaluated in this work via elastic and plastic shell finite element analyses. Plate-lattice geometries of cubic symmetry are examined, such as the simple cubic (SC), the body-centered cubic (BCC), the face-centered cubic (FCC) structures and their combinations (SC-BCC, SC-FCC) over a range of relative densities between $\rho$*=0.5\% and $\rho$*=25\%. Imperfections are characterized by modal shapes at five different imperfection amplitudes. Finally, knockdown factors are recommended for these metamaterials

Defect-Defect Interactions in the Buckling of Imperfect Spherical Shells

We perform finite element simulations to study the impact of defect-defect interactions on the pressure-induced buckling of thin, elastic, spherical shells containing two dimpled imperfections. Throughout, we quantify the critical buckling pressure of these shells using their knockdown factor. We examine cases featuring either identical or different geometric defects and systematically explore the parameter space, including the angular separation between the defects, their widths and amplitudes, and the radius-to-thickness ratio of the shell. As the angular separation between the defects is increased, the buckling strength initially decreases, then increases before reaching a plateau. Our primary finding is that the onset of defect-defect interactions, as quantified by a characteristic length scale associated with the onset of the plateau, is set by the critical buckling wavelength reported in the classic shell-buckling literature. Beyond this threshold, within the plateau regime, the buckling behavior of the shell is dictated by the largest defect

Cross-Neutralisation of Novel Bombali Virus by Ebola Virus Antibodies and Convalescent Plasma Using an Optimised Pseudotype-Based Neutralisation Assay.

Ebolaviruses continue to pose a significant outbreak threat, and while Ebola virus (EBOV)-specific vaccines and antivirals have been licensed, efforts to develop candidates offering broad species cross-protection are continuing. The use of pseudotyped virus in place of live virus is recognised as an alternative, safer, high-throughput platform to evaluate anti-ebolavirus antibodies towards their development, yet it requires optimisation. Here, we have shown that the target cell line impacts neutralisation assay results and cannot be selected purely based on permissiveness. In expanding the platform to incorporate each of the ebolavirus species envelope glycoprotein, allowing a comprehensive assessment of cross-neutralisation, we found that the recently discovered Bombali virus has a point mutation in the receptor-binding domain which prevents entry into a hamster cell line and, importantly, shows that this virus can be cross-neutralised by EBOV antibodies and convalescent plasma

Cyclic Performance of Steel Sheet Connections for CFS framed Steel Sheet Sheathed Shear Walls

The main objective of this research is to study fastener-level force-deformation response appropriate for standard cold-formed steel (CFS) framed steel sheet sheathed shear walls under cyclic loads. Recently completed CFS-framed shear wall tests employing thin steel sheets screw-fastened to thicker CFS-framing have recorded higher capacity and ductility for the CFS-framed steel sheet sheathed shear walls. For the seismic performance of these shear walls, the cyclic nonlinear response of the fastener connection is especially important and should incorporate the impact of shear buckling of the steel sheet on the strength and ductility of the connection. Minimal cyclic fastener-level shear test data exists, especially for combinations of screw fastened thin steel sheet and thick framing steel. To address this, a unique lap shear test following AISI S905 was designed to elucidate and characterize the cyclic fastener behavior. The specimens were loaded with an asymmetric cyclic loading protocol which intentionally buckles the sheet in the compression direction, and progressively increases in the tension direction. A total of 93 tests demonstrating a wide range of framing thickness, sheet thickness, fastener size, and loading types were conducted. Key experimental statistics, including the characterization with a multi-linear backbone curve, are provided. Fastener connection strength is sensitive to whether the thin steel sheet ply is buckling away from or towards the fastener head in some test series. AISI S100-16 screw shear strength provisions performance is evaluated. The work is aimed at providing critical missing information for CFS-framed steel sheet sheathed shear walls for use in both simulation and design.This work is part of the research project Seismic Resiliency of Repetitively Framed Mid-Rise Cold-Formed Steel Building (CFS-NHERI) which is supported by the National Science Foundation under Grant No.1663348 and No. 1663569. Test materials were provided by ClarkDietrich and are gratefully acknowledged. The tests conducted herein were assisted by Gbenga Olaolorun and Joel John, the authors would like to express gratitude to their great help. Moreover, the testing would not have been possible without the support from lab staff Nick Logvinovsky, we greatly appreciate his assistance. Any opinions, findings, and conclusions or recommendations expressed in this publication are those of the authors and do not necessarily reflect the views of the sponsors and employers

Lateral Response of Cold-Formed Steel Framed Steel Sheathed In-line Wall Systems Detailed for Mid-Rise Build

Buildings constructed with cold formed steel (CFS) framing have shown great potential as a modern efficient building system. However, full understanding of their lateral structural behavior, particularly the contribution from non-designated systems, under seismic events is limited. The current North American Standards provide information that can be used to design CFS framed steel sheet shear walls which meet the seismic demands for low- to mid-rise (3-6 story) buildings. However, there is a paucity in experimental data to support design guidelines for taller mid-rise (>6 stories) and high-rise buildings (>10 stories), where large lateral load resistance is required. Moreover, existing code guidelines are based primarily on experiments involving shear walls subject to quasi-static monotonic and reversed cyclic loading protocols. In the current research project, shear walls placed in-line with gravity walls were tested at full-scale first under a sequence of increasing amplitude (in-plane) earthquake motions, and subsequently (for select specimens) under slow monotonic pull conditions to failure. Experiments were performed at the NHERI Large High-Performance Outdoor Shake Table at the University of California, San Diego. The selection of wall details was motivated by a CFS archetype building designed at 4 and 10 stories, as well as available experimental data. This paper documents the experimental response and physical damage observations of four wall specimen pairs in the test program. These particular specimens adopt compression chord stud packs with a steel tension tie-rods assembly, are either unfinished or finished on their exterior face, and laid out in a symmetric or asymmetric fashion. In addition, both Type I and “Type II” shear wall detailing are investigated.The research presented is funded through the National Science Foundation (NSF) grants CMMI 1663569 and CMMI 1663348, project entitled: Collaborative Research: Seismic Resiliency of Repetitively Framed Mid-Rise Cold-Formed Steel Buildings. Ongoing research is a result of collaboration between three academic institutions: University of California, San Diego, Johns Hopkins University and University of Massachusetts Amherst, two institutional granting agencies: American Iron and Steel Institute and Steel Framing Industry Association and ten industry partners. Industry sponsors include ClarkDietrich Building Systems, California Expanded Metal Products Co. (CEMCO), SWS Panel and several others who each provided financial, construction, and materials support. Regarding support for the test program, the efforts of NHERI@UCSD staff, namely, Robert Beckley, Darren McKay, Jeremy Fitcher, and Alex Sherman, and graduate student Filippo Sirotti are greatly appreciated. Findings, opinions, and conclusions are those of the authors and do not necessarily reflect those of the sponsoring organizations

Comparison of lentiviral and vesicular stomatitis virus core SARS-CoV-2 pseudotypes and generation of a stable cell line for use in antibody neutralisation assays

Betacoronavirus SARS-CoV-2, the causative agent of COVID19, is a single stranded positive sense RNA virus. Since its emergence there has been great efforts to identify correlates of protection,which is crucial for vaccine evaluation studies. However, handling SARS-CoV-2 requires BSL-3 containment facilities slowing research efforts. Pseudotype viruses (PV) are a safe alternative to authentic virus that can be handled at low containment. PVs are chimeric viruses containing the core of a virus where its genome has been completely or partially replaced by a reporter gene, displaying a correctly folded SARS-CoV-2 spike on its surface. We developed lentiviral and vesicular stomatitis virus (VSV) core PVs alongside a stable A549 cell line expressing receptor ACE2 and protease TMPRSS2 responsible for S protein priming, for use in neutralization assays. Lentiviral PVs were generated by transfection with plasmids encoding the spike, HIV-1 gag-pol and a luciferase reporter. For VSV PVs, producer cells pre-transfected with the spike were infected with recombinant VSV expressing luciferase,before harvesting. The stable A549 cell line was generated by sequential infection of VSV-G PVs bearing lentiviral vectors encoding ACE2 and TMPRSS2 genes followed by antibiotic selection, before being tested in neutralization assays. We compared lentiviral and VSV PV platforms using monoclonal antibodies and convalescent sera with our stable A549 cells or HEK293T cells pre-transfected with plasmids encoding ACE2 and TMPRSS2. Antibody titres showed equivalence however VSV had the advantage of a shorter incubation therefore enabling a higher throughput. PVs offer a robust platform for future seroepidemiology and vaccine evaluation studies

AP205 VLPs based on dimerized capsid proteins accommodate RBM domain of SARS-CoV-2 and serve as an attractive vaccine candidate

COVID-19 is a novel disease caused by SARS-CoV-2 which has conquered the world rapidly resulting in a pandemic that massively impacts our health, social activities, and economy. It is likely that vaccination is the only way to form “herd immunity” and restore the world to normal. Here we developed a vaccine candidate for COVID-19 based on the virus-like particle AP205 displaying the spike receptor binding motif (RBM), which is the major target of neutralizing antibodies in convalescent patients. To this end, we genetically fused the RBM domain of SARS-CoV-2 to the C terminus of AP205 of dimerized capsid proteins. The fused VLPs were expressed in E. coli, which resulted in insoluble aggregates. These aggregates were denatured in 8 M urea followed by refolding, which reconstituted VLP formation as confirmed by electron microscopy analysis. Importantly, immunized mice were able to generate high levels of IgG antibodies recognizing eukaryotically expressed receptor binding domain (RBD) as well as spike protein of SARS-CoV-2. Furthermore, induced antibodies were able to neutralize SARS-CoV-2/ABS/NL20. Additionally, this vaccine candidate has the potential to be produced at large scale for immunization programs

Serological evidence of virus infection in Eidolon helvum fruit bats: implications for bushmeat consumption in Nigeria

Introduction: The Eidolon helvum fruit bat is one of the most widely distributed fruit bats in Africa and known to be a reservoir for several pathogenic viruses that can cause disease in animals and humans. To assess the risk of zoonotic spillover, we conducted a serological survey of 304 serum samples from E. helvum bats that were captured for human consumption in Makurdi, Nigeria. Methods: Using pseudotyped viruses, we screened 304 serum samples for neutralizing antibodies against viruses from the Coronaviridae, Filoviridae, Orthomyxoviridae and Paramyxoviridae families. Results: We report the presence of neutralizing antibodies against henipavirus lineage GH-M74a virus (odds ratio 6.23; p < 0.001), Nipah virus (odds ratio 4.04; p = 0.00031), bat influenza H17N10 virus (odds ratio 7.25; p < 0.001) and no significant association with Ebola virus (odds ratio 0.56; p = 0.375) in this bat cohort. Conclusion: The data suggest a potential risk of zoonotic spillover including the possible circulation of highly pathogenic viruses in E. helvum populations. These findings highlight the importance of maintaining sero-surveillance of E. helvum, and the necessity for further, more comprehensive investigations to monitor changes in virus prevalence, distribution over time, and across different geographic locations

Production, Titration, Neutralisation, Storage and Lyophilisation of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Lentiviral Pseudotypes

This protocol details a rapid and reliable method for the production and titration of high-titre viral pseudotype particles with the SARS-CoV-2 spike protein (and D614G or other variants of concern, VOC) on a lentiviral vector core, and use for neutralisation assays in target cells expressing angiotensin-converting enzyme 2 (ACE2) and transmembrane serine protease 2 (TMPRSS2). It additionally provides detailed instructions on substituting in new spike variants via gene cloning, lyophilisation and storage/shipping considerations for wide deployment potential. Results obtained with this protocol show that SARS-CoV-2 pseudotypes can be produced at equivalent titres to SARS-CoV and Middle East respiratory syndrome coronavirus (MERS-CoV) pseudotypes, neutralised by human convalescent plasma and monoclonal antibodies, and stored at a range of laboratory temperatures and lyophilised for distribution and subsequent application