Finite Element Modeling and Validation of Steel Sheathed Cold-Formed Steel Framed Shear Walls

The objective of this paper is to validate the concept of utilizing a truss-element based finite element model for capturing the in-plane cyclic response of steel sheathed cold-formed steel (CFS) framed shear wall. The model is developed within the OpenSees finite element platform. Steel sheathed CFS shear walls show shear buckling of their sheathing as a tension field develops. This inelastic behavior of the shear walls is replicated by using the Pinching4 material for truss elements acting along the tension field. Importantly, the model employs beam-column elements for framing members, rotational springs for representing frame stiffness and vertical springs for modelling hold-downs. The wall models were calibrated using experimental data available for 0.030-in. and 0.033-in. steel sheet sheathed shear walls with 2:1 and 4:1 aspect ratios and 6-in., 4-in. and 2-in. fastener spacing at panel edges. The specimens were subjected to symmetric reverse cyclic displacement-controlled loading using the CUREE protocol. Comparison amongst the experimental and numerical models demonstrate a high degree of accuracy in the estimated shear strength and hysteretic response of the shear walls and as such has the potential to be an important building block towards modeling full structural systems constructed of cold-formed steel framing

Seismic Behavior of Cold-Formed Steel Shear Walls during Full-Scale Building Shake Table Tests

Cold-formed steel sheathed shear walls are now emerging as a strategic vertical lateral load resisting component in seismic design. However, although a number of component cyclic test programs have been conducted in recent years to characterize their hysteretic behavior and guide design, system-level test programs to investigate their performance are so far lacking in the literature. To this end, a unique full-scale CFS-framed mid-rise building shake table test program was conducted to contribute to understanding the behavior of mid-rise cold-formed steel (CFS) wall-braced buildings under a multi-hazard scenario. The centerpiece of this project involved earthquake and live fire testing of a full-scale six-story CFS wall braced building constructed on the Large High Performance Outdoor Shake Table (LHPOST) at UCSD. This paper first provides a brief overview of the test program and summarizes the system-level (global) response of the test building during the shake table tests. Subsequently, a key focus of this paper is comparison of the component-level responses of various shear wall systems of the test building as well as their physical damage

3-D Reconstructions and Numerical Simulations of Precarious Rocks in Southern California

Reliable estimates of seismic hazard are essential for the development of resilient communities; however, estimates of rare, yet high intensity earthquakes are highly uncertain due to a lack of observations and recordings. Lacking this data, seismic hazard analyses may be based on extrapolations from earthquakes with more moderate return periods, which can lead to physically unrealistic earthquake scenarios. However, the existence of certain precariously balanced rocks (PBRs) has been identified as an indicator of an upper bound ground motion, which precludes toppling of the balanced rock, over its lifetime. To this end, a survey of PBRs was conducted in proximity to the Elsinore fault east of San Diego, CA. Each identified PBR is modeled using point clouds derived from ground-based laser scanning and images from an unmanned aerial vehicle. The resultant geometric reconstructions are then used in a probabilistic overturning analysis and compared to the anticipated seismic hazard at the site. Accounting for an estimated age range and 50% probability of overturning for the PBRs, approximately half of the surveyed PBRs indicate a potential overestimation of seismic hazard at the site

Seismic Analysis of the 10-Story CFS-NHERI Building

A 10-story full-scale cold-formed steel building is scheduled to be tested on the newly upgraded 6-DOF Large High- Performance Outdoor Shake Table (LHPOST6) at the University of California San Diego serving as the capstone effort to the NSF-funded Collaborative Research: Seismic Resiliency of Repetitively Framed Mid-Rise Cold-Formed Steel Build- ings (CFS-NHERI) project. In preparation for this test program, a simplified pancake model is developed in OpenSees to predict the dynamic characteristics and to simulate the behavior of this 10-story test building under nonlinear dynamic re- sponse history analysis. The pancake model is composed of rigid diaphragms and nonlinear shear springs representing the hysteretic behavior of the lateral load resisting shear walls. Pinching4 material properties calibrated using past experiments defined the properties of shear springs with scaling based on geometric properties. To evaluate the robustness of the ap- proach, a similar model of a 6-story CFS building, tested under uni-directional shaking was also developed. For the 6-story modeling effort, the dynamic characteristics and response under the same series of ground motions used in the shake table tests are compared with the test results and good agreement is observed. Thus, for the 10-story CFS-NHERI building (pre- test) analyses, a suite of 22 far-field ground motion pairs provided in FEMA P695 are chosen to perform nonlinear response history analysis. The responses under these scaled ground motions are compared to investigate the effect on the seismic response of the 10-story CFS-NHERI building. In future work, the responses of the pancake model will be compared with other numerical models being developed by fellow researchers within the CFS-NHERI team using more complex wall line representations for example. At present however, it is recognized that the simplified pancake model provides a fast compu- tational turnaround time, while effectively capturing the characteristics and providing reasonable estimates of the responses, which makes it useful for pre-test analyses to identify a candidate suite of ground motions to be used for the future shake table test program.The first author is funded through the Structural Engineering Distinguished Fellowship from the Department of Structural Engineering at the University of California San Diego. The research presented is also funded through the National Sci- ence Foundation (NSF) grants CMMI 1663569 and CMMI 1663348, project entitled: Collaborative Research: Seis- mic 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 Mas- sachusetts Amherst. The authors appreciate the continued idea exchange and collaboration of all students and PIs in the CFS-NHERI project. In addition, the authors also thank the granting agencies and industry sponsors of the CFS-HUD project. Findings, opinions, and conclusions are those of the authors and do not necessarily reflect those of the sponsor- ing organizations

Optimal Hardware and Software Design of an Image-Based System for Capturing Dynamic Movements

In contrast to conventional image-capture systems, which attempt to minimize the amount of data collected during capture, typically by using hardware filters, the more general condition of using all information captured on a camera sensor is much more challenging and requires rigorous consideration of the hardware and software pipelines to obtain accurate tracking results. In this paper, this issue is specifically addressed by describing a unique hardware and software design implemented for use as a fully image-based capture system. An attempt is made to minimize the cost of this system by maximizing hardware control through software implementation. The hardware and software requirements are described in the context of the desired highspeed capture suitable for earthquake motions or other dynamic movements in a scene. Experiments are conducted and presented illustrating the good performance and stability of the system. This system is deemed suitable for the general condition of a building interior

PEER Testbed Study on a Laboratory Building: Exercising Seismic Performance Assessment

From 2002 to 2004 (years five and six of a ten-year funding cycle), the PEER Center organized the majority of its research around six testbeds. Two buildings and two bridges, a campus, and a transportation network were selected as case studies to “exercise” the PEER performance-based earthquake engineering methodology. All projects involved interdisciplinary teams of researchers, each producing data to be used by other colleagues in their research. The testbeds demonstrated that it is possible to create the data necessary to populate the PEER performancebased framing equation, linking the hazard analysis, the structural analysis, the development of damage measures, loss analysis, and decision variables. This report describes one of the building testbeds—the UC Science Building. The project was chosen to focus attention on the consequences of losses of laboratory contents, particularly downtime. The UC Science testbed evaluated the earthquake hazard and the structural performance of a well-designed recently built reinforced concrete laboratory building using the OpenSees platform. Researchers conducted shake table tests on samples of critical laboratory contents in order to develop fragility curves used to analyze the probability of losses based on equipment failure. The UC Science testbed undertook an extreme case in performance assessment—linking performance of contents to operational failure. The research shows the interdependence of building structure, systems, and contents in performance assessment, and highlights where further research is needed. The Executive Summary provides a short description of the overall testbed research program, while the main body of the report includes summary chapters from individual researchers. More extensive research reports are cited in the reference section of each chapter

Earthquake Input Motions and Seismic Site Response in a Centrifuge Test Examining SFSI Effects

This paper describes the ground motion selection process and reports observed seismic site response and SFSI effects during a dynamic centrifuge test (Test-1). The centrifuge test is the first in a series of tests examining the effects of SFSI in dense urban environments. The objective of Test-1 is to examine SFSI effects for two structures that are located a significant distance apart and essentially isolated. The model structures represent a three-story building founded on spread footings and a nine-story structure founded on a threestory basement. The structures are sited on a dry, dense bed of Nevada Sand. The centrifuge model is subjected to a series of shaking events that represent near-fault and “ordinary” ground motions at a site in Los Angeles. Results show that site periods degrade as ground motion intensity increases with more pronounced degradation observed for near-fault ground motions as compared with ordinary ground motions. Additionally, the results indicate the importance of kinematic effects of embedded structures when considering SFSI effects

Seismic Performance Assessment in Dense Urban Environments: Evaluation of Nonlinear Building-Foundation Systems Using Centrifuge Tests

In dense urban areas, buildings are generally constructed in clusters, forming city blocks. New buildings are designed assuming their response is independent of adjacent buildings, which ignores potentially important structure-soil-structure-interaction (SSSI) effects. Although a few studies have revealed the significance of SSSI effects, validated simulation and design tools do not exist. In this paper, we present the results from the first in a series of centrifuge tests intended to investigate SSSI effects. Results herein are focused on the design and measured response of two model building-foundation systems placed on dense dry Nevada sand and tested at 55-g. The two models represent prototypical nine-story and three-story special moment resisting frame buildings, with the former structure supported by a three-level basement-mat and the later on isolated spread footings. Nonlinear response-history simulations are performed to aid in the design of the models, with particular attention to reproducing prototype building periods and nonlinear characteristics. Yielding of the model buildings is achieved using custom-designed fuses placed strategically throughout the superstructures. At present, the two models are placed as far apart as possible to characterize soil-structure interaction on individual buildings; subsequent experiments will move the structures in near proximity, allowing direct experimental assessment of structuresoil- structure-interaction

Mortality and pulmonary complications in patients undergoing surgery with perioperative SARS-CoV-2 infection: an international cohort study

Background: The impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) on postoperative recovery needs to be understood to inform clinical decision making during and after the COVID-19 pandemic. This study reports 30-day mortality and pulmonary complication rates in patients with perioperative SARS-CoV-2 infection. Methods: This international, multicentre, cohort study at 235 hospitals in 24 countries included all patients undergoing surgery who had SARS-CoV-2 infection confirmed within 7 days before or 30 days after surgery. The primary outcome measure was 30-day postoperative mortality and was assessed in all enrolled patients. The main secondary outcome measure was pulmonary complications, defined as pneumonia, acute respiratory distress syndrome, or unexpected postoperative ventilation. Findings: This analysis includes 1128 patients who had surgery between Jan 1 and March 31, 2020, of whom 835 (74·0%) had emergency surgery and 280 (24·8%) had elective surgery. SARS-CoV-2 infection was confirmed preoperatively in 294 (26·1%) patients. 30-day mortality was 23·8% (268 of 1128). Pulmonary complications occurred in 577 (51·2%) of 1128 patients; 30-day mortality in these patients was 38·0% (219 of 577), accounting for 81·7% (219 of 268) of all deaths. In adjusted analyses, 30-day mortality was associated with male sex (odds ratio 1·75 [95% CI 1·28–2·40], p\textless0·0001), age 70 years or older versus younger than 70 years (2·30 [1·65–3·22], p\textless0·0001), American Society of Anesthesiologists grades 3–5 versus grades 1–2 (2·35 [1·57–3·53], p\textless0·0001), malignant versus benign or obstetric diagnosis (1·55 [1·01–2·39], p=0·046), emergency versus elective surgery (1·67 [1·06–2·63], p=0·026), and major versus minor surgery (1·52 [1·01–2·31], p=0·047). Interpretation: Postoperative pulmonary complications occur in half of patients with perioperative SARS-CoV-2 infection and are associated with high mortality. Thresholds for surgery during the COVID-19 pandemic should be higher than during normal practice, particularly in men aged 70 years and older. Consideration should be given for postponing non-urgent procedures and promoting non-operative treatment to delay or avoid the need for surgery. Funding: National Institute for Health Research (NIHR), Association of Coloproctology of Great Britain and Ireland, Bowel and Cancer Research, Bowel Disease Research Foundation, Association of Upper Gastrointestinal Surgeons, British Association of Surgical Oncology, British Gynaecological Cancer Society, European Society of Coloproctology, NIHR Academy, Sarcoma UK, Vascular Society for Great Britain and Ireland, and Yorkshire Cancer Research