Design models for predicting shear resistance of studs in solid concrete slabs based on symbolic regression with genetic programming

Accurate design models for predicting the shear resistance of headed studs in solid concrete slabs are essential for obtaining economical and safe steel-concrete composite structures. In this study, symbolic regression with genetic programming (GPSR) was applied to experimental data to formulate new descriptive equations for predicting the shear resistance of studs in solid slabs using both normal and lightweight concrete. The obtained GPSR-based nominal resistance equations demonstrated good agreement with the test results. The equations indicate that the stud shear resistance is insensitive to the secant modulus of elasticity of concrete, which has been included in many international standards following the pioneering work of Ollgaard et al. In contrast, it increases when the stud height-to-diameter ratio increases, which is not reflected by the design models in the current international standards. The nominal resistance equations were subsequently refined for use in design from reliability analyses to ensure that the target reliability index required by the Eurocodes was achieved. Resistance factors for the developed equations were also determined following US design practice. The stud shear resistance predicted by the proposed models was compared with the predictions from 13 existing models. The accuracy of the developed models exceeds the accuracy of the existing equations. The proposed models produce predictions that can be used with confidence in design, while providing significantly higher stud resistances for certain combinations of variables than those computed with the existing equations given by many standards

Natural History of Patients with Ischemia and No Obstructive Coronary Artery Disease: The CIAO-ISCHEMIA Study

Background: Ischemia with no obstructive coronary artery disease (INOCA) is common and has an adverse prognosis. We set out to describe the natural history of symptoms and ischemia in INOCA. Methods: CIAO-ISCHEMIA (Changes in Ischemia and Angina over One year in ISCHEMIA trial screen failures with INOCA) was an international cohort study conducted from 2014-2019 involving angina assessments (Seattle Angina Questionnaire [SAQ]) and stress echocardiograms 1-year apart. This was an ancillary study that included patients with history of angina who were not randomized in the ISCHEMIA trial. Stress-induced wall motion abnormalities were determined by an echocardiographic core laboratory blinded to symptoms, coronary artery disease (CAD) status and test timing. Medical therapy was at the discretion of treating physicians. The primary outcome was the correlation between changes in SAQ Angina Frequency score and change in echocardiographic ischemia. We also analyzed predictors of 1-year changes in both angina and ischemia, and compared CIAO participants with ISCHEMIA participants with obstructive CAD who had stress echocardiography before enrollment, as CIAO participants did. Results: INOCA participants in CIAO were more often female (66% of 208 vs. 26% of 865 ISCHEMIA participants with obstructive CAD, p\u3c0.001), but the magnitude of ischemia was similar (median 4 ischemic segments [IQR 3-5] both groups). Ischemia and angina were not significantly correlated at enrollment in CIAO (p=0.46) or ISCHEMIA stress echocardiography participants (p=0.35). At 1 year, the stress echocardiogram was normal in half of CIAO participants and 23% had moderate or severe ischemia (≥3 ischemic segments). Angina improved in 43% and worsened in 14%. Change in ischemia over one year was not significantly correlated with change in angina (rho=0.029). Conclusions: Improvement in ischemia and improvement in angina were common in INOCA, but not correlated. Our INOCA cohort had a similar degree of inducible wall motion abnormalities to concurrently enrolled ISCHEMIA participants with obstructive CAD. Our results highlight the complex nature of INOCA pathophysiology and the multifactorial nature of angina

Headed Steel Stud Anchors in Composite Structures: Part II - Tension and Interaction

The current AISC Specification for Structural Steel Buildings (AISC, 2005a) is the lead specification for composite construction in the U.S. However, these provisions do not provide a recommendation for computing the strength of headed steel stud anchors (traditionally used as shear connectors) under tension or combined tension and shear. Headed stud anchors are subjected to these types of forces in composite structures such as infill walls, composite coupling beams, the connection region of composite columns, or composite column bases. While ACI 318-08 Appendix D (ACI, 2008) and PCI 6th Ed. (PCI, 2004) includes provisions for such conditions, those provisions are geared for more general anchorage conditions than are typically seen in composite construction. It would thus be beneficial to have design guidance specifically for the case of headed steel stud anchors subjected to tension or combined tension and shear in composite construction, evaluated within the context of the AISC Specification. In this work, different strength equations to compute the nominal tensile strength of a headed stud are reviewed and compared to experimental results. The resulting recommendations seek to ensure a ductile failure in the steel shank instead of a brittle failure within the concrete. Several criteria are proposed to ensure that a ductile failure controls in composite construction, and, different headed stud configurations and detailing reinforcement recommendations are proposed to improve the ductile behavior of headed stud anchors subjected to tension and combined tension and shear.published or submitted for publicatio

Capstone Scenario Applications of Consequence-Based Risk Management for the Memphis Testbed

A capstone goal of the Memphis Testbed (MTB), and the MAE Center research program in consequence-based risk management, is to complete a detailed study of seismic event effects on the city of Memphis, Tennessee. The completion of this study relies heavily on the aggregated research results from the ten-year period of MAE Center research, culminating in implementation within MAEViz, the consequence-based risk management (CRM) software system developed by the MAE Center (Elnashai and Hajjar, 2006; Hajjar and Elnashai, 2006; Myers and Spencer, 2005; Spencer et al., 2005; MAEviz, 2008).National Science Foundation EEC-9701785unpublishe

Headed Steel Stud Anchors in Composite Structures: Part I - Shear

The formula in the 2005 American Institute of Steel Construction Specification to compute the strength of headed steel stud anchors (shear connectors) in composite steel/concrete structures has been used in the United States since 1993 after being proposed based primarily on the results of push-out tests. In the past several decades, the range of members used in composite structures has increased significantly, as has the number of tests in the literature on the monotonic and cyclic behavior of headed studs in composite construction. This work reviews 391 monotonic and cyclic tests from the literature on experiments of headed stud anchors and proposes formulas for the limit states of steel failure and concrete failure of headed stud anchors subjected to shear force without the use of metal deck. Detailing provisions to prevent premature pryout failure are also discussed. This work also reviews proposals from several authors and provides recommended shear strength values for seismic behavior of headed studs. The limit state formulas are proposed within the context of the 2005 AISC Specification, and comparisons are made to the provisions in the ACI 318-08 Building Code and the PCI Handbook, 6th Edition. The scope of this research includes composite beam-columns [typically concrete-encased steel shapes (SRC) or concrete-filled steel tubes (CFT)], concrete-encased and concrete-filled beams, boundary elements of composite wall systems, composite connections, composite column base conditions, and related forms of composite construction.published or submitted for publicatio

Systemic Validation of Consequence-Based Risk Management for Seismic Regional Losses

The Mid-America Earthquake (MAE) Center has performed much research since its inception relating to all facets of seismic loss assessment and risk management, from hazard definition through social and economic loss modeling. The culmination of this work is the integration of the research results into a comprehensive system for loss assessment, decision support, and consequence-based risk management (CRM). One vehicle through which the integration process takes form is MAEViz, a software program developed in a joint effort by the MAE Center and the National Center for Supercomputing Applications (NCSA). The purpose of this document is to present findings for systemic validation of the integration of research data threads within MAEViz. The validation effort is presented as part of the Memphis Testbed Project within the MAE Center, a comprehensive testbed in which much of the MAE Center research is being implemented. The general approach of the validation plan is to seek reports of risk assessments published in the literature that are sufficiently well documented that MAEViz can be used to perform a similar study. As part of the validation exercise, it was found that even relatively well documented studies rarely supplied sufficient data such that the study could be replicated in detail. The most suitable study was determined to be a risk assessment developed for the state of South Carolina using HAZUS, the program developed by the Federal Emergency Management Agency to perform loss assessments for natural disasters on the regional scale. The data reported in the South Carolina study has been used to define necessary parameters and execute a risk assessment for the region in MAEViz. Results of MAEViz analyses have been evaluated relative to the published results in this document, and it is found that while MAEViz is a suitable engine for performing risk assessments, the results of any risk assessment are sensitive to the specific algorithmic formulation implemented for the study. In this validation study, it was determined that differences in results obtained from MAEViz and HAZUS originate primarily from differences in the damage prediction and loss estimation methodologies. The damage estimation algorithm in MAEViz, using vulnerability formulations based on time history analyses of nonlinear structural response, provides an alternative estimation of damage prediction as compared to the Capacity Spectrum Method, a nonlinear static analysis method implemented in HAZUS, when determining probabilities of damage states. With regard to loss estimation algorithms, the general frameworks employed in MAEViz and HAZUS are similar, however, damage factors correlating damage states to economic losses are framed within a probabilistic context for MAEViz, leading to higher predicted damage for very lightly damaged structures, and lower predicted damage for very heavily damaged structures.National Science Foundation EEC-9701785unpublishe

Nonlinear Seismic Analysis of Circular Concrete-Filled Steel Tube Members and Frames

Accurate nonlinear formulations are necessary for the assessment of structures under seismic and other extreme loading. In this work, a three-dimensional distributed plasticity beam element formulation for circular concrete-filled steel tubes has been developed for nonlinear static and dynamic analyses of composite seismic force resisting systems. A mixed basis for the formulation was chosen to allow for accurate modeling of both material and geometric nonlinearities. The formulation utilizes uniaxial cyclic constitutive models for the concrete core and steel tube that account for the salient features of each material, as well as the interaction between the two, including concrete confinement and local buckling of the steel tube. The accuracy of the formulation was verified against a wide variety of analytical and experimental results. The verification confirms the capability of the formulation to accurately produce realistic simulations of element and frame behavior.published or submitted for publicatio

Data Processing of Laser Scans Towards Applications in Structural Engineering

This research is investigating the use of high resolution 3D terrestrial laser scanners as tools to capture geometric data of complex scenes for structural engineering applications. Laser scan technology is continuously improving, with commonly available scanners now able to capture over 100,000 points per second with an accuracy of ~1 mm. This research focuses on determining the applicability of laser scanning to structural engineering applications, including structural health monitoring, collapse assessment, and post-hazard response assessment. One of the keys to this work is to establish a process for extracting important information from raw laser-scanned data sets. Once such a process is fully developed, laser scanning has the potential to play an important role in linking and sharing experimental and computational structural research. Previous work in this area has created a foundation of basic data processing steps. Additional steps and modifications to existing algorithms are presented to advance the performance of data processing on complete point clouds. The outcome of this research enables processing of lasers scans of complex structures to assist with advanced analysis, monitoring, and assessment.published or submitted for publicatio

Integrated Data Flow and Risk Aggregation for Consequence-Based Risk Management of Seismic Regional Loss

This report documents the integrated flow of data within the Consequence-based Risk Management (CRM) framework established within the Mid-America Earthquake (MAE) Center for seismic regional loss assessment. This data flow is being implemented in MAEviz, the risk management software of the MAE Center. The report also provides an efficient framework for incorporating the uncertainties systematically into each key contribution to the loss assessment process. Supplementary documents to this report provide detailed examples of the quantitative data flow and associated aggregation of uncertainty. This report first identifies the algorithmic methodologies and inputs/outputs (I/O) used in the MAE Center research efforts on seismic hazard, inventory, structural damage, and social and economic losses, from source to society. This helps identify possible incompatibilities between I/O???s and missing information, and enables gaps in the data threads to be identified. This report then provides recommendations for filling of several of these identified gaps in the CRM data threads. Based on these results and the CRM framework encompassed within the MAE Center, this report also suggests a method to systematically incorporate aleatory and epistemic uncertainties identified by MAE Center research efforts into MAEviz. In the sections that follow, the general flow of the document is intended to first outline suggested modifications to MAEViz, accompanied by examples, then proceed into a more detailed description of the information available for use in MAEViz. The examples focus on applications for the Memphis Testbed.National Science Foundation EEC-9701785unpublishe

Characterization of Behavior of Steel-Concrete Composite Members and Frames with Applications for Design

Steel-concrete composite frames are seeing increased use in practice. Their excellent structural characteristics, including high strength, stiffness, and ductility, make them an appealing option for many building configurations. However, there exist gaps in the knowledge of behavior and the design provisions for these structures. This work seeks to document composite member and frame behavior and address key design issues through targeted studies utilizing advanced computational formulations and detailed examination of experimental results. A three-dimensional distributed plasticity beam finite element formulation suitable for nonlinear static and dynamic analyses of steel-concrete composite frames has been developed. The formulation is suitable for both concrete-filled steel tubes (CFT) and steel reinforced concrete (SRC) members, as well as steel wide-flange and hollow structural steel sections that are part of composite frames. A mixed basis for the formulation was chosen to allow for accurate modeling of both material and geometric nonlinearities. The formulation utilizes uniaxial cyclic constitutive relations for the concrete and steel that account for the salient features of each material, as well as the interaction between the two, including concrete confinement and local buckling. The accuracy of the formulation was verified against a wide variety of monotonic and cyclic experimental results of composite members, demonstrating the capability of the formulation to accurately produce realistic simulations of element and frame behavior. Aspects of the behavior of composite columns were assessed through an examination of results from a series of experiments on full-scale slender CFT beam-columns conducted by project collaborators. Additionally, comparative computational analyses were performed using the mixed beam formulation and detailed data interpretation focusing on the beam-column interaction strength was conducted. Several aspects of the design of steel-concrete composite structures were examined. The natural bond behavior of CFT columns was investigated through an examination of prior experimental work and new provisions were developed for the assessment of natural bond strength of CFT connections. The in-plane stability behavior of steel-concrete composite members and frames was assessed through a parametric study on small non-redundant benchmark frames, leading to the development of new elastic flexural rigidities for elastic analysis of composite members; new effective flexural rigidities for calculating the axial compressive strength of SRC members; new Direct Analysis stiffness reductions for composite members; and new recommendations for the construction of the interaction diagram for composite members. The seismic behavior of composite moment and braced frames was assessed through static pushover and incremental dynamic analyses. The analyses were performed on a suite of 60 archetype frames that were designed according to current design provisions. Connections were assumed to be strong; however, panel zone behavior for the moment frames and bond-slip behavior for SRC columns were included in the model. Using the analysis results, system performance factors were developed for the composite frames based on the methodology described in FEMA P695.This material is based upon work supported by the National Science Foundation under Grant Nos. CMMI-0619047 and CMMI-0530756 as part of the George E. Brown, Jr. Network for Earthquake Engineering Simulation (NEES); the American Institute of Steel Construction; the Georgia Institute of Technology; and the University of Illinois at Urbana-Champaign. Computational analyses in this work were executed in part on the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant No. OCI-1053575. Any opinions, findings, and conclusions expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation or other sponsors.Ope