Summary of large-scale nonplanar reinforced concrete wall tests

Nonplanar wall configurations are prevalent in engineering practice, yet relatively little research has addressed nonplanar walls and the earthquake response of these components remains poorly understood. A recent experimental test program conducted by the authors investigated the earthquake response of modern, ACI Code compliant C‐shaped walls subjected to unidirectional and bidirectional lateral loading. To compare the results of this study with previous experimental investigations conducted by others, this document examines laboratory tests of slender nonplanar walls available in the literature. Response histories, damage patterns, drift capacity and failure mechanisms are used to characterize the behavior of each nonplanar wall test specimen. The impact on behavior of various design parameters as well as unidirectional versus bidirectional load history is investigated. Results are synthesized to provide improved understanding of behavior and guidance for design of nonplanar walls. Section 2 provides an overview of the nonplanar wall test found in the literature. Section 3 provides a more in‐depth overview of C‐ and U‐shaped walls, including the C‐shaped wall tests conducted as part of this study. Section 4 presents failure and response mechanism observed during nonplanar wall tests. Section 5 summarizes observations and presents conclusions about nonplanar wall behavior

Empirically derived effective stiffness expressions for concrete walls

In most cases, analysis to determine component demands for seismic design of concrete buildings employs linear elastic models in which reduced, effective component stiffnesses are used. This document i) reviews the recommendations for defining the effective flexural, shear and axial stiffness of concrete walls that are included in current design codes, standards and guidelines and ii) compares these recommendations with stiffness expressions derived directly from experimental data by the authors and others. Section 2 reviews existing empirically derived and code‐, standard‐, and guideline‐based expressions for the effective stiffness of concrete walls. Section 3 presents the process used by the authors to compute effective stiffness values from laboratory data. Sections 4 through 6 present effective stiffness values derived from laboratory test data for C‐shaped wall specimens tested as part of this study, for planar wall specimens tested by the authors as part of a previous study, and for non‐planar wall specimens tested by others. Section 7 presents the results of a study in which recommended effective stiffness values were used to compute the yield displacements of seven coupled‐wall specimens tested in the laboratory by the authors and others. Section 8 summarizes the results of this investigation

Summary of large-scale C-shaped reinforced concrete wall tests

Flexural concrete walls (i.e., walls the yield in flexural prior to failure) are used commonly as the lateral load resisting system for mid‐ and high‐rise buildings on the West Coast. They are relatively stiff under service‐level loading, can take on various configurations to accommodate architectural constraints, and are generally assumed to exhibit ductile response under severe earthquake loading. Despite heavy reliance on concrete walls, relatively little research has been done to investigate the earthquake performance of walls with modern design details. Few data exist characterizing the performance of modern walls under variable levels of earthquake loading or the impact of various design parameters on this performance. Few data exist to support evaluation and validation of numerical models for modern walls. In 2004 a research study funded by the National Science Foundation (NSF), through the Network for Earthquake Engineering Simulation Research (NEESR) program, was initiated to investigate the earthquake performance of slender modern walls. This study is being conducted primarily by faculty and graduate students at the Universities of Washington and Illinois, with experimental testing conducted using the NSF‐funded NEES laboratory at the University of Illinois, Urbana‐Champaign (UIUC). The objectives of this study are to generate experimental data characterizing the seismic response and performance of modern concrete walls, develop numerical models for simulating wall response to support design and research, and develop recommendations for performance‐based seismic design of these systems. The NSF‐funded study included experimental testing of planar rectangular walls, a planar coupled wall, and a C‐shaped wall, with experimental testing limited to unidirectional lateral loading and constant axial loading. In 2009 the Charles Pankow Foundation (CPF) provided supplemental funding to expand the scope of this study to include investigation of the impact of bidirectional loading on the earthquake performance of isolated C‐shaped walls and C‐shaped walls in coupled core‐wall systems. This document presents the results of the three C‐shaped wall tests conducted as part of the NSF and CPF funded study. All three specimens had nominally the same design. The specimens were designed to represent C‐shaped walls in a coupled core‐wall system in a modern mid‐rise building. Specifically, specimens represented the bottom three stories of a C‐shaped wall in a ten‐story core‐wall building; loads were applied to the top of the specimen to achieve a load pattern at the base of the specimen representative of that which would develop in the ten‐story building. All three specimens were subjected to quasi‐static cyclic lateral loading in combination with axial loading. The first specimen, identified as Wall 6 of the NSF‐CPF project, was subjected to unidirectional lateral loading in the direction of the web of the C‐shaped wall and a constant axial load. The second specimen, Wall 7, was subjected to a cruciform lateral load pattern (i.e. loading in the direction of the web of the wall followed by loading in the direction of the wall flanges) as well as bidirectional lateral loading and a constant axial load. The third specimen, Wall 8, was subjected to a cruciform lateral load pattern, bidirectional loading and varying axial load. For Wall 8, a constant axial load was applied when the wall was subject to lateral loading in the direction of the web of the wall; a varying axial load was applied when the wall was subjected to lateral loading in the direction of the wall flanges to simulate the variation in axial load resulting from coupling action in the core‐wall system. The response of test specimens was monitored using multiple instrumentation systems. Multiple fixed and roaming still cameras were used to document damage. A close range photogrammetric system and 2 a Nikon metrology / Krypton system were used to generate displacement field data. Displacement transducers were used to measure specimen deformation and specimen displacement. External concrete strain gages and embedded steel strain gages were used to monitor local strains. Load cells were used to monitor applied loads. This report employs data from load cells and displacement transducers as well as still camera images to characterize wall behavior and provide a preliminary assessment of performance. In the future, data from other instrumentation systems will be employed to refine the preliminary characterization and performance assessment. All data will be archived and made available to the public via NEEShub (http://www.neeshub.org). The presentation of the C‐shaped wall tests is organized as follows. Section 2 presents the specimen design and construction. Section 3 presents material data for the concrete and steel used in specimen construction. Section 4 presents the test setup and the loading protocol used for the tests. Section 5 presents the instrumentation systems and data collection protocol. Section 6, 7, and 8 presents results for the individual wall tests. Section 9 compares the observed behavior of the three specimens. Section 10 presents preliminary conclusions of the experimental investigation

Experimental and numerical investigation of flexural concrete wall design details

Reinforced concrete structural walls are common in mid- to high-rise structures in high seismic regions, and are expected to have good strength and ductility characteristics if designed in accordance with ACI 318-14. However, experimental and analytical investigations of reinforced concrete structural walls and isolated boundary element prisms indicate that the existing design provisions may be insufficient to provide ductile, flexure-dominated response under cyclic loading. Walls designed with an ACI compliant boundary element length are susceptible to shear-compression failures below the maximum ACI allowable shear stress of 10Acv√fc’. Also of concern is the frequent use of thinner walls in modern design; as the wall’s cross-sectional aspect ratio increases, such brittle shear-compression failures occur at even smaller shear stress values. In regards to detailing, special boundary elements with intermediate cross-ties exhibit a minimal improvement in confinement compared to ordinary boundary elements. This response can be linked to inadequacies in multiple code design parameters, including: vertical spacing and area of confinement steel, horizontal spacing and type of restraint to longitudinal bars, and development length provided for transverse reinforcement. Recent in-field wall failures have prompted concerns related to the minimum code required vertical and horizontal web shear reinforcement, as well as the relative amount of vertical-to-horizontal web steel. This paper examines ACI 318-14 special boundary element and web reinforcement provisions and provides design recommendations intended to improve wall performance as compared with current ACI requirements

Impact of Bi-directional Loading on the Seismic Performance of C-shaped Piers of Core Walls

Reinforced concrete structural walls are commonly used as the primary lateral load resisting system in modern buildings constructed in high seismic regions. Most walls in high-rise buildings are C-shaped to accommodate elevators or other architectural features. C-shaped walls have complex loading and response including: (1) symmetric response in the direction of the web, (2) asymmetric response in the direction of the flange and (3) high compression and shear demands when used as a pier in a coupled-wall configuration. A research study was conducted on C-shaped walls tested under (1) uni-directional and (2) bi-directional loading of an isolated walls and (3) bi-directional loading of a c-shaped pier in a coupled wall system. Each of the walls failed in flexure with strength loss resulting from low-cycle fatigue of the boundary element longitudinal reinforcement with buckling followed by fracture. The damage progression was as follows: (1) cracking at the wall-foundation interface, (2) concrete spalling in the web, (3) buckling and fracture of web reinforcement, (4) spalling in the flanges, (5) buckling and fracture of the bars in the boundary elements. Concrete spalling and steel bar damage occurred at lower strong-axis drift levels for the bi-directionally loaded, resulting in lower drift capacities for these loading protocols. However, for the strong-axis direction, bi-directional loading does not reduce flexural or shear effective stiffness values suggesting that current values are appropriate for design and evaluation of buildings with c-shaped walls

Increase in West Nile Neuroinvasive Disease after Hurricane Katrina

After Hurricane Katrina, the number of reported cases of West Nile neuroinvasive disease (WNND) sharply increased in the hurricane-affected regions of Louisiana and Mississippi. In 2006, a >2-fold increase in WNND incidence was observed in the hurricane-affected areas than in previous years

The experiences of Chinese general practitioners in communicating with people with type 2 diabetes - a focus group study

BACKGROUND: China has more ascertained cases of diabetes than any other country. Much of the care of people with type 2 diabetes (T2DM) in China is managed by GPs and this will increase with the implementation of health care reforms aimed at strengthening China’s primary health care system. Diabetes care requires effective communication between physicians and patients, yet little is known about this area in China. We aimed to explore the experiences of Chinese GPs in communicating with diabetes patients and how this may relate to communication skills training. METHODS: Focus groups with Chinese GPs were undertaken. Purposive sampling was used to recruit 15 GPs from Guangzhou city in China. All data were audio-recorded and transcribed. A thematic analysis using the Framework Method was applied to code the data and identify themes. RESULTS: Seven males and 8 females from 12 general practices attended 4 focus groups with a mean age of 37.6 years and 7.5 years’ work experience. Four major themes were identified: diversity in diabetic patients, communication with patients, patient-doctor relationship, and communication skills training. GPs reported facing a wide variety of diabetes patients in their daily practice. They believed insufficient knowledge and misunderstanding of diabetes was common among patients. They highlighted several challenges in communicating with diabetes patients, such as insufficient consultation time, poor communication regarding blood glucose monitoring and misunderstanding the risk of complications. They used terms such as “blind spot” or “not on the same channel” to describe gaps in their patients’ understanding of diabetes and its management, and cited this as a cause of ineffective patient-doctor communication. Mutual understanding of diabetes was perceived to be an important factor towards building positive patient-doctor relationships. Although GPs believed communication skills training was necessary, they reported rarely received this. CONCLUSIONS: Chinese GPs reported facing challenges in communicating with diabetes patients. Some of these were perceived as being due to the patients themselves, others were attributed to system constraints, and some were seen as related to a lack of clinician training. The study identified key issues for the development of primary care-based management of diabetes in China, and for developing appropriate communication skills training programs for the primary care workforce. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12875-021-01506-9

Analytical Evaluation of Reinforced Concrete Pier and Cast-in-Steel-Shell Pile Connection Behavior considering Steel-Concrete Interface

The seismic design of bridges may require a large-diameter deep pile foundation such as a cast-in-steel-shell (CISS) pile where a reinforced concrete (RC) member is cast in a steel casing. In practice, the steel casing is not considered in the structural design and the pile is assumed to be an RC member. It is partially attributed to the difficulties in evaluation of composite action of a CISS pile. However, by considering benefits provided by composite action of the infilled concrete and the steel casing, both the cost and size of CISS pile can be reduced. In this study, the structural behavior of the RC pier and the CISS pile connection is simulated by using an advanced 3D finite element (FE) method, where the interface between the steel and concrete is also modeled. Firstly, the FE model is verified. Then, the parametric study is conducted. The analysis results suggest that the embedment length and the friction coefficient between the steel casing and the infilled concrete affect the structural behavior of the RC pier. Finally, the minimum embedment length with reference to the AASHTO design guideline is suggested considering the composite action of the CISS pile

ATC-114 Next-Generation Hysteretic Relationships for Performance-based Modeling and Analysis

Nonlinear analysis has become an increasingly useful and important tool for evaluation, upgrade and design of structures for seismic resistance. However, despite steady improvements in analysis capability, most practice remains anchored to guidelines developed more than 20 years ago. Under its ATC- 114 project, the Applied Technology Council is developing updated hysteretic envelope models for use in seismic analysis of new and existing buildings. The intent of this project is to support the development of updated building code criteria contained in such standards as ASCE 7 and ASCE 41. Project support is provided by the National Institute of Standards and Technology