Inquiry-based learning to explore the design of the built environment

Typically in introductory structural engineering courses with a lab component, the instructional approach is to present the underlying theory via pre-lab lecture/reading and subsequently have students conduct guided experiments that affirm that theory. The new Fall 2015 course offering described in this paper takes the reverse approach where students’ hands-on exploration of a concept occurs prior to formal instruction. As such, the course is based upon Da Vinci’s perspective that: “[i]n the examination of physical problems I begin by making a few experiments,…we must commence with experience, and strive by means of it to discover truth.” In the course, student exploration of fundamental structural engineering concepts was facilitated through the following activities: • Full-class physical demonstrations led by the instructor during lecture • Small-group experimentation in a laboratory setting • Case studies highlighting both failures and exemplary natural/engineered structures presented via instructor lectures and supplementary multi-media materials The paper describes the open-ended course framework where instructors posed targeted questions for students/teams to investigate based on the demonstrations, experiments and case studies. The students explored these questions in the manner they (individually or in teams) deem appropriate, while documenting relevant quantitative and qualitative observations in their lab notebooks. Reflecting on their gathered information, students developed evidence-based responses to the questions. These learning exercises were followed by instructor-facilitated discussion where students/teams share their observations and collaboratively draw conclusions that point towards related engineering theory. Finally, the instructor formally defined the associated theory. The objective of this paper is demonstrate how the “exploration before theory” approach can be implemented and what is required to accomplish the hands-on, inquiry, discussion, and formal teaching aspects that comprise this teaching style. Associated with this objective, the authors also share student feedback on the course that will be collected through mid- and end-of-semester surveys for about twenty undergraduate students. These surveys solicited student input on the inquiry-based learning atmosphere as well as individual course activities. The authors believe that a classroom environment that emphasizes discovery – where students act as researchers and play an active role in building their own knowledge – is a format that can be readily adapted to other engineering disciplines; furthermore, it can inspire higher-level thinking and lead to a more engaging learning experience

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

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

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

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

A Novel Metagenomic Short-Chain Dehydrogenase/Reductase Attenuates Pseudomonas aeruginosa Biofilm Formation and Virulence on Caenorhabditis elegans

In Pseudomonas aeruginosa, the expression of a number of virulence factors, as well as biofilm formation, are controlled by quorum sensing (QS). N-Acylhomoserine lactones (AHLs) are an important class of signaling molecules involved in bacterial QS and in many pathogenic bacteria infection and host colonization are AHL-dependent. The AHL signaling molecules are subject to inactivation mainly by hydrolases (Enzyme Commission class number EC 3) (i.e. N-acyl-homoserine lactonases and N-acyl-homoserine-lactone acylases). Only little is known on quorum quenching mechanisms of oxidoreductases (EC 1). Here we report on the identification and structural characterization of the first NADP-dependent short-chain dehydrogenase/reductase (SDR) involved in inactivation of N-(3-oxo-dodecanoyl)-L-homoserine lactone (3-oxo-C12-HSL) and derived from a metagenome library. The corresponding gene was isolated from a soil metagenome and designated bpiB09. Heterologous expression and crystallographic studies established BpiB09 as an NADP-dependent reductase. Although AHLs are probably not the native substrate of this metagenome-derived enzyme, its expression in P. aeruginosa PAO1 resulted in significantly reduced pyocyanin production, decreased motility, poor biofilm formation and absent paralysis of Caenorhabditis elegans. Furthermore, a genome-wide transcriptome study suggested that the level of lasI and rhlI transcription together with 36 well known QS regulated genes was significantly (≥10-fold) affected in P. aeruginosa strains expressing the bpiB09 gene in pBBR1MCS-5. Thus AHL oxidoreductases could be considered as potent tools for the development of quorum quenching strategies

Nontraditional Limitations on the Shear Capacity of Prestressed Concrete Girders

Code based shear design provisions principally use a sectional force design procedure in which it is assumed that plane sections remain plane. However, the shear capacity of a member may be limited by other shear related phenomena that are not captured in codes of practice. These nontraditional limitations on the shear capacity of a member can result from incorrectly evaluating the shear stress that needs to be transmitted across a crack, shearcompression failure along a web-flange interface, or insufficient capacity of longitudinal tension reinforcement at the support. A series of 20 shear tests were completed on ten 52-foot long and 63-inch deep prestressed bulb-tee bridge girders cast with high-strength concrete. An extensive amount of experimental data was gathered and advanced data analysis tools were utilized to evaluate these nontraditional limitations on shear capacity. It was determined that interface shear transfer resistance in high-strength concrete is predicted well by relationships developed from tests on normal-strength concrete specimens. It was further observed that the angle of web-shear cracking was generally steeper than the angle of principal compressive stress as given by the AASHTO LRFD Bridge Design Specifications. This difference in angles creates a significant shear demand on a crack that is not accounted for in the LRFD Specifications. A method is presented for determining if a shear-compression failure along a webflange interface is a potential mode of failure for a prestressed bridge girder. This approach provides a means of calculating the shear stress that must be transmitted across the interface as a function of the geometry and loading on the member as well as a means of calculating the shear resistance along the web-flange interface. This method can be used to guard against a shear-compression failure by placing a limitation on the maximum shear capacity a member. It was also determined that the requirement for longitudinal tension reinforcement near the support included in the 4th edition of the AASHTO LRFD Bridge Design Specifications may underestimate the demand on longitudinal tension reinforcement. Alternatively an equilibrium based approach is presented for determining demand on longitudinal tension reinforcement near the support.published or submitted for publicatio

Seismic Fragility Assessment for Reinforced Concrete High-Rise Buildings

In contrast to the worldwide rapid growth of high-rise buildings, no probabilistic assessment procedures have been proposed or developed for seismic risk evaluation of this special building group. The new purpose of this report is to provide the earthquake engineering community with an integrated probabilistic seismic fragility assessment framework and a reference application for this special building population.National Science Foundation EEC-9701785published or submitted for publicatio

Shear Behavior and Capacity of Large-Scale Prestressed High-Strength Concrete Bulb-Tee Girders

The current shear design provisions of the AASHTO LRFD Bridge Design Specifications limit the concrete compressive strength to 10 ksi due to a lack of experimental evidence for their extension to high strength concrete. To overcome this limitation, the National Academy of Sciences funded National Cooperative Highway Research Program (NCHRP) Project 12-56 “Application of the LRFD Bridge Design Specifications to High-Strength Structural Concrete: Shear Provisions”. This report presents an analysis of project 12-56 experimental test data from which an in-depth understanding of the shear response of prestressed girder was obtained and new models were developed. The experimental work comprised a total of 20 tests on ten 52-foot long and 6-foot deep bulb-tee girders. All girders were designed to satisfy the requirements of the LRFD Bridge Design Specifications and then subjected to a uniformly distributed load until failure occurred in shear. The primary test variables were concrete compressive strength (ranging from 10 to 18 ksi), the maximum shear design stress (0.7 to 2.5 ksi), strand anchorage details (straight, unbonded, and draped), and end reinforcement detailing (bar size, spacing, and level of confinement). A large number of both traditional and advanced instrumentation systems were used to measure response. A new data visualization tool was developed to provide a detailed analysis of the dense experimental test data. It was concluded that the AASHTO LRFD Sectional Design Method, as well as the AASHTO Standard Specifications and the Canadian Standard Association A23.3-04 Design Method, could be extended to up to 18 ksi concrete. It is also recommended that the maximum shear design stress be reduced from 0.25 fc’ to 0.18fc’. Both the angle and the strength of diagonal cracking could be accurately predicted using Mohr’s circle of stress. The web shear behavior could be characterized as a tri-linear relationship separated by web cracking, stirrup yielding, and failure and the inelastic tangent stiffness before stirrup yielding could be modeled as a polynomial function of shear reinforcement ratio. Based on the development of 350 crackbased free-body diagrams, the components of the concrete contribution to resistance (two flanges and web) over the loading history was characterized as a function of the geometric and material properties of the girders. A general expression, which adopted the calculated crack angle for the computation of shear reinforcement contribution and provided clear physical explanation for every part of concrete contribution, was suggested for the future shear design practice. From the measured test results, an analytical model, Crack Displacement Field Theory (CDFT), was developed for predicting the shear response of prestressed/reinforced concrete members. Compared to other existing models, it could capture the discrete displacement due to crack opening and crack slip along crack surface and can take account the variation of stresses in reinforcement due to bond. Based on this model, expressions were derived for shear stiffness and shear resistance at stirrup yielding, and the derived equations produced good agreement with test results.published or submitted for publicatio