Ahmad Itani

Rebar cages form the skeletal framework of reinforced concrete structural members. They comprise longitudinal and transverse reinforcing bars, usually connected by tie wires. Past studies have identified tie-wire connections as the "weak links" in large, prefabricated rebar cages, leading to their failure during site handling and construction stages. Recent research has explored the use of mechanical U-bolt connectors to bolster stability and safety of rebar cages while reducing their vulnerability and risk of failure. This paper presents a comprehensive experimental and numerical investigation of a new type of mechanical connector, referred to as "Cage Clamp", to enhance rebar cage stability and safety. Component-level experimental tests are conducted to determine the force-displacement response of Cage Clamp connectors for crossbar connections in different degrees of freedom. The results highlight the remarkable strength and stiffness of Cage Clamp connectors, significantly outperforming traditional tie-wire connections. Furthermore, full-scale experimental tests are performed on a circular underground pile-shaft rebar cage with Cage Clamp connectors to assess its behavior under various site handling conditions. The data obtained from these experiments are used to construct and refine detailed 3D finite element models of the rebar cages, capable of capturing the complex behavior of rebar cages with Cage Clamp connectors. Using the numerical model, a sensitivity analysis is performed to assess the effect of the number of Cage Clamps on the deflection and stability of the rebar cage. The findings show that using cage clamps to connect pick-up rebar with lateral reinforcement at every 8 to 10 feet is sufficient to ensure the stability of the cage during typical site handling conditions. The results of this study serve as a basis for establishing analysis, design, fabrication, and handling guidelines for rebar cages, contributing to safe and efficient construction practices.

Rebar cages are the skeletons of reinforced concrete structures. These temporary structures consist of longitudinal and transverse reinforcing bars connected by tie-wires. Given the relatively low strength of tie-wire connections, replacing tie-wires with mechanical connectors such as U-bolts can improve the stability and strength of rebar cages. This paper aims to understand the behavior of large prefabricated rebar cages reinforced with mechanical U-bolt connectors through experimental and analytical investigations. Twenty-six full-scale experimental tests are performed on five different underground pile-shaft rebar cages with tie-wire and U-bolt connectors to determine their behavior during different site handling conditions. The data obtained from the experiments are used to develop and calibrate detailed finite element models that can predict the complex response behavior of rebar cages reinforced with U-bolt connectors. The results show that U-bolt connectors can effectively ensure rebar cage integrity even under extreme loading conditions. Additionally, it is concluded that the presence of U-bolt connectors allows for the elimination of internal stiffening elements, which are common for large rebar cages, adding to the simplicity and efficiency of the construction process. The results of this study can be used as a basis for establishing analysis, design, fabrication, and handling guidelines for rebar cages.

Rebar cages are commonly used in reinforced concrete constructions. These cages consist of longitudinal and transverse reinforcing bars usually connected by tie wires. Numerous incidents of rebar cage failure and collapse have been reported at construction sites, often leading to injuries, fatalities, construction schedule delays, and added costs. Using mechanical connectors such as U-bolts instead of tie wires can improve stability and strength of rebar cages. This paper aims to investigate the mechanical behavior of U-bolt connections through experimental tests and to explore the potential application to rebar cages through analytical models. Experiments were conducted on U-bolt connectors to determine the force-deformation response behavior in different degrees of freedom and for different rebar conditions. Then, the data obtained from a previously completed experimental study on a full-scale tie-wired rebar cage were used to develop and calibrate a nonlinear finite-element model of the test specimen. The force-deformation response of U-bolt connections was then included in the model, replacing the tie wires, to investigate the effect of mechanical connectors on the lateral stiffness and strength of the rebar cage. The results showed that application of mechanical connectors for cross-bar connections in the rebar cages can increase the lateral strength of rebar cages, rendering U-bolt connectors as a potential solution to improve stability and safety of rebar cages.

News from an old acquaintance: The streptavidin (STV)‐biotin binding system is frequently used for the decoration of DNA origami nanostructures (DON) to study biological systems. Here, a surprisingly high dynamic of the STV/DON interaction is reported, which is affected by the structure of the DNA linker system. Analysis of different mono‐ or bi‐dentate linker architectures on DON with a novel high‐speed atomic force microscope (HS‐AFM) enabling acquisition times as short as 50 ms per frame gave detailed insights into the dynamics of the DON/STV interaction, revealing dwell times in the sub‐100 millisecond range. The linker systems are also used to present biotinylated epidermal growth factor on DON to study the activation of the epidermal growth factor receptor signaling cascade in HeLa cells. The studies confirm that cellular activation correlated with the binding properties of linker‐specific STV/DON interactions observed by HS‐AFM. This work sheds more light on the commonly used STV/DON system and will help to further standardize the use of DNA nanostructures for the study of biological processes.

A prerequisite to the implementation of accelerated bridge construction (ABC) in moderate and high seismic regions is reliable data proving that bridges constructed by assembling precast elements can emulate the seismic performance of cast-in-place bridges. Previous seismic studies have not provided sufficient information about the interaction of conventionally reinforced precast concrete elements and connections when they are integrated within a bridge system. This paper addresses this knowledge gap by conducting biaxial shake table tests on a 0.35-scale, two-span bridge model that incorporated 38 precast reinforced and prestressed concrete elements. The elements were joined by using six connection types joining column to footing, column to cap beam, girder to cap beam, deck panels (two types), and deck to girder. The bridge and the connections performed well even under earthquake motions beyond the design-level earthquake and combined large drift ratio demands and substantial in-plane rotation. Although the load path was affected by the interaction among different components, no adverse effect was observed.

Shake-table studies were conducted on a large-scale, two-span accelerated bridge construction (ABC) bridge model that incorporated 38 precast concrete elements and six emulative ABC connection types. The studies were aimed to assess the seismic performance of the bridge model and the six ABC connections under biaxial horizontal ground motions simulated at the Earthquake Engineering Laboratory at the University of Nevada, Reno. The bridge model was subjected to successive earthquake motions ranging from 20% to 200% of the design earthquake motion. Test results showed that the ABC bridge model matched the target performance of cast-in-place (CIP) bridges by limiting plastic hinging to columns and maintaining other components as damage-free. The ABC connections maintained the structural integrity of the system even under drift ratio demands on the columns higher than 7.5% combined with substantial in-plane rotation (e.g., larger than 0.008 rad) of the superstructure.

2004-3130 Nevada Teachers Integrating Engineering into Science Pamela Cantrell, Norma Velasquez-Bryant, Gokhan Pekcan, Ahmad Itani University of Nevada, Reno Introduction The Teachers Integrating Engineering into Science (TIES) Program is a collaborative project among faculty from the College of Education and the College of Engineering at the University of Nevada, Reno and teachers and administrators from four Nevada school districts. The TIES partnership presents opportunities for both university professors and middle school science teachers to work collaboratively for the development and implementation of best practices in science and mathematics education. This paper describes our project, which is currently in progress. The two-part focus of the project is to first, provide professional development for 7th- 8th grade science teachers to upgrade their content knowledge in engineering and learn integrated technology that supports effective science and mathematics instruction, and second, to facilitate the teachers in developing three engineering education modules for their classrooms. The modules include engineering design activities and are aligned with district and state standards for science and mathematics. Based on a review of current literature in engineering and science education, we developed a best practices model we call the Triangulated Learning Model (TLM) that was presented to the teachers as the delivery mode for the modules. The TLM employs three major elements designed to reinforce student learning: Simulation, Construction, and Connection. A variety of classroom and interactive Web-based learning activities are used throughout the TLM in order to reach a wide range of students. Theoretical Framework This project draws heavily upon the research in scientific inquiry, teacher efficacy, and engineering education. The engineering design modules developed by the teachers will provide a rich opportunity for their students to engage in scientific inquiry. The process of inquiry is critical to scientific literacy.1,2 Improving scientific literacy among teachers of science has become a national goal. The report to the nation by the National Commission on Mathematics and Science Teaching for the 21st Century3 identifies professional development as prerequisite for a well-qualified teaching force and encourages teachers to take responsibility for their own professionalism as they work to improve their skills. The Commission also stresses the need for professional development that provides opportunities for teachers to upgrade content knowledge and to learn how to integrate technology into the teaching of mathematics and science. Proceedings of the 2004 American Society for Engineering Education Annual Conference & Exposition Copyright ©2004, American Society for Engineering Education

A large-scale, two-span bridge model constructed by assembling precast elements was tested under a series of bi-axial ground motionssimulated on a shake table at the Earthquake Engineering Laboratory at the University of Nevada, Reno. The response of the bridge wasestimated before the tests using a three-dimensional computational model developed in OpenSees software. After the tests, key measuredseismic responses were compared to those predicted by the computational model to assess the modeling assumptions. Relatively largeerrors for the displacements, base shears, and hysteretic response of the bridge were observed. The influence of the earthquake loading,materials, connectivity of the precast elements, and boundary conditions in the computational model on the errors are discussed in thispaper. Future modeling directions are proposed to reduce these errors.