Lehigh University

About: Lehigh University is a education organization based out in Bethlehem, Pennsylvania, United States. It is known for research contribution in the topics: Catalysis & Fracture mechanics. The organization has 12684 authors who have published 26550 publications receiving 770061 citations.

Experimental studies of full-scale posttensioned steel connections

Abstract: Six full-scale interior connection subassemblies of posttensioned wide flange beam-to-column moment connections were subjected to inelastic cyclic loading up to 4% story drift to simulate earthquake loading effects. Bolted top and seat angles are used in the connection, along with posttensioned high strength strands that run parallel to the beam. These strands compress the beam flanges against the column flange to develop the resisting moment to service loading and to provide a restoring force that returns the structure to its initial position following an earthquake. The parameters studied in these experiments were the initial posttensioning force, the number of posttensioning strands, and the length of the reinforcing plates. The experimental results demonstrate that the posttensioned connection possesses good energy dissipation and ductility. Under drift levels of 4%, the beams and columns remain elastic, while only the top and seat angles are damaged and dissipate energy. The lack of damage to the beams, columns, and the posttensioning enable the system to return to its plumb position (i.e., it self-centers). Closed-form expressions are presented to predict the connection response and the results from these expressions compare well with the experimental results.

Flow structure from an oscillating cylinder. part 2: mode competition in the near wake

Abstract: A circular cylinder subjected to forced oscillations at angle α with respect to the free stream shows a number of admissible modes of vortex formation synchronized with the body motion. These modes can be categorized into two basic groups: symmetrical vortex formation; and antisymmetrical vortex formation. Whereas there is a single symmetrical mode, there are four basic antisymmetrical modes. Three of these antisymmetrical modes show period doubling relative to the classical Karman mode. This doubling arises from the symmetrical perturbation component induced by the cylinder motion at α ± 90°. Synchronization, i.e. phase-locking of the vortex shedding with the cylinder motion, is possible for all of these modes. It occurs even when streamwise (α = 0°) motion induces an antisymmetrical mode.When synchronization does not occur, there is competition between the symmetrical and antisymmetrical modes; the near-wake structure successively locks-on to each mode over a defined number of cycles, abruptly switching between modes. The number of occurrences of each mode is a well-defined function of excitation frequency and angle α.If, in contrast to steady-state motion of the cylinder, there is an initial transient motion, the transition between symmetrical and antisymmetrical modes has a markedly different character, emphasizing the importance of initial conditions. Abrupt onset of sinusoidal motion produces an initially synchronized symmetrical mode, which gradually decays to an antisymmetrical mode. The number of excitation cycles to onset of decay to antisymmetrical mode is highly repeatable. Moreover, the mechanism of decay of the near wake from the symmetrical to antisymmetrical mode can occur deterministically over a defined number of cycles.

Seismic Performance of Post-tensioned Steel Moment Resisting Frames With Friction Devices

Abstract: A post-tensioned friction damped connection (PFDC) for earthquake resistant steel moment resisting frames (MRFs) is introduced. The connection includes friction devices on the beam flanges with post-tensioned high strength strands running parallel to the beam. The connection minimizes inelastic deformation to the components of the connection as well as the beams and columns, and requires no field welding. Inelastic analyses were performed on a six-story, four-bay steel MRF with PFDCs to study its response to strong ground motions. The PFDC–MRF was designed using a performance based design approach. Results show the MRF with PFDCs has good energy dissipation, self-centering capability, and strength. Variability in the maximum friction forces that develop in the friction devices was determined not to have a significant effect on the MRF performance. The analyses indicate that the seismic performance of a MRF with PFDCs can exceed that of a MRF with conventional moment resisting connections.

CHARMM-GUI ligand reader and modeler for CHARMM force field generation of small molecules

Abstract: Reading ligand structures into any simulation program is often nontrivial and time consuming, especially when the force field parameters and/or structure files of the corresponding molecules are not available. To address this problem, we have developed Ligand Reader & Modeler in CHARMM-GUI. Users can upload ligand structure information in various forms (using PDB ID, ligand ID, SMILES, MOL/MOL2/SDF file, or PDB/mmCIF file), and the uploaded structure is displayed on a sketchpad for verification and further modification. Based on the displayed structure, Ligand Reader & Modeler generates the ligand force field parameters and necessary structure files by searching for the ligand in the CHARMM force field library or using the CHARMM general force field (CGenFF). In addition, users can define chemical substitution sites and draw substituents in each site on the sketchpad to generate a set of combinatorial structure files and corresponding force field parameters for throughput or alchemical free energy simulations. Finally, the output from Ligand Reader & Modeler can be used in other CHARMM-GUI modules to build a protein-ligand simulation system for all supported simulation programs, such as CHARMM, NAMD, GROMACS, AMBER, GENESIS, LAMMPS, Desmond, OpenMM, and CHARMM/OpenMM. Ligand Reader & Modeler is available as a functional module of CHARMM-GUI at http://www.charmm-gui.org/input/ligandrm. © 2017 Wiley Periodicals, Inc.

Iron-Based Catalysts for the High-Temperature Water–Gas Shift (HT-WGS) Reaction: A Review

Abstract: This article critically reviews the literature on iron-based catalysts for the high-temperature water–gas shift (HT-WGS) reaction. The reaction mechanism, reaction intermediates, rate-determining step, kinetics, active site, and promoters are covered. Unlike the low-temperature water–gas shift (LT-WGS) reaction by Cu/ZnO catalysts that has received intensive analysis with modern in situ and operando spectroscopy and DFT studies, the corresponding HT-WGS reaction by Fe-based catalysts still lacks a fundamental understanding because of the absence of modern catalysis studies of this important catalytic system. Given the role of the WGS catalysts on production of H2 for a hydrogen economy, it is imperative that the fundamental molecular-level understanding of the HT-WGS catalyst be advanced.