Doctor of Philosophy

dissertationAccelerated bridge construction (ABC) has been practiced in the United States because of the efficiency it offers as a bridge construction method. Prefabricated reinforced concrete components have been frequently used as part of ABC. The connections between such precast components may be subjected to large earthquake-induced deformations resulting in a considerable permanent damage. The present study investigates the seismic performance of grouted splice sleeve (GSS) connections with the connectors placed in the column, footing, or cap beam of bridge subassemblies. Quasi-static cyclic loads were used to test five half-scale precast subassemblies and two cast-in-place control specimens. Two different GSS connectors were used; the column-to-footing connections incorporated one type of GSS with the bars grouted at both ends, whereas the column-to-cap beam connections used another type where one bar was threaded into one end and the other bar was grouted into the opposite end. Experimental results show that the precast subassemblies had similar strength but lower displacement capacity compared to the control specimens. Improved seismic response was observed when the location of the connectors was changed or when debonding was applied to dowel bars adjacent to the connectors. Computational models were developed and validated with the experiments to further investigate the application of such precast connections in bridge bents with full-size configurations. Force-based beam-column elements with fiber sections were used to construct the computational models based on plastic hinge weighted integration. The modeling strategy is based on transformation of the model for the precast column with GSS connectors, to an idealized equivalent cast-in-place column with a fictitious plastic hinge length that is capable of simulating both the global and local response. Bond-slip effects as well as low-cycle fatigue were included to address the performance differences between the precast and cast-in-place alternatives. Prototype precast bridge bent models designed with GSS connections were subjected to scaled ground motion records compatible with the earthquake demand in downtown Salt Lake City. Comparing the capacity and demand levels, the GSS connection was found to be promising for applications in high-seismic areas

Structures Division 1994 Annual Report

The NASA Lewis Research Center Structures Division is an international leader and pioneer in developing new structural analysis, life prediction, and failure analysis related to rotating machinery and more specifically to hot section components in air-breathing aircraft engines and spacecraft propulsion systems. The research consists of both deterministic and probabilistic methodology. Studies include, but are not limited to, high-cycle and low-cycle fatigue as well as material creep. Studies of structural failure are at both the micro- and macrolevels. Nondestructive evaluation methods related to structural reliability are developed, applied, and evaluated. Materials from which structural components are made, studied, and tested are monolithics and metal-matrix, polymer-matrix, and ceramic-matrix composites. Aeroelastic models are developed and used to determine the cyclic loading and life of fan and turbine blades. Life models are developed and tested for bearings, seals, and other mechanical components, such as magnetic suspensions. Results of these studies are published in NASA technical papers and reference publication as well as in technical society journal articles. The results of the work of the Structures Division and the bibliography of its publications for calendar year 1994 are presented

Micro Scale Sediment - Fluid Interactions

This thesis was inspired by the inherent limitations in the quantification of the physical parameters (e.g. flow speed, grain size and density) controlling sediment-fluid interactions in the direct vicinity of the sediment water interface of a seabed. For this, the transport behaviour of layered - and mixed sediment beds consisting of a simplified two-grain fraction distribution (silt and sand) was tested in an analogue laboratory-based annular flume. The results showed that the sediment bed stabilized with increasing silt composition. To investigate this effect in more detail, a high resolution 3D numerical model was designed for the simulation of sediment transport by a fluid by coupling two numerical techniques i.e., Finite Difference Method (FDM) and the Distinct Element Method (DEM). It verified that in the case of the deposition of fine particles on top of, or mixed into, a coarse matrix, the bed stability increased significantly. The model was also used to examine the role of grain density variations on the threshold conditions and erosion behavior of sediment beds. The experiments showed that bed stability increased when the heavy mineral concentrations were increased, which validated the process of heavy mineral enrichment

Seismic Performance of Anchored Brick Veneer

A study was conducted on the out-of-plane seismic performance of anchored brick veneer with wood-frame backup wall systems, to evaluate prescriptive design requirements and current construction practices. Prescriptive requirements for the design and construction of anchored brick veneer are currently provided by the Masonry Standards Joint Committee (MSJC) Building Code, the International Residential Code (IRC) for Oneand Two-Family Dwellings, and the Brick Industry Association (BIA) Technical Notes. Laboratory tests were conducted on brick-tie-wood subassemblies, comprising two bricks with a corrugated sheet metal tie either nail- or screw-attached to a wood stud, permitting an evaluation of the stiffness, strength, and failure modes for a local portion of a veneer wall system, rather than just of a single tie by itself. Then, full-scale brick veneer wall specimens (two one-story solid walls, as well as a one-and-a-half story wall with a window opening and a gable region) were tested under static and dynamic out-of-plane loading on a shake table. The shake table tests captured the performance of brick veneer wall systems, including interaction and load-sharing between the brick veneer, corrugated sheet metal ties, and wood-frame backup. Finally, all of these test results were used to develop finite element models of brick veneer wall systems, including nonlinear inelastic properties for the tie connections. The experimental and analytical studies showed that the out-of-plane seismic performance of residential anchored brick veneer walls is generally governed by: tensile stiffness and strength properties of the tie connections, as controlled by tie installation details; overall grid spacing of the tie connections, especially for tie installation along the edges and in the upper regions of walls; and, overall wall geometric variations. Damage limit states for single-story residential brick veneer wall systems were established from the experimental and analytical studies as a function of tensile failure of key tie connections, and the seismic fragility of this form of construction was then evaluated. Based on the overall findings, it is recommended that codes incorporate specific requirements for tie connection installation along all brick veneer wall edges, as well as for tie connection installation at reduced spacings in the upper regions of wall panels and near stiffer regions of the backup. Residential anchored brick veneer construction should as a minimum be built in accordance with the current prescriptive code requirements and recommendations, throughout low to moderate seismicity regions of the central and eastern U.S., whereas non-compliant methods of construction commonly substituted in practice are generally not acceptable.published or submitted for publicatio