Browsing by Author "Mervyn Kowalsky, Committee Chair"

Now showing 1 - 6 of 6

Analysis of an Instrumented Jointless Bridge
(2003-04-09) Wing, Kenneth Michael; Mervyn Kowalsky, Committee Chair; Paul Zia, Committee Co-Chair; Tasnim Hassan, Committee Member
Costs of replacement and maintenance of expansion joints are often a large part of the costs associated with bridge maintenance. To replace these expansion joints or eliminate some of them on structures could greatly reduce the costs. Link slab is a new design approach, which could replace the traditional expansion joints. A link slab is the portion of the bridge deck that connects two adjacent simple-span girders. Link slabs also reduce the damage to the substructure of bridges due to water penetration and debris accumulation in the expansion joint. The objective of this research is to validate the design assumptions associated with designing link slabs, investigate a limit states design procedure and develop a program for the long-term monitoring of an instrumented link slab. This thesis provides details about testing and analysis, which were useful in accomplishing the research objectives. It also provides information about the datalogger software that was used in this project and also details the computer program that was written in Microsoft Excel to aid in the data collection and sorting.
Implementation of Direc Displacement Based Design for Pile and Drilled Shaft Bents
(2006-02-08) Suarez, Vinicio; Vernon Matzen, Committee Member; Mohammed Gabr, Committee Member; Mervyn Kowalsky, Committee Chair
The work in this thesis attempts to implement the Direct Displacement Based Design (DDBD) method to the seismic design of long reinforced concrete pile and drilled shaft bents embedded in soft soils. DDBD has been successfully used to design bridge columns that are fixed at ground level and without soil interaction. The implementation of DDBD for column bents, however, requires the consideration of soil-structure interaction effects--namely added flexibility and damping. The main objective of this research is to develop an equivalent model to predict yield displacement and ductility and to assess the equivalent viscous damping as a function of ductility demand and soil type. The proposed equivalent cantilever model replaces a nonlinear soil-column system. In the equivalent model, the column is considered fixed at some depth below ground at the point of maximum moment and possible formation of an underground plastic hinge. The yield displacement of the column is matched with the yield displacement of the soil-column model by introducing a coefficient and the energy dissipation characteristics are matched by the introduction of equivalent viscous damping as function of ductility and soil type. Charts and equations are provided to compute all the parameters involved in the equivalent formulation. These aids resulted from parametric studies that involved nonlinear static and nonlinear time history analyses of soil-column systems.
Implementation of Direct Displacement-Based Design for Highway Bridges
(2008-08-20) Suarez, Vinicio Andres; Mervyn Kowalsky, Committee Chair
In the last decade, seismic design shifted towards Displacement-Based methods. Among the several methodologies that have been devolved, the Direct Displacement-Based Design Method (DDBD) has been shown to be effective for performance-based seismic design of bridges and other types of structures. The main objective of this Dissertation is to bridge the gap between existing research on Direct Displacement-Based Design (DDBD) and its implementation for design of conventional highway bridges. Real highway bridges have complexities that limit the application of DDBD. This research presents new models to account for: limits in the lateral displacement capacity of the superstructure, skewed configurations, P-Δ effects, expansion joints and different types of substructures and abutments. Special interest is given to the definition of predefined displacement patterns that can be used for direct application of DDBD to several types of bridges. The results of the research show the effectiveness of the proposed models. One of the most relevant conclusions is that bridge frames of bridges with seat-type abutments, which comply with the balanced mass and stiffness requirements of AASHTO, can be designed with DDBD using rigid body translation patters, which greatly simplifies the application of DDBD. Another objective of the research was to compare the execution and outcome of DDBD to the design method in the new AASHTO Guide Specifications for LRFD Seismic Bridge Design. This was accomplished by a comparative study of four real bridges designed with the two methods. Results of that study indicate that DDBD is compatible with the new AASHTO Guide Specification and furthermore, it has several advantages over the design method in that specification. Important products of this research are the computer programs DDBD-Bridge and ITHA-Bridge for design and assessment of highway bridges.
Point of Fixity Analysis of Laterally Loaded Bridge Bents
(2008-01-02) Possiel, Benjamin Allen; Roy Borden, Committee Member; Mervyn Kowalsky, Committee Chair; Mohammed Gabr, Committee Co-Chair
Research work in this thesis deals with the effects of lateral loads in the longitudinal direction on a substructure's point of fixity. Full scale tests were performed to model and test a section of a bridge where the superstructure is connected to the substructure through elastomeric bearing pads. The connection rotational stiffness between the super and substructure was measured as an effect of applying a lateral load to the foundation element and creating a moment at the connection joint. A circular concrete pile, square concrete pile, and steel H-pile were tested in connection with both type V and type VI elastomeric bearing pads. The response of these full scale tests were then modeled in FB-MultiPier as tested and as an equivalent single foundation element. The model response was then compared to the measured results. Through the use of FB-MultiPier, three existing North Carolina bridges' foundation elements were analyzed to determine an effective range of partial head fixity and its compounding effects on the development of a foundation element's depth to fixity.
Seismic Analysis and Design of Type FR Steel Frames Using Displacement-Based Design and Advanced Analysis
(2002-09-17) Harris, John Leroy III; Mervyn Kowalsky, Committee Chair; James Nau, Committee Member; Tasnim Hassan, Committee Member
Current design office methodologies for seismic design of steel moment frames include forced-based methods for calculating equivalent lateral forces and a static elastic analysis. Research has revealed erroneous assumptions in forced-based methods and proposes that displacement-based methods, due to modeling inelastic systems, result in more reasonable lateral force distributions. Additionally, LRFD1 member design interaction equations implicitly account for geometric and material non-linear effects. This philosophy does not satisfy compatibility between the actual inelastic member response and the elastic system as assumed by conventional elastic analysis. Displacement-based lateral force distributions in combination with a second-order inelastic static analysis that sufficiently determines the limit state strength and stability of a structural system, or "Advanced Analysis," is advantageous to the design of steel moment frames. Second-order geometric and inelastic effects are directly accounted for in the analysis. This allows engineers to predict actual frame behavior with greater accuracy and results in a more efficient and economical frame. Another advantage is that force reduction factors outlined in current seismic codes are not required since the frame is designed for inelastic behavior. This approach eliminates discrepancies between initially assumed force reduction factors and final frame ductility capacity. Also, individual member capacity checks outlined in design specifications are similarly not required. The goal of this research is to advance the validity and accuracy of displacement-based design methods and Advanced Analysis for the engineering of seismic resistant steel moment frames. This research will allow the development of alternate seismic analysis and design procedures, as well as refined practical methods that can be incorporated in a design office. 1) Manual of Steel Construction – Load and Resistance Factor Design, American Institute of Steel Construction
The Seismic Behavior of Reinforced Concrete Members at Low Temperatures
(2005-09-28) Sloan, John Elliot; James Nau, Committee Member; Mervyn Kowalsky, Committee Chair; Tasnim Hassan, Committee Member
While reinforced concrete structures depend on ductility for acceptable seismic performance, research on the material behavior of concrete and steel has indicated that the loss of ductility may occur under low temperatures. The current research program investigates the behavior of reinforced concrete column-type members under low temperatures (-20 degrees Celsius, -30 degrees Celsius, and -40 degrees Celsius, approximately) and compares the results to an identical specimen tested at ambient laboratory temperature (23 degrees Celsius). The columns are lightly reinforced, and were loaded in a reversed cyclic manner while inside of an environmental chamber. The results of the experimentation indicate moderate increases in column strength as the temperature decreases, as well as moderate decreases in ultimate displacement capacity as the temperature decreases. The hysteretic damping properties of the columns were not significantly affected by low temperatures, and the specimen tested at -40 degrees Celsius exhibited a shortening of the extent of plasticity.