Browsing by Author "Dr. Abhinav Gupta, Committee Member"

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Behavior of Infill Masonry Walls Strengthened with FRP Materials
(2009-05-05) Lunn, Dillon Stewart; Dr. Sami Rizkalla, Committee Chair; Dr. Abhinav Gupta, Committee Member; Dr. Rudolf Seracino, Committee Member
Collapse of unreinforced masonry (URM) structures, including infill walls, is a leading cause of property damage and loss of life during extreme loading events. Many existing structures are in need of retrofit to bring them in compliance with modern design code provisions. Conventional strengthening techniques are often time-consuming, costly, and add significant weight to the structure. These limitations have driven the development of alternatives such as externally bonded (EB) glass fiber reinforced polymer (GFRP) strengthening systems, which are not only lightweight, but can be rapidly applied and do not require prolonged evacuation of the structure. The objective of this research program was to evaluate the effectiveness of strengthening infill masonry walls with externally bonded GFRP sheets to increase their out-of-plane resistance to loading. The experimental program comprises fourteen full-scale specimens, including four un-strengthened (control) specimens and ten strengthened specimens. All specimens consisted of a reinforced concrete (RC) frame (which simulates the supporting RC elements of a building superstructure) that was in-filled with solid concrete brick masonry. The specimens were loaded by out-of-plane uniformly distributed pressure in cycles up to failure. Parameters investigated include the aspect ratio, the strengthening ratio, the number of wythes, and the type of FRP anchorage used. The type of FRP anchorage was found to greatly influence the failure mode. Un-strengthened specimens failed in flexure. However, strengthened specimens without overlap of the FRP onto the RC frame failed due to sliding shear along the bed joints which allowed the walls to push out from the RC frames in a rigid body fashion. In the case where GFRP sheets were overlapped onto the RC frames, the aforementioned sliding shear caused delamination of the GFRP sheets from the RC frames. Use of steel angles anchored along the perimeter of the walls as shear restraints allowed these walls to achieve three times the service load without any visible signs of distress. GFRP strengthening of infill masonry walls was found to be effective, provided that proper anchorage of the FRP laminate was assured.
A Distributed Simulated Annealing framework for Engineering Optimization
(2003-09-11) Pabolu, Sivakumar V; Dr. G. (Kumar) Mahinthakumar, Committee Co-Chair; Dr. John W. Baugh Jr., Committee Co-Chair; Dr. Abhinav Gupta, Committee Member
Engineering optimization problems are known to be difficult to solve using mathematical programming techniques because of large search spaces, complex objective and constraint functions, and, in many cases, their combinatorial nature. Simulated annealing is a well known heuristic optimization technique that has been used to solve a number of problems in discrete, non-differential, and combinatorial optimization and hence is suitable for solving such engineering optimization problems. However, computationally intensive problems are frequently encountered in the field of engineering optimization, in which case the use of simulated annealing can be prohibitively time consuming. The objective of this thesis is to develop an object oriented framework that implements a distributed simulated annealing algorithm, which can be easily extended to solve computationally intensive engineering optimization problems. A distributed simulated annealing algorithm (DSA Algorithm) was developed and incorporated into a distributed simulated annealing framework called the DSA Framework. The framework defines interfaces, through which optimization problems can be modeled, utilizing a distributed computing framework, Vitri, to engage multiple desktop computers in a collective effort to solve problems. The framework was used to solve a 40 variable knapsack problem as a benchmark problem to analyze the performance of the algorithm. The framework was also used to optimize support locations in a piping system subject to seismic loads. The DSA framework proves to be an efficient, fairly scalable tool that shows consistent reduction in execution time with increasing number of servers, thus proving to be a valuable tool in solving computationally intensive engineering optimization problems.
A Parallel Optimization Framework for Inverse Problems
(2004-04-08) Sayeed, Mohamed; Dr. G. Mahinthakumar, Committee Chair; Dr. John. W. Baugh Jr, Committee Co-Chair; Dr. Abhinav Gupta, Committee Member; Dr. Ranji S. Ranjithan, Committee Member
Inverse problems that are constrained by large-scale partial differential equation (PDE) systems demand significant computational resources. These problems generally require the solution of a large number of complex PDE systems. Three dimensional subsurface characterization inverse problems fall under this category. A parallel hybrid optimization framework using global search and local search (LS) techniques is developed. The global search uses genetic algorithms (GAs). For LS several non-gradient based algorithms such as Nelder-Meade simplex, Hooke-Jeeves pattern search and Powell's method of conjugate directions and a gradient based algorithm namely, Fletcher-Reeves conjugate gradient method are implemented in the framework. Subsurface inverse characterization problems are posed as optimization problems and solved using this framework. The GA or hybrid GA-LS optimizer is employed to drive a parallel finite-element (FEM) groundwater transport simulator. Multilevel parallelism opportunities exist at the coarse-grained optimization level and the fine-grained function evaluation level. Coarse-grained parallelism (task parallelism) in the optimizer is exploited using a self-scheduling algorithm. Fine-grained parallelism (data parallelism) in the FEM transport simulator is achieved through a domain decomposition strategy. The MPI (Message Passing Interface) communication library is used for the parallel implementation. Parallelism is enhanced for local searches by enabling concurrent execution of multi-start or multi-type local searches. Performance results for convergence are examined for different test problems including biological activity zone identification, contaminant source zone identification (location and concentration) and contaminant sources release history reconstruction problems showing the applicability of the proposed approach. The size and complexity of problems solved in this research far exceed what has been reported to date in the literature. The implementation has been extensively tested on a single supercomputer and on the grid (TeraGrid). This research illustrates that the hybrid approaches are generally more effective than either standalone GA or LS for solving inverse problems.
Post-Tensioned Clay Brick Masonry Walls for Modular Housing in Seismic Regions
(2002-07-16) Rosenboom, Owen Arthur; Dr. Mervyn Kowalsky, Committee Chair; Dr. Abhinav Gupta, Committee Member; Dr. James Nau, Committee Member
From past research post-tensioned concrete masonry walls have performed well due to in-plane loading, yet despite the advantage of being more aesthetically pleasing, post-tensioned clay brick masonry walls have not been investigated under this loading. Five half scale structural specimens using this system were constructed and tested, and the results from these tests plus a proposed force-displacement analysis procedure are included herein. The results show that post-tensioned clay brick masonry walls are well suited for seismic regions when the walls are grouted and unbonded, and the presence of confinement plates in the compression region greatly enhances the overall performance of the wall. In addition, the force-displacement analysis shows that in order to account for the overall behavior of the wall, cyclic degradation characteristics must be included.