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Title
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Evaluation of plastic hinge models and inelastic analysis tools for performance-based seismic design of RC bridge columns
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Creator
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Fedak, Lauren Kimberly
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Date
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2012
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Collection
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Electronic Theses & Dissertations
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Description
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For over 50 years, the notion of an equivalent region under constant plastic curvature, i.e., the plastic hinge length (Lp), has been the main approach for evaluating the inelastic response of reinforced concrete (RC) columns for seismic bridge design. Most of the proposed Lp models have been calibrated on columns with modest slenderness to predict ultimate displacement. However, modern design approaches require predicting intermediate damage levels, or limit states, and urban congestion is...
Show moreFor over 50 years, the notion of an equivalent region under constant plastic curvature, i.e., the plastic hinge length (Lp), has been the main approach for evaluating the inelastic response of reinforced concrete (RC) columns for seismic bridge design. Most of the proposed Lp models have been calibrated on columns with modest slenderness to predict ultimate displacement. However, modern design approaches require predicting intermediate damage levels, or limit states, and urban congestion is leading to increasingly slender columns; thus bringing doubt on the reliability of plastic hinge models. The performance of Lp models in lumped plasticity elements was assessed by conducting analyses on 34 columns from the PEER Column Database. Results show that the Lp definition in lumped plasticity analyses produces drastic and random differences for varying limit states. Distributed plasticity elements can capture inelastic global and local response throughout the element without explicit definition of an inelastic zone. Lumped and distributed plasticity elements were thus assessed by comparing the global and local responses for five columns of increasing slenderness; the most slender of which was constructed and tested as part of this research to expand the current database for slender columns. Performance was found to be sensitive to aspect ratio; indicating behavior controlled by P-delta effects. The study has highlighted the need for a unified definition of limit states, as well as improved methods to accurately and efficiently predict inelastic behavior at each limit state. Inaccuracy in current numerical tools was found not only at intermediate limit states but also when predicting the global behavior of slender columns.
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Title
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Cost overruns and time delays in highway and bridge projects in developing countries : experiences from Cameroon
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Creator
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Bella Akoa, Bertin
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Date
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2011
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Collection
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Electronic Theses & Dissertations
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Description
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COST OVERRUNS AND TIME DELAYS IN HIGHWAY AND BRIDGE PROJECTS IN DEVELOPING COUNTRIES - EXPERIENCES FROM CAMEROON By Bertin Bella AkoaCost and time performance is a concern for construction project stake-holders and specifically for highway and bridge projects, due to the uncertainty that characterizes these projects. Cost overruns and time delays have been recorded for centuries, and still occur during projects today. Despite technological innovations in project management, there has been...
Show moreCOST OVERRUNS AND TIME DELAYS IN HIGHWAY AND BRIDGE PROJECTS IN DEVELOPING COUNTRIES - EXPERIENCES FROM CAMEROON By Bertin Bella AkoaCost and time performance is a concern for construction project stake-holders and specifically for highway and bridge projects, due to the uncertainty that characterizes these projects. Cost overruns and time delays have been recorded for centuries, and still occur during projects today. Despite technological innovations in project management, there has been little improvement in cost and time performance of transportation projects for over eighty years (Flyvbjerg, 2008). For developing countries, there is a need for statistically sound studies that describe cost overruns and time delays from which appropriate solutions can be derived. This research aimed to contribute to filling this gap, through case-study research at the Ministry of Public Works (MINTP) in Cameroon.Literature on cost overruns and time delays was reviewed, historical contract data was collected, and a survey was administered to construction professionals in Cameroon. After contract data analysis, it was found that projects funded by foreign aid had the largest project overrun rates, and small projects had higher project overruns. Project overrun rates decreased when project size or duration increased. Inadequate site visits during technical studies and the bidding phase for construction projects were found to be the main causes of cost overruns and time delays for MINTP. Causes of project overruns were found in all phases of project development, specifically in the bidding phase.
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