No description available.

The routine procedure for designing bridge superstructures relies heavily on the past experience of the designer and is extremely time consuming and costly to try out alternative designs. Typically, a designer is more concerned about satisfying the design requirements laid down by the American Association of State Highway and Transportation Officials (AASHTO) than in coming up with the best possible design from the economic point of view. Thus, application of suitable mathematical programming techniques to determine optimal designs can result in tremendous savings. In this thesis, a procedure based on Generalized Geometric Programming (GGP) is developed to optimally design and select bridge superstructures. The bridge superstructure design problems are formulated as GGP problems incorporating all the design considerations as specified by AASHTO and the Virginia Department of Transportation (VDOT). A primal based algorithm is used in which, the resulting optimization problems are transformed to the solution of a series of Linear Programming problems that are easy to solve. A computer implementation of the algorithm is also developed. The software is extremely versatile and user friendly. It provides several options to help determine the optimal solution under varying design conditions, and is implemented on several representative problems provided by VDOT. Comparison of the resulting optimal with the existing designs promises huge savings in terms of both cost and effort. The methodology that is developed can be used to solve other Engineering Designs Problems as well. / Master of Science

The increase in the speed of the automobile and the increase in the volume of traffic has presented many problems to the highway designer, one of the most important being the elimination of grade crossings. The rigid frame bridge, introduced in this country in the early 1920's, offered a very satisfactory solution to the problem of grade separation. This type of structure was used quite extensively by the Westchester County Park Commission in the expansion of the highway system of lower New York State. The rigid frame is more economical, has greater simplicity, and is more adaptable to architectural treatment than the more conventional deck or through girder bridge. The problem of grade separation was simplified to a still greater degree by the use of the skewed rigid frame, but due to the complexity of analyzing this type of structure its use was limited in early installations. Early theories for the analysis of the skewed type of structure were based on the theories of the right rigid frame and arch, but when these theories proved inadequate it was necessary to develop a more rigorous analysis. Although the new theories were accurate, they were also much too involved for practical use and certain assumptions were made to reduce their complexity. Although the newly developed theories did solve the problem of analyzing the skewed rigid frame, another problem arose, namely that or the validity of the assumptions. Although structural failures were few, the use of high, and in some respects indeterminate, factors of safety may well have compensated for any errors in the assumptions. Committee 314 of the A.C.I . is now making a study of the rigid frame bridge. It is hoped that at some time in the near future a theory, more in keeping with the true behavior of the skewed rigid frame, will be developed. The Committee has decided that model tests offer a convenient solution to many of the problems arising in the development of a new theory. It is the purpose of this thesis to find the stress distribution at the knee of a skewed rigid frame bridge model for various loading conditions. / Master of Science

The undermining of bridge foundations can lead to either costly repairs or a bridge collapse. These foundations must be designed to counter the effects of scour. Current practice does not allow for accurate estimates of scour in erodible rock. Scour in rock can be related to geotechnical and hydraulic properties. A field study of eleven bridge sites provided samples of the bedrock where the abrasive resistance of the rock was determined and hydraulic properties of the channel were calculated. Laboratory abrasion resistance values from a modified slake durability test and hydraulic variables such as stream power were compared to recent and past stream channel cross-sections. A preliminary model has been proposed wherein the degradation of the stream channel is related to the abrasive resistance of the bedrock and the area under the daily stream power. This method provides an estimate of the degradation of the stream bed due to abrasion by bedload and flood events, not necessarily local or contraction scour. / Graduation date: 1998

published_or_final_version / Architecture / Master / Master of Landscape Architecture

Typescript (photocopy). / Digitized by Kansas Correctional Industries

Design of engineering projects involve a certain amount of uncertainty. How should design decisions be taken in face of the uncertainty? What is the most efficient way of handling the data? Decision theory can provide useful answers to these questions. The literature review shows that decision theory is a fairly well developed decision method, with almost no application in hydrology. The steps of decision theoretic analysis are given. They are augmented by the concept of expected expected opportunity loss, which is developed as a means of measuring the expected value of additional data before they are received. The method is applied to the design of bridge piers and flood levees for Rillito Creek, Pima County, Arizona. Uncertainty in both the mean and the variance of the logarithms of the peak flows of Rillito Creek is taken into account. Also shown are decision theoretic methods for: 1) handling secondary data, such as obtained from a regression relation, 2) evaluating the effect of the use of non - sufficient statistics, 3) considering alternate models and 4) regionalizing data.It is concluded that decision theory provides a rational structure for making design decisions and for the associated data collection and handling problems.

Design of engineering projects involve a certain amount of uncertainty. How should design decisions be taken in face of the uncertainty? What is the most efficient way of handling the data? Decision theory can provide useful answers to these questions. The literature review shows that decision theory is a fairly well developed decision method, with almost no application in hydrology. The steps of decision theoretic analysis are given. They are augmented by the concept of expected expected opportunity loss, which is developed as a means of measuring the expected value of additional data before they are received. The method is applied to the design of bridge piers and flood levees for Rillito Creek, Pima County, Arizona. Uncertainty in both the mean and the variance of the logarithms of the peak flows of Rillito Creek is taken into account. Also shown are decision theoretic methods for: 1) handling secondary data, such as obtained from a regression relation, 2) evaluating the effect of the use of nonsufficient statistics, 3) considering alternate models and 4) regionalizing data. It is concluded that decision theory provides a rational structure for making design decisions and for the associated data collection and handling problems.

No description available.

Progressive collapse is a failure mechanism that causes local damage of one structural element to progress throughout the whole structure leading to collapse of the entire structure. Recent catastrophic structural collapses in the world have drawn attention from structural engineers to the importance of designing structures that will continue to be operational even after some local failures occur. For some bridge types, although the design of each single member follows the proper design standards, they still cannot provide sufficient degree of redundancy to withstand a local failure without the total collapse of the entire structural system. In this study, two truss-type bridges, a half-through pedestrian bridge and a through-truss bridge, are investigated. The design configurations follow the AASHTO specifications, and they are usually classified as fracture-critical, non-redundant structures. Furthermore, traditional design and evaluation procedures generally classify through-truss bridges as single-load-path structures. However, due to the configuration of this bridge type, alternative load paths in the bridge could exist, indicating that this type of structural system has the ability to continue sustaining further loads after one of its members reaches its ultimate capacity by using different load paths. It is important to note that, since the structural load-carrying capacity strongly depends on the location of the damaged area, the progressive collapse mechanism of a structure could change substantially under different damage conditions. For the pin-connected pedestrian bridge model, the analysis showed that the failure of a local member is not responsible for the bridge’s collapse. Instead, it is the global buckling (instability) of top chord system that led the bridge to collapse. A modified 2D structure was studied to properly match the buckling load and its associated deformed shape with those obtained in the 3D model’s top chord system. The conclusions of this study verified that the collapse mechanism of this type of bridge is linked to the instability of the top chord system. For the same pedestrian bridge with beam-type connection, the bridge’s failure mechanism is instead associated with the local buckling of an upper chord element that led the bridge to collapse. Therefore, the pedestrian bridge should not be considered a fracture-critical structure since the failure mechanisms that led to its collapse were associated with large compression forces in the upper chord. Looking at deterioration effects on bridge performance, corrosion is one of the dominant causes of deterioration in steel bridges due to aggressive environment and inadequate maintenance. The effects of corrosion damage could alter significantly the bridge behavior depending on the extent of deterioration on the bridge structure. Comprehensive nonlinear analyses were conducted to investigate the changes in collapse mechanisms considering various corrosion level and different corroded locations. Results from the deteriorated pedestrian bridge analyses showed that the deterioration of corroded top chord members could significantly reduce the load-carrying capacity of the bridge and lead the structure to sudden catastrophic failure even for a load lower than the one used in the original design. For the through-truss bridge model, the cases with a corroded middle diagonal member revealed similar load-carrying capacities and collapse mechanisms to the undamaged bridge. These models show similar collapse mechanisms, related to the bending failure of the middle bottom chord and the local buckling of the middle top chord. When the corrosion of the top chord element is severe, the collapse mechanism of the bridge is still linked to the buckling failure of upper chord together with the bending failure of the middle bottom chord. However, the load-carrying capacity of this damaged bridge could drop considerably when compared to that of the undamaged model. Among all the cases analyzed in this study, the corrosion of the end post element represents the most critical case: here, the results indicated a considerable decrease in the load-carrying capacity of this damaged bridge model when compared to that of the undamaged bridge. In addition, this study also focused on the effects of support settlements on the load-carrying capacity and on the collapse mechanism of deteriorated bridges. It was found that, even with only a slight differential settlement support, the bridge model with a localized corroded diagonal element reached its ultimate capacity much earlier in the loading process than the bridge with fixed boundaries, with a reduction of the original load-carrying capacity of about 15%.