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Autar Kaw - One of the best experts on this subject based on the ideXlab platform.
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Analysis of heating and cooling methods for assembly of steel fulcra in Bascule Bridges
Bridge Structures, 2018Co-Authors: Sri Harsha Garapati, Autar KawAbstract:Assembly procedures for assembling steel fulcra of simple-trunnion Bascule Bridges by heating the girder with heating coils instead of dipping an already stressed trunnion-hub assembly in liquid nitrogen are studied for decreasing the likelihood of failure by cracking and yielding. In the assembly procedure called AP3-A, only the girder is heated to shrink-fit the trunnion-hub assembly in the girder. This assembly procedure AP3-A is found to be infeasible because the girder fails by yielding if heating is expected to be completed in a reasonable amount of time. An alternative assembly procedure called AP3-B is suggested for shrink-fitting where the heating of the girder is combined with cooling the trunnion-hub assembly in dry-ice/alcohol mixture. This assembly procedure AP3-B is found to be feasible. A complete design of experiments study is conducted on AP3-B to find the influence of parameters like hub radial thickness, and radial interference at trunnion-hub interface on the design parameter of critical crack length-a measure of likelihood of fracture. Critical crack lengths during the assembly procedure AP3-B are quantitatively compared with currently used assembly procedures. The results of this work suggest that increasing the hub radial thickness decreases the likelihood of fracture significantly. For hubs with large radial thickness, heating the girder combined with cooling the trunnion-hub in dry-ice/alcohol mixture (AP3-B) is recommended but for hubs with high radial thickness, multistage cooling of the trunnion-hub assembly in dry-ice/alcohol mixture followed by dipping in liquid nitrogen (AP1- multistage cooling) is recommended.
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Comparing two procedures for assembling steel fulcra in simple-trunnion Bascule Bridges
Bridge Structures, 2018Co-Authors: Sri Harsha Garapati, L. Snyder, Autar KawAbstract:Involving shrink fitting, two procedures for assembling steel fulcra of simple-trunnion Bascule Bridges are quantitatively compared for the likelihood of fracture during assembly. In assembly procedure called AP1, the trunnion is shrink fitted into a hub, followed by shrink fitting the trunnion-hub assembly into the girder of the bridge. In assembly procedure called AP2, the hub is conducted to find the influence of geometrical parameters such as the radial thickness of the hub radial interference, and various shrink-fitting methods on the design parameter of critical crack length - a measure of likelihood of fracture. For single-staged shrink-fitting methods, for high and low hub radial thickness to hub inner diameter ratio, and where staged shrink-fitting methods are used, for AP2, cooling the trunnion in dry-ice/alcohol and heating the girder, and for AP1, cooling the trunnion-hub assembly into dry-ice/alcohol following by immersion in liquid nitrogen is recommended. For fulcra with high hub radial thickness to hub inner diameter ratio and where staged shrink-fitting methods are used, cooling the components in dry-ice/alcohol and heating the girder is recommended for both AP1 and AP2.
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Effects of Staged Cooling in Shrink-Fitting Compounded Cylinders
The Journal of Strain Analysis for Engineering Design, 2006Co-Authors: Nathan Collier, Autar Kaw, Glen H. Besterfield, M.m. RahmanAbstract:This paper studies the effect of staged cooling of compounded cylinders in avoiding cracking due to the presence of large interference stresses and low fracture toughness in the presence of cryogenic temperatures. This study is motivated by the assembly procedure of the fulcrum (a compounded trunnion-hub assembly) of Bascule Bridges, where the fulcrum is shrunk by immersion in liquid nitrogen so that it can then be fitted into the girder of the bridge. In a few cases, the fulcrum developed cracks during the immersion in liquid nitrogen. To study the effect of staged cooling to avoid such cracking, a finite difference model was developed of a long compounded cylinder with axisymmetric response with temperature-dependent properties. The study showed that the resistance to failure was increased by as much as 50 per cent when the compounded cylinder is cooled first in a refrigerated air chamber and followed by immersion in liquid nitrogen.
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Hub Assemblies for the Next Generation of Bascule Bridges
2006Co-Authors: Glen H. Besterfield, Autar Kaw, Niranjan PaiAbstract:The objective of this project was to establish the basis for updating the current guidelines for design of Bascule bridge hub assemblies with emphasis on recommnedations for the various hub geometry parameters. Review of recent Bascule bridge designs plans revealed that some Florida Department of Transportation guidelines for hub geometry are not consistently followed in practice. Simplified design equations and finite element models were used to determine the stresses developed in the hub assembly due to the shrink fit between the hub and trunnion. The analysis indicated that tensile hoop stresses developed in the hub may exceed the allowable static stress limits in many Bridges designed based on the current FDOT design guidelines. A MathCAD worksheet was developed to generate preliminary hub assembly design to meet all the performance and strength requirements. Sample computations performed using design loads from representative Bridges revealed that it is possible to obtain satisfactory designs by using the current FDOT recommendations for hub geometry. Structural finite element analysis result showed that the true behavior of the structure is more complex than indicated by the analysis used for design. Thermal finite element analysis revealed that current assembly procedure which allows heating of the hub, leads to acceptable levels of thermal stresses. Finally, hub geometry recommendations based on castability are presented. Also, guidelines for acceptance criteria of hub casting are proposed.
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HUB-GIRDER BOLT ASSEMBLY WITHOUT AN INTERFERENCE FIT IN Bascule Bridges
2004Co-Authors: Glen H. Besterfield, Autar Kaw, Daniel Hess, Niranjan PaiAbstract:Trunnion-hub-girder (THG) assemblies of Bascule Bridges are currently assembled using shrink fits. Previous studies found that one of the two assembly procedures currently used results in high likelihood of hub cracking. One of the possible means to avoid such failures is to modify the assembly procedure by eliminating the shrink fit between the hub and the girder. This project presents the result of a study aimed at developing such hub-girder assemblies without shrink fits. The proposed design scheme utilizes slip-critical bolted connection between the hub, girder and a backing ring. The bolted connection design utilizes turned bolts with locational clearance fit. Loads to be resisted by the connection are identified and computed individually and subsequently combined to arrive at the net required slip resistance. Using this value, the bolt size and number of bolts are determined using a spreadsheet developed for this purpose. In addition to slip resistance, the bolted connection is also checked for bolt shear strength and bearing stresses of the bolted members. The design procedure presented here was refined using results from an axisymmetric finite element model. The model proved useful in highlighting the behavior of friction force resulting from the interference fit between the backing ring and the hub. Six representative Bridges were analyzed using this design scheme. The analysis revealed that the proposed design is unlikely to adversely impact practice since most THG assemblies utilize more bolts than required for achieving a slip-critical connection. This may be because hub flange dimension ratio to trunnion size is dictated by American Association of State Highway and Transportation Officials (AASHTO) and Florida Department of Transportation standards, and results in sufficient room on the hub flange to accommodate extra bolts.
Glen H. Besterfield - One of the best experts on this subject based on the ideXlab platform.
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Effects of Staged Cooling in Shrink-Fitting Compounded Cylinders
The Journal of Strain Analysis for Engineering Design, 2006Co-Authors: Nathan Collier, Autar Kaw, Glen H. Besterfield, M.m. RahmanAbstract:This paper studies the effect of staged cooling of compounded cylinders in avoiding cracking due to the presence of large interference stresses and low fracture toughness in the presence of cryogenic temperatures. This study is motivated by the assembly procedure of the fulcrum (a compounded trunnion-hub assembly) of Bascule Bridges, where the fulcrum is shrunk by immersion in liquid nitrogen so that it can then be fitted into the girder of the bridge. In a few cases, the fulcrum developed cracks during the immersion in liquid nitrogen. To study the effect of staged cooling to avoid such cracking, a finite difference model was developed of a long compounded cylinder with axisymmetric response with temperature-dependent properties. The study showed that the resistance to failure was increased by as much as 50 per cent when the compounded cylinder is cooled first in a refrigerated air chamber and followed by immersion in liquid nitrogen.
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Hub Assemblies for the Next Generation of Bascule Bridges
2006Co-Authors: Glen H. Besterfield, Autar Kaw, Niranjan PaiAbstract:The objective of this project was to establish the basis for updating the current guidelines for design of Bascule bridge hub assemblies with emphasis on recommnedations for the various hub geometry parameters. Review of recent Bascule bridge designs plans revealed that some Florida Department of Transportation guidelines for hub geometry are not consistently followed in practice. Simplified design equations and finite element models were used to determine the stresses developed in the hub assembly due to the shrink fit between the hub and trunnion. The analysis indicated that tensile hoop stresses developed in the hub may exceed the allowable static stress limits in many Bridges designed based on the current FDOT design guidelines. A MathCAD worksheet was developed to generate preliminary hub assembly design to meet all the performance and strength requirements. Sample computations performed using design loads from representative Bridges revealed that it is possible to obtain satisfactory designs by using the current FDOT recommendations for hub geometry. Structural finite element analysis result showed that the true behavior of the structure is more complex than indicated by the analysis used for design. Thermal finite element analysis revealed that current assembly procedure which allows heating of the hub, leads to acceptable levels of thermal stresses. Finally, hub geometry recommendations based on castability are presented. Also, guidelines for acceptance criteria of hub casting are proposed.
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HUB-GIRDER BOLT ASSEMBLY WITHOUT AN INTERFERENCE FIT IN Bascule Bridges
2004Co-Authors: Glen H. Besterfield, Autar Kaw, Daniel Hess, Niranjan PaiAbstract:Trunnion-hub-girder (THG) assemblies of Bascule Bridges are currently assembled using shrink fits. Previous studies found that one of the two assembly procedures currently used results in high likelihood of hub cracking. One of the possible means to avoid such failures is to modify the assembly procedure by eliminating the shrink fit between the hub and the girder. This project presents the result of a study aimed at developing such hub-girder assemblies without shrink fits. The proposed design scheme utilizes slip-critical bolted connection between the hub, girder and a backing ring. The bolted connection design utilizes turned bolts with locational clearance fit. Loads to be resisted by the connection are identified and computed individually and subsequently combined to arrive at the net required slip resistance. Using this value, the bolt size and number of bolts are determined using a spreadsheet developed for this purpose. In addition to slip resistance, the bolted connection is also checked for bolt shear strength and bearing stresses of the bolted members. The design procedure presented here was refined using results from an axisymmetric finite element model. The model proved useful in highlighting the behavior of friction force resulting from the interference fit between the backing ring and the hub. Six representative Bridges were analyzed using this design scheme. The analysis revealed that the proposed design is unlikely to adversely impact practice since most THG assemblies utilize more bolts than required for achieving a slip-critical connection. This may be because hub flange dimension ratio to trunnion size is dictated by American Association of State Highway and Transportation Officials (AASHTO) and Florida Department of Transportation standards, and results in sufficient room on the hub flange to accommodate extra bolts.
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Integrating a Research Problem in a Course in Applied Elasticity
International Journal of Mechanical Engineering Education, 2004Co-Authors: Autar Kaw, Glen H. Besterfield, Sanjeev NichaniAbstract:An example of integrating a single research problem over a broad range of topics in a graduate-level course in applied elasticity (advanced strength of materials) is given in this paper. The research problem was obtained from an investigation of failures during the assembly of fulcrums of Bascule Bridges. Topics exemplified by using this problem included interference fits, axisymmetric problems, transformation of strains and stresses, comparison of failure theories, and the effect of temperature-dependent thermoelastic properties.
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assembly procedures of trunnion hub girder for Bascule Bridges
Theoretical and Applied Fracture Mechanics, 2003Co-Authors: Glen H. Besterfield, Autar Kaw, Sanjeev Nichani, B. Ratnam, T.a. Cherukara, M. DenningerAbstract:Abstract This work is concerned with avoiding failures during the assembly of a trunnion–hub–girder (THG) for Bascule Bridges. In the current assembly procedure, AP#1, the trunnion is shrunk fit into the hub, followed by the shrink fitting of the trunnion–hub assembly into the girder. Two separate incidents during assembly prompted this study. The first incident involved the development of cracks in the hub during the assembly process using AP#1. The second incident involved the trunnion getting stuck in the hub before the trunnion could be fully inserted. A complete analytical, numerical, and experimental study was conducted to understand these failures, and the results were used to develop specifications and recommendations for assembly. The causes of failures include the development of high stresses at low temperatures during assembly, while noting that fracture toughness of THG materials decreases with temperature. Recommended specifications included following an alternative assembly procedure that nearly doubles allowable crack length, and that lowers cooling temperatures to avoid trunnion sticking in the hub.
Gary T. Fry - One of the best experts on this subject based on the ideXlab platform.
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Implementation of a Structural Impairment Detection System on a 100 Year-Old Bascule Bridge
Structural Health Monitoring-an International Journal, 2013Co-Authors: Brett A. Story, Gary T. FryAbstract:Critical instances of reliable bridge functionality arise in situations where waterway transportation conflicts with bridge traffic. Bascule Bridges, or drawBridges, are one class of movable Bridges that can be designed to accommodate both flows of traffic. While popular, heel trunnion Bascule Bridges have not been without problems and failures. Bascule Bridges are subject to multiple cycles of opening and closing on a daily basis, and thus structural members undergo large stress ranges. This paper presents an implementation of a Structural Impairment Detection System (SIDS) that incorporates finite element modeling, instrumentation, and continuous evaluation of a testbed Bascule bridge structure. Heel trunnion Bascule Bridges experience significant stress ranges in critical truss members. Finite element modeling of a testbed bridge provided (1) an estimate of nominal structural behavior, (2) an indication of types and locations of possible impairments, (3) a basis for the design of an instrumentation program appropriate for detecting possible impairments, and (4) data streams with which to train a neural SIDS. Analytical modeling was initially performed in SAP2000 and then refined with ABAQUS. Finite element models and experimental observations indicated maximum stress ranges of approximately 22 ksi on main chord members of the counterweight truss. Instrumentation used to observe structural behavior included electrical resistance strain gages, clinometers, and quadrature encoders. Ultimately, data streams from the testbed bridge are autonomously recorded and interrogated by competitive arrays of artificial neural networks for patterns indicative of specific structural impairments. A quasi static array of competitive neural networks was developed to provide an indication of the operating condition at specific intervals of the bridge’s operation. Based on neural algorithms trained on modeled impairments, the testbed operates in a manner most resembling one of two operating conditions: 1) unimpaired, or 2) an impaired member embedded at the southeast corner of the counterweight.
Kaw Autar - One of the best experts on this subject based on the ideXlab platform.
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Comparing Two Procedures for Assembling Steel Fulcra in Simple-Trunnion Bascule Bridges
'IOS Press', 2011Co-Authors: Garapati S.h., Snyder L., Kaw AutarAbstract:Involving shrink fitting, two procedures for assembling steel fulcra of simple-trunnion Bascule Bridges are quantitatively compared for the likelihood of fracture during assembly. In assembly procedure called AP1, the trunnion is shrink fitted into a hub, followed by shrink fitting the trunnion-hub assembly into the girder of the bridge. In assembly procedure called AP2, the hub is shrink fitted into the girder, followed by shrink-fitting the trunnion in the hub-girder assembly. A formal design of experiments is conducted to find the influence of geometrical parameters such as the radial thickness of the hub, radial interference, and various shrink-fitting methods on the design parameter of critical crack length - a measure of likelihood of fracture. For single-staged shrink-fitting methods, for high and low hub radial thickness to hub inner diameter ratio, assembly procedure AP1 and AP2 are recommended, respectively. For fulcra with low hub radial thickness to hub inner diameter ratio and where staged shrink-fitting methods are used, for AP2, cooling the trunnion in dry-ice/alcohol and heating the girder, and for AP1, cooling the trunnion-hub assembly in dry-ice/alcohol followed by immersion in liquid nitrogen is recommended. For fulcra with high hub radial thickness to hub inner diameter ratio and where staged shrink-fitting methods are used, cooling the components in dry-ice/alcohol and heating the girder is recommended for both AP1 and AP2
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Problem-Centered Approach in a Numerical Methods Course
'American Society of Civil Engineers (ASCE)', 2008Co-Authors: Kaw Autar, Yalcin AliAbstract:This paper is an illustration of using a problem-centered approach in an undergraduate course in numerical methods. The problem used in the course was first encountered in a research project that related to the assembly procedure of the fulcrum of Bascule Bridges. It involved the study of the fulcrum assembly procedure where a trunnion cooled in a dry-ice/alcohol mixture for shrink fitting became stuck halfway in the hub before full insertion could take place. The solution of the problem and its implementation involved numerical solutions of mathematical procedures taught in a typical numerical methods course. The effect of the problem-centered approach in the classroom was quantitatively and qualitatively surveyed over a two-semester period. The results indicate very high student satisfaction in helping them: acquire basic knowledge and skills; reinforce information presented in class, reading assignments, and problem sets; learn to clearly formulate a specific problem and then work it through to completion; develop generic higher-order thinking and problem solving skills; and develop a sense of competence and confidence and see the relevance of the course material to their major
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Incorporating a Research Problem in a Numerical Methods Course for Mechanical Engineers
Scholar Commons, 2007Co-Authors: Kaw AutarAbstract:This paper presents an example of incorporating a research problem in a course - Numerical Methods for Mechanical Engineers. In Bascule Bridges, the fulcrum is assembled by shrink-fitting a trunnion into a hub. In one case, the trunnion cooled in a dry-ice/alcohol mixture for shrink fitting got stuck halfway in the hub. Answering the question why the trunnion got stuck in the hub and finding a solution to the problem, involved numerical solution of mathematical procedures including nonlinear equations, simultaneous linear equations, interpolation, regression, integration, and ordinary differential equations. Students and faculty highly appreciate using this problem-centered approach to teaching the course
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Avoiding Failures during Assembly of a Trunnion-Hub-Girder for Bascule Bridges
'ASME International', 2002Co-Authors: Besterfield, Glen H, Nichani Sanjeev, Kaw Autar, Eason Thomas, Cherukara ThomasAbstract:This paper is a study of avoiding failures during the assembly of a trunnion-hub-girder (THG) for Bascule Bridges. The currently used assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. During assembly, using AP#1, development of cracks on the hub was observed in one THG assembly. Yet, during another assembly, the trunnion got stuck in the hub before it could be fully inserted. A complete analytical, numerical, and experimental study was conducted to understand these failures, and the results were used to develop specifications and recommendations for assembly. The causes of failures include development of high stresses at low temperatures during assembly, while noting that fracture toughness of THG material decreases with temperature. Recommended specifications included following an alternative assembly procedure that doubled allowable crack length, and lower cooling temperatures to avoid trunnions sticking in the hub
Brett A. Story - One of the best experts on this subject based on the ideXlab platform.
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Implementation of a Structural Impairment Detection System on a 100 Year-Old Bascule Bridge
Structural Health Monitoring-an International Journal, 2013Co-Authors: Brett A. Story, Gary T. FryAbstract:Critical instances of reliable bridge functionality arise in situations where waterway transportation conflicts with bridge traffic. Bascule Bridges, or drawBridges, are one class of movable Bridges that can be designed to accommodate both flows of traffic. While popular, heel trunnion Bascule Bridges have not been without problems and failures. Bascule Bridges are subject to multiple cycles of opening and closing on a daily basis, and thus structural members undergo large stress ranges. This paper presents an implementation of a Structural Impairment Detection System (SIDS) that incorporates finite element modeling, instrumentation, and continuous evaluation of a testbed Bascule bridge structure. Heel trunnion Bascule Bridges experience significant stress ranges in critical truss members. Finite element modeling of a testbed bridge provided (1) an estimate of nominal structural behavior, (2) an indication of types and locations of possible impairments, (3) a basis for the design of an instrumentation program appropriate for detecting possible impairments, and (4) data streams with which to train a neural SIDS. Analytical modeling was initially performed in SAP2000 and then refined with ABAQUS. Finite element models and experimental observations indicated maximum stress ranges of approximately 22 ksi on main chord members of the counterweight truss. Instrumentation used to observe structural behavior included electrical resistance strain gages, clinometers, and quadrature encoders. Ultimately, data streams from the testbed bridge are autonomously recorded and interrogated by competitive arrays of artificial neural networks for patterns indicative of specific structural impairments. A quasi static array of competitive neural networks was developed to provide an indication of the operating condition at specific intervals of the bridge’s operation. Based on neural algorithms trained on modeled impairments, the testbed operates in a manner most resembling one of two operating conditions: 1) unimpaired, or 2) an impaired member embedded at the southeast corner of the counterweight.
