Distortion-induced Fatigue Cracking in Steel Bridges PDF Download

Author: John W. Fisher
Publisher: Transportation Research Board
ISBN: 9780309048590
Category : Technology & Engineering
Languages : en
Pages : 60

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Author:
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 340

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Distortion-induced fatigue cracking has occurred in many types of steel bridge structures, especially the welded structures where high local stresses exist. However, out-of-plane distortion-induced stresses have not been fully considered in the AASHTO design specifications. This research studies the behavior around web-gap of I-beam in steel bridges under cyclic loading and applies the linear elastic fracture mechanics concepts for prediction of fatigue cracking behavior. Besides, effects of various parameters on the distortion-induced fatigue cracking behavior are considered experimentally and numerically. The results show that finite element modeling with SED criterion is applicable for the crack path prediction. In addition, mode I and mode III affected the fatigue crack direction and fatigue crack growth rate.

Author:
Publisher:
ISBN: 9781109386073
Category : Bridges
Languages : en
Pages :

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Distortion induced fatigue is a common problem for aging steel bridges. The distortion creates secondary bending stresses at web gap locations that are not accounted for in design, thereby initiating fatigue cracks. A large number of such distortion-induced fatigue cracks have recently been found on Delaware Bridge 1-501 in Newport, Delaware. This multi box steel tub girder bridge has cracking that has initiated in the weld which connects the web to the internal bracing via connection plates. To investigate this problem, global finite element models of two of the bridge's spans were created. In order to calibrate the models for use in analysis, a diagnostic load test was performed using strain transducers to measure strains associated with bending of the girders. Once the models were found to reasonably represent the actual response of the structure, the model was then refined for local modeling of the web gap region. As expected, stresses within the gap were found to be large. Reduction of the stresses within these gap locations is required to increase the remaining life of the bridge. Several retrofit methods were designed to accomplish this stress reduction, based on effective retrofits used to correct similar problems in the past. These retrofit methods include drilling holes at the crack tips, positively attaching the connection plates to flanges, increasing the length of the web gaps, and removing the diagonal elements in the diaphragms. The retrofits were modeled and analyzed under fatigue loading and the resulting stresses were compared to the original structure. Of these methods, the positive attachment was found to be most effective in reducing the web gap stresses; however, all of the approaches provided significant reductions in the stress range. Recommendations for applying this type of retrofit detail along with the drilling of holes at the end of crack tips are provided.

Author: Dmitri Jajich
Publisher:
ISBN:
Category : Diaphragms (Structural engineering)
Languages : en
Pages : 296

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This report summarizes the findings of a project with the following goals: to implement a field instrumentation and monitoring program for a typical multi-girder steel bridge on skew supports that may be susceptible to web-gap distortion; to assess the frequency and magnitude of the distortional fatigue stresses at the web-stiffener connections; and to evaluate the impact of these stresses on fatigue life. Measurements from 12 independent strain gauges were continuously monitored and recorded for more than three months on Minnesota Department of Transportation (Mn/DOT) bridge #27734. Truck loading tests also were conducted. Predicted web-gap fatigue life based on the long-term monitoring data from Mn/DOT bridge #27734 ranges from 45 to 75 years. Comparison of web-gap stresses with primary design stresses reveals that web-gap distortional stresses are comparatively high. The report also highlights a detailed finite element study to better understand the web-gap stress mechanism and to compare experimental results with theoretical predictions. Study results have important implications for investigators of distortion-induced web-gap fatigue. They indicate that the actual stress at the so-called hotspot may be as much as twice the stress measured at the strain gauge. The report includes a method for estimating girder deflections and web-gap stress.

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Publisher:
ISBN: 9781109385977
Category : Bridges
Languages : en
Pages :

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In 2006, a consulting firm was hired to perform an in-depth interior box inspection on Delaware Department of Transportation (DelDOT) Bridge Number 1-501, also known as the Newport Viaduct. Upon inspection, 655 fatigue cracks were observed, occurring at the weld metal between the transverse cross frame connection plate and girder webs. At the cracked locations, a 2.5 in. web gap exists between the connection plate termination and the girder flanges. This is a known fatigue prone detail that has been widely documented to be susceptible to out-of-plane deformation and distortion-induced fatigue. Although the mode of cracking is relatively familiar, there are remaining questions that should be answered to ensure the proper functioning of the structure. Specifically, is the observed fatigue cracking consistent with expected behavior? Secondly, should additional cracks be expected to initiate in locations that currently do not have observable cracks? These questions were approached by focusing on a portion of the overall structure, Spans 9-11 in the southbound direction. Field testing was performed to capture the in-situ response of the structure to known live loads via the implementation of 23 strategically placed strain transducers. The field testing was used to calibrate and validate a finite element model. The finite element mesh was constructed using the FEMAP preprocessor and solved using ABAQUS. Sensitivity analyses were performed on the model to investigate the influence of the transverse truck position within the travel lane, the concrete deck stiffness, and the concrete parapets. The results of each analysis showed that the finite element model was insensitive to variations in transverse truck position, concrete stiffness, and the exclusion of the parapets. The finite element model was ultimately utilized to perform a fatigue evaluation. The fatigue evaluation showed that fatigue cracking is within reason given the stress range and the number of accumulated stress cycles from lifetime truck traffic on the structure. The fatigue evaluation and anticipation of future cracking establishes the need for developing crack retrofit and mitigation strategies for the web gap details within the structure. These strategies will extend the longevity of the bridge and enable it to remain in service.

Author: Mark Douglas Bowman
Publisher: Transportation Research Board
ISBN: 030925826X
Category : Technology & Engineering
Languages : en
Pages : 125

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"TRB's National Cooperative Highway Research Program (NCHRP) Report 721: Fatigue Evaluation of Steel Bridges provides proposed revisions to Section 7--Fatigue Evaluation of Steel Bridges of the American Association of State Highway and Transportation Officials Manual for Bridge Evaluation with detailed examples of the application of the proposed revisions."--Publisher's description.

Author: Kathleen S. McElrath
Publisher:
ISBN:
Category :
Languages : en
Pages : 126

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A steel girder twin bridge structure located near Park City, Kansas, has experienced extensive distortion-induced fatigue cracking in its web-gap regions. Due to the bridge's skewed, staggered configuration, the majority of these cracks have occurred in the bottom web-gap region. The bridge was previously the subject of a series of detailed finite element analyses that investigated the effectiveness of several types of retrofits in repairing its distortion-induced fatigue cracks. One of these retrofits, the "angles-with-plate" retrofit, was developed and tested at the University of Kansas as a new retrofitting technique aimed at providing a more economical and easy-to-install distortion-induced fatigue cracking repair. The retrofit is made up of a pair of angles and a backing plate that connect the cross-frame connection plate and girder web in order to stiffen the web-gap region. Results from the finite element analyses determined that the angles-with-plate retrofit was the most effective and economical choice for repairs in the bridge, and plans were made for its installation. To investigate the performance of the angles-with-plate retrofit, two field tests were performed that monitored behavior of the bridge both before and after the retrofit was installed. Results from these field tests were compared with results from complementary finite element analyses to determine the overall effectiveness of the retrofit. In the bottom web-gap region, where cracking is most prevalent in the bridge, the angles-with-plate retrofit was successful at lowering stress demands that would lead to crack propagation. The same conclusion could not clearly be made for all cases in the bridge's less problematic top web-gap region, so a secondary set of finite element analyses was performed to gain a better understanding of what was happening in that region. Further analyses of the two common types of distortion-induced fatigue cracking determined that, while not always large, the angles-with-plate retrofit was successful in reducing stress demands in the top web-gap region. Therefore, it was concluded that the angles-with-plate retrofit was an effective repair for the problematic bottom web-gap regions of the bridge, and if needed, can be used effectively in the less demanding top web-gap region.

Author: John W. Fisher
Publisher: Wiley-Interscience
ISBN:
Category : Technology & Engineering
Languages : en
Pages : 348

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This book provides a detailed review and summary of twenty-two case studies of fracture and fatigue in bridge structures. Its two parts cover cracks formed as a result of low fatigue resistant details, and cracks resulting from unanticipated secondary or displacement induced stresses.

Author:
Publisher:
ISBN:
Category : Finite element method
Languages : en
Pages : 108

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Many older steel girder bridges exhibit distortion-induced fatigue cracking at the cross-frame to girder connections. In a two-girder bridge like the Tuttle Creek Bridge there are no redundant load paths and this problem is of even greater concern. The primary girders of the bridge structure are fatigue critical elements and even when such cracks are relatively small they must be examined extensively. The Tuttle Creek Bridge, built in 1962, developed distortion-induced fatigue cracks in the web gap region. The crack prevention repairs of 1986 were not effective and continued crack growth was observed. The bridge was again repaired recently in the summer of 2005. A finite element study is performed in this study for a typical intermediate girder span, to characterize the behavior of fatigue critical details and to evaluate the effectiveness of the newly installed retrofits. A dual-level finite element analysis was performed using macro-level models of the entire bridge structure and micro-level models of some portions of the bridge under investigation. The finite element procedure was found to be efficient and accurate. The models were calibrated using field strain data obtained from two field tests done before and after the retrofits. The analytical results were in good agreement with the measured field data. The analysis shows that the top flange web gap region is the most susceptible to distortion-induced fatigue. The study successfully explains the observed crack patterns on the bridge. The study indicates a significant reduction in web gap stresses after the retrofit. The retrofit also reduces stresses in the gusset plate region and eliminates the stress concentration near the weld terminations. Based upon the most critical detail and assuming that the traffic volume doubles from the present ADTT of 65, the service life of the bridge is estimated to be over one hundred years.

Author: Yared Shifferaw Bayleyegn
Publisher:
ISBN:
Category :
Languages : en
Pages : 194

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Crack formation due to out-of-plane distortion in the web-gap region has been a common occurrence in multi-girder steel bridges. These cracks result from the fatigue stresses that are induced in the web-gap due to cyclic diaphragm forces resulting from differential deflections between girders. The study presented herein investigated the different repair methods that can be used to control formation of these cracks. The study involved field testing and analytical modeling of a skewed multi-girder steel bridge designated as Design No. 1283, which is built on county road D-180 that crosses over I-380 in the state of Iowa. Different repair methods were suggested to reduce the induced stresses and strains in the web-gap under truck loads. These methods included loosening of the bolts connecting the cross-bracing to the stiffener, connecting the stiffener to the girder top flange or adding another stiffener on the opposite side of the girder web. The results indicated that the first two of these repair alternatives were effective in reducing induced stresses and strains in the web-gap region. The impact of web-gap height on the distortion induced in the web-gap was also studied. Furthermore, influence surfaces for different responses such as, web-gap strains, stresses, out-of-plane displacements at critical locations, and forces in the adjacent diaphragm were developed. Moreover, relationships between the relative out-of-plane displacements and vertical stresses induced within the web-gap region were also provided. These developed relationships and surfaces serve as a quick estimate of induced stresses at critical locations in other web-gap regions of the bridge.