Author: Dmitri Jajich Publisher: ISBN: Category : Diaphragms (Structural engineering) Languages : en Pages : 296
Book Description
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.
Author: Publisher: ISBN: 9781109386073 Category : Bridges Languages : en Pages :
Book Description
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: Yared Shifferaw Bayleyegn Publisher: ISBN: Category : Languages : en Pages : 194
Book Description
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.
Author: Publisher: ISBN: Category : Languages : en Pages : 448
Book Description
The goal of this study was to develop and evaluate the performance of retrofit techniques for existing steel bridges that have already sustained damage due to distortion-induced fatigue, or are anticipated to experience distortion-induced fatigue cracking within their design life. A second goal was to evaluate the use of new technologies and materials for repairing distortion-induced fatigue damage in steel bridges. While a number of retrofit techniques exist for repairing distortion-induced fatigue cracking, many of them require partial or full bridge closure to perform the repair. The retrofits developed under this project are intended to be able to be installed with minimal disturbance to traffic. Four primary subject matters are reported on within this document: (1) the development of the "angles-with-plate" distortion-induced fatigue repair; (2) development of fiber reinforced polymer (FRP) repairs for distortion-induced fatigue and in-plane fatigue; (3) development of Piezoelectric Induced Compressive Kinetics (PICK) technology for treatment of crack-arrest holes; and (4) a series of analytical investigations aimed at better understanding distortion-induced fatigue susceptibility of skewed bridge systems.
Author: Mark Douglas Bowman Publisher: Transportation Research Board ISBN: 030925826X Category : Technology & Engineering Languages : en Pages : 125
Book Description
"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: Huijuan Li Publisher: ISBN: Category : Girders Languages : en Pages : 113
Book Description
Distortion-induced fatigue cracking in unstiffened web gaps is common in steel bridges. Previous research by the Minnesota Department of Transportation (Mn/DOT) developed methods to predict the peak web gap stress and maximum differential deflection based upon field data and finite element analyses from two skew supported steel bridges with staggered bent-plate and cross-brace diaphragms, respectively. This project aimed to test the applicability of the proposed methods to a varied spectrum of bridges in the Mn/DOT inventory. An entire bridge model (macro-model) and a model encompassing a portion of the bridge surrounding the diaphragm (micro-model) were calibrated for two instrumented bridges. Dual-level analyses using the macroand micro-models were performed to account for the uncertainties of boundary conditions. Parameter studies were conducted on the prototypical variations of the bridge models to define the sensitivity of diaphragm stress responses to typical diaphragm and bridge details. Based on these studies, the coefficient in the web gap stress formula was calibrated and a linear prediction of the coefficient was proposed for bridges with different span lengths. Additionally, the prediction of differential deflection was calibrated to include the influence of crossbrace diaphragms, truck loading configurations and additional sidewalk railings. A simple approximation was also proposed for the influence of web gap lateral deflection on web gap stress. This research studied the effect of two enzymes as soil stabilizers on two soil types to determine how and under what conditions they function. Researchers evaluated the chemical composition, mode of action, resilient modulus, and shear strength to determine the effects of the enzymes A and B on the soils I and II. The enzymes produced a high concentration of protein and observations suggest the enzymes behave like a surfactant, which effects its stabilization performance. The specimens were subjected to testing of varying lengths of time to determine their performance. Researchers observed an increase in the resilient modulus as the curing time increased but that an increase in application rate, as suggested by manufacturers, did not improve the performance of the enzymes. The study also suggests noticeable differences between the two enzymes and their effects on the soils in terms of resilient modulus and the stiffness of the soil.
Author: Dmitri Jajich
Author: John W. Fisher
Author: 
Author: Yared Shifferaw Bayleyegn
Author: 
Author: Mark Douglas Bowman
Author: National Research Council (U.S.). Transportation Research Board
Author: Huijuan Li
Author: Jyr-Jong Lee
Author: Transportation Research Board