› › Fatigue Life Analysis Of A Steel Trapezoidal Box Girder Bridge Using Measured Strains

Fatigue Life Analysis of a Steel Trapezoidal Box Girder Bridge Using Measured Strains

Author : Jose Luis Soto Fuentes

Publisher :

Page : pages

File Size : 28,69 MB

Release : 2011

Category : Box beams

ISBN :

Get eBook

Book Description

The Newport Viaduct is a 1,984 feet long bridge owned by the Delaware Department of Transportation located in Newport, DE. During an in-depth inspection in 2006, approximately 665 cracks were discovered near the internal cross frame diaphragm connection plates and the girder webs. A 2.5 inch gap exists between the termination of the diaphragm connection plate and the flanges of the girder. This is a known fatigue prone detail subject to out of plane deformations which lead to the formation of distortion induced fatigue cracks. Previous research done on the Newport Viaduct used global finite element models to estimate the fatigue life of the web gap details and analyze potential retrofit options. The purpose of this project is to measure site specific strains caused by variable traffic loads and use this data to carry out a fatigue life analysis of the web gap details. In order to assist in the fatigue life analysis, localized finite element models of the web gap details were created. Given geometric differences, separate models were created for the top and bottom web gap details. The finite element models were created using FEMAP and solved using ABAQUS. The analysis results showed a high stress gradient in the web gap region with a maximum near the weld toe. Moreover, the results showed that the bottom web gap detail experienced higher stresses than the top web gap detail given the same loading. In-service monitoring of the Newport Viaduct was carried out for 23 days. Resistive foil type strain gages were installed directly in the top and bottom web gap regions and data was collected and processed at 100Hz using the Rainflow algorithm to count the number of load cycles and their magnitude. The recorded data was used in conjunction with the bottom web gap finite element model and Miner's Rule to determine an effective stress at the weld toe. The results predict a mean fatigue life of 22 years for the bottom web gap detail. Furthermore, current uncracked web gap details are expected to crack in the future.



Analysis of Distortion-induced Fatigue Cracking of a Trapezoidal Steel Box Girder Bridge Including Retrofit Investigation

Author :

Publisher :

Page : pages

File Size : 36,75 MB

Release : 2009

Category : Bridges

ISBN : 9781109386073

Get eBook

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.



Distortion-induced Fatigue in Multi-girder Steel Bridges

Author : Dmitri Jajich

Publisher :

Page : 296 pages

File Size : 39,64 MB

Release : 2000

Category : Diaphragms (Structural engineering)

ISBN :

Get eBook

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.



Analysis of Distortion-induced Fatigue Cracking in a Steel Trapezoidal Box Girder Bridge

Author :

Publisher :

Page : pages

File Size : 46,63 MB

Release : 2009

Category : Bridges

ISBN : 9781109385977

Get eBook

Book Description

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.





Advances in Weigh-in-motion Using Pattern Recognition and Prediction of Fatigue Life of Highway Bridges

Author : Nicolas Gagarine

Publisher :

Page : 104 pages

File Size : 39,91 MB

Release : 1992

Category : Girders

ISBN :

Get eBook

Book Description

The two main objectives of the present study were to: (1) demonstrate the advantages of using the Weigh-in-Motion and Response (WIM+R) system to evaluate the fatigue life of existing bridges and (2) introduce pattern recognition methods in the analysis of WIM+R data. Four steel girder bridges were instrumented to obtain strain data at fatigue critical details, and at sections of maximum strain to compute the gross vehicle weight (GVW) of each truck. Two were simple spans, and two continuous spans. A comparative study of three of the four alternatives suggested by AASHTO showed that the fatigue life computed with direct measurements of the stress ranges were greater than those computed with the simplified approaches. The effect of secondary cycles was negligible for the four bridges. The damage equivalent secondary cycle factor for fatigue was defined. The applicability of three pattern recognition methods for WIM+R was investigated. The dynamic time warping, hidden Markov model, and feed forward neural network methods can classify trucks with the measured strain patterns alone.



Steel Box Girder Bridges

Author :

Publisher : Thomas Telford Publishing

Page : 328 pages

File Size : 12,58 MB

Release : 1973

Category : Technology & Engineering

ISBN :

Get eBook

Book Description



Estimating the Remaining Fatigue Life of Steel Bridges Using Field Measurements

Author : Jeremiah David Fasl

Publisher :

Page : 676 pages

File Size : 16,76 MB

Release : 2012

Category :

ISBN :

Get eBook

Book Description

As bridges continue to age and budgets reduce, transportation officials often need quantitative data to distinguish between bridges that can be kept safely in service and those that need to be replaced or retrofitted. One of the critical types of structural deterioration for steel bridges is fatigue-induced fracture, and evaluating the daily fatigue damage through field measurements is one means of providing quantitative data to transportation officials. When analyzing data obtained through field measurements, methods are needed to properly evaluate fatigue damage. Five techniques for evaluating strain data were formalized in this dissertation. Simplified rainflow counting, which converts a stress history into a histogram of stress cycles, is an algorithm standardized by ASTM and the first step of a fatigue analysis. Two methods, effective stress range and index stress range, for determining the total amount of fatigue damage during a monitoring period are presented. The effective stress range is the traditional approach for determining the amount of damage, whereas the index stress range is a new method that was developed to facilitate comparisons of fatigue damage between sensors and/or bridges. Two additional techniques, contribution to damage and cumulative damage, for visualizing the data were conceived to allow an engineer to characterize the spectrum of stress ranges. Using those two techniques, an engineer can evaluate whether lower stress cycles (concern due to electromechanical noise from data acquisition system) and higher stress ranges (concern due to possible spike from data acquisition system) contribute significantly to the accumulation of damage in the bridge. Data from field measurements can be used to improve the estimate of the remaining fatigue life. Deterministic and probabilistic approaches for calculating the remaining fatigue life were considered, and three methods are presented in this dissertation. For deterministic approaches, the output of the equations is the year when the fatigue life has been exceeded for a specific probability of failure, whereas for probabilistic approaches, the probability of failure for a given year is calculated. Four different steel bridges were instrumented and analyzed according to the techniques outlined in this dissertation.



Fatigue Life of Riveted Steel Bridges

Author : Björn Åkesson

Publisher : CRC Press

Page : 170 pages

File Size : 33,27 MB

Release : 2010-04-21

Category : Technology & Engineering

ISBN : 0203847768

Get eBook

Book Description

Many old riveted railway bridges are replaced too soon due to a general lack of knowledge about the expected life span. This indicates the need for more information on fatigue and brittle fracture of riveted bridges. This book unveils extensive research and literature results on riveted bridges' fatigue live and shows how to take fatigue properly i



Composite Action During Construction of Steel Trapezoidal Box Girder Bridges

Author :

Publisher :

Page : 58 pages

File Size : 50,8 MB

Release : 2005

Category : Box girder bridges

ISBN :

Get eBook

Book Description

In steel trapezoidal box girder bridge systems, the U-shaped steel girder is designed to act compositely with the concrete deck to form a closed box for live loading. During the construction stage, however, the behavior is not well understood. The usual practice of assuming the system to be non-composite during construction requires substantial top flange bracing to form a quasi-closed box section. Composite box girders with live loading, and girders during construction, have to be evaluated during the design of curved steel trapezoidal box girder bridges. Considering both cases, the design for construction loading is the least understood and is the most important. Stresses due to construction loading can reach up to 60-70 percent of the total design stress for a given cross section. A three-phase study was undertaken to investigate the behavior of curved trapezoidal box girders during construction.