Browsing by Author "Schultz, Arturo E"
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Item Analysis of Girder Differential Deflection and Web Gap Stress for Rapid Assessment of Distortional Fatigue Stress in Multi-Girder Steel Bridges(2005-10-01) Li, Huijuan; Schultz, Arturo EDistortion-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 macro- and 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 cross-brace 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.Item Analysis Tools and Rapid Screening Data for Distortional Fatigue in Steel Bridge Girders(2001-11-01) Berglund, Evan; Schultz, Arturo EFatigue Cracking often occurs in composite bridges with unstiffened girder web gaps at the ends of transverse stiffeners. In this project, researchers sought to better understand bridge diaphragm deflection behavior and advance the ability to estimate web gap distortional stress. Trends from the parametric studies led to general observations that may assist in identifying fatigue-prone bridges. Variables that influence diaphragm deflection behavior include girder spacing, bridge skew, span length, and deck thickness. Transverse load distribution properties appear to play the most significant role in determining the magnitude of differential deflection. Parameter study stress trends indicate that out-of-plane distortional stress in fatigue prone web gaps primarily depends on web gap properties, bridge span length, and angle of skew. Differential deflection and web gap dimension trends apply to a varied spectrum of bridge configurations. The research resulted in a method to assess bridge girder differential deflection and distortional stress in actual steel bridges without complex analysis and modeling. Proposed procedures for evaluating out-of-plane stress should prove practical and aid in screening, identifying, and assessing bridges vulnerable to distortion -induced fatigue cracking.Item Condition and Durability of Segmental Concrete Block Retaining Walls Along Roadways in Minnesota(2001-07-01) Embacher, Rebecca A; Schultz, Arturo E; Snyder, Mark BThis research project assesses the nature and extent of premature deterioration of segmental concrete block retaining walls (SCBRWs) along roadways in the Minneapolis-St. Paul area. Researchers conducted a two-stage condition survey on 104 SCBRWs. The first stage, a general distress survey, focused on determining the type, severity, and extent of distresses present. The second stage, a peak winter survey, assessed the extent of snow/ice cover and exposure to winter sun. According to research results, only 7 percent of the SCBRWs surveyed were in poor or very poor condition. But researchers observed many distress types in 50 percent or more of the walls surveyed, including freeze-thaw damage, scaling, manufacturing flaws, and efflorescence. Freeze-thaw damage and scaling were most highly associated with decreases in overall wall condition. Efflorescence and freeze-thaw damage were found to be at least partly dependent upon SCBRW age and block manufacturer. Durability problems appear to be directly related to the lack of durability of the block units, which suggests problems with the use of inadequate mix designs, non-durable aggregate, and/or inadequate curing procedures. The report includes recommendations to address possible deficiencies in manufacturing processes and quality.Item Distortion-Induced Fatigue in Multi-Girder Steel Bridges(2000-05-01) Jajich, Dmitri; Schultz, Arturo E; Bergson, Paul; Galambos, TheodoreThis report summarizes the findings of a project with the following goals: 1. 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; 2. to assess the frequency and magnitude of the distortional fatigue stresses at the web-stiffener connections; and 3. 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.Item Earth Pressure Behind A Retaining Wall(2005-03-01) Bentler, Joseph G; Labuz, Joseph F; Schultz, Arturo EEarth pressure cells, tiltmeters, strain gages, inclinometer casings, and survey reflectors were installed in fall 2002 during construction of a 26-ft (7.9-m) high Minnesota Department of Transportation (Mn/DOT) reinforced concrete cantilever retaining wall. A data acquisition system with remote access monitored some 60 sensors on a continual basis. Analyses of the data indicated the development of active earth pressure at the end of backfilling, with a resultant at about one-third of the backfill height. Translation of 0.45 in. (11 mm), or about 0.1% of the backfill height, was responsible for development of the active condition. The wall also rotated 0.03 degrees into the backfill as a rigid body, while the top of the stem deflected 0.16 in. (4 mm) away from the backfill. Sensor readings showed the earth pressure distribution to be quite complex during the backfilling process. Evidence was found for residual lateral stresses from compaction. Translation of the wall overnight following the construction workday reduced the compaction-induced lateral stresses. Changes in earth pressure and wall deflection weeks after backfilling were attributed to changes in temperature and rainfall. The data showed that the wall design, while reasonable, could be made more efficient by removing the shear key, which was ineffective.Item Investigation of Deterioration of Stainless Steel Dowel Tubes Under Repeated Loading(2005-12-01) Schultz, Arturo E; Khazanovich, Lev; Yut, Iliya; Tompkins, DerekThe Minnesota Department of Transportation (Mn/DOT) has selected a 316L stainless steel schedule 40 pipe as a new dowel bar to be used as a bid alternative for its high performance Portland Cement Concrete (PCC) pavements. Although this dowel bar should provide sufficient shear transfer capacity and low concrete bearing stresses, there was a concern that lack of a solid core may not provide sufficient resistance of the cross-section to distortion under a heavy axle loading. In this study, long-term performance of the 316L stainless steel schedule 40 pipe was investigated by subjecting a doweled joint to accelerated repeated loads through the use of the Minnesota Accelerated Loading Facility (Minne-ALF-2). Assessment of the new dowel bar performance was performed based on comparison with the standard 1.5 inch diameter epoxy -coated round steel dowel. The following tasks were accomplished: redesign, assembly and calibration of new version of Minne-ALF, development of experimental design matrix, conduct of accelerated full-scale testing, and post-testing evaluation. The results from the MinneALF-2 tests illustrated that while the LTE for the stainless steel dowel tubes was lower than the LTE for the epoxy-coated dowels, the stainless steel tubes are capable of providing over 70% LTE in the long-term when installed in concrete pavement joints. The ability to withstand deformation and corrosion while providing sufficient long-term performance suggests that the stainless steel tube dowel is an attractive alternative to the solid epoxy-coated dowel for use in long-life pavementsItem Performance Testing of Experimental Dowel Bar Retrofit Designs Part 1 - Initial Testing(2003-12-01) Odden, Trevor R; Snyder, Mark B; Schultz, Arturo EAn area of concern common to portland cement concrete (PCC) pavements is load transfer across joints and cracks. The current design standard for load transfer in new jointed PCC pavements and the rehabilitation of old PCC pavement is to place steel dowel bars at mid-depth of the pavement across the joint or crack (1). The main issues with the use of retrofit and/or new dowels are the high expense associated with the retrofitting operation and the corrosion that has been associated with the use of steel dowels. Three new and experimental dowel bar retrofit designs, that address the issues of high retrofit cost and corrosion susceptibility, were tested in an accelerated manner in order to determine the potential viability of their use for the restoration of load transfer in PCC pavements. Innovations in the three designs included the use of fiber reinforced polymer dowels, grouted stainless steel pipe dowels, and a change in the geometric configuration of the design. An evaluation of test results and recommendations, regarding the use of the designs for the restoration of load transfer in PCC pavements, are presented. Relates to 2004-17B.Item Performance Testing of Experimental Dowel Bar Retrofit Designs Part 2 - Repeatability and Modified Designs(2003-12-01) Pophen, Nicholas A; Snyder, Mark B; Schultz, Arturo EEffective load transfer across Portland cement concrete pavement joints significantly decreases pavement deterioration. Dowel bars placed transversely across a joint or crack provide a mechanism for effective load transfer to take place. Dowel bars are used in new construction as well as retrofitted into existing pavements for restoration of load transfer. Areas of concern with using dowel bars include high costs, due to the labor-intensive procedure of retrofitting, and corrosion associated with standard mild steel epoxy-coated dowels. This research addresses these problems by evaluating four dowel bar details tested in an accelerated manner. Retrofit testing was performed using mild-steel epoxy coated dowels and fiber reinforced polymer (FRP) dowels. The details tested provide comparisons among dowel bar materials, depth of placement, number of dowels used, and dowel diameter. Verification testing of previously tested details is also presented. Relates to 2004-17A.Item Rapid Assessment and Distortional Stresses in Multi-Girder Steel Bridges(2003-06-01) Severtson, Benjamin; Beukema, Frederick; Schultz, Arturo EMulti-girder steel bridges are found as part of the transportation infrastructure of countries throughout the world. These bridges are typically constructed with a steel reinforced concrete deck rigidly attached to the top flange of steel girders. The deck and the transverse steel members distribute loads laterally between bridge girders. The weld connecting transverse stiffeners to the girder web are commonly terminated several inches away from the girder flanges to avoid overlapping with the web-to-flange connection weld, leaving a short, unstiffened portion of the girder web--the web gap. The large flexibility of the web gap region relative to the other components forces it to accommodate the majority of the distortion. Since 1998, several research efforts have investigated methods for predicting the amount of web gap stress a bridge will experience during its service life. Phase I of this research resulted in a simple equation for estimating web gap stress using data collected during field testing and subsequent finite modeling of a skew supported bridge with staggering bent-plate diaphragms. Phase II produced an approximate method for predicting diaphragm differential deflection of skew supported bridges with bent-plate diaphragms. The combined result of Phase I and Phase II was a useful method for predicting peak web gap stress in skewed multi-girder steel bridges with staggered bent-plate diaphragms. The next step was to develop a reliable procedure for the rapid assessment of distortional stresses in steel bridges that includes a test of the applicability of this procedure to bridges with geometries differing from those that formed the basis of the previous research. As a consequence of this most current research, the authors propose changes and recommend modifications of previously developed methods of field measurement and assessment.