1,720,997 research outputs found
Evaluation of the Performance of A709 Grade 65 QST Bridge Steel
Get PDFThe primary goal for this project was to evaluate the efficacy of A709 Grade QST 65 steel for use in Iowa bridge projects. The objectives of the project were as follows: Identify the current state of use of A709 Grade QST 65 steel in bridge projects; Identify the ductility and strength characteristics of A709 Grade QST 65 steel through full-scale laboratory testing; Identify the fatigue characteristics of A709 Grade QST 65 steel through cyclic fatigue testing; Observe and compare bridge construction similarities and differences to conventional steel construction using a new bridge planned over Sand Creek in Buchanan County, Iowa; Compare relative costs of using A709 Grade QST 65 steel versus conventional steel; and, Measure the live load response at various points in time on the Sand Creek Bridge, which was constructed using A709 Grade QST 65 steel. The ductility and strength of the steel was observed through the various laboratory tests completed for this project as well as the testing performed by others. Minimum requirements for this steel grade have been established, and the results of this study indicate that the requirements were met and surpassed. The modified design of this first-in-the-nation bridge using Grade QST 65 steel over Sand Creek allowed for a reduction in beam size for this relatively short-span, low-traveled bridge due to the increased strength of the steel beams. The total steel cost for these beams resulted in a 20% material cost savings. The results should give confidence to engineers considering use of this steel grade on bridge construction projects with longer spans and higher traffic counts
Investigation of high-strength bolt-tightening verification techniques : tech transfer summary.
Get PDFSPR RB07-014The primary objective of this project was to explore the current state-of-practice and the state-of-the-art techniques for high-strength bolt tightening and verification in structural steel connections. This project was completed so that insight could be gained on available technologies that could lead to investigating the feasibility of developing and implementing new alternatives
Investigation of the Causes of Transverse Bridge Deck Cracking
Get PDFTransverse cracks in concrete bridge decks sometimes initiate in the early stages of the bridge service life, usually just after construction. Cracks in the bridge deck can accelerate the deterioration of the deck concrete, provide a direct pathway for the intrusion of water and chlorides to the deck reinforcement, and detract from the aesthetics. This eventually results in increased maintenance costs and reduced bridge service life. The goal of this research was to identify factors that consistently lead to the formation of early-age transverse cracks for mitigation in the future. To obtain a comprehensive evaluation and include as many factors as possible in the research, the primary research investigation was conducted in three stages with varying numbers of bridges and factors considered in each stage. The first stage was carried out on 2,675 bridges constructed in Iowa between 1900 and 2020. The goal of this stage was to identify the correlation between deck cracking and six parameters: deck concrete type (high-performance concrete [HPC] or non-HPC), maximum span length, maximum structure length, Iowa Department of Transportation (DOT) District, year built, and main structure type. The second stage was conducted to include additional bridge parameters\u2014but with a smaller number of bridges. A group of 20 bridges was selected after reviewing inspection reports for 116 bridges constructed between 2013 and 2018. Various bridge parameters in three main categories, structural, construction, and material, were investigated. The third stage was carried out based on data collected from six field visits while deck concrete was being placed. The parameters investigated in this stage included evaporation rate (lb/ft2/h), air temperature (\ub0F), concrete temperature (\ub0F), relative humidity (%), and wind speed (mph). The results from the three investigation stages were compared with the research results documented in another Iowa DOT report. Based on the research findings from each stage of investigation, the various parameters were classified as having either direct correlation, no correlation, slight positive correlation, or slight negative correlation
Development of a Rapid Assessment Tool for Pile Capacity and Stability in Response to Scour Situations
Get PDFThe Iowa Department of Transportation (DOT) rating engineer is sometimes asked by field personnel to make quick decisions regarding pile capacity and stability when scour is identified around bridge pile bents. A numerical evaluation program was developed and implemented to offer a user-friendly assessment tool that can be used to quickly evaluate pile strength. The numerical program consists of finite element (FE) models established for steel H-piles with or without concrete encasement with consideration of linear and non-linear buckling and behavior. The research team validated the FE models against capacities calculated based on the provisions outlined in the American Institute of Steel Construction (AISC) Steel Construction Manual. After validating the FE modeling techniques, the researchers performed parametric studies to understand the influence of concrete encasement on the pile buckling strength. The individually encased pile bents in the P10L standard with five H-pile sections (HP10
742, HP10
757, HP12
753, HP14
773, and HP14
789) were utilized for the parametric studies. These studies took into account different combinations of the unbraced pile lengths and concrete encasement lengths. The relationships between buckling strength of the steel H-piles with concrete encasements under concentric and eccentric loading conditions were derived from the results of the parametric studies. The stiffness contributions of concrete encasements are not taken into account using the AISC Steel Construction Manual and American Association of State Highway and Transportation Officials (AASHTO) load and resistance factor design (LRFD) specifications for estimating the buckling strength of steel H-piles. The pile assessment tool that the researchers developed to quickly calculate the buckling strength of steel H-piles with concrete encasements includes the relationships between the buckling strength of steel H-piles with concrete encasement lengths for five cross-sections and two loading conditions. For the user\u2019s convenience, the researchers developed a graphical user interface for the tool, which requires the input of four parameters: loading eccentricity, H-pile section type, unbraced pile length, and concrete encasement length. This pile assessment tool can be utilized to quickly calculate the pile capacity and to assist state rating engineers in making rapid decisions regarding pile capacity
Field Demonstration of an Innovative Box Beam Connection
Get PDFThe objective of this project was to demonstrate the field implementation of an innovative longitudinal joint design developed during a previous phase of research. To achieve this objective, a yet-to-be-constructed box girder bridge in Washington County, Iowa, was selected to demonstrate the construction and performance of the joint. In order to evaluate the joint\u2019s performance, a seven-day period of field monitoring was conducted shortly after construction was completed. In addition, long-term evaluation of the joint was performed through the completion of live load field tests and deck concrete crack inspections. The live load tests were performed every 12 months, and crack inspections of the bridge deck were performed every six months. During the field tests and monitoring, temperature, strain, and displacement data were collected at critical locations and analyzed to evaluate joint performance with respect to cracking resistance and load distribution. The results indicate that the innovative joint is sufficient to resist early-age longitudinal joint cracking. Joint cracks that were seen on another box girder bridge with traditional narrow joints were not observed in this case. The innovative joint performed well with respect to load distribution. The whole bridge superstructure behaved as an integrated structure regardless of the transverse location of a passing truck. In addition, the box girder bridge was constructed using integral abutments, which added transverse restraint and positively affected the strain distribution at the joint ends
Evaluation of the Use of IRI Data to Estimate Bridge Dynamic Impact Factor (DIF)
Get PDFThe objectives of this project were to correlate international roughness index (IRI) data (which are widely collected and directly related to bridge deck roughness) to impact factors and develop a process for determining the impact factor to use for all bridges in Iowa. To achieve the project objectives, a sample of 20 bridges was selected for bridge monitoring to collect dynamic strain data. To estimate the static strain data, the locally weighted scatterplot smoothing (LOWESS) function was used to smooth the dynamic strain time history. The dynamic impact factor (DIF) value was then calculated using maximum dynamic and static strain data. IRI data were extracted from PathWeb, a web-based application provided by the Iowa Department of Transportation (DOT) for all bridges considered in the field test program. Once the bridge was identified in PathWeb, the IRI data from four locations near each bridge deck approach were extracted and used to study the relationship between the IRI and DIF. Based on the results from this research, these were the key findings: \u2022 The DIF value decreases as the bridge skew angle increases. Based on linear regression, the DIF value decreases about 0.037 to 0.043 per 10-degree increment of bridge skew. \u2022 The DIF value decreases as the bridge deck condition index increases, meaning that the dynamic response is lower when the bridge deck condition is better. \u2022 For bridges with zero skew, the DIF value increased by 0.006 per 100 in/mile increment of the IRI value. According to the research findings, an equation was developed for the prediction of DIF on existing bridges with consideration of the bridge skew and the maximum IRI value near the bridge deck approach. Although the proposed equation was validated using data from 13 bridges, the researchers recommend using the equation with the limitation that the actual bridge dynamic response could deviate \ub110% from the equation predicted value
Investigation of the effect of speed on the dynamic impact factor for bridges with different entrance conditions : tech transfer summary.
No full textInTrans project 14-521The dynamic interaction of vehicles and bridges results in live loads being induced into bridges that are greater than the vehicle\u2019s static weight. Consideration of this phenomena has been included in the American Association of State Highway Transportation Official (AASHTO) Bridge Design Specifications for many years. While the specifications have been modified over the years, questions remain about how much of an effect dynamic interaction plays.In recognition of this interaction, the Iowa Department of Transportation (DOT) currently requires that, in some instances, permitted trucks slow to five miles per hour and span the roadway centerline when crossing a bridge. Such a slowing is consistent with current specifications, which indicate that a lower dynamic impact factor may then be used for permitted vehicles. The positive effect of this is that larger loads may be allowed to cross Iowa\u2019s bridges.However, this practice has other negative consequences. For example, the reduction in speed increases the potential for crashes, uses additional fuel, and, in some cases, may be downright impractical for bridges with high traffic volumes. In addition, the reduction in speed can have an impact on the orderly flow of traffic.Phares, Brent M. orcid.org/0000-0001-5894-4774)Deng, Yaohua (orcid.org/0000-0003-0779-6112
Investigation of the effect of speed on the dynamic impact factor for bridges with different entrance conditions
Get PDFThe dynamic interaction of vehicles and bridges results in live loads being induced into bridges that are greater than the vehicle\u2019s static weight. To limit this dynamic effect, the Iowa Department of Transportation (DOT) currently requires that permitted trucks slow to five miles per hour and span the roadway centerline when crossing bridges. However, this practice has other negative consequences such as the potential for crashes, impracticality for bridges with high traffic volumes, and higher fuel consumption. The main objective of this work was to provide information and guidance on the allowable speeds for permitted vehicles and loads on bridges.A field test program was implemented on five bridges (i.e., two steel girder bridges, two pre-stressed concrete girder bridges, and one concrete slab bridge) to investigate the dynamic response of bridges due to vehicle loadings. The important factors taken into account during the field tests included vehicle speed, entrance conditions, vehicle characteristics (i.e., empty dump truck, full dump truck, and semi-truck), and bridge geometric characteristics (i.e., long span and short span). Three entrance conditions were used: As-is and also Level 1 and Level 2, which simulated rough entrance conditions with a fabricated ramp placed 10 feet from the joint between the bridge end and approach slab and directly next to the joint, respectively. The researchers analyzed and utilized the field data to derive the dynamic impact factors (DIFs) for all gauges installed on each bridge under the different loading scenarios. Based on the calculated DIFs and the change trends for the associated important factors, the conclusions were as follows:\uf0b7 The DIF increases with the increase of truck speed, entrance condition level, and bridge span length.\uf0b7 For all investigated bridges under Level 1 and Level 2 entrance conditions, the DIFs exceeded 0.3; under the As-is entrance condition, the DIFs were less than 0.3 for the steel and concrete girder bridges and less than 0.1 for the concrete slab bridges.\uf0b7 The empty dump truck induced the greatest impact factors, followed by the full dump truck and then the semi-truck.\uf0b7 To limit the DIF to no more than 0.1, for all bridge types, the allowable truck speeds are 30 mph for As-is entrance conditions and crawl for bridges with Level 1 and Level 2 entrance conditions.\uf0b7 The researchers recommend that currently collected road roughness information be examined for use as an indicator of entrance condition. If successful, the international roughness index (IRI) data could then be used to determine the speed limitation to put in place as well as which DIF values to use in permitting analysis.Yaohua Deng and Brent M. Phares (orcid.org/0000-0003-0779-6112 and orcid.org/0000-0001-5894-4774
Assessment, Repair, and Replacement of Bridges Subjected to Fire
Get PDFAlthough bridge fires are not frequent events, they pose impacts on safety, traffic flow, and the economy given bridge repairs or replacement can be costly. A lack of information and the tools needed to evaluate fire damage to concrete bridges and to aid in decisions for both immediate and long-term use of fire-damaged bridges was the impetus for this research. On October 30, 2019, multiple items within a homeless encampment were set on fire beneath the I-29 northbound bridge over the Perry Creek conduit in Sioux City, Iowa. The fire was exacerbated when a propane tank became engulfed by the flames. The bridge girders and deck were particularly vulnerable to the ground fire because of the minimal ground clearance (about 6 ft) in comparison to that of most other bridges. Despite this unfortunate incident, it provided an opportunity to learn more about the residual condition and strength of the bridge girders through a research study. The Iowa Department of Transportation (DOT) elected for the removal and replacement of the bridge, which allowed for girders to be removed and undergo testing. Three fire-damaged girders were selected from the bridge, carefully removed, and transported to the Iowa DOT maintenance yard in Ames, Iowa. Each girder was visually assessed and selected based on the apparent level of damage incurred: one low-level, one mid-level, and one higher-level. The goal was to compare and contrast apparent levels of damage and assess the impacts each level of damage had on the serviceability and strength of the girder. This report provides the results and recommendations resulting from the completed load testing. The results will assist in providing more technical information with respect to fire-damaged girders to help bridge owners to develop guidelines for assessment and repair
Study of the Impacts of Implements of Husbandry on Bridges Volume III: Appendices
Get PDFThe objectives of this study were to develop guidance for engineers on how implements of husbandry loads are resisted by traditional bridges, with a specific focus on bridges commonly found on the secondary road system; provide recommendations for accurately analyzing bridges for these loading effects; and make suggestions for the rating and posting of these bridges. To achieve the objectives, the distribution of live load and dynamic impact effects for different types of farm vehicles on three general bridge types\u2014steel-concrete, steel-timber, and timber-timber\u2014were investigated through load testing and analytical modeling. The types of vehicles studied included, but were not limited to, grain wagons/grain carts, manure tank wagons, agriculture fertilizer applicators, and tractors. Once the effects of these vehicles had been determined, a parametric study was carried out to develop live load distribution factor (LLDF) equations that account for the effect of husbandry vehicle loads. Similarly, recommendations for dynamic effects were also developed. The live load distribution factors and dynamic load allowances are covered in the first volume of the report. Finally, suggestions on the analysis, rating, and posting of bridges for husbandry implements were developed. Those suggestions are covered in the second volume of the report. This third volume of the report contains six appendices that include the 19 mini-reports for field tested and analytically modeled steel-concrete, steel-timber, and timber-timber bridges, the farm implement and bridge inventories for the project, and survey responses
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