Federal Highway Administration Guidelines Research Articles

An automated approach for the design of Mechanically Stabilized Earth Walls incorporating metaheuristic optimization algorithms

Considered as cost-efficient, reliable and aesthetic alternatives to the conventional retaining structures, Mechanically Stabilized Earth Walls (MSEWs) have been increasingly used in civil engineering practice over the previous decades. The design of these structures is conventionally based on engineering guidelines, requiring the use of trial and error approaches to determine the design variables. Therefore, the quality and cost effectiveness of the design is limited with the effort, intuition, and experience of the engineer while the process transpires to be time-consuming, both of which can be solved by developing automated approaches. In order to address these issues, the present study introduces a novel framework to optimize the (i) reinforcement type, (ii) length, and (iii) layout of MSEWs for minimum cost, integrating metaheuristic optimization algorithms in compliance with the Federal Highway Administration guidelines. The framework is conjoined with optimization algorithms such as Genetic Algorithm (GA), Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), and Differential Evolution (DE) and tested with a set of benchmark design problems that incorporate various types of MSEWs with different heights. The results are comparatively evaluated to assess the most effective optimization algorithm and validated using a well-known MSEW analysis and design software. The outcomes indicate that the proposed framework, implemented with a powerful optimization algorithm, can effectively produce the optimum design in a matter of seconds. In this sense, DE algorithm is proposed based on the improved results over GA, PSO, and ABC.

FE Analysis of Back-to-Back Mechanically Stabilized Earth Walls Under Cyclic Harmonic Loading

Back-to-back mechanically stabilized earth walls (BBMSEW) are encountered in bridge approaches, ramp ways, rockfall protection systems, earthen dams, levees and noise barriers. However, available literature studies and design guidelines for BBMSEW are limited and not supported by the numerical modeling when back-to-back walls perform interaction. Under static condition, the distance between two opposing walls is a key parameter used for determining the analysis methods of BBMSEW in the Federal Highway Administration Guidelines. Moreover, existing design methodologies do not provide a clear and justified answer how the required tensile strength of reinforcement and the external stability change with respect to the distance of the back-to-back walls under seismic conditions. For this purpose, an attempt has been made, in this paper, to analyze the performance of BBMSEW under earthquake loading conditions using a geotechnical finite element code, PLAXIS 2D. The main focus of this research is to investigate the effect of the reduction of the distance between the opposing walls on internal and external stability of BBMSEW under harmonic cyclic loading. Parametric studies were carried out by varying the distance, associated with different BBMSEW width to height ratio, to investigate its effects on the behavior of interacted walls. The effect of the height of walls was separately presented. By keeping the distance between walls as constant, the influences of the peak ground acceleration and frequency of the harmonic cyclic loading were also investigated. The results were evaluated in terms of horizontal walls displacements and the tensile loads on the reinforcement layers.

Instability of steel gusset plates in compression

As a result of the structural failure of the I-35W Bridge in Minneapolis in 2007, the Federal Highway Administration (FHWA) issued guidelines for the load rating of gusset plates and recommended that the capacity of these plates on non-redundant steel truss bridges be verified. The purpose of this study is to examine the buckling behaviour of steel gusset plates in greater detail, accounting for parameters that were not explicitly included in the guidelines, such as initial deformations of the gusset plate, stiffness of the framing members, load distribution from the framing members to the plate and load eccentricity. For this purpose, a finite-element model of a gusset plate was developed and verified against experimental measurements. Results show that, for in-plane compressive loads with no moment and no eccentricity, the FHWA guidelines for load rating are conservative and safe for initial out-of-plane deformations up to one plate thickness.

The Impact of Intersection Design on Simulated Driving Performance of Young and Senior Adults

Purpose. The Federal Highway Administration (FHWA) proposed guidelines for highway design to increase the safe driving ability of older drivers; however, little empirical evidence exists to support the effectiveness of these guidelines. The purpose of this study was to investigate the effects of implementing these guidelines (in 4 pairs of intersections) on safe driving performance of older and younger drivers using a high-fidelity driving simulator. Design and Methods. We replicated four intersection pairs (improved versus unimproved) in a high-fidelity, virtual reality driving simulator. Simulator scenarios were created from actual road locations, replicating road geometrics and traffic control devices. The simulator's controls were integrated with an actual vehicle to make the driving experience as realistic as possible. Kinematic measures were obtained from the simulator in conjunction with driving errors recorded by trained driving evaluators sitting in the cab of the car. Thirty-nine subjects, 19 younger and 20 older adults, participated in the study. Results. For the kinematic data we found greater lateral control, as indicated by significantly smaller maximum yaw during the turn phase, at all of the improved intersections when compared to the unimproved intersections. We found some significant age differences, but mostly in only one of the intersection-pairs. For the behavioral data, there were significant differences in driving errors between improved and unimproved intersections in two intersection-pairs; however, there were no significant differences in driving errors between the older and younger drivers. Implications. The findings suggest that both young and older drivers may benefit from roadways with safety features recommended by the FHWA guidelines as indicated by the increased lateral control of the vehicle when negotiating these intersections. These findings generate critical information for those involved in the design of roadway systems.

The Impact of Roadway Intersection Design on Driving Performance of Young and Senior Adults

The Federal Highway Administration (FHWA) proposed highway design guidelines to increase safe driving ability of older drivers, but little empirical evidence exists to support these guidelines. Using kinematics measures from an instrumented vehicle and on-road evaluations, the authors examined the safety effects of improved versus unimproved intersections in older (65–85) and younger (25–45) drivers. Kinematics measures showed that 4 maneuvers had significantly poorer lateral stability for the unimproved conditions, and significantly greater speed for the improved conditions. Behavioral measures showed that drivers had significantly fewer errors for 2 improved left-turn maneuvers, and fewer total errors overall, with older drivers having a higher mean number of errors. These findings suggested that the FHWA guidelines for safe road conditions result in safer driving by older and younger adults.

Case-based reasoning in steel bridge engineering

The current inventory of the Ohio Department of Transportation (ODOT) contains about 12000 bridges. The great majority of the bridges rated by ODOT engineers are based on the working stress design (WSD) method. The new Federal Highway Administration guidelines require that all bridge ratings be done using the load factor design (LFD) method. Consequently, thousands of bridges have to be re-rated according to the LFD code. The WSD-based data files for existing bridges do not contain the detailed information about steel sections and cross frames needed for the LFD-based rating. In this research a case-based reasoning (CBR) system has been developed to assist the bridge engineer in converting the WSD-based ratings for existing bridges to new LFD-based ratings. A domain model has been created to represent the ODOT standard design cases of bridges.

Service Life and Impact of Virginia Environmental Exposure Condition on Paint on Steel Girder Bridges

A number of state departments of transportation (DOTs) have established bridge management systems (BMSs) to assist in prioritizing and optimizing bridge improvement programs within budgetary constraints. Several factors, including age, traffic, and environment, have been identified in current BMS literature as having a direct impact on the deterioration of bridge components or elements. However, no formal methodology—using bridge inspection data—exists to determine the effects of the environment. Estimating bridge element service lives without considering environmental effects may lead to biased estimates. Further, existing deterioration models are incapable of using the nonnumeric element level inspection data (G=good, F=fair, P=poor, and C=critical), which most state DOTs have been collecting for nearly 30 years per Federal Highway Administration guidelines. A methodology is proposed using statistical analysis to determine the effects of environmental regions on mean service life estimates of paint on steel girder bridges, using bridge inspection field data collected by bridge inspectors. The data were based on the nonnumeric condition appraisal (G-F-P-C) format used for a bridge element or protective system condition evaluation. The methodology proposed an environmental classification system and service life estimates for use in BMS programs.

Comparison of Load Restriction Timings Determined Using FHwA Guidelines and Frost Tubes

The Federal Highway Administration (FHwA) method and frost-tube measurements are used in Wisconsin to determine the timing and duration of spring load restrictions. In both methods, depth of freeze or thaw is used to determine when to apply load restrictions and to determine their duration. Average daily air temperatures are used in the FHwA method to predict the start and end of freeze and/or thaw. Frost tubes are used to directly determine depth of freeze and/or thaw. An analysis is conducted to compare these two methods using air-temperature data (for the FHwA method) and frost-tube data obtained in Wisconsin. The analysis shows that differences exist between predicted (FHwA method) and measured (frost tubes) freeze and thaw conditions. The FHwA method is early (unconservative) in predicting the start of freeze and late (unconservative) in predicting the start of thaw. However, the method is late (conservative) when used to predict the end of thaw. A case history is also presented to compare the two methods.

Environmental Analysis by State DOT's—A Survey

State departments of transportation are found to comply with Federal Highway Administration guidelines governing preparation of environmental documents in varying degrees. The 50 states were querie...