AASHTO Specifications Research Articles

Effect of live loads on top slab of cast-in-place reinforced concrete box culverts

Reinforced concrete box culverts (RCBCs) designed according to old codes, using lighter truck weights (e.g., H15), may require posting when rated for current design and permit vehicles. When load ratings are calculated based on current AASHTO Specifications, they can be negatively affected by the conservative live-load attenuation through soil fill. This study evaluates the positive bending strains induced by live-load distribution through soil fill when load rating cast-in-place (CIP) RCBCs. Eighteen (18) single and multicell RCBCs in Kentucky were load tested and the effects of truck live loads analyzed. Fill heights, HF, varied from 0 m (0 ft) to 3.57 m (11.7 ft), clear cell spans, S, from 3.05 m (10.0 ft) to 6.71 m (22.0 ft), and culvert spans from 6.71 m (22.0 ft) to 18.59 m (61.0 ft). Field data were collected using strain gauges attached to the interior surfaces of culverts. Irrespective of how many cells the RCBCs had, strain variations with fill height in the top slabs were similar. At fill heights greater than 3.05 m (10.0 ft), maximum strains in the top slabs measured less than 10 microstrain, a value at which live-load effects are considered negligible. Combining live-load strains measured on the Kentucky culverts with ones from field tests in Missouri and Louisiana, a live-load tensile strain envelope is proposed to load rate the top slabs of RCBCs for positive bending when cell spans are less than 4.6 m (15.0 ft).

Evaluation of Linear Amplitude Sweep data analysis techniques and failure criteria for High Polymer-Modified binders

High Polymer Modified Binders (HiPMBs) have gained attention for their resilience to environmental and traffic stressors, yet their fatigue cracking resistance remains insufficiently explored. Even though the Linear Amplitude Sweep (LAS) test is an AASHTO standardized procedure, various data analysis techniques and failure criteria can be found in the literature. It is unclear whether they produce divergent results and whether any of them provide better insights into bitumen behavior. The research showcased in this paper aimed to assess the factors affecting the evaluation of HiPMBs' fatigue life through the LAS test. Additionally, asphalt concrete was produced with bitumen previously tested and subjected to Push-Pull (PP) fatigue cracking evaluation for direct comparison. Results show significant differences between analysis methods, regardless of the failure criteria applied. The methods that rely on the Viscoelastic Continuum Damage (VECD) analysis were affected by the inaccuracy of the material integrity function fitting. The failure criterion significantly impacts the ability to detect the benefits of the high polymer content, which becomes increasingly noticeable for failure criteria different from those suggested in the AASHTO specification. Meanwhile, the Fatigue Resistance Energy Index (FREI) approach has a great advantage of not being tight to the VECD formulations and was able to capture the differences between the Neat Binders (NBs) and the HiPMBs. As for the corresponding binders' performance on the HMA level, similarities in the ranking were noticed; however, no full agreement was recognized.

Design method for cross-section behaviour of hybrid I-girders under uniform bending

Hybrid steel I-girders, characterised by different strength grades for the flange and web, offer the potential to optimise material utilisation in various loading scenarios. The current American and European standards for steel bridges (AASHTO specification and Eurocode 3) have incorporated specific provisions for the design of hybrid I-girders with the web strength grade lower than the flange. Based on the data obtained from the validated numerical investigation, the limiting slenderness ratio for cross-section classification and applicability of the designated bending moment resistance (flexural strength) in standards are assessed. The assessment results reveal that the compact/Class 1 sections with flange yield strength of 690 N/mm2 fail to meet the current codified ductility requirement, and the non-compact flange slenderness limits in AASHTO specification are demonstrated to be excessively lenient. A reduction factor of 1.2 is suggested to narrow down the Class 1 width-to-thickness ratio in Eurocode 3 for I-girders with compression flange steel grade equivalent to S690. Furthermore, the design moment expression of the Direct Strength Method (DSM) is proposed for the cross-section resistance design of hybrid I-girders, and the design approach for the Continuous Strength Method (CSM) is also derived through analytical analysis. Instead of addressing the slenderness of the flange and web individually, the DSM and CSM adopt the concept of overall cross-section slenderness, which allows for a more accurate consideration of the flange-web interaction and offers the potential to streamline the calculation process for cross-section resistance. The statistical and reliability analyses indicate that all the design methods could achieve the reasonable moment resistance predictions for the cross-section resistance of hybrid I-girders.

Transient Thermal Analysis of Concrete Box Girders: Assessing Temperature Variations in Canadian Climate Zones.

This study examines the temperature distributions and thermal-induced responses in reinforced concrete bridge elements, focusing on the Canadian climate regions. The Canadian Highway Bridge Design Code (CHBDC) currently utilizes a fixed thermal gradient profile that does not account for regional climatic variations. Historical environmental data determines the effective maximum temperatures in the CHBDC. In order to investigate temperature behaviors and distributions, a transient finite element (FE) model is developed using recorded and calculated 3-month thermal loads data for representative cities in different climate regions. The results indicate that the predicted daily maximum effective mean temperatures and extreme daily positive vertical thermal gradients do not align. A linear correlation exists between the daily maximum effective mean temperature and the daily maximum air temperature, with a coefficient of determination (R2) of 0.935. The proposed effective mean temperatures obtained from the FE thermal analysis are higher than the CHBDC recommendations. New thermal gradient profiles are proposed for Canadian climate zones, consisting of two straight lines and a linear gradient at the top and bottom sections. A comparison between the proposed profiles and the CHBDC and AASHTO specifications reveals that a single fixed thermal gradient profile is inadequate to account for the variation in thermal gradients across Canadian climate regions.

Experimental and Analytical Studies of Continuous Steel-Stringer Lateral-Torsional Buckling Resistance

In the 1950s and 1960s, some Louisiana’s bridges were constructed using steel twin-girder or truss systems, in which floorbeams are carried by the main members and continuous (spliced) stringers are supported by the floorbeams. The main members are either two-edge (fascia) girders or trusses. One of the byproducts of this type of design is that stringer bottom flanges are in compression in the negative moment region over the floorbeams, which could result in lateral torsional buckling (LTB) should inadequate lateral bracing be provided. When the continuous stringers are load-rated using AASHTOWare Bridge Rating analysis software (BrR 7.1), their LTB resistance is calculated in accordance with American Association of State Highway Officials (AASHTO) LRFD Bridge Design Specifications, which do not account for potential bracing provided by a noncomposite deck and could underestimate flexural strength. As a result, the rating may be low enough to require restrictive load posting or even bridge closure. This paper summarizes extensive experimental and numerical studies investigating the behavior of this type of floor system by testing two-span, continuous, steel stringers in a grillage that included three stringer lines, an interior transverse support (floorbeam), and transverse diaphragms at the end supports. The tests and finite-element analysis studies encompassed a variety of unbraced lengths and support conditions with steel diaphragms or timber ties acting as bracing members. The findings demonstrated that, for the systems examined, minimal bracing could substantially enhance LTB resistance and supported the use of higher flexural strengths than those currently predicted using AASHTO Specifications. This paper illustrates the use, challenges, and successes in LTB modeling beams with various support and bracing conditions. The most flexible cases were the most difficult to achieve close agreement with experimental results.

Terrace Soil Suitability for Highway Construction: Case Study in Lesser Himalaya (CPEC Project E-35), North Pakistan

In this study, terrace soil investigation was carried out in project E-35 (phase-I) China-Pak Economic Corridor, Lesser Himalayas, North Pakistan. The methodology in current research is based on tests that include sieve analysis, plastic index, proctor, California Bearing Ratio, Los Angeles, sand equivalent and specific gravity. The results of these tests for different layers were compared with AASHTO and NHA specifications. The results show that the embankment, subgrade and subbase layers were composed of silt, sand and gravel, respectively while the aggregate base coarse was composed of sand, aggregate and less amount of fine clay material. The sieve analysis test shows that soil and aggregate base coarse has less clay with high silt, sandy material and index plastic to low plastic, which is appropriate for the construction. The California Bearing Ratio shows that the soil and aggregate base coarse have high load-bearing capacity. The Los Angeles abrasion reveal that the sub base and aggregate base coarse are resistive. The sand equivalent shows that aggregate base coarse has high sand material. The specific gravity illustrates that aggregate base coarse material is denser. The current study shows that terrace soil is suitable for the construction of the road in project E-35 (phase-I) China-Pak Economic Corridor.

Suitability of the Lower Zab River Sediments for Concrete Works / Southwest of Kirkuk - Northern Iraq

An Engineering study was carried out for five stations in the Lower Zab basin, southwest of Kirkuk, to determine the viability of the Quaternary age sediments for concrete works. The geotechnical evaluation results included that the coarse aggregate's grain size analysis is identical to the gradient class (63.0 mm) according to the [1] classification. As for the gradation of fine aggregate for the sediments of the study area, the results of the granular gradient of the samples after matching them with the limits of AASHTO specification showed that they are identical to the specification with slight differences on some sieves. The elongation and flatness tests showed that the highest percentage of the longitudinal shape is (19.2%) and flat-shaped particles is (28.8%), within permissible limits according to British standard [2], the specific gravity for coarse aggregate was between (2.60 - 2.64) and saturated specific gravity (2.61 - 2.65), and the values of specific weight for fine soil ranged from (2.72 - 2.64) which is suitable for use in concrete works. The results of the laboratory test of the durability tests - The Los Angeles test for the samples showed that the highest percentage for weight loss was (20%), which is suitable for use in the concrete according to the Iraqi standard [3], the results of the laboratory test for stability showed that the percentage of weight loss for coarse aggregate (gravel) by the effect of sodium sulfate solution and for the number of 5 cycles of the samples ranged between (8.3% - 4.1%), which is valid for use in concrete works according to the American specification [4]. The results of the resistance tests - the point load test for stations (S1, S3, S4) within the classification range of very strong - extremely strong, and the two stations (S2, S5) within the class strong - very strong - extremely strong compared to the classification of [5], and they are good for concrete works. It was found from the results of the chemical tests the gypsum content, organic matter content, Total soluble salts, and the sulfate content of the samples of the study area are suitable to for concrete works according to British Standard [6], which is suitable for concrete works, testing the compressive strength of concrete cubes ranged between (24.93 - 18.22 MPa) for age seven days and ranged between (33.02 - 29.76 MPa) for 28 days for reference mixture, Which is (4:2:1 by weight). According to the Iraqi standard specification [7], the compressive strength values of the samples are suitable for regular unreinforced concrete, and in comparison with [8] classification, it was apparent that the concrete produced is of moderate endurance. And suitable for concrete works According to [9].

A Critical Evaluation of Moment Gradient (Cb) Factror Calculation Procedures for Singly Symmetric I-Section Members

This paper explores the manual calculation of the elastic lateral-torsional buckling resistance of prismatic singly symmetric I-section members having a variation in the bending moment between the brace points. The paper shows that the quarter-point moment gradient factor, Cb, equation in the AISC Specification (2016), as modified by its Commentary, is inaccurate for reverse-curvature bending of singly symmetric I-section members. In addition, the paper explains that the Cb equations in the current AASHTO Specifications (2020) provide some accounting for the different patterns of compression in the separate flanges for cases involving moment reversal. To rectify the limitations of the ASC and AASHTO methods, the paper recommends a modified form of an alternative quarter-point Cb equation proposed by Wong and Driver (2010). For singly symmetric cases involving moment reversal, the terms in the quarter-point equation are replaced by the ratio of the moments to the corresponding elastic buckling moment based on Cb = 1, considering which flange is in compression at each of the locations where the moments are sampled. The studies show that the Wong and Driver equation, with this modification, provides substantially improved accuracy compared to the existing AASHTO and ASC equations for reverse-curvature bending with slightly less calculation effort. In addition, the paper demonstrates the accuracy of the direct application of the Wong and Driver equation for single-curvature bending cases.

Finite Element Model Updating of RC Bridge Structure with Static Load Testing: A Case Study of Vietnamese ThiThac Bridge in Coastal and Marine Environment.

Diagnostic load testing refers to the use of the measured historical responses of the structure in the field data to better understand its dynamic and static structural behaviours. It is important and necessary to predict the health state, load capacity, and aging of the structure by updating the finite element (FE) model, which can give useful information to aid the design of retrofits and the maintenance of the existing bridge in the future. The paper presents an update of the full-scale FE model for the reinforced concrete (RC) bridge structure over the seawater river based on the experimental strains under the static load testing in which the representative FE model of the actual structure is determined from the optimisation procedures. The optimisation variables are applied, including the cross-sectional properties and concrete material calibrated through the genetic algorithm (GA) optimisation in the MATLAB software, which interfaces with the FE modelling in the scripting of the SOFISTIK TEDDY software automatically. The bending moments at the mid-span of the RC girders are determined in the FE modelling to compute stresses, which are compared with the measured stresses through optimisation scenarios with a percentage error of the objective function less than 10%. The measured data of concrete strains are recorded from reusable strain transducers installed on the mid-span girders for every bridge span, which are used to calibrate the bridge model in static load testing. The novelty of the solution is to implement innovative techniques using field data as an improved approach for calibrating automatically the analytical FE model parameters of all RC spans of the bridge until its static behaviours are very similar to those of the actual bridge. The final updated FE modelling is used to apply truck load configurations according to bridge design standards such as the AASHTO specifications, which can predict the load limits of the existing bridge structure more accurately and reliably. These proposed approaches can be applied to large bridges as well as complex structures with supporting FE analysis software and data processing software.

Predicting the Influence of Shear on the Seismic Response of Bridge Columns

In the seismic design and evaluation of bridges, a method is required for determining the shear strength of reinforced concrete columns to avoid brittle shear failures. In addition, detailed design and evaluation often require predictions of the complete hysteretic response of bridge columns to accurately model the nonlinear dynamic response of the bridge. Predictions of the shear strength of columns using the provisions of the AASHTO Specifications are compared with the reversed-cyclic loading test results of shear-critical columns. It is found that the Simplified Procedure results in very conservative predictions of the seismic shear strength. The General Procedure provides conservative and more accurate predictions of the seismic shear strength. It is suggested that the AASHTO reduction factor on the concrete contribution resisting shear for low compressive axial load levels be removed. Nonlinear finite element analysis predictions are made for a selection of rectangular and circular columns tested in reversed-cyclic loading and are compared with the experimental results. The ability of nonlinear finite element analysis to predict the reversed-cyclic loading responses of columns with a wide range of variables and having different failure modes is demonstrated.

The comparative study on the performance of bamboo fiber and sugarcane bagasse fiber as modifiers in asphalt concrete production

Highway pavement structures are expected to be adequately strong and durable for their design life which can be achieved only when the pavements are properly designed, constructed, maintained, and managed. In Ethiopia, most of the asphalt pavement is suffering from fatigue, creep, and rutting in long term. These stresses may be occurred due to the shortage in the mechanistic properties of either the binder or the asphalt mixtures as well as due to the increase in traffic loads. Failures of some roads can be attributed to the poor design of the asphalt mixes and materials being used. The properties and dosage of additive materials in hot mix asphalt affect the overall performance of pavement structure. Hence, modifying the properties of asphalt is necessary to enhance the performance of HMA. This study aims to investigate the performance of bamboo fiber and sugarcane bagasse fiber on the mechanical properties of Hot Mix Asphalt production. This research was conducted by using an experimental research design method and Non-Probability sampling techniques were adopted to collect samples. A sample preparation method of asphalt mixture specimens for asphalt mix design was performed based on AASHTO, ASTM and EN Standard specifications. The tests required were aggregate tests, a Bitumen test, Marshall test, and performance tests such Indirect Tensile Strength test and Rutting Test (RT) were conducted to evaluate a comparative study on the performance of bamboo fiber and sugarcane bagasse fiber as a modified Hot Mix Asphalt production. The preparing HMA mixes using crushed stone coarse aggregate, Fine aggregate, Mineral fillers 60/70 Bitumen, and by using bamboo and sugar cane bagasse fiber as additives were used to compare the results at a varying bitumen content of 4.5,5,5.5,6% bitumen. The Asphalt additives were used in the range from 0.2% to 0.5% of the total weight of the sample. Then, finally, the results of the laboratory were compared to standards of specifications. The optimum both fibers content obtained at 0.3% and OAC & OMF (5.2% & 4%) respectively, suggests that using both BF & SCBF fibers in asphalt concrete mixture improves the performance of asphalt pavements to resist external loads. Both fibers at 0.3% content better modify asphalt marshal stability, ITS of HMA, and Rutting resistance of AC. Finally, based on this study it was proved that the performance and properties of Asphalt concrete are affected by Fiber type and its content.

Fatigue behavior of rib-to-floorbeam welded connections in UHPC reinforced OSDs subjected to longitudinal flexural

In recent years, ultra-high-performance concrete (UHPC) has been extensively used in orthotropic steel decks (OSDs) to improve their structural characteristics and extend their fatigue lives. In the present study, an experimental investigation was conducted on three full-scale rib-to-floorbeam welded connections to study the influence of utilizing UHPC overlay on fatigue behavior of such welded connection in OSDs. Two rear axle loads of HL-93 fatigue truck codified in the AASHTO specification were applied in the tests and the effect of longitudinal flexural were considered. Fatigue tests were conducted with full fatigue performance including the failure modes, crack initiation and propagation paths, fatigue lives, and vertical rigidity degradations fully reported. The obtained fatigue test results demonstrated that the application of UHPC overlay remarkably extended the fatigue life of the studied rib-to-floorbeam connections; the fatigue lives at the test end (Nf) were extended by 74.6% under the effect of the same hot spot stress range. The vertical rigidity of the two UHPC reinforced specimens were degraded by 12.3% and 7.3% compared to 15.1% for the unreinforced specimen, indicating that the UHPC reinforced specimens still have considerable load-carrying capacities until the fatigue failure. Moreover, it is demonstrated that the FAT100 fatigue curve provided in IIW fatigue design recommendations could be employed to predict the fatigue resistance of rib-to-floorbeam welded joints in OSDs.

Vehicle Load Spectrum and Fatigue Vehicle Model of a Long‐Span Concrete‐Filled Steel Tube (CFST) Arch Bridge Based on Measured Data of Weight‐In‐Motion System

Highway traffic load, speed, and volume have been increasing continuously over the years. Because of its special structural form, the fatigue problem of a long‐span concrete‐filled steel tube arch bridge becomes more and more serious. To research the vehicle load spectrum and fatigue vehicle model of a long‐span concrete‐filled steel tubular arch bridge, the traffic data of the arch bridge were collected using the weight‐in‐motion system. The vehicle type and vehicle load in the actual traffic flow have strong stochastic characteristics, which cannot be directly applied. Therefore, according to the measured data, 10 representative models are proposed to facilitate the classification and screening of vehicle data. The wheelbase, mass, axle load, and overload data of the representative vehicle types were analysed, and the axle load distribution characteristics of vehicles in different lanes were studied. It is found that the vehicle load is not uniformly distributed in different lanes but concentrated in one lane. Moreover, a vehicle load spectrum for the fatigue assessment of the long‐span concrete‐filled steel tubular arch bridge is proposed. Based on the fatigue damage equivalence principle, a fatigue vehicle model and a simplified fatigue vehicle model of bridge heavy‐duty vehicles are proposed. Compared with the model in the AASHTO specification, it is found that the weight of the local fatigue vehicle load model is 15.1 t heavier than the vehicle model given in the specification. This study could be further referenced in bridge‐fatigue life prediction, management and maintenance, etc.

Enhancing fatigue resistance of rib-to-floorbeam welded connections in orthotropic steel bridge decks by using UHPC layer: An experimental study

This study investigates the fatigue performance of rib-to-floorbeam welded connection in orthotropic steel decks (OSDs) reinforced by using ultra-high-performance concrete (UHPC) overlay. Three full-scale rib-to-floorbeam welded connections were fabricated and tested, one specimen represents the conventional OSD type, and the other two specimens represent the UHPC reinforced OSD type, so that the effect of employing UHPC layer can be explored. One rear axle load of HL-93 fatigue truck provided in AASHTO specifications was considered in the fatigue tests. The behaviors including fatigue crack initiation and propagation process, fatigue failure mode, characteristic fatigue life, and vertical rigidity degradation were all observed in the fatigue tests. Experimental results indicated that, under the effect of the same load amplitude, three cracks were observed for the unreinforced specimen, while only one crack for UHPC reinforced specimen was detected. It was observed that using UHPC overlay significantly extended the fatigue life of the rib-to-floorbeam welded connections, where the crack initiation life (N0) and through U-rib thickness fatigue life (N1) were increased by 236 % and 268 %, respectively, under the same load range. Moreover, vertical rigidity was significantly enhanced by employing UHPC layer, which could be due to the fact that the maximum rigidity degradation of the unreinforced and UHPC reinforced specimens were 25% and 14% under the effect of 0.64 and 1.64 million load cycles, respectively.

Terrace Soil Suitability for Highway Construction: Case Study in Lesser Himalaya (CPEC Project E-35), North Pakistan

In this study, terrace soil investigation was carried out in project E-35 (phase-I) China-Pak Economic Corridor, Lesser Himalayas, North Pakistan. The methodology in current research is based on tests that include sieve analysis, plastic index, proctor, California Bearing Ratio, Los Angeles, sand equivalent and specific gravity. The results of these tests for different layers were compared with AASHTO and NHA specifications. The results show that the embankment, subgrade and subbase layers were composed of silt, sand and gravel, respectively while the aggregate base coarse was composed of sand, aggregate and less amount of fine clay material. The sieve analysis test shows that soil and aggregate base coarse has less clay with high silt, sandy material and index plastic to low plastic, which is appropriate for the construction. The California Bearing Ratio shows that the soil and aggregate base coarse have high load-bearing capacity. The Los Angeles abrasion reveal that the sub base and aggregate base coarse are resistive. The sand equivalent shows that aggregate base coarse has high sand material. The specific gravity illustrates that aggregate base coarse material is denser. The current study shows that terrace soil is suitable for the construction of the road in project E-35 (phase-I) China-Pak Economic Corridor.

Seismic fragility of concrete bridges designed to current and older Aashto specifications

Bridges are essential components of transportation systems and their unacceptable performance following a disaster may lead to disruption to relief operations. Many existing bridges all around the world were designed based on early editions of seismic codes and the performance of some old bridges following seismic events has revealed that they are seismically vulnerable. This paper provides a comparison of the seismic performance of reinforced concrete (RC) bridges designed according to recent code editions and according to earlier provisions. To this end, a probabilistic seismic safety assessment of RC bridges was conducted. Non-linear response history analyses were performed for each set of bridge samples subjected to earthquake ground motions with different severities employing three-dimensional models. The effect of the earthquake focal mechanism on the seismic vulnerability of the bridges was investigated. Moreover, fragility curves were developed for RC bridges designed according to the latest edition of the American Association of State Highway and Transportation Officials (Aashto) specifications (so-called new bridges) and those designed based on pre-1980 specifications (so-called old bridges). The fragility curves are presented in terms of the geometrical specifications of the bridges and the focal mechanism associated with input motions for both new and old bridges.

The Influence of Arch Flexibility On The Floor Deck Structural Characteristics For Composite Arch Steel Bridge

This paper presents an optimizing design for the floor deck for the composite arch steel bridge depending on the arch flexibility (the bridge’s main component). The design is based on second-order effects using nonlinear p-delta analysis. Many variables are considered in the parametric study, which is the arch’s in-plane flexibility, the out-of-plane flexibility of the arch, and the number and stiffness of the lateral bracing between the twin arches. The design has been done by graphical design software SAP2000 and based on AISC and AASHTO specifications. A numerical example is studded herein for the new proposed bridge of Batta in Al-Hilla city in Iraq which crossover Al-Hilla river for a width of 108m from bank to bank, the bridge has an overall width of 18 m including two lane-two way of 15.6 m width and walkways of 1.2 m on both sides. This study’s main objectives are the number and size of floor beams, deck thickness, and hence the overall weight of the bridge will be minimum, the goal of design is to select the lightest and most economical and practical composite floor decks. It has been concluded that the deflection decreases with the increase in the number of the floor beam, and the best result was the case of the distance between the floor beam is 1.95 m with a deflection of 71.95 mm, meaning that the flexibility is less as the number of floor beam increases. As for the change of the arch’s cross-section, the best result of the lesser girder deflection was in the case that the arch section with dimensions (0.8 x1.2x0.035) m. This indicates that the greater the moment of inertia, which leads to less deflection for cross over the main girder.

Fatigue evaluation and CFRP strengthening of diaphragm cutouts in orthotropic steel decks

The cracking at the transverse diaphragm cutout is one of the most severe fatigue failures threatening orthotropic steel decks (OSDs), whose mechanisms and crack treatment techniques have not been fully studied. In this paper, full-scale experiments were first performed to investigate the fatigue performance of polished cutouts involving the effect of an artificial geometrical defect. Following this, comparative experimental testing for defective cutouts strengthened with carbon fiber-reinforced polymer (CFRP) was carried out. Numerical finite element analysis was also performed to verify and explain the experimental observations. Results show that the combinative effect of the wheel load and thermal residual stress constitutes the external driving force for the fatigue cracking of the cutout. Initial geometrical defects are confirmed as a critical factor affecting the fatigue cracking. The principal stress 6 mm away from the free edge of the cutout can be adopted as the nominal stress of the cutout during fatigue evaluation, and the fatigue resistance of polished cutouts is higher than Grade A in AASHTO specification. The bonded CFRP system is highly effective in extending the fatigue life of the defective cutouts. The present study provides some new insights into the fatigue evaluation and repair of OSDs.

Safety Factor for Drilled Shaft Foundations Subjected to Wind-Induced Torsion

Public transportation agencies commonly use drilled shaft foundations as support of mast arm traffic signs and signal pole structures. These structures and their foundations are subjected to wind-induced torsion. Design provisions can be found in AASHTO specifications for structural supports for highway signs, luminaires and traffic signals; nevertheless, those standards do not provide guidance to estimate the torsional resistance of drilled shaft foundations, or what an appropriate factor of safety (or resistance factor) for design could be. Although load and resistance factors format is desired because AASHTO is moving in that direction, still many Departments of Transportation design requirements are based on factors of safety. In this study, a probabilistic approach is used to recommend a rational procedure to determine factors of safety that consider the uncertainties and the consequences of failure. This procedure can be modified for load and resistance factors design calibration, as well. The skin friction approach was calibrated employing reliability analysis, available statistics, published experimental data, and simulations. However, a lack of field test data has been noticed. Factors of safety for cohesive, cohesionless, and layered soils are recommended. They are presented as a function of the target reliability index, and which in-situ test is performed to obtain the soil strength properties. Three alternatives were considered: standard penetration test, cone penetration test, and vane shear test. The procedure described can be used by practitioners to select appropriate factors of safety based on local conditions when statistical parameters from a particular site investigation are available.

Fragility analysis of drilled shafts in sand – an analytical correspondence between reliability index and factor of safety

This paper establishes an analytical correlation between factor of safety (FS) and reliability index β values commonly used in the design of drilled shafts in sand. This is achieved through fragility analysis of unit shaft and base resistances, calculated using finite element analysis-based capacity calculation equations, for drilled shafts. Analytical fragility curves are developed for allowable unit resistances along the pile shaft and at the pile base. Developed fragility curves are used to map FS values with corresponding values of β. Such analytical FS–β correspondence is not well established in literature. Comparison of results from fragility analysis with those obtained through conventional Monte Carlo simulations reveals excellent agreement. Developed FS-β correlation is employed in reliability analysis to estimate load and resistance factors corresponding to different FS values. Evaluated load and resistance factors compare very well with AASHTO specifications.