The ESAL11 procedure calculates the daily ESALs for each year of truck count data entered. The authors declare that they have no competing interests. skews over 30o, while the 1996 AASHTO standard specification has not. 11b and 12. Total number of lanes in both directions 4 or less, the Lane Distribution Factor is 1.0. ii. Reliability is a statistical tool used in pavement design that assumes a standard normal distribution exists for all pavement design parameters and allows the designer to account for deviation from the average equally for all parameters. The Office of Technical Services monitors truck counts and axle weights. Even though the AASHTO Design Guide is several years old, it is still used throughout the industry for pavement thickness design. Research has shown that global chemical stabilization increases the stiffness of the subgrade and the effects are long lasting. This indicates a need to develop new equations with which to calculate live load distribution factors for compressive stress, tensile stress and deflection that are closer to the actual values. The effects of various structural parameters on stress and the deflection distribution factors were investigated to identify the parameters affecting the load distribution factors under live loads. Multiple presence factors are not to be applied to the fatigue limit state for which one design truck is used, regardless of the number of design lanes. The modernized AASHTO analytical engines improve the analysis runtime performance of all structure types and paves the groundwork for future performance optimization. This study adopted the HL-93 truck loading designated in the AASHTO LRFD (2017) (Fig. There are two design lane factors. Lane Load 3.6.1.3 LRFD 2004 TruckandLaneLoadTruck and Lane Load 64 lbs across a 10 ft width DLAnotappliedDLA not applied LRFD LRFD 2005 2005 Truck onlyTruck only St d d S ifi tiStandard Specification 37113.7.1.1 Either truck or Lane Load Truck governs for shorter spans The top and bottom slab thicknesses were 20cm and 15cm, respectively. There are two design lane factors. In the case of compressive stresses, the differences between FEA and AASHTO were reduced. Found inside Page 104According to AASHTO standards, the formulas of the moment and shear distribution factors for exterior steel girders in a non-skewed bridge are as following: For one design lane loaded The moment and shear distribution factors (gext) is (9). It does not apply to below ground structures. Found inside Page 8-20The cumulative expected 18-kip (80-kN) ESAL (W18 ) during the designed life in the design lane is then determined as In this step the structural numbers required above TABLE 8.6 Lane Distribution Factor (AASHTO, 1993) No. of Lanes To determine these constants, the ratio of the positive (tensile) stress distribution factor, R1, calculated from FEA using Eq. It was revealed that they obtain conservative values for tensile stresses and unconservative values for compressive stresses. The current AASHTO LRFD live load distribution factors are based on lanes. Multiple presence factors have been applied to the distribution factors based on the lever rule and special analysis. 2003; Huo and Zhang 2008), only the following parameters were investigated in this study: the span length, the number of lanes and the number of boxes. TrafficAnalysis-Lane Distribution Factor The lane distribution factors recommended by the AASHTO design guide are shown in Table 6.16. This relationship was developed in the 1950's by testing hundreds of soil samples. The California bearing ratio (CBR) is a value representing a soil's resistance to shearing under a standard load, compared to the resistance of crushed stone subjected to the same load. PSR is a rating of pavement ride based on a scale of zero, for impassible, to 5, for perfect. 14a is due to the absence of the other key parameters, NB and NL, in the Eq. Examples of the calculation of design ESALs are provided in Figures 302-1 and 402-1. The AASHTO pavement design method was developed around the concept of serviceability. While the live loads of the AASHTO specifications (2) LRFD is HL93 which consists of truck loading and distributed load of 9.3 KN/m as shown in Figure 2. The maximum positive (tensile) stress, \(\sigma_{p}\), and negative (compression) stress, \(\sigma_{n}\), for the bridges were then obtained for the three-dimensional bridges using FEA. Journal of Zhejiang University: Science A, 13, 915925. A newer design program called the Mechanistic-Empirical Pavement Design Guide (MEPDG) is available, however, it is costly and requires a great deal of data to be effective. Improved design specifications for horizontally curved steel girder highway bridges. It is important to ensure the truck percentage is a 24-hour percentage and not a peak-hour percentage. 2010): where LDFi=live-load distribution factor of the ith girder; Li=moment or deflection of ith girder, Li=sum of all girder actions; and n=number of bridge girders (bridge webs in box-girder bridges). The concept of a live load distribution factor (LDF) was first used in the bridge specifications issued by the American Association of State Highway Officials (AASHTO) in 2002 through empirical S/D expressions (known as S-over equations), where S is the girder spacing and D is a constant that depends on the bridges superstructure and the type of lane loading. The overall standard deviation (variance) is a measure of the spread of the probability distribution for ESALs vs. Serviceability, considering all the parameters used to design a pavement. Relationship between the stress distribution factor and the number of lanes of three box bridges with different lengths. The results for the tensile and compressive stress and the deflection for the selected bridges are compared in Fig. The page also discusses how the manual is formatted and gives a listing of external reference documents. Computers & Structures, Inc. (2017). Approximately 80% of all states use the AASHTO pavement design procedures, with the majority using the 1993 version. Note: The lever rule for shear distribution on exterior beams typically only applies to one lane loading or three beam cross-sections (except as given in Aashto Lrfd 4.6.2.2.1). Where: D1) = Directional distribution factor, which is generally 50% D!, = Lane Distribution Factor The D L factor may be calculated using Table 1. The resulting empirical equations were determined based on a statistical analysis and the elastic response of each bridge for the standard AASHTO (2014) truck loading in order to estimate the live load distribution across a bridge. Use a 6-inch (150 mm) pipe if the outlet interval is greater than 500 feet (150 m) or if the subgrade is saturated. On resurfacing projects, where prefabricated edge underdrains already exist, existing outlets should be inspected and replaced where they no longer function. They can be also applicable under AASHTO LRFD truck loading. DFM - Distribution Factor for Moment. Distribution of stress and deflection from various methods. In fine-grained soils, excess water in the subgrade is the principal cause of unstable soil conditions during construction. Questions regarding the use of CSiBridge may be directed to the Structural Analysis Committee. Development of new distribution factor equations of live load moment and shear for steel open-box girder bridges. Based on limited research and several current publications, ODOT has adopted a standard relationship between modulus of resilience (Mr) and the California bearing ratio (CBR) shown below. In the case of a zero slope, hydrostatic pressure is sufficient to ensure the proper drainage of the base and subgrade. Early-age behavior of an adjacent prestressed concrete box-beam bridge containing UHPC shear keys with transverse dowels. Curves should not be designed with side friction factors greater than the values shown in Table 1. = where: = Live Load Distribution Factor Calculation Options: Calculate the Live Load Distrtibution Factors using: AASHTO LRFD with TxDOT policies When using AASHTO LRFD: When using the Lever Rule: ignore the Range of Applicability for the Skew Factor for live load distribution factors of multicell box-girder bridges with two or more lane loading as follows: (9), so using a similar process to that utilized in the previous section, FN becomes: The proposed equation for the negative stress distribution in MCB bridges that is equivalent to Eq. Found inside Page 280AASHTO's WSD method calculates the required safe minimum member capacity of a bridge utilizing a live load envelope represented by AASHTO's truck and lane loads. An approximate analysis procedure determines a girder distribution factor Found inside Page 18As the HL-93 loading and the AASHTO legal trucks represent typical commercial traffic, the critical distribution factor, single lane or multiple lanes loaded, was used for these loads. For routine permit vehicles, the MBE provisions 1.3.2.1-1) (a) For loads for which a maximum value of i is appropriate: i =DRI 0.95 (LRFD Eq. Ashebo, D. B., Chan, T. H. T., & Yu, L. (2007). (5) becomes: To find an equation for the negative stress distribution factor, \(D\sigma_{ne}\), for MCB bridges, \(D\sigma_{n,sb}\) from Eq. Similarly the constant a in Eq. Samaan, M., Sennah, K. M., & Kennedy J. 1993), but their accuracy has not been reevaluated in the light of recent research in this area. Distribution of wheel loads on highway bridges. Lane Load 3.6.1.3 LRFD 2004 TruckandLaneLoadTruck and Lane Load 64 lbs across a 10 ft width DLAnotappliedDLA not applied LRFD LRFD 2005 2005 Truck onlyTruck only St d d S ifi tiStandard Specification 37113.7.1.1 Either truck or Lane Load Truck governs for shorter spans The maximum positive (tensile) stress, \(\sigma_{p,I}\), and negative (compression) stress, \(\sigma_{n,I}\), at the bottom fiber were calculated using a simple beam bending formula. AASHTO Load and Resistance Factor Design (LRFD) Table 4.6.2.2.2b-1 Distribution of Live Loads Per Lane for Moment in Interior Beams. Equivalency factors are a function of pavement type and thickness, among other factors. Re-examination of the simplified method (Henrys Method) of distribution factors for live load moment and shear. Distribution factor for maximum deflection, Distribution factors for the maximum negative stresses, Distribution factors for the maximum negative stresses for steel spread open box girder bridges, Distribution factors for the maximum positive stresses, Distribution factors for the maximum positive stresses for steel spread open box girder bridges, Live-load distribution factor of the ith girder, Live-load distribution factor of multicell box girder bridges, Ratio of the positive (tensile) stress distribution factor, Maximum deflection at the midspan of simple ideal girder, Maximum negative (compression) stress for the bridges were then obtained for the three-dimensional bridges using FEA, Negative (compression) stress at the bottom fiber were calculated using a simple beam bending formula, Maximum positive (tensile) stress for the bridges were then obtained for the three-dimensional bridges using FEA, Maximum positive (tensile) stress at the bottom fiber were calculated using a simple beam bending formula, Poissons ratio of elasticity of the concrete, Poissons ratio of elasticity of the steel. Total number of wheel lines divided by number of beams. https://doi.org/10.1016/j.engstruct.2016.03.004. Base pipe and shallow pipe underdrains are typically 4 or 6 inches (100 or 150 mm) in diameter. The 4 and 6 inch (100 and 150 mm) pipes are considered equivalent in hydraulic capacity for the base pipe and shallow pipe underdrains. Final Report, Tennessee DOT Project No. Once built, pavements may or may not actually degrade to that level but the design terminal serviceability remains the same. Huo, X., & Zhang, Q. https://doi.org/10.1061/(ASCE)BE.1943-5592.0001034. The term \(L^{0.023}\) in Eq. I have a beam slab bridge configuration that requires distribution factors by lever rule. %T24=24-hour truck percentage of ADT ESAL conversion factors corresponding to the year of the truck counts are used in the calculations instead of using ten-year averages. The results reveal that both \(D\sigma_{po}\) and \(D\sigma_{ne}\) decreased as NB increased. In order to design the required pavement thickness, the ADT needs to be adjusted to represent the loading on the design lane. The fluctuations of less than 2% for both stress and deflection confirm that these factors do not depend on the number of spans if the distribution factors obtained from the adapted equations are applied. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Moment and shear load distribution factors for multigirder bridges subjected to overloads. 1993; Bae and Oliva 2012; Terzioglu et al. Interestingly, the distribution factors for tensile stresses obtained from FEA were significantly smaller than those calculated using the current AASHTO (2002) standard and AASHTO LRFD (2017) specifications by 33% and 46%, respectively. The work reported here was supported by Grants (17CTAP-C132629-01, 17CTAP-C132633-01, 18CTAP-C144787-01) funded by the Ministry of Land, Infrastructure and Transport (MOLIT) of the Korean Agency for Infrastructure Technology Advancement (KAIA). The live load distribution factor for bending moment of AASHTO (2002) standard and AASHTO LRFD (2017) specifications were reviewed for applicability to MCB bridges. distribution factor is 0.796 lane. Refer to Figure 202-1 for ODOT's most current lane factors. Excess moisture in the base and subgrade reduces the amount of stress the subgrade can tolerate without permanent strain. The flexible design method in this Manual does not include the drainage factor. Arabian Journal for Science & Engineering, 8(60836094), 97. https://doi.org/10.1631/jzus.A1200098. For superelevated pavements, spacing should be at 25 feet (7.5 m) and drains should be located on the low side only. 2001; Higgins et al. d. The lane distribution factor shall be as follows: i. The old AASHTO Standard Spec was based on wheel loads. Found inside Page 72_*** * 14 = 0.595 lanes (controls) Live load distribution factor for shear 1. Interior girder (AASHTO Table 4.6.2.2.3a-1) One lane loaded: [ S ) { d ) LDV =| | | 9.5 12L (#) 625 \" - || - | = 0.535 lanes 9.5 12(157) Two or more Individual Truck Load Factors 0.189 0.857 0.857 ESAL = 1.903. Figure6 shows the comparison between distributions of stress and deflection for selected bridges obtained from Lis study, CSIbridge software, and conventional beam theory. Figures 205-1 to 205-10 provide details on the placement of subsurface drainage systems.
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