Evaluation of AASHTO Live Load and Line Load Distribution Factors for I-Girder Bridge Decks

Kocsis, Peter

doi:10.1061/(asce)1084-0680(2004)9:4(211)

“…and span length close to 18 m (60 ft), whereas the predictability of the formulas was not accurate when the properties of a bridge were varied. Kocsis (2004) also reported the inaccuracy of the AASHTO Standard method, based on a structural analysis program using the semi continuum method. Kocsis proved that the AASHTO Standard formulas in some cases underestimate the live load moments by as much as 40%.…”

Section: Aashto Standard Specifications For Highway Bridgesmentioning

confidence: 99%

Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Iranmanesh

2024

Preprint

0

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<p>Skew bridges in modern highways have become increasingly popular for economic and aesthetic considerations. The current Canadian Highway Bridge Design Code (CHBDC) specifies skew factor equation for shear at the obtuse corner for braced steel I-girder bridges. However, skew factors for concrete I-girder bridges for girder moment and shear at obtuse and acute corners as well as middle supports due to CHBDC truck loading are yet unavailable. Also, CHBDC load distribution factor equations for moment and shear in straight bridges do not include the presence of concrete traffic barriers and intermediate diaphragms as integral parts of highway bridges. Moreover, literature review revealed that CHBDC overestimates the moment and shear at fatigue limit state design of slab-on-girder bridges. Despite the availability of computer software for bridge analysis, designers prefer simplified analysis methods to reduce the time and cost spent in the design. A practical-design-oriented parametric study was conducted, using the finite element modelling to address the shortcomings and gaps found in CHBDC. The first study included the analysis of straight and skew concrete I-girder bridges under dead load, while the second study included the analysis of such bridges under CHBDC truck loading conditions. The third study included the effect of concrete barrier stiffness and concrete intermediate diaphragms on the moment and shear distribution factors for this type of bridge. Different bridge configurations were considered to cover key parameters such as span length, skew angle, number of girders and girder spacing. The obtained results were compared with those available in CHDBC, AASHTO LRFD Bridge Design Specifications and previous research related to slab-on-girder bridges. Using the data generated from the parametric study, sets of empirical equations for moment and shear distribution factors for the studied bridge configurations under dead and live load were deduced to design such bridge types more reliably and economically. Results show that inclusion of intermediate diaphragms and concrete barriers built integrally with the deck slab generally affect bridge performance. This conclusion can be used to evaluate existing bridges since any additional girder strength would decide on keeping the bridge in service or address its structural deficiency.</p>

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“…and span length close to 18 m (60 ft), whereas the predictability of the formulas was not accurate when the properties of a bridge were varied. Kocsis (2004) also reported the inaccuracy of the AASHTO Standard method, based on a structural analysis program using the semi continuum method. Kocsis proved that the AASHTO Standard formulas in some cases underestimate the live load moments by as much as 40%.…”

Section: Aashto Standard Specifications For Highway Bridgesmentioning

confidence: 99%

Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Iranmanesh

2024

Preprint

0

View full text Add to dashboard Cite

<p>Skew bridges in modern highways have become increasingly popular for economic and aesthetic considerations. The current Canadian Highway Bridge Design Code (CHBDC) specifies skew factor equation for shear at the obtuse corner for braced steel I-girder bridges. However, skew factors for concrete I-girder bridges for girder moment and shear at obtuse and acute corners as well as middle supports due to CHBDC truck loading are yet unavailable. Also, CHBDC load distribution factor equations for moment and shear in straight bridges do not include the presence of concrete traffic barriers and intermediate diaphragms as integral parts of highway bridges. Moreover, literature review revealed that CHBDC overestimates the moment and shear at fatigue limit state design of slab-on-girder bridges. Despite the availability of computer software for bridge analysis, designers prefer simplified analysis methods to reduce the time and cost spent in the design. A practical-design-oriented parametric study was conducted, using the finite element modelling to address the shortcomings and gaps found in CHBDC. The first study included the analysis of straight and skew concrete I-girder bridges under dead load, while the second study included the analysis of such bridges under CHBDC truck loading conditions. The third study included the effect of concrete barrier stiffness and concrete intermediate diaphragms on the moment and shear distribution factors for this type of bridge. Different bridge configurations were considered to cover key parameters such as span length, skew angle, number of girders and girder spacing. The obtained results were compared with those available in CHDBC, AASHTO LRFD Bridge Design Specifications and previous research related to slab-on-girder bridges. Using the data generated from the parametric study, sets of empirical equations for moment and shear distribution factors for the studied bridge configurations under dead and live load were deduced to design such bridge types more reliably and economically. Results show that inclusion of intermediate diaphragms and concrete barriers built integrally with the deck slab generally affect bridge performance. This conclusion can be used to evaluate existing bridges since any additional girder strength would decide on keeping the bridge in service or address its structural deficiency.</p>

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“…Recent studies on the live LDFs of AASHTO LRFD specifications indicate that their equations provide conservative results for the moment and shear distribution factors of skewed bridges (8)(9)(10)(11)(12)(13)(14)(15). A similar finding was obtained with the simplified Henry's method.…”

mentioning

confidence: 99%

Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads

Mohseni

¹

,

Khalim

²

,

Kang

³

2015

Transportation Research Record

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The multicell box girder bridge is a popular choice of designers because of its large torsional stiffness. The skewness at the support line of bridges has a significant influence on distribution of live loads. The current American bridge design code, AASHTO load and resistance factor design (LRFD), defines several correction factor expressions to account for the skew effect in bridges. In addition, the effect of skewness on reactions of continuous multicell box girder bridges is obtained by using the skew correction factor of shear or by the shear distribution factor of straight bridges, despite a significant disparity between the shear and reaction that is observed in skewed bridges. This study investigated the effect of skewness on the reactions and shear distribution factors for three continuous multicell box girder bridges. There was a significant difference between reactions at the piers and the shear distribution factors of skewed bridges. Thus, a statistical analysis was used to propose new equations for the skew correction factors and the external girder correction factor of shear and reaction to improve the accuracy of the AASHTO LRFD specifications.

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Evaluation of AASHTO Live Load and Line Load Distribution Factors for I-Girder Bridge Decks

Cited by 9 publications

References 2 publications

Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Load Distribution Factors in Straight and Skew Concrete I-Girder Bridges

Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads

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