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Junsuk Kang - One of the best experts on this subject based on the ideXlab platform.
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Development of Live Load Distribution Factor Equation for Concrete Multicell Box-Girder Bridges under Vehicle Loading
International Journal of Concrete Structures and Materials, 2019Co-Authors: Won Choi, Iman Mohseni, Jongsup Park, Junsuk KangAbstract:The evaluation and design of concrete bridges in large part depend on the transverse Distribution characteristics of the live Load carried and the service level. The live Load Distribution for continuous concrete multicell box-girder bridges varies according to bridge configuration, so when designing such bridges, it is important to determine the maximum negative stress at the piers, the midspan positive (tensile) stress and the deflection of the bridge when subjected to live Loads. This paper reports an extensive parametric study to determine the maximum stress, deflection, and moment Distribution Factors for two span multicell box-girder bridges based on a finite element analysis of 120 representative numerical model bridges. Bridge parameters were selected to extend the parameters and ranges of current live Load Distribution Factors defined by AASHTO LRFD specifications. The results indicate that the span length, number of boxes, and the number of lanes all significantly affect the positive (tensile) and the negative (compression) stress Distribution Factors. A set of equations proposed to describe the behavior of such bridges under AASHTO LRFD live Loads yielded results that agreed closely with the numerically derived results for the stress and deflection Distribution Factors.
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Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads
Transportation Research Record, 2015Co-Authors: Iman Mohseni, A. R. Khalim, Junsuk KangAbstract: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 equatio...
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Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads
Transportation Research Record: Journal of the Transportation Research Board, 2015Co-Authors: Iman Mohseni, A. R. Khalim, Junsuk KangAbstract: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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Effect of intermediate diaphragm on lateral Load Distribution Factor of multicell box-girder bridges
KSCE Journal of Civil Engineering, 2014Co-Authors: Iman Mohseni, Abdul Khalim Abdul Rashid, Junsuk KangAbstract:The current American bridge design codes state that intermediate diaphragms should be used to preserve section geometry against accidental overturning of girders and during construction of a bridge. There is inconsistency in practice for the design of intermediate diaphragms, such that most specifications either ignore or underestimate the contribution of these members to the lateral Distribution of live Load. Current studies indicate that neglecting the effect of intermediate diaphragms might lead to highly conservative values for bending moment Distribution Factors and result in non-economic designs for skew bridges. This paper reports on a parametric study performed on 160 prototypes of straight and skew concrete multicell box-girder bridges. The obtained results were used to develop practical expressions to account for the diaphragm effects on American Association of State Highway and Transportation Officialsformulas for live Load Distribution Factors. It was observed that decks with internal transverse diaphragms perpendicular to the longitudinal webs are the best arrangement for Load Distribution in skew bridges. Thus, a sufficient number of diaphragms should be provided between span lengths and over the supports of bridge decks.
J M Stallings - One of the best experts on this subject based on the ideXlab platform.
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tests and ratings of short span steel bridges
Journal of Structural Engineering-asce, 1993Co-Authors: J M StallingsAbstract:A series of diagnostic tests were performed on three short‐span, two‐lane, steel‐girder bridges. Tests were performed with stationary and moving test trucks placed on the bridges one at a time and side by side. Wheel‐Load Distribution Factors were calculated from results of the stationary‐truck test, and impact Factors were calculated from results of the moving‐truck test. Girder strains were calculated using the American Association of State Highway and Transportation Officials' simplified bridge analysis with the measured wheel‐Load Distribution Factors. The calculated girder strains were consistently larger than measured values. The results illustrate some of the inaccuracies of the wheel‐Load Distribution‐Factor approach. Impact Factors are calculated by various methods. Comparisons are made between impact Factors for the most critically Loaded girder and impact Factors determined from the combined response of all the girders. The impact Factors based on the combined response of all the girders tend t...
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Tests and Ratings of Short‐Span Steel Bridges
Journal of Structural Engineering, 1993Co-Authors: J M Stallings, C. H. YooAbstract:A series of diagnostic tests were performed on three short‐span, two‐lane, steel‐girder bridges. Tests were performed with stationary and moving test trucks placed on the bridges one at a time and side by side. Wheel‐Load Distribution Factors were calculated from results of the stationary‐truck test, and impact Factors were calculated from results of the moving‐truck test. Girder strains were calculated using the American Association of State Highway and Transportation Officials' simplified bridge analysis with the measured wheel‐Load Distribution Factors. The calculated girder strains were consistently larger than measured values. The results illustrate some of the inaccuracies of the wheel‐Load Distribution‐Factor approach. Impact Factors are calculated by various methods. Comparisons are made between impact Factors for the most critically Loaded girder and impact Factors determined from the combined response of all the girders. The impact Factors based on the combined response of all the girders tend t...
Iman Mohseni - One of the best experts on this subject based on the ideXlab platform.
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Development of Live Load Distribution Factor Equation for Concrete Multicell Box-Girder Bridges under Vehicle Loading
International Journal of Concrete Structures and Materials, 2019Co-Authors: Won Choi, Iman Mohseni, Jongsup Park, Junsuk KangAbstract:The evaluation and design of concrete bridges in large part depend on the transverse Distribution characteristics of the live Load carried and the service level. The live Load Distribution for continuous concrete multicell box-girder bridges varies according to bridge configuration, so when designing such bridges, it is important to determine the maximum negative stress at the piers, the midspan positive (tensile) stress and the deflection of the bridge when subjected to live Loads. This paper reports an extensive parametric study to determine the maximum stress, deflection, and moment Distribution Factors for two span multicell box-girder bridges based on a finite element analysis of 120 representative numerical model bridges. Bridge parameters were selected to extend the parameters and ranges of current live Load Distribution Factors defined by AASHTO LRFD specifications. The results indicate that the span length, number of boxes, and the number of lanes all significantly affect the positive (tensile) and the negative (compression) stress Distribution Factors. A set of equations proposed to describe the behavior of such bridges under AASHTO LRFD live Loads yielded results that agreed closely with the numerically derived results for the stress and deflection Distribution Factors.
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Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads
Transportation Research Record, 2015Co-Authors: Iman Mohseni, A. R. Khalim, Junsuk KangAbstract: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 equatio...
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Live Load Distribution Factor at the Piers of Skewed Continuous Multicell Box Girder Bridges Subjected to Moving Loads
Transportation Research Record: Journal of the Transportation Research Board, 2015Co-Authors: Iman Mohseni, A. R. Khalim, Junsuk KangAbstract: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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Effect of intermediate diaphragm on lateral Load Distribution Factor of multicell box-girder bridges
KSCE Journal of Civil Engineering, 2014Co-Authors: Iman Mohseni, Abdul Khalim Abdul Rashid, Junsuk KangAbstract:The current American bridge design codes state that intermediate diaphragms should be used to preserve section geometry against accidental overturning of girders and during construction of a bridge. There is inconsistency in practice for the design of intermediate diaphragms, such that most specifications either ignore or underestimate the contribution of these members to the lateral Distribution of live Load. Current studies indicate that neglecting the effect of intermediate diaphragms might lead to highly conservative values for bending moment Distribution Factors and result in non-economic designs for skew bridges. This paper reports on a parametric study performed on 160 prototypes of straight and skew concrete multicell box-girder bridges. The obtained results were used to develop practical expressions to account for the diaphragm effects on American Association of State Highway and Transportation Officialsformulas for live Load Distribution Factors. It was observed that decks with internal transverse diaphragms perpendicular to the longitudinal webs are the best arrangement for Load Distribution in skew bridges. Thus, a sufficient number of diaphragms should be provided between span lengths and over the supports of bridge decks.
Elisa D. Sotelino - One of the best experts on this subject based on the ideXlab platform.
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Influence of Secondary Elements and Deck Cracking on the Lateral Load Distribution of Steel Girder Bridges
Journal of Bridge Engineering, 2006Co-Authors: Wonseok Chung, Judy Liu, Elisa D. SotelinoAbstract:The AASHTO LRFD Load Distribution Factor equation was developed based on elastic finite element analysis considering only primary members, i.e., the effects of secondary elements such as lateral bracing and parapets were not considered. Meanwhile, many bridges have been identified as having significant cracking in the concrete deck. Even though deck cracking is a well-known phenomenon, the significance of pre-existing cracks on the live Load Distribution has not yet been assessed. The purpose of this research is to investigate the effect of secondary elements and deck cracking on the lateral Load Distribution of girder bridges. First, secondary elements such as diaphragms and parapets were modeled using the finite element method, and the calculated Load Distribution Factors were compared with the code-specified values. Second, the effects of typical deck cracking and crack types that have a major effect on Load Distribution were identified through a number of nonlinear finite element analyses. It was established that the presence of secondary elements may produce Load Distribution Factors up to 40% lower than the AASHTO LRFD values. Longitudinal cracking was found to increase the Load Distribution Factor by up to 17% when compared to the LRFD value while the transverse cracking was found to not significantly influence the transverse Distribution of moment.
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Applicabiliy of the simplified Load Distribution Factor equation to PSC girder bridges
KSCE Journal of Civil Engineering, 2005Co-Authors: Wonseok Chung, Judy Liu, Kitjapat Phuvoravan, Elisa D. SotelinoAbstract:AASHTO LRFD specifications first introduced a new Load Distribution Factor equation as a result of the NCHRP12-26 project. However, this equation involves a longitudinal stiffness parameter, which is not initially known in design and thus introduces an iterative procedure. Practicing engineers perceive this need for an iterative design procedure as the major impediment to wides pread acceptance of the AASHTO LRFD equation. Recently, a non-iterative simplified equation based on the AASHTO LRFD formula was developed for steel girder bridges. The applicability of this equation to Prestressed Concrete (PSC) girder bridges is investigated in this paper. A total of 17 PSC girder bridges are selected and analyzed using a sophisticated finite element model. It has been found that the new simplified equation produces LDF values that are always conservative when compared to those obtained from the finite element analyses and are generally greater than the LDF obtained using AASHTO LRFD specification. Therefore, the simplified equation provides a simple yet safe specification for LDF calculation.
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Simplified Load Distribution Factor for Use in LRFD Design
2004Co-Authors: Elisa D. Sotelino, Judy Liu, Wonseok Chung, Kitjapat PhuvoravanAbstract:The "S-over" equation for the Load Distribution Factor (LDF) was first introduced in the 1930s in the AASHTO Standard. Finite element (FE) studies, however, have shown it to be unsafe in some cases and too conservative in others. AASHTO LRFD 1994 introduced a new LDF equation as a result of the NCHRP 12-26 project. This equation is based on parametric studies and FE analyses. It is considered to be a good representation of bridge behavior. However, this equation involves a longitudinal stiffness parameter, which is not initially known in design. Thus, an iterative procedure is required to correctly determine the LDF value. This need for an iterative design procedure is perceived by practicing engineers as the major impediment to widespread acceptance of the AASHTO LRFD equation. In this study, a new simplified equation that is based on the AASHTO LRFD formula and does not require an iterative procedure is developed. A total of 43 steel girder bridges and 17 prestressed concrete girder bridges in the state of Indiana are selected and analyzed using a sophisticated FE model. The new simplified equation produces LDF values that are always conservative when compared to those obtained from the FE analyses and are generally greater than the LDF obtained using AASHTO LRFD specification. Therefore, the simplified equation provides a simple yet safe specification for LDF calculation. This study also investigates the effects of secondary elements and bridge deck cracking on the LDF of bridges. The AASHTO LRFD LDF equation was developed based on elastic FE analysis considering only primary members, i.e., the effects of secondary elements such as lateral bracing and parapets were not considered. Meanwhile, many bridges have been identified as having significant cracking in the concrete deck. Even though deck cracking is a well-known phenomenon, the significance of pre-existing cracks on the live Load Distribution has not yet been assessed in the literature. First, secondary elements such as diaphragms and parapet were modeled using the FE method, and the calculated Load Distribution Factors were compared with the code-specified values. Second, the effects of typical deck cracking and crack types that have a major effect on Load Distribution were identified through a number of nonlinear FE analyses. It was found that the presence of secondary elements can result in a Load Distribution Factor up to 40% lower than the AASHTO LRFD value. Longitudinal cracking was found to increase the Load Distribution Factor; the resulting Load Distribution Factor can be up to 17% higher than the LRFD value. Transverse cracking was found to not significantly influence the transverse Distribution of moment. Finally, for one of the selected bridges, both concrete cracking and secondary elements are considered to investigate their combined effect on lateral Load Distribution. The increased LDF due to deck cracking is offset by the contributions from the secondary elements. The result is that the proposed simplified equation is conservative and is recommended for determination of LDF.
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Simplified Live Load Distribution Factor Equation for Steel Girder Bridges
Transportation Research Record, 2004Co-Authors: Kitjapat Phuvoravan, Wonseok Chung, Judy Liu, Elisa D. SotelinoAbstract:The "S-over" equation for Load Distribution Factor (LDF) was first introduced in the 1930s in the AASHTO standard. Finite element studies, however, have shown it to be unsafe in some cases and too conservative in others. AASHTO LRFD 1994 introduced a new LDF equation as a result of the NCHRP12-26 project. The equation is based on parametric studies and finite element analyses. It is considered to be a good representation of bridge behavior. However, it involves a longitudinal stiffness parameter that is not initially known in design and thus requires an iterative procedure to correctly determine the LDF value. The need for an iterative design procedure is perceived by practicing engineers as the major impediment to wide acceptance of the AASHTO LRFD equation. A new, simplified equation that is based on the AASHTO LRFD formula but does not require an iterative procedure is developed. Fortythree Indiana bridges were selected and analyzed with a sophisticated finite element model. The new, simplified equatio...
Hani Nassif - One of the best experts on this subject based on the ideXlab platform.
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Verification of shear live-Load Distribution Factor equations for I-girder bridges
KSCE Journal of Civil Engineering, 2013Co-Authors: Nakin Suksawang, Hani Nassif, Dan SuAbstract:The “S-over” Load Distribution Factor (LDF) has been used for many years for determining the distributed moments and shear forces of a girder. Only until recently after the adaptation of the AASHTO LRFD Bridge Design Specification, new LDF equations are proposed using power functions. Although these new equations can more accurately predict the distributed moments and shear forces similar to both field and finite element analysis results, they are complex and they do not represent the fundamental background of LDF but rather based on regression analysis. Therefore, a more fundamental equation such as the S-over LDF is needed for the engineer to have a better understanding of the relationship between the girder sizes and spacing. The primary objective of this study is to develop a simplified S-over LDF for shear for steel and prestressed concrete I-girder bridges. Actual field testing of seven I-girder bridges were evaluated and validated to the developed Finite Element Analysis (FEA) model. A parametric study of bridges with various girder spacing and length were performed to develop the proposed equations. Results show that the proposed equations have excellent correlation with the more exact FEA model as well as the computer-based analysis.
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Simplified Live-Load Distribution Factor Equation for Prestressed Concrete I-Girder and Spread Box-Girder Bridges
2008Co-Authors: Nakin Suksawang, Hani NassifAbstract:One of the many changes introduced in the American Association of State Highway and Transportation Officials Load and resistance Factor design (AASHTO LRFD) is the live-Load Distribution Factor equations. The AASHTO LRFD equations are more accurate than the AASHTO Standard Specification “S-over” equations but they are more complex and take the form of power functions. Furthermore, the equations contained stiffness parameters that are unknown when designing new bridges, thereby allowing the design procedure to be iterative. These complexity and iterative nature are perceived by many practicing engineers as impractical and has raised questions regarding the desired level of simplicity in bridge design calculations. Simplified live-Load Distribution Factor equations for prestressed concrete I-girder and spread box-girder bridges are proposed in this paper. The simplified equations take the form of AASHTO Standard Specification “S-over” equation but in lieu of using constant denominators, the denominators are expressed as functions of girder spacing and span length. Results containing 92 and 54 prestressed concrete I-girder and spread box-girder bridges, respectively, are compared with those from AASHTO LRFD equations. The proposed simplified equations have excellent correlation with the AASHTO LRFD. It is highly recommended that the equation be adopted in future AASHTO LRFD code.
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Development of Live Load Distribution Factor Equation for Girder Bridges
Transportation Research Record, 2007Co-Authors: Nakin Suksawang, Hani NassifAbstract:Live Load Distribution Factor (LDF) equations are among the most important bridge design calculations because they provide the distributed moment and forces, which are needed for designing new or for evaluating existing bridges. The AASHTO Load and resistance Factor design specification is the current standard for bridge design. It uses a power function containing parameters that are often unknown when bridges are being designed and thereby allows the design procedure to be iterative. This iterative design procedure is perceived by many practicing engineers as impractical and has raised questions regarding the desired level of simplicity in bridge design calculations. Therefore, simpler but more accurate LDF equations are needed. An experimental program to evaluate the behavior of girder bridges was launched. The program consisted of live Load testing of actual girder bridges. A parametric study was carried out by using a detailed three-dimensional finite element analysis to determine how sensitive various bridge parameters are to the LDF. On the basis of the parametric study, new simplified LDF equations are proposed for various types of girder bridges, including steel, prestressed, and spread box girder bridges. The equation format is simplified as a function of two bridge parameters only (girder spacing and span length) while an equal level of accuracy is maintained. Results are compared with those from other available equations and are shown to have excellent correlation with the more exact finite element method.