Analytical and field investigation of horizontally curved girder bridges

Nationally, concerns have been raised regarding the relatively new design approach of combining the use of integral abutments with horizontally curved steel I-girder bridges. In order to address concerns regarding the superstructure behavior, this research experimentally and analytically investigated four in-service, horizontally curved, steel I-girder bridges with integral and semi-integral abutments. These bridges are located at the major interchange of Interstates I-235 and I-80. For the research, a monitoring system was installed on the bridges using an array of strain gauges. The implications of the critical data that the monitoring system produced will enable further development of design specifications for similar bridge types, particularly with respect to thermal effects. In addition to the measured field data, an analytical model for one of the instrumented bridges was established using a commercial finite element analysis software package. Several conclusions were formed from both of the experimental and analytical results. First, the short term experimental results produced moment distribution factors that were most heavily influenced by the degree of curvature. Also from the short term results, a simplified analysis method, referred to as the V-Load method, provided only an approximate preliminary assessment of the lateral bottom flange bending based on the degree of curvature with minimal skew. Next, the long term experimental results indicated that an effective thermal range of 100⁰F may cause up to 12 ksi of additional stress in the girders due to restrained expansion and contraction of the bridge. Lastly, results from the analytical investigation indicated that the stresses in the lower flange of the girder, due to applied thermal loads, were greatest at the fixed pier locations. These stresses were mostly due to lateral flange bending caused by the fixed pier restraining lateral movement of the curved girder. Based on the experimental and analytical investigations, the findings within this research suggest that similar bridges require a refined method of analysis when incorporating integral abutments and fixed piers. More importantly, bridges with increased curvature and skew may require special attention in future practice as lateral bending stresses may increase due to temperature loads

Field Monitoring of Curved Girder Bridges with Integral Abutments

Nationally, there are questions regarding the design, fabrication, and erection of horizontally curved steel girder bridges due to unpredicted girder displacements, fit-up, and locked-in stresses. One reason for the concerns is that up to one-quarter of steel girder bridges are being designed with horizontal curvature. There is also an urgent need to reduce bridge maintenance costs by eliminating or reducing deck joints, which can be achieved by expanding the use of integral abutments to include curved girder bridges. However, the behavior of horizontally curved bridges with integral abutments during thermal loading is not well known nor understood. The purpose of this study was to investigate the behavior of horizontal curved bridges with integral abutment (IAB) and semi-integral abutment bridges (SIAB) with a specific interest in the response to changing temperatures. The long-term objective of this effort is to establish guidelines for the use of integral abutments with curved girder bridges. The primary objective of this work was to monitor and evaluate the behavior of six in-service, horizontally curved, steel-girder bridges with integral and semi-integral abutments. In addition, the influence of bridge curvature, skew and pier bearing (expansion and fixed) were also part of the study. Two monitoring systems were designed and applied to a set of four horizontally curved bridges and two straight bridges at the northeast corner of Des Moines, Iowa—one system for measuring strains and movement under long term thermal changes and one system for measuring the behavior under short term, controlled live loading. A finite element model was developed and validated against the measured strains. The model was then used to investigate the sensitivity of design calculations to curvature, skew and pier joint conditions. The general conclusions were as follows: (1) There were no measurable differences in the behavior of the horizontally curved bridges and straight bridges studied in this work under thermal effects. For preliminary member sizing of curved bridges, thermal stresses and movements in a straight bridge of the same length are a reasonable first approximation. (2) Thermal strains in integral abutment and semi-integral abutment bridges were not noticeably different. The choice between IAB and SIAB should be based on life – cycle costs (e.g., construction and maintenance). (3) An expansion bearing pier reduces the thermal stresses in the girders of the straight bridge but does not appear to reduce the stresses in the girders of the curved bridge. (4) An analysis of the bridges predicted a substantial total stress (sum of the vertical bending stress, the lateral bending stress, and the axial stress) up to 3 ksi due to temperature effects. (5) For the one curved integral abutment bridge studied at length, the stresses in the girders significantly vary with changes in skew and curvature. With a 10⁰ skew and 0.06 radians arc span length to radius ratio, the curved and skew integral abutment bridges can be designed as a straight bridge if an error in estimation of the stresses of 10% is acceptable

Analytical and field investigation of horizontally curved girder bridges

Nationally, concerns have been raised regarding the relatively new design approach of combining the use of integral abutments with horizontally curved steel I-girder bridges. In order to address concerns regarding the superstructure behavior, this research experimentally and analytically investigated four in-service, horizontally curved, steel I-girder bridges with integral and semi-integral abutments. These bridges are located at the major interchange of Interstates I-235 and I-80. For the research, a monitoring system was installed on the bridges using an array of strain gauges. The implications of the critical data that the monitoring system produced will enable further development of design specifications for similar bridge types, particularly with respect to thermal effects. In addition to the measured field data, an analytical model for one of the instrumented bridges was established using a commercial finite element analysis software package. Several conclusions were formed from both of the experimental and analytical results. First, the short term experimental results produced moment distribution factors that were most heavily influenced by the degree of curvature. Also from the short term results, a simplified analysis method, referred to as the V-Load method, provided only an approximate preliminary assessment of the lateral bottom flange bending based on the degree of curvature with minimal skew. Next, the long term experimental results indicated that an effective thermal range of 100⁰F may cause up to 12 ksi of additional stress in the girders due to restrained expansion and contraction of the bridge. Lastly, results from the analytical investigation indicated that the stresses in the lower flange of the girder, due to applied thermal loads, were greatest at the fixed pier locations. These stresses were mostly due to lateral flange bending caused by the fixed pier restraining lateral movement of the curved girder. Based on the experimental and analytical investigations, the findings within this research suggest that similar bridges require a refined method of analysis when incorporating integral abutments and fixed piers. More importantly, bridges with increased curvature and skew may require special attention in future practice as lateral bending stresses may increase due to temperature loads.</p

Field Monitoring of Curved Girder Bridges with Integral Abutments

Nationally, there are questions regarding the design, fabrication, and erection of horizontally curved steel girder bridges due to unpredicted girder displacements, fit-up, and locked-in stresses. One reason for the concerns is that up to one-quarter of steel girder bridges are being designed with horizontal curvature. There is also an urgent need to reduce bridge maintenance costs by eliminating or reducing deck joints, which can be achieved by expanding the use of integral abutments to include curved girder bridges. However, the behavior of horizontally curved bridges with integral abutments during thermal loading is not well known nor understood. The purpose of this study was to investigate the behavior of horizontal curved bridges with integral abutment (IAB) and semi-integral abutment bridges (SIAB) with a specific interest in the response to changing temperatures. The long-term objective of this effort is to establish guidelines for the use of integral abutments with curved girder bridges. The primary objective of this work was to monitor and evaluate the behavior of six in-service, horizontally curved, steel-girder bridges with integral and semi-integral abutments. In addition, the influence of bridge curvature, skew and pier bearing (expansion and fixed) were also part of the study. Two monitoring systems were designed and applied to a set of four horizontally curved bridges and two straight bridges at the northeast corner of Des Moines, Iowa—one system for measuring strains and movement under long term thermal changes and one system for measuring the behavior under short term, controlled live loading. A finite element model was developed and validated against the measured strains. The model was then used to investigate the sensitivity of design calculations to curvature, skew and pier joint conditions. The general conclusions were as follows: (1) There were no measurable differences in the behavior of the horizontally curved bridges and straight bridges studied in this work under thermal effects. For preliminary member sizing of curved bridges, thermal stresses and movements in a straight bridge of the same length are a reasonable first approximation. (2) Thermal strains in integral abutment and semi-integral abutment bridges were not noticeably different. The choice between IAB and SIAB should be based on life – cycle costs (e.g., construction and maintenance). (3) An expansion bearing pier reduces the thermal stresses in the girders of the straight bridge but does not appear to reduce the stresses in the girders of the curved bridge. (4) An analysis of the bridges predicted a substantial total stress (sum of the vertical bending stress, the lateral bending stress, and the axial stress) up to 3 ksi due to temperature effects. (5) For the one curved integral abutment bridge studied at length, the stresses in the girders significantly vary with changes in skew and curvature. With a 10⁰ skew and 0.06 radians arc span length to radius ratio, the curved and skew integral abutment bridges can be designed as a straight bridge if an error in estimation of the stresses of 10% is acceptable.See also 2-page Techn Transfer Summary "Field Monitoring of Curved Girder Bridges with Integral Abutments" for overview of the report. Transportation Pooled Fund partners: Ohio DOT, Pennsylvania DOT, Wisconsin DOT, and Iowa DOT (lead state),</p