Continuity diaphragms used in prestressed girder bridges on skewed bents have caused difficulties in detailing and construction. The results of the field verification for the effectiveness of continuity diaphragms for skewed, continuous, and prestressed concrete girder bridges are presented. The current design concept and bridge parameters that were considered include skew angle and the ratio of beam spacing to span (aspect ratio). A prestressed concrete bridge with continuity diaphragms and a skewed angle of 48° was selected for full-scale test by a team of engineers from Louisiana Department of Transportation and Development and the Federal Highway Administration. The live load tests performed with a comprehensive instrumentation plan provided a fundamental understanding of the load transfer mechanism through these diaphragms. The findings indicated that the effects of the continuity diaphragms were negligible and they can be eliminated. The superstructure of the bridge could be designed with link slab....

Full-Scale Test of Continuity Diaphragms in Skewed Concrete Bridge Girders

Parameters analysis and design of transverse connection strengthening prestressed concrete T-girder bridge

Over the years, bridge engineers have been concerned about the response of prestressed concrete (PC) girder bridges that had been hit by over-height vehicles or vehicle loads. When a bridge is struck by an over-height vehicle or vehicle load, usually the outside and in some instances one of the interior girders are damaged. The effect of intermediate diaphragms in providing damage protection to the PC girders of a bridge is not clearly defined. This analytical study focused on the role of intermediate diaphragms in reducing the occurrence of damage in the girders of a PC girder bridge that has been struck by an over-height vehicle or vehicle load. The study also investigated whether a steel, intermediate diaphragm would essentially provide the same degree of impact protection for PC girders as that provided by a reinforced concrete diaphragm. This investigation includes the following: a literature search and a survey questionnaire to determine the state-of-the-art in the use and design of intermediate diaphragms in PC girder bridges. Comparisons were made between the strain and displacement results that were experimentally measured for a large-scale, laboratory, model bridge during previously documented work and those results that were obtained from analyses of the finite element models that were developed during this research for that bridge. These comparisons were conducted to calibrate the finite element models used in the analyses for this research on intermediate diaphragms. Finite element models were developed for non-skewed and skewed PC girder bridges. Each model was analyzed with either a reinforced concrete or two types of steel, intermediate diaphragms that were located at mid-span of an interior span for a PC girder bridge. The bridge models were analyzed for lateral impact loads that were applied to the bottom flange of the exterior girders at the diaphragm's location and away from the diaphragm's location. A comparison was conducted between the strains and displacements induced in the girders for each intermediate diaphragm type. These results showed that intermediate diaphragms have an effect in reducing impact damage to the PC girders. When the lateral impact load was applied at the diaphragm's location, the reinforced concrete diaphragms provided more protection for the girders than that provided by the two types of steel diaphragms. The three types of diaphragms provided essentially the same degree of protection to the impacted PC girder when the lateral impact load was applied away from the diaphragm's location.

Steel Diaphragms in Prestressed Concrete Girder Bridges

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=22050&context=rtd

Lateral impact response for prestressed concrete girder bridges with intermediate diaphragms

As shear requirements for prestressed concrete girders have changed, some structures designed using older specifications do not rate well with current methods. However, signs of shear distress have not been observed in these bridge girders and they are often deemed to be in good condition. The primary objective of this research program was to investigate the accuracy of existing shear distribution factors, which are used to estimate bridge system live load effects on individual girders, and provide recommendations on shear distribution to be used in Minnesota with four components: a full-scale laboratory bridge subjected to elastic and inelastic behavior, field testing of bridges, a numerical parametric study, and integration of results to develop a screening tool to determine which structures benefited from refined analysis. Laboratory bridge inelastic testing indicated shear force redistribution after cracking and before ultimate failure. Use of elastic distribution factors is conservative for shear distribution at ultimate capacity. Elastic laboratory testing was used to validate the finite element modeling technique and study the behavior of a barrier and end diaphragm, which affected shear distribution; ignoring their effects was conservative. Parametric study results indicated that a ratio of longitudinal stiffness to transverse stiffness could be used as a screening tool. If the stiffness ratio was less than 1.5, shear demand from a simple, conservative grillage analysis may be more accurate than shear demand from AASHTO distribution factor methods. Grillage analysis shear demand results due to permit trucks may also be more accurate, regardless of the screening tool ratio.

Investigation of Shear Distribution Factors in Prestressed Concrete Girder Bridges

Four scale microconcrete model bridges were tested. Experimental variables included span, skew angle, stiffness, location and number of diaphragms. Service load level behavior was studied under static, cyclic and impact loads with successive removal of diaphragms. Behavior at overload and ultimate load conditions was documented from ultimate static and impact load tests. Characteristics studied were load distribution under static service loads and overloads, ultimate load capacities and failure modes of girders, cracking and ultimate load capacities of slabs, dynamic amplification, bridge damping, fundamental modes of vibration and natural frequencies, response to lateral impacts, and stresses in diaphragms. A computer program was verified with experimental results and used to generalize findings. The only significant role of interior diaphragms found is to distribute the load more evenly. In no case was an appreciable reduction in the governing design moment found. A cost analysis showed it would be more economical to provide increased girder strength than to rely on improved distribution of load decreasing the girder design moment due to provision of diaphragms. Design live loads for girders determined from the distribution factors of the 1969 AASHO specifications were found to be conservative even without diaphragms. Provision of interior diaphragms made the girders more vulnerable to damages from lateral impacts. It was recommended that interior diaphragms not be provided in simply supported prestressed concrete girder and slab bridges. Provision of exterior diaphragms or some alternate method of supporting or strengthening the free edge of the transverse slab was considered necessary for reliable serviceability. /FHWA/

The effect of diaphragms in prestressed concrete girder and slab bridges

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The effect of diaphragms in prestressed concrete girder and slab bridges