developing composite action in existing non-composite steel girder ...

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capacity in its overall load-deformation response due to the higher slip capacity of thisconnector. It is believed that high slip capacity of the HTFGB connectors enabled the shearconnectors at the steel-concrete interface to redistribute interface shear among the connectors.However, the HTFGB connectors are more difficult and time-consuming to install than theHASAA and DBLNB connectors. Because of the easier installation characteristics of the HASAAand DBLNB connectors, an approach was developed to increase the deformation capacity ofbeams retrofitted with these connectors.Oehlers and Sved (1995) indicate that concentrating shear connectors near zero momentregions, resulting in the increase of Ashin Eq. 2, can reduce slip at the steel-concrete interfacewhen the beam reaches its full capacity. This suggests that simply supported beams with shearconnectors concentrated near the supports can likely show higher deformation capacity thanbeams with uniformly distributed shear connectors along the span.Finite element analysis was used to evaluate the effect of moving shear connectors near thezero moment regions. First, the full-scale beam test specimens were modeled with ABAQUS.Figure 11 shows load-deflection relations for Specimen HASAA-30BS from the test along withthe finite element analysis results. As shown in the analysis result of Specimen HASAA-30BS,the model used in this research could not simulate the behavior after shear connector failure.However, the model is considered useful for predicting the behavior before shear connectorfailure and the failure of the shear connectors. Figure 12 shows the longitudinal stressdistribution of Specimens HASAA-30BS from the FE analysis. As shown in the figure, neutralaxis of the beam moved toward the beam top flange due to composite action between the twostructural components.Figure 11 also shows the analysis results of a partially composite beam with shear connectorsconcentrated near the supports. In the FE model, shear connectors were moved near thesupports and were located at a 300-mm spacing. The total number of shear connectors was notchanged in the model. The analysis model with concentrated shear connectors was same withthe analysis model of Specimen HASAA-30BS except the shear connector locations. ForSpecimen HASAA-30BS, the connectors were uniformly distributed along the length of thebeam, at a spacing of 725 mm. Compared to Specimen HASAA-30BS, the deformation capacityof the partially composite beam with shear connectors relocated near the supports wasincreased significantly. The increase of its deformation capacity can be attributed to thedecrease in slip at the steel-concrete interface as shown in Fig. 13. The partially compositespecimen with concentrated shear connectors near the support shows much less slip than thespecimen with uniformly distributed shear connectors in ABAQUS.Load (kN)120010008006004002000HASAA-30BS (Test)HASAA-30BS (ABAQUS)Specimen with 300mmconnector spacing (ABAQUS)0 50 100 150 200 250 300Deflection (mm)Figure 11 – Test vs. FE Analysis resultsFigure 12 – Longitudinal stressdistribution of a composite beam
End Slip (mm)302520151050HASAA-30BS (ABAQUS)HASAA-30BS1 (ABAQUS)HASAA-30BS (Test)0 50 100 150 200Deflection (mm)Load (kN)120010008006004002000max: 1042 kNmax: 1065 kNmax: 726 kNNON-00BSHASAA-30BS1HASAA-30BS0 50 100 150 200 250 300Deflection (mm)Figure 13 – Load-End slip relationships Figure 14 – Load-deflection curves for test specimensTest Results for Partially Composite Beam with Concentrated Shear ConnectorsSpecimen HASAA-30BS1 was tested to verify the FE analysis results and evaluate the globalbehavior of partially composite beams with post-installed shear connectors concentrated nearzero moment regions. Specimen HASAA-30BS1 had the same number of shear connectors asSpecimen HASAA-30BS. For Specimen HASAA-30SB1, the shear connectors were movedtowards the ends of the beam, and were spaced at 300 mm.Figure 14 compares test results for Specimens HASAA-30BS1 and HASAA-30BS. Thedeformation capacity of Specimen HASAA-30BS1 (concentrated connectors) is much greaterthan that of Specimen HASAA-30BS (uniform connectors), and is comparable to that ofSpecimen NON-00BS. Specimen HASAA-30BS1 showed first shear connector failure at a 170-mm deflection, after which the applied load increased slightly before another shear connectorfailure at 210 mm. The maximum load was 1043 kN at 197-mm deflection. It appears thatconcentrating shear connectors near the supports not only decreases slip at the steel-concreteinterface, but also helps redistribute loads among shear connectors.Test results from Specimen HASAA-30BS1 indicate that the stiffness and strength of noncompositebeams can be improved significantly by using relatively small number of postinstalledshear connectors without sacrificing deformation capacity.SUMMARYThe study reported herein was the final phase of a research project to develop methods forstrengthening existing non-composite bridge girders using post-installed shear connectors.Previous phases of this study identified possible post-installed shear connectors and evaluatestatic and fatigue performance of those shear connectors. Based on this earlier works, threetypes of post-installed shear connectors were selected for full-scale beam tests.The number of post-installed shear connectors needed to strengthen an existing bridge girder isdetermined based on the concept of partial composite design. Partial composite design is notnormally used for new composite bridge girders, because fatigue typically controls the requirednumber of shear connectors. Because of the superior fatigue characteristics of the post-installedshear connectors tested in this study, however, fatigue is not likely to control the requirednumber of shear connectors, and partial composite design is therefore possible.With partial composite design, 50 to 70 percent of the shear connectors normally needed for fullcomposite design can be eliminated, while still achieving a 40- to 50-percent increase in loadcarryingcapacity in positive-moment regions of a girder. Based on the test data from singleshear connector tests, overall performance of girders retrofitted with post-installed shear
Page 5 and 6: connectors. All specimens were an 1
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