EVALUATING EXTERNAL CFRP STRIPS AND INTERNAL MMFX STEEL SHEAR BARSFOR SHEAR STRENGTHENING OF PRECAST CONCRETE CHANNEL BEAMS

Prior to the mid 1970's a large number of short span bridges were constructed throughout Arkansas using a, then standard, 5.79m long precast, non-prestressed concrete channel beam designed for H15 loading without any provisions for shear reinforcement. A national survey of departments of transportation has concluded that thirteen additional states have similar bridge elements in their highway inventory. A statewide survey indicates that 389 of these bridges remain in service with nearly one-third experiencing potentially serious deterioration. An investigation of the structural integrity of these beams by the University of Arkansas revealed that the shear capacity was inadequate for the updated HS20 design loading. Two shear strengthening retrofit methods were evaluated. One option consisted of placing fiber reinforced polymer (FRP) strips externally on the inside stem portion of the beam. This method of retrofit was selected for its superior mechanical properties over other methods of repair. Another retrofit alternative involved inserting high strength steel reinforcement (MMFX Steel) bars internally in each stem of the beam. The shear bar retrofit was chosen for its ease of implementation and cost effectiveness. In either retrofit, the bars or strips were spaced at an interval to prevent the full formation of diagonal shear cracks within a spacing interval. Four beams retrofitted with the FRP strips and two beams retrofitted with MMFX Steel shear bars were load tested to evaluate the effectiveness of the repair. Both retrofit methods were found to improve deflection behavior when compared to un-retrofitted beams. In addition, these retrofit designs allow for more ductility of the beam, ensuring a flexural failure rather than a catastrophic shear failure.

• INTRODUCTION

• SHEAR STRENGTH EVALUATION

• CARBON FIBER REINFORCED POLYMER STRIPS

• MMFX STEEL SHEAR BAR

• EVALUATION OF RETROFIT METHODS

• CONCLUSIONS

• ACKNOWLEDGEMENTS

• REFERENCES