Shear and flexural strengthening of reinforced concrete beams with titanium alloy bars

Abstract

Many older reinforced concrete (RC) structures are identified as deficient in flexure and/or shear when applying modern design standards for their evaluation. The deficiencies most often are due to inadequate amounts of reinforcing steel and/or poor reinforcing details. To prevent the need for expensive replacements it is desirable to extend their service life by strengthening them. Strengthening approaches must be both structurally efficient and cost-effective. Titanium alloy bars (TiABs) offer a new opportunity to strengthen such existing structures that has not previously been investigated, due primarily to the perception of high cost. However, titanium's combination of strength, ductility, durability, and ability to form mechanical anchorages are essential characteristics for effective repair and retrofit applications and are advantageous over competing materials such as steel and fiber-reinforced polymer (FRP) products. Round TiABs with unique deformation patterns were specially developed for strengthening RC griders. Research using the TiABs to strengthen RC bridge girders in both flexure and shear was undertaken in the laboratory through full-scale tests. Realistic girder specimens were constructed, instrumented, and tested to failure. The specimens mimicked the in situ materials, loading interactions, and geometry of typical mid-20th century reinforced concrete deck girder bridges that were widely used in the US. The details and proportions of these structures are similar to others around the world. Using the findings, the flexural strengthening techniques were applied to a bridge overcrossing of a major interstate highway in the US. This first ever application of titanium alloy bars to a reinforced concrete bridge was completed at a 30% cost savings compared to alternative designs.