Developing optimized strengthening systems for shear‐deficient concrete members

Abstract

Austrian Federal Railways ÖBB, Austrian motorway operator ASFINAG Strengthening methods for shear-deficient bridges were developed and tested in cooperation with the HILTI Corporation and SIKA Austria. In order to identify the strengthening effect in shear, a number of 12 T-shaped RC-beams with a length of 5.38 m were designed. In the experimental campaign two different types of strengthening systems were applied and subjected to shear loading until failure. The successful use of a modern digital image correlation system provided the basis for an in-depth analysis of failure mode and crack pattern as well as shear degradation at each load stage. Finally, the applicability of existing shear design models with consideration of the strengthening elements analogously to cast-in shear reinforcement was evaluated.anchorage, carbon fiber, FRP, postinstalled, shear, shear test, strengthening, undercut anchor 1 | INTRODUCTION Subsequent strengthening of existing structures has gained in importance over the last decades due to the decreasing number of new structures and the ever-growing number of existing ones. The ongoing increase in traffic loads, continuous updating of design codes, and also paradigm shifts lead to the fact that a number of existing bridge structures do not fulfill the required safety level concerning the shearbearing capacity as required by codes of practice such as Eurocode 2. 1 Meanwhile, there exist refined methods for the verification of the shear load-bearing capacity 2-7 , developed from more consistent mechanical models. MC2010 8 provides advanced design approaches allowing for a better utilization of the real structural resistance. Nevertheless, the need for sound technical solutions in the subsequent shear strengthening of existing reinforced concrete (RC) structures is constantly increasing.While the flexural strengthening of RC members has become a routine task, the retrofitting of shear-deficient members is still a challenging issue for the following reasons:• Local shear retrofitting requires the introduction of forces over very short distances. In comparison, flexural strengthening is oriented in the longitudinal direction of a structural member and usually applied over larger sections. Therefore, adequate stiffness and proper anchorage solutions are needed when strengthening in shear. • The strengthening system must be reliably activated without the necessity of large additional live loads or deformations of the structure. • Currently, there are no harmonized recommendations for RC shear design itself available; therefore, the rather complex design of shear strengthening is even more disputable.A few established methods to strengthen RC structures in shear already exist (see e.g., overview in Reference 9). Selected popular methods for shear strengthening are discussed and compared on the basis of experimental investigations in Reference 10. With respect to the affected sections of a structure and the impact on the overall structural behavior, such strengthening solutions can generally be...

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