Bent up bars were prescribed as shear reinforcement in the first half of the twentieth century, stirrups after the 1960’s. In current Eurocode, bent up bars can be applied again, but restrictions with respect to the maximum shear strength should be followed. Goal of this report is to provide background for this shear strength restriction and provide an assessment method for concrete structures reinforced with bent up bars.

First part of the report analyses critical design aspects of bent up bars in the transfer of shear stresses with help of truss models. Second part explores the shear strengths of reinforcement sections and concrete struts with help of outcomes of experiments performed in the past. In last part, the obtained insights are collected and captured into a conceptual model. This model is employed to describe the expected failure mechanism of bent up bars and reflect on assessment methods and maximum shear strengths of specimen reinforced with bent up bars.

Consequence of the application of bent up bars in concrete structures is the formation of cracks in the supporting concrete strut by curved sections of bent up bars. The remaining shear strength of concrete structures depends on the shear resistance of cracked concrete struts.

The findings in this report implies that any model based on the tensile strength of inclined members is applicable for the analysis of bent up bars as long as the applied shear stresses are limited to ten percent of the compressive strength. Also, the application and assessment of bent up bars in concrete structures requires special attention to: shear and flexural reinforcement inclusive designs, cover spalling mechanisms, and detailing of anchorage regions flexural reinforcement bars.