Evaluation of Impact-Critical RC Beams Strengthened with a Bottom Layer of HPFRCC

One of the most hazardous consequences of impacts on concrete structures is the high tendency to develop shear or punching failures, with debris generation and associated flying fragments split out. In order to reduce such hazards, concrete structures can be strengthened with a thin bottom layer of high performance fiber-reinforced cement composites (HPFRCCs). As strengthening and anti-spalling layers, the most demanding application is for shear-critical elements, where extensive diagonal cracking leads to multiple fragments, besides concrete cover spalling typical of bending-critical members. An experimental campaign has been carried out on 21 beams to investigate their failure mode. Different configurations were studied for the HPFRCC to determine the influence of the fiber amount (2-4%) and the introduction of embedded steel bars in the strengthening layer. Specimens were subjected to drop weight tests and quasi-static reference tests. The tests have shown that a membrane-type resisting mechanism can be activated by the HPFRCC layer, which can retain potentially falling generated fragments and improve the carrying capacity. Embedding steel bars in the strengthening layers can avoid HPFRCC rupture. Moreover, members strengthened using tensile strain-hardening HPFRCC mixes have shown enhanced strength compared with unstrengthened members, while mixes without strain-hardening did not.

Automated summary

One of the most hazardous consequences of impacts on concrete structures is the high tendency to develop shear or punching failures, with potential debris generation and associated flying fragments. Strengthening concrete structures with a thin bottom layer of high performance fiber-reinforced cement composites (HPFRCCs) can reduce such hazards. Experimental results showed that the HPFRCC layer can activate a membrane-type resisting mechanism, which can retain potentially falling generated fragments and improve the carrying capacity.