Strengthening of hollow core precast prestressed reinforced concrete slabs using different techniques

Hollow-core precast prestressed reinforced concrete (HCPPRC) slabs have been widely available since the 1980s in different structures due to many advantages. Since no shear reinforcement is arranged in HCPPRC slabs before casting, concrete itself provides the shear resistance, especially in the zones close to the supports, which are the most popular regions for shear failure. This experimental study aims to investigate some shear strengthening techniques for HCPPRC slabs, including using carbon fiber reinforced polymer (CFRP) sheets, concrete topping, filling 50% of the slab voids in shear zones with concrete, filling all shear zone voids with concrete, steel through anchors in shear zones, and mixing between filling 50% of the slab shear zone voids in addition to using steel anchors. The experimental program consists of two control specimens and six shear-strengthened specimens that were tested using two-line loads up to failure. Cracking load, cracking deflection, ultimate load, maximum deflection, and failure mode are recorded and discussed for all specimens. The results show that filling 50% and 100% of shear voids with concrete increases slab concrete strength by about 79% and 61.45%, respectively, while using steel through anchors decreases slab concrete strength. Moreover, filling 50% of the shear voids is the best technique for strengthening the shear capacity of HCPPRC slabs due to increasing the cross-section area of the slab's shear strength. In contrast, using screws with nuts only is not preferred for shear strengthening of HCPPRC slabs.