Slab – column connections that are subjected to combined gravity and horizontal loading during an earthquake are prone to premature failure due to punching shear. Traditional solutions to avoid punching failure and to increase the displacement capacity of this type of connection include using stirrups and double-headed studs as shear reinforcement. The use of High-Performance Fiber Reinforced Concrete (HPFRC) in a small region of the slab around the column as a substitute for traditional solutions is investigated in this paper, because this material has the potential to reduce labor and material costs. To fulfill this objective, four slab specimens with a thickness of 150 mm were tested under combined gravity and reversed horizontal drifts. The results are discussed in detail. The experimental variables considered were the top flexural reinforcement ratio, the size of the HPFRC zone and the intensity of the gravity load. Previously published tests that serve as reference specimens are used to compare the results. The behavior of the specimens with HPFRC was substantially improved compared to the reference specimens in terms of drift capacity: from only 1.0% drift to above 5.5%, even though a very small quantity of HPFRC was used, extended up to only 1.5 times the effective depth of the slab from the face of the column. Specimens with HPFRC also behaved better when compared to specimens with High-Strength Concrete (HSC). Side effects of using HPFRC in the slab in the vicinity of the column include an increase of the unbalanced moment transfer capacity and lateral stiffness, as well as a reduction of the deflections of the slab.

The following dissertation studies the behavior of flat slabs when subjected to constant vertical loads and cyclic horizontal displacements, as a continuation of previous studies developed at FCT/UNL. The main focus of this research is to study the influence of flexural reinforcement on the seismic response of flat slabs. Therefore, three reinforced concrete flat slabs with varying flexural reinforcement ratio were tested, two having the same top reinforcement ratio of !=0,64% and one with !=1,34%. One of the specimens with lower longitudinal ratio was reinforced with studs as specific punching shear reinforcement. All slabs had overall dimensions of 4,15 × 1,85 × 0,15 m3 and a gravity shear ratio, ratio between the gravity load and the punching shear resistance, approximately equal to 55%. For a more complete analysis the results obtained were compared to two other specimens from previous experimental campaigns also conducted at FCT/UNL. These two slabs were designed with top flexural reinforcement ratio (!=0,96%) that lies between the two tested in this dissertation, one with no shear-reinforcement and the other with headed studs. Results showed that the reduction of flexural reinforcement resulted in a more ductile behavior of the specimens and in a higher drift capacity. The high flexural ratio added to one specimen improved the maximum unbalanced moment capacity but also made the slab fail in a more brittle mode. As expected, the specimen with shear headed studs supported the highest drifts and ended up not failing during this experimental campaign, reaching the test setup upper limit.