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In the paper the results of experimental investigations concerning flat slabs made from reinforced lightweight concrete with sintered fly ash aggregate CERTYD were presented. In the research program 6 models made in a natural scale were included. The main variable parameter was slab longitudinal reinforcement ratio. The aim of investigation was the experimental verification of efficiency of double-headed studs as punching shear reinforcement. In the existing technical approvals such kind of reinforcement was allowed only in normal concrete slabs. It was demonstrated that double-headed studs can be an effective transverse reinforcement of lightweight aggregate concrete slabs. The use of double-headed studs resulted in increase in the ultimate load from 19% to 44%, depending on the slab reinforcement ratio which ranged from 0.5% to 1.2%. The comparative analysis showed that the Eurocode 2 provisions were conservative in relation to the experimental results, which were on average 42% higher than the theoretical ones however with a very low 7% coefficient of variation.

A punção é uma forma de ruptura por cisalhamento que pode ocorrer em ligações laje-pilar que pode ser evitada utilizando-se armaduras de cisalhamento na ligação. Este artigo apresenta comparações entre resultados experimentais de 36 ensaios realizados em ligações laje-pilar interno, armadas com conectores de cisalhamento do tipo pino de duas cabeças, populares na América do Norte, Europa e Ásia, com resultados teóricos utilizando as recomendações do ACI 318, NBR 6118, Eurocode 2, além da Teoria da Fissura Crítica de Cisalhamento (TFCC). Para o banco de dados utilizado, o ACI 318 mostrou tendências conservadoras, enquanto que a NBR 6118 mostrou baixo coeficiente de variação, mas um grande número de resultados contra a segurança. Tanto o Eurocode 2, quanto a TFCC apresentaram resultados satisfatórios, com o Eurocode 2 apresentando desempenho ligeiramente superior. Punching shear is a brittle failure mode that may occur in slab-column connections, which may be prevented by using shear reinforcement in the slab-column connection. This paper presents comparisons between experimental results of 36 tests in internal slab-column connections with double- headed shear studs, which are largely used in North America, Europe and Asia, with theoretical results using recommendations presented by ACI 318, NBR6118, Eurocode 2 and also the Critical Shear Crack Theory (CSCT).Considering the database used it is possible to observe that ACI 318 presents conservative trends, whereas NBR 6118 showed a low coefficient of variation, but with a large number of unsafe results. Both Eurocode 2 and CSCT showed satisfactory results with Eurocode 2 presenting slightly higher performance. OLIVEIRA, D. R. C. Pós-Dr. Docente da Universidade Federal do Pará, Instituto de Tecnologia, Faculdade de Engenharia Civil FERREIRA, M. P. Pós-Dr. Docente da Universidade Federal do Pará, Instituto de Tecnologia, Faculdade de Engenharia Civil

Current code requirements for the design of beam-coumn joints shear reinforcement for earthquake resistance result in steel congestion, and consequently poor quality of the joint, construction difficulties and high cost. Based on previous research, steel studs with plain (non-deformed) stems and a head at each end can replace conventional closed hoops and cross ties for shear reinforcing the beam-column joints. Use of the headed studs in the joint results in reduction of the steel congestion, and hence, easier assemblage of the reinforcing cage and improved joint performance. The present research investigates experimentally the use of steel double-headed studs with deformed stems and Glass Fibre-Reinforced Polymer (GFRP) double-headed bars in lieu of the steel double-headed studs with plain stems. The experimental program consists of constructing and testing nine full-scale beam-column joint specimens under quasi-static cyclic loading. The specimens represent exterior beam-column joints subassembly isolated at the points of contra-flexure in a multi-storey multi-bay moment resisting concrete frame. The test parameters include the material and type of double-headed studs and their amount in the in-plane and out-of- plane directions and the concrete strength. Envelopes of the load-displacement hysteresis loops, moment-lateral drift angle, load-ductility, storey shear-drift angle, and the joint shear strength-deformation are plotted and analyzed. The stiffness degradation, the strains in the joint reinforcement, the contribution of specimen elements (joint, beam, and column) to the drift angle, and the energy dissipation capacity of the specimens are presented and discussed. Performance of the tested specimens is checked against the requirements and acceptance criteria of the ACI 374.1-05, ACI 252R-02 and CSA A23.3-04. The use of steel deformed studs or GFRP headed bars proved to be an acceptable replacement of closed hoops and cross-ties as shear reinforcement of beam-column joints. All of the tested specimens exhibited acceptable behavior satisfying the code requirements. Some specimens demonstrated better behavior in comparison with the specimen designed and reinforced according to the code provisions.