This paper provides an experimental investigation on the moment-rotation response of typical moment resisting beam-column connections, employing continuous negative bars consolidated with cast in place concrete over the precast beam and passing through grouted corrugated sleeves into an intermediate column. According to [1], the relative beam-column rotation is highly dependent on the elongation mechanism of the negative bars related to both the embedment length into the grouted sleeves and the development length over the beam end, being also inversely dependent on the vertical distance between the position of the top bars and the centre of rotation at end beam section. The flexural secant stiffness of the moment-rotation response is caused by a sum of the joint opening mechanisms at the beam-column interface and crack propagation within the connection zone, wherein the bond-slip at crack positions occurs prior to the first yielding of the negative bars. Therefore, the semi-rigid behaviour of the beam-column connections is associated with deformation mechanisms that occur at the SLS, but which also affects the global behaviour and stability analysis of precast frames at the ULS.Cruciform tests of full scale beam-column connections were carried out at the Precast Research Centre of the Federal University of Sao Carlos (Brazil), where 6 prototypes were studied varying the detailing of the positive connectors over the concrete corbel. The first pair of connectors employed elastomeric bearing pads with 2 vertical dowel bars, the second pair of connectors employed horizontal joints filled with grout with 2 vertical dowel bars and the last pair of connectors employed positive welded plates. The comparison between the experimental results showed that the smallest secant stiffness, which was obtained from the connector with elastomeric bearing pad, was corresponded to 89% and to 82% of the highest secant stiffness obtained for the connectors with welded plates and grouted joint, respectively. Therefore, the experimental results indicate that the major deformation mechanism within the beam-column connections is mostly dependent on the elongation of the top bars. Finally, a simplified analytical equation has been calibrated against the experimental results of the studied beam-column connections.
RESUMO No presente artigo, apresenta-se o resultado de uma investigação experimental sobre o comportamento semirrígido de ligações típicas viga-pilar em estruturas pré-moldadas de concreto armado, projetadas para resistir ao momento fletor negativo por meio de armadura de continuidade solidarizada no local passante em bainhas corrugadas com preenchimento de graute em pilar central. O programa experimental envolveu 6 ensaios de protótipos cruciforme de ligações viga-pilar em escala real, onde o detalhamento da armadura negativa foi mantido igual para todos os modelos, mas variou-se o detalhamento das ligações positivas n o apoio da viga sobre o consolo, sendo 2 modelos com almofadas de elastômero e chumbadores verticais, 2 modelos com junta grauteada e chumbadores verticais e 2 modelos com chapas soldadas positivas. Com base nos resultados experimentais, observou-se que o detalhamento na ligação positiva apresentou influência secundária sobre a rigidez secante negativa da ligação viga-pilar, onde a rigidez média obtida nos modelos com chapas soldadas foi cerca de 11% superior à rigidez média obtida nos modelos com almofadas de elastômero. Portanto, pode-se concluir que a rigidez secante negativa é fortemente associada com o mecanismo de deformação por alongamento da armadura negativa, com escorregamento aço-concreto nas posições fissuradas da região da ligação anterior ao escoamento da armadura, com intensificação deste mecanismo com a abertura na interface viga-pilar a partir do arrancamento parcial de graute de preenchimento na bainha corrugada. Considerando uma viga de concreto armado com rigidez secante (EcI)sec = 0,5EcI e comprimento virtual L = 12h (h = altura da viga), obteve-se um coeficiente médio de engastamento parcial em torno de 65%.
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