Marcelo de Araujo Ferreira

Estudo do comportamento de ligações viga-pilar em estruturas pré-moldadas de concreto: análise experimental

Due to the large increase in the use of precast concrete structures in multistory buildings, this work covers a study on the behavior of beam-column connection with emphasis on the continuity provided by the slab reinforcement. Two prototypes were tested, each one with a different detail of the continuity reinforcement distribution. In both connections, the steel area used on the concrete cover of the hollow core slab was the same, varying the amount of bars that passed through the column and the ones that were placed adjacent to the column. The experimental results showed that the connection with bars adjacent to the column presented stiffness increase and a better cracking control. According to the classification the two tested connections can be considered semi-rigid.

Engastamento parcial de ligações viga-pilar em estruturas de concreto armado

This paper presents the results of experimental tests on reinforced concrete beam-column connections carried out at the Engineering School of Sao Carlos - USP. The experimental results concentrate on relative rotations between beam and column, which are importante parameters for the evaluation of the moment-rotation curves and the characterization of semi-rigid behavior of the connections. The experimental results were obtained from tests on specimens of edged beam-column connections. The influence of concrete compressive strength and joint transverse reinforcement ratio on relative rotations was investigated. The experimental results were compared with results obtained from the theoretical model proposed by Ferreira [1] for partially restrained connections, which provided an evaluation of the percentage of restriction obtained by the types of monolithic connections considered in this study.

Moment-Rotation Response of Beam-Column Connections in Precast Concrete Structures

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.

The Use of Moment-Resisting Frames and Braced Frames for Lateral Stability of Multy-Storey Precast Concrete Structures

Precast structures for multi-storey buildings can be designed with economy, safety and high performance. However, depending on the height of the building and the intensity of the lateral loads, the lateral stability system must be carefully chosen in order to maximize the global structural performance. In Brazil, the most common method for lateral stability is achieved by moment resisting precast-frames, wherein the moment-rotation response of the beam-column connections are responsible to provide the frame action, which will govern the distribution of internal forces and the sway distribution along the building height. On the other hand, in Europe, bracing systems comprised by shear walls or infill walls are mostly used, wherein beam-column connections are designed as hinged. The aim of this paper is to present a comparison between these methods for lateral stability, applying nine structural simulations with moment resisting precast-frames, shear walls and infill walls solutions, divided in three groups - 3 building with 5 storeys (21 meters high), 3 buildings with 10 storeys (41 meters high) and 3 building with 20 storeys (81 meters high). All first storeys are 5 meters high, while all the others are 4 meters high. The results from all structural analyses are compared. As conclusion, while moment-resisting beam-column connections are more feasible for applying in low-rise precast buildings, the use of shear walls and infill walls are more efficient for tall buildings due to decrease of lateral displacements, having a reduction of second order effects but also increasing the reactions at the foundations of bracing elements.

Determination of reinforcing bars for tests of hollow core slabs with continuity

© 2013 IBRACON The structural designs of floors formed by hollow core slabs usually consider these as simply-supported slabs. In recent years there have been project changes and hollow core slabs with continuity are widely used. The objective of this study is to suggest a way to calculate the reinforcement bars to be used in tests with continuity provided by a structural topping. Thus, this paper presents a method based on the maximum positive resistance moment and maximum shear strength of a hollow core slab. The method is applied to a test in hollow core slab specimens which have the following dimensions: 2 m width, 6 m long, and 21 cm high. The results indicated that the method was satisfactory to the performed test, and can therefore be applied to the other test configurations or even designs.

Study of Shear Capacity in Brazilian Prestressed Hollow Core Slabs

Hollow core slabs have a bold design and can be used in a wide variety of structural systems, performing like floor slabs or wall panels. These slabs are economical due to geometrical and mechanical efficiency of its cross sections, allowing the rationalization of materials consumption (concrete and prestressed strands). The increase of the use of hollow core slabs within the Brazilian construction market has caused a significant boost of production, demanding the assessment of the actual strength capacity of these elements. This paper presents results relative to several hollow core slabs produced in a Brazilian factory, subjected to shear tests according to FIB recommendations. The experimental results were compared with those obtained with the equations from the Guide to Good Practice: Special Design Considerations for Precast Prestressed Hollow Core Floors, published by FIB in 2000.