Guilherme S. Melo

Model to Simulate the Contribution of Fiber Reinforcement for the Punching Resistance of RC Slabs

AbstractIn this paper analytical formulations are developed for predicting the punching resistance of flat slabs of steel fiber–reinforced concrete (SFRC) flexurally reinforced with steel bars. By performing statistical analysis with a database that collects experimental results on the characterization of the postcracking behavior of SFRC, equations are determined for evaluating the residual flexural tensile strength parameters (fRi) from fundamental data that characterize steel fibers. The fRi strength parameters proposed by CEB-FIP 2010 were used for the definition of the stress-crack width law (σ-w) that simulates the fiber-reinforcement mechanisms in cement-based materials. The second part of the paper describes an analytical formulation based on the concepts proposed by Muttoni and Ruiz, where the σ-w law is conveniently integrated for simulation of the contribution of steel fibers for the punching resistance of SFRC slabs. By using a database composed of 154 punching tests with SFRC slabs, the good ...

Punching of Reinforced Concrete Flat Slabs with Double- Headed Shear Reinforcement

Twelve slabs, 11 of which contained double-headed studs as shear reinforcement, were tested supported by central column and loaded concentrically. Their behavior is described in terms of deflections, rotations, strains of the concrete close to the column, strains of the flexural reinforcement across the slab width, and strains of the studs. All failures were by punching, in most cases within the shear reinforced region. The treatments of punching resistance in ACI 318, Eurocode 2 (EC2), and the critical shear crack theory (CSCT) are described, and their predictions are compared with the results of the present tests and 39 others from the literature. The accuracy of predictions improves from ACI 318 to EC2 to CSCT—that is, with increasing complexity. However, the CSCT assumptions about behavior are not well supported by the experimental observations.

Punching Shear of Reinforced Concrete Flat Plates with Openings

Punching shear tests were conducted on 13 reinforced concrete flat plates with and without openings or/and shear reinforcement. The openings (one or two) were adjacent to the shorter sides of rectangular supports and had widths equal to those of the supports. The methods of calculating punching shear strengths given in ACI 318-11 and MC90/EC2 are reviewed along with some proposed formulations, and their predictions are compared with the test results. Conclusions are drawn on the influence of plate depth on the unit shear resistance from the concrete; the possibility of using straight projections of openings onto control perimeters, rather than radial ones, to evaluate the effect of openings; and the case for considering eccentricity in a pattern of openings as an influencing factor and the detailing of shear reinforcement. It is shown that for the relatively small openings considered, the provision of continuous bars adjacent to openings--to replace the areas of reinforcement--seems to be an adequate approach to flexural design. It is suggested that the shear stress used for the concrete in ACI 318-11 could be increased for the assessment of strengths at the edges of zones with shear reinforcement (outer control perimeter).

Punção em lajes lisas de concreto armado sem armadura de cisalhamento

Punching strength is a critical point in the design of flat slabs and due to the lack of a theoretical method capable of explaining this phenomenon, empirical formulations presented by codes of practice are still the most used method to check the bearing capacity of slab-column connections. This paper discusses relevant aspects of the development of flat slabs, the factors that influence the punching resistance of slabs without shear reinforcement and makes comparisons between the experimental results organized in a database with 74 slabs carefully selected with theoretical results using the recommendations of ACI 318, EUROCODE 2 and NBR 6118 and also through the Critical Shear Crack Theory, presented by Muttoni (2008) and incorporated the new fib Model Code (2010).

Punching Shear in Post-Tensioned Flat Slabs with Stud Rail Shear Reinforcement

ACI Structural Journal, V. 108, No. 5, September-October 2011. MS No. S-2007-184.R4 received January 30, 2010, and reviewed under Institute publication policies. Copyright

Punção em lajes lisas de concreto armado com furo adjacente ao pilar e transferência de momento

The structural behavior and the ultimate punching shear resistance of internal reinforced concrete flat slab-column connections, with one hole adjacent to the column, with or without flexural moment transfer of the slab to the column was investigated. Main variables were: the existence whether or not hole, flexural reinforcement layout and ratio, the direction and sense of the moment transferred and the eccentricity of the load (M (moment transferred to column) / V (shear)) ratio at the connection - 0,50 m or 0,25 m. Seven internal slab-column joining were tested and ultimate loads, cracking, deflections, concrete and reinforcement strains were analyzed. The existence of hole adjacent to the smaller column dimension, the hole dimension, flexural reinforcement rate and placing, the variation of relation Mu/Vu in function of the load, and, than, of eccentricity of the load, influenced the slabs behavior and rupture load. Test results were compared with the estimations from CEB-FIP/MC1990 [7], EC2/2004 [12], ACI-318:2011 [1] and NBR 6118:2007 [5]. ACI [1] and EC2 [12] presented most conservative estimates, although have presented some non conservative estimates. Brazilian NBR [5], even though being partly based in EC2 [12], presented smaller conservative estimates and more non conservative estimates. A modification on all codes is proposed for taking in account the moment caused by the eccentricity at the critical perimeter for slabs with holes.