Ronaldo Barros Gomes

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).

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.

Behavior of reinforced concrete columns strenghtened by partial jacketing

This article presents the study of reinforced concrete columns strengthened using a partial jacket consisting of a 35mm self-compacting concrete layer added to its most compressed face and tested in combined compression and uniaxial bending until rupture. Wedge bolt connectors were used to increase bond at the interface between the two concrete layers of different ages. Seven 2000 mm long columns were tested. Two columns were cast monolithically and named PO (original column) e PR (reference column). The other five columns were strengthened using a new 35 mm thick self-compacting concrete layer attached to the column face subjected to highest compressive stresses. Column PO had a 120mm by 250 mm rectangular cross section and other columns had a 155 mm by 250mm cross section after the strengthening procedure. Results show that the ultimate resistance of the strengthened columns was more than three times the ultimate resistance of the original column PO, indicating the effectiveness of the strengthening procedure. Detachment of the new concrete layer with concrete crushing and steel yielding occurred in the strengthened columns.