The ACI Code design equation for concentric punching shear is often criticized for failing to account for the effect of flexural reinforcement. This criticism is based on the poor performance of the code equation as a predictor of test results. However, in thecontext of design, the code works as well as any detailed analytical model available, witha fraction of the computation effort. This is because for non-prestressed slabs the codeequation correctly identifies the transition between flexural failure and shear failure,assuming the slab has been correctly designed for flexure. It is concluded that a strongargument can be made for retaining the current equation for concentric punching.

Presented in this paper is an experimental program involving the testing offive 3/4 scale, interior slab-rectangular column connections subjected to combinedeffects of gravity and biaxial unbalanced moments. This experiment investigates theeffects of biaxial loading, and use of stud shear reinforcement, on the performance ofthe connections for rectangular columns with aspect ratio of 5. The main parametersstudied are the strength, drift capacity, ductility, and stiffness of the slab-columnconnections. It was found that biaxial unbalanced moments reduce considerably thestrength, ductility, drift capacity, and stiffness of the connection. It was also found thatslab-column connections with rectangular columns having column aspect ratio of fiveand loaded biaxially may not be able to sustain a drift ratio of 1.5% even if gravity shearratio Vg/Vo is kept less than 0.4.

The effects of the column dimensions on the punching shear strength andductility of slab-column connections are investigated. For this purpose, five edgecolumn-slab connections were tested. The parameters were the column aspect ratioand the perimeter length of the critical shear section. The test results in addition to testresults from the literature for interior columns are compared with the shear strengthprovisions of the ACI Code. The validity of applying the shear strength equationsoriginally developed for interior connections is investigated, in particular with respect tothe effect of the column dimensions.

The bearing capacity under punching shear has been addressed in a seriesof experiments. Three types of shear reinforcement of the stirrups type have beenopted as well as the most suitable position of the shear reinforcement. Reinforcementquantities have been modified versus code requirements. Tests results indicate that thesuggested shear reinforcement performed very well. Some requirements in the twoNorth American Codes appear to be conservative compared to the European codes.Bearing capacity assessment in some codes appears to be conservative (bearing inmind, however, that a variety of additional considerations are taken while codedrafting) . Behavior in serviceability was very satisfactory.

SP-232 The development of high-performance materials and advanced computational tools has allowed the building of relatively thin concrete slabs supported on columns. The simple appearance of such structural systems and ease of their construction make them economically attractive and popular. However, these structures develop complex three-dimensional stresses in the slab, at the columns, which can eventually lead to a potentially catastrophic brittle punching shear failure. Although structural failures are rare, in part due to high safety factors, understanding punching shear phenomenon is crucial for safe and rational design of flat reinforced concrete slabs supported on columns. As part of the activities of the ACI/ASCE Committee 445, Shear and Torsion, members of Subcommittee 445-C, Punching Shear, organized a symposium in conjunction with this special publication devoted to the state of the art on punching shear. The symposium will be held during the ACI Fall 2005 Convention under the sponsorship of ACI/ASCE Committee 445. The last significant and comprehensive overviews on this topic were completed several years ago by the fédération internationale du béton (fib) in their state-of-the-art report on punching shear (2001)1 and in the Proceedings of the International Workshop on Punching Shear Capacity of RC Slabs (2000)2 published by the Royal Institute of Technology in Sweden. Subcommittee 445-C has compiled a series of papers that present updated developments in the state of the art and research regarding behavior, rational design, and evaluation of code provisions related to punching shear. The papers are grouped into two parts. The first part contains a report, coauthored by members of Subcommittee 445-C, on issues related to design philosophy, code provisions, contributions of flexural and shear reinforcements, and seismic and blast loads. The second part includes papers on new developments obtained from different research centers from around the world. The aim is to present comprehensive and objective information on the topic of punching shear. It is hoped that this publication will be important for the engineering design community in its efforts to improve long-term strength and ductility of slab-column structural systems.