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Showing 1-5 of 16 Abstracts search results

Document: 

SP232

Date: 

October 1, 2005

Author(s):

Editor: Maria Anna Polak

Publication:

Symposium Papers

Volume:

232

Abstract:

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.

DOI:

10.14359/14960


Document: 

SP232-13

Date: 

October 1, 2005

Author(s):

H. Sundquist, Ph.D.

Publication:

Symposium Papers

Volume:

232

Abstract:

At the department of Structural Engineering, formerly the Department ofBuilding Statics and Structural Engineering and the Department of Bridge Structures,Royal Institute of Technology in Stockholm (KTH), now merged into the Department ofArchitectural and Civil Engineering, research on punching of concrete slabs and plateshas been conducted for many years. The first report published in English was thefamous “Punching of Concrete Slabs without Shear Reinforcement” Nylander &Kinnunen (1961). [22] Since then, a large number of punching tests have beenconducted, many of these are unpublished or only published in Swedish. This paper willsummarize some of the tests performed and also present new findings in this importantfield.

DOI:

10.14359/14945


Document: 

SP232-14

Date: 

October 1, 2005

Author(s):

A. Pisanty

Publication:

Symposium Papers

Volume:

232

Abstract:

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.

DOI:

10.14359/14946


Document: 

SP232-15

Date: 

October 1, 2005

Author(s):

A.B. Ajdukiewicz and J.S. Hulimka

Publication:

Symposium Papers

Volume:

232

Abstract:

To improve punching shear capacity of slab-column connections, and toreplace other kinds of strengthening, the composite joints were introduced. The idea isto use combined head-and-column precast members and cast on site remaining partsof slabs. Following this general idea the precast parts from high performance concrete(HPC) and fiber reinforced high-performance concrete (FRHPC) were introduced. Thetests of such axi-symmetrical joints were done by the authors. The first two series ofmodels with the composite joints were tested to compare results and behavior ofconnections with HPC precast heads and formerly tested models with prefabricatesfrom ordinary concrete. The size of models was 2.7 ´ 2.7 m, with a total slab thicknessof 0.26 m. Three different sizes and two shapes of heads – circular and square – wereused in the tests. The final series of models was prepared with FRHPC heads. Eachseries contained four models, so the experimental data from 16 tests are presented.The heads from FRHPC appeared satisfactory to carry punching forces over two timesgreater than heads from the same HPC without fibers. Advantages from use of FRHPChead-and-column precast members have been confirmed in multi-phase failure as wellas in the significant increment of punching shear capacity of connections. On the basisof experiments, the analytical model of punching failure was calibrated. This model istaking into account the recent simplified physical models for homogenous slab-columnconnections and the failure criterion based on facture mechanics.

DOI:

10.14359/14947


Document: 

SP232-11

Date: 

October 1, 2005

Author(s):

N.J. Gardner

Publication:

Symposium Papers

Volume:

232

Abstract:

Flat slabs are an economical structural system for medium height residentialand office buildings. Prestressed concrete flat slabs have the additional advantagesthat longer spans can be used and deflection problems are less significant. Punchingshear of reinforced or prestressed concrete flat slabs is an undesirable mode of failurein that it occurs without warning and can lead to progressive collapse of large areas ofslab or even complete structures. Modelling the punching shear strength ofprestressed concrete slabs is conceptually difficult as the tendons can be bonded orunbonded, the tendons can pass through the columns or not, the stress in the tendonsat punching failure is indeterminate, the tendons can be banded and the tendons canbe draped resulting in beneficial vertical components of the prestressing force.The paper describes the code provisions, ACI 318-05, BS 8110-97, CEB-FIP 1990 ModelCode (Comité Euro-International du Béton and Federation International de laPrecontrainte), CSA A23.3-04, DIN 1045-1:2001-07 and Eurocode 2-2003. In general, thecode provisions for punching shear of prestressed concrete flat slabs are extensions ofthe punching shear provisions for reinforced concrete flat slabs. Most codes requiresupplementary bonded reinforcement in negative moment regions which complicatesanalysis.The literature has been reviewed to locate experimental results of punching shear testsfor isolated prestressed concrete flat plates, continuous prestressed flat plate systemsand tests of flat plate column connections under shear and moment transfer. Recentresearch has indicated that the limitations on concrete strength in code equations andignoring the precompression close to the slab edge are too conservative.The simplifications of an effective slab depth not less than 80% of the slab depthpermitted by ACI 318 and CSA A23.3 in calculations of the punching shear capacity ofprestressed concrete flat slabs should be eliminated.

DOI:

10.14359/14943


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