Title: Effect of HPC and FRHPC Precast Heads on Punching Shear Resistance of Flat Plates

Author(s): A.B. Ajdukiewicz and J.S. Hulimka

Publication: Symposium Paper

Volume: 232

Issue:

Appears on pages(s): 277-298

Keywords: composite joints; concrete structures; fiber-reinforcedHPC; flat-plate slabs; high-performance concrete; slab-columnconnections; strengthened heads

DOI: 10.14359/14947

Date: 10/1/2005

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.