Punching shear failures occur suddenly and produce catastrophic results. The effect of fiber reinforcement on the deformation and strength characteristics of punching shear failures is discussed in this paper. The fibers were used throughout the slab or in the punching shear zone of the column head, and comparative tests were carried out on connections with bent-up steel bars. The results show that fibers reduce deformations at all stages of loading, increase ultimate punching shear loads, and produce ductile shear failures. Substantial increases in ductility and energy absorption can be obtained by using fiber concrete. Fibers can not only produce flexural failures for the same load capacity in shear but can achieve it with considerable saving in flexural steel. Bent-up bars are clearly more effecti•·e than fiber reinforcement but are very labor-imensive.

Punching Shear Behavior of Reinforced Slab-Column ConnectionsMade with Steel Fiber Concrete

A method for analyZing forces in shores and res hares during construction of slab buildings and of long-time deflections is developed that accounts for creep of concrete, differences in its age, and the precise construction sequence. Numerical comparisons of computer solutions with the existing elastic solutions indicate that the effects of creep on the forces in the shores and the loads carried by the slab are small when no reshoring is done. In the case of reshoring, the effect of creep is more significant, but still not very large. The practical usefulness of the solution consists mainly in that long-lime deflectIOns as influenced by the early-age load history can be calculated.

Creep Deflections in Slab Buildings and Forces in Shores during Construction

Large span concrete flat-slab systems with internal spherical void formers (SVF) have been used in Europe for over a decade. They are bi-axially reinforced concrete flat-slab systems with a grid of internal spherical void formers. 
This paper addresses three issues associated with SVF slab systems: their shear resistance, their short-term elastic deflections and their economical value in a South African context. 
Due to the ''loss'' (or reduction) of aggregate interlock required for shear resistance in SVF slabs, the design requirements of the reinforced concrete design code are affected. Research at the Technical University of Darmstadt (TUD) in Germany proved a shear resistance reduction factor of 0,55 to be conservative, while research at the University of Pretoria suggests a greater factor of 0,85 when taking into account the shear capacity of the permanent steel cages that hold the spheres in position in some SVF slab systems. 
Laboratory tests at the TUD, supported by theoretical calculations, further showed reduced deflections for SVF slabs compared to solid slabs. Stiffness is not reduced as much as the selfweight, resulting in smaller overall deflections for SVF slabs compared to those of solid slabs with the same thickness. 
In this paper the economical value of SVF slabs in South Africa will be investigated by comparing the direct construction cost to that of two other large span slab systems, namely coffer and post-tensioned slabs.

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Spherical void formers in concrete slabs

In this paper a number of serviceability issues related mainly to excessive deflections of structural floor elements (beams and slabs) are discussed. Field data of serviceability damage caused by excessive deflections of structural floor elements have been collected from various sources and probabilistic models are developed. Current serviceability specifications for allowable deflection limits in Australian, U.S., and other concrete structure codes have been compared against these probabilistic distributions of damaging deflections. Preliminary results confirm that allowable deflection limits in these design codes represent realistic lower-bound values of damaging deflections.

Probabilistic Models of Damaging Deflections for Floor Elements

Construction Loading in High-Rise Buildings

To enable structural designers to make more accurate assessments of the long-term deflection performance of reinforced concrete flat slabs and plates, the deflections of several actual slabs were measured for up to 9 years, and the results were compared with calculated values. It was found that the measured values were up to five times the values calculated by normal methods. A more ac­ curate method of calculation was developed. This paper provides additional research information for one previous investigation, and summarizes others for the purposes of comparison.

J. L. Heiman

Papers

Long-Term Deflection of Reinforced Concrete Flat Slabs and Plates