Influence of reinforcement arrangement in flexural fire behavior of hollow core slabs
Abstract This paper describes standard scale fire tests conducted on four precast prestressed hollow core slabs configurations under flexure. The influence of the reinforcement arrangement was investigated using two test parameters: the average axis distance (from 30.1 to 46.7 mm), and the type of reinforcement (5 mm diameter wires and 9.5 mm diameter strands). An ISO 834 standard fire was applied maintaining the load level in a four-point test arrangement constant. The results presented different failure mechanisms, types of cracks, spalling patterns, and fire resistance ratings and it was shown that wires displayed optimal behavior as opposed to strands. A comparison was carried out with the current verification methods provided in Eurocode 2 part 1–2, and showed that verification methods tend to overestimate the calculation of fire resistance when both wire and strands are moved away from the exposed surface.
Shear Tests of Extruded Hollow-Core Slabs
T hrough the years, hollow-core slabs have undergone extensive tests to verify their compliance with the provisions of the ACI Building Code. The advent of the 1971 ACI Code brought with it a number of provisions which were markedly different from prior codes to the extent that an updated, comprehensive testing program for hollow-core slabs seemed in order. The specific code area containing the most ambiguous requirement was the section dealing with minimum web reinforcement. Also, since several hollow —core extruded slab systems are made with zero slump concrete, there is an additional reason to examine their characteristics experimentally since the shear strength provisions of the ACI Code were developed from tests of wet cast concrete. While this investigation was originally developed to provide proprietary information, certain observations were deemed appropriate for publication. First, dry cast, extruded hollow-core slabs depend on compaction of a zero slump concrete to achieve a monolithic cross section. Too little data on full scale tests of such slabs is available to the profession. Secondly, shear tests also provide information on the bond strength of the prestressing strands. The Commentary to the ACI Code' specifically cautions the user on the applicability of development length equations for noslump concrete. Considerable discussion'7 has also been generated on development length in general, including some recommendations for increased development length requirements. The tests described herein provide data relative to development length. Because of the differences in production techniques of various extruded hollow-core slabs, it is necessary to state that the test specimens were Spancrete, produced in the Waukesha, Wisconsin plant owned by Spancrete Industries. Shear and bond strength are dependent
Shear Resistance of PHC Slabs Supported on Beams. I: Tests
Ten large-scale tests on floors comprising hollow-core slabs supported on beams were carried out. All tests ended in web shear failure of slabs close to the supports of the beam. In one test the shear resistance was not reduced, but in others was only 40–77% of the reference value measured on non-flexible supports. In one test yielding of the reinforcement in the supporting beam preceded failure. In other tests the beams did not yield and their deflection at slab failure was very small, typically \db\N/1,000–\iL\i\db/300. Reduction of shear resistance is due to transverse deformation of the slab ends resulting from deflection of the beam. The reduction is so great that it must be considered in design, even though collapses due to such reduction, thanks to the high safety factors applied, have neither occurred nor are likely to occur in conventionally designed floors.