International Concrete Abstracts Portal

This CD-ROM contains 10 papers that were presented at sessions sponsored by Joint ACI-TMS Committee 216 at the ACI Fall 2008 Convention held in St. Louis, MO, and the ACI 2010 Spring Convention in Chicago, IL. The papers present some of the latest research findings on the fire performance of concrete. They provide research results from both experimental and numerical studies on various aspects, ranging from high temperature material properties to advanced computer models for tracing the fire response of reinforced concrete structural members. Note: The individual papers are also available. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP-279

In this study, effect of various heating and cooling regimes on the residual compressive stress-strain behavior of confined high strength concrete is investigated. To this end, a total of 57 hoop confined and 21 unconfined high strength concrete cylindrical specimens of size 5.90 x 17.71 inch (150 mm × 450 mm) were tested. The specimens were exposed to seven different temperatures ranging from room temperature to14720F (8000C). Two different heating rates (50C/minute and 150C/minute) and two cooling rates (natural air cooling and water quenching) were employed in the study. Measurements were taken for thermal gradient, spalling and residual axial load-displacement properties of confined high strength concrete. Test results indicate that the residual strength, strain corresponding to the peak stress and the post-peak strains of confined high strength concrete are affected only in the temperature range of 9320F to 14720F (500 to 8000C). Experimental results show that faster rate of heating does not have any detrimental effects on the residual behavior of confined concrete. Lesser thermal induced effects were noticed in specimens exposed to faster rate of heating than in specimens subjected to slower rate of heating irrespective of the temperature of exposure. However, the results suggest that cooling with water quenching has adverse effect on the residual stress-strain properties of confined high strength concrete. Compared with natural cooling, thermal shock induced by water quenching caused more severe damage to confined high strength concrete, in terms of greater losses in confined concrete strength and increase in strains. The results of this study may be useful for designing the confining reinforcement of reinforced concrete columns against the multiple hazards of fire and earthquake.

The assessment of fire safety in a rather slender pretensioned simply-supported beam with a V section is presented in this paper. Such architecturally-valuable thin-walled beams have been used in Italy for the last forty years in the roofs of large industrial or office buildings, where a series of V girders (= secondary beams, with interposed concrete or glass panels) are supported by other girders resting on columns (= primary beams). After several decades since their construction, many of these members exhibit severe symptoms of distress, often in the form of longitudinal cracks, that can significantly reduce the bearing capacity in shear. (These span-wise cracks are mostly due to transverse bending and start propagating close to the supports, along the extrados of the secondary beams, where rain may accumulate because of insufficient or damaged water proofing). The beam in question, with thin and inclined webs, is checked both at the ultimate limit state (ULS) and in fire, with reference to bending, shear (where the traditional truss model is used), and shear-slip close to the supports, where the aforementioned longitudinal cracking may cause a sort of delamination resisted by the partially-corroded stirrups. Reference is mainly made to the provisions of Eurocode 2, but in the check concerning shear transfer along the longitudinal cracks ACI 318-08 comes into play as well. Even if it is rather peculiar for its unusual cross-section, the beam in question offers the opportunity to focus the attention on some general aspects concerning the behavior of prestressed concrete members in fire conditions, and on some weaknesses of past design provisions.

This paper presents an experimental study on the fire behavior of seven restrained RC beams strengthened with carbon fiber sheet (CFS) and provided with fire insulation. The influence of some parameters (i.e., axial and rotational restraint stiffness, thickness of the fire insulation, and load ratio) on the deformations and internal forces of the beams is analyzed. The test results indicate that: (a) for a restrained beam in fire, the maximum axial elongation decreases with increasing stiffness of the axial restraint, and increasing thickness of the fire insulation, while the maximum additional axial force increases with increasing stiffness of the axial restraint, and decreasing thickness of fire insulation. The maximum additional bending moment at the beam ends increases with decreasing thickness of the fire insulation, but on the whole the influence of the thickness of the fire insulation within the investigated range (10~20 mm [0.394~0.787 in]) is rather limited; (b) the additional axial force in a restrained beam recovers slightly during the cooling phase, while the additional bending moment at beam end of a restrained beam recovers significantly in the cooling phase; (c) the peak value of the bending moment of a strengthened and insulated beam occurs much later than in the case of an ordinary RC beam (i.e., without strengthening and fire insulation), while the maximum additional bending moment at beam end is lower; and (d) the influence of the rotational restraint stiffness on the maximum additional bending moments at beam ends is rather limited.

Concrete structures fabricated with high strength concrete (HSC) experience degradation of strength and spalling when exposed to extreme fire conditions. To mitigate fire induced spalling in HSC; different types of fibers are often added to concrete. Presence of fibers influence the properties of HSC and knowledge of high temperature properties is essential for evaluating the fire response of structures made of fiber reinforced HSC. In this paper, thermal and mechanical properties of four types of HSC are evaluated. The four types of concrete comprise of plain HSC, and HSC with 3 types of fibers namely steel, polypropylene and hybrid (steel + polypropylene) fibers. For thermal properties specific heat, thermal conductivity, and thermal expansion are measured, whereas for mechanical properties compressive and tensile strength are measured in the temperature range of 20-800°C (68-1472°F). Results from mechanical property tests show that addition of steel fibers enhances tensile strength of HSC which is beneficial against fire induced spalling. Results from thermal property tests show that presence of fibers increase the specific heat and thermal expansion of fiber reinforced concrete that will affect the development of fire induced thermal gradients and thermal stresses in HSC cross-section. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of fiber reinforced HSC (FRHSC) as a function of temperature. The proposed thermal and mechanical property relationships can be used as input data in computer models for evaluating fire response of structures made of FRHSC.