International Concrete Abstracts Portal

One of the new techniques to reduce explosive spalling in concrete subjected to fire is to add a cocktail of polypropylene fibers and steel fibers into the concrete mixture. This method is still in the early stages of development and requires more research to investigate the efficiency of introducing such a combination of fibers in reducing explosive spalling in fire. The purpose of this paper is to present the results of an experimental study conducted to investigate the performance of reinforced concrete columns containing steel and polypropylene fibers under different loadings and subjected to severe fire conditions. Two loading levels were investigated representing 0.6 and 0.76 of the ultimate strength limits of ACI 318. Columns containing polypropylene (1 kg/m3) and steel fibers (80kg/m3) showed a higher fire resistance by an average factor of 1.76 compared to columns containing PP fibers (1 kg/m3) only. The paper also assesses the effect of adding steel and polypropylene fibers on the severity of concrete explosion under fire. Measurements of axial displacements and concrete temperatures are presented in this paper. The paper compares the obtained experimental values of the axial displacements with theoretical values calculated using a previously developed simple approach.

Adequate information may not be readily available to justify the development of alternative methods for evaluating and predicting the performance of concrete exposed to fire and elevated temperatures. The recent trends to use alternatives to ASTM E119 such as small-scale testing and computer models is driven primarily by the costs associated with ASTM E119 tests and a desire by some to be able to model the performance of concrete in actual fires. Increased measurement and reporting may be needed to validate these alternative test methods, and analytical computer models and simulations methods to correlate the results of alternative testing techniques and models are needed. These considerations are becoming increasingly more important due to recent efforts to refine existing and develop new methods for the design of buildings to resist fire, including being able to undergo total burnout without collapse.

Unbonded post-tensioned (PT) concrete slabs have been widely used in Canada and the United States since the 1960s, as they allow increased span-to-depth ratios and excellent control of deflections compared to non-prestressed reinforced concrete flexural members. The satisfactory fire performance of unbonded, PT concrete slabs in North America was established by a series of standard fire tests performed in the United States during the 1960s. However, there is a paucity of data on the effect of elevated temperatures on cold-drawn prestressing steel, both in terms of post-fire residual mechanical properties and high-temperature stress relaxation, which can lead to significant prestress loss both during and after a fire. To aid in the post-fire evaluation of PT concrete floors, a series of high-temperature residual tension tests on prestressing steel is presented, along with a second series of tests that illustrate the irrecoverable and significant loss of prestress force that may result from steel relaxation (creep) during a fire. A preliminary model is presented that can be used to predict the change in prestress force and allow for the computation of flexural capacity of a PT slab after a fire.

The connection details of precast, prestressed hollow-core floor units to supporting reinforced concrete beams have a significant influence on the structural behavior of the floor systems during earthquakes. Connections are also one of the most dominant components affecting the fire performance of such floor systems. However, since it is often too complicated to conduct performancebased structural design of hollow-core concrete flooring systems for fire exposure or earthquake attack, engineers are inclined to carry out design using tabulated data and they subsequently overlook the influence of the connections. In this research, an analytical study has been conducted using the finite element tool SAFIR on the structural fire performance of hollow-core floor systems with new connection details that have been experimentally verified to provide better seismic performance. The analytical results show that rotationally rigid end and side connections provide better fire resistance than rotationally flexible connections.

This paper presents the state-of-the-art review and research needs assessment of the fire performance of reinforced concrete (RC) columns. The literature review revealed that almost all of the fire tests have been undertaken on RC columns under standard fire scenarios and were narrow in scope due to limitations in test equipment and loading capacities. There have been limited analytical studies on modeling the fire behavior of RC columns and were mainly based on elemental approach and either neglected spalling or used a very simple and crude model for representing spalling. Most of the current provisions, in codes and standards, for evaluating fire resistance are based on prescriptive approaches and do not include significant parameters that affect fire resistance. Based on this comprehensive review, research needs for developing rational fire design methods for RC columns through a performance-based approach, is highlighted.