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Barr, in Comprehensive Structural Integrity1. At one end of the spectrum, bridge parapets are subjected to impact loading from vehicles, which can cause significant damage; and, at the other end of the scale, buildings can be subject to aircraft impact, leading to collapse due to the intense fire which follows, as in the case of one of the World Trade Center buildings.
Fire has also caused major damage to a number of tunnels, e. Fire damage to concrete structures has been studied for many years. The Concrete Society formed a Working Party to investigate methods of advancing the use of concrete as a material for protecting structures against fire in the late s.
This report contains a summary of the philosophy and procedures to be adopted by an engineer assessing fire damage, and describes the repairs necessary so that a structure can be restored to fulfill its original performance requirements, including fire resistance.
The residual strength of fire-damaged concrete depends to a large extent on the temperature attained in the fire. As expected, the elastic modulus of concrete is similarly reduced by fire damage.
This discoloration affect is useful, since it coincides with the temperature where strength reduction is taking place The Concrete Society, This pink discoloration is more evident with siliceous aggregates than with calcareous and igneous aggregates, and hence care should be exercised if the pink discoloration is not observed in fire-damaged concrete.
Perhaps the main factor contributing to the good performance of concrete structures in the event of a fire is the temperature gradient created within the concrete members.
In fires of relatively short duration, only the outside layers of concrete are subject to a very high temperature, and the temperature at the core of the member may be significantly less.
The American Concrete Institute (ACI) is a leading authority and resource worldwide for the development and distribution of consensus-based standards, technical resources, educational programs, certification programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a . 22 February 12 Concrete strength at a time t () Expressions are given for the estimation of strengths at times other than 28 days for various types of cement. Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place ("tilt up"). In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast concrete using a fine aggregate in the.
The most obvious damage which occurs during a fire is spalling, which has been reported in detail in CIRIA report Malhotra, The spalling of concrete has been summarized by The Concrete Society as follows: Exploding spalling appears to occur only for concrete within a limited range of moisture content.
The reinforcement is also affected after a fire, depending on the temperature attained. Steel loses a significant amount of its strength at high temperatures, leading to residual deflections in fire-damaged structures.
If the temperature exceeds these values, some loss of strength will occur upon cooling. The fire resistance of a range of typical structural members has been assessed via fire tests carried out at the Fire Research Station in the UK and by similar authorities world-wide.
The subject of fire damage is likely to be a focus of much future research in this field, following the failure of the World Trade Center in New York. The best example of a case study of the damage caused to concrete as a result of a fire is the study triggered by the Channel Tunnel fire in November, Two major papers have been published which present the main findings of an investigation of the fire contracted to LCPC, Paris which destroyed a part of the concrete tunnel rings by thermal spalling.
The first paper by reports on the development of a material model for the in situ behavior of rapidly heated concrete, which can account explicitly for the dehydration of concrete and its cross-effects with deformation chemomechanical couplings and temperature chemothermal couplings.
In the second paper bythe model was used in a finite element analysis of the tunnel rings which had been exposed to the fire.
The second paper by describes the fire in the tunnel as follows: The fire caused severe damage to the tunnel rings by thermal spalling on a length of a few hundred meters. In some parts, the entire tunnel ring up to the chalk substratum was destroyed by spalling.
Furthermore, the fact that the spalling occurred over some few hundred meters with regular spalling depth means—from a statistical point of view—that the observed damage patterns may be considered as representative of the in situ concrete behavior. Full details of this case study are reported in the papers and space does not allow further discussion here.
During the s concern was expressed regarding the performance of HSC in a fire. It was considered by some that the steam formed during heating would be contained by the impermeability of the concrete, leading to tensile stresses that would cause spalling of the concrete.
Lennon and Clayton carried out fire tests at the BRE on high- strength, unreinforced concrete columns. It was concluded that the inclusion of the polypropylene fibers did not have a significant effect on the maximum temperature obtained before collapse, but did substantially increase the temperature at which first cracking occurred and reduced or eliminated spalling.Structural concrete work of any kind is self-performed by our staff of quality trained managers and workforce.
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Concrete structures with steel-reinforced rebar are in a continuous and losing battle with corrosive elements that naturally occur from long-term exposure to an aggressive environment. Additionally, because such structures are now required to perform longer than mandated by their original design, many are now woefully obsolete.
Reinforcing Concrete Structures with Fibre Reinforced Polymers ISIS CANADA RESEARCH NETWORK The Canadian Network of Centres of Excellence on Intelligent Sensing for.
Inspection and Repair of Concrete Highway Structures Summary: This Advice Note is intended to assist the Engineer responsible for carrying out Principal Inspections, Special Inspections and the repair of concrete.
Precast Concrete Structures Association of Florida. The PCSA is a non-profit organization dedicated to the advancement of precast concrete structures through improved technology and product application.