Kristian Dahl Hertz

Limits of spalling of fire-exposed concrete

Abstract Spalling may be a violent effect to fire-exposed concrete destroying the entire cross-sections or reducing the load-bearing capacity of a construction substantially. Spalling must therefore be considered when designing a concrete construction for fire. The paper discusses the present knowledge on the nature of spalling, add the latest findings from the research of the author, and derives limits within which spalling should not take place. Some guidelines are formulated based on experience from research and practice for reducing the spalling risk for constructions beyond the safe design limits. The limits provided are those, which can be stated at present, but further research is in progress, identifying more precisely the range of materials susceptible to spalling and contributing to the full understanding of the phenomenon.

A coherent description of the process of design

A description of the creative design process is given based on Empiricism and using the theory of sets on conceptual and subconscious representations of the human mind. More precise definitions are given of a number of common concepts such as association, synthesis, culture, creation, art and others. Doing so, a corresponding number of philosophical problems are solved, and the description becomes a coherent theory. The author has shown that it is possible to make a computer program for conceptual modelling based on the theory presented, and the principles of a CAD system including the program and supporting the creative process of the designer is described.

Assessment of Performance-based Requirements for Structural Design

The paper presents how actions can be assessed for a performance-based structural fire safety design from the first formulations in the building program to the final derivations of the fire load to be applied for each structural member. In order to indicate what is of importance for the assessment of the requirements, a couple of simple analyses of structural response are made. The examples are chosen deliberately to show the difference between a traditional design based on standard fire resistance and a performance-based approach. A methodology is developed for a decision on the safety level and for a detailed assessment of the requirements. The design requirements to be used for a factory producing elements for industrial housing for unknown costumers are discussed, and a fully developed fire is recommended as a common requirement for domestic houses, hotels, offices, schools and hospitals. In addition it is shown how a fire brigade can be expected to perform in a building designed by means of the methodology. It has been the aim to give a simple and clear presentation and several simplifying concepts are introduced, because it has been experienced that this subject has led to many misunderstandings, and simplicity is needed if the methods presented should be operational.

Fire resistance of concrete walls with light aggregate

The purpose of this paper is to present the design methods for fire-exposed concrete columns and walls. In addition, it presents analyses and tests showing that the methods are applicable for designing columns and walls of lightweight aggregate concrete based on expanded clay aggregate as well as heavy normal weight concrete and that the methods fit smoothly with cold design, when the fire exposure varies towards no fire.,During the 1990s, some of these design methods were included in the Eurocode as “the zone method”. They are still a part of the code. The rest of the methods, which were not included, served in practice, teaching and research. The present paper derives calculation methods proving their connection with common design for load cases without fire exposure. Furthermore, the paper presents full-scale tests proving the validation of the design methods for structural members of light aggregate concrete in addition to the full-scale tests of heavy concrete members.,The design methods give correct estimates of the load-bearing capacity of eccentric loaded concrete columns. An extended version of the methods estimates load-bearing capacity for walls with fire exposure on one side with sufficient accuracy for the purpose of design.,The author developed the main parts of the design methods in the 1980s and 1990s and others have from time to time referred to some parts of them mainly the minor parts published in the Eurocodes. However, owing to work overload, the author has not published the derivation and verification of them before. This paper provides in particular a verification against full-scale tests of light-aggregate concrete walls not published before.

Fire resistance of extruded hollow-core slabs

Purpose Prefabricated extruded hollow-core slabs are preferred building components for floor structures in several countries. It is therefore important to be able to document the fire resistance of these slabs proving fulfilment of standard fire resistance requirements of 60 and 120 min found in most national building regulations. The paper aims to present a detailed analysis of the mechanisms responsible for the loss of load-bearing capacity of hollow-core slabs when exposed to fire. Design/methodology/approach Furthermore, it compares theoretical calculation and assessment according to the structural codes with data derived from a standard fire test and from a thorough examination of the comprehensive test documentation available on fire exposed hollow-core slabs. Findings Mechanisms for loss of load-bearing capacity are clarified, and evidence of the fire resistance is found. Originality value For the first time, the mechanisms responsible for loss of load-bearing capacity are identified, and test results and calculation approach are for the first time applied in accordance with each other for assessment of fire resistance of the structure.