Erich Hugi’s research while affiliated with Swiss Federal Laboratories for Materials Science and Technology and other places

Purpose This paper aims to present the results of an extensive experimental programme on the fire behaviour of timber beam-to-column shear connections, loaded perpendicularly to the grain. Design/methodology/approach The experimental programme comprised tests at normal temperature and loaded fire resistance tests on beam-to-column connections in shear. Twenty-four full-scale tests at normal temperature were performed covering nine different connection typologies, and 19 loaded fire resistance tests were conducted including 11 connections typologies. Findings The results of the fire resistance tests show that the tested typologies of steel-to-timber dowelled connections reached more than 30 and even 60 minutes of fire resistance. However, aspects such as a wider gap between the beam and the column, reduced dowel spacing, and the presence of reinforcement with self-drilling screws all have a negative influence on the fire resistance. Originality/value The experimental programme addressed the fire behaviour of timber beam-to-column shear connections loaded perpendicularly to the grain in a systematic way testing a wide range of common connection typologies significantly enlarging their experimental background.

Optimised, high-performance concrete elements, prestressed with carbon fibre reinforced polymer (CFRP) tendons offer great potential within the sustainable modern built environment. However, the performance of these elements in fire is not well known and must be better understood for applications where fire resistance is required. Findings from large-scale fire resistance tests on thin CFRP prestressed concrete slabs are presented and discussed. Results show that explosive spalling in fire results in sudden collapse, and when spalling is avoided failure occurs by loss of anchorage, which is in turn governed by the temperature of the tendons.

Optimized concrete elements have been developed using high-performance, self-consolidating, fibre-reinforced concrete (HPSCC) reinforced with high-strength, lightweight, non-corroding pre-stressed carbon fibre reinforced plastic tendons. This new type of thin-walled precast carbon FRP (CFRP) pretensioned HPSCC slab has been used in building façades and is under consideration for a range of other applications in buildings. However, it is well known that the bond strength between both steel and FRP reinforcements and concrete deteriorates at elevated temperature, and that HPSCC has a comparatively high risk of heat-induced concrete spalling. Reductions in bond strength, the occurrence of heat-induced concrete spalling, and their impacts on the load-bearing capacity of precast CFRP pretensioned HPSCC slabs during fire are not well understood. This paper gives insights into the fire behaviour of precast CFRP pretensioned HPSCC slabs by evaluating the influence of concrete mixture, slab thickness and the presence of local reinforcement (CFRP grids) in the prestress transfer zones. Selected results and analysis of a large scale fire resistance test on five HPSCC slabs are presented in this paper. It is shown that the occurrence of heat-induced concrete spalling resulted in sudden failure of the specimens, and that in cases where no spalling occurred failure was due to loss of bond strength.

Connections are often the weakest link in timber structures so that their failure during fire exposure may result in local or total collapse of a building. The failure modes are complex and poorly understood due to wood’s orthotropicity, the temperature and moisture dependency of wood’s properties, and the presence of metal fasteners that complicates the stress distribution and changes the process of heat transfer into the timber element. In this study, we investigated the coupled physics of heat and mass transfer in a test specimen made from spruce, with a steel fastener inserted in a pre-drilled hole. It imitates a central slice of a timber-to-timber connection exposed to the elevated temperature of 523 K from one side. The heat induced redistribution of the hygroscopic moisture in wood was quantified and visualized by means of neutron radiography. The temperature gradient was measured inside the specimen, at different distances from the heated surface. As the temperature increased in wood, moisture was displaced downstream of the heat source, resulting in a zone with increased moisture content ahead of the drying front and beneath the steel fastener. This wet front occurred where the temperature was below the water evaporation point. It was shown that the steel fastener affected the transport of heat and moisture within the test specimen. The occurring phenomena during the transient state may play a critical role in the embedment strength of wood and therefore influence the load-carrying capacity of timber connections in fire.

This paper presents the results of an extensive experimental campaign on the fire behaviour of beam-to-column timber connections loaded perpendicular-to-the-grain. The experimental campaign addressed the fire behaviour of beam-to-column timber shear connections in a systematic way, testing a wide range of common connection typologies, significantly enlarging their experimental background.

Fire design models for timber structures usually consider both the loss in cross section attributable to charring and the temperature-dependent reduction of strength and stiffness of the uncharred residual cross section. For bonded timber elements such as glued laminated timber beams, it is assumed that the adhesive in use does not significantly influence the resistance of structural timber beams. To investigate the influence of adhesives in bonded timber elements, a comprehensive research project is currently in progress. The aim of this project is the development of a simplified design model for the fire resistance of bonded structural timber elements, taking into account the behavior of the adhesive at elevated temperature. The paper presents the results of an extensive test series on finger-jointed timber members loaded in tension and exposed to a transient ISO 843 standard fire. The fire tests were performed with different adhesives that fulfill current approval criteria for the use in load-bearing timber components in Europe. Taking into account the different failure modes under observation, the results showed no significant influence of the adhesive on the load-bearing capacity of finger-jointed timber boards.

Optimized concrete elements have been developed using high-performance, self-consolidating, fibre-reinforced concrete (HPSCC) reinforced with high-strength, lightweight, non-corroding pre-stressed carbon fibre reinforced plastic tendons. This new type of thin-walled precast carbon FRP (CFRP) pretensioned HPSCC slab has been used in building façades and is under consideration for a range of other applications in buildings. However, it is well known that the bond strength between both steel and FRP reinforcements and concrete deteriorates at elevated temperature, and that HPSCC has a comparatively high risk of heat-induced concrete spalling. Reductions in bond strength, the occurrence of heat-induced concrete spalling, and their impacts on the load-bearing capacity of precast CFRP pretensioned HPSCC slabs during fire are not well understood. This paper gives insights into the fire behaviour of precast CFRP pretensioned HPSCC slabs by evaluating the influence of concrete mixture, slab thickness and the presence of local reinforcement (CFRP grids) in the prestress transfer zones. Selected results and analysis of a large scale fire resistance test on five HPSCC slabs are presented in this paper. It is shown that the occurrence of heat-induced concrete spalling resulted in sudden failure of the specimens, and that in cases where no spalling occurred failure was due to loss of bond strength.

Nesta comunicação são apresentados os resultados de uma extensa campanha experimental relativa à resistência ao fogo de ligações estruturais viga-pilar, em madeira, sujeitas a esforço transverso. Nesta campanha, o comportamento ao fogo destas ligações foi abordado de forma sistemática, tendo sido ensaiadas várias tipologias vulgarmente utilizadas, contribuindo-se de forma significativa para o estudo do seu desempenho em situação de incêndio e para o desenvolvimento de métodos de dimensionamento.

The objectives of this study are to assess the influence of reinforcement with self-drilling screws on the fire resistance of timber connections, namely steel-to-timber dowelled connections with multiple shear planes. The study included two series of experimental campaigns aimed at analysing the behaviour of different connection typologies at room temperature and under ISO 834 fire exposure. The first campaign took place in 2003 and covered tests at normal temperature and under fire exposure of four typologies of unreinforced connections, some of them also tested with additional fire protection (gypsum or timber boards). The results from the first campaign were used to prepare the second campaign, conducted in 2012, comprising tests at normal temperature and under fire exposure of similar and new connection typologies reinforced with self-drilling screws.