Fretting Fatigue Performance of Unidirectional, Laminated Carbon Fibre Reinforced Polymer Straps at Elevated Service Temperature

The fretting fatigue performance of laminated, unidirectional (UD), pin-loaded, carbon fibre-reinforced polymer (CFRP) straps that can be used as bridge hanger cables was investigated at a sustained service temperature of 60 °C. The aim of this paper is to elucidate the influence of the slightly elevated service temperature on the tensile fatigue performance of CFRP straps. First, steady state thermal tests at ambient temperature and at 60 °C are presented, in order to establish the behaviour of the straps at these temperatures. These results indicated that the static tensile performance of the straps is not affected by the increase in temperature. Subsequently, nine upper stress levels (USLs) between 650 and 1400 MPa were chosen in order to establish the S–N curve at 60 °C (frequency 10 Hz; R = 0.1) and a comparison with an existing S–N curve at ambient temperature was made. In general, the straps fatigue limit was slightly decreased by temperature, up to 750 MPa USL, while, for the higher USLs, the straps performed slightly better as compared with the S–N curve at ambient temperature

Fire hazard of compressed straw as an insulation material for wooden structures

The construction sector continues to adapt to the challenges posed by climate change. Architects and engineers aim to build sustainable, energy, resource, and cost‐efficient structures by increasingly using bio‐based building materials. However, fire safety has always been a significant concern for timber building construction internationally. The objective of the study presented in this article is to document fire hazards of compressed straw when used as thermal and acoustic insulation within wood‐framed building assemblies. Three densities of compressed straw (75, 125, and 175 kg/m3) were selected and their combustion and thermal responses were evaluated at various scales, in attempt to define the optimal density considering various factors. The performance of the straw was also compared with commercially available insulation materials and then tested under exposure to severe heating in medium‐scale wood‐framed assemblies to evaluate the impacts of the straw as compared with a noncombustible insulation. The compressed straw with a density of 75 kg/m3 was found to have the best behavior with respect to both reactions to fire and insulation properties. The results suggest that compressed may have similar or better behavior under the heating conditions investigated when compared to a commercially available combustible insulation material. The use of this material as a primary insulation in a buildings is considered manageable by thoughtful design, construction, and building use without unduly increasing risks associated with fire

Experimental assessment of post-fire retrofitted RC columns tested under cyclic loading

Multiple combined hazards can affect the structures during their live span and may conditionate the future structural behaviour for some types of loading. That is the case of a structure previously damaged by fire and then loaded under seismic loading. For seismic hazard zones it is important assess the seismic performance of existing reinforced concrete (RC) structures designed according to old codes and without seismic detailing. This structural seismic assessment is even more important for buildings that were previously damaged by fire. Therefore, it is critical develop and validate fire retrofitting methods that can also improve the seismic behaviour. This paper presents the results of a novel experimental campaign carried out on four (two of them repaired and strengthened with CFRP wrapping after fire exposure) full-scale reinforced concrete columns previously damaged by a 30 or 90 minutes standard fire and then tested under uniaxial cyclic lateral loading up to failure. Moreover, two additional control columns, one as-built and another strengthened, were cyclically tested for comparison. A considerable decrease in the deformation capacity and dissipated energy was observed in the columns after fire exposure, even for the 30 minute fire. Moreover, the post-fire repaired and strengthened columns may reach similar seismic performance than analogous strengthened columns without previous fire damages

Investigations on the Fatigue Behaviour of 3D-Printed Continuous Carbon Fibre-Reinforced Polymer Tension Straps

The focus of this research is an investigation on the fatigue behaviour of unidirectional 3D-printed continuous carbon fibre-reinforced polymer (CFRP) tension straps with a polyamide matrix (PA12). Conventionally produced tension straps are becoming established components in the mechanical as well as the civil engineering sector, e.g., as rigging systems for sailing boats and cranes and—recently introduced—as network arch bridge hangers. All these structures are subjected to high fatigue loads, and although it is commonly reported that carbon fibre-reinforced polymers show excellent fatigue resistance, there is limited understanding of the behaviour of CFRP loop elements under such loads, especially in combination with fretting at the attachment points. Research on this topic was performed at Empa in the past decade on thermoset CFRP straps, but never before with 3D-printed continuous CFRP straps with a thermoplastic matrix. This paper examines an additive manufacturing and post-consolidation method for producing the straps and presents initial results on their fatigue performance, which show that the fatigue endurance limit of the investigated 3D-printed and post-consolidated CFRP strap design is acceptable, when compared to steel tendons. However, it is still 20% lower than conventionally produced CFRP straps using out-of-autoclave unidirectional carbon fibre prepregs. The reasons for these findings and potential future improvements are discussed

The Tisova fire test part 2: heat transfer analysis

This report is the second of two reports into the Tisova fire test. It compares the results of three different groups’ attempts to model the temperature response of the structure in Tisova which was subject to a large scale travelling fire test. Generally it is observed that the different approaches have relatively close results, although one shows systematically hotter temperatures closer to the heated surface than the others; and differences between all three increase further from the heated surface.A comparison between the average calculated results and the experimental results is also shown for illustration. While an absolute comparison is not attempted because of experimental errors present the results do show the possible need for further data to support the heat transfer analysis required to carry out structural design for travelling fires

The Tisova fire test part 2: heat transfer analysis

This report is the second of two reports into the Tisova fire test. It compares the results of three different groups’ attempts to model the temperature response of the structure in Tisova which was subject to a large scale travelling fire test. Generally it is observed that the different approaches have relatively close results, although one shows systematically hotter temperatures closer to the heated surface than the others; and differences between all three increase further from the heated surface.A comparison between the average calculated results and the experimental results is also shown for illustration. While an absolute comparison is not attempted because of experimental errors present the results do show the possible need for further data to support the heat transfer analysis required to carry out structural design for travelling fires

Cyclic behaviour of as-built and strengthened existing reinforced concrete columns previously damaged by fire

A structure, during its life, may be subjected to multiple hazards. These hazards are sometimes combined over a short period of time, or in some cases occur many years apart, with the first hazard influencing the structural response under a second hazard. A reinforced concrete (RC) structure previously damaged by fire and then exposed to seismic loading is one such example. To assess such structures, the effects of fire on the cyclic performance of RC elements needs to be better understood. Moreover, it is also important to develop and validate strengthening methods that can reinstate or improve the seismic performance of fire-damaged RC elements. This paper presents the results of a novel experimental campaign where six full-scale RC columns with detailing representing existing Mediterranean buildings designed to old seismic codes are subjected to fire and then cyclic loading. Four RC columns were damaged after exposure to 30 or 90 min of the ISO 834 standard fire curve in a furnace and then tested under uniaxial cyclic lateral loading up to failure. Two of these columns were repaired and strengthened post-fire with Carbon Fibre Reinforced Polymer (CFRP) wrapping. The strengthening method aimed to increase the concrete strength through confinement, and to increase the displacement ductility and energy dissipation capacity under seismic loading. Two additional control columns, one as-built and another strengthened, were cyclically tested for comparison with the fire-damaged columns. It was found that the 30 min fire exposure resulted in few concrete cracks, whilst cover spalling and general cracking was observed in the 90 min fire exposure. A significant decrease in the displacement ductility and dissipated energy of the columns was observed following fire exposure, even for the 30 min fire. The columns that had post-fire repair and CFRP strengthening, showed better cyclic performance than the control column without fire exposure. It was also found that post-fire strengthened columns may reach similar seismic performance than similarly strengthened columns without previous fire damage