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

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.</jats:p

Development and characterization of thin iron-based shape memory alloy prestressing wire

Iron-based shape memory alloys (Fe-SMA) have been used successfully in the previous years as prestressing reinforcement in the form of rebars, rods and flat strips, for various types of structural elements and loading scenarios. This paper introduces a new application of this material in the form of thin wire. An experimental characterization study is presented herein for Fe-SMA wire that was drawn to a diameter of 0.5 mm, regarding its tensile stress-strain response and recovery stress development upon heating, for different activation temperatures and prestraining levels. Furthermore, an investigation is presented regarding the effects of heat treatment conditions on the mechanical response and prestressing performance of the wire. For the optimum heat treatment conditions and activation temperature range considered in this study, the measured tensile strength and recovery stress of the Fe-SMA wire was 1117 MPa and up to 390 MPa, respectively. The results indicate a strong potential of Fe-SMA as a candidate prestressing material where flexible wire cross-sections of small diameter are desired instead of larger, solid cross-section tendons (e.g., multi-strand wire ropes or concrete confinement spirals), or as novel short fiber reinforcement for concrete with prestressing capabilities.LPMA

Seismic performance of Fe-SMA prestressed segmental bridge columns with 3D printed permanent concrete formwork

The integration of digital fabrication technology with prestressed segmental column construction offers significant potential for accelerated bridge construction with material-efficient design. This study aims to explore this potential by developing a novel prestressed segmental column system that utilizes permanent 3D printed concrete (3DPC) formwork for column segment fabrication. Prestressing is achieved in the proposed system by using partially bonded iron-based shape memory alloy (Fe-SMA) reinforcement. Large-scale experiments were conducted on two columns under combined gravity and lateral loading to evaluate the seismic performance and feasibility of the proposed system. The ratio of steel to Fe-SMA reinforcement in the column design was the variable considered in this study. The experimental results showed that the columns could withstand lateral drifts of up to 5% without collapse and the permanent 3DPC formwork showed no premature failure or delamination. Furthermore, the columns exhibited self-centering characteristics, maintaining a residual drift of 1% up to a target drift of 4% when the reinforcement ratio of steel to Fe-SMA rebars was 0.3. The results highlight the potential of the proposed prefabrication concept in designing material-efficient and seismically resilient bridge columns with low damage characteristics.ISSN:0141-029

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