Numerical Modelling of Masonry Arches Strengthened with SFRM

The adoption of effective strengthening techniques of historical constructions is one of the most widely debated aspects in structural engineering. Within this topic, the application of steel fiber reinforced mortar (SFRM) has been recently proposed as a low invasive and effective way to obtain a considerable structural benefit in the safety of existing masonry structure. To this purpose, in this paper the experimental results obtained on a circular masonry arches are presented. The considered specimens, subjected to a vertical increasing static load, is tested in the unstrengthened and strengthened configurations, and is part of a wider experimental campaign. After presenting and discussing the experimental results, they are compared with those relative to numerical simulations conducted by means of a discrete macro-element (DME) strategy, based on a simple mechanical scheme, able to model the nonlinear behavior of masonry structures with a limited computational effort. Such an approach is here extended to model the SFRM strengthening technique accounting for the main failure mechanisms associated to the combined presence existing masonry and the additional strengthening layer applied at the intrados of the arch. Numerical and experimental results demonstrate the efficacy of the proposed retrofitting strategy both in terms of bearing capacity and increase of ductility

Evaluation of the vertical load capacity of masonry arch bridges strengthened with FRCM or SFRM by limit analysis

The large number of existing masonry bridges still in service in the world roadway and railway networks requires that transportation system managers carry out ordinary and extraordinary maintenance. In many of these networks, the need for increasing the speed and/or weight of the traffic loads also entails the design of strengthening interventions aimed at enhancing the load-carrying capacity of masonry bridges. Among the available techniques for the strengthening of these structures, the use of fiber reinforced cementitious matrix (FRCM) composites has gained popularity due to their advantages with respect to more traditional techniques. More recently, the use of steel fiber reinforced mortars (SFRM), has also been investigated for the strengthening of masonry bridges, with promising results. In this paper, a limit analysis for assessing the vertical load-carrying capacity of single-span bridges strengthened with FRCM or SFRM, applied at the intrados, is described, and calibrated using available experimental results. The document highlights the variables that should be considered in such procedure and also discusses the similarities and differences between the two strengthening techniques. A subsequent parametrical analysis shows that both techniques produce comparable increments in the load carrying capacity of the masonry bridges when compared to unstrengthened conditions. In addition, it was seen that if the finite friction between blocks is not considered when performing the limit analysis of masonry bridges, the ultimate load capacity of the arches can be overestimated as the failure mode can be attained due to shear sliding of the masonry blocks, a hinge mechanism or a combination of both

Confinement of low-strength concrete with fiber reinforced cementitious matrix (FRCM) composites

This paper presents the results of an experimental campaign aimed at assessing the effect of varying influencing parameters on the behavior of low-strength concrete prisms confined with fiber reinforced cementitious matrix (FRCM) composites. For this scope, 60 specimens were casted and tested to derive experimental stress-strain curves under monotonic axial loading. The following test variables were adopted: two types of fibers, i.e. carbon and glass fibers; four section geometries, i.e. circular, square and intermediate with two corner radius values (22 and 38\u202fmm); two specimen dimension values, maintaining the same slenderness h/d\u202f=\u202f2, but with two height values, i.e. 200 and 300\u202fmm; and lastly, the presence of a pre-existing damage, with two different levels. Stress vs. axial strain and fibers hoop strains were analyzed and results were then discussed in terms of strength gain and ductility, highlighting how carbon and glass fibers jackets improve the confinement of bare specimens. Experimental evidences show how the extent of strength and ductility gains depend on composite type, cross-section geometry and specimen dimension. Also, full strength recovery of damaged specimens was achieved by carbon-FRCM system, whereas this was not possible by means of glass fibers-based jackets

Behavior of RC beams strengthened in shear with FRP and FRCM composites

This paper presents the results of an experimental campaign carried out to investigate the behavior of reinforced concrete (RC) beams strengthened in shear with externally bonded composites. Two different types of composites were studied: Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) composites. In addition, different types of fiber (carbon and steel) were employed, and the influence of internal transverse steel reinforcement ratio and the presence of composite anchors were investigated. Internal-external shear reinforcement interaction, i.e. reduction of the stirrup strain due to the presence of the composite, was observed for both FRP and FRCM strengthened beams, but the inter- action was less pronounced for those with FRCM composites. The anchors employed in this study did not affect the shear strength of the beams, but changes in the concrete crack pattern, mid-span displacement, and failure mode were observed. For FRCM strengthened beams, strains measured in the fibers showed higher exploitation ratios, i.e. the ratio between the maximum measured fiber strain and the rupture strain, for beams with carbon FRCM than those with steel FRCM. Effective strains computed using avail- able models were considerably lower than the maximum measured fiber strains

Study of the matrix-fiber bond behavior of carbon and glass FRCM-composites

Strengthening and retrofitting of existing reinforced concrete (RC) elements have been gaining interest in recent decades. Among the strengthening solutions available, fiber reinforced composites present certain advantages, such as high strength-to-weight ratio and low invasivity, which make them attractive in some applications. In particular, fiber reinforced polymer (FRP) composites have been successfully employed for bending and shear strengthening and for confinement of axially loaded elements, however they suffer from UV degradation, (relatively) high temperature exposure, and cannot be applied onto wet surfaces. To overcome these limitations, which are mostly related to the use of organic binders (usually epoxy resins), a new type of composite comprised of a fiber mesh embedded within an inorganic matrix has recently been developed and is referred to as fiber reinforced cementitious matrix (FRCM) composites. While FRCM composites have proven effective for strengthening RC elements, each specific composite presents a different behavior and needs to be properly characterized. In this paper, the results of single-lap direct-shear tests of carbon and glass FRCM-concrete joints are presented and discussed. Specimens with different composite bonded lengths were tested in an attempt to identify the effective bond length of each composite. The debonding stress experimentally obtained for carbon FRCM composites is also compared with that obtained through a fracture mechanics approach based on fiber strains measured on the same material using strain gauges bonded to the longitudinal fibers

Performance of different types of FRCM composites applied to a concrete substrate

This research aimed to investigate the performance of fiber reinforced cementitious matrix (FRCM) composites employed as externally applied strengthening system for reinforced concrete members. The results of an experimental campaign conducted on FRCM composites applied to a concrete substrate are shown and discussed. The composites were comprised of different types of fibers, namely carbon, glass, steel, and basalt fibers, and different types of cementitious matrix. Single-lap direct-shear tests were performed to study the behavior of the different composites. Specimens with different bonded lengths were tested to investigate the stress-transfer mechanism and to investigate the existence of an effective bond length. Comparisons between the peak loads obtained with the direct-shear tests and the tensile strength of the fibers, which provide an indication of the exploitation of the fibers, were carried out

State of research on shear strengthening of RC beams with FRCM composites

This paper summarizes the state of research on the topic of shear strengthening of RC beams using exter- nally bonded FRCM composites. In the first part of this paper, a detailed bibliographical review of the lit- erature on the shear strengthening of RC beams using FRCM composites is carried out, and a database of experimental tests is developed. Analysis of the database shows that FRCM composites are able to increase the shear strength of RC beams. The effectiveness of the strengthening system appears to be influenced by parameters including the wrapping configuration, matrix compressive strength relative to the concrete compressive strength, and axial rigidity of the fibers. Different failure modes have been reported, including fracture of the fibers, detachment of the FRCM jacket (with or without concrete attached), and slippage of the fibers through the mortar. A possible interaction between the internal transverse steel reinforcement and the FRCM system has also been observed. In the second part of this paper, four design models proposed to predict the contribution of the FRCM composite to the shear strength of RC beams are assessed using the database developed. Results show that the use of the prop- erties of the FRCM composite in Models 3 and 4 instead of the fiber mechanical characteristics does not significantly increase the accuracy of the models. A simple formulation such as that proposed by Model 1, based on the bare fiber properties, is found to be more accurate for beams with or without composite detachment

Pressure Distribution Patterns Between the Ballast and the Concrete Slab in Railway Trough Bridges

In Sweden, a substantial amount of railway bridges is approaching their intended lifespans and are planned to be replaced. However, it is not sustainable neither from a financial nor an environmental perspective to replace these bridges if they are still sound and safe. Thus, an evaluation of their actual capacity is required with the aim of extending their lifespans. A way to obtain a more accurate capacity is to determine the loads that are acting on them. Available literature points out the lack of experimental investigations on sleeper-ballast contact pressure, as well as on the stress distribution along and across the ballast. Consequently, railway bridge design has been based on traditional rather than rational assumptions, which can be quite conservative. In this paper, a review of models is carried out for evaluating stress patterns on the surface of the slab on ballasted concrete bridges. Then, a simplified finite element model of a concrete trough bridge, a common type of structure in Sweden, is used in a parametric analysis aimed to understand how the identified pressure distribution patterns affect the performance of this type of structure. Finally, with the purpose of studying how some parameters influence the bridge safety, a probabilistic reliability analysis is used. The reliability index beta (b) is obtained using the polynomial response surface method and its value is compared for different boundary condition scenarios. Also, the sensitivity factors for the considered random variables are compared and analyzed. Results show that the assumption of support condition and pressure pattern has a significant impact on the capacity, failure mode and probability of failure of this type of structure.ISBN för värdpublikation: 978-981-18-2016-8</p

Response Surface Method strategies coupled with NLFEA for structural reliability analysis of prestressed bridges

The Response Surface Method (RSM) has become an essential tool to solve structural reliability problems due to its accuracy, efficacy, and facility for coupling with Nonlinear Finite Element Analysis (NLFEA). In this paper, some strategies to improve the RSM efficacy without compromising its accuracy are tested. Initially, each strategy is implemented to assess the safety level of a highly nonlinear explicit limit state function. The strategy with the best results is then identified and used to carry out a reliability analysis of a prestressed concrete bridge, considering the nonlinear material behavior through NLFEA simulation. The calculated value of is compared with the target value established in Eurocode for ULS. The results showed how RSM can be a practical methodology and how the improvements presented can reduce the computational cost of a traditional RSM giving a good alternative to simulation methods such as Monte Carlo.

Natural and industrial wastes for sustainable and renewable polymer composites

By-products management from industrial and natural (agriculture, aviculture, and others) activities and products are critical for promoting sustainability, reducing pollution, increasing storage space, minimising landfills, reducing energy consumption, and facilitating a circular economy. One of the sustainable waste management approaches is utilising them in developing biocomposites. Biocomposites are eco-friendly materials because of their sustainability and environmental benefits that have comparable performance properties to the synthetic counterparts. Biocomposites can be developed from both renewable and industrial waste, making them both energy efficient and sustainable. Because of their low weight and high strength, biocomposite materials in applications such as automobiles can minimise fuel consumption and conserve energy. Furthermore, biocomposites in energy-based applications could lead to savings in both the economy and energy consumption. Herein, a review of biocomposites made from various wastes and their related key properties (e.g. mechanical and fire) are provided. The article systematically highlights the individual wastes/by-products from agriculture and materials processing industries for composites manufacturing in terms of their waste components (materials), modifications, resultant properties, applications and energy efficiency. Finally, a perspective for the future of biowastes and industrial wastes in polymer composites is discussed