Composite materials based on natural fibres applied for structural reinforcement

Environmental problems and environmental protection triggered a rapid development of natural fibres as sustainable materials for the reinforcement of reinforced concrete structures. Synthetic fibre polymer composite materials have been widely accepted by the construction industries as an effective external reinforcement material to rehabilitate deficiencies in existing structures. These materials have exceptional performance such as high strength to weight ratio, corrosion resistance and lightness. However, the disadvantages include high costs during manufacturing and end-of-life services, less environmentally friendly and causing adverse effects on human health. This article presents an experimental program on the use of natural fibres as reinforcement in composite materials for structural strengthening. Different types of natural fibre fabrics (hemp, flax, mixed hemp and cotton) in terms of their mechanical properties were studied. The fibre and fibre fabric sheets were tested in tension test and compared with carbon and glass fibre fabric sheet as reference. So, this study carries out the effect of natural hemp and flax fibre fabric thickness on ultimate loads of specimens. In addition, the ultimate load and stiffness of strengthened beams were investigated. In fact, the results show that the reinforcement technique allows to increase the load-bearing of strengthened structure by 8% to 35% in bending tests.

The flexural strength of glue laminated timber beams based on deflection and strain rate with four point bending loading system

The development of utilization of low quality wood as construction material is needed to reduce the exploitation of natural forests. However, low quality wood species have disadvantages in terms of mechanical properties. The mechanical properties of Sengon wood are relatively low, so it does not qualify as a structural element. Therefore, the system glulam can be applied to overcome this problem. The system glulam can produce relatively light structural elements with adequate performance. This system has been extensively developed, even at the stage of applying external reinforcement, to improve the performance of structural laminated beams. On that basis, this study aims to determine the flexural strength of laminated beams of Sengon wood as a low quality wood species. In order to achieve this goal, the laminated beam was tested using method four point bending test method. Tests were carried out on long span laminated beams (L = 2750 mm) to observe flexural strength. There are five (5) laminated blocks tested, namely (BLS-1, BLS-2, BLS-3, BLS-4 and BLS-5). Each group has dimensions of 55 mm in width and 155 mm in height. Each specimen consists of six layers of wood boards with a density Falcata 0.3 g / cm3. The thickness of each layer was 26 mm and bonded with resin urea formaldehyde cold setting. Double-sided adhesive laying of 350 gr / m2 at a compressive force of 2 MPa. The analysis result shows that the load-deflection relationship between BS-L consists of linear and nonlinear phases. The load performance characteristics of the two types of laminated beams are expressed as the ratio of the proportional limit load to the maximum load. The ratio value is expressed in the form P eBL-s = 0.7P max BL-S andM eBL-s = 0.7M max BL-S. This form is similar to previous studies with a Pe to Pmax ratio of 0.80.9. In this case, the average flexural strength of the laminated beam is 17 MPa with a maximum strain of 0.004.

Fiber-Reinforced Polymers in Freeform Structures: A Review

This article is a survey discussing the application of fiber-reinforced polymer composites in freeform structures and their impact on the design and shape generation process. The analysis of case studies showed that the use of FRP composites not only helps to overcome some challenges in the construction of objects with complex geometry, but also creates brand new types of structures and design approaches. On the other hand, there is a problem—although FRP materials are frequently used in construction, the shapes of structures and design methods are often traditional and are simply copied from materials such as wood, concrete, and steel. FRP composites have been applied in civil engineering for several decades, since the 1960s, as building envelopes, façade skins, load-bearing structures, and internal and external reinforcement. The article aims to analyze this accumulated experience and to explore the role of FRP materials in the design of buildings with free, complex, fluid, and organic shapes. A new classification of freeform composite structures is proposed. They are classified in this article according to the methodology applied at the conceptual design stage: structures created by using a geometric approach, a form-finding (equilibrium) approach, or a biomimetic approach. Each approach is described in its own separate section, with a thorough literature and state-of-the-art review.

EXPERIMENTAL STUDY OF STRENGTHENING OF METAL STRUCTURES WITH EXTERNAL REINFORCEMENT BY THE METHOD OF GLUING HIGH-STRENGTH CARBON FIBRE-REINFORCED POLYMER (FRP) MATERIALS

Introduction. Reinforcement methods, which are mainly used in domestic practice to strengthen metal structures, based on adding an additional section to metal elements by bolting or welding them. These methods, of course, are reliable and effective, but they cannot always be applied when it is necessary to preserve not only the building as a whole, but also its original internal and external appearance. Moreover, metal elements increase the stress on the structure and the building as a whole and are susceptible to corrosion and fatigue. There are often cases when it is difficult to fix a reinforcement element to the main structure, both from a technological and constructive point of view. In these situations, it becomes necessary to reinforce metal structures with high-strength materials with low weight and high manufacturability. Among the various strategies for reinforcing structures, bonding of high-strength composite carbon materials (FRP — Fiber-reinforced polymer) is becoming more and more popular in the world, especially for reinforced concrete structures, although application to metal structures is also quite common in Europe. But it should be noted that in Ukraine, unfortunately, this material is not yet widely used to strengthen metal structures. Problem Statement. The restoration of metal structures becomes necessary every time there are design, manufacturing or construction errors. Strengthening is also necessary in cases of long-term operation of buildings without timely maintenance and major repairs, insufficient strength of structural materials, as well as changes in weather conditions and current regulatory documents in Ukraine. So there is a need to strengthen metal structures with the most effective methods, both from the point of view of the reliability of building structures and from the point of view of profitability, which is influenced by the long shutdown of enterprises and the halt of the production process to carry out reconstruction work. Purpose. Investigate a modern method of reinforcing metal structures using high-strength carbon fibre-reinforced polymer (CFRP) materials in order to increase the bending capacity of a metal structural element, in particular, to check the reliability of adhesion of a metal beam to a reinforcing layer of TM «Mapei» composite material, which is glued using epoxy-based glue. Methods of research. Experimental testing of metal I-beams reinforced with external reinforcement by gluing high-strength carbon-based material (CFRP) TM «Mapei» by means of a static concentrated load in the middle of the beam span. Results. By analyzing the results of the experimental test, data were obtained indicating that after the inclusion of the carbon fibre-reinforced polymer in the operation, the percentage decrease in vertical deflection at a load of 75 kN was 39.5 %, and the value of the prmissible load, taking into account the stiffness condition (checking of building structures the established conditions of limiting deflections), increased by 11.8 %. When testing the phenomena of delamination of the composite from the base was not detected. Conclusions. Reinforcement of steel beams with a carbon fibre-reinforced polymer material led to a decrease in element deformations and, as a consequence, to the possibility of increasing the bearing capacity. An experimental test confirms the theoretical calculations to maximize the bearing capacity of a metal beam using the fibre-reinforced polymer material. A significant effect from the reinforcement of metal structures with composite materials can be achieved when strengthening the building structures of large-span buildings and structures, when reinforcing by traditional methods, they require complex design solutions, high labor costs, stopping the production process to perform reinforcement work, when the weight of the reinforcing structure is often significant.

Models of heterogeneous dopamine signaling in an insect learning and memory center

The Drosophila mushroom body exhibits dopamine dependent synaptic plasticity that underlies the acquisition of associative memories. Recordings of dopamine neurons in this system have identified signals related to external reinforcement such as reward and punishment. However, other factors including locomotion, novelty, reward expectation, and internal state have also recently been shown to modulate dopamine neurons. This heterogeneity is at odds with typical modeling approaches in which these neurons are assumed to encode a global, scalar error signal. How is dopamine dependent plasticity coordinated in the presence of such heterogeneity? We develop a modeling approach that infers a pattern of dopamine activity sufficient to solve defined behavioral tasks, given architectural constraints informed by knowledge of mushroom body circuitry. Model dopamine neurons exhibit diverse tuning to task parameters while nonetheless producing coherent learned behaviors. Notably, reward prediction error emerges as a mode of population activity distributed across these neurons. Our results provide a mechanistic framework that accounts for the heterogeneity of dopamine activity during learning and behavior.

REINFORCEMENT OF REINFORCED CONCRETE STRUCTURES WITH COMPOSITE MATERIALS

Recently, in the Republic of Kazakhstan, as well as in other countries of theAsian region, it is becoming more and more urgent to strengthen the operated reinforcedconcrete structures with external reinforcement systems with carbon materials during thereconstruction of any engineering structures. In order to eliminate the consequences of concretedestruction and reinforcement corrosion as a result of long-term exposure to natural factors andaggressive environments, carbon fiber external reinforcement systems are widely used during the operation of structures designed to repair and strengthen the load-bearing structures of artificialstructures. External reinforcement is used to increase the seismic resistance, strength andreliability of the structures being built, as well as to increase the time between repairs. The repairsystem provides for the use of materials and technologies that ensure stopping and preventingfurther corrosion of reinforcement and concrete, reliable adhesion of repair compounds with oldconcrete, increased water resistance, frost resistance and chemical resistance. This articledescribes FibARM carbon materials that are used to strengthen columns and pylons, broadbandreinforcement of slabs, beams, crossbars and structures with increased requirements forreinforcement joints, covering reinforcement of concrete with large-scale grid cracking.The mainmethods of strengthening the stretched and bent elements of building structures of artificialstructures are considered, and the technology of work on strengthening the structures of artificialstructures is also given.

Reinforcement of metal structures by external reinforcement by gluing high-strength fiber-reinforced systems: analytical approach

Ukraine's construction heritage includes numerous examples of the use of metal structures, especially those used in industrial buildings and high-span structures. The use of metal structures in construction is due primarily to their mechanical properties. They are frost-resistant and can withstand temperatures down to -65 degrees, hard, durable, strong and reliable. They can also be used in areas with high seismic activity. But, as in the case of other types of structures, there is a need to restore or strengthen metal structures due to structural defects, wear of load-bearing elements, as well as to increase the load-bearing capacity. In some cases, reinforcement with fiber-reinforced polymer composites (FRP) gives a better result compared to traditional methods of reinforcement using metal