Flexural Behavior of Six Species of Italian Bamboo

The good mechanical performance of bamboo, coupled with its sustainability, has boosted the idea to use it as a structural material. In some areas of the world it is regularly used in constructions but there are still countries in which there is a lack of knowledge of the mechanical properties of the locally-grown bamboo, which limits the spread of this material. Bamboo is optimized to resist to flexural actions with its peculiar micro structure along the thickness in which the amount of fibers intensifies towards the outer layer and the inner part is composed mostly of parenchyma. The flexural strength depends on the amount of fibers, whereas the flexural ductility is correlated to the parenchyma content. This study focuses on the flexural strength and ductility of six different species of untreated bamboo grown in Italy. A four-point bending test was carried out on bamboo strips in two different loading configurations relating to its microstructure. Deformation data are acquired from two strain gauges in the upper and lower part of the bamboo beam. Difference in shape and size of Italian bamboo species compared to the ones traditionally used results in added complexity when performing the tests. Such difficulties and the found solutions are also described in this work. The main goal is to reveal the flexural behavior of Italian bamboo as a functionally graded material and to expand the knowledge of European bamboo species toward its use as a structural material not only as culm but also as laminated material.

Improvement of Flexural and Shear Strength of RC Beam Reinforced by Glass Fiber-Reinforced Polyurea (GFRPU)

The Glass Fiber-Reinforced Polyurea (GFRPU) which is the composite by the elastic polyurea and milled glass fiber have the mechanical characteristics to enhance tensile strength as well as ductility. It must be reinforcement materials in repair and retrofit applications for strengthening structural capacity and has a merit of simple construction of spray coating to prevent the debonding from concrete surfaces unlike the existing strengthening methods such as Fiber-reinforced polymer (FRP) or steel plate. This work compares the improvement degree in load-carrying capacity as well as flexural ductility of RC beam reinforced externally by polyurea or GFRPU. Seven specimens of four reinforced concrete (RC) beams for evaluating flexure-resisting capacity and three beams for shear-strengthening capacity are tested. The mechanical behavior and characteristics of the specimens reinforced by local and global reinforcement method classified according to strengthened area are compared. It is shown that the polyurea- or GFRPU- reinforcement leads to the enhancement in the load-resisting capacity up to 8~11% and flexural ductility within the range of 8.41~13.9 times of the non-reinforced beam. And the global reinforcement method has more improvement in the shear- and flexure-resisting capacity than the local method. It is also observed that the GFRPU can be more effectively utilized in enhancing the structural shear-resisting capacity than the flexure-carrying capacity. Doi: 10.28991/cej-2021-03091662 Full Text: PDF

FLEXURAL BEHAVIOR OF REINFORCED LIGHTWEIGHT CONCRETE BEAMS MADE WITH ATTAPULGITE AND ALUMINUM WASTE

Lightweight concrete reduces the total dead load of structural elements and seismic loads significantly. This paper presents the production Attapulgite Lightweight aggregate concrete (ALWAC) and its effect on the flexural behavior of reinforced concrete beams. Attapulgite was treated with sodium hypochlorite of 6% concentration for 24 hours. The variable considered was the aluminum waste (AW), used as a fiber, of fraction (0, 0.5 and 1%) by concrete volume. Behavior was investigated in terms of cracking and ultimate load, load-deflection relationship, failure mode, crack patterns and flexural ductility. The mechanical properties of the ALWAC were studied. It was observed that, Attapulgite improves the mechanical properties of concrete when comparing the experimental value with theoretical ones for the reference mixture. AW has a disparate effect on the mechanical properties of ALWAC. The increase in the proportions of AW showed an increase in the cracking load and decrease in the ultimate load by 37.14% and 22.45 %, respectively, at AW of 1%. Experimental value of ultimate load in all beams was higher than the theoretical value (ACI simplified method). AW increases the deflection at the same magnitude of applied load, and reduces the number and propagation of the flexural cracks in beams. All beams exhibited a typical tension failure mode and failed in ductile manner.

Reassessment of the flexural behavior of high-strength reinforced concrete beams under short-term loads

This work aims at describing the behavior of high-strength reinforced concrete (HSRC) beams under short-term ultimate loads with concrete compressive strengths higher than 50 MPa. A plastic approach besides a cross sectional analysis is employed to primarily trace the nonlinear response of nineteen HSRC simply supported beams for which experimental results are available. This proposed theoretical approach is able to acceptably match the experimental data with minor overestimation of flexural moments. Closed-form expressions to evaluate ductility indexes regarding deflections and curvatures as well as plastic rotation capacities are also proposed herein. Predictions of the National Brazilian Regulation for design of concrete structures NBR6118 in terms of ultimate flexural moments are also computed for comparison. A complete assessment of ductility in which plastic rotation capacities are computed for the studied beams is also given. It is found that the flexural ductility of a member could be increased with the use of high strength concrete. The use of a maximum tension steel ratio to guarantee a minimum flexural of ductility is highlighted.

Influence of Nano Particles in the Flexural Behavior of High-Strength Reinforced Concrete Beams

High strength concrete (HSC) characterized by high compressive strength but lower ductility compared to normal strength concrete. This low ductility limits the benefit of using HSC in building safe structures. Nanomaterials have gained increased attention because of their improvement of mechanical properties of concrete. In this paper we present an experimental study of the flexural behavior of reinforced beams composed of high-strength concrete and nanomaterials. Eight simply supported rectangular beams were fabricated with identical geometries and reinforcements, and then tested under two third-point loads. The study investigated the concrete compressive strength (50 and 75 N/mm2) as a function of the type of nanomaterial (nanosilica, nanotitanium and nanosilica/nanotitanium hybrid) and the nanomaterial concentration (0%, 0.5% and 1.0%). The experimental results showed that nano particles can be very effective in improving compressive and tensile strength of HSC, nanotitanium is more effective than nanosilica in compressive strength. Also, binary usage of hybrid mixture (nanosilica + nanotitanium) had a remarkable improvement appearing in compressive and tensile strength than using the same percentage of single type of nanomaterials used separately. The reduction in flexural ductility due to the use of higher strength concrete can be compensated by adding nanomaterials. The percentage of concentration, concrete grade and the type of nanomaterials, could predominantly affect the flexural behavior of HSRC beams.

A Study on the Strengthening Performance of Concrete Beam by Fiber-Reinforced Polyurea (FRPU) Reinforcement

Polyurea coating helps improve the ductility and toughness of structural members. A fiber-reinforced polyurea (FRPU) composite provides high load-carrying capacity and is applied by simply spraying it onto the member surface. Unlike existing reinforcement approaches, the FRPU coating method can prevent the ductility of concrete beams from deteriorating and the concrete surface from debonding. In this study, 20 concrete beams were tested with respect to their load-carrying capacity and flexural ductility using polyurea or FRPU reinforcement. The test variables included the type of reinforcing fibers, coating thickness, and weight-to-content ratio of the fibers in the FRPU. Moreover, the load-carrying capacity and mechanical behavior of all specimens were compared according to the content of the steel fibers, milled glass fibers, or carbon nanotubes (CNTs). Specimens reinforced using polyurea or FRPU were confirmed to retain the load-carrying capacity and flexural ductility to a certain degree after concrete failure at the tension face of the midspan section. The concrete beams ultimately failed through the fracture of polyurea or FRPU without debonding. Experiments were conducted to illustrate the strengthening effect by FRPU and determine its superiority.