Papers by Keyword: Ductile Behavior

Abstract: Concrete is extremely vulnerable against impact loading due to its low tensile strength and pronounced brittleness. The application of thin strengthening layers, containing Textile Reinforced Concrete (TRC) and Strain-Hardening Cement-based Composites (SHCCs) in a ductile cement-based composite, is a promising solution to enhance the impact resistance of existing concrete structures. Three-dimensional (3D) textile structures exhibit numerous advantages over two-dimensional (2D) ones, most importantly higher shear, bending and energy absorption capacity, hence, appear to be instrumental in providing sufficient reinforcement to the target strengthening layers. However, design variability and optimization possibility of available 3D textile reinforcement are restricted. This paper presents the development of novel textile-based 3D truss reinforcement that can overcome these limitations. On the basis of woven 3D cellular structures, innovative pyramidal 3D truss reinforcement with favorable load-bearing capacity as well as notable energy absorption capability is developed and successfully realized. To investigate the feasibility and efficacy, cement-based composite consisting SHCC and newly developed pyramidal 3D truss reinforcement is prepared and tested under high-speed tensile loading as well as transversal impact loading. The experimental results show that woven 3D truss reinforcement is highly compatible with SHCC, and significantly enhances its impact resistance. Furthermore, SHCC reinforced with novel pyramidal 3D truss structure remarkably outperforms that with 2D carbon reinforcing structure approved for commercial use.

Abstract: The purpose of this study was to reduce production costs for UHPFRC members by using a bundle of longitudinal reinforcement bars as a substitute for steel fiber. Experiments on the ductile behavior of Ultra High Performance Concrete (UHPC) rectangular beams with a combination of steel fiber and longitudinal reinforcement bars were performed.The volume fractions of steel fiber were 0%, 0.7%, 1%, 1.5%, 2%, and the reinforcement ratios of longitudinal reinforcement bars that promoted ductile behavior were 0.0036, 0.016, 0.029 and 0.036.Fifteen UHPC beams were made with the combination of these test factors. Both the steel fiber and the longitudinal reinforcement bars had the effect of induciing ductile behavior for UHPC structural members. The load-deflection relationship, the concrete stress variation and the crack pattern indicated the usefulness of the bundle of longitudinal bars that have a small diameter with close arrangement.

Abstract: The bamboo species Guadua angustifolia is a natural functionally graded material with a high potential to help solving the housing deficit in Latin American countries. Bamboo plantations also play an important role to help reducing the devastation of tropical forests. Many studies have demonstrated the excellent mechanical properties of bamboo along the length of the culm. However, other properties like the strength under circumferential tension and shear are low and the associated types of failure are fragile. Therefore, longitudinal fissures are often initiated in the structural joints which avoid taking advantage of the high resistance along the longitudinal direction. To the best of our knowledge, no study has been devoted to study the mechanical behavior of bamboo along the thickness of the culm or radial direction. This characterization may be crucial to improve the performance of the joints in bamboo structures. The aim of this study was to determine the strength and the Young ́s modulus of Guadua angustifolia along the radial direction. Thus, 27 small hexahedral elements of approximately 11 mm × 6 mm × 7 mm were tested under compression along the thickness of the culm. The stress-strain curves depicted a typical ductile behavior with an average failure strain of 37.8 ± 5.4 %. The failure was characterized by fissures on planes parallel to the fibers and forming angles in the range 35° - 55° with respect to the axis of loading. The secant Young ́s modulus and the radial strength were equal to 44.50 ±9.60 MPa, and 18.50 ±4.20 MPa respectively and there was no significant difference with position along the culm. The initial Young ́s modulus was equal to 96.73 ±52.30 MPa, 37.00 ±24.35 MPa and 48.90 ±7.31 MPa for the bottom, middle and upper portions of the culm and there was a significant difference (p=0.025) between the bottom and middle locations. The high variations of the initial Young ́s modulus may be explained by the irregular form of the surfaces of contact with the testing machine, that were not cut perfectly flat in order to preserve the intact material. These experiments show that Guadua behaves as a ductile material under compression along the thickness of the culm. This property may be used to improve the efficiency of structural joints by applying radial compression.

Abstract: To induce the ductile behavior of ultra high performance concrete beams, the experiments to find out the best composition of volume fraction of steel fiber and ratio of reinforcement bar were carried out. 15 UHPC beams which have various combinations of volume fraction of steel fiber and ratio of reinforcement bar. The reinforcement bars was consist of 2×1, 3×3, 4×4, 5×4. The volume fractions of steel fibers were 0%, 0.7%, 1%, 1.5%, 2%. The beam which has 0% volume fraction with the close placement reinforcement bar has little effect on ductile behavior. At least 0.7% volume fraction with the close placement reinforcement bar guarantees the ductile behavior of UHPC beam.

Abstract: This study includes the development of the seismic retrofit technology that structural frame of building is strengthened by installing additional wall with embedded form after demolition of the inner walls of unreinforced masonry wall including the exterior design walls. In addition, this paper involves the earthquake resistant performance evaluation of the system through an experimental work. From the test, it was turned out that as for the maximum strength of the specimens, the maximum load was similar regardless of whether using the embedded form. However, EF-IW-H1(embedded form) specimen with the form hardware embedded in the wall during retrofit resulted in ductile behavior of the, which shows the effect on the embedded form in a sense.

Abstract: This paper presents an experimental study on the flexural fatigue characteristics of Ultra-High Toughness Cementitious Composites (UHTCC), in contrast with plain concrete and Steel Fiber Reinforced Concrete (SFRC) which have similar compressive strength. The results show that UHTCC improves fatigue life and exhibits a bi-linear fatigue stress-life relationship. The deflection ability, failure characteristics of UHTCC were investigated in the tests. It was observed that, similar to static loading situation, multiple cracks were formed under fatigue loading, while the number of cracks decreased with the degradation of stress levels. For this reason, the deformability is much weaker at lower fatigue stress levels than that at higher stress levels. Moreover, the failure section is divided into three different districts, and the proportion of fiber rupture to fiber pullout is different under different stress levels.