262 research outputs found
A Review of Basic Mechanical Behavior of Laminated Bamboo Lumber
Over the past decade, the physical and mechanical performances of laminated bamboo lumber (LBL)–a bamboobased structural material, have been extensively studied using experimental, analytical, and numerical approaches.
This paper presents a review of existing knowledge in the literature about the mechanical properties of LBL. The
paper involved the review of the response of LBL to different types of loading such as tension, bending, compression, and shear. Based on results of the literature reviewed, the strength of LBL parallel to grain was 90–124 MPa
with MOE of 10700 MPa in tension, 29.55–72.60 MPa, and MOE of 8396–11022 MPa in compression, 63.87–
128.4 MPa, and MOE of 8320–10912 MPa in bending, and 7.15–17.5 MPa in shear. The average strength of
LBL was similar and in some cases exceeded the average values of bamboo- or wood-based materials, while
the variability of its mechanical parameters was lower. The variability in strength values of LBL was affected
by bamboo species, density and thickness of bamboo strips, growth portion, type of treatment, strips arrangements, and type of adhesive which in turn calls for classification of LBL by strength grades, degree of hardness,
the capability of impregnation and penetration, as well as by areas of application in construction. The study provided and discussed concluding observations, the current research gap, and future research directions on the
mechanical properties of LBL
Nodes Effect on the Bending Performance of Laminated Bamboo Lumber Unit
This research studied the ultimate bearing capacity of laminated bamboo lumber (LBL) unit and thereby calculated the maximum bending moment. The load-displacement chart for all specimens was obtained. Then the flexural capacity of members with and without bamboo nodes in the middle section was coMPared. The bending experiment phenomenon of LBL unit was concluded. Different failure modes of bending components were analysed and concluded. Finally, the bending behaviour of LBL units is coMPared with other bamboo and timber products. It is shown that the average ultimate load of BS members is 866.1 N, the average flexural strength is 101 MPa, the average modulus of elasticity is 8.3 GPa, and the average maximum displacement is 17.02 mm. The average ultimate load of BNS members is 1008.1 N, the average flexural strength is 118.02 MPa, the average modulus of elasticity is 9.9 GPa, and the average maximum displacement is 18.26 mm. Laminated bamboo lumber (LBL) unit without bamboo nodes (BNS) has relatively higher flexural strength coMPared with LBL unit with bamboo nodes (BS). The presence of bamboo nodes reduces the strength of the entire structure. Three failure modes were concluded for BS members, and two failure modes were observed for BNS members during the experimental process. According to a coMParison between the LBL unit and other products, the flexural strength and bending modulus of elasticity of the LBL unit are similar as bamboo scrimber and raw bamboo components, which is much higher than timber components
Asma y actividad fÃsica. Revisión
El asma es una enfermedad inflamatoria crónica de elevada prevalencia a nivel mundial, siendo el colectivo más afectado el formado por niños y adolescentes. Su sintomatologÃa se caracteriza por la aparición de tos, disnea, sibilancias, sensación de opresión en el pecho y broncoconstricción. Tradicionalmente se habÃa pensado que el deporte y el ejercicio fÃsico estaban contraindicados en pacientes asmáticos. Por otro lado, el paciente asmático suele presentar niveles de condición fÃsica y práctica deportiva menores que los sujetos sanos. Actualmente se ha propuesto la actividad fÃsica regular como un camino válido para mejorar la percepción y el autoconocimiento personal sobre esta enfermedad. Se aconseja la prescripción de actividad fÃsica como forma de mejorar su sintomatologÃa y evolución. La práctica de una actividad fÃsica regular en pacientes asmáticos deberÃa ser considerada dentro de los actuales y futuros programas de salud como un objetivo fundamental.Asthma is a chronic inflammatory disease of high prevalence worldwide, being the group comprised of children and adolescents the most affected. Its symptoms are characterized by cough, dysnea, wheezing, feeling of tightness in the chest and bronchoconstriction. Traditionally, it was thought that sport and physical exercise were contraindicated in asthmatic patients. Furthermore, the asthmatic patient usually presents less fitness levels and sport practice as well as healthy subjects. Currently regular physical activity has been proposed as a valid way to improve staff awareness and self-knowledge about the disease. It is recommended the prescription of physical activity as a way to improve their symptoms and evolution. Regular practice of physical activity in asthmatic patients should be considered within the current and future health programs as a main aim
Whose Needs Does Service Serve? Complicating the Citizen Soldier Narrative
The growth of conscript militaries was integral to the creation of civil rights in European nation-states, which established militaries as a key site of claims-making. However, the United States military has diverged from these models, and most cases of inclusion or integration of social groups are not directly connected with claims-making. What has influenced the U.S. military’s responsiveness to pressures, both internal and external, and how has this changed over time? I employ a comparative historical approach to three cases—African-Americans, women, and non-heterosexuals—to unpack the U.S. military as a state institution and a site of claims-making. By incorporating elements unique to American institutions into existing models of militaries, I find that the U.S. military has become increasingly vulnerable to domestic political, international political, internal economic, and internal and external cultural pressures since the World War period. Despite its enormous economic and physical strength, the U.S. military is more responsive now than ever before to internal and external demands
Effects of chemical modification and nanotechnology on wood properties
As a green material, wood is widely used in building decoration, railway construction, and other fields. However, the wood itself has inherent defects of being easy to absorb water and deform, rot, and decrease in strength. The physical and mechanical strengths and stability of artificial fast-growing forest wood are even worse. As wood modification can improve the dimensional stability, durability, strength, and other properties of wood, it has been widely used. Chemical modification is the main method of wood modification. The development of nanotechnology has brought more possibilities for wood modification. Owing to the extensive literature available, this article summarizes the representative achievements of wood chemical modification and nanotechnology. The principle, production process, advantages, and disadvantages of various wood chemical modification methods were analyzed, compared, and evaluated. Finally, according to the application status of wood-modified materials, the problems existing in the current wood chemical modification methods and the application of nanotechnology, and the development trend in the future are analyzed
Review on Connections for Original Bamboo Structures
Bamboo is a green construction material in line with sustainable development strategies. The use of raw bamboo in architecture has existed since ancient times. In the long development years of original bamboo buildings, many areas in the world gradually formed unique bamboo buildings, which have become an important local cultural feature. For building structures, joints are the key to ensure structural load transfer. Because of hollow and thin-walled material property of bamboo, the connection in raw bamboo buildings has always been a major difficulty and problem in the application of bamboo, which seriously hinders the development of original bamboo structures. In order to promote the use of raw bamboo, two traditional connection methods in raw bamboo structures are described in this paper firstly, with the advantages and disadvantages of the two methods pointed out. Also, research progress on four categories of raw bamboo building joints is described namely, bolt joints, steel member joints, filler reinforced joints and other types of joints. This work can provide a reference for future research and engineering applications
Slenderness Ratio Effect on the Eccentric Compression Performance of Chamfered Laminated Bamboo Lumber Columns
Eccentric compression tests on 15 chamfered laminated bamboo lumber (LBL) columns with a height ranging
from 600 to 3000 mm were conducted in order to study the eccentric mechanical performance. The failure of
all specimens was caused by the crack of bamboo fiber in the tensile region. When the ultimate strength was
reached, except specimens with a height of 600 mm, all other specimens could bear large deformation, showing
good ductility. The lateral displacements of the specimens under eccentric compression were approximately parabolic in the direction of column height. The ultimate bending moment of LBL columns with different slenderness
ratios under compression with the same initial eccentricity was a fixed value. The relationship between ultimate
capacity, axial displacement, lateral displacement, and slenderness ratio was analyzed based on test results. It was
found that the plane section assumption could be used to express the stress and strain distribution of chamfered
LBL columns under eccentric compression. A method for calculating the ultimate bearing capacity was proposed
using a constitutive model based on the Ramberg-Osgood relation and the empirical formula for calculating the
ultimate capacity was given on the basis of the former research as well as the test results in this paper
Characteristics of pedaling muscle stiffness among cyclists of different performance levels
Background and Objectives: The aim of the present study was to compare the impact of an incremental exercise test on muscle stiffness in the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and gastrocnemius (GL) among road cyclists of three performance levels. Materials and Methods: The study group consisted of 35 cyclists grouped according to their performance level; elite (n = 10; professional license), sub-elite (n = 12; amateur license), and recreational (n = 13; cyclosportive license). Passive muscle stiffness was assessed using myometry before and after an incremental exercise test. Results: There was a significant correlation between time and category in the vastus lateralis with stiffness increases in the sub-elite (p = 0.001, Cohen’s d = 0.88) and elite groups (p = 0.003, Cohen’s d = 0.72), but not in the recreational group (p = 0.085). Stiffness increased over time in the knee extensors (RF, p < 0.001; VL, p < 0.001), but no changes were observed in the knee flexors (GL, p = 0.63, BF, p = 0.052). There were no baseline differences among the categories in any muscle. Conclusions: Although the performance level affected VL stiffness after an incremental exercise test, no differences in passive stiffness were observed among the main muscles implicated in pedaling in a resting state. Future research should assess whether this marker could be used to differentiate cyclists of varying fitness levels and its potential applicability for the monitoring of training load. © 2021 by the authors. Licensee MDPI, Basel, Switzerland
Properties and Applications of Bamboo Fiber-A Current-State-of-the Art
Fibers are used in many forms in engineering applications–one of the most common being used as reinforcement.
Due to its renewable short natural growth cycle and abundance of bamboo resources, bamboo fiber has attracted
attention over other natural fibers. Bamboo fiber has a complex natural structure but offers excellent mechanical
properties, which are utilized in the textile, papermaking, construction, and composites industry. However, bamboo fibers can easily absorb moisture and are prone to corrosion limiting their use in engineering applications.
Therefore, a better understanding of bamboo fiber is particularly important. This paper reviews all existing
research on the mechanical characterization of bamboo fiber with an emphasis on the extraction and treatment
techniques, and their effect on relevant properties. The chemical composition of bamboo fibers has also been
thoroughly investigated and presented herein. Current applications and future opportunities for bamboo fibers
in various fields have been presented with a focus on research needs. This work can serve as a reference for future
research on bamboo fiber
Review of connections for engineered bamboo structures
Bamboo is a green building material that is environmentally friendly and has great development value. However, the limited mechanical properties and heterogeneous dimensions of natural bamboo poles curb the application of bamboo in building structures. A transverse section of engineered bamboo is regular and compact, and its mechanical properties are stable, which can meet the requirements for physical and mechanical properties of materials in modern building structures. Though application of engineered bamboo has just started, it is of great significance to study the connection performance and corresponding influence factors for popularization and application of modern bamboo structures. This paper is focused on a review of research progress for connections in engineered bamboo structures. Firstly, a study on embedding strength and the performance of bolted joints is presented, including calculation methods described with a proposal for future development of standards suitable for the characteristics of engineered bamboo materials. Secondly, research on carpentry joints is introduced, namely tenon-mortise joints, nail joints and truss plate joints. Finally, some engineering examples are briefly introduced. This work can provide a reference for further research on connections in engineered bamboo structures
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