Key Engineering Materials Vol. 517

Abstract: Removed due to double publication.

Abstract: The use of EVA (Ethylene Vinyl Acetate) waste, from shoes industry, in the production of pre-molded block (EVA block) has been researched in the last 12 years. The results have shown great potential for these wastes to be used as lightweight aggregate, to replace natural aggregate in the manufacture of bricks made of cement based composites. This article examines the potentiality of waste EVA blocks recyclability, as aggregate in the production of new EVA blocks. In the experiment EVA blocks were molded in the mix proportion of 1:5 in volume (20% of sand and 80% of EVA) and determined the mass and compressive strength at 28 days. Then the EVA blocks were crushed and resulting aggregate was reused in part (portion retained on a 4.8 mm sieve) in the molding of new EVA blocks, using in dosages two different proportions of crushed aggregate (50% and 70%, EVAr - waste of crushed EVA blocks) in relation to the total volume of coarse aggregate of original EVA (EVA - waste from shoes industry). The average compressive strength at 28 days of the original EVA block was 1.2 MPa, whereas the block EVAr₇₀ was 2.2 MPa and the block EVAr₅₀ was 1.7 MPa. Thus, there was an 83% increase in the compressive strength on the block EVAr₇₀ and 44% on the block EVAr₅₀. It was also noticed there was no significant difference among the weights of all the blocks produced. So, it appears that the EVAr aggregate impacted more in the compressive strength than in the mass of the blocks. Thus, the recyclability of the EVA block appears viable.

Abstract: Chemical analysis of household waste from the sanitary ware industry is of fundamental importance in order to detect the presence of AAR (alkali-aggregate reaction), the same in field or laboratory. There are several test methods, these methods can detect pre-reactivity of aggregates compared to the sodium or potassium hydroxide present in hydrated cement paste. For the preparation of both the concrete and the mortar, from the recycled material, the aggregates were reduced until it had texture, close to the river sand and gravel. The analyses stayed in determining the potential of the alkali-aggregate reactivity. Thus the results of chemical and physical characterization of the material, indicated a willingness to be used as aggregate in mortar and concrete, due to the availability of waste, the good properties given and the gains in cost, beyond the environmental management, they promote the viability of the process of recycling of waste. ¹

Abstract: Wood, as a green and environment-friendly building material, is widely used in building engineering. Naturally grown, wood has various defects like knots, cracks and inclined grain. Fracture Mechanics is thus an efficient tool to investigate the mechanical behavior of wood and wood-based composite products. According to Linear-elastic Fracture Mechanics (LEFM), fracture toughness can be introduced to measure the resistance to crack propagation. Crack was assumed to occur when the stress intensity factor K reached a critical value K_C. Fracture in wood usually involves not only the Mode I type (open) fracture, but also the Mode II type (shear) fracture. For getting a better understanding of the crack growth phenomenon of Northeast China Larch, it is, therefore, essential to assess the K_IC and K_IIC, which are the critical stress intensity factors for Mode I and Mode II type fracture, respectively. In the current study, K_IC and K_IIC, of Northeast China Larch were determined through tests with compact tension specimens and tests with compact symmetric shear specimens, respectively. In addition, the material properties tests were also performed. All of the specimens were cut from the same batch of Glulam beams. Based on the obtained data from experiments, LEFM was employed to explain the fracture failure in the form of crack propagation. Using Extended Finite Element Method (XFEM), simulation of the crack propagation in Mode I and Mode II was performed incorporating ABAQUS. The crack propagation and the load-displacement curves of numerical simulation were in good agreement with experiments, which validated that the proposed numerical approach is suitable for analysis of crack growth in the specimens. As part of a larger program to investigate the fracture behavior of Glulam beams made of Northeast China Larch, this study provides the material properties and validation of the numerical simulation approach. A series of experiments of full-size curved Glulam beams subject to bending and the corresponding simulations extending the numerical approach of this study to the cases of full-size wood composite members are under development.

Abstract: Yingxian Wood Pagoda, built in 1056, is located in the town of Yingxian County, Shanxi Province, China. It is the oldest and highest standing ancient wood structure in China. The pagoda is octagon-shaped in plan, with a total height of 67.31m and a base diameter of 30.27m. It appears as a five-storeyed structure, but actually consists of nine storeys, with four shorter but stiffer storeys hidden between the five apparent storeys. Yingxian Wood Pagoda was built without any metal connectors like nail, screw, or bolt. Instead, Tenon-Mortise connections and Dou-Gong brackets were used to connect all posts and beams. Tenon-Mortise connections and Dou-Gong brackets have been playing a vital role for the pagoda to resist severe winds, earthquakes and some human-induced disasters for nearly a thousand years. To evaluate the safety of the pagoda, it is, therefore, useful to investigate the structural performance of the beam-column joints, most important for Yingxian Wood Pagoda to resist lateral load. In this study, two models of typical beam-column joints of the pagoda, MBCJ-I and MBCJ-II, were manufactured following a ratio of 3.4 to the prototype of the joints. Non-destructive cyclic loading test of the models under different vertical load and destructive cyclic test of the models under vertical load of 20kN were conducted. The hysteretic stiffness of MBCJ-I was lager than MBCJ-II, and increased linearly with vertical load N. The relationship between and N was obtained by regression of the test results using the least square method. The stiffness of model joint under vertical load was 70.6kN/mm. The failure modes, energy-dissipation performance, moment resistance and bending stiffness of both model joints were derived and discussed.

Abstract: The defects, especially for knot, seriously affect the bending properties of wood. In this paper, full scale specimens and clear specimens for bending test, cut from dimension lumbers of Larix gmelinii with different kinds of knots, aimed to predictive accuracy of the modulus of elasticity (MOE) in bending and to improve the accuracy of MOE by multivariate regression analysis with density and knot information. According to the regression analysis results, the [(IK/Ig)·(MK/Mo)] of all knots and the average density ρa showed the best predictive accuracy of MOE for full scale specimen (Efull), with 0.674 of R2 and 1.15 of RMSE. Based on the ratio of regression parameter B/A of independent variables for density and knots information, the knots had less influential than density on influencing Efull. Finally, a simplified theoretical model that can be used to calculate MOE for dimension lumber, was defined as Efull/Eclear = B[(IK/Ig)·(MK/Mo)]+C .

Abstract: Larch dimension lumber bending strength properties from full-size bending test were used to establish preliminary grade boundary settings for mechanical grading of lumber by modulus of elasticity. Simulated production using the grade boundary settings were evaluated for modulus of rupture, ultimate tensile strength, and ultimate compressive strength. The results showed a good relationship between modulus of rupture and modulus of elasticity, and the observed relationships between strengths properties were consistent with that assumed for the standard grades. Through mechanical grading, larch dimension lumber could be sort grades: M14, M30 and M40. Assuming the visual requirements are met, the M30 and M40 grades account for more than 80% of the total production. Mechanical grading of larch appears to be a viable approach for grading Chinese large for structural applications.

Abstract: Thin shell masonry structures are ideal for low-cost housing. Curved structures are ideally suited to resist external forces and are the most efficient structures. In shell structures, the forces are primarily in-plane, referred to as membrane forces. Shells, dominated by compressive stresses, are an absolute requirement in masonry structures, to minimize cracking. However, shell structures which are designed for pure compression still exhibit cracking on the external surface. Cracked shells are unsightly and a precursor to durability problems. For this reason, several studies have been undertaken to determine the cause of cracking in shells. This study is an investigation into the effects of thermal loading. The research includes the mapping of thermal loads by experimentation, an assessment of the effects of thermal loading and possible solutions to prevent cracking in the shell.

Abstract: Presented in this paper are the results of practical tests to determine some key material properties of engineered timber, in particular glulam. The results are discussed and compared with three known failure criterion, Hankinsons formula, The Tsai-Wu criterion and Maximum stress theory to determine if they are appropriate models for predicting the properties of glulam. The properties considered have been chosen with respect to a connection system for use in folded plate structures utilizing embedded rods. This paper considers the effect of the timber grain angle on the compression, tensile and steel dowel rod pull-out strengths. The test data shows that Hankinson and Tsai-Wu are both good models to predict both the compression and tensile behavior of engineered timber products at non-tangential angles, whereas maximum stress theory had less correlation and over predicts the results and would not be recommended for use in engineered timber materials.

Abstract: As a kind of low-carbon, sustainable and environmental-friendly building material, wood has been widely used in ancient timber-frame buildings in China. Chinese ancient timber-structure buildings can not only provide a comfortable indoor environment, but also has an excellent structural behavior. Based on the study of horizontal and vertical layout of structural system, special constructional measures such as Cejiao and Shengqi, the structural behaviors of Chinese ancient timber-frame buildings were studied. Those conclusions were achieved: structural system layout in both horizontal and vertical comply with the existing anti-seismic conceptual design thoughts. When subjected to earthquake, the seismic actions are reduced by means of base sliding isolation, energy dissipation and shock absorption of mortise-tenon joints and tou-kung sets, which make Chinese ancient timber building a multiple aseismic system. Cejiao and Shengqi are equivalent to passive control in modern buildings, which improve the structural integrity, stability and aseismic capacity greatly. The post-and-lintel roof truss is a good way of saving material.