Papers by Keyword: Column

Abstract: The traditional design method of machine tool column easily leads to material redundancy and it is difficult to achieve the best structural efficiency. A bionic method is proposed, bamboo was used as the biological archetype, to design the column structure of an extra-heavy duty CNC boring and milling machine. The macroscopical and microscopic structural characteristic and the mechanical property of the bamboo are analyzed, and the intrinsic relationship between the microstructure and mechanical properties is obtained. The column is designed as cylindrical structure firstly, and the relationship between the number of transverse ribs and the whole bending deformation is ascertained. The transverse ribs are designed for cylindrical structure .By evolving the cylindrical member, A, B two kinds of bionic column are designed and compared. The specific stiffness of B type structure is increased 10.9% and its overall performance is better than the A. So the B scheme is selected as the final bionic structure of the column.

Abstract: The main objective of this study is to help the structural designers so they can, quickly and efficiently, study the concrete columns’ fire resistance. The most expeditious methods of fire resistance verification in terms of ease of application by structural designers, the methods given in EN 1992-1-2 [1] in the form of tables (Method A, Method B and Method C), were used in the fire resistance verification of 12243 rectangular columns inserted in the stability projects of 63 buildings, carefully selected in order to be representative of the ones licensed in Portugal [2]. Noting that these methods lead to excessively conservative results, the authors developed an alternative methodology, also with expedite application, but leading to substantially less conservative results (although designed on the safety side). This methodology consists on the consultation of adimensional interaction diagrams in fire situation, N_fi/M_fi, developed using the 500oC Isotherm Method. In the development of these diagrams unexpected results were obtained in some columns’ cross-sections, for which the resistance at room temperature was lower than the one corresponding to a fire situation at level R60. Some of the factors that can contribute to the occurrence of these results are pointed out.

Abstract: The use of high strength concrete (HSC) in multi-story buildings has become increasingly popular. Selection of HSC over normal strength concrete (NSC) allows for reducing the dimensions of the columns sections. However, this reduction has consequences on the structural performance in case of fire, as smaller cross sections lead to faster temperature increase in the section core. Besides, HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling than NSC. The fire performance of a column can thus be affected by selecting HSC over NSC. This research performs a comparison of the fire performance of HSC and NSC columns, based on numerical simulations by finite element method. The thermal and structural analyses of the columns are conducted with the software SAFIR^®. The variation of concrete strength with temperature for the different concrete classes is adopted from Eurocode. Different configurations are compared, including columns with the same load bearing capacity and columns with the same cross section. The relative loss of load bearing capacity during the fire is found to be more pronounced for HSC columns than for NSC columns. The impact on fire resistance rating is discussed. These results suggest that consideration of fire loading limits the opportunities for use of HSC, especially when the objective is to reduce the dimensions of the columns sections.

Abstract: Nowaday, we require higher capacity and ductility of structural member particulary in reinforced concret column in construction world. One way to improve the ductility and carrying capacity of concrete is confining the concrete. To investigate the effects of external confinement on column capacity, an analytical study is carried out. A steel ring external confinement is used in this study. The stress-strain diagrams design for confined concrete are developed by considering different proposed confined models based on width variations of the steel ring. The test results showed that steel ring are effective as external confinement in confining the concrete. Capability of concrete to support load simultaneously is increasing along the width of the ring. Its effect on column capacity is studied in terms of load – moment interaction diagram of column. The presence of external reinforcement expands the interaction diagram of the column particularly when it is in the compression-controlled region.

Abstract: FRP confinement of sub-standard columns with low quality concrete, light transverse reinforcement and improper reinforcement detailing is widely accepted as an efficient retrofitting strategy. This paper introduces an improved method using carbon fiber reinforced polymers (CFRP) and external steel ties for seismic retrofitting of full-scale rectangular reinforced concrete columns loaded in their weak directions. Three cantilever columns with a cross-sectional aspect ratio of two (600 mm x 300 mm) are tested under constant axial load and reversed cyclic lateral loads. The columns are representative of existing substandard members with characteristics such as low concrete quality, low transverse reinforcement ratio, plain bars and high axial load level. The test results indicate that columns retrofitted with FRP jacketing and external steel ties significantly benefit from the applied retrofit scheme particularly in terms of ductility and energy dissipation. Additionally, the experimental results are compared with the performance predictions of seismic assessment and design documents.

Abstract: In order to get a reasonable and effective adaptable structure design solution, fuzzy comprehensive evaluation method was applied to evaluate various schemes synthetically which has adopted the method of data normalization of the grey correlation evaluation method in pre process. Through the integrated calculation, the result of evaluation can be obtained accurately and rapidly from the static and dynamic value of the structures. An example of column of vertical grinding machine improvement design was given to explain the process of evaluation in details. Result of evaluation indicates that this method performs well in operability and practicability and can be used in the practice of product design and development.

Abstract: The dynamic characteristic is one of the important indicators which determine the performance of a machine tool, in this paper, the finite element model of a plane grinder is established with consideration of the behavior of joint, the static dynamic characteristics of machine tools are analyzed to reveal the vibration weak link, the column structure is topology optimized and redesigned based on the variable density degradation method. Static and dynamic characteristics of the original and new column are compared, and the dynamic characteristics of the machine tool before and after modification are discussed. The results indicate that the static and dynamic characteristics of the plane grinder are all improved after optimization.

Abstract: Basing on the combining of the stone carving technology and the traditional machining technology, some parts of the design of five-axis linkage machine tool has been done and the virtual prototyping of the machine tool has been finished. This paper focuses on the whole structure’s modal analysis and column’s structural optimization of the five-axis machine tool. In view of normal surface with a large length to width ratio, we can optimize the wall thickness of the column to ensure a better dynamic performance. In the process, when the wall thickness is 10mm, the result shows a reasonable modal frequency and fitting weight.

Abstract: Copper ore is classified into three groups; primary copper sulfide, copper oxide and secondary copper sulfide. Leaching copper from primary copper sulfide, such as chalcopyrite, with sulfuric acid takes longer time than from copper oxide and secondary copper sulfide. As such, an oxidant is required to extract copper from chalcopyrite. In this study, column leaching tests were carried out using primary copper sulfide ores produced in an iron oxide copper gold (IOCG) deposit and rich in iron in coparison to porphyry copper ores. The columns of 10 cm diameter and 100 cm long had a double tube structure so that the column temperature can be kept at desired temperature by circulating warm water in the outer tube. The oxidation-reduction potential (ORP) of the leaching solutions were adjustedto 400, 450 and 500 mV vs Ag/AgCl. The column leaching test using just pH 2.0 sulfuric acid without adjustment of ORP at 45 °C got a copper recovery rate of 37 % in 400 days. On the other hand, with ORP adjusted leaching solutions of pH 2.0 sulfuric acid containing 500 mg/L Fe, the copper recovery rate reached up to 87 % in 400 days.In addition, it was necessary to keep the temperature above 45 oC to enhance copper leaching by ORP adjusted leaching solution. The result of the column leaching test at room temperature (around 30 °C) using ORP adjusted leaching solution shows that the recovery rate of copper is lower than the result at 45 °C. The ORP adjustment of leaching solution is effective for leaching copper from primary copper sulfide ore, however, the leaching temperature needs to be kept above 45 °C. As a result, it makes clear that copper leaching is enhanced by utilization of ORP adjusted leaching solutions and suggests that the solution ORP control is important to the application of bioleaching.

Abstract: In Colombia, as in other developing regions, social housing shortage related problems has led local authorities to propose low cost housing projects that allow its quickly and easy construction. Among the requirements of this type of construction are solicitations for vertical and lateral loads caused by wind or earthquake forces, as well as the sustainable use of natural resources Considering this, the use of Guadua angustifolia Kunth (Guadua a.) as a structural material has awaken a great interest, considering its renewability, high-speed growth, ecological benefits and because is easily obtainable all across the country. Due to the lack of additional information, structural joints in this type of materials, are usually pinned, assuming that there is no moment transmission between the different elements, however, some types of connections can partially restrict the rotation in the supports. Additionally, the degree of constrain that any support can provide to the column is a variable that has not been studied enough, despite being essential for modeling and structural design.In this work a connection between a column of Guadua a. and its foundation was studied. The influence of each component on the connection behavior under horizontal loads was assessed, testing seven different configurations. Monotonic and dynamic testing of connections as well as the characterization of the materials used in its construction were included in the experimental schedule. It was determined that the presence of mortar grouting together with the use of longitudinal bolts slightly increases the connection strength as drastically reduce its ductility. The use of transversal bolts is the best alternative to obtain a strong, stiff and ductile connection, especially when are combined with the use of hoops.