Cold-formed circular hollow sections under axial compression
- Authors: Dundu, Morgan , Chabalala, Vongani
- Date: 2014
- Subjects: Columns, Concrete , Concrete slabs , Reinforced concrete construction , Concrete beams , South African Design Standards
- Type: Article
- Identifier: uj:5068 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13639
- Description: Two series of experiments were carried out to investigate the behaviour of pinned-ended circular hollow section (CHS) columns, subjected to axial compressive load. A total of 30 columns were tested in this investigation; 20 columns in Series 1 and 10 columns in Series 2. The outside diameter-to-thickness ratio (d/t) and the slenderness ratio (KL/r) ranged from 29.7 to 46.4 and 20.8 to 82.2 for Series 1, respectively, and from 55.0 to 62.9 and 10.7 to 34.9 for Series 2, respectively. In general, Series 1 columns failed by overall flexural buckling and, whilst Series 2 columns failed by local ring-type buckling. The test strengths of the columns were compared with the strengths predicted by the South African design standard (SANS10162-1) and the European design standard (EN 1993-1-1).
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Performance of concrete-filled double-skin circular tubes in compression
- Authors: Essopjee, Yoosuf
- Date: 2015
- Subjects: Prestressed concrete construction - Design and construction , Prestressed concrete construction - Testing , Reinforced concrete construction , Columns, Concrete , Tubes, Steel
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/384770 , http://hdl.handle.net/10210/55708 , uj:16303
- Description: Abstract: CFDSCT columns are structural members that are filled with concrete and supported by circular steel tubes on the interior and exterior. These steel tubes serve as formwork and hence these members are economical and quicker to construct when compared to conventional concrete reinforced columns. They are also efficient because they take advantage of the high compressive strength of the concrete and high tensile strength of steel. Despite the fact that much research is ongoing internationally in the field of CFDSCTs, no experimental tests have been conducted on intermediate and slender CFDSCTs. Current research has been focused on short CFDSCT columns and varying amounts of confinement have been found in these tests. Design codes also do not cover CFDSCTs. In order to gain a more comprehensive understanding of the behaviour of CFSDSCTs, experimental tests were conducted on 32 concrete-filled double-skin circular tube (CFDSCT) columns. The CFDSCT columns were loaded in axial compression till failure. The parameters that were varied were the lengths and diameters of the outer steel tubes, and the strength of the outer steel tubes. The lengths ranged from 1 and 2.5 m, in half a metre increments. The CFDSCTs of one metre lengths, failed by yielding of the steel tubes. All the other CFDSCTs failed by overall buckling due to their large slenderness. Using the same philosophy as SANS 10162-1 and EC4, new formulas were developed to predict the results of the strengths of the CFDSCTs. The new formulas are in a similar format to SANS 10162-1 and EC4, and are 5% and 6% more conservative than the tests results, respectively. The ratio of the predicted results over the test results versus the slenderness was plotted and shows that the results were predicted fairly well. , M.Ing. (Civil Engineering)
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Concrete filled double skin circular tubes : a review
- Authors: Essopjee, Yoosuf , Dundu, Morgan
- Date: 2014
- Subjects: Prestressed concrete construction , Columns, Concrete , Plates, Iron and steel
- Type: Article
- Identifier: uj:5083 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13654
- Description: A review of the research conducted on the compressive strength of concrete filled double skin circular tubes (CFDSCT) columns is conducted. Variables of the CFDSCT considered in this review include the concrete strength, steel strength, inner and outer tube diameter, steel thickness and length of the stub columns. Test results show that the composite columns had compressive strengths of up to 41% higher than the sum of the individual strengths of the section. All the outer tubes of these composite columns by failed local buckling. A review of the design equations proposed are presented and discussed. The paper also identifies gaps for further research for these types of columns.
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Preliminary study of strength of coal composites
- Authors: Moatlhodi, Lerato J. , Okonta, Felix N.
- Date: 2014
- Subjects: Columns, Concrete , Composite materials , Pillar failure
- Type: Article
- Identifier: uj:5081 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13652
- Description: Large scale floor convergence and sudden failure of pillars in room-and pillar underground mining have been reported in various countries over many years. Failure of these mines has been attributed, amongst other causes, to the stiffness criterion used by the mining operators and most importantly mine design practices, that tend to reduce the width-to-height ratio i.e. slender pillars in pursuit of greater coal recovery yields, in order to maximize coal recovery in the seam. It is recorded that the room-and-pillar method can leave behind about 40% of the total coal available for mining. The current study seeks to determine the appropriate width-height ratio for coal composite and stabilized coal pillars. Pure coal was mixed with granular soil and stabilized with cement to form cylindrical composite columns which were crushed to determine their unconfined compressive strength at different width-to-height ratios. The strength increased with the increase in W/H of the columns. Increase in coal percentage in a composite reduces the strength. The stabilized coal pillars mobilized less strength than the composite pillars. Based on limited data, relationships amongst column strength W/H and mix ratios were formulated and are proposed for the estimation of strength of mine support structures. More data is however required to formulate a general regression equation.
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