Compression tests of Mi Panels
- Authors: Bukasa, G. M. , Dundu, M.
- Date: 2014
- Subjects: Reinforced concrete construction , Concrete beams , Flexure , Concrete - Deterioration
- Type: Article
- Identifier: uj:5073 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13644
- Description: A number of compression tests of Mi Panels are presented. The use of lightweight Mi Panels as building system allows the reduction of construction time and waste in the building environment. The compression tests are performed to simulate the behaviour of the wall, when subjected to vertical loads from the roof. Two LVDTs were placed at mid-height of the panels during the compression tests, to record the lateral displacement. Mi Panels failed by fracturing into two parts at mid-height. No cracks in the panel were observed before overall flexural buckling failure. The tests showed that the panels are capable of carrying the required loads, and can be used in place of brick walls.
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Flexural tests of Mi Panels
- Authors: Bukasa, G. M. , Dundu, M.
- Date: 2014
- Subjects: Concrete beams , Flexure , Fiber cement , Fiber-reinforced concrete
- Type: Article
- Identifier: uj:5074 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13645
- Description: Two series of flexural tests on 2700x600x75 mm Mi Panels are presented. The inner core of these lightweight panels is made from mixing polystyrene beads called Neopor, high strength cement, and water. A chemical is used as binding agent to bond the inner core to the external fibre cement sheets of 4.5 mm thickness. The experimental programme consists of two series of tests with different loading conditions; the first series has line loads at one-third point from each end support and the second series has line loads, at quarter and three quarter span of the panels. All flexural tests are performed to simulate the behaviour of the wall, when subjected to wind loads. Although the panels failed by fracturing, the tests showed that the panels are capable of carrying the required loads.
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Use of angle cleats to restrain cold-formed channels against lateral torsional instability
- Authors: Bukasa, G.M. , Dundu, M.
- Date: 2016
- Subjects: single channels , Restrained , Purlin–angle cleat
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/123374 , uj:20783 , Citation: Bukasa, G.M & Dundu, M. 2016. Use of angle cleats to restrain cold-formed channels against lateral torsional instability.
- Description: Abstract: It is common practice in the steel construction industry to restrain members that largely in flexure and torsion using a combination of angle cleats, connected at the top flange, and fly-bracings. This system is complicated and expensive, especially when used to restrain channels in bending. This paper investigates experimentally the use of angle cleats, connected to the webs of both the purlin and the channels, as a restraining system. Pairs of channels were subjected to a two point loading system in order to simulate a distributed load. Variable in the tests include the unbraced length between the two-point loads and the size of the channels. Failure of the channels occurred by lateral torsional buckling and catastrophic distortional buckling of the intermediate unbraced length. Tests showed that the purlin-cleat restraining system is able to resist lateral torsional buckling of the channels, and that this system can be used without any fly bracing. Distortional buckling was the final failure mode, and it occurred at moments less than the predicted lateral-torsional buckling moment of resistance. Distortional buckling is more critical in frames with shorter unbraced lengths and thicker channels.
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Short-term elongation variation of post-tensioned tendons
- Authors: Dundu, M.
- Date: 2015
- Subjects: Elongation variation , Post-tensioning , Tendon
- Language: English
- Type: Article
- Identifier: http://ujcontent.uj.ac.za8080/10210/386978 , http://hdl.handle.net/10210/73220 , uj:18384 , Citation: Dundu, M. 2015. Short-term elongation variation of post-tensioned tendons.
- Description: Abstract: When tension is applied to steel tendons they elongate in proportion to the tensile force, as predicted by Hooke’s law. This elongation is used by the South African standard on concrete structural works (SANS 2001-CC1) and South African standard specification for road and bridgeworks (COLTO) to determine the adequacy of the force applied in a tendon. The standards prescribe an elongation variation limit of ±6% and an average elongation variation limit of ±3%. According to these standards, if the elongation variation of the tendon falls outside these prescribed limits it must be brought to the attention of the engineer. The scatter of tendon elongation results is often greater than the range prescribed by these standards. This usually requires the contractor to re-tension the tendons at huge financial costs. In most cases the results obtained after re-tensioning are the same. This paper analyses tensioning data obtained from a variety of projects that have been completed in South Africa in recent years. The aim of this investigation is to determine the causes of variation in elongation and suggest adjustments, if any, to the current elongation variation.
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Column buckling tests of hot-rolled concrete filled square hollow sections of mild to high strength steel
- Authors: Dundu, M.
- Date: 2016
- Subjects: Square concrete-filled steel tubes , Hot-rolled , Slenderness ratio
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/123382 , uj:20784 , Citation: Dundu, M. 2016. Column buckling tests of hot-rolled concrete filled square hollow sections of mild to high strength steel.
- Description: Abstract: This paper examines the behaviour of 29 square concrete-filled steel tubes (CFST) under concentric axial compression. The cross-section of the hot-rolled steel tubes ranges from 60x60x3.0mm to 150x150x4.5mm, and are grouped in three series (Series 1, 2 and 3). For the sections tested, the slenderness ratio (L/b) for Series 1, 2 and 3 ranges from 6.67 to 24.61, 27.00 to 45.00 and 18.00 to 27.0, respectively; and the depth-to-wall thickness (b/t) ranges from 33.87 to 42.86, 13.33 to 33.33 and 22.22 to 50.00, respectively. The slenderness ratio provides a range of columns, from relatively short to slender composite columns. Particular attention is paid to the existence of circumferential strain in the square composite columns. The compressive resistance of the composite columns are compared with the design strengths predicted by the South African standard (SANS 10162-1), as well as the European design standard (EN 1994-1-1). SANS10162-1 is based on the Canadian steel code (CAN/CSA-S160-01). A two-stage equation is proposed to model the results of short columns (Equation 4) and intermediate to slender columns (Equation 5).
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Mathematical model to determine the weld resistance factor of asymmetrical strength results
- Authors: Dundu, M.
- Date: 2017
- Subjects: Skewed , Normal distribution , Histogram
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/250615 , uj:26119 , Citation: Dundu, M. 2017. Mathematical model to determine the weld resistance factor of asymmetrical strength results.
- Description: Abstract: A normal distribution model is usually used to determine the structural steel resistance factors. This distribution has a symmetric probability density curve. When test results are skewed, a normal distribution model is not an efficient mathematical model to determine the resistance factors. Other mathematical models which have a skewed density probability curve should be used in such situations. The objective of this study is therefore to determine the mathematical model that is most suitable to determine the resistance factors of skewed set of test results. To accomplish this, 21 weld strength values were used in this investigation to determine the weld resistance factor. A histogram of the weld strengths illustrated that the weld strengths are skewed. Distributions are skewed, especially if the values under investigation cannot be negative, the mean are low and the variances are large. Since weld strengths are skewed, a beta distribution, chi-square distribution and gamma distribution were used to analyse the results, and the mathematical function, which was found to fit the sample data best was selected and used to compute the design strength of the 21 weld strengths, using 0.01 probability of failure. Among the distribution analysed, the beta probability distribution was found to be the most effective model.
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Tensile strength of circular hollow sections with squashed ends
- Authors: Dundu, M.
- Date: 2021
- Subjects: Circular hollow sections , Flat ends , Three bolt configurations
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/488251 , uj:44474 , Citation :Dundu, M., 2021. Tensile strength of circular hollow sections with squashed ends. Engineering Structures, 234, p.111971.
- Description: Abstract : Experiments were performed to investigate the behaviour of 28 circular hollow sections (CHSs) in tension, with flat ends and three bolt configurations (2, 3 and 4 bolts). The length of the members between the flat ends was kept constant at 1500 mm for all CHSs, and the sizes of the sections ranged from 60.3x2.0 to 101.6x4.5. Two modes of failure were observed, viz; bearing failure (BF) and net-section fracture (NSF). CHSs connected with 2 bolts failed in bearing, whilst net-section fracture was dominant in sections with 3 and 4 bolts. The notion that the change in the number of bolts can lead to different behaviours of the connections is a significant contribution to knowledge, particularly if flat-ended CHSs are used as structural truss elements. This paper demonstrates that the sections are capable of supporting large loads, however, the capacity of the tested specimen did not reach the full yield strength. It is apparent from the tensile strengths that a larger increase in strength was accomplished when the number of bolts was increased from 2 to 3 bolts than from 3 to 4 bolts. A comparison of the tensile strength with the strengths predicted by the North American standard (AISI S100-16w/S1-18), Australia/New Zealand standard (AS/NZS-4600:2018) and European standard (EN 1993-1-3) confirm that both standards provides a reasonable assessment of the strength of the 3 and 4 bolt configuration, which failed purely by net-section fracture. However, for the 2-bolted connections, which failed in bearing, it is proposed to use AS/NZS 4600:2018, with a bearing coefficient of C = 2.85, instead of C = 3.0, to increase the accuracy of the bearing strength expression for these specimens.
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Local buckling requirements of carbon cold-formed circular hollow steel sections of mild-to-high strength steel
- Authors: Dundu, M.
- Date: 2021
- Subjects: Cold-formed , Circular hollow steel sections , Diameter-to-thickness ratio
- Type: Article
- Identifier: http://hdl.handle.net/10210/488267 , uj:44476 , Citation : Dundu, M.,2010. Local buckling requirements of carbon cold-formed circular hollow steel sections of mild-to-high strength steel.
- Description: Abstract : This paper assess the current local buckling requirements of carbon cold-formed steel hollow sections under axial compression, using data from literature. A total of 39 circular hollow steel sections (CHSSs) are analysed, and these include 19 columns of mild steel and 20 columns of high strength steel. Variables in the study includes the length, diameter, thickness and material properties. The outside diameter-to-thickness ratio (d/t) for CHSSs of mild steel ranged from 48.72 to 249.23, while the outside diameter-to-thickness ratio (d/t) for CHSSs of high strength steel ranged from 16.15 to 46.84. The corresponding yield stress for mild steel ranged from 203.80 MPa to 622.80 MPa, while that of high strength steel ranged from 1341.00 MPa to 1405.00 MPa. A comparison with CAN/CSA-S16-09 and EN 1993-1-1, shows the limits of both standards to be too conservative. New slenderness limits are proposed to improve the design of these sections.
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Impact of adhesive thickness on the capacity of the surface mounting steel plates strengthening techniques
- Authors: Olajumoke, A. , Dundu, M.
- Date: 2016
- Subjects: Steel plates , Epoxy , Strengthening
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/91863 , uj:20155 , Citation: Olajumoke, A. & Dundu, M. 2016. Impact of adhesive thickness on the capacity of the surface mounting steel plates strengthening techniques.
- Description: Abstract: Please refer to full text to view abstract
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Static behaviour of steel plate-strengthened reinforced concrete slabs in bending
- Authors: Olajumoke, A.M. , Dundu, M.
- Date: 2016
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/123344 , uj:20779 , Citation: Olajumoke, A.M & Dundu, M. 2016. Static behaviour of steel plate-strengthened reinforced concrete slabs in bending.
- Description: Abstract: This paper reports on an investigation on a reinforced concrete (RC) strengthening technique carried out by the authors, using surface bonding steel plates (SBSP). To accomplish this investigation, the tension face of one-way spanning RC slabs was scabbled and bonded with one or two sandblasted steel plate(s) of different thicknesses, using epoxy glue. The steel plate thicknesses were varied in order to deter-mine the width-to-thickness ratios that can promote yielding (and not premature debonding) of the RC slabs before failure. A low flexural reinforcement percentage (≈ 0.314% bh) was used in order to prevent over-reinforcement and to ensure that failure of the slabs under static loading was due to flexure. Static two-point line loading was adopted to simulate the worse loading condition. Based on the deformation response of the slabs, the most appropriate parameters of the steel plates, for strengthening distressing reinforced concrete slabs were determined. The SBSP strengthening technique was found to possess effective composite proper-ties as all the strengthened RC slabs failed essentially by flexural yielding before steel plate separation, with enhanced load carrying capacity of at least 89% above that of control slabs.
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Effectiveness of surface preparation on the capacity of plated reinforced concrete beams
- Authors: Rakgata, S. M. , Dundu, M.
- Date: 2018
- Subjects: Reinforced concrete , Surface preparation , Strengthening
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/270606 , uj:28765 , Citation: Rakgata, S.M. & Dundu, M. 2018. Effectiveness of surface preparation on the capacity of plated reinforced concrete beams.
- Description: Abstract: One of the most important methods for strengthening and repairing reinforced concrete beams is to use external bonded steel plates, however, the success of this technique depends on the effectiveness of the surface preparation of the steel and concrete beams. The International Concrete Repair Institute (ICRI) recognises ten standard concrete surface profiles (CSP), according to the level of roughness, which ranges from CSP 1 (nearly smooth) to CSP 10 (very rough). Each level of roughness is associated with particular bond strength. The purpose of this investigation is to study the effectiveness of four different levels surface preparation, namely; no surface preparation (NSP), wire brushing (WB), scabbling (SC) and hand chipping (HC), on the capacity of plated reinforced concrete beams The quality of the surface preparation established was measured based on the flexural performance of the externally strengthened steel-concrete beams. A total of 9, 250x450x3600 mm reinforced concrete beams were prepared, strengthened with glued steel plates on their soffits, and tested under two-point static loading until failure. The results showed that beams with rougher surface preparation have a high bond strength as compared to smoother surface preparations. The increase in flexural capacity of the roughened beams in Group A ranges from 18% to 32% as compared to the control beam, whilst the increase in flexural capacity of the roughened beams in Group B ranges from 20% to 42%.
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Strength and ductility of simple supported r/c beams retrofitted with steel plates of different width-to-thickness ratios
- Authors: Rakgate, S. M. , Dundu, M.
- Date: 2018
- Subjects: Steel plates , Width-to-thickness ratio , Reinforced concrete beams
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/270599 , uj:28767 , Citation: Rakgate, S.M. & Dundu, M. 2018. Strength and ductility of simple supported r/c beams retrofitted with steel plates of different width-to-thickness ratios.
- Description: Abstract: The concept of strengthening reinforced concrete beams using epoxy-bonded steel plates (EBSP) is a well-known solution in structural engineering, however, there is little information about the effect of the width-to-thickness ratio of steel plates on the behaviour of steel-concrete composite beams. This paper presents an experimental study of the flexural behaviour of under-reinforced concrete beams, strengthened in flexure by externally-bonded steel plates (EBSP) of varying widthto- thickness ratios. A total of 23 reinforced concrete beams were tested; 6 beams in Series 1 tests and 17 beams in Series 2 tests. One beam in Series 1 tests and two beams in Series 2 tests were regarded as control specimens, whilst the remaining beams were strengthened with steel plates of different width-to-thickness ratios. In each group, the width of the bonded steel plate varied from 75 mm to 175 mm, in increments of 25 mm. The beams were tested as simply supported, under two-point static loadings until failure. From the experimental results, it was observed that the externally bonded steel plates led to substantial increase in flexural stiffness, which resulted in an increase in the capacity and cracking load of the strengthened beams and a decrease in vertical deflections and crack-widths, compared to the control beams. It was also found that the width-to-thickness ratio of steel plates as low as 12.5 can promote flexural yielding and extensive ductility in strengthened beams.
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Internal eaves connections of double-bay cold-formed steel portal frames
- Authors: Tshuma, B. , Dundu, M.
- Date: 2017
- Subjects: Double-bay portal frames , cold-formed channels , eaves connections
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/241736 , uj:24917 , Citation: Tshuma, B. & Dundu, M. 2017. Internal eaves connections of double-bay cold-formed steel portal frames.
- Description: Abstract: Double-bay or multi-bay portal frames of hot-rolled steel have been in existence since the development of the plastic analysis theory, and the behaviour of the eaves connections of these frames are well established. With the increasing use of cold-formed steel in portal frames, it is necessary to develop connecting structural systems that are favourable to these elements, and to understand the behaviour of these connections. The purpose of this investigation is to develop internal eaves connections of double-bay portal frames of cold-formed steel channels, with the main frames members connected back-to-back. In double-bay portal frames, the columns of two single-bay portal frames, positioned adjacent to each other, are replaced by one internal column. Two internal eaves connections were developed and investigated, and are referred in this paper as Eaves Connection Type 1 (ECT-1) and Eaves Connection Type 2 (ECT-2). Tests were then performed to determine the capacity and failure mechanism of these connections, including the members forming these connections. Although the failure mechanisms included local buckling of the compression zone of the web and flange of the channels, and bolt-bearing deformations, all frames finally failed by local buckling of the web and flange of the channels. The moment-curvature graphs show that enough plasticity could not be achieved in both connections.
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Gusseted rafter-to-column connections of double-bay single channel portal frames
- Authors: Tshuma, B. , Dundu, M.
- Date: 2016
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/123336 , uj:20778 , Citation: Tshuma, B & Dundu, M. 2016. Gusseted rafter-to-column connections of double-bay single channel portal frames.
- Description: Abstract: Double-bay portal frames have several advantages over two single portal frames positioned adjacent to each other, however the connecting system can be a challenge, especially if the portal frame is formed from single cold-formed channels. The portal frames described in this paper consists of a column and two rafter members, formed from single cold-formed channels sections, and bolted back-to-back at the eaves joint through a gusset plate. Tests were performed to evaluate the structural performance of the eaves region of double-bay portal frames. The eaves region represents the distance from the point of maximum moment (eaves joint) to the point of zero moment (contraflexure) in the rafters and columns respectively. The structures failed by local buckling in the compression flange and web of the rafters, outside the joints. The moment- curvature graphs proved that plasticity could not be achieved in these connections.
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Eaves connections of double-bay portal frames with staggered single channel cold-formed rafters
- Authors: Tshuma, B. , Dundu, M.
- Date: 2016
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/123328 , uj:20777 , Citation: Tshuma, B & Dundu, M. 2016. Eaves connections of double-bay portal frames with staggered single channel cold-formed rafters.
- Description: Abstract: Experimental tests were performed to evaluate the structural performance of the eaves region of double-bay portal frames with staggered cold-formed rafters. This region represents the distance from the point of maximum moment at the eaves joint to the point of zero moment (contraflexure) in the rafters and columns respectively. The column and two rafter members are formed from single cold-formed channel sections, which are bolted back-to-back at the eaves joint. In order to simplify the connections the rafters are connected directly to the back of the web of the column at different levels. Particular attention was focused on the failure modes of the structures, the strength (resistance to moment) of the connection, the momentcurvature performance and the connection’s ability to form plastic hinges. In all the tested structures, the column failed by local buckling in the compression flange and web, between the upper and lower rafters. The moment-curvature graphs proved that plasticity could not be achieved in these connections.
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