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Analysis of elongation variance of tendons using stress-strain graphs

  • Authors: Dundu, Morgan , Rupieper, Sebastian
  • Date: 2014
  • Subjects: South African Design Standards , Tendons (Prestressed concrete) , Bonded tendons , Building materials
  • Type: Article
  • Identifier: uj:5079 , http://hdl.handle.net/10210/13650
  • Description: The South African design standards (SANS 2001-CC1 and COLTO) prescribes an elongation variation limit of ±6% and an average variation limit of ±3%. Most often these limits are exceeded in practice. If the elongation variation of a tendon falls outside the prescribed elongation limits it must be assessed by the engineer. This paper analyses data of bonded tendons from post-tensioned structures. The aim of this study is to explain the elongation variance of tendons in post-tensioned structures using selected stress-strain graphs. These structures include a reservoir (Mthatha 1-10) and a viaduct (Gautrain Jean Avenue P80).
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Application of HEC-HMS model for evaluation of rainwater harvesting potential in a semi-arid city

Buckling of short cold‑formed lipped channels in compression

  • Authors: Dundu, Morgan
  • Date: 2014
  • Subjects: Cold-formed lipped channels , Short columns , Compressive resistance , Local buckling , Distortional buckling
  • Type: Article
  • Identifier: uj:4816 , http://hdl.handle.net/10210/12257
  • Description: This paper presents an experimental investigation of short cold-formed lipped channel columns compressed between pinned ends. The short columns are subjected to pure axial compressive loading. Twelve column specimens are tested and the columns are categorised into three groups, depending on the length and thickness. The buckling modes of failure that occurred include local buckling and distortional buckling. A comparison of the experimental results with the loads predicted by the South African standard for the design of cold-formed steelwork (SANS 10162-2) shows that the code is not conservative enough to cater for these columns.
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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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Composite action of pre-cracked reinforced concrete beams repaired with adhesive bonded steel plates

  • Authors: Ngidi, Sandile D. , Dundu, Morgan
  • Date: 2018
  • Subjects: Flexural strength , Pre-cracked reinforced concrete beams , Repairing
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/270588 , uj:28764 , Citation: Ngidi, S.D. & Dundu, M. 2018. Composite action of pre-cracked reinforced concrete beams repaired with adhesive bonded steel plates.
  • Description: Abstract: Previous studies demonstrated that significantly cracked beams can be repaired by bonding steel plates, however, there is a lack of comprehensive information about the effect of the width-to-thickness ratio of steel plates on repaired composite beams, and the use of thicker plates to repair failed RC beams. This paper presents an assessment of the performance of precracked reinforced concrete beams repaired with adhesive bonded steel plates, of varying width-to-thickness ratio, at the soffit. A total number of 12 beams were tested under a twopoint static loading. Group 1 consisted of two control specimens, Group 2 comprised of five beams that were pre-cracked to 60% (serviceability load), and Group 3 consisted of another five beams that were pre-cracked to 85% of the ultimate load. Subsequently, the pre-cracked beams were repaired by bonding steel plates of 6 mm thickness and 75 – 175 mm widths, which varied in increments of 25 mm. Externally bonding steel plates to pre-cracked reinforced concrete beams increased their load capacities by more than 100%, compared to the control beams. Except for specimen PB60-175, there is generally increase in the capacity of the repaired beams with increase in the width-to-thickness ratio of the steel plates. Beams that were pre-cracked at a lower load level (serviceability load) reached higher strengths than the beams that were pre-cracked at a higher load level (85% of the ultimate load capacity). In all tested beams, the experimental moment of resistance did not reach the code-predicted moment of resistance, calculated using EN 1992-1-1.
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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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Effect of width-to-thickness ratio of steel plates in Composite steel-concrete beams

Evolution of stress–strain models of stainless steel in structural engineering applications

  • Authors: Dundu, Morgan
  • Date: 2018
  • Subjects: Stainless steel , Stress–strain , Non-linear
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/270603 , uj:28766 , Citation: Dundu, M. 2018. Evolution of stress–strain models of stainless steel in structural engineering applications.
  • Description: Abstract: Stainless steel is a family of steel alloys with a minimum of approximately 10.5% mass of chromium. Unlike carbon steel, it has high corrosion and heat resistant properties. Stainless steel does not easily corrode because it forms an invisible thin passive film of about 5x10-6mm of chromium oxide (Cr2O3), which is impervious to water and air. If this film is damaged by scratching, it repairs itself as chromium in the steel reacts rapidly with oxygen and moisture in the environment to re-form the oxide layer. Since the early 20th century a lot of research work has been performed to understand the stress-strain response and mechanical properties of materials which exhibit non-linear behaviour over the complete shape of the stress-strain curve. Significant progress was achieved when the Ramberg– Osgood model was developed, however, there is consensus amongst researchers that this model is only accurate up to the 0.2% proof stress. As designs become more complicated and refined, it is clear that the behaviour of non-linear materials cannot be fully described by the Ramberg–Osgood model. Advanced numerical analysis and design requires knowledge of the stress-strain relationship of the alloys over a full range of the stress-strain curves. This paper provides a detailed review of the evolution of the stress-strain models of stainless steel, in literature.
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Factors that influence friction in tendons of unbonded post-tensioning systems

  • Authors: Dundu, Morgan , Ward, Michelle
  • Date: 2014
  • Subjects: Tendons (Prestressed concrete) , Corrosion and anti-corrosives , Steel, Structural - Protection
  • Type: Article
  • Identifier: uj:5059 , ISSN 9781614994657 , ISSN 9781614994664 , http://hdl.handle.net/10210/13621
  • Description: The coefficient of friction in an unbonded post tensioning system is influenced by many factors, and these factors include the thickness of lubricant or grease present in the system, clearance between the strand and the plastic sheath, surface characteristics of the strand and plastic sheath. In order to determine the effect of these factors, a series of friction tests were performed on two different diameters of strand, namely; 12.7 mm and 15.24 mm diameters. Through a regression analysis, it was found that the frictional force decreases with increase in the thickness of the grease and that friction increases with increase in the mass of the strand. The amount of friction was found to be dependent on the surface characteristics of the strand and plastic sheath, clearance between the plastic sheath and the strand and the extrusion process of the plastic sheath.
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Flexural failure modes of steel plate-strengthened reinforced concrete elements

Influence of different surface preparations on the capacity of composite steel-concrete beams

  • Authors: Rakgate, Sylvester M. , Dundu, Morgan
  • Date: 2017
  • Subjects: Concrete , Steel plate , Surface roughness
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/248161 , uj:25790 , Citation: Rakgate, S.M. & Dundu, M. 2017. Influence of different surface preparations on the capacity of composite steel-concrete beams.
  • Description: Abstract: External bonding of steel plates to structural concrete members has widely gained popularity in recent years, particularly for repairing and strengthening reinforced concrete beams. The success of this bonding technique depends on the effectiveness of the surface preparation of the steel and concrete beams. Studies have shown that most of the beams strengthened using this technique usually fail prematurely by debonding. In this study, concrete beams with different types of surface preparations were investigated, such as no surface preparation (NSP), wire brushing (WB), scabbling (SC) and hand chipping (HC). The quality of the surface preparation established was measured based on the flexural performance of the externally strengthened steel-concrete beams. Eight (8), 250x450x3600 mm reinforced concrete beams were prepared and strengthened with glued steel plates on their soffits. All the specimens were tested under two-point static loading and failure modes were observed. The results showed that beams with rougher surface preparation have a high bond strength as compared to smoother surface preparations. The increase in the average capacity of strengthened beams with the surface prepared by hand-chipping, scabbling, wire brushing was found to be 75.3%, 67.5% and 46.9% respectively, compared to the capacity of the beam strengthened without surface preparation.
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Limits of elongation variation of tenadons in post-tensioning

  • Authors: Dundu, Morgan , Rupieper, Sebastian
  • Date: 2014
  • Subjects: Tendons (Prestressed concrete) , Prestressed concrete construction , South African Design Standards
  • Type: Article
  • Identifier: uj:5069 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13640
  • Description: This paper analyses tensioning data obtained from a variety of projects that have been completed in South Africa in recent years in order to determine the causes of variation in elongation and suggest practical elongation limits. Current limits, prescribed by the South African standards (SANS 2001-CC1 and COLTO), of elongation variation limit of ±6% and an average elongation variation limit of ±3% are causing huge problems to the post-tensioning industry. 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.
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Methods for flexural strengthening of reinforced concrete elements using steel plates

  • Authors: Olajumoke, Akinropo Musiliu , Dundu, Morgan
  • Date: 2014
  • Subjects: Concrete beams , Plates, Iron and steel , Reinforced concrete , Flexure
  • Type: Article
  • Identifier: http://ujcontent.uj.ac.za8080/10210/380017 , uj:5078 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13649
  • Description: When reinforced concrete elements are incapable of safely sustaining the anticipated load, flexural strengthening may be necessary. Two major construction methods have been reported in literature for strengthening reinforced concrete (RC) elements in bending. These methods include Externally Bonded Reinforcement (EBR) and Near Surface Mounting (NSM). The aim of this paper is review these methods, including the extensive surface preparation that must be performed on bonded elements. Previous investigations have shown that these techniques are effective in salvaging old and distressed reinforced concrete structures. This paper identifies the problems associated with the utilisation of steel plates as strengthening material for RC elements in EBR and NSM techniques.
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Plastic response of laterally restrained adhesive-bonded 1 compound steel beams

  • Authors: Dundu, Morgan , Chikore, Lance T.
  • Date: 2021
  • Subjects: Compound beams , Epoxy adhesive , Local buckling
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/489268 , uj:44605 , Citation: Dundu, M. and Chikore, L.T., 2021. Plastic response of laterally restrained adhesive-bonded compound steel beams. Journal of Constructional Steel Research, 187, p.107007.
  • Description: Abstract: Compound beams are generally formed by welding or bolting steel elements to the flanges of an 9 I-section or universal beam. A compound beam is used where the depth is limited and the universal 10 beam is not strong enough to resist the bending stresses. Steel plates or other steel elements are 11 welded or bolted on both flanges of the I-section to enhance its capacity. The purpose of the study 12 is to determine the suitability of using an adhesive as an alternative to bolting or welding in 13 fabricating compound beams. Unlike welding and bolting, adhesive bonding eliminates stress 14 concentration and residual stresses, however, adequate bonding techniques are required if this 15 method is to be applied more widely. Two series of compound cross-sections of four specimens 16 each were fabricated and tested in flexure under a two-point loading, and the results compared to 17 the theoretical plastic capacity of the compound section. Of the eight specimens tested, six failed 18 by flexural yielding, proving that adhesives can serve as a suitable alternative to bolting and 19 welding in manufacturing a compound beams.
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Repair of reinforced concrete beams with adhesive Bonded steel plates

Steel contribution effect on beams bonded with steel plates of different width-to-thickness ratios

  • Authors: Rakgate, Sylvester M. , Dundu, Morgan
  • Date: 2017
  • Subjects: Steel plates , Steel contribution factor , RC beams
  • Language: Engliah
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/248242 , uj:25800 , Citation: Rakgate, S. & Dundu, M. 2017. Steel contribution effect on beams bonded with steel plates of different width-to-thickness ratios.
  • Description: Abstract: The concept of strengthening reinforced concrete (RC) beams using epoxy-bonded steel plates (EBSP) is a well-known solution in structural engineering. Experimental investigations conducted in the past has proved that strengthening RC beams with steel plates are the most efficient, effective, and costeffective technique of increasing the flexural performance of these elements. However, the focus has been on effect of the external bonded steel plate, and not on the effect of the overall steel contribution ratio on the behaviour of the strengthened beams. Several codes give the minimum reinforcement ratios for concrete beams in order to encourage/improve their flexural behaviour such as cracking and ductility failure. The purpose of this present study is to investigate the effect of the steel contribution ratio on the flexural behaviour of concrete beams strengthened on their tension face with epoxy bonded steel plate, using the experimental results obtained by various researchers in this field. The outcomes of strengthening RC beams are decrease in mid-span deflections, decrease in crackwidths, and increase in first crack load, and consequently increase in both serviceability load and ultimate load, thus making it to be the most feasible strengthening technique.
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Stress-strain models for stainless steel

The effects of lubricant and tendon mass variances on the coefficient of friction in unbonded post-tensioning tendons

  • Authors: Dundu, Morgan , Ward, Michelle
  • Date: 2016
  • Subjects: Post-tensioning , 7-wire strand , Grease
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/123366 , uj:20782 , Citation: Dundu, M & Ward, M. 2016. MENDED: The effects of lubricant and tendon mass variances on the coefficient of friction in unbonded post-tensioning tendons.
  • Description: Abstract: In unbonded post-tensioning tendons, the coefficient of friction varies from one design standard to another. This variation is caused by the large number of complex factors that must be considered in design. These factors include the thickness of lubricant or grease present in the system, clearance between the strand and the plastic sheath, surface characteristics of the strand and plastic sheath. In order to determine the effect of these factors a series of friction tests were performed on two different diameters of strand, namely; 12.7mm and 15.24mm diameters. Through a regression analysis, it was found that the frictional force decreases with an increase in the thickness of the grease and that friction increases with an increase in the mass of the strand. The degree of friction was found to be dependent on the surface characteristics of the strand and plastic sheath, clearance between the plastic sheath and the strand and the extrusion process of the plastic sheath.
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