Strengtening of concrete slabs using bonded steel plates
- Authors: Bruwer, C P C , Dundu, M
- Date: 2011
- Subjects: Reinforced concrete construction , Building, iron steel
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/17195 , uj:15855 , Citation: Bruwer, C.P.C & Dundu, M. 2011. Strengtening of concrete slabs using bonded steel plates.The 2011 World Congress on Advances in Structural Engineering and Mechanics (ASEM'11+), 18-22 September, 2011, Seoul, Korea.
- Description: Abstract This paper analyses the results of several series of tests performed on composite concrete-steel slabs. The objectives of the tests are to: 1) determine the bending moment capacity 2) study the different failure modes 3) compare the theoretically calculated bending moment with the experimentally tested bending moment. The following variables are included in the test series: 1) length of the composite slabs, 2) width of the composite slab 3) thickness of the composite slab 4) steel plate cross sectional dimensions (width and thickness), 5) number of bonded steel plates and 6) loading configurations applied onto the simply supported slab (mid span line load or third span line load to simulate uniformly distributed loads). The reinforcing bars within the composite slab were kept the same for all series of tests. The composite concrete-steel slabs were formed by bonding steel plates to the soffits of reinforced concrete slabs by means of epoxy glue. In order to obtain full composite action the epoxy glue between the concrete slab and steel plate must be able to transfer the generated shear forces. To achieve the bond between the concrete and steel plate surfaces, the bonded surfaces had to be roughened. The concrete surfaces were roughened by either exposing the main concrete aggregate using brushes, chiselling the concrete paste layer to expose the main aggregate or by scabbeling the cement laitance to expose the main aggregate as per the epoxy supplier’s specifications. The mild steel plates were sand blasted with a dry grid to a white metal finish in order to obtain a 100-140 micron blast profile as per the epoxy supplier’s specification. Pro-StructLV low viscosity epoxy adhesive was used to bind the epoxy to the concrete surface and Pro-Struct 617NS non-sag epoxy was used to bind the steel to the concrete surface. In tests where full composite action between the steel plates and the concrete slabs was realised, an increase of up to 200% in the bending moment capacity of the slab was realised. The composite concrete-steel slabs failed either by debonding of the steel plate(s), flexural bending or vertical shearing of the composite system
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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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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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Identifying the effects of excessive deflection in reinforced concrete beam
- Authors: Ogbeifun, E. , Pretorius, J. H. , Mbohwa, Charles , Ogbeifun, E
- Date: 2014
- Subjects: Reinforced concrete construction , Concrete beams , Floors, Concrete - Design and construction
- Type: Article
- Identifier: uj:5084 , http://hdl.handle.net/10210/13655
- Description: In framed reinforced concrete structure, the beams transfers the dead and live loads to the column and then to the foundation. When there are observed structural failure in the systems supported by the beam, especially where the beam has a large unsupported clear span at a lower level, before any further detailed investigations are initiated, the functional state of the beams should be ascertained. The correct diagnosis of the source of problem is essential for the design of effective rehabilitation scheme. Simple visual inspection corroborated with field test for true horizontality of the beam can provide the lead information that will guide the client on the scope of further investigations. The case study method of qualitative research was adopted to address the research questions, while the research data was collected by reviewing previous investigation reports on a three-storey building, physical inspection and conducting simple site experiment to identify the lead information. The research outcome reveals that the multiple cracks observed in the partition walls especially in the second floors were as a result of excessive deflections in the beams supporting the first and second floors. Based on recommendation, subsequent investigation confirmed this lead information and appropriate rehabilitation scheme was adopted.
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Thin spray rock liners with different concentrations of nanoclays
- Authors: Van Tonder, P. , Booysen, C.J , Van Tonder, P
- Date: 2014
- Subjects: Nanostructured materials , Polymer-impregnated concrete , Reinforced concrete construction
- Type: Article
- Identifier: uj:5080 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13651
- Description: This study investigates the possibility of effectively replacing polymers in thin sprayed liners (TSL’s) with nanoclay particles. In the industry Nano particles are used in many different products to enhance their properties. The strength properties was analysed to see if the addition of nanoclays improve the strengths of the TSL product. Different concentrations of nanoclay were added to a standard TSL mixture in the place of polymer particles. The different composites were tested for Tensile Strength, Compression Strength, Shear Strength and Shear Bond Strength. Though there are other parameters to be tested, the study will only focus on those mentioned above, as they were considered to be the most important. The materials used for testing these characteristics were supplied by Oxyfibre. The mixtures have consisted of four different composites that included the standard mixture, 2% nanoclays, 4% nanoclays and 6% nanoclays.
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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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Towards practical carbonation prediction and modelling for service life design of reinforced concrete structures
- Authors: Ekolu, S. O.
- Date: 2015
- Subjects: Reinforced concrete construction
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/58040 , uj:16412 , Citation: Ekolu, S.O. 2015. Towards practical carbonation prediction and modelling for service life design of reinforced concrete structures. International Conference on Innovative Structures and Technologies, 2015. DOI: 10.1088/1757-899x/96/1/012065 , 10.1088/1757-899x/96/1/012065
- Description: Abstract: Amongst the scientific community, the interest on durability of concrete structures has been high for quite a long time of over 40 years. Of the various causes of degradation of concrete structures, corrosion is the most widespread durability problem and carbonation is one of the two causes of steel reinforcement corrosion. While much scientific understanding has been gained from the numerous carbonation studies undertaken over the past years, it is still presently not possible to accurately predict carbonation and apply it in design of structures. This underscores the complex nature of the mechanisms as influenced by several interactive factors. Based on critical literature and some experience of the author, it is found that there still exist major challenges in establishing a mathematical constitutive relation for realistic carbonation prediction. While most current models employ permeability /diffusion as the main model property, analysis shows that the most practical material property would be compressive strength which has a low coefficient of variation of 20% compared to 30 to 50% for permeability. This important characteristic of compressive strength, combined with its merit of simplicity and data availability at all stages of a structure’s life, promote its potential use in modelling over permeability. By using compressive strength in carbonation prediction, the need for accelerated testing and permeability measurement, can be avoided. This paper attempts to examine issues associated with carbonation prediction, which could underlie the current lack of sound established prediction method. Suggestions are then made for possible employment of different or alternative approaches.
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Validation of concrete elastic modulus estimation methods
- Authors: Sun, Ryan Wok
- Date: 2015
- Subjects: Elastic analysis (Engineering) , Concrete - Testing , Reinforced concrete construction , Concrete products , Strength of materials
- Language: English
- Type: Master’s Thesis
- Identifier: http://hdl.handle.net/10210/56194 , uj:16341
- Description: Abstract: The modulus of elasticity (E) is an important property of concrete that needs to be quantified when designing complex structures. The methods to best quantify this property are empirical within the laboratory, but outside the laboratory, designers may depend on estimation models. There exists numerous estimation models at the designer’s disposal but the accuracy and reliability of those models have not been comprehensively and comparatively assessed. The actual E values of 108 specimens, whose properties differed in aggregate type, cement type, concrete strength and curing age, were measured. The actual E values were compared to the predictions made by 23 estimation models. The accuracy of each model was analysed statistically to conclusively determine which of the models was most accurate. The Noguchi et al (2009) model was found to be the most accurate and consistently so, rendering an overall coefficient of variation of 15.94%. The CEB-FIP (1970) model was found to be the least accurate, resulting with an overall coefficient of variation of 31.81%. In addition to the primary objective, this study included the analysis of the degree of influence of aggregate percentage content, compressive strength, curing age and concrete density on the actual elastic modulus of concrete. The concrete’s density was found to be a major factor in the resulting E of concrete as the statistics had shown that the correlation was highly significant (P = 2.39 x 10-7 %). Concrete strength on the other hand, a factor that most models use as a primary basis for their estimations, was not as influential as assumed. In fact, the statistical results showed the correlation to have a level of significance of 11.1 %. It was therefore highly recommended that E estimation models should, at least, include the density of concrete as a common parameter more than the inclusion of concrete strength. Separate to the topic of concrete E, this research also assessed the average strength relationship between concrete cylinders and concrete cubes. The average cylinder-cube strength relationship slightly increases with the increase in curing age indicated by a correlation coefficient of 0.998. The strength of the cylinders were found to be, on average, approximately 85 % of the cube strengths. , M.Tech. (Civil Engineering)
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Structural behaviour of composite concrete-steel slabs
- Authors: Bruwer, Carl Pieter Cronje
- Date: 2016
- Subjects: Concrete slabs , Reinforced concrete construction , Building, Iron and steel , Composite construction
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/225109 , uj:22728
- Description: Abstract: Reinforced concrete structural elements can be strengthened by bonding external steel plates onto the concrete surface by means of an epoxy adhesive and are referred to as composite structural members. The objectives of this Master’s research project on the Structural Behaviour of Composite Concrete-Steel Slabs were as follows: To determine whether steel plates bonded externally to existing reinforced concrete structural elements can control the deflection To determine whether steel plates bonded externally to existing reinforced concrete structural elements can increase the flexural resistance To determine whether the various debonding mechanisms of the steel plate from the concrete surface of existing reinforced concrete structural elements can be theoretically predicted by existing theories. Twenty-four reinforced concrete specimens were constructed using 25 MPa concrete and 5 Y12 internal bars in the longitudinal direction. The concrete and steel plate surfaces were prepared by scabbling and sandblasting respectively. The steel plates, which varied in thickness (from 6 mm to 8 mm), width (from 110 mm to 150 mm) and number (1 or 2), were bonded externally to the soffit of the concrete structural elements by means of epoxy glue. These composite concrete-steel specimens were simply supported and loaded until destruction by applying either a third-span line load (TSLL), mimicking a uniformly distributed load, or a mid-span line load (MSLL). The applied load, vertical deflection and strain on the bonded steel plates at mid-span were electronically logged. The vertical deflection within the elastic range of the unplated and plated reinforced concrete structural elements was obtained using the double integration method. The cracked second moment of area (Icr) was calculated by transforming the cross-sectional area of the steel reinforcement to an equivalent area of concrete. It was found that the deflection of composite concrete structural elements decreased as the cross-sectional area of the bonded steel plates increased. A comparison between the theoretically analysed and experimentally measured deflections was done as part of this research study. The findings of this study indicate that steel plates externally bonded to reinforced concrete structural elements increase the flexural and shear resistance of the members. The externally bonded plates are not, however, enclosed by the concrete as in the case of internal reinforcement and are therefore not as well anchored. This results in premature debonding of the steel plate from the concrete surface. Two design philosophies for the theoretical prediction of the flexural resistance were considered. The first was the anchorage design philosophy developed in Europe (fib-14, 2001) where the tension face plates are terminated in the uncracked region, which is beyond or at least to the point of contraflexure. The second is the hinge design philosophy developed in Hong Kong and Australia (Handbook 305-2008, Standards Australia) whereby the tension face plates are terminated short of the points of contraflexure; this latter philosophy was adopted as the bonded steel plates stopped 250 mm short of the support, which is also the point of contraflexure for simply supported structural elements. The following debonding mechanisms due to flexure and shear were investigated:.. , M.Ing. (Civil Engineering)
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Repair of cracked reinforced concrete beams with adhesive bonded steel plates
- Authors: Ngidi, Sandile Daniel
- Date: 2017
- Subjects: Concrete beams - Maintenance and repair , Reinforced concrete construction , Plates, Iron and steel , Steel, Structural
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/269693 , uj:28652
- Description: M.Ing. (Civil Engineering) , Abstract: Concrete structures often suffer from cracking and deterioration caused by factors such as impact and dynamic loading, static overload and construction faults. This requires immediate repair to prevent further degradation and to restore structures integrity. Externally bonded steel plates are used to repair such damaged concrete structures in a number of projects in various parts of the World, but their overall performance is still not fully understood. The main objective of this study is to investigate the flexural behaviour of pre-cracked reinforced concrete beams, repaired by bonded steel plates on their soffit, using epoxy adhesives. This implied an experimental investigation, which took place in Material Laboratory of the Department of Civil Engineering Science at the University of Johannesburg. Twelve full-scale beams of 175 mm wide x 300 mm deep x 3200 mm long were pre-cracked, repaired with steel plates and tested to failure in flexure under a two-point loading. Two variables were included in this investigation, namely; plate size and loading conditions. The plate size was varied by changing its width, which ranged from 75 mm up to 175 mm, in increments of 25 mm and the beams were pre-cracking at serviceability load and at 85% of the maximum load. During the experiments, the following aspects were evaluated and recorded regarding the response of tested beams: flexural strength, stiffness, maximum deflections and failure modes. Externally bonding the steel plate to the pre-cracked reinforced concrete (RC) beams resulted in increased stiffnesses and maximum load capacities up to 153% and decreased in the maximum midspan deflections up to 38%. The strength and rigidity of the repaired beams were found to increase with increasing the width-to-thickness ratio of the steel plate from 12.5 to 29.17. The results also showed that bonded external steel plate can only enhance the maximum load capacity of the repaired beams to a limited extent. There exists a limit in the width-to-thickness ratio for which the load can increase. The experimental results showed that the structural integrity of the repaired beam not only can it be restored but also enhanced. The bonded external plate contributed more to the control of maximum load capacities than to the control of deflections.
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