Browsing by Author "Van Zijl, Gideon Pieter Adriaan Greeff"

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    Alternative wall‑to‑slab connection systems in reinforced concrete structures
    (South African Institution of Civil Engineering, 2017-09) Gerber, Johann; Van Zijl, Gideon Pieter Adriaan Greeff
    ENGLISH ABSTRACT: In many reinforced concrete structures the walls precede the construction of the connecting floors. A system is, therefore, required to connect the floors to the already cast walls. There are many different floor-to-wall connection systems available in South Africa, but their behaviour and capacity are not always fully understood, especially when the moment capacity of the joint is to be utilised. This study focuses on four systems: continuous starter-bars, pre-bent site-installed starter-bars, preassembled starter-bars and cast-in anchors with mechanical couplers. The design procedure for the continuous starter-bar system is well understood and documented in design codes, but not enough information is available on the design procedure for the other systems. Certain practical aspects of the installation process are also not fully understood. Cold-bending and straightening of the starterbars are inevitable in both bend-out systems. Previous research shows that this cold-working of the reinforcement can reduce the yield stress and E-modulus of the steel. In order to investigate these findings, a series of tensile tests are conducted. The results indicate that a significant reduction can be expected in both the yield stress and modulus of elasticity of the steel. Low-cycle fatigue tests further suggest that cold-bent steel also has a reduced ductility. The tensile tests are followed by the construction and testing of the systems in full-scale wall-to-slab connections. The effect of the coldbending on the starter-bars is clearly visible, as both the responses of the bend-out systems are less satisfying than the results from the continuous starter-bar system. The experimental phase is followed by numerical analysis of the connection systems. The finite element analyses show that the structural performance is significantly more sensitive to a reduction in the yield stress of the starter-bars, than to the use of a lower concrete grade. It is concluded that all the alternative connection systems can be implemented successfully in a moment-fixed wall-to-slab connection, but that the site-installed bendout system is the preferred method. However, in order to ensure that the system performs on the same level as conventional systems, it is recommended that the design should be conducted with a set of modified steel properties to allow for the negative effect of the cold-working on the starter-bars.
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    Contributions to structural mechanics and durability in structural engineering
    (Stellenbosch : Stellenbosch University., 2016-12) Van Zijl, Gideon Pieter Adriaan Greeff; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: Contributions to structural engineering have been made since 2001 from the basis of the Department of Civil Engineering of Stellenbosch University (SU). The inauguration of the Centre for Development of Sustained Infrastructure (CDSI) in 2002 has been instrumental in defining, directing and scoping the research and development in the categories Advanced cement-based construction materials, Crack formation and durability towards durability design, Renovation and retrofitting towards extended life span and Sustainable energy harvesting structures. The contributions are structured along these categories as chapters of this dissertation. Early career background in structural Engineering at the Institute for Structural Engineering (1987-1989) and Bureau for Mechanical Engineering (1989-1992) and higher education in computational and structural mechanics (PhD 1995-1999, Research Fellow 1999-2001, TU Delft), shaped the research interests in these fields. Continued affiliation with TU Delft (30%) and SU (70%) in the years 2001-2009 provided access to collegial expertise in related fields of experimental research, materials engineering, risk and reliability, and structural design at these institutions and beyond. In this way, national and international collaboration complemented structural and computational mechanics in well-rounded research programs in the mentioned categories. Clearly, the contributions are the result of collaboration in which the author to various degrees led, participated in and supervised research and development. Highlights of the contributions in the four categories are described at a relatively high level towards conveying the contributions in the national and international context. To a degree selective reporting is done, and the reader directed to detailed elaborations in roughly 200 dissertations, theses and technical papers supervised or co-supervised, authored and co-authored. Approach by the infrastructure pre-fabrication industry in South Africa towards development of accelerated and new product lines led to the development of advanced cement-based construction materials (ACM) with local ingredients, and appropriate adaption of the materials to industrial fabrication process of high-pressure extrusion. What started as fibre inclusion towards reduced traditional steel reinforcement in concrete pipes, led to development, characterisation, manufacturing and constitutive modelling of steel fibre concrete and strainhardening cement-based composites (SHCC). Roles of international leadership in co-chairing and chairing RILEM technical committees followed, as well as co-editing of books on the state-of-the-art of Durability of SHCC and a Framework of durability design with SHCC respectively. Particular contributions of significant potential towards the ability to design for durable, sustainable infrastructure, were made in chloride-induced corrosion and alkali silica reaction. In both cases crack formation and durability, i.e. structural durability in service conditions are the points of departure in order to assess actual structural performance in presence of such deteriorating processes. The work in ACM was extended to ultra-high strength concrete, and recently to lightweight aerated concrete (LWAC) and lightweight foam concrete (LWFC). The thermal, acoustic and potential mechanical advantages of LWAC and LWFC are subjects of a current significant research effort in the CDSI towards developing these lightweight materials for structural application in residential infrastructure. Constitutive models developed for traditional construction materials, as well as several of the ACM, enabled the iterative computationalexperimental development and validation of retrofitting strategies for both unreinforced load-bearing masonry and reinforced concrete structures for new functionality or extended structural life span. Finally, a role of leadership and collaboration was fulfilled in research of the solar chimney power plant concept with national and international partners, bringing the concept for harvesting of sustainable energy to a pre-feasibility level. The contributions have laid the link between construction material properties, structural behaviour and durability. Through the fundamental experimental research, structural mechanics and computational mechanics, it has been made possible to utilise the advanced properties of ACM to advance structural performance and durability. Human capital well-versed in the fundamental principles of this multi-level structural engineering approach has been developed in the process of research supervision by the author.
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    Corrosion deterioration of steel in cracked SHCC
    (SpringerOpen, 2017) Paul, Suvash Chandra; Van Zijl, Gideon Pieter Adriaan Greeff
    The presence of cracks is unavoidable in reinforced concrete structures and also a gateway for chloride into concrete, leading to corrosion of steel reinforcing bars. So, crack control, crack width limitation and chloride threshold levels are well-established concepts in durability of reinforced concrete structures. This paper reports on accelerated chloride-induced corrosion in cracked reinforced strain-hardening cement-based composites and reinforced mortar beams, both in loaded and unloaded states. Corrosion rates are monitored and loss of mass and yield force, as well as corrosion pitting depth in steel bars are reported. The chloride content at different depths in specimens is also determined through XRF, and through chemical testing of acid and water soluble chloride content by titration. Finally, different relationships are drawn between crack properties, mass loss, yield force, corroded depth and chloride levels at the steel surface for different cover depths. It is found that the crack spacing and free chloride at the steel surface level are best correlated to the corrosion damage in the specimens.