Retrofitting of Cross-Sections

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Many existing buildings and structures often require to be retrofitted due to lack of capacity to resist the applied actions. This chapter discusses various reasons why structures may require retrofitting and focuses on various techniques for the retrofitting of cross-sections to improve their capacity. Enhancement of capacity for axial loads, bending moments, shear and torsion is discussed separately. Several typical techniques and materials for retrofitting of cross-sections of reinforced concrete beams, columns and slabs, etc., are presented. A brief discussion of various informative references related to the evaluation and retrofitting of structures is included for practical applications. The methods to calculate the capacity of retrofitted cross-sections using the formulations presented in Chapters 2–4 are presented. A detailed discussion of evaluation of sections subjected to high temperatures is also discussed.

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... Since the construction sector is responsible for a large part of global energy consumption and accounts for a significant share of global GHG emissions [18], it is also important to take environmental aspects into account when renovating buildings. Building renovation is a process that is carried out to improve the existing structure [19]. It assumes a new phase in the life cycle of existing buildings by using components and structures already built, with the addition of new materials, and thus offers a unique opportunity to reduce the impact of such an improvement by assessing its environmental performance. ...
A common occurrence in building renovation is the modification in the usage category that can lead to higher imposed loads, and consequently the need for structural improvements to the existing structure or to a structural element, such as timber floors. Strengthening practices oftentimes affect the originality of the building or a structural element under consideration. However, the preservation of the originality of timber floors having historical, architectural and cultural interest can be of high importance. This article provides insight into the field of timber floor strengthening techniques with regards to the requirements for conservation of the wooden built heritage. Moreover, a new strengthening technique using structural glass as a strengthening element for timber floors is presented, as reinforcing the bottom side of timber floors without compromising the appearance of the floor is an important objective of a successful intervention. In order to evaluate the performance of the newly proposed strengthening technique from a structural and environmental point of view, structural analysis and a life cycle assessment on a timber floor strengthened with cross-laminated timber panels and structural glass strips are performed. The structural analysis shows the possibility to use structural glass and still achieve a significant increase in the load-carrying capacity of the timber floor. Furthermore, the proposed strengthening technique has a lower global warming potential (GWP) and non-renewable cumulative energy demand compared to renovation and replacement with a cross-laminated timber panel, and a lower GWP compared to replacement with a reinforced concrete slab. This study not only represents the first holistic approach to evaluate the structural and environmental performance of the proposed strengthening technique, but it also addresses the aesthetically-aware design and technical limitations in the utilization of glass for the renovation of timber floors and thoroughly presents the possibilities to overcome these limitations.
... Structural repair and retrofitting is a predominantly cheaper solution to dealing with aging, damaged or failing structures compared to a complete replacement. Steel, concrete, fiber reinforced polymers and many other hosts of engineered materials have been used as wraps, jackets or casings to enhance the structural performance of distressed or damaged structural elements by inducing initial compressive stresses in them [1] [8]. A study conducted by Kankam [9] to assess the structural behaviour of concrete beams prestressed with ordinary mild steel bars that were post-tensioned by end bolting to induce compressive stresses in the concrete beams, reported significant improvement in the structural behaviour of the stressed beams compared with the unstressed beams. ...
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This present study assessed the structural potential of collapsed beams retrofitted by re-stressing with ordinary low strength steel bars that were end-threaded and tensioned against steel plates at the beam ends by means of tightening nuts. The applied prestress forces were estimated from the central upward deflection of the beams taking into account the downward deflection due selfweight and the short-term prestress losses. Eight stressed beams were subjected to monotonic loading and four to 20 cycles of loading. Four unstressed beams served as control. The ratio of the experimental failure load over the theoretical failure load averaged more than 570% and 380% before and after retrofit respectively. The ratio of the experimental failure load before retrofit, and after retrofit under monotonic loading averaged 70%. There was a 22% increase in the load carrying capacity of the retrofitted beams relative to the unstressed beams. For the stressed beams, the ratio of first crack load over theoretical cracking load averaged 260%. Cyclic loading for the retrofitted beams was characterized by crack closure on removal of the applied load and maximum crack widths were observed to range from 0.08 to 0.70mm while that for the control beams ranged from 2.00 to 4.00mm.
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