Strengthening of steel structures

The use of fiber-reinforced polymer (FRP) composite materials in the reinforcement of concrete structures has shown important results. These interventions are based on the application of carbon fiber, glass, or aramid impregnated with thermosetting polymers. The effectiveness of these interventions is demonstrated both by extensive research in the laboratory and by applications to existing structures. 

Even metal structures may require an intervention of reinforcement due to changes in land uses, increases in loads, corrosion, or issues related to the phenomenon of fatigue. Currently, reinforcement methods used to restore the capacity of metal structures are based on the application of steel plates to the original structure. These types of interventions have negative aspects, such as new loads on the structures and oxidation phenomena. 

The use of welding is not recommended, considering the possible occurrence of the phenomenon of fatigue due to any welding defects. 

The problems related to the use of these traditional methods are outdated in the interventions that are characterized by the use of FRP composite materials. The fibers have superior mechanical and physical characteristics, and are distinguished by their considerable tensile strength. 

Reinforcement for steel structures with FRP can be realized using fabrics or pultruded laminates, and, usually, high-modulus carbon fiber is used because its value of the modulus of elasticity is close to that of steel. In this case, it is necessary, however, to intervene in the coupling between the two materials with an element 

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The aforementioned FRP products concern mainly reinforced concrete structures. Yet, carbon FRP plates (with or without prestress) and wraps have been widely used for the retrofit and strengthening of steel structures (increase of member and connection structural capacity. 

The second part of this book is devoted to current and potential applications of adhesive materials in construction. Chapter 6 deals with both the repair and the strengthening of concrete structures, covering applications ranging from non-structural patch repairs and resin overlays to externally bonded steel plate reinforcement. The theme of repair and strengthening is extended to applications involving steel, timber and masonry structures. A number of case histories are reviewed and discussed with reference to the successes and failures, and the results of allied research work are presented. In Chapter 7 a number of applications of adhesives in new construction are described, and specific examples are given. The final chapter. Chapter 8, examines the potential for future developments in adhesive usage. 

Fig. 1.8. Strengthening of bridge structure with externally bonded steel plate reinforcement.

Tavakkolizadeh, M. and Saadatmanesh, H. (2003), Strengthening of steel-concrete composite girders using carbon fibre reinforced polymer sheets , Journal of Structural Engineering, ASCE, Vol. 129, Issue 1, pp. 30-40. 

Retrofitting and Strengthening of Contemporary Structures Materials Used, Fig. 3 Typical stress-strain curves of steel reinforcements and cured FRP sheets... 

Retrofitting and Strengthening of Contemporary Structures Materials Used Steel Structures... 

Iron has been the dominant structural material of modem times, and despite the growth in importance of aluminum and plastics, iron still ranks first in total use. Worldwide production of steel (iron strengthened by additives) is on the order of 700 million tons per year. The most important iron ores are two oxides, hematite (Fc2 O3) and magnetite (Fc3 O4). The production of iron from its ores involves several chemical processes that take place in a blast furnace. As shown in Figure 20-22. this is an enormous chemical reactor where heating, reduction, and purification all occur together. 

To finalize this section, I would like to mention that some papers delve into the studies of radiation tolerance of laminated composites with the thickness of layers not increasing tens of nanometers. By varying the thickness of such materials, we can investigate the main mechanisms of influence produced by interphase boundaries on the behavior of radiation defects. The irradiation of multilayered structures with the ions of inert gases first of all with helium allows for the modeling of processes that may arise during the reactor-induced irradiation of oxide dispersion-strengthened steels and alloys. 

Monnet, L, Dubuisson, R, Serruis, Y. et al. 2004. Micro structural investigation of the stability under irradiation of oxide dispersion strengthened ferritic steels. J. Nucl. Mater. 335 311-321. 

Structural members made of concrete have to be strengthened with reinforcements, usually made of steel. To prevent the rebar from corrosion, concrete covers of more than 35 mm are required according to current design codes, e.g. CEB-FIB Model Code 1990 [1]. The use of corrosion-resistant technical textiles reduces concrete covers significantly, and thus allows for light-weight and slender concrete structures. 

Externally bonded FRP plates, sheets and wraps for the strengthening of reinforced concrete, steel, aluminium and timber structural members... 

Tests to measure the bond which can be obtained with the concrete of the structure to be strengthened are best carried out on the structure itself. A possibility is to utilise a pull-off test as developed for the non-destructive testing of concrete(21). A circular steel probe is bonded to the concrete surface and specially designed portable apparatus is then used to pull off the probe, along with a bonded mass of concrete, by applying a direct tensile force. Any defects in bond would be revealed by the occurrence of failures at the adhesive-concrete interface. 

The purpose of the above is to specify requirements for a cold-cure adhesive to permit either the repair or strengthening of existing concrete structures by bonding on additional external steel plate reinforcement, or the construction of steel/concrete composite units in which wet concrete is poured on to steel freshly coated with a layer of adhesive. In both cases the adhesive serves to resist the interfacial shear stresses necessary to ensure structural composite action between the steel and concrete. For these purposes a cold-cure adhesive is defined as one which is capable of curing to the required strength between the temperatures of 10 °C and 30 °C. 

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