PSI - Issue 18

Muhammad Fawad et al. / Procedia Structural Integrity 18 (2019) 189–197 M. Fawad/ Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The number of the existing bridges in many of the European countries exhibit insufficient performance over a period of time, both in terms of the functionality and safety of structure [1]. Suitable and cost affective retrofitting techniques are needed for the assessment of structures and design phases to specify some specific types of vulnerabilities of each bridge class besides this seismic retrofit is also very important for structural monitoring, especially in areas of high seismic activities [2, 3]. The ultimate purpose is to cut down the construction interventions to a lower minimum level, which is a goal that is clearly in accordance to the principles of a sustainable development [3]. In case of the Bridge Management System, the definition of the bridge inventory shows the starting point of the system, concerns the basic identification of the bridge including its geographical position, road, etc., the description of the technical data like material, geometry, structural system, etc.), and of the maintenance data like condition, inspections, evaluation monitoring, etc. A preliminary condition rating of RC, steel and masonry bridges is generally done at network level by means of simple visual inspection [4]. Based on the preliminary information, the managing authorities of the network can define a priority plan and available resources for the detailed assessment, evaluation, verification and intervention on structures in the worst state of condition along with its monitoring [4]. In this regard, it is of great importance to define some methodological approaches for the detailed assessment, structural rehabilitation and upgradation of the current functional standards of common bridge typologies, also accounting for their seismic vulnerability [5]. There are several procedures for the static strengthening of bridge structural RC members, all are generally aiming to increase the live-load capacity [7]. It is fundamental to consider the physical and chemical compatibility between the new material and the existing ones to develop a proper bond between them, and those material are chosen, which ensure the best performance in terms of durability over time, depending on the environmental conditions in which they operate e.g stainless , composite material (FRP) for flexural and shear strengthening of RC members, lightweight concrete for substitutive or additional RC deck slabs, thixotropic shrinkage-compensated mortar for the renewal of concrete cover [8]. Retrofitting of structures can be done by using the Post-Tensioning technique which is not only used for the construction of new buildings and bridges, but also for the strengthening of damaged structures or structures with inadequate load carrying capacity.This is usually applied to eliminate excessive cracks like bending cracks, shear cracks and cracks due to local force transfer like support region of beams, anchorage zone of pre-stressing tendons, etc and deformations along with the removal of certain defects [9]. Strengthening By Steel Plates is also an important retrofitting technique in which external steel strips or plates that are fixed with steel anchor bolts can strengthen reinforced concrete structures subjected to bending (e.g. beams, slabs)[10]. In this case, external steel plate is cooperating with the internal steel bars to take the tensile forces due to bending. The steel strip or plate can be fixed to the concrete surface by special steel anchors [11]. For the purposes of structural strengthening, post-installed fasteners are used, where the force between the concrete and the fastener is transferred by friction (expansion anchors), mechanical interlock (undercut anchors) or bond (bonded anchor) [12].Externally bonded steel plates can also increase the load carrying capacity of reinforced concrete structures subjected to bending (beams, slabs and columns) [13]. In this case, an adhesive agent continuously bonds the steel plates to the original structure. The bonded steel plate strengthening can be applied with or without anchorage at the plate end. To avoid the delamination of the steel plate, it’s end section can be anchored by steel anchors or bonded steel sections [12]. Retrofitting using the FRP Strips or Sheets is also an important strengthening technique which uses the fiber Reinforced Plastic (FRP) Material. It is a composite material that consists of two constituents: a series of carbon fibers surrounded by a solid matrix. A layer of composite material is defined as a lamina and stacking laminas forms an FRP laminate. The fibers inside the composite carry the loads while the matrix keeps the fibers together and protects them against environmental and mechanical damages [14]. Typical fibers used in composite material are Carbon (or graphite) fibers, Glass fibers, Aramid fibers (Kevlar) and Metal fibers. Post-tensioning of existing structures can also be performed using CFRP bars [15]. Strengthening using the Sprayed Concrete technology is also an important retrofitting technique in which concrete is not a special concrete material but it is rather a special concrete casting procedure, where the mixture is transported to the construction area in pipes under pressure (~6 atm) and it is sprayed to the application surface with high speed (~100 m/s) [16]. Older structures especially the very old bridges constructed over the waterbeds always have major problems of the scour due to excessive contact with moist environment over a long life span. The most problematic aspects of real structures are that they are always prone to damages, disfunctioning and the most unwanted structural health scenarios. As a result, several measures of inspection, monitoring and maintenance, needed to be taken for this kind of structure