Management and economic analysis of an experimental study for strengthening and rehabilitation of reinforced concrete frame with CFRP

The Bulgarian building heritage’s evaluation showed that large percent of the buildings needed to be rehabilitated. Thereby, the development of effective and affordable rehabilitation techniques is an urgent need. The Fiber Reinforced Polymer (FRP) composites can provide rehabilitation alternative for unreinforced masonry walls. In addition to their outstanding mechanical properties, the advantages of the FRP composites versus conventional materials for rehabilitation and strengthening of structural elements include: unchanged dynamic properties of the structures because little addition of weight and stiffness, lower installation cost, improved corrosion resistance, onsite flexibility of use, minimum changes in the member size after repair, minimized disturbance to the structures’ occupants, minimized loss of usable space during the rehabilitation. The main objectives of the presented and analyzed experimental study is to be develop an advanced method for strengthening and rehabilitation of reinforced concrete frame with CFRP Composites, standing new and pendant research topic and activities for Bulgaria. case, the reinforcing fiber provides FRP composite with strength and stiffness, while the matrix gives rigidity and environmental protection. In addition to their outstanding mechanical properties, the advantages of the FRP composites versus conventional materials for rehabilitation and strengthening of structural elements include: unchanged dynamic properties of the structures because little addition of weight and stiffness, lower installation cost, improved corrosion resistance, onsite flexibility of use, minimum changes in the member size after repair, minimized disturbance to the structures’ occupants, minimized loss of usable space during the rehabilitation. Different fibre types can be used, but most commonly carbon, glass or aramid are applied The corresponding composites are indicated as CFRP, GFRP or AFRP. The good mechanical properties of the FRP materials are only available in the fibre direction. Mainly, two types of FRP reinforcement are available on the market: hardened plates and flexible sheets (wet lay up). The end result, the fibres embedded in a resin matrix is often indicated by the term “laminate”. In the early stage, the hardened FRP plates were autoclaved, which limited the available length. Later on, FRP plates produced without autoclaving came on the market. These plates are available in different thicknesses, widths and stiffness and with nearly unlimited length. The application of these hardened FRP plates is analogous to the application of steel plates. Another type of FRP reinforcement is the UD-sheets, which are very flexible and can easily be cut by means of scissors, figure 1. At application, the flexible sheets are impregnated with the right ratio of epoxy resin components and the chemical reaction starts. When the first layer has hardened enough, the second layer can be applied in the same manner. The sheets are completely impregnated on the site. Both types of FRP, the sheets and the plates, are available on roll, which means that they are available in any length, whereas the steel plate length is limited in practice to 6 meters. The FRP materials consist of continuous fibres embedded within a thermosetting resin system. The resin is required to bond the fibres together and transmit loads between fibres. Some mechanical properties such as in-plane and interlaminar shear are highly resin dependent, whilst others such as longitudinal strength and stiffness are highly fibre dependent. The most common resins used in FRP are polyester based, which are economical and of low-moderate strength. Numerous grades of polyester resin are available, but the most common consist of either orthophthalic or isophthalic saturated acids. Orthophthalic resins are more economical but exhibit low mechanical properties and chemical resistance and are less likely to be suitable for the reinforcement of concrete structures, where good resistance to alkaline environments and low shrinkage may be required. Vinylester and epoxy based resins offer improved mechanical properties but with increased cost. However, if high performance fibres such as aramid or carbon are being used, the resin will only form a very small portion of the total cost. This is another reason why for structural purposes nearly always an epoxy resin will be used. Carbon fiber is higher-performance fiber available for civil engineering application. They are manufactured by controlled pyrolysis and crystallization of organic precursors at temperatures above 2000 oc. In this process, carbon crystallites are produced and orientated along the fiber length. There are three choices of precursor used in manufacturing process of carbon fibers-rayon precursors, polyacrylonitrile (PAN) precursors, and pitch precursor. PAN precursors are the major precursors for commercial carbon fibers. It yields about 50% of original fiber mass. Pitch precursors also have high carbon yield at lower cost. However, they have less uniformity of manufactured carbon fibers. Carbon fibers have high elastic modulus and fatigue strength than those of glass fibers. Considering service life, studies suggests that carbon fiber reinforced polymers have more potential than aramid and glass fibers. The main objectives of the presented and analyzed experimental study is to be develop an advanced method for strengthening and rehabilitation of reinforced concrete frame with CFRP Composites, standing new and pendant research topic and activities for Bulgaria. Regardless of the well known advantages of FRP one critical issue need to be justified. The important issue that must be determined is the competitiveness of FRP strengthening method on a cost basis in the future, compare to conventional methods such as strengthening with steel. Life Cycle Cost is probably the best process to answer that issue. Life Cycle Cost of FRP strengthening method includes the Initial Costs, Maintenance/Inspection/Repair Costs, and Disposal Costs. The use of FRP composites as a strengthening solution for reinforced concrete frame is expected to increase service life and lower maintenance costs. The main problem encountered is the initial costs of FRP strengthening method are significantly higher than those from steel. Hence, the initial costs of FRP strengthening must be reduced to be cost competitive with the steel on a life cycle cost basis. The initial future costs can be estimated by utilizing improvement (learning) curve theory and various improvement models to predict future costs are under development. The various models apply the improvement theory with different bases and the results obtained are varied. The preliminary results indicate that CFRP strengthening method become economically feasible. 2 EXPERIMENTAL SET UP For the goals of the experiment there were prepared two reinforced concrete beams, particularly connected with two columns (frames). The beams is reinforced with 2N10 bottom reinforcement and 2N10 top reinforcement, and stirrups O6,5 by 20 cm. The columns are reinforced with 4N14 and stirrups O6,5 by 20 cm. Between the columns and beams are implemented a masonry for realization of the real task of the experimental study. The shoulder with columns and beam masonry is loaded with horizontal and vertical force. After frames’ collapse they were strengthened: one of them with CFRP system, and one with shaped steel and steel plates and tires: Figure 1. Reinforced Concrete Frame strengthened with CFRP