Strengthening And Repair Of Concrete Column Using CFRP

Uses of CFRP in Civil Engineering

Question:

Discuss about the Collapse Vulnerability and Fragility Analysis.

This project proposal is mainly based on strengthening and repair of concrete column using CFRP (Carbon Fiber Reinforced Polymer). CFRP generally includes different variations of carbon polymer made of different proportions of other strengthening materials to develop fiber-reinforced plastic. This type of material provides high strength-to-weight ratio and hence, they can be used to build materials that should be light in weight but rigid and strong (e.g. tail of radio controlled helicopter) (Jain, Chellapandian and Prakash 2017). The CFRP material is becoming more and more popular as it is also environment friendly and relatively cheaper than other alternative materials. CFRP finds uses in various fields that include aeronautical engineering, automotive engineering, civil engineering, sports goods and others. However, the focus of this paper is entirely on civil engineering and hence, an application of CFRP will be discussed within the field of civil engineering.

CFRP is generally used as one of the most important components for repair and strengthening of concrete columns in civil engineering. The main advantage is that due to the use of CFRP, the concrete column has lesser weight than normal columns without CFRP but the strength and rigidity increases considerably. This paper is based on the analysis of CFRP in the strengthening concrete column as well as a proposal for experimental analysis of the same.

The most recent report by Joint ACI-ASCE Committee 352 (ACI 352R-02) states that joints in structures worked in front of the improvement of current design rules must be learned to find and analyze the characteristics and uses of the FRP materials in repair and strengthening of concrete structures. As indicated by Fakharifar et al. (2015), preceding the development of new strengthening plans, it is critical that the other strategies for repair and strengthening of concrete structures should be known. Every strategy for repair or strengthening is analyzed on its application points of interest, required work, cluster of relevance, and execution. Relative advantages and disadvantages of each method should be analyzed in order to choose the best technique or method. These techniques analyzed are as follows: 1) epoxy repair; 2) expulsion and substitution; 3) concrete jacketing; 4) concrete stone work unit jacketing; 5) steel jacketing and expansion of outer steel components; and 6) strengthening with fiber-reinforced polymeric (FRP) composite applications.

Parvin and Brighton (2014) said that usage of fiber reinforced plastic (FRP) composite materials for strengthening and repair of basic individuals is turning into an inexorably well known range of research and application inside the most recent decade. Be that as it may, the technique is yet to wind up standard application due to number of efficient and design related issues. From a basic mechanics point of view, a fundamental concern concerning the adequacy and safety of this strategy might be the capability of fragile debonding failures. Such failures, unless sufficiently considered in the design procedure, may altogether diminish the power of the strengthening or repair application. As of late, there is a centralization of research endeavors on portrayal and displaying of debonding failures. FRP composite materials have seen a consistent increment of utilized as a part of auxiliary strengthening and repair applications around the world inside the most recent decade (Singh et al. 2014). High firmness to-weight and quality to-weight proportions of those materials consolidated utilizing their predominant natural durability have made them a contending other option to the regular strengthening and repair materials. Nearby and government offices stood up to with the undertaking of monetarily updating the regularly expanding number of maturing and substandard structures have put resources into this district prompting various research studies and applications.

Comparison of CFRP with other alternatives

It has been appeared through trial and hypothetical examinations that remotely reinforced FRP composites might be utilized to support the coveted execution of an auxiliary part such as its load conveying limit and solidness, malleability, execution under cyclic and fatigue loading and ecological durability (Yang et al. 2015). However, the methodology is yet to end up standard application as a result of number of sparing and design related issues. Paultre et al. (2015) said that as of the last few years, outside FRP frameworks are getting popular in construction industry in spite of just restricted exploratory research information on the seismic reaction of FRP-wrapped examples. The objective of the current research is to learn the power of CFRP and GFRP to fortify reinforced concrete columns, put through virtually recreated seismic tremor loading, utilizing both redesign and repair procedures. This research is a component of a broad examination to identify and analyze the aftereffects of imprisonment support on the seismic conduct of roundabout and square concrete columns. Correlations may likewise be made between the strength of CFRP and of transverse steel to supply seismic protection.

This research study is mainly based on the analysis of the properties of CFRP and its applicability in strengthening and repairing of concrete column. Hence, the research questions for the proposal can be defined as follows.

• How can CFRP be used for strengthening of concrete pillars?
• What are the properties and characteristics of CFRP?
• What are the advantages of CFRP over other strengthening materials?

In order to conduct this research, it is extremely important to determine the characteristics, composition and properties of CFRP. Moreover, it is important to determine the properties of CFRP in order to compare it with other similar alternative materials. This comparison will help to determine its advantages over others. Hence, the above research questions must be addressed accordingly.

In this proposed research project, concrete structures have been repaired using weight implantation of epoxy; another strategy for epoxy repair is vacuum impregnation. For vacuum impregnation, epoxy narrows ports were arranged in the base of each beam and at the base of the column repair range. Researchers consider the quality of both epoxy techniques to repair two one-route inside joints that were respectably hurt due to insufficient breakwater of tireless beam bars. The vacuum was associated through three hoses joined at the most astounding purpose of the repair range in the column. Extraordinary physical bond breaking down in the repaired joints occurred just a single half-cycle sooner than expected. Both repair techniques were successful in restoring over 85% of the strength, quality, and imperativeness scattering properties of the fundamental cases. The standard conclusion was that vacuum impregnation shows a compelling technique for repairing significant parts of damage instantly and that it could be balanced for joints with less open sides.

Literature Review

This research is mainly based on literature review and experimental analysis. In the literature review, sufficient data has been collected regarding the use of CFRP for strengthening and repair of concrete columns. This data has been used to prepare the theoretical basis and research hypothesis that will be further applied in the experimental analysis of the topic. The sources of the literature review include literary works and research papers of reputed researchers as well as some data from organizations that have successfully implemented the use of CFRP in concrete columns for strengthening purposes.

The execution of beam-column joints has for a very long time been perceived as a noteworthy factor that influences the whole process of reinforced concrete (RC) confined structures subjected to extensive parallel burdens. Buildings developed before 1976 may have critical lacks in the joint areas. The principal design rules for strengthened concrete beam-column joints were distributed in 1976 in the U.S. (ACI 352R-761) and in 1982 in New Zealand (NZS 3101:19822) (Triantafillou et al. 2016). Particularly considering that the Mexico earthquake of 1985, a lot of research has been committed in order to identify the basic subtle elements of non-seismically designed buildings and also to creating sorts of strengthening. The vast majority of the repair and strengthening plans proposed to date, in any case, utilize a constrained cluster of materialness either because of insufficient thought of floor individuals or to building limitations (Kaya, Dawood and Gencturk 2015). Through their audits of specifying manuals and design codes from yesteryear five decades and their counsel with rehearsing engineers, scientists distinguished seven points of interest as regular and conceivably basic to the safety of gravity stack designed (GLD) structures in a major seismic activity.

In this experiment, a total of 12 specimens are going to be tested. Every specimen will join a 356 mm measurement and 1.47 m long column cast necessarily by utilizing a 510 x 760 x 810 mm stub. The stub will represent a broken point or discontinuity, e.g. a beam column joint or maybe a footing balance. Each one of the columns will contain six 25M (500 mm2) longitudinal steel bars, and furthermore the spirals will be produced using U.S. No. 3 (71 mm2) bars. In each specimen, precisely the center zone measured to the centerline of winding to the gross division of the column area will be set consistent at 74%.

The design of the specimens will be focused at compelling the failure in the potential plastic pivot locale of the column, that might be, within a period 800 mm from the facial skin of the stub. The span of 800 mm will be picked in light of past tests where it has been watched that the whole most harmed area of the column was roughly equivalent to the segment profundity and found around 100 to 200 mm outside the stub. Far from the test locale, the dispersing of winding support will seem diminished to around 2/3 of the predefined separating in the examination zone.

Experimental Analysis

All columns will be tested during the experiment process under parallel cyclic stacking while at the same time being distressed by consistent pivotal load in the test. The support for the stub will consolidate 10M (100 mm2) vertical and even stirrups at 64 mm dispersing. Moreover, 10M bars with 135 degree snares will be put at the best and base of the stub at definitely a similar dividing. The column will represent a bridge column or a building column between the segment of most extreme minute and the point of contraflexure. The longitudinal bars in the columns will be totally reached out on the stub, though the winding support will be stretched out on the stub for 100 mm. In this experiment, all specimens are going to be cast together in vertical positions.

The data has been evaluated using experimental analysis following the literature review process. The impact of strengthening insufficiently constructed square columns with CFRP is assessed utilizing examinations of comparative examples tried under indistinguishable loading conditions while specimen AS-1NS served in light of the fact that the control column, examples ASC-2NS and ASC-6NS were retrofitted with one and also 2 CFRP layers, separately. Strengthened concrete columns worked before 1971 are known to have insufficient transverse fortification and might fail without adequate cautioning during any high scale seismic activity (Yan 2016).

Examples AS-1NS, ASC-2NS, and ASC-6NS contained comparable inadequate amounts of seismic transverse steel weighed against code necessities (ACI 318-027). Every column was put through a pivotal load that was 33% of the ostensible column limit Po. This load level spoke to a power somewhat more than the adjusted load for each situation. The entire arrangement of columns considered in these investigations is 305 mm². Among the open retrofit techniques, CFRP jacketing is picking up prevalence with which has no trouble capacity of establishment (He, Sneed and Belarbi 2014). The reported research was directed to inspect the execution of lacking and harmed columns retrofitted with CFRP under tremor loading conditions. It is foreseen that the real result acquired should be relevant to columns with various area sizes accepting that parameters for example volumetric proportion of parallel steel, locale of FRP keeping support, and the subsequent hub load are fittingly scaled.

Performance highlights and forward projections of outcomes of the CFRP repair scheme are identified through the comparison of Specimen ASC-2NS with Specimen ASCR-7NS. Both had 42% of the lateral steel content mandated in ACI seismic provisions and each carried an identical axial load of 0.33P_o. The parameters recorded indicate Specimen ASCR-7NS displayed ductility which had been comparable with Specimen ASC-2NS up a great approximately 20% drop in capacity beyond the peak (Frascadore et al. 2015). The whole ductility parameters, however, were significantly lower for Specimen ASCR-7NS. Specimen ASC-2NS was tested with one CFRP layer added while Specimen ASCR-7NS was initially lightly damaged for unretrofitted column (AS-7NS) before being retrofitted with one CFRP layer and retested to failure. Hysteresis loops presented confirm the behavior of the repaired column was subordinate to, yet closely resembled, that of the undamaged wrapped specimen both in availablility of excursions and ultimate strength quantities (Rousakis, Kouravelou and Karachalios 2014). Nevertheless, the CFRP repair restored much of the inherent seismic capabilities of Specimen ASCR-7NS and vastly improved its performance weighed against its unretrofitted control column AS-1NS. The substantial difference while in the total ductility parameters reflects previous damage sustained during cycling of Specimen AS-7NS before retrofit.

Research Questions

Usage of carbon and GFRP resulted in significant upgrade inside execution of columns, creating expansive increments in malleability, vitality scattering limit, and quality. In steel strengthened columns, area and part pliability diminished fundamentally with a lifted winding pitch and negligible measure of winding fortification. Dissimilar to the inner winding fortification that lone limits the center concrete, the FRP wraps successfully restrict the whole column area. For a column subjected with a hub stack equivalent to 0.27P_o, which is roughly equivalent to some adjusted load, one layer of carbon or GFRP expanded the vitality dissemination limit by a part of more than 100. The adverse results of an insignificant measure of winding support and bigger separating are frequently made up for by the imprisonment made accessible from FRP. The characteristic nature of FRP retrofitted columns under recreated tremor loads coordinated or surpassed the execution of slab fortified columns designed great seismic arrangements with the ACI Code.

Conclusion

From the entire analysis, it can be concluded that CFRP is the best reinforcing material that can be suitably used for strengthening concrete columns. It is better, stronger, more rigid as well as cheaper than all other similar alternatives. As a result, it is now widely used in construction industry for building large structures like multistoried buildings, bridges and others. However, there are some issues with it as well due to which, it is still not used by many contractors. The performance of beam-column joints has been recognized as a significant factor that affects the entire behavior of reinforced concrete framed structures subjected to large lateral loads. In recent years, external FRP systems are becoming widespread in construction industry despite only limited experimental research data on the seismic response of FRP-wrapped specimens. Hence, it can finally be concluded that with the ongoing research activities and experimental analyses, CFRP materials will become the mostly used strengthening material for concrete structures in the near future.

References

Al-Saidy, A.H., Saadatmanesh, H., El-Gamal, S., Al-Jabri, K.S. and Waris, B.M., 2016. Structural behavior of corroded RC beams with/without stirrups repaired with CFRP sheets. Materials and Structures, 49(9), pp.3733-3747.

Fakharifar, M., Chen, G., Dalvand, A. and Shamsabadi, A., 2015. Collapse vulnerability and fragility analysis of substandard RC bridges rehabilitated with different repair jackets under post-mainshock cascading events. International Journal of Concrete Structures and Materials, 9(3), pp.345-367.

Frascadore, R., Di Ludovico, M., Prota, A., Verderame, G.M., Manfredi, G., Dolce, M. and Cosenza, E., 2015. Local strengthening of reinforced concrete structures as a strategy for seismic risk mitigation at regional scale. Earthquake Spectra, 31(2), pp.1083-1102.

Conclusion

Hadi, M.N. and Tran, T.M., 2014. Retrofitting nonseismically detailed exterior beam–column joints using concrete covers together with CFRP jacket. Construction and Building Materials, 63, pp.161-173.

He, R., Sneed, L.H. and Belarbi, A., 2014. Torsional repair of severely damaged column using carbon fiber-reinforced polymer. ACI Structural Journal, 111(3), p.705.

Jain, S., Chellapandian, M. and Prakash, S.S., 2017. Emergency repair of severely damaged reinforced concrete column elements under axial compression: An experimental study. Construction and Building Materials, 155, pp.751-761.

Jiang, S.F., Zeng, X., Shen, S. and Xu, X., 2016. Experimental studies on the seismic behavior of earthquake-damaged circular bridge columns repaired by using combination of near-surface-mounted BFRP bars with external BFRP sheets jacketing. Engineering Structures, 106, pp.317-331.

Kaya, A., Dawood, M. and Gencturk, B., 2015. Repair of corroded and buckled short steel columns using concrete-filled GFRP jackets. Construction and Building Materials, 94, pp.20-27.

Li, Y., Liu, X., Wu, M. and Bai, W., 2017. Research of electrochemical chloride extraction and reinforcement of concrete column using MPC-bonded carbon fiber reinforced plastic sheet & mesh. Construction and Building Materials, 153, pp.436-444.

Parvin, A. and Brighton, D., 2014. FRP composites strengthening of concrete columns under various loading conditions. Polymers, 6(4), pp.1040-1056.

Paultre, P., Boucher-Trudeau, M., Eid, R. and Roy, N., 2015. Behavior of Circular Reinforced-Concrete Columns Confined with Carbon Fiber–Reinforced Polymers under Cyclic Flexure and Constant Axial Load. Journal of Composites for Construction, 20(3), p.04015065.

Rousakis, T.C., Kouravelou, K.B. and Karachalios, T.K., 2014. Effects of carbon nanotube enrichment of epoxy resins on hybrid FRP–FR confinement of concrete. Composites Part B: Engineering, 57, pp.210-218.

Singh, V., Bansal, P.P., Kumar, M. and Kaushik, S.K., 2014. Experimental studies on strength and ductility of CFRP jacketed reinforced concrete beam-column joints. Construction and Building Materials, 55, pp.194-201.

Triantafillou, T.C., Choutopoulou, E., Fotaki, E., Skorda, M., Stathopoulou, M. and Karlos, K., 2016. FRP confinement of wall-like reinforced concrete columns. Materials and Structures, 49(1-2), pp.651-664.

Vijay, P.V., Soti, P.R., GangaRao, H.V., Lampo, R.G. and Clarkson, J.D., 2016. Repair and Strengthening of Submerged Steel Piles Using GFRP Composites. Journal of Bridge Engineering, 21(7), p.04016038.

Wu, Z., Wang, X., Zhao, X. and Noori, M., 2014. State-of-the-art review of FRP composites for major construction with high performance and longevity. International Journal of Sustainable Materials and Structural Systems, 1(3), pp.201-231.

Yan, L., 2016. Plain concrete cylinders and beams externally strengthened with natural flax fabric reinforced epoxy composites. Materials and Structures, 49(6), pp.2083-2095.

Yang, Y., Sneed, L., Saiidi, M.S., Belarbi, A., Ehsani, M. and He, R., 2015. Emergency repair of an RC bridge column with fractured bars using externally bonded prefabricated thin CFRP laminates and CFRP strips. Composite Structures, 133, pp.727-738.