Retrofitting and strengthening of masonry structures with advanced composite fiber wrap system

M. Saroja Lolitha, D. Aditya Sairam

Abstract


A large number of masonry structures exist all over the world. These structures need strengthening due to many reasons such as lack of strength, stiffness, ductility and durability. Generally the old structures are not designed for earthquake loads, and hence many such important structures have suffered during the past earthquakes all over the world. Along with loss of human lives and socio-economic problems, damages and collapse of historically important structures take place due to earthquake. Apart from earthquake requirements, buildings need strengthening due to modifications done in existing structure or change in use of the building. Deterioration of material strength on aging is another significant reason for need of strengthening or retrofitting. There are various methods for strengthening of Masonry Structures among which the use of FRP has received increased attention due to the advantages of FRP, mainly lower specific weight, resistance to corrosion, ease of application and cost effectiveness. One of the important features of FRP that makes it suitable for Masonry is its adaptability to curved and rough surfaces. The use of FRP material for strengthening of reinforced concrete material is well established. As compared to concrete less work has been done on masonry. A large number of masonry structures including historic monuments are required to be strengthened or retrofitted in India and FRP can be a better option; however research work is required in this context. Effectiveness of FRP wrapping to masonry structural elements to enhance the performance, is required to be assessed experimentally. The present work focuses on the experimental investigations of FRP wrapped masonry load bearing members. The experimental program consists of testing on FRP strengthened masonry columns and FRP retrofitted masonry walls. The enhancement in load carrying capacity of masonry columns due to confinement by FRP strips has been found. An ‘Advanced Composite Fiber Wrap System’ with combination of vertical and horizontal FRP strips has been proposed. Behaviour of un-strengthened and FRP strengthened masonry columns subjected to uniaxial compression has been studied. The contribution of FRP anchors in enhancement of load carrying capacity has been quantified. In the next phase six masonry walls have been tested.

Finite element analysis for un-strengthened masonry elements and FRP retrofitted walls has been done using the ANSYS software. The experimental and analytical results are compared. CNR-DT-200 42 provides guidelines for the strengthening of masonry structures using FRP. As no Indian Standard code is available till now for the application of FRP on masonry structures, the applicability of CNR-DT-200, for the experimental work carried out in present study was checked by evaluating the results as per provisions of CNR-DT-200 and comparing with experimental results. A mathematical model has been proposed using the experimental results for predication of compressive strength of brick masonry column confined with FRP for Indian conditions. Further the estimation of load carrying capacity of FRP confined masonry columns with different strip widths has been done by using proposed mathematical model. The same model has been used to compare performance of ‘Advanced Composite Fiber Wrap System’ and ‘Continuous Wrapping System’. This study reflects, FRP wrapping is an effective strengthening and retrofitting technique for the load bearing members of brick masonry structures. ‘Advanced Composite Fiber Wrap System’ is found to be is more effective and economical as compared to Continuous wrapping system. Substantial increase in load carrying capacity of masonry columns was obtained by proposed discontinuous fiber wrap system. FRP anchors were effective in delaying the failure of specimens as well as enhanced the load carrying capacity of columns by 16-18% in case of both the composite materials; GFRP and CFRP. In case of masonry walls, different failure modes were observed for different FRP patterns. In case of Masonry Walls, lateral load carrying capacity was increased significantly due to discontinuous wrapping technique using composite materials. The results of Finite Element Analysis using ANSYS for masonry columns and masonry walls are in line with experimental results.  .


Keywords


Finite Element Analysis, Retrofitting, masonry structures, composite fiber wrap system, FRP.

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