Application of polymer based retrofitting methods for the unreinforced masonry ( URM ) edifices to prolong temblors has late gained attending due of their advantages such as low cost, good sustainability, environmental friendly, easiness in application and efficient public presentation. However, the loss of shear strength and stiffness of polymer support due to non-equally distributed emphasiss still needs to be addressed and resolved. In this paper, the application of shear-thickening fluid ( STF ) is proposed for polymer based seismal retrofitting of the URM edifices. The chief aim of the research discussed in this proposal is to extinguish high stressed countries in the polymer support by heightening its strength, stiffness and energy absorption/dissipation belongingss. The shear emphasiss created by the seismal burden will be transferred from the URM edifices to the complex and so to STF taking to the addition in viscousness of STF.
Finally, the dissipation of energy in the complex will be compensated by the addition in elastic modulus of STF. Two methods are chosen to fix polymer-STF complex: ( 1 ) STF impregnated microporous geotextile being sandwiched between two geomenbranes, and ( 2 ) STF coated or filled fibres to be incorporated into the polymer matrix. Rheologic belongingss, surface morphology, scattering, thermic stableness, lastingness, and mechanical belongingss of STFs and complexs will be characterized utilizing rheometer, SEM, TEM, TGA, accelerated weathering trials and DMA severally. Shear wall testing will be used to prove the concluding polymer-STF complex in order to measure up for retrofitting of the URM edifices.
Unreinforced masonry ( URM ) edifices
Non-engineered and unreinforced masonry edifices are prevailing in developing states due to low building and stuff costs.
In fact, 40 % to 50 % of the universe ‘s population lives in these types of edifices. URM edifices by and large experience a sudden prostration during temblors ensuing in big population and economic losses1. The major cause for this sudden prostration was the usage of stiff and brickle building stuffs. Common failure manners of these edifices include shear walls clefts, out-of-plane failure, diagonal clefts, separation of roofing from walls, and separation of wall corners. These failures occur chiefly because of higher magnitudes of sidelong seismal forces over the ultimate tensile strength of the howitzer joints2.The past two decennaries have seen rapid development in building stuffs with accent on retrofitting methods. Some of the retrofitting methods include grout-epoxy injections, shotcrete sheathing coatings, natural fibre support, steel mesh coop, post-tensioning, and polymer based retrofitting. All these retrofitting methods have shown important betterment in sidelong opposition and ductileness of the URM structures3.
Among these methods, polymer based retrofitting methods that include polymer support either externally or internally have many advantages over other methods in footings of public presentation, sustainability, economic feasibleness and pertinence. Additionally, these methods have shown to supply better shear opposition to the structural elements compared to non-polymer based methods. The most normally used polymer based retrofitting methods are fiber strengthened polymers ( FRP ) , polypropylene strip and polymer mesh4-7.
Polymer based retrofitting methods have restrictions on their ability to defy the non-uniform distribution of emphasiss generated by the seismal loadings3, 5. This non-uniform emphasis distribution creates extremely concentrated emphasiss in both the construction and polymer stuff, which leads to a shear failure. The common shear failures for polymer based retrofitting are diagonal tensile rupture ( Figure 1a ) and peeling-off or debonding ( Figure 1b ) 8, 9.Figure 1.
( a ) Shear failure due to tensile rupture, ( B ) shear failure to debonding8, 9The shear failure of polymer support due to non-equally distributed emphasiss is related to the shear strength of polymer support. The entire shear strength of strengthened construction ( Vt ) can be expressed in footings of single shear strengths of unreinforced construction ( Vm ) and polymer support ( Vp ) 10.Vt = Vm + VpIn general, truss theoretical account is widely used to depict the shear behaviour of assorted constructions. Harmonizing to this theoretical account, Vp is defined asVp = ? ?cr Ep T R omega ( Cos?/Sin? )Where ? represents the non-uniform distribution of stains/stresses, ?cr represents maximal allowable strain, Ep represents elastic modulus of support, t represents thickness of support and R represents agreement, omega represents the tallness of structural component to be reinforced. And ? and ? are the disposition of cleft and the angle between the strain and support agreement respectively10.This theoretical account describes polymer support as linearly rubber band, which indicates that different strains cause different emphasiss. When emphasiss localize and redistribution of the tonss through the polymer support does non happen, the localized stress/strain will transcend the critical strain or maximal allowable strain ( ?cr ) in the support taking to a sudden shear failure that is similar to brittle failure.
Since this toffee and shear failure mechanism arises due to preponderantly additive elastic nature of polymer support, the energy dissipation belongings that usually occurs from non-linear scope is minimized in the polymer reinforcement10, 11.
Shear Thickening Fluid ( STF )
Shear-thickening behaviour is found in certain fluids which undergo passage from fluid to solid when stressed. The viscousness addition in these fluids due to shear-thickening behaviour could be sometimes tremendous. STFs including colloid scatterings possess alone belongingss such as increased energy dissipation and enhanced elastic modulus that make them one of the of import stuffs for muffling and shock-absorption applications12. Recently, these belongingss have been explored for assorted shock-absorbing applications such as featuring equipment, automotive and organic structure armour where these stuffs cut down the quivers and dazes without losing their strength and stiffness 13-15. As of today, the application of STFs in temblor immune edifice stuffs has non been tested or implemented.As shown in Figure 2 ( a ) , the hysteresis cringle of force versus supplanting for different frequences in a STF filled damper can be used to gauge the energy dissipation matching to the country for each rhythm.
The behaviour of effectual stiffness and muffling changeless with regard to lading frequence of the STF damper is shown in Figure 2 ( B ) . The muffling changeless attacks maximal value during the passage province and beads to comparatively lower value in shear-thickened state16. At this province, the effectual stiffness reaches the maximal value. It can be inferred that the betterment in the stiffness and energy dissipation belongingss can be achieved with shear inspissating consequence in the system.Figure 2. ( a ) Damping force versus supplanting at assorted frequences, ( B ) the tantamount stiffness and muffling coefficient versus frequency16.
Shear thickener in colloidal scatterings depends on assorted factors such as atom size, volume fraction, surface chemical science, interparticle and hydrodynamic forces, polydispersity, and the belongingss of suspending medium17. Several research workers have studied the shear inspissating behaviour in colloidal scatterings under steady and dynamic shear18-20. As shear inspissating passage occurs at critical shear rate under steady shear and at critical frequence under dynamic shear severally, it is imperative to command these parametric quantities to accomplish the needed belongingss.
The proposed technique will present polymer-STF complex as a fresh retrofitting stuff in polymer support of the URM edifices. The incorporation of STF into polymer matrix is proposed to heighten the strength, stiffness and energy dissipation belongingss of the support during high shear emphasiss or distortions. When shear emphasiss addition during seismal burden, the addition in viscousness of STF will assist the composite support to redistribute the tonss and minimise the localisation of emphasiss.
In response to the land gesture during temblors, it is expected that the viscoelastic behaviour of STF in the complex would alter consequently to accomplish the shear thickener province depending on the nature of shear rate and thereby dissipate the energy being created by the shear emphasiss.When strengthened structural elements see the distortions due to sidelong seismal forces, the emphasiss that are developed inside the walls will be transferred to the composite as a consequence of the bond between them. At higher emphasis degrees, these emphasiss will be relocated to the STF at the interface between matrix and STF doing STF ‘s viscousness addition. Hence, an advent grade of non-linear muffling consequence in the complex will take to energy dissipation before the happening of shear failure in the polymer support.
The polymer-STF complex can be used in the signifier of a sheet, a mesh or sets. Examples of its possible application are shown in Figure 3, where the structural elements of the URM edifices such as walls, columns, roof borders and corners can be either externally or internally reinforced utilizing the composite associated with STF.Figure 3. Masonry walls and wall corners reinforced with the polymer-STF complex
Aims and Hypothesiss
The end of this research is to develop a polymer-STF complex as a fresh retrofitting stuff that will assist a construction to defy seismal forces and prevent from sudden shear failures.
The major aims of this research proposal are:To synthesise a polymer-STF complex.To qualify the synthesized complex for assorted belongingss including ( I ) rheological belongingss of STF such as viscousness, stress-strain relationship, critical shear rate and critical frequence under steady and dynamic shear ( two ) mechanical belongingss such as dynamic moduli, force-displacement curves for energy dissipation, shear strength and tensile strength ( three ) morphological belongingss such as surface texture of composite, scattering of atoms in STF, and fibres in the polymer matrix, ( four ) shear wall testing of the concluding complex.To look into public presentation of this engineering in two different methods of polymer support: ( I ) without fibre for comparatively low cost applications, ( two ) with fibre engineering for cost-efficient applications.The major hypotheses of this proposal are:Use of STFs in the polymer support can bring forth better public presentation when STF shows shear inspissating behaviour in the frequence scope of seismal shear rates.Higher shear and tensile strengths are obtained with the combination of polymer matrix and STF when STF reaches its maximal stiffness.Shear failure such as tensile rupture and debonding clefts will be minimized in the polymer support with the consequence of increased energy dissipation via shear inspissating behaviour in STF.
Synthesis of STF polymer support
This subdivision describes the choice of stuffs for the synthesis of assorted STFs, synthesis of polymer-STF complex without fibre, and synthesis of polymer-STF composite with STF coated and filled fibres.
Choice of stuffs
Materials pick will depend upon assorted factors such as cost, toxicity, compatibility, physical, rheological and chemical belongingss.
As seen in the old literature studies for energy dissipation applications, either silicon oxide or titanium dioxide scatterings have been normally used. Furthermore, scatterings of silicon oxide and titanium dioxide have been investigated for assorted other applications in great item. It is because the assortment of their readying strategies utilizing sol-gel processing is tremendous. They can be obtained comparatively for lower costs ( $ 0.105/1gm ) . Though the present undertaking will get down with the usage of silicon oxide and titanium dioxide atoms for the readying of STFs, several other types of atoms such as aluminum oxide, zirconium oxide, and oxides of Sn and Zn may besides be considered for farther research. Assorted sizes of the atoms and different classs will be used to obtain a scope of informations for concluding rheological belongingss.Rheology of scatterings of hydrophilic silicon oxide in different polar organic media has been investigated by S.
R.Raghavan21. It was found that the colloids behaved as colloidal suspensions when there were strong H adhering interactions between hydroxyl groups on silica atom surface and the suspending medium. The viscousness of colloids at 25 & A ; deg ; C was found to increase with the addition in the molecular weight of polythene ethanediol ( PEG ) and polypropylene ethanediol ( PPG ) . In our survey, assorted molecular weights of PEG ( 250 and 500g/mol ) and PPG ( 400-3000g/mol ) will be investigated.
Figure 5: Conventional representation of procedures used to fix complexs with STFsAfter the readying of STF, the synthesis of polymer-STF complexs can be performed in two ways as shown in Figure 5: ( 1 ) without fibres: STF impregnated geotextile sandwiched between two geomembranes, and ( 2 ) with fibres: STF coated or filled fibres incorporated into a polymer matrix.When taking stuffs for the readying of polymer-STF complex without fibre, it is extremely indispensable to see factors such as compatibility of geotextile with STF, cost and lastingness. STF being polar liquid should hold good adhesion with the walls of microporous geotextile. Therefore, polyester, polyurethane and polymeric amide can be considered as geotextiles for impregnation with STF. As geomembranes are used to forestall escape of STF from geotextile, polythene and polypropene will be used to encapsulate the geotextile.
For fibre reinforced polymer composite, short discontinuous fibres can be classified harmonizing to four features: ( 1 ) fiber material such as natural and semisynthetic, ( 2 ) physical/chemical belongingss such as denseness, surface raggedness, non-reactivity and chemical stableness, ( 3 ) mechanical belongingss such as tensile strength, elastic modulus, stiffness and surface adhesion belongingss, and ( 4 ) geometric belongingss such as length, diameter, and cross-sectional form. Therefore even with a individual fibre stuff such as glass, there can be many possible combinations to orient the concluding belongingss of composite. In order to do this fibre engineering cost-efficient, it is likely that the material pick can be really tricky22.
The readying of STFs utilizing assorted stuffs and their word picture utilizing assorted techniques will be discussed in the undermentioned subdivisions.
Synthesis of polymer-STF complex without fibre
In the sonochemical procedure, different weight per centums of silicon oxide ( 40 % and 50 % ) and polyethylene ethanediol ( PEG ) ( 60 % and 50 % ) will be assorted with ethyl intoxicant and sonicated under ultrahigh sonication with Misonix sonicator for 5h at 10 & A ; deg ; C. The attendant mixture will be used as the STF to infuse the cloth. 300mm Ten 300mm beds of Kevlar and Nylon cloths will be used for impregnation with STF. Each sheet will be soaked in STF solution for 1min and so squeezed with a rod to take extra sum of STF.
The complex will be hanged and dried at room temperature for 48h as shown in Figure 6.Figure 6. Procedure for doing composite holding colloidal scatterings as STF23Experimental Design for STF of colloidal scatterings is shown in Table 1. After preliminary trials, different classs and atom sizes of SiO2 and TiO2 will be used. If required, surface alteration of atoms will besides be tried. Different polymers such as PEG and PPG with assorted molecular weights will be used as suspending media for scatterings.
Table 1: Experimental Design for STF of colloidal scatterings
Atom Volume Fraction
Colloidal scatteringsSiO2,TiO2 ( Anatase and Rutile )Polyethylene ethanediol ( PEG ) ,Polypropylene ethanediol ( PPG )20-100nm15 % to 60 %The complex of STF without fiber will be prepared by infusing the porous geotextile such as polyester with above synthesized STF. In the work by Deshmukh et al. , smart complexs stuffs have been developed utilizing cellular solids, a porous interpenetrating web or froth impregnated with field-responsive fluids such as Magneto-Rheological ( MR ) fluids or STFs24. The chief advantage of utilizing porous stuff is to forestall the deposit of STF and increase the rate of procedure of shear thickener. The cellular stuff with its absorbent belongingss is able to keep the STF intact on its porous walls. Figure 7 shows the porous froth stuff before and after the impregnation with MR fluid.Figure 7. Elastomeric froth before and after impregnation with MR fluid24After the impregnation, the porous geotextile will be encapsulated on both sides with two geomembranes such as polythene or polypropene in order to forestall the escape of STF out of the porous geotextile.
Geomembranes will function as the insulating bed or separation bed to protect geotextile from environmental effects such as wet soaking up and heat. Figure 8 shows the construction of polymer-STF composite containing geotexile and geomembrane beds.Figure 8. Conventional of polymer-STF composite containing geotextile and geomembrane beds
Synthesis of polymer-STF composite with STF coated or filled fibres
Several research workers have attempted to better the stiffness and muffling belongingss of fibres in FRP complexs by surfacing the fibres with assorted organic polymers25.
These polymers such as styrene-maleic anhydride copolymers and methyl acrylate-acrylonitrile copolymers and polymeric amides incorporating functional groups can interact with both fibres and matrix. Surface intervention enhances the muffling consequence at the interface by making the interfacial bonding between fibres and matrix.STF associated fibres may heighten the public presentation to be ratio of fiber composite by cut downing the sum of needed fibres with the incorporation of STF. Fischer et Al. demonstrated that the incorporation of STF into dynamically loading construction improved the stiffness and muffling belongingss of the construction. Sandwich structures incorporating STF sandwiched between polymer matrixes, for illustration polyvinyl chloride ( PVC ) beams, have besides been investigated in order to better the stiffness and muffling belongingss of complexs under dynamic stresses26.
Figure 9. ( 1 ) STF coated fibres incorporated into a strengthened complex ; ( 2 ) STF filled fibres incorporated into a strengthened complexThe incorporation of hollow fibres filled with two pot epoxy rosin into FRP complex was investigated as self-healing stuffs when the fibres were fractured during high stressed distortions. Recently, several self-repairing glass fibre reinforced complexs have been developed and used to reconstruct the mechanical belongingss of composite such as flexural, compaction and tensile strength.In the present proposal, the attendant STFs from colloidal scatterings in subdivision 4.1.
2 can be used to surface the solid fibres or make full the hollow fibres, and later be incorporated into a polymer matrix as shown in Figure 9. Three types of fibres glass, C and Kevlar will be chosen by comparing their mechanical belongingss and lastingness. In general, epoxy rosin is used as the composite matrix. Some of the established methods can be followed to fix FRP composite affecting STF27, 28.
This subdivision includes the word picture of STF for rheological, mechanical, and morphological belongingss, and thermic stableness. It besides includes the shear wall proving for the concluding polymer-STF complex.
The STF samples will be tested for their rheological belongingss such as stress-strain behaviour, energy dissipation and output emphasis utilizing the TA Instruments ‘ ARES Rheometer available in CNSE, NDSU. Testing will be carried out at room temperature with assorted shear rate inclines ( 0-125/s ) in steady-state strain expanses, dynamic frequence expanses and dynamic strain expanses. The steady and dynamic viscousnesss of STFs will be determined at different shear rates and strive amplitudes severally.
From the history of old temblor records, it was found that the scope of frequence of most of the temblors that cause terrible harm was about 1 – 2Hz and the mean amplitude of acceleration was about 0.5g. Therefore, in order to fit the frequence of the temblor with the critical shear rate for shear thickener in STF, the viscousness addition in STF should be adjusted to happen at the frequence below 1 Hz. In the seismal active control systems where Electro-rheological ( ER ) fluids are used, the behaviour of ER fluid alterations from liquid to a giving up solid within msecs in response to seismic burden.
Hence, it is required to find the clip period for shear inspissating response of assorted STFs so as to guarantee that the stuff undergoes the needed viscousness alteration with regard to seismal quivers.
Thermohydrometric analysis ( TGA )
Thermohydrometric analysis ( TGA ) will be conducted utilizing the Q500 Thermogravimetric Analyzer to find the weight per centums of colloidal atoms and suspending liquid in the as-prepared STF samples. Thermal stableness of assorted STFs can besides be determined utilizing TGA.
Transmission negatron microscopy ( TEM )
Transmission negatron microscopy will be performed utilizing the JEOL JEM-100CX II transmittal negatron microscope to analyze the scattering of colloidal atoms in STF, morphology of coated and filled fibres, and permeating webs of tie ining polymers.
Scaning negatron microscopy ( SEM )
Scaning negatron microscopy ( SEM ) and Atomic force microscopy ( AFM ) will be used to look into the grade of impregnation of cloth with STF. The alterations at the micro-level in the surface texture of cloth with impregnation would besides assist to find the adhesion and uniformity of surface assimilation of STF onto the fabric surface.
Dynamic mechanical analysis ( DMA )
Dynamic mechanical analysis ( DMA ) will be used to find the dynamic belongingss of the composite such as dynamic moduli and muffling energy.
The consequences will supply an apprehension of the consequence of interfacial interactions among assorted ingredients in the complex ( interactions between STF and polymer matrix, and STF and fibres ) .
Accelerated weathering trials
Accelerated weathering trials will be carried out to find the stableness of polymer-STF complexs in footings of tensile strength and shear strength. They will be exposed to a high alkalic solution of pH stopping point to 13.5 at a high temperature ( 60 & A ; deg ; C ) for periods of 2-3 months, which corresponds to 50 old ages of exposure in a Northern clime. Trials will besides be performed to measure the lastingness of polymer-STF complexs under lading and submergence at 60 & A ; deg ; C.
Shear wall proving
For shear wall testing, the process used by Meguro et Al. for retrofitting based on polypropene ( PP bands ) will be followed29.
The process describes the usage of PP sets arranged in a mesh manner and inserted in a cement howitzer wall. Initially, the stuff belongingss including compaction strength, immature ‘s modulus, and tensile strength of brick, howitzer and cement will be measured.In order to happen out the efficiency of retrofitting method, it is one of the indispensable elements to find the distortion opposition of masonry walls to in-plane and out-of-plane burden for both retrofitted and non-retrofitted samples. Our technique is supposed to supply the strength and stiffness to the walls in order to forestall it from checking, separation from roof and separation of walls at the corners.Figure 10.
( a ) Reinforced wall theoretical account before howitzer sheathing, ( B ) Experimental set-up for perpendicular and horizontal pre-compression burden ( hundred ) In-plane and out-of-plane displacements29Trials will be carried out harmonizing to ASTM C1314-07. Concrete masonry walls with and without support will be constructed utilizing the blocks shipped from National Concrete Masonry Association. The wall dimensions will be estimated to be 985mm-1072mm-100mm consisting of 15 brick rows with 6 bricks each row. The force-displacement curves will be obtained by using different forces ( 10kN to the failure ) and supervising the supplantings.
Timeline, Budget and Possible Funding Agencies
The undertaking is expected to go on for about 2 old ages. The proposed budget is shown below.
Wages are estimated for the research squad that will dwell of one Principal Investigator ( PI ) , one full-time Graduate Student, and one part-time Undergraduate Student. Tuition fees waiver will be considered for the alumnus pupils working on this undertaking. Chemicals, stuffs and equipment for word picture and proving intent have besides been included in the budget. Instrumental charges are given for utilizing instruments on and off the campus. Travel funding includes airfare, hotel and enrollment for two conferences each twelvemonth for PI and the Graduate Student to show the research work. Funding for this undertaking will be pursued from the National Science Foundation-Engineering Research Centre ( NSF-ERC ) , the United States of Geological Survey ( USGS ) , and the National Institute of Standards and Technology ( NIST ) .
Timeline for this undertaking is shown in below Gantt Figure
Figure 11. Gantt Chart of Timeline for this undertakingTable 3: Budget of the current proposal