SHEAR AND FLEXURAL BEHAVIOR OF FERRO CEMENT DEEP BEAMS

Transcription

1 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: SHEAR AND FLEXURAL BEHAVIOR OF FERRO CEMENT DEEP BEAMS Md Itesam Hussain 1,Vaijanat Halalli, P.M.B Raj kiran Nanduri 3 1, 3 Lecturer, Department of Civil Engineering, Adama Science and Tecnological University, ETHIOPIA Professor, Department of Civil Engineering, PDA College of Engineering Gulbarga itesam89@gmail.com, vaijanatalalli@yaoo.com, rajkiran.n1987@gmail.com Abstract Te recent application of Ferro cement includes prefabricated roofs elements, load bearing panels, bridge decks and oters. However tere ave been many structural applications in different parts of te world especially in eastern emispere considerable efforts ave been made by many individuals and researc organization around te world to study te engineering of Ferro-cement. Tis present study deals wit te beavior of Ferro cement deep beams under central point load. A total of 7 rectangular deep beams ave been casted of dimension 15 x 50mm and te lengts of beams ave been varied along wit te variation of wire mes and mortar strengt. Before testing, te top surfaces of tese beams were wite wased, to get a clear picture of ack pattern. Along wit tese beams 7 cubes ave been casted wit te dimensions 7.06 cm x 7.06 cm x 7.06 cm. te compressive strengt of mortar is determined. Keywords: Admixture, Deep Beams, Ferro cement, Sear Span *** INTRODUCTION Ferrocement, a composite comprising cement mortar as te matrix and fine wire mes as te reinforcement, as been regarded as a igly versatile construction material. Te closer distribution and uniform dispersion of reinforcement transform te oterwise brittle matrix into a composite tat exibits superior performance over conventional reinforced conete wit respect to acking, tensile strengt, ductility and impact resistance. Being tin-walled in nature Ferrocement as found to be most suited for structures like sells and folded plates, were te applied load is primarily carried troug te action of in-plane sear and axial stress. Wen te out-of-plane action becomes predominant, Ferro cement in its traditional form beaves rater poorly because of its low flexural rigidity. Efforts ave been made to inease te flexural performance of Ferrocement by introducing ribs and ollow cores, or resorting to a sandwic-type construction. Oter alternatives include te use of tin-walled structural sections, typically employed for steel or fibre-reinforced polymer like box, cannel, T- and I- sections. Te uniform distribution and ig surface area to volume ratio of its reinforced results in better ack arrest mecanism i.e. te propagation of acks are arrested resulting in ig tensile strengt of te material. Deep beam is a beam aving large clear span to dept ratio and sear span dept ratio less tan.5 for concentrated load and less tan 5.0 for distributed load. It is a reinforced conete member in wic te total span or sear span is exceptionally small in relation to its dept. Deep beams play a very significant role in design of mega and as well as small structures. Some times for arcitectural purposes buildings are designed witout using any column for a very large span. CIRIA is te Construction Industry Researc and Information Association; it is non-profit distributing organization carrying out on Researc work of bealf of its members. Te CIRIA Guide simple rules for designing reinforced conete deep beams of span/dept ratio below for single span or.5 for multi-span Te Guide as been prepaid by a team of designers and as been approve by a panel of assessors as autoritative statements of te art and of good practice in designing reinforced conete deep beams. Al-Kubaisy and Ned Well [1] studied on te location of te diagonal ack in ferrocement rectangular beams. Te variables covered in te study were, a/d volume fraction and compressive strengt of te mortar fcu. Te effect of te volume fraction, Vf on te location itical diagonal ack is not well defined. It is also concluded tat te ACI-ASCE committee 36 expression for predicting te location of te diagonal ack in conventional reinforced conete beams underestimates te location for ferrocement beams wit a/d = 1.0 and over estimates te location for beams wit a/d > 1.5. Mansur, M.A. and Ong, K.C.G [] conducted sear tests on te ferrocement beam sections and concluded tat, te beavior of tese structural sections is similar to tat of structural reinforced ferrocement beams. It is also mentioned tat te ferrocement beams exibit numerous acks and IC-RICE Conference Issue Nov-013, ttp:// 85

2 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: sections are serviceable up to 90% of te ultimate load. Naaman and Sa s [3] (1974) work indicated tat te stress level at wic te first ack appeared and te ack spacing were a function of te specific surface of reinforcement. Te ultimate load of te ferrocement specimen was te same as te load carrying capacity of te reinforcement in tat direction. Desayi [4] proposed a semi empirical formula for predicting te sear strengt of ferrocement elements. Mansur and Paramasivam (1986) [5] proposed a metod to predict te ultimate strengt of ferrocement in flexure based on te concept of plastic analysis were ferrocement is considered as a omogenous perfectly elastic-plastic material. It was found tat te ultimate moment inease wit ineasing matrix grade (deeasing water cement ratio) and ineasing volume fraction of reinforcement. 4. MIX PROPORTIONS After deciding all te parameters and water cement ratio, dosage of super-plasticizers was fixed. Trougout te wole program te cement to sand ratio was varied from 1:1 to 1: and w/c ratio from 0.5 to 0.4 based upon te mortar strengt required and to obtain te desired workability a superused in all te mixes. plasticizer (HRWA) was 5. TEST PROCEDURE: All beams are simply supported on two edges. All specimens were tested under concentrated single point load. Te test setup is sown in te Figure 1. Te deflections and te corresponding applied loads were recorded at te specified displacement intervals. Till today no codal formula is available to assess te sear strengt of ferrocement elements. Tus tere is a need to verify, were te sear resistance equations given by existing codes of practice for reinforced conete can be extended to ferrocement also?. EXPERIMENTAL PROGRAMME.1 Objectives 1. Te aim is to study te sear and flexurall beavior of ferrocement deep beams and to study te effect of te following parameter. a) Volume fraction of reinforcement (V f ) b) Sear span to overall dept ration (a/) c) Cube compressive Strengt (f cu ). To study te load deflection relationsip and sear beavior. 3. To compare te test ultimate load (V u ) wit te design code (ACI ) and CIRIA guide. 4. To compare te test acking sear stress (τ u ) wit te design code (ACI ) and CIRIA guide and too generate a linear empirical equation for predicting te ultimate strengt of ferro-cement deep beams. Fig 1 Test setup to determine sear and flexural strengt 3. EXPERIMENTAL INVESTIGATION Te experimental investigation includes casting and testing of 7 rectangular deep beams and cubes. Tree groups of specimens were casted. In Group-A nine beams of size 10mm x 50mm were tested. Te parameter considered in tis group is varying sear span to dept ratio (a/) wile te wire mes (N) and mortar strengt (f cu ) weree kept constant. In Group B, again nine beams of same size were tested. Te parameter considered in tis group is varying mortar strengt (f cu ) wile te sear span to dept ratio (a/) and wire mes (N) were kept constant. In te tird group nine beams of size 10mm x 50mm were tested. Te parameter considered in Group-C is number of wire mes(n) wile keeping oter parameters unvaried. IC-RICE Conference Issue Nov-013, ttp:// 86

3 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: RESULTS AND DISCUSSIONS Table 1: Details of test specimens Beam designation Parameter to be investigated Sear span to dept ratio (a/d) No. of layers of wire mes (N) Total volume fraction of mes reinforcement (V f ) Cube compressive strengt of motar (f cu ) N/mm A1 A A3 B1 B B3 C1 C C3 a/ f cu N Load Deflection Relationsip: Fig Load-Deflection Beavior of Beams of Group-A Fig 3 Load deflection beavior of beams of Group-B IC-RICE Conference Issue Nov-013, ttp:// 87

4 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: Fig 4 Load deflection beavior of beams of Group-C 6. Cracking Beavior and Modes of Failure In all specimens, flexural acks occurred first irrespective of te study parameters of te present study. As te load was ineased, additional vertical acks appeared on beam surface, followed by te formation of diagonal acks. In te present study, diagonal tension acks in te specimens wit a/> 0.65 generally originated as vertical flexural acks tat extended from te tensile surface of te beam to sligtly above te level of te bottom layer of wire mes ten became inclined and propagated towards te nearer concentrated load. In cases of beams wit sorter sear span (a/ < 0.65). Diagonal tension acks originated at about mid-dept of te beam and ten progressed towards nearer concentrated load and tensile reinforcement. Te oter type of failure occurred in beams wit a/=0.7. Tis was typically sear compression failure caracterized by using of te mortar near te concentrated load. 6.3 Effect of study parameters on te ultimate sear strengt Te figure5 sows tat wit te inease in te volume fraction of reinforcement ineases te sear strengt of ferrocement beams wen te dimensions of te beam and mortar grade aren t varied. Fig5 Comparison of test parameter volume fraction of V reinforcement (V f ) and ( u ) b Te figure 6 sows tat wit te deease in a/ ratio ineases te ultimate sear strengt of ferrocement deep beams tat means te lengt of te beam is only varied and oter parameters suc as number of mes layers and grade of mortar are kept constant. Fig 6 Test parameter sear span to dept ratio (a/) v / s b IC-RICE Conference Issue Nov-013, ttp:// 88

5 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: Te figure7 below sows tat wit te inease in te mortar strengt te ultimate strengt of ferrocement deep beams ineases and te oter test parameters are kept unvaried during tis analysis. Te grap sows a linear variation of sear strengt wit mortar grade. R =0.590 R = Fig 9 Comparison of Test and Predicted ultimate sear stresses V u Fig 7 Test parameter mortar strengt (f cu ) v/s b 6.4 Comparison of experimental ultimate load wit design codes: Te codal provision for te ultimate strengt of ferrocement deep beam given in ACI is considered in te present analysis. V = 0.16bd uc f cu bpv d M (1) Were V = Cracking load in KN p = Reinforcement ratio = A st / bd M = Bending moment N-mm 6.5 CIRIA Guide: According to CIRIA Guide: V [ λ V ( V = β uc 1 x + + )] b. () ms Vo + Vwv V Fig 8 Regression between te parameters u f and b cu Vf a Were = dept of beam λ = for normal weigt conete. V x = conete sear parameter as tabulated in table 4 of te CIRIA guide. V ms = Main steel sear stress parameter as tabulated in Table -6 of te CIRIA guide. Vw = Horizontal web steel as tabulated in table 7 of te CIRIA guide Vwv = Vertical web steel as tabulated in table 8 of te CIRIA guide β = 1 for deformed bars. IC-RICE Conference Issue Nov-013, ttp:// 89

6 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: τ 6.6 Comparison of test ultimate sear stress ( u ) wit design code: 1) As per ACI Te available equations for predicting te acking sear stressτ. uc bd V uc f cu = (3) M pv Were V = Cracking load in KN p = Reinforcement ratio = A st / bd A st = Area of steel in mm M c r = Bending moment N-mm ) As per CIRIA Guide: c = λ 1 Vx + β ( Vms + Vo + Vwv ). (4) b Were λ = for normal weigt conete. V x = conete sear parameter as tabulated in table 4 of te CIRIA guide. V ms = Main steel sear stress parameter as tabulated in Table -6 of te CIRIA guide. Vw = Horizontal web steel as tabulated in table 7 of te CIRIA guide Vwv = Vertical web steel as tabulated in table 8 of te CIRIA guide β = 1 for deformed bars. 6.7 Proposed equation by Mau & Hsu: Te ultimate sear strengt is given by 1 Vn = fc[k( ω ) + K ( ω ) + 4( ωv )] 0.3f c' (5) Wit te limitations ω = ρ f / f ' 0. 6 and ρ f v y / f c ' 0.. Te coefficient K, representing te sear span effect, is given by. d f cu y c d v 4 a K = for 0.5 < a 3 3 K = 0 for a / >.0 a / Empirical formula for te ultimate strengt of ferrocement deep beams: Te ultimate strengt depends upon te following parameters. a. Mortar strengt (f cu ). b. Ratio of sear span to te dept (a/) c. Volume fraction of reinforcement (V f ) From te earlier discussion it is clear tat, a separate formula for predicting te diagonal acking strengt of ferrocement elements is necessary. Sear resistance of ferrocement elements is mainly due to te contribution of mortar matrix and longitudinal reinforcement. Te results of te present tests are compared. It sows tat tere is large difference between te experimental values wit te code values. Te ACI code formula Eq. (1) greatly underestimates te diagonal acking strengt for most of te beams. In an attempt to develop an expression wic migt predict more closely te diagonal acking strengt of beams over te entire range of parameters covered in tis investigation, te following expression, wic is similar to te one proposed by Zsutty, was selected. = K f cuv f (6) b a Were K and n are constant and f cu is expressed in N/mm. A multiple regression analysis was carried out using te results of te present tests, wic yields K =.7 and n = n 0.80 =.7 f cuvf. (7) b a Tis is te required expression for estimating te ultimate sear capacity of ferrocement deep beams. Using tis equation te sear stress of te tested beams are computed and compared wit observed and proposed value. Te average of te observed to te proposed values is wit S.D. of and tat of observed to te predicted values is 0.97 wit S.D of Te correlation coefficient for te present test is d v K = for 0< a / 0.5 CONCLUSIONS Te diagonal acking strengt of ferrocement ineases as te a/ ratio is deeased or volume fraction of reinforcement and strengt of te mortar are ineased. Ferro cement deep beams IC-RICE Conference Issue Nov-013, ttp:// 90

7 IJRET: International Journal of Researc in Engineering and Tecnology eissn: pissn: demonstrate excellent ack control caracteristics. Te empirical formula ( =.7 f cuvf ) proposed b a ere in terms of and V f provide good predictions of te diagonal acking strengt for te entire range of variables considered in tis study. REFERENCES [1]. Al-Kubaisy. M.A., and Nedwell, P.J., Location of Critical Diagonal Crack in Ferrocement Beams, Journal of Ferrocement, 8 (1998) []. Mansur, M.A. and Ong, K.C.G Sear strengt of ferrocement beams. ACI Structural Journal 84(1): [3]. Naaman, A.E.; and Sa, S.P., Tensile Tests of Ferrocement, ACI Journal, Proceeding V.68, No. 9, Sept. 1971, pp [4]. Desayi, P., and Nandakumar, N., A semi-empirical approac to predict sear strengt of ferrocement, Cement and Conete Composities, 17(1995) [5]. Mansur M.A., Paramasivam, P., Study of Sandwic Wall Panels Journal of Ferro cement 16(3): IC-RICE Conference Issue Nov-013, ttp:// 91