c O N F E R E N C E Sen

Transcription

1 12TH INTERNATIONAL BRICK/BLOCK Masnry c O N F E R E N C E Sen INFLUENCE OF BEO JOINT ORIENTATION ON THE STRESS-STRAIN CHARACTERISTICS OF SANO PLAST BRICK MASONRY UNOER UNIAXIAL COMPRESSION ANO TENSION R. SenthiveP, S.N. Sinha 2, Alk Madan 3 1 Research Schlar; ' Prfessr; 'Assistant Prfessr Department f Civil Engineering Indian Institute f Technlgy, Delhi New Delhi , INDIA. ABSTRACT Simplified nnlinear stress-strain relatins are derived fr brick masnry cnstructed with sand plast (a frm f calcium silicate) bricks based n the results f uniaxial tests n square panels with varius angles f the bed jint t the hrizntal including 0, 22.5, 45, 67.5 and 90. The macrscpic elastic and inelastic strains are calculated frm displacement measurements ver gauge lengths which included a number f mrtar jints. C/se agreement is bserved fr the initial elastic behaviur. The nnlinear behavir is fund t be significant/y influenced by jint defrmatins. A nn-dimensinal stress-strain relatinship f the brickwrk under uniaxial cmpressive 100- ding is presented. Empirical equatins are develped n the basis f the test data t estimate shear strength and cmpressive strength as functins af nrmal stress and rientatin f nrmal stress with respect t the bed jint directin. 80th equatins are shwn t be nn-linear. The variatin f lateral strain with axial strain is 0150 addressed. The present study 0150 cmpared with an extensive wrk dne by Alshebani and Sinha (2, 3) n sand plast brick masnry fr lad nrmal and paral/el t the bed jint. Key wrds: bricks; sand plast; cmpressive strength; shear stress; masnry; stressstrain relatinships; bed jint. 165

2 1. INTRODUCTION Brick masnry exhibits distinct directinal prperties due t planes f weakness intrduced by the mrtar jints (18). The rientatin f bed jint, therefre, plays a significant rle in the failure mde f brick masnry. The bed jint rientatin f the masnry may vary frm nrmal t parallel with respect t the lading directin. It is well established that the strength f brick masnry prism is influenced by the directin f lading t bed jint (14,23). Failure f an istrpic material under the cmbined effect f tensile and cmpressive stresses can be evaluated by translating the applied stresses int an equivalent state f principal stresses. Hwever, since brickwrk is an anistrpic tw-phase material, cnsisting f predminantly elastic bricks embedded in thin layers f inelastic mrtar which thus act as planes f weakness. Thus, t accunt fr a third variable, the influence f the bed jint rientatin relative t the principal stresses, must als be cnsidered fr characterizing the ultimate limit state f brick masnry. Depending upn the rientatin f the bed jints relative t the directins f the applied stresses, failure may manifest as a sliding shear mde alng the mrtar jints alne r splitting f mrtar jints r cmbined mechanism invlving the mrtar and the masnry units (1,10,16). This paper presents the results f an investigatin f the behaviur f brick masnry mdels subjected t uniaxial cmpressive and tensile lading at varius angles f inclinatin t the hrizntal, and the influence f bed jint rientatin n the cmpressive strength and tensile strength. A ttal f 30 brick masnry panels with different bed jint inclinatins (0, 22.5, 45, 67.5 and 90 ) were tested under uniaxial mntnic cmpressive and tensile lading up t failure. The present study is part f a research prject based n the behaviur f brick masnry under mntnic and cyclic lading at different angles f rientatin t the bed jint. Five specimens were tested fr each inclinatin and fr each lading case. The bserved failure mde was shear- cmpressin r tensin, sliding and splitting in the bed jints depending n the inclinatin f the bed jint t the hrizntal and nature f lading either cmpressin r tensin. The stress-strain characteristics under uniaxial tensin were nt mdeled since the brittle and abrupt tensile failure allwed extremely small defrmatins which culd nt be measured meaningfully. Only the test prcedure and mdes f failure were thus identified fr the specimens tested under tensile lading. The experimental data fr e equal t 0 and 90 inclinatins were als btained frm the extensive research wrk dne n sand plast brick masnry by Alshebani and Sinha(2,3) under similar labratry cnditins as the present wrk. 2. TEST PROGRAMME 2.1. Test Specimens A full-scale slid sand plast brick unit measures 230x11 Ox70mm. Eight half-scale brick units measuring 11 Ox55x35mm were sawn ut frm each full brick. The 656

3 average cmpressive strength f half-scale brick was 23.4N/mm 2 with a standard deviatin Of 2.1 N/mm 2 based n a sample f 30 single unit bricks. A 1:1/2:4 mix f cement, lime and sand by vlume with water/cement rati f 0.95 by weight was used fr mrtar. The average cmpressive strength f 70mm mrtar cube was 1 0.2N/mm 2 at 28 days with standard deviatin f 1.5N/ mm 2 based n a sampie f 30 mrtar cubes. Fifty English bnd panels with 5mm thick mrtar jints were fabricated with varying bed jint inclinatins by cutting individual bricks t the shape required. The dimensins f the test panel were adpted as 360x360xl15mm. Ali panels were cured fr 28 days. The details f test panel is as shwn in Fig Lading Arrangement The sand plast brick masnry panels were tested in cmpressin and tensin using an Avery Universal Testing Machine (UTM) f 1000 KN capacity. Fr cmpressin test, the lad was distributed thrugh steel bx f 150 mm x 200 mm crss-sectin. A lad cell f 1000 KN capacity was placed between the testing machine and the steel bx at its centre as shwn in Fig. 2. Fr tensin test, the panels were glued t steel plates using an epxy (Araldite) at its bearing area. The tensile lad was applied by cnnecting tp side f the panel t the machine ram thrugh a steel bar f 32 mm dia meter and anchring the bttm face f the pa T70 I V (a) Full size brick ( b) Brick uni! I I I I I I I I I I I I I I I I L +, I I L I I I I I I f l (e) Briekwrk ali dimensins in mm Figure 7. Details af Test Pane/ 162

4 Figure 2. Experimental Set-up fr Cmpressin Test. Figure 3. Experimental Set-up fr Tensin Test. nel t a fixed base. The lad cell was placed at the centre under the fixed base as shwn in Fig Instrumentatin and Data Acquisitin The masnry panels were instrumented with LVDTs (Linearly Variable Displacement Transducers) aligned in mutually rthgnal directins n bth sides f the pane\. The LVDTs were installed t measure the axial and lateral displacement ver a fixed gauge length. A gauge length f 250 mm was adpted fr measurement f bth axial and lateral defrmatins. A Pentium based Real Time Data Acquisitin and Cntrl System was used t mnitr and recrd the lad and displacement measurements. The axial displacement versus lad was pltted in real time during the test at the tw lcatins n each side f the pane\. The plt faxial displacement versus lateral displacement was als btained at the same lcatins. 2A. Test Methdlgy The masnry panels were subjected t uniaxial cmpressive, and tensile ladings in rder t develp different cmbinatins f nrmal stress and shear stress in the bed jints. Five sets f panels were tested fr each case f lading fr three diffe- 658

5 rent angles f inclinatin f bed jint (8) t the hrizntal including 0, 22.5, 45, 67.SOand 90 prducing shear stress ('t) t nrmal stress (a n ) ratis f 0,0.41, 1.0, 2.41 and 00 respectively. Mntnic lading were applied at unifrm rate such that failure ccurred within ne minute. 3. TEST RESUL T AND DISCUSSION 3.1 Stress- Strain Curve The nn-dimensinalised stress-strain envelpe curves fr different angles f inclinatin f the bed jint based n the average f data btained frm the five specimen tested fr each bed jint inclinatin are presented in Fig. 4. The stress is nrmalised with respect t the failure (peak) stress, and the strain is nrmalised with respect t strain crrespnding t the peak stress. The sftening branches f the curves were btained frm the envelpe f cyclic lading hysteresis curves. 1.2 Alshebani and Sinha [2] Present study b Envelpe curve (a) O., Strain rati ( e: ) Envelpe curve fr 0 0 and U LO :;: Vi O. Envelpe curve t O LO Slrain rali ( l (b) Envelpe curves fr 22.5,'5 and 67.5 Figure 4. Nn-dimensinal Stress-Strain Envelpe Curves. 16

6 The shapes f the stress-strain curves fr five inclinatins are nn-linear in nature with an initial linear elastic branch. It is evident that the bed jint rientatin f the applied lad has a distinct effect n the elastic prperties f brickwrk. A best fit higher rder plynmial fr the curve crrespnding t 0, 90, third rder plynmial fr the curve crrespnding t 22.5 angle f inclinatin and secnd rder plynmial relatinships fr curves crrespnding t 45 and 67.5 were develped using the least square methd. The nrmalised stress-strain relatinships btained frm the curve fitting are: (j = E E' E E Fr 22.5, (j = E E E Fr 45, (j = 1.024E E (1.1 ) (1.2) (1.3) Fr 67S, (j = E E (1.4) Fr 90, (j = E E' E E' t (1.5) 3.2. lateral Strains Sme typical curves shwing experimental variatin faxial strain versus lateral strain fr five cases f inclinatins are presented in Fig. 5. A large increase in lateral strain was bserved at higher leveis faxial strain fr ali the five cases f inclinatins. The higher variatin in the rati f lateral strain t axial strain can be accunted fr by the frmatin f cracks traversing thrugh the lateral gauge lengths. These cracks varied in size and number, thus resulting in a large variatin f the measured lateral displacements. Nting that the slpe f the curves represents the Pissn's rati f the material, it is bserved that the Pissn's rati's increases with stress levei. The Pissn's rati als varies with the bed jint angle with respect t the directin f the applied lad. At very lw stress leveis, it appears that it is apprximately the same fr bth e equal t 0 and e equal t Mdes f Failure The mde f failure was gverned by the rientatin f the bed jint. When 10- ad acted perpendicular t the bed jints, a typical splitting mde f failure thrugh bricks and perpendicular jints ccurred which was induced by the differing strain characteristics f the weaker mrtar and the strnger bricks. Numerus micr-cracks parai lei t the directin f applied lad were bserved. Cmplete cllapse f the panels was accmpanied by a few majr cracks. The specimens with bed jint angle f 67Sand 45 t the hrizntal exhibited a failure cnfined t the jints whereas the specimens with 22.5 t the hrizntal exhibited a failure mde similar t that in case f vertical cmpressin (i.e. e equals O case). In the latter case, hwever partial bnd failures in the jints were accmpanied by brick splitting and als central splitting at tp bearing area and sides f the panels were bserved fr 0 and 22.5, Fig. 6c. When the lad was applied parallel t the bed jints the panel spilt alng the vertical face jints. The splitting initia- 660

7 c: E -;;; 'x « Laleral slrain lei) l ) 9 = 0 Laleral slrain ( El ) I b) 8 = _ c: "ê ;;; Õ :i O.OOl.O Ô c: "ê ;;; Q x <t am Lateral strain ( l) ( c) e = Ô c: 'e ;;; <t O.OOl. Lateral strain ( l) ( d ) e = Lateral strain ( l) (0)9= Figure 5. Envelpes faxial-lateral 5trains. tes at free edges and gradually prpagates twards the center f the pane!. Thereafter, the separated parts f the panel behave Iike individual cmpressin members. The details f failure mdes are as shwn in Figs. 6a and 6c. In the uniaxial tensin tests, ali the panels failed alng the jints. The panel with 0 bed jint angle t the hrizntal failed in tensin mde with the failure plane passing thugh the hrizntal bed jint. In the case f panels with bed jint angle f 90 t the hrizntal, a staggered jint failure pattern was induced due t 1661

8 lw bnd strength between bricks and mrtar. In the case f brick panels with 0 < e < 90, intermediate failure mdes with staggered and hrizntal failure patterns were bserved. The details f failure mdes are as shwn in Fig. 6b Failure Criteria Figure 7 presents the average variatin f ultimate shear strength with nrmal cmpressive stress bserved in ali the tests. A failure criterin in terms f the cmpres- Figure 6. Mdes f failure. () Und(>r un lxial c.mpressin (b) Under unix ial tensin 11 "" 11 N e 3.0.!; z...,.c:.' 2.0 Õ> c Vi 1.0.,.c:. V) -- Presenl sludy ---- Alshebani and Sinha 12 ) I<>.., Nrmal sires5 (a;, I N/ mm O Figure 7. Shear Strength vs Nrmal Cmpressive Stress. 1662

9 1. Alshebani and Sinha (2) A Present study u 0.8 Õ 0.6 C7l c (li L- (li 0 L, > 'Vi VI a. 0.2 u ==-'"=------:--::'-::---=--_::_: Bed jint angle ( 6) Figure 8. Envelpe f 8ed Jint Angle Versus Cmpressive Strength Rati. sive stress nrmal t the bed jints, O n. and the shear stress, 't may be derived frm Fig. 7. It can be seen that distinct variatin in slpe ccurs in ascending zne as the cmpressive stress increases reflecting changes in the failure mde frm jint bnd failure t a cmbined brick and mrtar jint failure and eventually t a primary cmpressin failure. A nn-linear third rder plynmial relatinship is prpsed t express the experimental failure envelpe. The relatinship may be expressed as, (2) where the stresses 't and O n are in N/mm2. The general frm f the relatinship is similar t that prpsed by Page(19), Mann et.al.(7) and Dau et.al.(3) fr fullscale brickwrk failing by jint failure r tensile splitting f the bricks. The test results may als be represented in nn-dimensinal frm by relating the cmpressive strength rati, f" t the angle f rientatin f the bed jints, 8, as shwn in Fig. 8. In this case the failure criterin can be represented reasnably well by a third rder plynmial relatinship, as fllws; fe = 7xl (3) where fe is the failure stress in cmpressin applied at an angle f inclinatin 8 f degrees rei ative t the bed jints. 7663

10 4. CONCLUSIONS Nn-dimensinal stress-strain relatinships are btained fr sand plast brick masnry frm results f uniaxial cmpressin test perfrmed n scaled square panels with varius angles f the bed jint t the hrizntal. Experimental investigatin established the failure mdes and criteria under cmpressin inclined t the bed jint. Failure criteria is defined in terms f bth shear strength and uniaxial cmpressive strength as fuctins f nrmal stress and bed jint rientatin. The dminant failure mde is gverned by the rati f shear stress t nrmal stress, 't/a n Fr high 't/a" ratis (Iw nrmal stress), failure ccurred as a bnd failure with n sign f distress in the bricks. Fr lw 't/a n rati (high nrmal stress), a cmbined mrtar-brick failure ccurred cmpressing tensile splitting in the brick with bnd failure in the jints. The salient cnclusins f the study may be summarized as fllws: 1. There are tw distinct mdes f failure f sand plast brick masnry under uniaxial cmpressin and tensin: (i) a shear mde f failure alng the bed r head jint planes, and (ii) a tensin mde f failure mainly distinguished by tensile fracture f the cmpnent materiais. There is als a mixed shear-cmpressin r tensin mde f failure. The relative magnitude f the shear and nrmal stresses develped alng the criticai bed and jints is the majr fact r cntrlling the mde f failure and cnsequently the sand plast brick assemblage capacity. 2. The strength and defrmatin characteristics f sand plast brick masnry assemblages vary with the directin f the applied stress relative t the bed jints indicating the nn-istrpic nature f brick masnry. 3. In the initial elastic behavir, the brick masnry was, n average istrpic. 4. Panels that failed by tensile splitting culd be assumed t be elastic upt failure. 5. Fr panels in which 't/a n <1, a bed jint sliding failure was preceded bya sharp change in slpe f the 't versus a n curve. 6. Only the failure patterns were identified fr sand plast masnry under uniaxial tensin. The stress-strain data was nt mdeled due t the negligible rder f magnitude f the data as a result f the brittle failure mdes and lw strengths assciated with tensin. The study highlights the highly directinal nature f the prperties f sand plast brickwrk, due t the influence f the mrtar jints acting as planes f weakness. The masnry strength is thus significantly affected by the directin f the applied stress relative t the bed jints. Semi-empirical relatinships have been prpsed fr the variatin f shear strength as a functin f nrmal stress and fr the cmpressive strength as a functin f the rientatin f stressing with respect t the bed jint directins. Since these relatinships are nn-linear in general, higher 1664

11 and lwer rder plynmial equatins are fund t prvide a gd fit t the experimentai results. NOTATION a nrmalised stress rati, a,/a m a, axial stress a m failure (peak) axial stress E nrmalised strain rati, E,/Em E, axial strain Em axial strain when peak is attained E, lateral strain a nrmal stress fe nrmalised cmpressive strength rati, fclfem f" axial cmpressive strength fem maximum axial cmpressive strength 1: shear stress e bed jint inclinatin REFERENCES 1. Allen, H., "Effect f Directin f Lading in Cmpressive Strength f Brick Masnry", Prc. Third Int. Brick Masnry Cnference. Edited by L. Fentig and K. Gbel, Bann Bundeswenband, der Deutschen Ziegelindustries, 1975, pp Alshebani, M.M., "Respnse f Brick Masnry under Cyclic Lading", Ph.D Thesis, guided by Prf. S. N. Sinha, Department f Civil Engineering, Indian Institute f Technlgy, Delhi, India, Alshebani, M.M., and Sinha, S.N., "Stress-Strain Characteristic f Brick Masnry under Uniaxial Cyclic Lading ", Jurnal f Structural Engineering, ASCE, Vl. (1-5), N. 6, June 1999, pp Dau, Y. and Hbbs, B., "Strength f Brickwrk Laded in Different Orientatins", Prc. 9 th IBMaC, Berlin, Germany, l3-16 Octber 1991, pp Dhanasekar, M., Kleeman, P.W. and Page, A. W., "Biaxial Stress Strain Relatins fr Brick Masnry", Jurnal f Structural Engineering, ASCE, Vl. 111, N.5-7, Dryadale, R.G, Hamid, A. A, and Heidebrecht, A.c., "Tensile Strength f Cncrete Masnry", Prc. ASCE, Vl. 105, ST7, July 1976, pp Drysdale, R.G. and Hamid, A. A., "Behaviur f Cncrete Blck Masnry under Axial Cmpressin " ACI Jurnal, Prc. Vl. 76, N. 6, June 1979, pp Drysdale, R.G., and Khattab, M.M., "In-Plane Behaviur f Gruted Cncrete Masnry Under Biaxial Tensin-Cmpressin ", ACI Structural Jurnal, Vl. 92, 1995, pp Hamid, A.A. Drysdal, R.G.. and Heidebrecht, A.c., " Effect f Gruting n the Strength Characteristics f Cncrete Blck Masnry", Prc. Nrth American Masnry Cnference, The Masnry Sciety, Aug. 1978, pp t Hamid, A.A. and Drysdale, R.G., " Cncrete Masnry under Cmbined Shear and Cmpressin alng the Mrtar Jints, Structural Jurnal, ACI, Sept. - Oct

12 11. Hamid, A.A and Drysda le, R.G., "Behaviur f Brick Masnry under Cmbined Effect f Shear and Cmpressin Lading". 2"d Canadian Masnry Sympsium, Ottawa, Hendry, A.W., "Structural Brickwrk", Mc Millin Press Lndn, Hendry, A.W. Sinha, B.P. and Davies, S.R., " Lad Bearing Brickwrk Design", Secnd Edn., Jhn Wiley &. sns, New Yrk, Hendry, A.W., "Reinfrced and Prestressed Masnry", Jhn Wiley and sns, Inc, New Yrk, Khalaf, F.M., "The Perfrmance f Cncrete Blck Laded Parallel t Bed Face. J. Brit. Mas. Se., Masnry Internatinal, 2(1), 20, Mann, W. and Muller, H., "Failure f Shear-Stressed Masnry - An En larged Thery, Tests and Applicatin t Shear Wa lls", Pre. British Ceramic Sciety, Vl. 30, 1982, pp Page, A.W., "A Mdel fr the In-Plane Defrmatin and Failure f Brickwrk". University f Newcastle, N.S.W., Australia, Engineering Bu lletin CE8, Page, A.W., "The Baixial Cmpressive Strength f Brick Masnry", Pre. Institutin f Civil Engineers, Part 2, Vl. 71, Sept. 1981, pp Page, A.W., "The Strength f Brick Masnry under Biaxial Tensin-Cmpressin", Int. J. f Masnry Cnstructin, V l. 3, N. 1, 1983, pp Page, A.W., " Influence f Material Prperties n the Behaviur f Brick Masnry Shear wa lls", Pre. 8 th Internatinal Blck/ Brick Masnry cnference, Dublin, Ireland, Sept. 1988, pp Samarasinghe, W., "The In-Plane Failure f Brickwrk", Ph. D Thesis, University f Edinburgh, Senthivel, R., Sinha, S. N. and Madan, A., "Behavir f Brick Masnry Laded at Different Angle f Orientatin t the Bed Jint" Pre. Int. cnference n advances in Structural Engineering, Edited by S.K. Kaushik" Ghaziabad, India, Sept. 1999, pp Sinha, B.P. and Hendry, A.w. "Racking Test n Stry Height Shear Wall Structures with Openings Subjected t Pre- cmpressin", Design ing, Engineering and Cnstructin w ith Masnry Prducts, Gulf Publishing Cmpany, Hustn, May 1969, pp