SHEAR STRENGTH OF GROUTED REINFORCED MASONRY .SHEAR STRENGTH OF GROUTED REINFORCED MASONRY BEAMS

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Transcript of SHEAR STRENGTH OF GROUTED REINFORCED MASONRY .SHEAR STRENGTH OF GROUTED REINFORCED MASONRY BEAMS

  • 4 . c .2

    SHEAR STRENGTH OF GROUTED REINFORCED MA SO NR Y BE AMS

    G, T , SUTER Ph . D. , P . Eng .

    Associate Pr ofessor of Civil Engineer i ng

    H, KELL ER B. Eng . , M. Eng.

    Research Engineer Department of Civil Engineering, Car leton Unive r sity , Ottawa, Canada

    SHEAR STRENGTH OF GROUTED REINFORCED

    MAC;ONRY BEAMS

    The authors carried out a systematic experimental

    study to answer tha question : Can the shear design

    of grouted r einforc3d mrlS0nry beams be treated as

    a combined case of yeinforced concrete and reinforced

    masonr-y? The investl:gation ir,volved a t otal of six-

    teen beams in which aU test parametel's e:ccept the

    ratio of shear span to effe ctive depth were hald con-

    stant . The papel' presents details of the test pro-

    gram and shows t hat the shear design of grouted

    rrasonry beams can indeed be consider-ed as a combined

    case of reinforce con:n'ete and reinforced masonry .

    RESISTANCE AU CISATLLEMENT

    DES POunES EN M4CONNERIE' ARMEE

    Les auteurs ont dvelopp W1e tude systmatique et

    expri.-rentale pour f'ouvoi r rpoildre la question

    suivante: Est-ce que la contra'in te de cisailZemant

    de poutres en terre cui te arme peut tre calcule

    cOmrle un cas corrbin de btan arme et de maonnerie

    armee?

    La recherche portait sur un total de seize poutres

    dans lesqu& lZes tous les parametres taient mainte -

    nus (?(JYlstants, except le rapport entre la porte et

    la hauteur e fre cti ve .

    L ' art i cle nous montre MS diJtails du prograrrone des

    essX1:s et dmontr e C/ U ?> le calcul de la cantrainte de

    cisaillemant de poutres en t erre cmte anne peut en

    effet tre considp co= un co,g c.ombin de bton

    arrr e t ma anneri e arrre.

    SCHUBFESTIGl(f;IT A USBETONIERTER

    BFWEHRTER MAUERwERKS2'R!JEGER

    Die Verfasser filhrten eine systematische lIersuchs -

    s tudie durch , um die Frage zu bean r..Jc rten :

    Kann der Schubnachweis von ausbetonie l't en, bewehr-

    ten Mauerwerkstriigern so gefiJhrt werde"l , als handle

    es sich um einen KombinationsfaZl lion Stch Zb etcrn zmd

    bewehrtem Maue rwerk? Die Unters uchung bestand aus

    16 Balken, bei we lchen alle Testpal'aJilJ ter , ausgenom-

    men das Verhltnis von Schub spanYl1Jeite zup eff ekti ve"l

    Hohe, konstant gehalten uJurden. Der Beitrag bringt

    Einze lheiten des Ve .1''Buchsprogn:vI1mG !lnd zeigt, doss

    der Schubnachweis ausbetonierter !.J,werw9rks triiger

    tatschlich als KorrbiYl~tiansfaZZ von Stahlbeton

    bewehrtem Maw rwer'k betrachtet werden kann.

    DE SCHUIFSTERKTE VAN MET BETON GEI'ULDE

    GEW,4PENDE Mf:TSELWE8KLIGGERS

    De auteurs hebben een systematische experimente?e

    studie uitgevoerd om de vr'aag te beantw oor den. :

    kan de schuifsterkte van met beton gevu lde ge~pende

    metselwer'kliggers behandeZd worden als een geKomb?:-

    neerd geval van gewapend metse lwerk en geUlapend be-

    ton? Het onderzoek omvatte in totaal aestien lig-

    gers, ulaarin aUe testparameters met uitzondering

    van de veY'houding overspanning tot effaktieve hoogte

    konstant wel'den gehouden .

    De mededeling geeft details van het ondeY'zoeksprogram-

    ma en toont aan da t de berekening van schuifsf'amzingen

    deze liggers inderdaad moeten beschouwd wcrden als

    een kombinatie van gewapend beton Ziggers en Zigger s

    in gewapend metselwel'k .

  • INTRooUCTIoN

    Gr outed rei.nforced masonry (GRM) beams are genera lly bui 1 t up fro;;; two oro more wythes Df brickwork wi th cavi ties between the wythes; these cavities co nta in the reinf orcement and are filled with grout, the grout normally :::o,l sisting Df high slump pegrvel concrete p~u red OI' pumped into place , After hardening Df the concrete , t he grouted reinforced beam i5 considered as a com;Josite unit in which both the masonry Ivythes and the grouted c oncrete saction resist applied moments and sh ears. The shear design Df such members is generally bas ed on stresses which are identical to the case Df rei.nforce d masonry (RM) beams, i . e . members that do not contain a grouted section ; in Canada an allovJabl e at ress Df 0 . 7~:: 50 psi (0 . 35 N/mm 2 ) is specified for both types mof members , where f' denotes t he compressive strength Df the br ickwork . m

    A review Df the shear strength Df r einforced concrete (RC) and RM beams shows that a RC member exhibits a s hea r resistance wh ich is typically two to three times that Df a RM member . The question then arises : Is the shear resis tn ce Df a GRM beam significantly greater than that of a non -grouted RM beam and moreover, can this resistance be considered as the combined strength of the brick~o rk wy thes and the grouted section? Since little published evidence i s available on grouted beams 1 , a systematic experimental investi-gation was undertaken to answer this question o

    TEST PRoGRAM

    Ge neral

    To determine if the shear resistance of GRM beams is grea ter than that of RM beams and can also be treated as the combined shear strength of the brickwork wythes and the grouted conc rete section, three separate series of beam tests dealing with GRM , RM, and RC beams are requi red . Since r eliab l e published evidence on RC beams is available 2 , the test program described in this papeI' comp rised two beam series of GRM and RM beams . Each be am series consisted of eight beams as shovJn in Figure 1 . For a constant cross section con-taining a pe rc entage of reinforcement p Df abou t 1.4%, the only test va riable was the ratio of shear span to effective depth a/do The a/d ratio was selected as the single test variab le for the following reasons: the shear resistance of PC beams depends mainly on a/d and p , and to a minor degree on f ', the compressive strength 2 , , Si.nce the shear capgcity of RM beams is infl ue nced primarily by a/d and only to a negligible degree by p' , a / d is the one common key variable on which the shea r strangth of both RC and RM beams de-pends and r,ence can be assumed to have a major in-fluence also in the case of GRM beams . The a/d ratio was varied between 1 and 7; a f airly large p value of about 1 . 4% was selected to obtain pronounced shear failures.

    Test 8aem Oetails

    oetails Df the GRM and RM beams cros s sections are shown i n Figure 1. A two - point loading set - up was adopted for alI beam test s except beams 15 and 16 . 8eams 15 and 16 were tested unde r a central single point load to accommodate the se l ong beams in the testing machine. For the GRM beams , the width of the gr out cavity was chosen to ac commodate the steel and to provide space for the plac emen t of web reinforce-ment in a later investigation .

    ThroughOlJ t t he test progr em 3-corod bricks Df the type "Red Supertex " were used . IUthough the front face of the bricks WS roughly textured , the opposite face, which i n the case of GRM beams serves as the form for the grout, was relati vely smooth . The bricks had

    4 . c.2-1

    nominal dimensions of 203 x 95 x 75 mm and a specified comp ressive strerlgth Df 69 N/mm 2 Average crushing strengths were 92 and 33 N/mm~ for sing le bric ks and five course brick prisms, respectively .

    A 1 : 0 . 5 : 4 . 5 normal Portland cement:lime:sand mortar mix by volume was used in accordance with CanBdian re qu irements for GRM construction s . At the time Df beam testing , the average mortar strength was 14 . 7 N/mm 2 Oesign mortar joint thicknesses we re 22 mm for the first bed joint at the steel leveI and 10 mm for alI othe r joints. For the GRM beams , a grout mix of one part normal Portland cement to four parts sand was used . At the time of beam testing, average grout strength s of 15.1 and 27 . 5 N/mm 2 were obtained for 75 x 150 mm cylinders and 50 x 50 x 114 mm prisms , re-spectively . Since the prisms we re made by pouring the grout into a space formed by bricks and lined wi th permeable papeI' , the prism results reflect more close-ly the true grout strength in the beams .

    Steel reinforcement was furnished by 6-16 mm bars and 2-16 mm bars for the GRM and RM beam series, respec-tively . The average yield stress was determined as 445 N/mm 2 To prevent bond anchorage failure wh ich might obscure the true shear capacity of beams, 10 mm thick anchorage plates (100 x 100 mm for RM be ams and 100 x 305 mm for GRM beams) were welded tc the ends Df the reinforcing steel . This method obviated the need for large beam overhangs to provide sufficient a ncho r-age length .

    Manufactu re and Testing of 8eams

    A typical daily production consi sted of the manufac -ture of two baams Df equal a/d together with the associated contraI specimens for compression, mortar and grout st rength tests . For each type of control specimen , five samples were produced . The wo r \

  • 4 . c . 2- 2

    cross section approximates the cross sections of the author~' investigetion . Since Kani used p values of 0 . 8 and 1 . 88% rath e r than th e 1 . 41% of the GRM beams , l jnear lnterpolati on was 8n~loye d to ar r i v8 at the RC beam shear capaci ties shown in laole 1 for p = 1 . 41% . Altllough nis test pro~ram included three f ' val ues and his result s showed merely a minor dependen~e of shea r str8r1gth un f ', only t he 17 beams tests for f ' = 26 N/mm 2 are repres e nt~d in l ab le 1, 5ince tllis corlcrete s trengt h appr Cl xJ mates th e grout st rength of the GRM beams . Kani did not test beams with a n a/d value gr eat er t han 6 , hen ce U,e result for a/d = 7 in lable 1 denot es a shear strRngth ost imat ed by the authors .

    CracKing rnd Fai 1 ure Mo des

    Sinc8 th e naturc Bnd ex ten t of flexural and shear crackin