Experimental Investigation of Bond Characteristics of Deformed and Plain Bars in Low. Strength Concrete

Transcription

1 Experimental Investigation o Bond Charateristis o Deormed and Plain Bars in Low Strength Conrete Dr. Sohaib Ahmad (Corresponding Author) Ph.D, Dept. o Civil and Strutural Engineering, University o Sheield, United Kingdom Tel: +44 (0) Mobile: Fax: +44 (0) Postal Adress: Dept. o Civil and Strutural Engineering, University o Sheield, Sir Frederik Mappin Building, Mappin Street, S1 3JD, Sheield, United Kingdom address: sohaibahmad@hotmail.om Pro. Kypros Pilakoutas Proessor, Dept. o Civil and Strutural Engineering, University o Sheield, United Kingdom Tel: +44 (0) Mobile: Fax: +44 (0) Postal Adress: Dept. o Civil and Strutural Engineering, University o Sheield, Sir Frederik Mappin Building, Mappin Street, S1 3JD, Sheield, United Kingdom address:k.pilakoutas@sheield.a.uk Pro. Muhammad Masood Rai Proessor, Dept. o Civil Engineering, NED University o Engineering and Tehnology, Karahi, Pakistan, Telephone: +92 (21) Mobile: +92(0) Postal Adress: Dept. o Civil Engineering, NED University o Engineering and Tehnology, Karahi, Pakistan, address: rai-m@neduet.edu.pk Pro. Qaiser Uz Zaman Khan Proessor, Department o Civil Engineering, University o Engineering and Tehnology, Taxila, Pakistan address: dr.qaiser@uettaxila.edu.pk Tel: +92 (51) Mobile: +92(0) Fax number: +92 (51) Postal Adress: Department o Civil Engineering, University o Engineering and Tehnology, Taxila, Pakistan Kyriaos Neoleous Researh Fellow, Department o Civil and Geomatis Engineering, Cyprus University o Tehnology. Tel: +357 (0) Mobile: +357(0) Fax: +357 (0) Postal Adress: Faulty o Engineering and Tehnology, Department o Civil and Geomatis Engineering, Cyprus University o Tehnology. P.O.Box 50329, Lemesos address: kyriaos.neoleous@ut.a.y 1

2 Experimental Investigation o Bond Charateristis o Deormed and Plain Bars in Low Strength Conrete Abstrat The use o inerior quality materials, inadequate detailing and poor onstrution praties are responsible or most o the brittle ailure modes o non-engineered reinored onrete strutures. Bond ailures in non-engineered reinored onrete elements due to short anhorages or low onrete over result in large slip deormations prevent the development o plasti deormations and redue energy dissipation apaity. Until now, little work has been arried out that an lead to the development o bond-slip relationships or low strength non-engineered reinored onrete strutures. To address this, experiments have been arried out on pullout and splitting speimens under monotoni loading to investigate bond harateristis o typially used steel bars in nonengineered reinored onrete strutures. Various deiient parameters are onsidered in the experiments in order to develop multi-parameter bond strength relations or low strength onrete 15MPa. The key parameters examined in the experiments are low strength onrete, bar development length, onrete over, re-bar types (deormed and plain) and re-bar diameter. This paper presents the experimental details and results whih are urther proessed to develop bond strength equations or dierent bar types in low strength onrete. These equations an be used to deine the bond-slip relation or onduting seismi vulnerability assessment o non-engineered strutures. Keywords: Low strength onrete, normal strength onrete, non-engineered reinored onrete, Reinored Conrete, bond-slip, deormed bar, old-ormed bar, plain bar 1 Introdution Non-engineered reinored onrete (NERC) buildings in developing ountries are known to be highly vulnerable to seismi motion, Naseer et al. [1]. Post earthquake damage surveys rom developing ountries (Naseer et al. [1], Duranni et al. [2], Nisikawa et al. [3], Naseer et al. [1], Peiris et al.[4], Bal et al.[5]) attribute the poor perormane o reinored onrete (RC) strutures to the use o poor materials, bad design, detailing, and inappropriate onstrution praties [1-5]. Most o the ollapsed 2

3 RC strutures in the Kashmir earthquake (2005), Pakistan had an average onrete ompressive strength ( ) o around 15MPa. Bal et al. [5] tested ores taken rom 1178 existing RC buildings, loated in Istanbul and its surroundings, and reported a mean o 17MPa. It is widely aepted that Low Strength Conrete (LSC) is one o the main reasons or many brittle ailures in NERC. Even in developed ountries suh as Japan, post-earthquake studies ater the Kobe Earthquake in 1995, have reported many existing RC buildings to have very low onrete strength (less than 13.5MPa) whih is basis o researh or Hong and Araki [6]. Pullout and splitting was ommonly observed bond ailure modes during the Kashmir earthquake and beame one o the auses or brittle ailures in RC buildings as shown by Ahmad [7]. The re-bar slip in strutural omponents due to bond ailure are shematially shown in Fig. 1a-b. Moreover, reports by Chaudat et al. [8] and Pinho and Elanashai [9] regarding seismi testing o various low strength RC rames, designed aording to old odes or onstrution praties, has also shown that insuiient lap splies and bond degradation are the predominant ator or strength and stiness degradation o these strutures at higher peak ground aeleration levels. Pullout and splitting ailures depend on the shear and tensile strength o onrete, respetively. The tensile and shear strength o onrete have a strong orrelation to ompressive strength less than 10000psi (69MPa), ACI408[10]. The ore is mainly transerred by bearing against the lugs, whih either exeeds the onrete tensile or shearing strength ausing the ailure to our by tensile splitting or pullout (shearing o onrete), respetive1y. Splitting usually ours due to lower onrete over (<2d b ) and insuiient oninement, ACI408.2[11]. When the bar moves with respet to onrete, splitting ailure initiates due to the wedging ation o ribs. Splitting is normally the ritial bond ailure mode or RC buildings and its apaity is lower than or pullout or a given anhorage length. Bar pullout usually ours in elements with enough oninement. Bond perormane is also related to rib geometry and an inrease in rib height, generally inreases initial bond stiness and enhanes bond strength [10-11]. Transverse reinorement resists splitting ailure ater raking o a member espeially under yli loading and provides oninement whih results in pullout ailure. Casting position and improper ompation also aet the bond strength [11]. 3

4 The problem o improper ompation is quite signiiant in poorly onstruted RC strutures, where the voids and water pokets are ormed due to plasti low o onrete [11]. The bond-slip (τ-s) behaviour o dierent bar types used typially in LSC has not been studied muh and past vulnerability assessment studies by Kyriakides (2008) [12] had to assume that the τ-s behaviour o re-bars in LSC is similar to that o Normal Strength Conrete (NSC). Only a ew studies examined this behaviour; or example, Mohamad [13] onduted pullout tests on extremely LSC speimens (200x300x300mm speimens with links and ~ 5MPa) to evaluate the o both top and bottom ast deormed and plain bars with varying over () to bar diameter (d b ) ratios. The typial LSC range or NERC buildings (10-15MPa) was not onsidered, Feldman [14] arried out pullout tests using 16 and 32mm d b plain bars in LSC (12 to 14MPa) to evaluate the τ-s harateristis o plain bars with dierent roughness levels. Experimental results showed an average slip value o 0.01mm at. The reported average value o ranges between 0.98 to 2.2MPa or dierent roughness levels. The eet o smaller over, shorter development lengths and other bar types on τ-s behaviour was not studied. More reently, Bedirhanoglu [15] arried out yli tests on 9 exterior beam-olumn joints made o LSC onrete (<10MPa) using plain bars. The mean was ound to be between 0.33 and 0.5 MPa. Hong and Araki [6] onduted pull-out tests under load reversal to study the bond harateristis o plain round bars having 13,19mm diameter and embedment length o 10d b in LSC (11.2MPa). The imum bond stresses o the speimens were less than the allowable stress in RC Codes o Japan Arhitetural Institute or the long term load, and that the degradations o bond stress were apparently ound to be inluened by the loading yles. The average bond strength value was 0.33MPa and 0.32MPa or 13 and 19mm d b, respetively. This main aim o onduting urrent researh work is to investigate the bond harateristis o typially used steel bars in NERC/ existing RC strutures by onsidering various deiient parameters and to develop bond strength relations or low strength onrete 15MPa. Previous researhes did not aount or the onsidered deiient parameters and provide multivariable bond strength equation or low strength onrete <15MPa. This paper initially presents the results o experiments undertaken on 4

5 pullout and splitting speimens. The main parameters o the study inluded low strength onrete, rebar type, diameter, onrete over and embedment length. The statistial variation o the experimental data is presented and the bond perormane o dierent bar types is disussed. The paper inally presents development o bond strength models or dierent bar types in LSC by using the urrent experimental data 2 Experimental Programme The experimental programme is planned to study pullout and splitting bond ailure modes in LSC under monotoni loading. This experimental work is part o researh work onduted by Ahmad[16], Ahmad et al.[17] or development o analytial seismi vulnerability assessment ramework or reinored onrete strutures in developing ountries. All the tested speimens were unonined and made rom plain onrete. The main parameters inluded LSC (~ 15MPa), bar development length (L d ), onrete over (), rebar type and diameter (d b ). Pullout and splitting tests have been onduted in a speially designed rig. The pullout and splitting experiments are designed so as to inlude the eet o dierent deiient parameters observed in the post-kashmir earthquake surveys and are more important or bond-slip o reinorement behaviour in RC strutures o developing ountries. Most ommon steel bars types used in old and new onstrution o RC strutures in Pakistan are used in experiments. Low strength onrete mix design is used to prepare pullout and splitting speimens. These speimens having varying development lengths, over, bar type and sizes are tested in testing setup. Mehanial properties o dierent steel bars and the LSC used are desribed in the ollowing setion. 2.1 Steel bars Two dierent types o steel bars were used in the experimental programme, with dierent surae deormations and diameter. These bars were: 1- hot-rolled deormed (de.) 2- plain. The mehanial harateristis o the dierent types o steel bars are presented in Tables 1. Table 2 gives the rib details o the deormed bar used in the tests and the bar pattern is also shown shematially in Fig. 2. 5

6 2.2 Conrete Sine the onrete ompressive strength or the majority o NERC strutures alls between 8 and 15MPa, the LSC mix proportions mentioned in Table 3 were used to ast all the pullout and splitting speimens. The ompressive strength was determined aording to BS [18] by asting 100mm x 200mm ylinders rom the mix. Indiret splitting tests in aordane with BS:EN [19] were also arried out to evaluate the tensile strength o onrete speimens. The mean (µ) and (σ) standard deviation values o mean and t o the pullout and splitting speimens are listed in Tables Test arrangement The test set-up inluding test rig and instrumentation used or onduting pullout and splitting tests is shown shematially in Fig. 3a. A 10mm rubber plate was plaed on the speimen s top ae to ensure an even pressure and minimum oninement on the onrete surae. The reation plate o the rig has appropriate holes, so that the LVDT s an pass through. A mounting rig was used or holding two LVDTs (or the splitting tests) or three LVDTs (or the pull-out tests) at the loaded end (L.E) o the speimen and the mounting rig was lamped with srews on the bar (see Fig. 3b). A small metal (aluminum) angle was glued on the unloaded end (U.L.E) o eah speimen to mount an LVDT. This transduer was positioned at the entre o the bar and was used to measure unloaded end slip. This arrangement orresponds to RILEM/CEB/FIP [20] in whih the bonded length is loated at the end o the speimen to avoid onial ailures near loaded end. An example o pullout and splitting speimen in testing rig is shown in Fig. 3 and Fig 3d, respetively. 2.4 Speimen details or pullout and splitting tests Pull out tests Pullout ube speimens with two bar types and three dierent development lengths, 5d b, 10d b, 15d b, were tested. The details o the bar size, type, speimen size and embedment lengths used or making pullout speimens are shown in Fig. 4a and Fig. 5a. For L d more than 150mm, 150mm (diameter) x 300mm (height) ylinders were used. A ubi and ylinder pullout speimens are shown in Fig. 4 b and 6

7 5 b, respetively. Bars were debonded with two layers o ling ilm and PVC tape to ahieve the desired embedment length. The bars were ut to 500mm to it the testing apparatus. To measure the loaded end slip or pullout speimens, three transduers were plaed in a radius o 50mm rom the entre o the bar. These transduers were mounted on a small rig at an angle o 120 degree rom eah other. The shemati arrangement o the LVDTs positioned over the speimen surae is shown in Fig. 6 All the tests were displaement ontrolled and the displaement rate was set to 0.5mm/min. The LVDTs used had a imum range o 10mm and the data reord was stopped when the slip reahed between 8 and 10mm. The bar was then pulled out ompletely at a aster rate. A typial rebar ater pullout is shown in Fig Splitting tests In the splitting test speimens, bars were positioned eentrially using varying onrete overs, (i.e. = 0d b, 1d b, 2d b ) with reerene to the onrete edge as shown in Fig. 8 a and b to ahieve splitting ailure mode. The embedment length in all the splitting speimens was 5d b and the speimens were ast up to the same height. The bars were ut to 500mm to it the testing apparatus. The average o the displaements rom three transduers was used to eliminate possible bending o the bar. The loaded and unloaded end slip or the splitting speimens having = 2d b, was measured using the same LVDT arrangement as used or pullout tests (Fig. 6) whereas loaded end slips or the speimens having = 0d b, 1d b were measured by making a 2 point arrangement o the LVDT s at the loaded end, as shown in Fig. 9 a and 9b. This arrangement was neessary due to lak o spae or third LVDT. The splitting speimens with varying onrete over ater splitting are shown in Fig. 10a-10, respetively. 3 Experimental Results Representative results or the deormed and plain bar pullout speimens, having d b =12mm, L d = 5d b are shown in Fig. 11 a and 11b. U.L.E. and L.E. represent the un-loaded and loaded end bond-slip 7

8 urves, respetively. The L.E. slip values are determined rom the average slip measurements, taken by either 2 or 3 LVDTs, minus the alulated extension o the bar outside the embedment length. The deormed bars in general showed low bond strength or onrete with < 10MPa. For plain bars, the slip orresponding to bond strength is very low and the load-slip urve deays gradually. Typial results or the deormed and plain bars splitting speimens having d b =12mm, L d = 5d b and =0-2d b are shown in Fig. 12a and 12b, respetively. The value o =0 represents extremely small onrete over and pratially represents exposed reinorement ondition in beams or olumns typially observed in developing ountries due to poor onstrution praties. Deormed bar split speimens with extremely small over showed a very low at a small slip value. The bond strength inreased by almost our times or urves =1 and 2d b (Fig. 12a). For plain bar split speimens (d b =12mm), splitting did not our in all ases. A ew speimens with =0 and =1d b showed brittle behaviour, but most o the speimens espeially with over 1 and 2d b showed a gradual deay o the load slip urve, as shown in Fig. 12b. 4 Diret omparison and statistial analysis (Part-1 Pullout speimens) A summary o results o tests along-with the average results or eah set o variables is presented in Table 5. The onrete strength eet on bond is traditionally taken into aount by normalizing with respet to. This use o or normalization has been proved to be eetive up to onrete strengths o 55MPa (ACI408 (2003)). The bar hart in Fig. 13 shows the mean values o or deormed and plain bar speimens with dierent development lengths. 4.1 Bond strength satter or pullout speimens Fig. 14a shows the results o pullout tests or the speimens with 12 and 16mm diameter deormed bars and L d =5d b. All these speimens had a low onrete strength (~10 to 15MPa). Bond strength o 8

9 speimens having onrete strength o around 10MPa is ound to be almost hal the bond strength o speimens with relatively higher onrete strength (~15-20MPa).The ailure o most speimens with L d =10 and 15d b was either due to bar yielding or onrete splitting. For plain bars, a lower variation an be seen (Fig. 14b) in the results as ompared to the deormed bars (Fig. 14a). As expeted an overall redution in normalized is evident with larger L d. 5 Diret omparisons and statistial analysis (Part-2 Splitting speimens) Table 6 presents a summary o results o splitting tests and the bar hart in Fig. 15 shows the mean value o or speimens tested or the splitting ailure mode. This inludes 13 and 17mm de. and 12 and 16mm plain bars having L d = 5d b and varying onrete over. 5.1 Bond strength satter or split speimens Fig. 16a shows that or /d b = 0, the normalized value or both diameters o deormed bar is signiiantly lower than or /d b = 1 and 2, whih highlights the severity o the problem when proper over is not maintained. In general, the splitting strength inreases rom /d b = 1 to 2 or both bar sizes. Nonetheless, the 16mm bar shows lower results than the 12mm bar whih indiates that bar diameter also aets the splitting strength. No splitting was observed in the plain bar speimens whih means that bar roughness is the dominant ator that mobilizes the rition between the bar and the onrete to give bond strength. As a result a lower variability is obtained in the results o plain bars (Fig. 16b). However, the value o normalized or the plain bars learly inreases with the inrease o /d b ratio or both 12 and 16mm diameter as shown in Fig. 16b. This means the over thikness leads to inreased oninement and as a result inreased ritional resistane. 9

10 6 Development o bond strength relation Multivariable nonlinear regression analysis is used to develop models by using suitable summation untion or both pullout and splitting ailure modes. Variables suh as onrete ompressive strength ( inluded in the ), development length (L d ), over (), diameter (d b ) and bar type are models. Orangun et al. [21] summation untion oers the best hoie or use as an input untion in the nonlinear regression analysis, sine it inludes all the important variables that were onsidered in the experimental work arried out by the authors. This untion an be alibrated to give a equation or both pullout and splitting bond ailure modes. The general orm o the seleted input untions or Orangun et al. [21] is given in Eq. (1). Y ) D ( A Bw Cx z Eq. (1) Where; A, B, C and D are the parameter values determined through alibration, Y is the dependant variable and w, x, and z are the independent variables. 6.1 Regression analysis o experimental data equations or deormed bar pullout/splitting ailure mode in LSC For evaluating a general equation or the pullout and splitting ailure mode o deormed bars, Eq. (1) was alibrated by onduting nonlinear regression analysis using the urrent experimental data and the derived new parameter values are given in Eq. (2). An additional dataset whih were seleted rom a report by Darwin et al [22] in whih an extended database rom dierent studies was used to develop an expression or evaluating the splie strength and development length without onsidering the eet o transverse reinorement. The speimens with onrete strength ranging between 15 and 21MPa were extrated rom eah dataset. The predominant ailure mode in all these test data was splitting and the beams were tested to evaluate the bond strength onsidering dierent parameters. It was observed rom the data that large bar diameter 10

11 and embedment lengths were used almost in all the speimens exept or the Tepers[23] dataset whih inludes speimens with bar diameters 12, 16 and 19mm. Moreover, /d b in the majority o the tests varied between 1 and 2 with very ew speimens having /d b ratio > 2. Due to the variability in the experimental data rom dierent soures, the error between predited and experimental values is assumed to be normally distributed and an unertainty ator in aordane with ±1σ was evaluated. The resulting equation is given in Eq. (2) with an unertainty ator o ±2.1 MPa d b d 3.22 L b d 2.1 R 2 =0.72 (MPa) Eq. (2) The bond strength preditions (, pred. ) rom Eq. (2) are ompared with the experimental bond strength values (, exp ) in Fig. 17a. The upper and lower bound has been set to ± 1σ MPa to assess the perentage o data above and below this range. It was ound that 15% o the data were out o this range. The requeny o ratio /, pred., exp For Eq. (2), a larger perentage ratio o ratios as a perentage o the total data is shown in Fig. 17b. pred was ound to be lose to one as /,., exp shown in Fig. 17b equation or plain bar pullout/splitting ailure mode Eq. (1) was urther alibrated or plain bars and the resulting equation is given as Eq. (3). The unertainty ator or this equation is alulated to be ± d b d L b d 0.96 R 2 =0.69 (MPa) Eq. (3) The preditions rom Eq. (3) are ompared with the experimental data in Fig. 17. The requeny o the ratio, pred /, exp as a perentage o total data is shown in Fig. 17d. 19% data was ound to be out o the set bound or the plain bar bond strength. In the urrent study the onrete strength power ator o 0.68 and 0.5 are evaluated or deormed, old ormed and plain bar. This suggests large dependeny o onrete strength on bond strength or deormed and old ormed bars as ompare to plain bars. In Orungun et al. Bond strength equation, 11

12 is normalized with respet to to represent the eet o (or the tensile strength) on the bond strength. However, Zuo and Darwin [24] suggested that normalization using overestimates bond strength or the HSC and underestimates bond strength or NSC. 1/ 4 was ound to have better orrelation with bond strength or all ranges o onrete strength. 7 Conlusions Due to large number o NERC strutures in the building stok o developing ountries, it is important to investigate eet o dierent deiient parameters on bond harateristis or more reliable seismi vulnerability assessment. a. Among the investigated parameters, low strength onrete and onrete over have more inluene on the bond strength. For the deormed bar speimens with onrete strength o around 10MPa, the pullout bond strength (1.98MPa) is almost hal the bond strength o speimens with relatively higher onrete strength (15-20MPa). Hene, NERC strutures with onrete strength o around 10MPa are expeted to have larger slip deormations and brittle ailures due to lower bond strength. b. The speimens with very small over (i.e. =0) whih is an exposed bar ondition, have very low splitting bond strength (0.46Mpa) and indiates high vulnerability o inerior quality strutures with exposed bars.. The plain bars did not show evidene o splitting in most o the speimens. However, the over still appears to have eet due to the additional oninement. Nonetheless, plain bars ail at a lower strength and have inerior post peak harateristis. d. The data rom this experimental study are used to develop the bond strength models or dierent bar types in LSC. The bond strength models rom the summation equations are thereore proposed, or predition both the splitting and pull-out behaviour o low strength strutures. The summation untion aounts or all the studied parameters and the bond 12

13 strength or pullout and splitting bond ailure modes is predited reasonably well using the developed equation. These equations an also be used in deining the τ-s behaviour. e. The higher power ator o 0.68 or onrete strength are evaluated or deormed bars as ompare traditional value o 0.5. This indiates larger inluene o low strength onrete on bond strength o deormed as ompare to normal and high strength onrete. Aknowledgement The irst author aknowledges the inanial support provided by the Higher Eduation Commission (HEC), Pakistan, to ondut this researh as a part o his Ph.D work, whih developed an analytial seismi vulnerability assessment ramework or reinored onrete strutures in developing ountries. Reerenes [1] Naseer, A. Ali, S.M. and Hussain, Z. Reonnaissane report on the 8th Otober, 2005 earthquake Pakistan, Earthquake Engineering Centre, Department o Civil Engineering NWFP UET Peshawar, Pakistan (2006). [2] Duranni, A.J. Elnashai, A.S. Hashash, Y.M.A. Kim and S.J. Masud A The Kashmir Earthquake o Otober 8, 2005, A quik look report Mid- Ameria Earthquake Center. University o Illinois at Urbana-Champaign (2005). [3] Nisikawa, T. Nakano, Y. Tsuhiya, Y. Sanada, Y. and Sameshima, H. Quik report o damage investigation on buildings and houses due to Otober 8, 2005 Pakistan earthquake. Japan Soiety o Civil Engineers (JSCE) and Arhitetural Institute o Japan (AIJ) (2005). [4] Peiris, N. Rossetto, T. Burton, P. and Mahmood, S EEFIT Mission: Otober 8, 2005 Kashmir Earthquake (2005). [5] Bal, I.E. Crowley, H. Pinho, R.F. and Gulay, F.G. "Detailed assessment o strutural harateristis o Turkish RC building stok or loss assessment models". Soil Dynamis and Earthquake Engineering, 28(10), pp (2008). [6] Hong and Araki "Bond harateristis between low strength onrete and plain round bar under reversal loading", 15 th WCEE, Lisboa (2012) 13

14 [7] Ahmad, S. "Assessment o damages aused to strutures due to Otober 8th, 2005 Kashmir Earthquake, Pakistan", The University o Sheield (2007). [8] Chaudat, T. Garnier, C. Cveji, S. Poupin, S. LeCorre, M. and Mahe, M. "Seismi tests on a reinored onrete bare rame with FRP retroitting-tests report eoleader projet no 2" (2005). [9] Pinho, R. and Elnashai, A.S. "Dynami ollapse testing o ull sale our storey RC rame". ISET Journal o Earthquake Tehnology Paper No. 406, 37(4), pp (2000) [10] ACI408R-03 "Bond and development o straight reinoring bars in tension", Amerian Conrete Institute (2003). [11] ACI408.2 "Bond under yli loading". Tehnial report. Amerian Conrete Institute (2005). [12] Kyriakides, N. "Seismi vulnerability assessment o RC buildings and risk assessment or Cyprus" The University o Sheield (2008). [13] Mohamad, A.Z. and Clark, L.A. "Bond behaviour o low-strength onrete". Mangzine o Conrete Researh, 44 (160), pp (1992). [14] Feldman, L.R. and Bartlett, F.M. "Bond strength variability in pullout speimens with plain reinorement" ACI Strutural Journal, 102(6), pp (2005). [15] Bedirhanoglu, L. Iiki, A. Pujol, S. and Kumbassar, N. "Behaviour o deiient joints with plain bars and low strength onrete. ACI Strutural Journal, 107 (3). (2010) [16] Ahmad, S. "Seismi vulnerability o non-dutile reinored onrete strutures in developing ountries" Ph.D Thesis, The University o Sheield, U.K. (2011). [17] Ahmad,S. Rai, M.M. Pilakoutas, K. Khan, Q.U.Z, Shabbir, F. and Tahir M.F. "Bond-slip Behaviour o steel bars in low-strength onrete", Institute o Civil Engineers, Strutures and Buildings, 169(SB7), (2016). [18] BS "Testing onrete -Part 121: Method or determination o stati modulus o elastiity in ompression"(1983). [19] BS:EN "Testing hardened onrete -Part 6: tensile splitting strength o test speimens"(2000). 14

15 [20] RILEM/CEB/FIP (1978) Reommendation RC 6 "Bond test or reinoring steel : Pullout test". [21] Orangun, C. O., Jirsa, J. O. and Breen, J. E. "The strength o anhored bars: a re-evaluation o test data on development length and splies", Researh Report No.154-3F, Center For Highway Researh,. The University O Texas At Austin (1975). [22] Darwin, D., Mabe, S. L., Idun, E. K. and Shoenekase, S. P. "Development length riteria: bars without transverse reinorement" The Civil Engineering Researh Foundation Contrat No 91-N6002" The National Siene Foundation, Researh Grant No. MSM ,.The Reinored Conrete Researh Counil, Projet 56. (1992). [23] Tepers, R. "A theory o bond applied to overlapped tensile reinorement splies or deormed bars". Publ 73:2. Division o Conrete Strutures, Chalmers University o Tehnology, Göteborg, May 1973, p Doktorsavhandling (1973). [24] Zuo, J. and Darwin, D. "Splie strength o onventional and high relative rib area bars in normal and high-strength onrete" ACI Strutural Journal, 97 (4), (2000). List o Figures Fig. 1 Bond related damages and detailing deiienies a) Bar pullout b) Short lap splie Fig. 2 Shemati diagrams o dierent bars with rib patterns Fig. 3 Test setup adopted or experiments: a) ross-setional view o pull-out rig with speimen and instrumentation, b) smaller mounting rig with LVDTs at loaded end, ) rig or splitting tests, d) side splitting o plain bar speimen Fig. 4 Pullout ube speimens with varying bar sizes, types and embedment lengths Fig. 5 Pullout ylinder speimens with varying bar sizes, types and embedment lengths Fig. 6 LVDTs arrangement in rig at the loaded end (pullout test) Fig 7 Steel reinoring bar ater pullout test Fig. 8 Splitting speimens with varying overs (= 0d b, 1d b, 2d b ) 15

16 Fig. 9 a and b Loaded and unloaded end slip measurement (splitting tests) Fig 10 a- Splitting speimen with dierent ailure modes Fig. 11 Typial bond-slip urves rom pullout tests a) 12mm deormed b) 12mm plain Fig. 12 Typial bond-slip urves rom splitting tests a) Deormed (=0, 1, 2d b ) b) Plain (=0, 1, 2d b ) Fig. 13 Mean normalized o dierent bar types and sizes (Pullout speimens) Fig. 14 Normalized at dierent development lengths or dierent bar types and sizes a) Deormed b) Plain (Pullout speimens) Fig. 15 Mean normalized speimens) o dierent bars types and sizes with varying over (Splitting Fig. 16 Normalized o dierent bar types with varying over a) Deormed b) Plain (Splitting speimens) Fig. 17 Assessment o dierent bars bond strength model a) Satter between deormed bar experimental and predited results b) % Frequeny o deormed bar normalized data ) Satter between plain bar experimental and predited results d) % Frequeny o plain bar normalized data. List o Tables Table 1: Mehanial properties o bars Table 2: Rib details o deormed bars Table 3: Details o the various mixes used or making LSC Table 4: Mean ompressive and tensile onrete strength or pullout and splitting speimens Table 5: Summary o the pullout tests using averages or eah set o variables Table 6: Summary o the splitting tests using averages or eah set o variables 16

17 (a) Fig.1 Bond related damages and detailing deiienies a) Bar pullout b) Short lap splie (b) (a) (b) () Fig.3 Test setup adopted or experiments: a) ross-setional view o pull-out rig with speimen and instrumentation, b) smaller mounting rig with LVDTs at loaded end, ) pullout speimen testing, d) splitting speimen testing (d) 17

18 (a) Fig. 4 Pullout ube speimens with varying bar sizes, types and embedment lengths (b) (a) Fig. 5 Pullout ylinder speimens with varying bar sizes, types and embedment lengths (b) Fig. 6 LVDTs arrangement in rig at the loaded end (pullout test) 18

19 Fig.7 Steel reinoring bar ater pullout test (a) Fig. 8 a and b Splitting speimens with varying overs (= 0d b, 1d b, 2d b ) (b) 19

20 / 1/2 (MPa) / 1/2 (MPa) (a) Fig. 9 a and b Loaded and unloaded end slip measurement (splitting tests) (b) (a) (b) () Fig. 10 a- Splitting speimen with dierent ailure modes a) V-noth splitting =1d b b) Exposed bar =0d b ) Side splitting =1d b mm de. L d =5d b, =12MPa U.L.E. L.E mm plain L d =5d b U.L.E. L.E Slip (mm) Slip (mm) (a) Fig.11 Typial bond-slip urves rom pullout tests a) 12mm deormed b) 12mm plain (b) 20

21 / 1/2 (MPa) / 1/2 (MPa) mm de. =0,1,2d b mm plain =0,1,2d b U.L.E. =0d b U.L.E. =0d b 2 L.E. =0d b U.L.E. =1d b 2 L.E. =0d b U.L.E. =1d b L.E. =1d b L.E. =1d b 1.5 U.L.E. =2d b 1.5 U.L.E. =2d b L.E. =2d b L.E. =2d b Slip (mm) Slip (mm) (a) Fig.12 Typial bond-slip urves rom splitting tests a) Deormed (=0, 1, 2d b ) b) Plain (=0, 1, 2d b ) (b) L d =5d b L d =10d b L d =15d b / 1/ de.12mm de.16mm plain12mm plain16mm Fig.13 Mean normalized o dierent bar types and sizes (Pullout speimens) mm de., =15MPa 12mm de., =10MPa 16mm de mm plain 16mm plain / 1/ / 1/ L d (mm) L d (mm) (a) (b) Fig.14 Normalized at dierent development lengths or dierent bar types and sizes a) Deormed b) Plain (Pullout speimens) 21

22 =2d b =1d b =0d b / 1/ de.12mm de.16mm plain12mm plain16mm Fig.15 Mean normalized Speimens) o dierent bars types and sizes with varying over (Splitting mm de. 16mm de mm plain 16mm plain / 1/2 1 / 1/2,pred. (MPa) %Frequeny /d b Fig.16 Normalized Speimens) (a) (b) o dierent bar types with varying over a) Deormed b) Plain (Splitting /d b Extended dataset ,exp (MPa) (a) /,pred.,exp (b) 22

23 ,pred. (MPa) %Frequeny Current dataset ,exp (MPa) /,pred.,exp () Fig. 17 Assessment o dierent bars bond strength model a) Satter between deormed bar experimental and predited results b) % Frequeny o deormed bar normalized ) Satter between plain bar normalized data. (d) experimental and predited results d) % Frequeny o plain bar Table 1 Mehanial properties o bars Bar type Bar diameter Youngs modulus Yield strength Ultimate strength Strain at yielding Ultimate strain (mm) (GPa) (MPa) (MPa) % % De De Plain Plain Table 2 Rib details o deormed bars Bar diameter Rib spaing(s) Rib height(h) (mm) (mm) (mm) Table 3 Details o the various mixes used or making LSC C S A w/ C:S:A Curing kg/m 3 kg/m 3 kg/m 3 days :2:3.8 5 Table 4 Mean ompressive and tensile onrete strength or pullout and splitting speimens 23

24 University, σ t, σ (MPa) (MPa) (MPa) (MPa) UoS (Pull and splitting) Table 5 Summary o the pullout tests using averages or eah set o variables d b Bar type L d *n µ µ σ COV mm mm MPa MPa MPa MPa De De De De De De De De De plain plain plain plain plain plain *n is the number o tested speimens Table 6 Summary o the splitting tests using averages or eah set o variables d b Bar type over /d b n µ σ COV mm mm MPa MPa MPa 1/2 MPa 1/ De De De De De De plain plain plain plain plain plain Nomenlature and Abbreviations E s modulus o elastiity o steel onrete ompressive strength 24

25 t onrete tensile strength bond strength L d development length onrete over d b bar diameter h rib height o re-bar s rib spaing o re-bar µ mean σ standard deviation LSC Low Strength Conrete NERC Non-Engineered Reinored Conrete RC Reinored Conrete Tehnial Biography o Authors 1. Sohaib Ahmad, B.S. Civil Eng., UET, Lahore, Pakistan, M.S. Eng. (Strutures), KAIST, South Korea, Ph.D. (Strutures), The University o Sheield, U.K. Dr. Ahmad has over 14 years o diverse ivil/strutural engineering and researh experiene. Dr. Ahmad is experiened in strutural analysis and design o ommerial and speialized industrial buildings. He has also done several assignments related to analytial and empirial seismi re-evaluation / saety assessment and retroitting o existing strutures. Moreover design reviews, ondition assessment, visual inspetions and retroitting works have been done by him. Dr. Ahmad s Ph. D is related to development o probabilisti analytial ramework or seismi vulnerability assessment o low strength reinored onrete strutures o developing ountries. He has several publiations in reputed international journals and has presented researh papers, posters in various onerenes. He has done a ellowship in seismi saety assessment o strutures, systems and omponents (SSC s). He has supervised / o-supervised several researh thesis at Masters and Ph.D level in dierent engineering universities. He is member o Researh Management Committee or PhD students at UET Taxila, Pakistan or evaluation o researh work. He is prinipal investigator or dierent projets. His researh interests inlude onrete material, seismi ragility and risk analysis o buildings and bridges, seismi retroitting using FRP, strutural health monitoring, aging o strutures. He also has won various awards 2. Kypros Pilakoutas, BS(Eng) University o London, ACGI Imperial College, DIC Imperial College, PhD University o London, DS(Eng Pro. Kypros Pilakoutas is the Proessor o Constrution Innovation in the Department o Civil and Strutural Engineering at The University o Sheield, U.K.. He is the Manager o the Centre or Cement and Conrete and the Chairman o the Conrete and Earthquake Engineering Researh Group. Pro Pilakoutas is the Departmental Commerialization Champion and is a Diretor o two tehnology spin-out ompanies. He has vast experiene in managing European Researh Networks and has had more than 10 EU grants. He has a large number o international ontats and 25

26 leads or partiipates in several international ommittees in his researh ields. Pro Pilakoutas was reently awarded an EU FP6 grant o 1,700,000 to investigate "Eonomial and Sustainable Pavement Inrastruture or Surae Transport". He has over 30 patents awarded worldwide. Two o his patents are ommerially exploited worldwide. Two more patents appliations have been made in the ield o using wire rom reyled tyres as reinorement. His researh is in the ields o strutural onrete, FRP and ibre reinorement, repair, onstrution innovation and earthquake engineering. Proessor Kypros has various publiations in well reputed international journals. He also has won various awards and honors. 3. Muhammad Masood Rai, BS(Eng) NED University, Karahi, Pakistan, M S Strutural Engineering, NED University, Ph.D, Strutural Engineering, University o Ulster Pro Rai is the Chairman o Department o Earthquake Engineering. He hairs the Board o Studies o the Department. In addition, he ontributes to the various University bodies. Pro Rai is partiularly interested in the internal appliations o Fibre Reinored Polymer (FRP) bars both at ambient and high temperatures. His urrent researh interests inlude behaviour o FRP reinored onrete strutures, inite element analysis o RC strutures, ire resistane o onrete strutures, deletion o onrete strutures, experimental analysis o RC strutures, reyling o onrete and seismi analysis and retroitting o reinored onrete and masonry strutures. Pro Rai is the Editor-in-Chie o the NED University Journal o Researh. He is also a member o the Editorial Board o Journal o Strutural Fire Engineering. Pro Rai regularly reerees tehnial papers or a number o alaimed international journals. Proessor Rai has various publiations in well reputed international journals. He also has won various awards and honors. 4. Dr. Qaiser Uz Zaman Khan, B.S. Civil Eng., UET, Lahore, Pakistan, M.S. Eng. (Strutures), University o Leeds, United Kingdom, Ph.D. (Strutures), Saitama University, Japan Pro. Qaiser has diverse researh and aademi experiene and has worked in various apaities (teahing, researh, laboratory, administration, onsultant et.) in department o Civil Engineering, UET Taxila. He is also member o various tehnial ommittees. His researh interests inlude onrete material, seismi ragility and risk analysis o buildings and bridges, seismi retroitting using FRP, strutural health monitoring. Proessor Qaiser has various publiations in well reputed international journals. He also has won various awards and honors. Kyriaos Neoleous, Ph.D, The University o Sheield, U.K. Dr. Kyriaos Neoleous is a researher at the Department o Civil and Geomatis Engineering o the Cyprus University o Tehnology. He has more than 12 years o researh experiene in the ield o strutural engineering, strutural onrete, novel onrete reinorements as well as testing tehniques or onrete and reinorement. Previous he held the position o Senior Researh Fellow at The University o Sheield, U.K. Dr. Neoleous has various publiations in well reputed international journals. He also has won various awards and honors. 26