serviceability limit states, bar anchorages and lap lengths in aci 318-08 and bs 8110-97...

8/14/2019 Serviceability Limit states, Bar anchorages and Lap lengths in ACI 318-08 and BS 8110-97 -Comparative Study-ICJ-

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29NOVEMBER 2013 THE INDIAN CONCRETE JOURNAL

Point of View

Serviceability, limit state, bar anchorage and lap lengthsin ACI318:08 and BS8110:97: A comparative study

Ali S. Alnuaimi and Iqbal Y. Patel

This paper presents a comparative calculation studyof the deection, control of crack width, bar anchorageand lap lengths of reinforced concrete beams using theACI 318 and BS 8110 codes. The predicted deectionsby the ACI code were larger than those by the BS. Inboth the codes, the short-term deflection decreaseswith the increase in the dead-to-live load ratio but thelong-term deection increases. In addition, the limits onthe maximum bar spacing to control crack width varysignicantly in the two codes. While the BS code predictsa constant bar spacing regardless of the concrete cover,the ACI reduces it with the increase in cover thickness. Inboth codes, the tension anchorage length decreases withthe increase in concrete strength. The tension anchorageand lap lengths vary with the values of the term

. The BS code requires a greater anchoragelength in compression than the ACI code does. Thecompression lap length requirement in the BS is morethan that in ACI code for the concrete of compressive

strength less than 37 MPa and the former stipulateslonger lap lengths for higher concrete strengths.

In the absence of a national design code, the structuralengineers in Oman use the ACI 318 and BS 8110structural design codes to calculate deections, crack

width, and anchorage and lap lengths.1,2 They nd thesecodes useful for complying with the legal stipulationsthere. However, designers and project owners frequentlycompare the stipulations in the two codes seeking pointsof similarities and differences. Yet, no comprehensivework of this kind is available in literature, thoughseveral researchers have used these codes for estimatingdeection, crack control and lap length developmentin reinforced concrete constructions. The followinghighlights the ndings of select researchers.

Nayak and Menon, conducted experimental investigationon six one-way slabs, monitored their short-termdeection and compared the existing provisions givenin IS 456:00, BS 8110, ACI 318 and Euro-code 2 withthe experimental results.3,4,5They found considerabledisparities among the three codes. The AC I318 and EuroCode 2 generally predicted acceptable deection at theleast and largest deection points respectively whereasthe BS and IS codes gave an acceptable intermediate

value. Santhi et alcompared the total deection includingthe creep and shrinkage for a two-way slab using ACI318:00, BS 8110:97 and IS 456:00 and found that the totaldeection based on ACI 318:00 and BS 8110:97 werealmost similar for the different slab thicknesses studiedwhile the IS 456:00 gave much larger deection in mostof the cases.6


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THE INDIAN CONCRETE JOURNAL NOVEMBER 201330

Point of View

Bacinskas et al statistically investigated the accuracyof the long-term deection predictions made by thevarious design codes including Eurocode 2, ACI 318,ACI 435, SP 52-101 and the exural layered deformationmodel proposed by Kaklauskas.7,8They found that theEurocode 2 overestimates the long-term deection whileACI 318 and ACI 435 underestimate it. The SP 52-101

slightly overestimates the deection and has the loweststandard deviation among the various code methodsstudied. Lee and Scanlon conducted parametric studyon the control of deection of reinforced concrete slabs,and compared the various design provisions in the ACI318:08, BS 8110:97, Euro-code 2 and AS 3600:01.9,10Theyconcluded that although the minimum thickness valuesare easy to apply, limitations need to be placed on theapplicability of current ACI 318:08 values due to theassumption that the slab thickness is independent ofapplied dead and live loads and no limits are speciedon the applicable range of span lengths. They proposed aunied equation. Bischoff and Scanlon came to a similar

conclusion.11

Bacinskas et aldeveloped a model for calculating thelong-term deection of cracked reinforced concretebeams considering creep, shrinkage and the tension-stiffening.12 They compared the ACI 318 and Eurocode2 provisions with 322 experimental results. Their ndingwas that the deections predicted by the ACI 318 werestrongly dependent on the loading duration but theresults had high variations. However, the predicteddeections by the Eurocode 2 and the proposed modelwere quite similar and independent of the loadingduration.

Subramanian suggested simple formulae, involvingthe clear cover and calculated stress in reinforcementat service load, to control crack width.13He criticisedthe provision made in the Indian code IS 456:00 forcrack width calculation and commended the ACI 318:02provisions. Alam et alcriticised the Euro code 2 for underestimating the crack width and crack spacing due toneglecting the structural member size inuence whichthey found had signicant effect.14

Khan et al compared the value of bar developmentlengths obtained using ACI 318:99, BS 8110:85 andIS 456:00. IS code gave the development length 8percent and 11 percent more than that by BS and ACIcodes respectively. The development length obtainedin compression using IS code was 3.5 percent and 17percent more than that used by BS and ACI codesrespectively.15 Subramanian compared the IS 450:00

provisions for the development length with the ACIcode. He suggested a formula to improve the existingIS provision.16,4The formula includes factors such asbar diameter, concrete cover spacing of bars, transversereinforcement, grade and confinement of concretearound the bars, type of aggregate, type of bars andcoating applied on bars, if any.

Haitao et alcompared the experimental test results of laplength development from eighteen reinforced concretebeams with eight international codes requirements.17They found that all the codes were conservative inspecifying lap length development for small diameterbars and that ACI 318:05 and ACI Committee 408provided the worst agreement for large diameter bars.Chul et al studied the experimental results of 72 testspecimens for compressive lap splices using concretecompressive strengths of 80 and 100 MPa.18 The effectof concrete strength, splice length and transversereinforcement were assessed. They proposed a simple

equation, which provides shorter lengths than the ACI318:08 does. Sarki et alreviewed the BS 8110 and Euro-code 2 recommendations on steel bar lap lengths andconcluded that the British code gave the best safetyindices in all the cases they evaluated.19

It is clear from these references that most of the researchwork compare experimental results with the codesrequirements or proposed models. But no comprehensivework was found in the literature comparing the ACI318:08 and BS 8110:97 codes in terms of deection,control of crack width, and anchorage and lap lengths fordifferent conditions including live-to-dead load ratios,

concrete strength, area of reinforcement, and bar type ordiameter. Accordingly, a comparative study with theseparameters was conducted on single-span, continuousrectangular reinforced concrete beams.

Control of deection

ACI 318:08 provisions for deection calculation

ACI 318:08 has two approaches for controlling deection.The rst indirect approach consists of setting suitableupper limits on the span-depth ratio. In the secondapproach, the deections are controlled directly bylimiting the computed deections to the values specied

in the code (Table 9.5 (b)). In this study, the secondapproach was adopted as follows:

Short-term deection

The initial or short-term deection iis calculated usingEquation 1. The PCA notes explain the details in this

Continued on page 35


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Point of View

regard particularly the ACI 318:05 sections 9.5.2.2 and9.5.2.3: 20

...... (1)

where, Ma= service moment, Ieis the effective moment ofinertia, and K = deection coefcient given in Table 1.Mo= Simple span moment at mid-spanMa= Service support moment for cantilever or mid-span

moment for simple and continuous beams

For each load combination (i.e. dead + live) the deectionis calculated using an effective moment of inertia i.e. (Ie)d,(Ie)d+land (Ie)suswith the appropriate service momentMa. The incremental deection caused by the additionof load, such as the live load, is then computed as thedifference between the deections computed for anytwo-load combination. Therefore, immediate deectiondue to the live load is given by Equation 2:

(i)l= (i)d+l (i)d ...... (2)

This calculated deflection should be less than theallowable deflection given in Table 9.5 (b) of ACI318:08.

Long-term deection

According to section 9.5.2.5 of the ACI 318:08, anadditional long-term deection due to the combinedeffects of shrinkage and creep from sustained loads isgiven by Equation 3:

...... (3)

where, = multiplier for the long-term effect. As persection 9.5.1 of ACI 318:08; the sustained load includesdead load and that portion of the live load which issustained. Equation 4 gives total deection:

...... (4)

This computed total deection should not exceed thelimits given in Table 9.5 (b) of ACI 318:08.

BS 8110-2:85 provisions for deection calculation

BS 8110-2 is based on the calculation of a sectionscurvature subjected to the appropriate moments, with anallowance for creep and shrinkage effects.21Deections

are calculated from these curvatures. In BS 8110-2, areduction in the applied moment causing deection ismade, as in reality the concrete below neutral axis cancarry limited tension between cracks. Its effect, called thetension stiffening, can be looked upon as a reduction ofmoment causing deection expressed as (M - M), whereM is the moment carried by the tension in concrete.

Short-term curvatures

The curvature of a section is the larger value obtainedby considering the section either un-cracked or crackedas appropriate.

The curvature of the short-term deection for un-crackedsection is given by Equation 5:

...... (5)

The curvature for the cracked section is given byEquation 6:

...... (6)

where, M = applied moment, Ec= modulus of elasticityof concrete, Ig = gross moment of inertia, Mc is themoment of resistance of concrete in tension, and M-Mcis the moment causing deection.

Long- term curvature

In calculating the long-term curvatures, the effects ofcreep and shrinkage are considered.

Equation 7 gives the long-term curvature due topermanent load:

...... (7)

Equation 8 gives the curvature due to shrinkage:

Support type K

Cantilever 2.4

Simple beams 1.0

Continuous beams

Table 1. Deection coefcient K (PCA Table 10.3)


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Point of View

smaller of 1) distance from centre of bar being developedto nearest surface and 2) one half the centre-to-centrespacing of bars being developed, and Ktr= transverse

reinforcement index =

where; Atr= total area of

all transverse reinforcement which is within the spacing,S = maximum spacing of transverse reinforcementwithin l

d

(centre-to-centre), and n = number of barsbeing developed. The code permits to use Ktr= zero as adesign simplication even if transverse reinforcement is

present. The term

cannot be taken greaterthan 2.5 to safeguard against pull-out type failure. Tosimplify computation of ld, preselected values for the

term

are chosen to as shown in section12.2.2 of ACI 318;08.

Anchorage length in compression

The anchorage length in compression is given by section12.3.2 of the ACI 318:08; as shown in Equation 14:

...... (14)

Forfc> 32 MPa, (0.043fy)dbgoverns the length.

British Code (BS 8110:97) provisions for

anchorage length

Section 3.12.8.3 of the BS 8110:97 species anchoragelength in tension and compression as given by Equation15:

...... (15)

where; = is the bar size,fs= is the ultimate tensile orcompressive stress in reinforcement (0.95fy) and fbu=

the ultimate anchorage bond stress = with =bond coefcient = 0.5 for bar Type 2 in tension and =0.63 in compression.

Lap length

ACI 318:08 provisions for lap length

Lap length in tensionSection 12.15.1 of the ACI 318:08 species the tensionlap lengths for class A and class B splice as 1.0ldand1.3ldrespectively but not less than 300 mm. Section12.15.2 of CAI318:08 species tension lap splicecondition. Since in practice class B splice condition ismore common it was considered in this research.

Lap length in compression

Section 12.16.1 of the ACI 318:08 species the compressionlap length as 0.071fydbforfy 420MPa and 0.13fy 24forfy> 420MPa but not less than 300 mm in both cases.These values are applicable for 21


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Point of View

shrinkage, whereas in the BS code, deections due tocreep and shrinkage are calculated separately. The ACIand BS limits on deection, for the same situations, are

close to each other.

Table 3 shows the applied loads and providedreinforcement for simply supported beams using ACIand BS codes having a span length (L) of 8m andsubjected to uniformly distributed loads with differentDL:LL ratios. Figures 1 and 2 show the total calculatedand allowable defections for the beams in Table 3. It isassumed that the beam is supporting non-structuralelements that are not likely to be damaged by a largedeection. The beam was 350x750 mm with an effectivedepth of 625 mm. The characteristic compressive strengthof concrete fcuwas 30 MPa and the cylinder compressive

concrete strength fc was 24 MPa. The yield strength ofsteel was taken as 460 MPa. It was assumed that 25% ofthe live load as permanent. The time dependent factor forsustained load, , as required in the ACI code, was takenas 2.0 (i.e. factor for a period of 5 years or more). The 30year creep coefcient, , as required by the BS code, wastaken as 2.0 for ambient relative humidity of 60% andage of loading as 14 days. The 30 years free shrinkagestrain, cs, as required in BS code, was taken as 0.000027for ambient relative humidity of 60%. From Figure 1, it isclear that the predicted short-term deection from bothcodes, decreases with the increase of the dead load tothe live load ratio. Contrarily, the long-term deection

increases with increasing dead load to live load ratio.Figure 2 shows that the predicted total deection isalmost constant for each code with a small drop whenthe dead load to live ratio was 2.5. The maximumallowable deections are constant for each code withvalues of ACI being 4.2 per cent larger than that of theBS. The predicted deections using ACI code are morethan those using BS code for short-term, long-term and

total deections. The differences between the ACI andBS results in short-term, long-term and total deectionsincrease with the increase in dead load to live load

ratio the maximum values being 8.58, 20.68 and 27.51per cent respectively for the given conditions. Thesedifferences are attributed to the different approachesadopted in ACI and BS for calculating EI, as discussedearlier. The differences in the long-term case increaseat a larger rate than those in the short-term case. Thislarge difference could be attributed to the fact that inthe ACI code, a combined effect of creep and shrinkageis considered, whereas in the BS code these effects arecalculated separately. This has in-turn affected the totaldeection with difference increasing as the dead loadto live load ratio increases from 24.36 to 27.51 per cent.While comparing the total predicted deection with

the deection limits (Figure 2), it was found that, inthe ACI code, the estimated deection is larger thanallowable limits, which means that the ACI limits canbe violated by the ACI equations used in estimatingthe total deection. The BS code estimated deectionsremain within the allowable limits. This indicates thatthe ACI limits should always be observed for possibleviolation.

Control of crack width

As pointed out earlier, ACI code does not give explicitcrack width calculation. The control of cracking is

deemed satisfactory as long as the limit on the bar spacingis satised. The BS code furnishes two approaches, adeemed-to-satisfy approach and the calculation of crackwidth. In deemed-to-satisfy approach, the maximumbar spacing is controlled in a similar way as in theACI code. It was shown in Equation 10 that the ACIprocedure is a function of service stress and concretecover, whereas the BS provision given in Equation 11 is


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Point of View

a function of service stress and bar size. Figure 3 showsthe effect of concrete cover on the bar spacing using

these equations. The values used were

, fy=460 MPa, and dp= 20 mm. It is clear that the limits onthe maximum spacing between bars vary signicantlybetween ACI and BS codes. The BS code has a constantspacing regardless of the concrete cover, whereas theACI bar spacing reduces with the increase in the concretecover thickness. The difference between the two codes

decreases as the concrete strength increases (Figure 3).With the given data, the highest difference is 57.8% whenconcrete strength is 30 MPa and the lowest is 0.6 %whenthe concrete strength is 70 MPa.

Anchorage length in tension

From Equations 13 and 15 for anchorage length intension, it can be seen that both the ACI and BS codesequations are the functions of concrete and reinforcementyield strengths and bar diameter. However, the ACIequation is more detailed and takes into account thelocation of reinforcement, coating factor, bar spacing,

effects of small cover, and connement provided bytransverse reinforcement. Table 4 shows the deducedequations of tension anchoragelength using both the codes fordifferent values of fc which istaken as 0.8 of fcu (using t= e= 1.0, and s= 0.8 for dp 20mmDia and = 1.0 for dp>20mm Dia).In the case of ACI, pre-selected

values of the term

were adopted which were 1.0, 1.5and 2.5. The resulting anchoragelength in tension, (Table 4), areplotted in Figure 4. It can be seenthat in both the codes, the tensionanchorage length decreases withthe increase in concrete strength.

When the term

has a

value of 1 and 1.5, ACI requires more tension anchoragelength than the BS does; varying from 14.1 to 114 percentrespectively for concrete strength change from 30 to 40

MPa. Whereas, when the term

has a valueof 2.5, BS requires more anchorage length; varying from16.8 to 46 per cent for concrete strength change from 30to 40 MPa. In this regard it clear that the ACI provision

Code fcu, MPa30 35 40

db20 db>20 db20 db>20 db20 db>20

ACI(ClassB)

(cb+Ktr/db)=1.0 (0.146fy)db (0.185fy)db (0.135fy)db (0.169fy)db (0.126fy)db (0.158fy)db


cb+Ktr/db)=2.5 (0.058fy)db (0.073fy)db (0.054fy)db (0.068fy)db (0.040fy)db (0.050fy)db

BS (0.087fy)db (0.087fy)db (0.09fy)db (0.09fy)db (0.076fy)db (0.076fy)db

Table 4. Equations for anchorage length in tension, using both ACI and BS codes


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Point of View

is more conservative since in most cases it requires alonger anchorage length than the BS.

Anchorage length in compression

From the Equations 14 and 15 for compression anchoragelength, it can be seen that both codes equations arefunctions of concrete and steel strengths and bar size.Table 5 shows equations and calculated values for theanchorage length in compression, as a multiple of barsize, using both ACI and BS codes, for different values of

fc. It can be seen that the BS code requires approximately40 per cent more anchorage length in compression than

the ACI code.

Lap length in tension

As discussed earlier, ACI andBS codes take into account barcoating factor, effect of smallcover and location of bars.However, ACI further considersthe effect of close bar spacingand confinement providedby transverse reinforcement.Table 6 was prepared based

on the equations of tension laplength in both codes for differentvalues of fc. The reinforcementlocation factor was taken as 1.0and reinforcement assumed asuncoated. In the case of ACI, pre-

Concrete strengthfcu, MPa

Equation of anchorage length incompression, ldc

Anchorage lengthin compression, ldc

% Diff. ofldc

ACI BS ACI BS

30 (0.049fy)db (0.069fy)db 23db 32db 40.5

35 (0.045fy)db (0.071fy)db 21db 29db 40.5

40 (0.043fy)db (0.060fy)db 20db 27db 38.6

Table 5. Equations for anchorage length in compression, using both ACI and BS codes, as multiple of bar size

fy= 460MPa, fc =0.8fcu

fcu, MPa30 35 40

db20 db>20 db20 db>20 db20 db>20

ACI(ClassB)



cb+Ktr/db)=2.5 (0.075fy)db (0.094fy)db (0.070fy)db (0.088fy)db (0.052fy)db (0.065fy)db

BS (0.087fy)db (0.087fy)db (0.090sfy)db (0.09fy)db (0.076fy)db (0.076fy)db

Table 6. Equations for lap length in tension

selected values of term

are adopted whichare 1.0, 1.5 and 2.5. Figure 5 shows resulting lap length intension, as a multiple of bar size, using both ACI and BS

codes. It can be seen that when the term

is1 or 1.5, ACI needs more lap length; varying from 48.4

to 178.2 percent. When the term

is 2.5, BSasks for 12.3 percent more lap length than ACI when thediameter of bar 20 mm but ACI required 11.3 percentmore lap length when the diameter of bar >20 mm.


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Point of View

Lap length in compression

The provision of compression lap length discussedearlier suggests that in the ACI code, the compressionlap length is a function of bar size and yield strengthof steel and is independent of the concrete strength.Whereas, in BS code, the compression lap length is equalto 1.25 times the compression anchorage length. Table 7gives the equations for lap length in compression, as a

multiple of bar size, using both ACI and BS codes andFigure 6 shows the resulting values, for the differentgrades of concrete. It can be seen that for concrete havingfcu= 30 MPa, BS required 10.5 per cent more lap lengththan the ACI whereas for the higher concrete grades,the differences of lap length is negligible as it variesfrom -4.5% to 2.3%. It is clear that BS code requiresmore compression lap length than does the ACI code tillconcrete compressive strength is 37 MPa, beyond that,ACI requires more compression lap length.

Concluding remarks

The predicted short-term deections from bothACI and BS codes, decrease with the increase inthe dead load to the live load ratio; ACI valuesbeing larger than the BS by a maximum 8.58per cent for the given conditions. Contrarily,the long-term deections increase with increasein the dead load to live load; ACI values being

larger for a maximum of 20.68 per cent for thegiven conditions.

In both codes, the total deection decreases withthe increase in the dead-to-live load ratio withthe ACI values being larger than the BS valueswith a maximum 27.51 per cent for the givenconditions.

The values of the deection limits in both ACI andBS codes are close to each other regardless of thedead-to-live load ratios with the values of ACIbeing 4.2 per cent larger than those of the BS.

The ACI estimated total deection is always largerthan the ACI limits for the given conditions. Thisimplies that the limits should always be observedfor possible violation.

The differences in short-term deections estimatedby ACI and BS could be attributed to the different

approaches adopted in ACI and BS code forcalculating EI. In ACI, the effective moment ofinertia, Ieff, is used, whereas the BS procedurecalculates EcI for short term and long termloading using separate Ec(short term) and Ec(longterm).

The differences in the long-term deflectionsestimated by ACI and BS could be attributed tothe fact that in ACI consider combined effect ofcreep and shrinkage, whereas in BS the effect ofcreep and shrinkage is calculated separately.

Limits on maximum spacing of bars to controlcrack width in rectangular beams vary highlybetween ACI and BS codes. The BS code has aconstant value regardless of the concrete coverwhile the ACI bar spacing reduces with theincrease in the concrete cover to reinforcement.ACI code allows more spacing than BS code doesfor low grades of concrete and difference in values

Concrete strengthfcu, MPa

Equation of lap lengthin compression

Lap lengthin compression

% Diff. ofcompression

lap lengthACI BS ACI BS

30 (0.078fy)db (0.086fy)db 36db 40db 10.5

35 (0.078fy)db (0.089fy)db 36db 37db 2.3

40 (0.078fy)db (0.075fy)db 36db 34db -4.5

Table 7. Lap length in compression as a multiple of bar size in ACI and BS codes

fy= 460MPa, fc =0.8fcu


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Point of View

between two codes decreases as the concrete coverthickness increases.

In both the codes, the required tension anchorageand lap lengths decrease with the increase inconcrete strength.

The ACI code lap length in compression isconstant regardless of the concrete strength whilethe BS code length decreases with the concretestrength.

For the term 1

< 2.5, ACI codeequations result in more tension anchorage andlap lengths than the BS. Whereas, when the term

has value of 2.5, BS code equationresult in more tension anchorage and lap lengths

than the ACI. In most cases, the ACI is moreconservative by requiring a longer anchoragelength.

BS code asks for more compression anchoragelength than ACI code does.

BS code demands more compression lap lengththan ACI code until concrete compressive cubestrength is 37 MPa, beyond which ACI requiresmore compression lap length than BS code.

Based on the above it can be stated that the

provisions in the ACI code are more conservativethan those in the BS code for both short- andlong-terms deflections, which give the ACIprovision a superior reliability. However, theACI limits for deflection are violated by theresults of the ACI equations, which allow thelimits to always dictate the length. On the otherside, the BS Code is more conservative in termsof bar spacing to limit crack width, anchorageand lap lengths. Therefore, it is not easy to givepreference to one code over the other. Howeverit is a fact that SI units are becoming more andmore enforced internationally, building material

and references available in Oman are mostly in SIunits. Therefore in order to unify the knowledgeof the code requirements among municipalityand site engineers, it is recommended to use theBS code as a rst choice until a national code isestablished.

References_______Amer ic an Con crete Inst it ute (ACI3 18 :08) , Building Code

Requirements for Structural Concrete and Commentary, 2008, FarmingtonHills,MI, USA._______British Standard Institution (BS8110:97 Part-1), Structural Use ofConcrete, Code of Practice for design and construction,1997, London, UK.

Nayak S.K. and Menon D., Improved procedure for estimating short termdeections in RC slabs, The Indian Concrete Journal, July 2004, v78, n7, p19-25.

_______Indian standard code of practice for plain and reinforced concrete forgeneral building construction, IS 456:2000, Bureau of Indian Standards, New

Delhi, India.

Eurocode 2, Design of concrete structures, general rules and rules for buildings,BS EN 1992.

Santhi A.S., Prasad J. and Ahuja A.K., Effects of creep and shrinkage onthe deection of RC two way Flat plates, Asian journal of Civil Engineering(Building and Housing), 2007, v8, n3, p267-282.

Bacinskas D., Gribniak V. and Kaklauskas G., Statistical analysis of long-term deections of RC beams, Creep, Shrinkage and Durability,Mechanicsof Concrete and Concrete Structures, Taylor & Francis Group, London, UK,2009, ISBN 978-0-415-48508-1.

Kaklauskas G., Flexural layered deformation model of reinforced concretemembers,Magazine of Concrete Research, 2004, v56, n10, p575-584.

Lee Y. H. and Scanlon A., Comparison of one-and two-way slab minimumthickness provisions in building codes and standards,ACI structural Journal,

March-April 2010, v107, n2, p157-163.Scanlon A. and Lee Y. H., Unied span-to-depth ratio equation for non-

pre-stressed concrete beams and slabs,ACI Structural Journal, Jan-Feb 2006,v103, n1, p142-148.

Bischoff P. H. and Scanlon A., Span-depth ratios for one-way membersbased on ACI318 deection limits, ACI Structural Journal, Sep- Oct 2009,v106, n5, p617-625.

Bacinskas D. Kaklausks G., Gribniak V., Sung W. P. and Shih M. H., Layermodel for long-term deection analysis of cracked reinforced concrete

bending members, Mech. Time-Depend Mater, 2012, v16, p117127, DOI10.1007/s11043-011-9138-9.

Subramanian N., Controlling the crack width of exural RC members, TheIndian Concrete Journal, November 2005, v79, n11, p31-36.

Alam Y. S., Lenormand T., Loukili A., and Region J. P., Measuring crackwidth and spacing in reinforced concrete members, Fracture Mechanics of

Concrete and Concrete Structures-Recent Advances in Fracture Mechanics of

Concrete - B. H. Oh, et al.(eds), 2010, Korea Concrete Institute, Seoul, ISBN978-89-5708-180-8.

Khan M. S., Reddy A. R., Shariq M. and Prasad J., Studies in Bond strengthin RC Flexural Members, Asian Journal of Civil Engineering (Building and

Housing), 2007, v8, n1, p89-96.

Subramanian N., Development length of reinforcing bars need to revise

Indian code provisions, The Indian Concrete Journal, August 2005, v79, n8,p39-46

Haitao L., Xiaozu S., Andrew d. J., Evaluation of adequacy of developmentlength requirements for 500MPa reinforcing bars, Advances in StructuralEngineering, June 2011, v14, n3, p367-378.

Chul C. S., Ho L. S. and Bohwan O., Compression splices in high-strength

concrete of 100MPa and less,ACI Structural Journal, November- December2011, v108, n6, p715-724.

Sarki Y. A., Murana A. A., and, Abejide S. O., Safety of Lap Lengths Predictionin Reinforced Concrete Structures, World Journal of Engineering and Pure and

Applied Science, 2012, v2, n3, pp 98 -106.Notes on ACI318:05, Requirements for structural Concrete with Designapplications, ACI Building code, 2005, Edited by: Mahmoud E. Kamara and

Basile G. Rabbat, Portland Cement Association, 5420 Old Orchard Road,Skokie, Illinois 60077-1083.

_______British Standard Institution (BS8110:85 Part-2) , Structural Use ofConcrete, Code of Practice for Special Circumstances, 1985, London, UK.

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Ali S. M. Alnuaimiholds an MSc in structuralengineering from the University of SouthernCalifornia, USA and PhD in structuralengineering from the University of Glasgow,UK (Title of thesis: Direct design of reinforcedand partially pre-stressed concrete beams forcombined torsion, bending and shear). He is an

Associate Professor at the Department of Civil andArchitectural Engineering, College of Engineering, Sultan

Qaboos University, Oman. He has published 29 journalpapers and 28 conference papers. Before being an academiche worked as structural engineer and Director of projects atSultan Qaboos University for ve years. Currently, he is also

the chair of the projects committee at Sultan QaboosUniversity. Dr. Alnuaimis main research interests arestructural design and analysis, estimating construction cost,and administration of contracts.

Iqbal Y. Patel holds an MSc in Civil Engineeringfrom Sultan Qaboos University, Oman. He is astructural engineer at Muscat Municipality,Oman. He has more than 25 years of experiencein structural design of concrete and steelstructures along with Project Managementexperience. He is procient with American

concrete and steel design codes ACI318, AISC360 as well asstructural design software STAAD, ETABS, SAP, SAFE and

familiar with ASCE7, UBC, IBC. Prior to this he worked as acivil and structural engineer in India, Saudi Arabia, and inprivate companies in Oman.

serviceability limit states, bar anchorages and lap lengths in aci 318-08 and bs 8110-97...

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