structural assessment of low rise reinforced concrete frames under tsunami loads

6
lo tsu typ pa to us re str m im dy an an di wh str is str m wa tsu in de tsu (B on di m D tsu 20 w H co ha of tsu En 00 an UK O AbstractTh ads on reinforc unami wave lo ypical substanda art of the EU-fu shake table tes sing Carbon Fi tested. Numeri rengthened con atch the test re mpact forces, t ynamic analys nalytical results nd at the “impa splacement of hen compared rengthening on more effect rengthening ot itigate damage KeywordsT aterborne objec N 24 th D (M w =9.3) unami which ncluding Sri L efense system unami produc Batticaloa) and n tourism. Th isaster ever re more than US $ omestic Prod unami also c 005. In the a were quickly b However, man onstruction st ave ground flo f tsunami wav unami wave l Mr Hussain Ji ngineering, The 0970526814893; ( Prof Kypros Pil nd Structural Eng K (e-mail: k.pilak Str O his study exam ced concrete (R oads and water ard full-scale tw unded Ecoleade sts in bare cond iber Reinforced ical models of nditions are ca sults. To invest the numerical es using forc are compared i act point” of a the CFRP-stre to the bare bu nly the mid-heig tive at reduc ther parts of t due to tsunami Tsunami loads cts, RC building I. IN December 200 hit the west h caused 250 Lanka. Sri L ms or mitigat ced severe de d South (Gall his was Sri L ecorded. The t $900 million, duct (GDP) [ caused a redu aftermath of built to speed ny of these s tandards. Mor oors with elev ves. Such expo oads (hydrody iffry is with th University of Sh (e-mail: mhmoha lakoutas and Dr gineering, The U koutas@sheffield ructur Conc mines analyticall RC) frame bui rborne objects wo-story RC fr er project. The dition, and sub d Polymers (C the building in alibrated in DR tigate the respo models are s ce time-history in terms of disp boat. The resu engthened buil uilding. The res ght of the impa cing damage the column. A i loads are sugg s, hydrodynam gs. NTRODUCTION 04 the Indian coast of Su 0,000 fatalitie Lanka did no tion measure evastation alon le), which eco Lanka’s most total economic i.e. approxim [1]. The neg uction of GD the tsunami, up recovery o structures we reover, many vated columns osed columns ynamic and im he Department heffield, Sheffie amedjiffry1@shef Reyes Garcia are University of She d.ac.uk, r.garcia@ al Ass crete F Hus ly the effect of ildings. The im are analyzed rame building t building was su bsequently stren CFRP) compos n both bare and RAIN-3DX soft onse of wave lo subjected to n y input record placements at th ults show that lding reduced sults also indic act column usin when compa Alternative solu gested. mic load, impa n Ocean eart umatra and ca es in 12 co t have any t es. As a resu ng the coast onomies rely t devastating c loss is estim mately 4.5% o gative effects P growth by coastline str of touristic fa ere built usin y of these str s to allow ‘fre can be vulner mpulsive) and of Civil and S ld, S1 3JD, UK ffield.ac.uk). with Departmen ffield, Sheffield, @sheffield.ac.uk). sessme Frame ssain Jiffry, K tsunami mpact of using a tested as ubjected ngthened ites and d CFRP- tware to oads and nonlinear ds. The he floors the roof by 63% cate that ng CFRP ared to utions to act load, thquake aused a untries, tsunami ult, the of East heavily natural mated in f Gross of the 1% in ructures acilities. ng poor ructures ee flow’ rable to d impact Structural K (phone: nt of Civil S1 3JD, for du bu qu to pa F on On sei wi da the loc the rei bu bu sof res (hy ob the hig Sri co flo hy im loa hy for ma ent of es und Kypros Pilak rces of waterb uring future ts uildings to re uestionable [2] waterborne ob artial structura Fig. 1 Damage Previous stud n structures, e ne of the mai ismically-desi ithstand tsuna amage. Howev e effect of tsu cated in Sri L e effect of t inforced conc uilt in Sri Lank uilding is m ftware. Nume sponse of ydrodynamic, bjects) applied e structure is gher than the i Lanka. Th mpared and oors and at the II. Typical tsu ydrostatic, hy mpulsive and ads act simul ydrodynamic, rce due to agnitude of th f Low- der Tsu koutas, Reye borne objects, sunamis. As esist future p ]. This is espe bjects, which l collapse as s on a column du dies have exam specially on w in conclusion igned buildin ami forces w ver, limited st unami loads o Lanka. Hence tsunami load crete (RC) fr ka during the modeled and erical analyse the RC f impulsive a d on an expo s situated 500 buffer zone a he results fro discussed in e “impact poin . ESTIMATION unami-induced ydrodynamic, debris impact ltaneously on impulsive ts waterborne hese forces are -rise R unami s Garcia and thus may a result, the potential tsun ecially true fo can cause sev shown in Fig. ue to tsunami w mined the effe well-designed s from these ngs have suf without exper tudies have ex on substandard e this paper a ds on a sub- rame building post-tsunami analyzed u es are perform frame under and impact fo sed open gro 0m from the allowed in the om the num n terms of di nt” of a boat. OF TSUNAMI L d force co surge, buo t forces. How n a structure. sunami wave objects are e expected to Reinfo Load y experience d resilience of nami loads c or impact forc vere damage o 1. waterborne obje ect of tsunam d new buildin studies is tha fficient stren riencing sign xamined analy d structures as assesses analy -standard two g as those ty reconstructio using DRAIN med to exami r tsunami orces of wate ound floor ass coastline wh coast of Wel erical analys isplacements LOADS omponents i oyant, drag wever, not all In this study forces and considered a be large and u orced ds damage f those can be ces due or even ct [3] mi loads ngs [4]. at well ngth to nificant ytically s those ytically o-story ypically on. The N-3DX ine the forces erborne suming hich is ligama, ses are at the include force, l these y, only impact as the usually World Academy of Science, Engineering and Technology International Journal of Civil, Structural, Construction and Architectural Engineering Vol:9, No:2, 2015 167 International Scholarly and Scientific Research & Innovation 9(2) 2015 International Science Index Vol:9, No:2, 2015 waset.org/Publication/10000677

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    AbstractThads on reinforcunami wave lo

    ypical substandaart of the EU-fu shake table tes

    sing Carbon Fitested. Numerirengthened conatch the test re

    mpact forces, tynamic analysnalytical resultsnd at the impasplacement of hen compared rengthening on

    more effectrengthening otitigate damage KeywordsT

    aterborne objec

    N 24th D(Mw=9.3)

    unami whichncluding Sri Lefense systemunami produc

    Batticaloa) andn tourism. Thisaster ever re

    more than US $omestic Produnami also c005. In the a

    were quickly bHowever, manonstruction stave ground flof tsunami wavunami wave l

    Mr Hussain Jingineering, The 0970526814893; (

    Prof Kypros Pilnd Structural EngK (e-mail: k.pilak

    Str

    O

    his study examced concrete (Roads and waterard full-scale twunded Ecoleadests in bare condiber Reinforcedical models of nditions are casults. To investthe numerical es using forc are compared iact point of a

    the CFRP-streto the bare bu

    nly the mid-heigtive at reducther parts of tdue to tsunami

    Tsunami loadscts, RC building

    I. INDecember 200

    hit the west h caused 250Lanka. Sri L

    ms or mitigatced severe ded South (Gallhis was Sri Lecorded. The t$900 million, duct (GDP) [caused a reduaftermath of built to speed ny of these standards. Moroors with elevves. Such expooads (hydrody

    iffry is with thUniversity of Sh(e-mail: mhmohalakoutas and Dr Rgineering, The Ukoutas@sheffield

    ructurConc

    mines analyticallRC) frame buirborne objects wo-story RC frer project. The dition, and subd Polymers (Cthe building in

    alibrated in DRtigate the respomodels are s

    ce time-historyin terms of dispboat. The resu

    engthened builuilding. The resght of the impacing damage the column. Ai loads are sugg

    s, hydrodynamgs.

    NTRODUCTION 04 the Indian

    coast of Su0,000 fatalitie

    Lanka did notion measure

    evastation alonle), which ecoLankas mosttotal economici.e. approxim

    [1]. The neguction of GDthe tsunami, up recovery o

    structures wereover, manyvated columnsosed columns ynamic and im

    he Department heffield, Sheffie

    amedjiffry1@shefReyes Garcia are

    University of Shed.ac.uk, r.garcia@

    ral Asscrete F

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    ly the effect of ildings. The im

    are analyzed rame building tbuilding was su

    bsequently strenCFRP) composn both bare andRAIN-3DX softonse of wave losubjected to ny input recordplacements at thults show that lding reduced sults also indic

    act column usinwhen compa

    Alternative solugested.

    mic load, impa

    n Ocean eartumatra and caes in 12 cot have any t

    es. As a resung the coast onomies rely t devastating c loss is estim

    mately 4.5% ogative effects P growth by coastline str

    of touristic faere built usiny of these strs to allow frecan be vulner

    mpulsive) and

    of Civil and Sld, S1 3JD, UKffield.ac.uk). with Departmenffield, Sheffield,

    @sheffield.ac.uk).

    sessmeFramessain Jiffry, K

    tsunami mpact of

    using a tested as ubjected

    ngthened ites and

    d CFRP-tware to oads and nonlinear ds. The he floors the roof by 63% cate that ng CFRP ared to

    utions to

    act load,

    thquake aused a untries, tsunami ult, the of East heavily natural

    mated in f Gross of the 1% in

    ructures acilities. ng poor ructures ee flow rable to

    d impact

    Structural K (phone:

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    onOnseiwidathelocthereibubusofres(hyobjthehigSricoflo

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    Kypros Pilak

    rces of waterburing future tsuildings to reuestionable [2]

    waterborne obartial structura

    Fig. 1 Damage Previous stud

    n structures, ene of the maiismically-desiithstand tsunaamage. Howeve effect of tsucated in Sri Le effect of tinforced conc

    uilt in Sri Lankuilding is mftware. Numesponse of ydrodynamic,

    bjects) appliede structure isgher than the i Lanka. Thmpared and

    oors and at the

    II.Typical tsu

    ydrostatic, hympulsive and ads act simul

    ydrodynamic, rce due to agnitude of th

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    borne objects, sunamis. As esist future p]. This is espebjects, which l collapse as s

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    the RC f impulsive a

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    . ESTIMATION unami-inducedydrodynamic, debris impactltaneously onimpulsive tswaterborne

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    es are performframe underand impact fosed open gro0m from the allowed in the om the numn terms of dint of a boat.

    OF TSUNAMI Ld force co

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    LOADS omponents ioyant, drag wever, not all

    In this studyforces and considered abe large and u

    orced ds

    damage f those can be ces due or even

    ct [3]

    mi loads ngs [4]. at well

    ngth to nificant ytically s those ytically o-story

    ypically on. The N-3DX ine the forces

    erborne suming hich is ligama, ses are

    at the

    include force,

    l these y, only impact as the usually

    World Academy of Science, Engineering and TechnologyInternational Journal of Civil, Structural, Construction and Architectural Engineering Vol:9, No:2, 2015

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  • dominate the response. The following sections summarize current standard procedures for the calculation of such forces.

    A. Hydrodynamic Force A moving tsunami wave with a velocity acts on a structural

    element for a certain period of time during inundation, thus applying a drag force which can be considered as a hydrodynamic force FH [5]. The force FH applied at the inundation depth h is given by.

    0.5 (1)

    where: = fluid density of tsunami flow (=1200 kg/m3); Cd = drag coefficient (Cd = 2 for square and rectangular columns); B = the breadth of structure in the plane normal to the direction of flow (in meters); hu2 = momentum flux per unit mass (u = flow velocity; h = flow depth).

    The most important parameter on tsunami loading is the velocity of the tsunami flow which influences both hydro-dynamic and impact force loadings. The velocity depends on the inundation depth. The fundamental expression for the velocity is u= k(gh). Different authors give different values of k [6]-[8]. The velocity obtained by assuming k = 2 relates to the conventional solution of the leading tip of a surge on a frictionless horizontal plane caused by a dam break with the quiescent impoundment depth of h [12]. However, [8] argues that the latter approach may be too conservative, as the computed tip velocity does not represent the velocity of a flow depth h. Therefore, Yeh concludes that the value k(gh) is not appropriate to represent the flow velocity for a tsunami flood passing through a structure [12]. Instead, [9] proposes the following simplified equation that depends on the parameters taken from the data of the region of study.

    0.125 0.235 0.11

    (2) where: R = maximum run-up height; Z = elevation from shoreline level; g = gravitational acceleration.

    Equation (2) was used by [4] to examine the response of buildings due to tsunami loads, and it is also used in this study to calculate the hydrodynamic force. The parameters from the region of study used in the calculations are: maximum run-up height R=11.0 m, inundation depth h=2.5 m and elevation Z=2.0 m.

    B. Tsunami Wave Impulsive Force The main tsunami load during inundation is the impulsive

    force which acts suddenly at the tip of the wave when the wave hits the structure. This force is also known as surge force. The Japanese guidelines [10] suggest considering this load as 3h of the hydrostatic load. Nonetheless, [8] defines the impulsive load as 1.5gh at the inundation height, and 0.5gh at the base level of the structure. The latter approach is used in this study to estimate the impulsive force.

    C. Debris Impact Force Due to Waterborne Object A high velocity tsunami travelling in land usually carries

    heavy debris that can impact structures and cause larger forces than those induced by the tsunami waves. Thus, debris impact loads due to waterborne objects are usually more damaging during tsunamis. Current design guidelines (e.g. FEMA P646 (FEMA 2008) and ASCE 7-10 (ASCE 2010)) provide guidance to determine the peak impact force on a structure.

    According to FEMA P646, the peak force can be calculated using the contact stiffness approach (3), where the contact stiffness is obtained with reference to the properties of the impact object and the structural element.

    (3) where: Cm = mass coefficient; keff = effective contact stiffness; v = velocity of the object at the point of impact; m = mass of the object.

    Conversely, ASCE 7-10 is based on the principle of impulse momentum and assumes a half sine pulse as the impact time-history (see (4)). The force is assumed to increase from 0 to Fp at time intervals of =0.003s, decreasing to zero at the restitution phase [11].

    (4) where, t = time to decrease object velocity to zero in the compression phase.

    To show the inconsistencies between the results yielded by the FEMA P646 and ASCE 7-10 approaches, a 20 shipping container with a tare weight of 2200 kg impacting on a column at a velocity of 6 m/s is assumed. ASCE 7-10 estimates a peak impact of 10,900 kN, whereas FEMA P646 estimates a force of 691 kN using keff=1.5x109 N/mm2. This inconsistency suggests that the load needs to be thoroughly analyzed using alternative numerical methods [11]. Therefore, this study uses the numerical approach by [11], who provided a set of peak impact forces due boats and shipping containers for analysis purposes. In this study, a boat of 1,500kg was assumed to impact the ground floor of the analyzed structure at an inundation height of 2.5 m (Fig. 2).

    Table I summarizes the forces considered in the analysis of the structure, as well as their duration and impact heights. As this study mainly focuses on the effectiveness of strengthening in the case of critical damage, both hydrodynamic and tsunami wave impulsive loads are be analyzed together, whereas debris impact force will be analyzed separately.

    III. CHARACTERISTICS OF CASE STUDY STRUCTURE The building considered in this study is the substandard

    full-scale two-story one-bay RC frame building shown in Fig. 2. The structure was built using inadequate construction practices as those used to build structures in Sri Lanka. The structure was subjected to a series of shaking table tests to assess the effectiveness of CFRP strengthening solutions for

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  • developing countries as part of the EU-funded Ecoleader project [13].

    Full details of the Ecoleader building can be found in [13] and only a summary is given in the following.

    TABLE I

    INPUT PARAMETERS FOR CALCULATED TSUNAMI LOADS Load type Duration (s) Force (kN) Impact height (m)

    Hydrodynamic 14.0 25.0 1.25 Tsunami wave impulsive 0.6 44.0 2.5 Debris impact force 0.1 234.0 2.0

    Fig. 2 View of case study structure and corresponding 2D model [13]

    The frame had a total height of 6.87m, whereas the cross

    section of columns and beams was 260x260mm and 260x400 mm, respectively. The slab thickness was 120mm. The concrete strength was 19.6 and 22.1 MPa for all 1st and 2nd floors, respectively. The longitudinal reinforcement used in beams and columns consisted of 14 mm bars with a yielding limit fy=551 MPa, whereas the transverse stirrups consisted of 8 mm bars and fy=582 MPa.

    The bare frame was initially subjected to a series of shake table tests using records of increasing Peak Ground Accelerations (PGA) ranging from 0.05g to 0.40g. After this, damage in the building was repaired using crack injection and mortar patching. Subsequently, the building was strengthened using CFRP and retested (up to PGA=0.50g) to assess the effectiveness of the strengthening intervention.

    IV. MODELING AND CALIBRATION OF ANALYTICAL TOOL The experimental results recorded during the shaking table

    tests are used to assess the accuracy of DRAIN-3DX software at predicting the displacement of the tested building. Element 15 was used to simulate the elements of the frame using a distributed plasticity approach. The cross section of beams and columns was discretized in concrete and steel fiber sections to account for the spread of plasticity both along the member and the cross section [4]. The element also allows accumulating strain, thus providing residual deformations. Rayleigh damping is assumed as 3% for both bare and CFRP-strengthened frame modeled in DRAIN-3DX. The stress-strain relationship of unconfined concrete was calculated according to Eurocode-2.

    Figs. 3 and 4 compare the 1st and 2nd floor displacements of the bare building calculated during the NTHA with the experimental displacements experienced during the shake table test at PGA=0.30g. It is shown that the analytical predictions compare well with the test results for the different parameters of damping, pullout properties and concrete stress-strain models used in the modeling.

    Fig. 3 Displacement-time history of bare frame for 1st floor at

    PGA=0.30g

    Fig. 4 Displacement-time history of bare frame for 2nd floor at

    PGA=0.30g The CFRP-strengthened frame was also calibrated in

    DRAIN-3DX. The CFRP sheets were modeled by changing the stress-strain constitutive relationship of concrete and by adding the CFRP sheets as additional linear fibers along the elements. The stress-strain relationship of CFRP-confined concrete was calculated according to CEB Model Code 1990.

    V. ANALYSIS OF BUILDING UNDER TSUNAMI FORCES Nonlinear time-history analyses (NTHA) are performed to

    examine the effect of the tsunami loading on the bare and CFRP-strengthened frame models calibrated in the previous section. Two analyses are considered:

    Analysis #1: it takes into account the hydrodynamic tsunami load using a time-history considered by [12]. The time-history load pattern includes 8.0 s of loading, followed by 6.0 s of gradual unloading up to zero load (at 14.0 s), as shown in Fig. 5. Fig. 5 also shows the impulsive load applied during the same analysis at the inundation height (h=2.5m) for a duration of 0.6 s.

    0.150.100.050.00

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    0.10

    0.15

    0.00 10.00 20.00 30.00 40.00

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    t (m

    )Time(s)

    Analytical Experimental

    0.20

    0.10

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    0.20

    0.00 10.00 20.00 30.00 40.00

    Disp

    lace

    men

    t (m

    )

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    Analytical Experimental

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  • -0.0400

    -0.0200

    0.0000

    0.0200

    0.0400

    0.0600

    0.0800

    0.0 1.0 2.0 3.0 4.0 5.0 6.0

    Disp

    lace

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    t (m

    )

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    Node 1820 (Load) Node 2010 (1st floor)Node 3010 (2nd floor)

    Analysis #2: The second analysis considers the load due to waterborne debris impact. The time-history pattern used for this analysis (see Fig. 6) applies a load for 0.1 seconds as recommended by CCH for RC frames. The impact of the boat is assumed to occur on the left column of the 1st floor (ground floor), as shown in Fig. 2. The analysis was performed for 12.0 s.

    Fig. 5 Force-time history of Analysis #1

    Fig. 6 Force-time history of Analysis #2

    VI. RESULTS AND DISCUSSION

    A. Bare frame The results from the combined load cases of hydrodynamic

    and impulsive loading (Analysis #1) for the bare frame are shown in Fig. 7. The plot includes the displacement results at the 1st and 2nd floors, as well as at the impact point where the load is applied (node 1810 in the figure).

    The results indicate that the peak roof displacement is 12.8 mm at 0.28 s, whereas the displacement at the impact section is 5.0 mm only and occurs at 0.6 seconds. The application of the loading scenario used in [12] leads to a maximum displacement of 9.4 mm in a two-story RC frame. The results indicate that no yielding of column reinforcement occurs within the duration of the maximum impact. As shown in Fig. 7, the structure experiences negligible negative residual displacement (0.472 mm at 14.0 s).

    The bare frame response due to debris impact (Analysis #2) due to a 1,500 kg boat is shown in Fig. 8. Whilst the analysis was performed for 12.0 seconds, Fig. 8 shows results up to 6.0 s only for clarity. The peak displacements at the impact node and at 1st floor are 34.7 and 42.3 mm, respectively. As shown in Fig. 8, such values are recorded at 0.12 s. The results also indicate that the maximum 2nd floor displacement is 58.2 mm and occurs at 0.26 s. This delay of response was expected as the load initially impacts the 1st floor column, whereas the 2nd floor displaces only after the 1st floor reaches its peak displacement. At the end of the analysis, the maximum

    residual displacement at the 2nd floor was 2.93 mm. Overall; these results indicate that the displacement due to debris impact is considerably larger (by up to 78%) when compared to that produced by the combined effect of hydrodynamic and impulsive loading.

    Fig. 7 Displacement-time history of bare frame for Analysis #1

    Fig. 8 Displacement time-history of bare frame for Analysis #2 The analytical results also indicated that the maximum

    strain in the longitudinal bars at the top part of the impact column was 0.0083. This suggests that some plastic activity occurred during the analysis, which may produce excessive rotations at the impact section and lead to potential failure of the column.

    The results in Figs. 7 and 8 show that, as expected the maximum amplitude of displacements occurs at the 2nd floor (roof) of the case study building. Hence, the comparison of displacements between bare frame and strengthened frame will only be discussed for 2nd floor and for the Analysis #2 as the impact load can cause more damage (or partial collapse) when compared to Analysis #1. Moreover, damage in buildings and structural performance is commonly associated to the amplitude of displacements (or dirift) at the roof level of the structures.

    B. CFRP Strengthened Frame Analyses #2 was carried out on the CFRP-strengthened

    model building developed in section IV. However, two cases

    0

    10

    20

    30

    40

    50

    0 2.5 5 7.5 10 12.5 15

    Forc

    e (k

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    Time (s)

    Tsunami wave Impulsive forceHydrodynamic force

    0

    100

    200

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    0 0.02 0.04 0.06 0.08 0.1 0.12

    Forc

    e (k

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    -0.0100

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    0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00

    Dis

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    )Time (s)

    Node 1810 (Load) Node 2010 (1st floor)Node 3010 (2nd floor)

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  • were analyzed: (i) the CFRP strengthening applied at the beam-column joints and base of columns as originally done in the Ecoleader building; and (ii) the CFRP strengthening applied at the beam-column joints and at the mid-height of the 1st floor columns (which is vulnerable for impact loads) as shown in Fig. 9.

    Fig. 9 CFRP strengthening cases analyzed in this study

    Fig. 10 compares the maximum 2nd floor displacement of

    the bare frame and those experienced by the CFRP-strengthened frame for cases (i) and (ii). The results in the figure are cut-off after 6.0 seconds for clarity. Compared to the bare frame response, the strengthening case (i) led to reductions in the maximum displacement of 11.4 mm (20%), whereas the residual displacement dropped by 1.65 mm (56%). Yielding of the longitudinal column reinforcement occurred at the impact section only.

    Fig. 10 Comparison of peak displacements of bare frame and

    strengthened frame for Analysis #2 The results from case (ii) in Fig. 10 indicate a significant

    reduction of 58% in the maximum displacement compared to the bare frame, and by 47% compared to the frame strengthened only at the joints (case (i)). The reduction in displacements prevented yielding of the longitudinal reinforcement in all elements of the frame. Fig 10 also shows that the residual displacement using strengthening case (ii) is 21% larger when compared to the bare structure. The results also suggest that the structure case (ii) comes to zero

    displacement (or rest state) faster. This can be attributed to the strengthening and confinement of the impact section, which is the weakest zone of the structure.

    In general, the analytical results prove that the CFRP strengthening intervention is very effective at improving the structural behavior of the case study building, thus being an alternative solution to reduce the potential damage of buildings subjected to tsunami loads.

    VII. ALTERNATIVES TO MITIGATE DAMAGE DUE TO TSUNAMI Whilst this paper has shown the effectiveness of structural

    strengthening at improving the behavior of a single existing structure subjected to tsunami load, other mitigation solutions are suitable to protect a group of structures in larger tsunami-prone regions. For instance, coastal vegetation or tsunami forests around vulnerable structures can be used to reduce, absorb and dissipate energy from impact forces. This is an environmentally friendly and cost-effective mitigation measure appropriate for developing countries, where the cost of materials such as CFRP may limit their use.

    Other more cost-effective strengthening options such post tensioned metal strapping (PTMS) can be used for strengthening [14], but it is still necessary to assess the effectiveness of the PTMS technique at reducing the effect of tsunami forces on buildings.

    VIII. SUMMARY AND CONCLUSIONS This paper assessed analytically the behavior of existing RC

    structures subjected to tsunami loads built during the post-tsunami reconstruction in Sri Lanka. From the analysis performed in this study, the following conclusions can be drawn: 1. The dominant effect in a tsunami situation is the impact

    due to waterborne objects. These results in the bare frame indicate that the displacement due to debris impact is up to 78% larger than that produced by the combined effect of hydrodynamic and impulsive loading.

    2. The bare frame building experiences significant displacements (up to 58.2 mm at the 2nd floor) when impacted by a water-borne object. The impact leads to yielding of reinforcement on a ground floor column, which may cause excessive rotations and eventually produce a catastrophic failure.

    3. The CFRP strengthening intervention was very effective at reducing potential failure of the strengthened building. The initial analysis (i) with CFRP strengthening at supports reduces moderately the displacement of the building by up to 20%. The application of CFRP at the impact section is more effective at reducing displacements up to 58%. These lower displacements are expected to lead to less damage in the structure.

    4. In addition to structural strengthening of single buildings, other alternatives to mitigate potential damage due to tsunamis such as coastal vegetation or tsunami forests can be implemented. These cost-effective and environmentally friendly solutions can absorb and

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  • dissipate energy from impact forces and can be suitable to protect groups of buildings in tsunami-prone regions of Sri Lanka and other developing countries.

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    [11] Madurapperuma K.M. & Wijeyewickrema A.C. (2008). Nonlinear response of RC buildings due to impact of tsunami water-borne boats and containers. 14th World Conference on Earthquake Engineering, International Association for Earthquake Engineering, October, Beijing, China.

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    [13] Garcia R, Hajirasouliha I, Pilakoutas K (2010) Seismic behaviour of deficient RC frames strengthened with CFRP composites. Eng Struct 32(10), 3075-3085.

    [14] Garcia, R., Hajirasouliha, I., Guadagnini, M., Helal, Y., Jemaa, Y., Pilakoutas, K. et al. (2014) Full-scale shaking table tests on a substandard RC building repaired and strengthened with Post-Tensioned Metal Straps. J Earthquake Eng, 18(2), 187-213.

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