SLS Reliability considering autogenous self-sealing in tension governed reinforced concrete water retaining structures

Way, Andrew Christopher (2021-03)

Thesis (PhD)--Stellenbosch University, 2021.

Thesis

ENGLISH ABSTRACT: This research considers the achieved serviceability limit state (SLS) reliability in tension-governed, re-inforced concrete water retaining structures (RC WRS). Currently, the level of achieved SLS reliabilityin WRS is unknown. Structural codes used to design WRS, such as EN 1992-3 and thefibModel Code2010 (MC 2010), typically specify a 50-year irreversible SLS target reliability index ofβ= 1.5. Whetheror not this level of reliability is actually achieved, however, has not been determined to date. Due tothis, the ability to optimally design these structures to realize cost and material savings is stifled.The design of RC WRS is governed by the limitation of leakage of the stored liquid to acceptablelevels. The limitation of crack widths is used as a critical design parameter in structural codes. Allstructural codes used to design RC WRS qualitatively mention the beneficial effect that autogenousself-sealing has on the reduction of crack widths and leakage over time in the concrete, however, fewattach any quantitative measure to this effect or link it to the specification of target crack widths. Thisdissertation thus aims to quantify the achieved level of SLS reliability in RC WRS by: 1. Probabil-istically characterizing the beneficial effect of autogenous self-sealing on the leakage through a singlecrack in a RC WRS, 2. Developing a probabilistic analysis that determines the achieved level of SLSreliability in an entire RC WRS considering the effect of self-sealing, 3. Comparing the results to thetarget reliability in structural design codes, and 4. Making recommendations based on the results andidentified trends. Two experimental databases were compiled to achieve the first aim. The first is for the probabilisticcharacterization of the initial flow through a tension crack in concrete. For this purpose, a novel initialflow prediction model factor was characterized by a Weibull distribution. The second database is usedto probabilistically quantify the effect that self-sealing has on the reduction of leakage flow over time,considering crack width and the ratio of water pressure head to wall thickness, (hD/hin EN 1992-3).A novel leakage accumulation factor is defined and characterized by a Weibull distribution for thispurpose.A Monte Carlo reliability analysis was used to determine the achieved level of leakage related SLSreliability in a tension governed RC WRS, incorporating the effect of autogenous self-sealing. The ana-lysis uses the MC 2010 crack prediction model for the stabilized cracking phase. The theory of leakagethrough a single crack in concrete was used to consider the leakage through all cracks in a RC WRS.A SLS reliability limit state was established as the difference between the allowable, and the predictedleakage. A sensitivity analysis was performed on the model using FORM, in order to determine upperand lower reliability limits and to identify which parameters contributed the most uncertainty to thelimit state. The limit state was evaluated for 235 combinations of round RC WRS geometries andcharacteristics, for four leakage regimes, which correspond to commonly used stabilization periods andtest times used in the water tightness test of WRS. Target crack widths were shown to be dependent on the water pressure head to wall thickness ratio,in agreement with EN 1992-3. The target crack widths given by EN 1992-3 were found to be tooconservative for three out of the four leakage regimes for an SLS reliability level ofβ= 1.5. The MC2010 recommendation of a target crack width of0.2mmresulted in consistently inadequate valuesofβ <1.5, and notably so for higher water pressure head to wall thickness ratios. A trend of targetcrack width vs the ratio of the maximum applied tension to the mean tensile resistance of the wall wasidentified as a means by which target crack widths may be specified. Recommendations are made fortarget crack width vs water pressure head to wall thickness ratio, as well as for target crack width vsthe ratio of the maximum applied tension to the mean tensile resistance of the wall, to achieve an SLSreliability ofβ= 1.5for the stabilized cracking phase. The novel leakage reliability analysis from thisresearch determines the level of SLS reliability in RC WRS and makes the design- and cost-optimizationof tension-governed, RC WRS possible.

AFRIKAANSE OPSOMMING: Die betroubaarheid van die diensbaarheid limietstaat (DLS) in trekspanning-beheerde, gewapendebeton waterhoudende strukture (GB WHS) word ondersoek. Strukturele kodes wat gebruik wordom WHS te ontwerp, soos EN 1992-3 en diefibModel Code 2010 (MC 2010), spesifiseer gewoonlik’n 50-jaar onomkeerbare DLS teiken betroubaarheidsindeks vanβ= 1.5. Die werklike vlak van bet-roubaarheid wat bereik word is onbekend, en moeilik om te bepaal. Koste- en materiaalbesparings kanbewerkstellig word deur die optimale betroubaarheidsgebaseerde ontwerp van hierdie strukture.Die ontwerp van GB WHS is onderworpe aan beperkings met betrekking tot aanvaarbare vlakke vanlekkasie van die gestoorde vloeistof. Die beperking van kraakwydtes word as ’n kritieke ontwerpparameter in strukturele kodes gebruik. Alle strukturele kodes wat gebruik word om GB WHS teontwerp noem die voordelige effek wat outogene self-verseëling op die vermindering van kraakwydtesen lekkasie oor tyd in die beton het, maar min heg egter ’n kwantitatiewe maatstaf hieraan of koppeldit aan die spesifikasie van kraakwydtes. Die doel van hierdie navorsing is dus om die bereikte vlakvan DLS-betroubaarheid in GB WHS te kwantifiseer deur: 1. Die waarskynlikheidskarakterisering vandie voordelige effek van outogene self-verseëling op die lekkasie deur ‘n enkele kraak in ‘n GB WHS,2. ’n waarskynlikheidsanalise te gebruik om die bereikte vlak van DLS betroubaarheid in GB WHS tebepaal, die effek van self-verseëling in ag genome, 3. Om die resultate met die teikenbetroubaarheidin strukturele ontwerpkodes te vergelyk, en 4. Om aanbevelings te maak, gebaseer op die resultate engeïdentifiseerde tendense. Twee eksperimentele databasisse is saamgestel ten einde die eerste doel te bereik. Die eerste databasisis gebruik vir die waarskynlikheidskarakterisering van die aanvanklike vloei deur ’n trekspanningskraakin beton. Hier is gevind dat Weibull verdelings aanvanklike vloei-voorspellingsmodelfaktore karakter-iseer. Die tweede databasis is gebruik om ‘n waarskynlikheids kwantifisering te maak van die effek watself-verseëling op die vermindering van lekvloei oor tyd het, met die kraakwydte en die verhouding vanwaterdrukhoogte tot wanddikte, (hD/hin EN 1992-3) in ag genome. Vir hierdie doel is ’n lekkasie-ophopingsfaktor gekarakteriseer, wat ook goed beskryf is deur Weibull-verdelings.’n Monte Carlo-analise is gebruik om die bereikte vlak van lekkasie-verwante DLS-betroubaarheid in’n trekspanning-beheerde GB WHS te bepaal, wat die effek van outogene self-verseëling insluit. Dieanalise maak gebruik van die MC 2010-voorspellingsmodel vir krake in die gestabiliseerde kraakfase.Die teorie van lekkasie deur ’n enkele kraak in beton is gebruik vir die beskouing van lekkasie deuralle krake in ’n GB WHS. ’n DLS-betroubaarheid limietstaat is vasgestel as die verskil tussen dietoelaatbare en die voorspelde lekkasie. ’n Sensitiwiteitsanalise is op die model uitgevoer met behulpvan FORM om die boonste en onderste betroubaarheidsgrense te bepaal en om te identifiseer watterparameters die grootste onsekerheid tot die limietstaat bydra. Die limietstaat is vir 235 kombinasiesvan ronde GB WHS-geometrieë en eienskappe, met betrekking tot vier lekkasie-regimes geeëvalueer.Die lekkasie-regimes stem ooreen met die algemeen gebruikte stabiliseringtydperke en toetstye watgebruik word in die waterdigtheidstoets van WHS. Daar is bevind dat die teikenkraakwydte afhanklik is van die verhouding van die waterdrukhoogtetot die wanddikte, in ooreenstemming met EN 1992-3. Daar is gevind dat die teikenkraakwydte vanEN 1992-3 te konserwatief is vir drie uit die vier lekkasie-regimes vir ’n DLS-betroubaarheidsvlakvanβ= 1.5. Die MC 2010 teikenkraakwydte van 0.2 mm is onvoldoende omβ >1.5te haal, veralvir hoër verhoudings van waterdrukhoogte tot wanddikte. ’n Tendens van teikenkraakwydte teenoordie verhouding van die maksimum toegepaste trekspanning tot die gemiddelde trekweerstand van diemuur, is identifiseer as ’n alternatiewe basis vir die spesifisering van teikenkraakwydtes. Aanbevelingsword gemaak vir die teikenkraakwydte teen die verhouding van waterdrukhoogte tot wanddikte, sowel as vir die kraakwydte teenoor die verhouding van die maksimum toegepaste spanning tot die gemiddeldetrekweerstand van die muur om ’n DLS-betroubaarheid vanβ= 1.5te bereik vir die gestabiliseerdekraakfase. Die bepaling van die DLS-betroubaarheid in GB WHS uit hierdie navorsing maak verbeterdeontwerp en koste-optimalisering van trekspanning-beheerde GB WHS moontlik.

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