Thermal actions considered on abutments of integral bridges by the European standard (Eurocode 1) might be in variety of certain situations underestimated. Based on this assumption, thermal monitoring system has been designed and installed into structure of bridge No. 27-117. Temperature profiles in five certain spots are being measured to provide sufficient basis for evaluation of real thermal actions on abutments of integral bridges. For purpose of measurement verification, elementary heat transfer models for finite element method solver were created. These models are being loaded by simplified temperature profiles reached in real time in-situ. Evaluated models provide verification data to compare with measured temperature profiles in structure and might provide information about temperature profiles probably reached during extreme weather situations

Jonáš, Martin

Zatloukal, Jan

English

CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)

https://doi.org/10.14311/APP.2022.34.0020Acta Polytechnica CTU Proceedings 34:20–25, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licencePublished by the Czech Technical University in PragueHEAT TRANSFER MODEL VERIFICATION FOR THERMALMONITORING SYSTEM OF INTEGRAL BRIDGESMartin Jonáš∗, Jan ZatloukalCzech Technical University in Prague, Faculty of Civil Engineering, Experimental Centre, Thákurova 7, 166 29Prague 6, Czech Republic∗ corresponding author: martin.jonas@fsv.cvut.czAbstract. Thermal actions considered on abutments of integral bridges by the European standard(Eurocode 1) might be in variety of certain situations underestimated. Based on this assumption, thermalmonitoring system has been designed and installed into structure of bridge No. 27-117. Temperatureprofiles in five certain spots are being measured to provide sufficient basis for evaluation of real thermalactions on abutments of integral bridges. For purpose of measurement verification, elementary heattransfer models for finite element method solver were created. These models are being loaded bysimplified temperature profiles reached in real time in-situ. Evaluated models provide verification datato compare with measured temperature profiles in structure and might provide information abouttemperature profiles probably reached during extreme weather situations.Keywords: Thermal actions, integral bridge, thermal monitoring, heat transfer.1. IntroductionWhile integral bridges do not allow free temperaturedilatation of bridge deck, shifts are transferred intoabutments and subsequently into surrounding soil.Therefore, proper investigation of interaction betweensoil and structure is necessary. Soil-structure interac-tion problem of integral bridges is widely described inliterature. More than sufficient background is avail-able for thermal actions on bridge decks and effectsbound with them. In case of temperature loading ofabutments is the situation weaker. Overall influenceof lack of more accurate approach to temperatureloading of abutments might not be very significant.However, in some cases it might be suitable to con-sider distribution of temperature in the structure moreprecisely.Thermal actions considered on integral bridges be-ing designed in the Czech Republic are given by Eu-ropean standard EN 1991-1-5 [1], its national annexČSN EN 1991-1-5[2] and in case of road bridges alsoby Technical conditions TP 261[3] issued by Ministryof Transport. These documents provide wide and spe-cific approach to consideration of thermal actions onbridge structures. However, in case of bridge piersand abutments, none of these documents can providespecific background sufficient enough for proper anal-ysis of specific temperature states of these parts ofstructures. On the other side, it is not expected, thatneglecting of more precise thermal action analysis ofstructure parts might lead to more or less seriousdamage of structure. Rather, it could lead to thelong-term negligible degradation of materials used instructure, which could result in reduced service life ofstructure.To cover these potential excess of standard back-ground, stationary measurement system was designedand installed into bridge No. 27-117. System is cre-ated to monitor temperatures in multiple profiles de-ployed across the whole structure.Last, but not least, heat transfer models of mea-sured spots were created for purpose of measurementverification. Their accessory use is for preliminarymodelling of potential temperature states reached instructure during the whole year, while the full opera-tion of system is not launched.2. Thermal actions on abutmentsof integral bridgesBackground given by standards and conditions [1][2][3]for thermal loading of piers and abutments is verysimple. Except of uniform temperature component,linear temperature component is given by recommen-dation [1]. National annex, nor Technical conditionsdoes not specify more precisely horizontal/verticaltemperature components, as they do in case of bridgedeck or beams, for example. Therefore, linear hori-zontal temperature component is used according torecommendation of values for concrete piers and walls.Linear temperature difference with value of 5 °C be-tween outer edges of concrete piers is used and lineartemperature difference with value of 15 °C betweeninner and outer edge of wall is used.3. Monitoring system on bridgeNo. 27-017For purpose of proper analysis of thermal actions onintegral bridges, stationary measurement system wasdesigned and installed into the bridge No. 27-017 inŽelezná Ruda - Alžbětín. This bridge was chosen forits suitable location in the Šumava mountains, wheremore extreme weather conditions can occur (during20vol. 34/2022 Heat transfer model verification for thermal monitoring system of integral bridgesthe winter 2020-21 temperatures reached about -20°C). The main function of monitoring system is mea-surement of temperatures in multiple spots deployedacross the bridge structure. Its secondary functionis measurement of strain and humidity in the bridgedeck. Whole system will be fully automatic and willsend measured data to the server on its own.Figure 1. Deployment of all the measured spots inthe ground plan of the bridge structure.Temperature profiles, which are being measuredare chosen according to expectations and purpose ofmeasurement. Two spots are deployed in bridge deck,where, on each spot, temperature of steel beam andconcrete is measured. For bridge deck, standards givemore possibilities of vertical temperature differenceconsideration. Therefore, it is not expected, thatmeasured temperature profiles in bridge deck wouldexceed values given by standard. Other three spots arelocated in abutment shaft, each spot is implementedby 6 thermometers. Measurements in the abutmentshaft are divided across the width of abutment, sothat possibility of sunlit thermal influence is covered.While the standard[1] gives temperature difference of5 °C, it is highly probable, this value will be exceededin measured abutment.PT 1000 thermometers were used due to their ro-bustness, accuracy and simplicity of operation. Ther-mometers dedicated for concrete temperature mea-surement are all specifically prepared for quick, accu-rate and safe installation into bridge structure. Thispreparation consists of thermometer encapsulationinto "shells" made of high-performance concrete (us-ing MSK-2 substance[4]) and further preparation ofprefabricated casing beams, where are thermometersprecisely deployed in accurate positions. Concretecasing beam is further installed into bridge structureFigure 2. Example of the thermometer deploymentinto the bridge deck with usage of the prefabricatedcasing beam.only by inserting into grid of reinforcement bars andfixating its position in proper place. Thermometersmeasuring temperature of steel are attached to thefiller steel beam by hot glue from the outer side, sothat the contact of thermometer and steel is secured.Figure 3. Installed casing beam with thermometersin abutment shaft. Cables are led along reinforcementrods for protection before damage during concretingof abutment shaft.Measurement is processed by the switchboard solelydesigned for purpose of inexpensive, reliable and sim-ple monitoring systems suitable for structures, wheremonitoring of specific values is required or suitable.Switchboard is designed for significant reduction ofcosts, while usually used loggers are expensive anddifficult to obtain in reduced time. Thus, price isreduced from few hundred thousand to several tensof thousands CZK. Core of switchboard is tiny Rasp-berry Pi computer, which processes measured data.Temperature measurement itself is processed by Lu-cid IO reading units, which are designed and widelyused for resistance sensors. Power supply might besecured by connection into power grid, or by usage ofsmall solar panel. Backup power supply is providedby common 12V batteries. Switchboard is connectedvia modem to the internet and sends measured datato the server regularly. Temperature measurementperiod is basically set to 30 minutes.21Martin Jonáš, Jan Zatloukal Acta Polytechnica CTU ProceedingsFigure 4. Installed switchboard on-site.4. Thermal modelsWhile the commissioning of measurement system wasdelayed, computer simulations seemed as a suitablereplacement of first data evaluation. 2D heat transfermodels of measured spots in structure were createdto simulate first data of temperature division alongthe thickness of abutment shaft or bridge deck duringseason extremes. However, their main purpose is veri-fication of measured data in following months, whenmeasurement system will fully start its operation.The thermal model is created for OOFEM solversoftware [5] and solves heat transport. Material prop-erties, such as density, thermal capacity and conduc-tivity are defined. The linear 2D elements are used inthese models and geometry with mesh were createdin Salome processor.4.1. Abutment modelAbutments model describes cross-section of measuredspot in the abutment shaft. Model consists of threelayers, 2 concrete layers and one layer of soil. Twolayers of concrete are used to enable finer elementmesh in the contact of concrete with air.Width of model is 3 m, height is 1,8 m, from whichlayer of concrete takes 0,6 m, rest height of 1,2 mrepresents soil. Concrete is split into two layers, firstlayer with height of 0,1 m, second of 0,5 m. Quad-rangle mesh was used, always 10 elements per edgeof face, resulting in 100 elements per one face. Sizeof mesh is chosen so that positions of sensors in realstructure are in mesh nodes.Initial and boundary conditions are set for thismodel very simple. Initial temperature is set for allnodes to equal initial value. Boundary condition isset for both edges. Dirichlet’s condition is used onbottom edge (immutable set temperature). Top edgehas two boundary conditions, Newton’s (contact withambient air) and Stefan-Boltzmann’s (heat radiation).Load is performed by temperature profile typical forextreme situations.Figure 5. Mesh for abutment shaft model with visiblelayers.4.2. Bridge deck modelTwo different models in bridge deck are created, ac-cording to deployment of sensors in real structure.First model replaces spot under traffic lane, secondone represents spot under granite pavement. Modelof bridge deck under traffic lane consist of cut outfrom cross-section of bridge deck. Model contains allmaterials of bearing structure, insulation and layers ofroadway. Bearing structure is a composition of steelfiller beams, CETRIS plates and concrete, which fillswhole remaining area. On the top of concrete, insula-tion made of asphalt strips (NAIP) is made. Threelayers of different asphalt concretes are laid on theinsulation. These three layers have parameters setidentical, while the thermal parameters are similar andit would be necessary to obtain them experimentally.Filler beams are of HEB240 profile with narrowedtop flange. On the bottom flanges, CETRIS plate of20 mm thickness is put as lost formwork. Concretelayer of 280 mm thickness is concreted. Insulationlayer (NAIP) is 10 mm thick. Three layers of asphaltconcrete are embedded into one, 135 mm thick. Wholemodel is 1200 mm wide.Triangular mesh with elements of minimal size with5 mm edge is used. Maximal element size with 100mm edge is set. Initial condition represents initialtemperature of all nodes varying to situation beingsolved. Three boundary conditions are used on thetop edge of model, Newton’s (contact with ambientair), Stefan-Boltzmann’s (heat radiation) and Neu-mann’s (sun glare). On the bottom edge is Neumann’sboundary condition omitted. Temperature and glarefunctions are set according to available information.Second one, model of cut-out from the bridge deckunder pavement contains all materials of bearing struc-ture and layers of pavement. Bearing structure is acomposition of steel filler beams, CETRIS plates andconcrete, which fills whole remaining area. Pavementconsist of two layers, bed layer of concrete and granitepavement.Filler beams are of HEA300 profile with narrowedtop flange. On the bottom flanges, CETRIS plate of20 mm thickness is put as lost formwork. Concrete22vol. 34/2022 Heat transfer model verification for thermal monitoring system of integral bridgesFigure 6. Mesh for bridge deck model under trafficlane with visible layers.layer of 440 mm thickness is concreted. Concrete bedlayer of pavement is 100 mm thick with 200 mm thicklayer of granite pavement on it. Whole model is 1200mm wide.Mesh, elements, elementary and boundary condi-tions are identical with the model of bridge deck undertraffic lane.4.3. Material propertiesMaterial parameters for each modelled material aredefined in the model. Heat capacity c, volumetric massdensity γ, thermal conductivity λ and emmisivity εhave to be specified. Most of the values are takenfrom EngineeringToolBox [6]. Parameters for concretewere measured at the laboratory and their values arefor concrete used in abutments c = 806 Jkg−1K−1, λ= 2.638 Wm−1K−1, γ = 2327 kgm−3 and for concreteused in the bridge deck c = 770 Jkg−1K−1, λ = 2.238Wm−1K−1, γ = 2253 kgm−3.5. Model situationsEach model was loaded by three extreme model situa-tions, representing coldest days in winter, most warmdays in summer and days with maximal temperaturedifference during 12 hours. These situations were con-sidered to simulate maximal temperature differenceacross the thickness of bridge deck or abutment shaft.5.1. Minimal temperatureAccording to data from CHMI[7], lowest reached airtemperature was -22 °C, what was considered intodesign of thermal loading function. Time period forcomputation was set to 200 hours (8 days and 8 hours)and model was loaded with following temperaturefunction:t(t) = 6 sin[(2π86400)∗ (t− 9 ∗ 3600)]− 16 (1)This function represents cold winter day with clearsky, when minimal temperature of -22 °C is reachedbefore sunrise and highest day temperature rises to-10 °C. Initial temperature was set to 0 °C for allnodes.Results confirmed expectation about standard val-ues exceeding in abutment shafts, reaching the differ-ence of about 14 °C, see Fig 7. In bridge deck, reachedvalues did not exceed standard values.Figure 7. Horizontal temperature difference in abut-ment shaft.5.2. Maximal temperatureMaximal temperature profile expects warm summerday with maximal temperature of 35 °C (maximalreached temperature was 34,8 °C) and minimal tem-perature of 21 °C in the night. Amplitude of temper-ature sin function was set to 7 °C, temperature shiftto 28 °C, period of time was 200 hours and initialtemperature 20 °C.Bridge deck models were loaded also by sun glare.Solar irradiance is represented by time-dependent func-tion of heat flux Q(t). To ensure exclusion of negativepart of sine wave, Heaviside step function was used.Amplitude of heat flux Q(t) was set to 800 Wm−2.Results have shown again, that in case of abutmentshaft, reached horizontal temperature differences aresignificantly higher than standard considers. However,the difference was lower than in minimal temperaturesituation. In case of bridge deck, values did not exceedstandard again.Figure 8. Heating of both surfaces during the day inthe bridge deck, in spot under pavement.5.3. Maximal temperature fluctuationMaximal temperature fluctuation might be repre-sented by a day with high afternoon temperatures,which falls deep in the night before dawn. This periodoccurs in the early autumn months. Representative23Martin Jonáš, Jan Zatloukal Acta Polytechnica CTU Proceedingsday with extreme temperature fluctuation was mod-elled. Maximal temperature is 26 °C and minimalduring the night falls to 0 °C (ground frosts). Initialtemperature was set to 10 °C and period of time to200 hours.Bridge deck models were loaded by sun glare again.Amplitude of heat flux Q(t) was set to 650 W−2.Results have confirmed the expectations again, inabutment shaft, temperature difference reached al-most 10 °C. The difference is therefore lower than inminimal temperature and comparable with maximaltemperature simulation. Temperature fluctuation inthe abutment shaft is shown in Fig 9 In case of bridgedeck, values did not exceed standard again.Figure 9. Temperature development in sensor spots,surface is represented by dark red line (600 ⇒ 600 mmfrom contact soil-concrete), contact with soil by blueline.6. First control measurementTogether with switchboard installation, first controlmeasurement was taken. Data from all the sensorswere taken and stored. Due to weather, measuredtemperature profiles were with minimal temperaturedifference between outer edges. Weather few daysaround installation dramatically changed more timesand during the installation, temperature was almostconstant during whole day. Therefore, computationof verification model was practically disabled, whilethe model needs few-day settled weather. However, itwas possible to evaluate at least temperature changein measured spots, what can be seen for abutmentshaft in Fig 10.7. Further progressTogether with full operation of the monitoring system,models will be finally used for their main purpose,verification of measured data, what was not possibleuntil today. During the verification process, modelparameters should be fitted. Special attention shouldbe dedicated to adjustment of loading functions, wheresome parameters are at least uncertain, especially solarirradiance, which may be highly influenced by manyimpacts.8. ConclusionAutomatic measurement system should provide long-term data for completion of thermal actions standardFigure 10. Measured temperature profiles in threespots in the abutment shaft (1 ⇒ 1 m from the edge ofabutment; 2 ⇒ 4 m from the edge; 3 ⇒ in the middleof the abutment).background needed for proper complex analysis of in-tegral bridges. According to models, evaluated beforefull system operation, thermal actions on abutmentsreach significantly higher effects than literature consid-ers. Therefore, detailed evaluation of long-term mea-surement will be important to implement into analysissources and consider in future designed bridges.Price and simplicity of used measurement systemis very strong argument for installation of similar sys-tems into newly constructed structures, where avail-able sources for analysis might be insufficient, or con-sider irrationally high load effects. E.g., almost identi-cal systems are now being installed into three tunnelsunder construction in Czech Republic.AcknowledgementsThis work has been supported by the Technology Agency ofthe Czech Republic under the project TH04010038 Systemfor permanent monitoring of material degradation in civilstructures.References[1] EN 1991-1-5: Eurocode 1: Actions on structures -Part 1-5: General actions - Thermal actions. Tech. rep.,The European Union Per Regulation, 2003.[2] ČSN EN 1991-1-5. Eurokód 1: Zatížení konstrukcí -Část 1-5: Obecná zatížení - Zatížení teplotou. Tech.rep., Úřad pro technickou normalizaci, metrologii astátní zkušebnictví, 2005.[3] M. Drahorád, M. Foglar, B. Polák, V. Hrdoušek.Integrované mosty, TP261. Tech. rep., Ministerstvodopravy, 2017.[4] Z. Bažantová, K. Kolář, P. Konvalinka, et al.Multifunkční silikátový kompozit programovatelnýchvlastností nejen pro rychlé opravy cementobetonovýchkonstrukcí. Materiály pro stavbu 22(9):34–37, 2016.[5] B. Patzák. OOFEM project home page.http://www.oofem.org, CTU in Prague, Faculty of CivilEngineering, Prague, since 2000.24vol. 34/2022 Heat transfer model verification for thermal monitoring system of integral bridges[6] EngineeringToolBox. Material Properties.https://www.engineeringtoolbox.com/material-properties-t_24.html.[7] ČHMÚ. Měsíční a roční data dle zákona 123/1998 Sb.http://portal.chmi.cz/historicka-data/pocasi/mesicni-data/mesicni-data-dle-z.-123-1998-Sb.25

Heat transfer model verification for thermal monitoring system of integral bridges

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Heat transfer model verification for thermal monitoring system of integral bridges

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