The paper describes innovative parapet solution based on special shaped blocks made form textile-reinforced concrete - TRC. The blocks are designed for a placement at the parapet of building with a flat roof. The solution is appropriate for buildings with precast-concrete bearing structure by following the principle of precast technology (short construction time, minimal technological pauses). However, presented parapet TRC blocks can be used for energy efficient buildings as well in combination with thick layers of thermal insulation. The technical solution was registered as utility model no. CZ27642(U1)

Hájek, Petr

Nývlt, Michal

Pazderka, Jiří

Žáková, Hana

English

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

https://doi.org/10.14311/APP.2022.33.0463Acta Polytechnica CTU Proceedings 33:463–466, 2022 © 2022 The Author(s). Licensed under a CC-BY 4.0 licencePublished by the Czech Technical University in PraguePARAPET STRUCTURE FROM SPECIAL SHAPED TRC BLOCKSJiří Pazderka, Petr Hájek, Michal Nývlt∗, Hana ŽákováCzech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7 166 29 Prague, CzechRepublic∗ corresponding author: michal.nyvlt@fsv.cvut.czAbstract.The paper describes innovative parapet solution based on special shaped blocks made form textile-reinforced concrete - TRC. The blocks are designed for a placement at the parapet of building witha flat roof. The solution is appropriate for buildings with precast-concrete bearing structure by fol-lowing the principle of precast technology (short construction time, minimal technological pauses).However, presented parapet TRC blocks can be used for energy efficient buildings as well in combina-tion with thick layers of thermal insulation. The technical solution was registered as utility model no.CZ27642(U1).Keywords: Concrete, parapet, prefabrication, roof, TRC.1. IntroductionNowadays, the emphasis is on energy savings in thefield of building construction. The solution of build-ing envelope details is important for contemporarydesign of buildings. An important part of this issueis the solution of the detail of flat roofs of buildings inthe form of a low parapet wall. For buildings whoseload-bearing structure consists of precast frame con-struction system, the parapet wall design is an im-portant part of the overall design. The main advan-tage of precast technology is the minimization of wetprocesses on site which resulting to short construc-tion time. In order to minimize the wet processesin precast construction systems, it is desirable thatthe parapet wall structure should also be prefabri-cated. However, this assumption is often not fulfilled,because at the present time the construction of theparapet wall in precast frame systems is commonlysolved in the form of a masonry wall from variousmaterials. In some cases, the parapet wall is in theform of a specially modified beam which combinesthe function of supporting the ceiling structure (spe-cially adapted bearing girder) with the function ofthe parapet wall. However, such prefabricates usu-ally represent a distinct architectural element (notsuitable for most buildings) and at the same time al-most do not consider the problem of linear thermalbridges (it cannot be used for modern energy effi-cient buildings). However, the requirement to mini-mize thermal bridges is one of the key parameters ofthe design of building envelope structures in today’sbuilding construction.The solution currently used for the construction ofa parapet wall on a flat roof in the form of aăma-sonry wall (mentioned above), presents several disad-vantages. This is especially addition of another wetprocess into site construction which resulting to re-duction of efficiency and speed of construction (notexploiting the potential of precast technology). An-other significant problem is the risk of deformationof the masonry parapet wall (displacement due toshear stress in masonry) over time, which is oftenassociated with aăfailure of the roof waterproofinglayer. The parapet made in the form of aăspeciallymodified beam (specially adapted bearing girder) isa more suitable solution in terms of in situ efficiencybut these elements are always part of standardizedconstruction systems with predefined dimensions (thepossibilities of using are limited due to architecturaldesign). Another problem may be the high weight ofthe parapet bearing beam and the resulting compli-cations in terms of handling the precast.2. Parapet structure fromspecial shaped TRC blocksThe above-mentioned disadvantages of existing para-pet structures of flat roofs of buildings based onprecast frame system (masonry and parapet bearingbeams) are largely eliminated using specially shapedparapet blocks made of textile reinforcement concrete(TRC) [1]. The essence of the parapet block is thatit is made of precast reinforced concrete with an op-timized (lightweight) shape solution with aăcrosssec-tion in the shape of the letter "L". The vertical wall ofthe parapet block is formed by a thin plate (30ămmthick), which is reinforced by reinforcing ribs (50×100mm) at distances of 0.7 − 0.8 m. The stiffening ribscomprise a bending reinforcement. The low platethickness between the reinforcing ribs is made possi-ble using high-performance concrete (HPC) in combi-nation with textile reinforcement (TRC). The bottomhorizontal slab of the block has a variable thicknesswhich increases towards the centre of the block (thick-ness 30−80 mm). The lower horizontal plate is madeof TRC and, like the vertical plate, is reinforced withreinforcing ribs (50×100 to 137 mm) spaced 0.7−0.8463J. Pazderka, P. Hájek, M. Nývlt, H. Žáková Acta Polytechnica CTU ProceedingsFigure 1. Special shaped parapet block (visualization).m apart. These ribs, together with the ribs of the ver-tical plate, form an "L" -shaped frame structure withreinforcement in the centre of the block. The variablethickness of the horizontal slab is advantageous bothin terms of precast technology (concreting will takeplace from the outer surface of the vertical slab) andin terms of better stability of the shaped piece (lowercentre of gravity).The parapet block is equipped with a horizontalcross rib (30×100 mm) at the top, which serves for an-choring of the flashing structure (through the spacerprofile). The rib on the top of the parapet block alsohas a reinforcing function in terms of the horizontalload on the parapet wall (wind pressure, suction, an-choring of other structures). To ensure the fixation ofthe position, the block is equipped with three holesin the lower horizontal plate, which are used for an-choring the block to the ceiling panel of the framesystem.The shape-optimized "thin-walled" design of theparapet block is advantageous both in terms of mini-mizing the weight of the precast element during trans-portation and subsequent handling on site. At thesame time, it is also advantageous the reducing ofoverall vertical load on the bearing structures andfoundations of the building. The subtle optimizedshape of the precast block using TRC is also advanta-geous in terms of eliminating thermal bridges. Onlya minimal cross-section of a part of the supportingstructure penetrates the thermal insulation envelopeof the building. In fact, it is not a thermal bridge, be-cause the parapet construction must always be thor-oughly insulated around its perimeter. This designpredetermines the parapet block for use in energy ef-ficient buildings. For handling by lifting means, theblock will be equipped with countersunk threads forscrewing in the anchorages. These threads will belocated on the upper surface of the horizontal rein-forcing rib at the position of the vertical reinforcingribs.3. Description of the functionalprincipleFigure 3 shows the installation of the precast parapetblock (no. 1) on the ceiling structure of a precastconcrete frame construction system comprising ceil-ing panels (no. 2) and beams (no. 3). The parapetblock (no. 1) is secured (fixed) against horizontalmovements by anchoring at the anchor holes (no. 4).The lower horizontal slab of the parapet block (no.5) is"weighted" by a layer of gravity concrete (no.ă6),which thus acts as a stabilizing layer. At its lower leftedge, the parapet block (no. 1) is separated from theconcrete layer forming a gradient (no. 7) by meansof an inserted thermal insulator strip (no. 8), whicheliminates the transfer of horizontal deformations ofthe concrete layer due to longitudinal thermal expan-sion.On the upper horizontal reinforcement rib of theparapet block (no. 9) is an anchored construction ofthe flashing (no. 10). The vertical panel of the para-pet block (no. 11) is supplemented by an additionalthermal insulating layer (no. 12), which compensatesfor the higher thermal conductivity coefficient HPC(compared to the adjoining masonry of the externalcladding (no. 13)). An additional thermal insulationlayer (no. 11) is connected to the thermal insulationsystem of the facade cladding (no. 14), which is tight-ened up to the thermal insulation under the flashing(no. 15). From the inside of the roof, a vertical layerof thermal insulator (no. 16) is anchored to the para-pet block. This layer follows the thermal insulationof the flat roof (no. 17). The thickness of the verticalthermal insulation (no. 15) is designed to overlap thereinforcing rib (no. 18) of the parapet block.Figure 4 shows precast parapet block (no. 1) whichforms the supporting structure of the parapet shownin Figure 3. The parapet block (no. 1) is character-ized in that it is made in the cross-sectional shapeof the letter"L", where the thin vertical plate of theblock (no. 11) is reinforced with ribs (no. 18). Thevertical ribs are reinforced at the point of connection464vol. 33/2022 Parapet Structure from Special Shaped TRC BlocksFigure 2. Installation of special shaped parapet block on the building (simplified visualization).Figure 3. Example of parapet block installation on the ceiling structure of precast concrete frame constructionsystem. Notes: 1 - parapet block, 2 - reinforced concrete ceiling panel, 3 - reinforced concrete beam, 4 - anchoring ofparapet block, 5 - horizontal part of parapet block, 6 - monolithic concrete - layer forming a gradient and stabilizesthe parapet block, 7 - monolithic concrete - layer forming a gradient, 8 - dilatation, elastic strip, 9 - the upperpart of the parapet block, 10 - anchoring of parapet block, 11 - vertical part of parapet block, 12 - lower thermalinsulation layer (compensation for reinforced concrete elements), 13 - filling masonry of perimeter wall, 14 - mainthermal insulation layer (ETICS), 15 - insulation of parapet extruded polystyrene (XPS), 16 - insulation of parapetblock, 17 - conventional roofing layers of flat roof, 18 - reinforcing rib of parapet block465J. Pazderka, P. Hájek, M. Nývlt, H. Žáková Acta Polytechnica CTU ProceedingsFigure 4. Precast parapet block. Notes: 1 - parapet block, 4 - anchoring of parapet block, 5 - horizontal part ofparapet block, 9 - the upper part of the parapet block, 11 - vertical part of parapet block, 18 - vertical reinforcementrib of parapet block, 19 - horizontal reinforcement rib of parapet block, 20 - rib reinforcement.to the ribs of the horizontal plate (no. 19) by triangu-lar haunches (no. 20) and together with the reinforc-ing ribs of the lower horizontal plate (no. 19) form"L"frame structure. The solved parapet block (no. 1) ischaracterized in that it comprises a lower horizontalplate (no. 5) of variable thickness which increasestowards the centre of the precast. This plate is rein-forced with ribs (No. 19) which have an increasingthickness towards the centre of the prefabricated el-ements. The lower horizontal plate (no. 5) has threeholes (no. 4) for anchoring the precast to the ceilingpanel of the framework system. The parapet block(no. 1) is provided with aătransverse rib (no.ă9) atthe top of the vertical plate (no. 11), which servesto anchor the parapet block flashing structure and toreinforce it in terms of horizontal loading.4. ConclusionThe technical solution of the parapet block for flatroofs described in the paper was registered as a util-ity model no. CZ27642(U1). The block is intendedprimarily for energy-efficient buildings based on pre-cast frame construction systems. However, it can beused without further modifications for parapet solu-tions in other building construction systems (e.g. ma-sonry buildings with precast concrete ceiling), wherethe advantage of the precast technology will be bene-ficial. The parapet block is the next element used forconstruction details in buildings, expanding the ex-isting set of thin-walled precast elements, developedat the Faculty of Civil Engineering CTU in Prague[2–4]. A potential industrial partner for productionis currently being searched. Testing of mechanicalproperties is planned after the production of the firstprototype series - based on the results, the final di-mensions of the elements for serial production will beoptimized.AcknowledgementsThis work was supported by the research projectSGS19/145/OHK1/3T/11.References[1] J. Pazderka, P. Hájek.Utility model CZ27642(U1) -Parapet structure, especially for building platformroofs, CTU in Prague, 2015.[2] J. Pazderka, M. Nývlt, H. Žáková. Undergroundventilated wall based on TRC blocks. IOP ConferenceSeries: Materials Science and Engineering 596(1),2019.https://doi.org/10.1088/1757-899x/596/1/012037.[3] J. Pazderka, P. Hájek. Two innovative solutionsbased on fibre concrete blocks designed for buildingsubstructure. IOP Conference Series: MaterialsScience and Engineering 246, 2017.https://doi.org/10.1088/1757-899x/246/1/012046.[4] J. Pazderka, E. Hájková, M. Jiránek. UndergroundAir Duct to Control Rising Moisture in HistoricBuildings: Improved Design and Its Drying Efficiency.Acta Polytechnica 57(5), 2017.https://doi.org/10.14311/ap.2017.57.0331.466

Parapet structure from special shaped TRC blocks

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Parapet structure from special shaped TRC blocks

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