Textile Reinforced Concrete – Realization in applications · Textile Reinforced Concrete – Realization in applications ... ABSTRACT: Textile Reinforced Concrete (TRC) is a composite

Tailor Made Concrete Structures – Walraven & Stoelhorst (eds)© 2008 Taylor & Francis Group, London, ISBN 978-0-415-47535-8

Textile Reinforced Concrete – Realization in applications

J. Hegger, M. Zell & M. HorstmannInstitute of Structural Concrete, RWTH Aachen University, Aachen, Germany

ABSTRACT: Textile Reinforced Concrete (TRC) is a composite material made of open-meshed textile struc-tures and a fine-grained concrete. Comparable to steel reinforcement the textile fabric bears the tensile forcesreleased by the cracking of the concrete. Only a minimal concrete cover is required for the bond of the textilefabrics. Thus, the application of TRC leads to the design of filigree and lightweight concrete structures with highdurability and high quality surfaces. In recent years, TRC has been successfully employed for the productionof ventilated façade systems. Current investigations enlarge the application range of TRC to façade systemswith large spans and load-bearing structures. In this paper, the investigations on self-supporting and structuralsandwich panels regarding production methods, results of bending and shear tests, tests on sound insulation andfire resistance as well as first prototypes of slender frames and shell elements are presented.

1 INTRODUCTION

Structural concrete has been an economic and oftenused building material for façade constructions andload-bearing structures in recent decades. The insuf-ficient architectural design range, the clumsy appear-ance and corrosion damages have led to a decreasingacceptance of the material in regard to façades forclients and architects.

Thus, non-corrosive reinforcement materials havegained importance in the last 3 decades to achievethe goal of precast, filigree and lightweight concretestructures with high durability, high quality surfacesand a wide-spread design range. Glassfibre ReinforcedConcrete (GRC) has been widely used for years forthe production of non-structural building elementseither of complex shape produced in manual spraytechniques or for plain elements with additional one-dimensional long-fiber reinforcements manufacturedin production lines.

The development and application of Textile Rein-forced Concrete (TRC) incorporates the advantagesof GRC adding a structural load-bearing capacity inarbitrary directions. The used textile fabrics can becustomized as 2D or 3D reinforcements to the produc-tion method and load-bearing behavior of the structure.Thus, TRC complements and broadens the design andapplication range opened up by GRC.

2 VENTILATED FAÇADE SYSTEMS

TRC allows economic savings in terms of material,transport and anchorage costs and thus has been

severally used for thin-walled and light-weight ven-tilated façade systems in recent years (Hegger et al.2006, Brameshuber 2006). At present, small panelsizes of 0.5–3 m2 are state-of-the-art in application ofTRC in Germany. Panel sizes of up to 7 m2 can onlybe realized in combination with bracing stud-framesystems (Engberts 2006).

Due to the missing design codes the application ofTRC façade elements in Germany requires either anindividual approval for each construction or a gen-eral approval for defined boundary conditions of theGerman building inspection (DIBt 2004).

3 SELF SUPPORTING SANDWICH ELEMENTS

The application of sandwich panels for façades of fac-tory and industrial buildings has gained importance inthe past 50 years due to the prefabrication irrespec-tive the weather conditions as well as the reduced timeeffort during mounting.

Common structural sandwich elements consist ofa structural, load-bearing layer (h = 10–14 cm), aheat insulation layer and an outer facing (h ∼ 7 cm).Although in standard non-composite action panels theouter facing has no structural function, a steel rein-forcement is necessary to bear constraint forces causedby constricted deformations induced by temperatureand shrinkage. In load-bearing structures as well asin façades a concrete cover of about 35 mm comply-ing with current design codes (DIN 1045-1, MC 90)has to be provided to avoid corrosion of the steel rein-forcement. If the massive outer layer of usual structuralconcrete panels is replaced by a thin-walledTRC-layer,

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Figure 1. Stress distribution of thick facings and core dueto bending and shear forces.

the overall thickness of the panel can be reduced about5–6 cm and the number of connectors between the con-crete layers diminishes. In case the inside facing isalso produced with TRC in combination with a sus-tainable, heat-insulating rigid polyurethane (PU) foamlight-weight sandwich structures with large spans canbe obtained.

3.1 Load-bearing behaviour

The load-bearing behaviour of sandwich panels withrigid facings depends primarily on the thicknesses ofthe layers, the overall height and the (shear) stiffnessof the core (Stamm & Witte 1974).

In contrast to panels with flexible facings the con-crete facings are not only stressed by diaphragm forcesbut also by bending and shear forces according to theirflexural stiffness related to the panel stiffness (Fig. 1).

The magnitude of the flexural and diaphragm forcesfollows the theory of the elastic composite. Facingsconnected by a core with a low stiffness react decou-pled to the loading (non-composite action, NCA,Seeber 1997). The relative shear deformations of thelayers cause large deformations and thus a non-validityof the Bernoulli-Hypothesis and large deformations(Fig. 2).

With an increasing shear modulus of the core thecomposite action of the upper and lower facing is moreactivated. This leads to decreasing deformations andfor an infinite core stiffness to full composite action(FCA, Seeber 1997). The relating stress and strain dis-tributions for both NCA and FCA panels is illustratedin Figure 2.

3.2 Production methods

For the experimental program prefabricated PU rigidfoams (hc = 150 mm) were used as a core beingattached to the TRC-facings (hf = 15 mm) either bygluing or by pressing a notched core into a freshconcrete layer (Fig. 3). The notches were orientedperpendicular to the beam axis with an interspace of

Figure 2. NCA and FCA of sandwich panels.

Figure 3. Production methods of sandwich interface.

Figure 4. Setup of four-point bending tests.

5 cm. The concrete facings were produced in a lam-ination process where concrete and three fabrics arealternately placed in the formwork.

3.3 Result of bending tests

In four-point-bending tests on sandwich panels withspans of 1.90 m and 4.90 m (Fig. 4) a satisfactoryload-bearing behavior was determined which mainlydepends on the (shear) stiffness of the core and thejoint quality between core and facings.

All cores were cut out of slabstocks and a fine dustof PU-cells covered the cutting edges. The dust couldnot be removed with compressed air nor be brushed offthe surfaces. If the core was pressed into the fresh con-crete the particles were easily bounded and showed nonoticeable influence on the bond quality. Comparedto panels with direct bond, the inferior joint qualityresulted in at least 30% lower ultimate loads (Fig. 5,Table 1).

The ultimate load in the tests was determined by abrittle shear failure of the core except for panel P3 witha high density core which failed by tensile rupture ofthe textile reinforcement in the lower facing.

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Figure 5. Load-deflection curves of panels P1 to P4.

Table 1. Selected results of test on sandwich beams.

Span Failure Load DeflectionPanel Core Interface (m) Fu (kN/m) (mm)

P1 PU 32 Notched 1.9 27.6 43.0P2 PU 32 Glued 1.9 18.1 29.2P3 PU 200 Notched 1.9 151.21) 28.0P4 PU 40 Notched 4.9 23.2 99.8

1) tensile failure of fabrics in lower facing.

For the panels P1 to P4 no connectors were used.The sandwich action was only established by the bondbetween the foam and the concrete layers. A suit-able calculation model for sandwich panels is givenin Hegger, Horstmann & Scholzen (2007).

For a durable load-bearing capacity productile con-nectors between the concrete layers are required,which, on the one hand reduce the stresses normalto the bond joint due to shrinkage and temperature,and on the other hand avoid constraint stresses. Con-venient devices adapated to the low anchorage lengthin the thin-walled TRC layers are currently developed.

3.4 Fire resistance and sound/heat insulation

A first examination of the fire resistance of the sand-wich panels was conducted with a SBI (single burningitem) test according to DIN EN 13823 (2002). Thepanels were categorized in the second highest classaccording to DIN EN 13501-1 (2002) as A2/B, S1, d0making them suitable for façades of office buildingsand factory floors. The airborne sound insulation wasdetermined in a testing facility according to DIN EN140-3 (2005). The measured sound reduction indexof R′

w = 43 dB is sufficient for factory floors andoffice buildings. The heat transfer coefficient U forthe homogeneous section was assessed to 0.22 W/m2Kwhich complies with the limit (U = 0.35 W/m2K)of the current German Energy Saving Regulation(EnEV 2001).

Figure 6. Modular sandwich building (Schneider et al.2006b).

4 SANDWICH PANELS FOR MODULARBUILDINGS

The advantages of the sandwich technology are alsoapplied to the design study of a modular buildingconsisting of load-bearing and demountable sandwichpanels for walls and roofing. Based on a basic gridof 1 m wall (clear height: 2.82 m) and roof elements(span 4.73 m) are assembled to a small demonstrationbuilding (Fig. 6).

4.1 Design of modular panels

The sandwich panels were designed with the theory ofthe elastic composite and a comparative finite elementanalysis. The inner TRC layer of the roof elementswas profiled and a PU foam density of 50 kg/m3 waschosen to reduce the shear portion and the thus inducedcreep deformations of the visco-elastic core material(Fig. 7).

The section of the inner layers of the wall elementswas designed similar to the roof elements but forminga hutch with additional horizontal beams at the top andthe bottom. In the horizontal beams cast-in channelsconnecting the wall elements to the foundation and theroof elements were integrated.

The sides of the vertical webs of the inner layerswere profiled as tongue and groove for both roof andwall elements.

4.2 Tailoring of 3D textile reinforcement

For a simple cast process a capable and rigid 3D AR-glass reinforcement was tailored. The fabrics werelaminated with a resin and cured on a metal form in anoven to shape them to e.g. rectangular reinforcementcages. These were fixed to the cnc-milled cores andin the knee points the transverse rovings of the cross-ing cages were removed to enable a penetration of the

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Figure 7. Sections and connections of modular elements.

Figure 8. Tailored AR-glass reinforcement for frame knees.

longitudinal rovings (Fig. 8). Additionally placed tex-tile gussets supported a sufficient frame knee actionin the vertexes.

The element was cast upside down in a three stepproduction method: (1) lamination of the upper plainlayer with GRC and one fabric, (2) positioning of coreassembled with the tailored reinforcement and the lat-eral formwork and (3) casting of the lower profiledlayer without short-fibers.

4.3 Bending tests on roof and wall elements

In Figure 9 the setup of the bending tests on a roofelement (P5) and a wall element (P6) is illustrated.

The roof element was tested with a positive flexuralload and supported true-to-detail, the wall element was

Figure 9. Setup for bending tests on roof/wall element(P5/P6).

Table 2. Results of bending tests on sandwich panels P5/P6.

Span Failure Load DeflectionPanel Core Ls (m) Fu (kN/m) w (mm)

P5 PU 50 4.73 28.0 108P6 PU 50 2.73 34.6 38.9

Figure 10. Comparison of panels P4, P5 and P6.

loaded by a negative flexural load and supported onthe horizontal beam of the inner hutch. The outsideconcrete facing thus was shortened and able to deformwithout any constraint.

Table 2 and Figure 10 show the results obtained bythe bending tests on panels P5 and P6.

In comparison to panel P4 the profiled inner con-crete layer and the slightly higher core density ledto a much stiffer load-deflection curve (Fig. 10) ofpanels P5 and P6. The ultimate load of the roofelement calculated in the design stage was exceeded

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Figure 11. Shear failure of panel P5.

due to a shear block action caused by a vault and thecompressive stresses at the supports.

Panels P5 and P6 both failed due to shear rupture ofthe core leading to a subsequent delamination betweenconcrete facings and the core (Fig. 11).

The sustainability of the sandwich bond wasensured by discrete stainless steel pins (Ø = 3 mm)bearing peeling stresses normal to the bond jointsowing to shrinkage, temperature and wind suction.Thecalculation model presented in Hegger, Horstmann &Scholzen (2007) is currently upgraded regarding theload-bearing portion of discrete connectors.

5 RHOMBIC LATTICE-GRID

Diamond-shaped lattice frameworks have alreadybeen applied for the construction of arched halls formore than one century by now. The structural principlehas originally been developed by Friedrich Zollingerin 1905 and was used for the construction of woodenarched halls (Winter 1992). The original principle ofthe constructive form “Zollinger” is a geometricalexpression of closely spaced timber arches intersectingwith each other diagonally. This way large spanningstructures can be assembled from small and slendersingle components.

Due to the relatively large concrete cover accom-panied by a large wall thickness, the high dead loadas well as the complex production process the appli-cation potential for the construction of frameworksmade of concrete with ordinary steel reinforcementhas diminished. The diamond-lattice grid principletogether with Textile Reinforced Concrete provides an

Figure 12. Prototype of a diamond-shaped lattice grid.

excellent opportunity to prefabricate extremely slen-der and lightweight, diamond-shaped components.Therefore, the use of slender TRC elements results ina fine spun appearance that has not been associatedwith concrete yet.

Within the scope of a collaborative research projectat RWTH University a diamond-shaped lattice archconsisting of a textile (carbon) reinforcement embed-ded in a fine-grained high strength concrete matrix hasbeen produced and erected in February 2005 (Fig. 12,Schneider et al. 2006a, Hegger et al. 2007).

The construction consisted of 36 single rhombic ele-ments jointed in 3 parallel rows with 12 elements each.The total span of the arc was 10 m, the height was 3 mand width 1.8 m.The single rhombic elements with thedimensions 1000 × 600 × 160 mm have been prefab-ricated in a cnc-milled formwork. The concrete wallthickness was 25 mm and the complete structure con-sisting of the single elements bolted together had atotal weight of 23 kg.

6 BARREL-SHELL STRUCTURES

Due to its material properties Textile Reinforced Con-crete is very well suited for the production of complexgeometries, e.g. for roof constructions. The bearingcapacity can be improved especially by the forma-tion (bending or folding) of two-dimensional buildingcomponents.The easy forming of the textiles enables asimple realization of curved surfaces as e.g. the barrelshell elements in Figure 13.

Even in reinforced concrete structures, simplechannel-section folded beams belong to the most eco-nomical types of construction. The shell effect of thinconcrete elements can be very effective in the case ofbarrel-shell roofs. With a material thickness of 25 mmin textile-reinforced concrete the structure is extremelylight-weight and the shell is rigid in both the longitu-dinal and lateral direction. A structural depth of about500 mm and a span of up to 8 m generate interestingforms of applications for this type of TRC structure,

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Figure 13. Design of TRC barrel shells (Schneider et al.2006b).

e.g. in smaller and medium-sized halls. The utiliza-tion of shotcrete is the easiest production method fortextile reinforced concrete shells with the placementof concrete and reinforcement in alternating layers.The manufacturing of such a barrel shell was success-fully tested on a 1.5 m long segment at the Institute ofBuildings Materials Research (ibac), RWTH AachenUniversity.

7 SUMMARY AND CONCLUSION

The presented investigations proved TRC to be aproper and capable construction material with a highadaptivity to the requirements of light-weight andfiligree building components. The potential of TRCcompliments the utilization of GRC and broadensthe application of load-bearing structures of complexgeometry. In addition to simple joining techniques andstatic dimensioning models the basis is formed for thedevelopment of future constructions with optimizedconcrete sections, sharp edges and excellent concretesurfaces. Combined with the manufacturing as precastelement and the entailed simple assembly and disas-sembly of buildings also the demand for a sustainablemethod of construction is fulfilled.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the financial sup-port of the Deutsche Forschungsgemeinschaft (DFG)within the Collaborative Research Center (SFB) 532“Textile Reinforced Concrete – Development of a newtechnology” and thank BAYER MaterialScience AG,Germany, for the financial and technical support.

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