Seminaretrsertg

THE USE OF GLASS FIBER–REINFORCED CONCRETEAS A STRUCTURAL MATERIAL

Glass fiber–reinforced concrete (GRC) consists basi-cally of a cementitious matrix composed of cement,sand, water, and admixtures, in which short-length glass fibers are dispersed. The effect of the

fibers in this composite leads to an increase in the tension andimpact strength of the material (Bentur and Mindess1). GRChas been used for over 30 years in several construction ele-ments, mainly nonstructural ones, like facade panels (about80% of the GRC production), piping for sanitation networksystems, decorative nonrecoverable formwork, and otherproducts (Bentur and Mindess1).

In the beginning of the GRC development, one of the mostconcerning problems was the durability of the glass fibers,which became fragile with time, due to the alkalinity of thecement mortar. Since then, significant progresses have beenmade, and presently, the problem is practically solved withthe new types of alkali-resistant glass fibers and with mortaradditives that prevent the processes that lead to the embrit-tlement of GRC (Bentur and Mindess1, Majumdar andRyder2, Cem-FIL3, Liang et al.4).

The light-weight characteristics and improved tensilestrength of GRC as compared with concrete led to a recentresearch program to study the viability of its use as a struc-tural material (Ferreira,5 Branco et al.,6–8 Branco,9 Viegas,10

Cian and Della Bella11). The research was developed in asso-ciation with concrete precast companies for which the referredimproved characteristics are especially appealing as thereduced weight of the precast elements is important for trans-portation and installation. To obtain a GRC with high dura-bility, reinforcement systems were also analyzed, consideringcarbon or glass strands and stainless steel bars, leading tocorrosion-free solutions (Ferreira5).

Although some of the average mechanical properties of GRCare known (Cem-FIL3 and Knowles12), currently used for non-structural elements, when structural design is considered,a much more complete characterization is needed. Experi-mental tests were then performed on GRC specimens to deter-mine its mechanical strength, Young’s modulus, creep andshrinkage behavior, and stress–strain diagrams.

As the material characteristics were very much dependent onthe production procedures, the experimental tests had to con-sider cementitious matrix with different plain mortar produc-tions, with several types of glass fibers and reinforced withcarbon or glass strands or with steel elements. These tests ledto a characterization of the production conditions to obtainoptimized material properties.

PRODUCTION OF GRC

There are two main production techniques of GRC, usuallyreferred as spray-up and premix (Bentur and Mindess,1 andCem-FIL3). In the spray-up process, the mortar is producedseparately from the fibers, which are mixed only at the jet ofthe spray gun. The glass fiber strands are cut within the spraygun to the required size, typically between 25 mm (0.98 inch)and 40 mm (1.57 inch), and are about 5% of the GRC totalweight. The subsequent compaction with a cylindrical rollguarantees the adaptation of GRC to the form, the impregna-tion of the fibers within the mortar, the removal of the airretained within the mix, and an adequate density.

In the GRC production method by premixture, mortar andprecut fibers are previously mixed. The quantity of fibersadded to the mortar is usually up to 3.5%, in terms of weight,and the length of the fibers is around 12 mm (0.47 inch).Longer fibers lead to an excessive reduction of the mix’s work-ability. Production with premix GRCmay involve several pro-cedures such as injection and vibration, pressing, orshotcreting (Fig. 1).

Production of GRC with homogeneous characteristicsrequires a strict quality control, at the production stage andin the final products. The European Standard EN 116913 orthe International Glassfiber Reinforced Concrete Associa-tion14 provide fundamental guidance and establish the gen-eral rules for production of GRC. The European Standard EN1170, parts 1 to 7,15 establishes the specific test methods forcontrol of GRC. At the production stage, the most importantparameters to control are the composition of slurry, the rela-tion between fiber and slurry delivery rates (bag test andbucket test, respectively), and the workability (slump test).The final products have to be tested, namely, in terms of sur-face finish, dimensional tolerances, density, and strength.The most widespread strength control is the flexural test, tobe performed also according to the European Standard EN1170.15

The production of GRC with the above methods leads to thegeneral average values for its properties (Table 1; Knowles12),values that will be analyzed with experimental tests in thefollowing.

COMPRESSION BEHAVIOR TESTS

Young’s ModulusTests were performed to determine the Young’s modulusof GRC, following the national standard LNEC E397,16 forconcrete.

The cylindrical specimens (Fig. 2) were produced with thespray-up method by injecting cylindrical molds. The mortarcomposition considered was as follows: white cement type BRI 42,5R, 100 kg (220 pounds); sand, 100 kg (220 pounds);polymer water dispersion Primal MC 76 S, 6.0 L (366 inch3);

TECHNIQUES by J.P.J.G. Ferreira and F.A.B. Branco

J.P.J.G. Ferreira (assistant professor) and F.A.B. Branco (full professor, vice-chairman of the IABSE Technical Commission, member of ACI Committee No.342 on ‘‘Evaluation of Concrete Bridges,’’ member of the CSCE and RILEM, andchairman of the Civil Engineering Division of the Portuguese Association ofEngineers) are affiliated with the Department of Civil Engineering and Architec-ture, Technical University of Lisbon, Instituto Superior Tecnico, ICIST, Lisboa,Portugal.

64 EXPERIMENTAL TECHNIQUES May/June 2007doi: 10.1111/j.1747-1567.2007.00153.x

� 2007, Society for Experimental Mechanics

fluidizer type Sikament: 163, 10.0 L (610 inch3); water, 34 L(2075 inch3); and fiber, 4–5% Cem-FIL 53/76. The water dis-persion of an acrylic polymer was added to achieve improveddurability by sealing the cementitious matrix.

Values of Young’s modulus for spray-up GRC around 17 GPa(2466 3 103 psi) were obtained, which are within the averagevalues (Table 1). These values are approximately half of thoseusually obtained for concrete and similar to those usuallyobtained for current mortars without coarse aggregates(Coutinho and Goncxalves17), which means that the structuralelements fabricated with GRC will be more flexible than con-crete elements, which can even be more important in thinnerelements.

Compression StrengthCompression strength was obtained with spray-up and pre-mix specimens. The compositions of each production tech-nique were optimized, based on former experience and onworkability tests. The specimens were tested according tothe national standard LNEC E226.18

Four series of specimens were tested (Table 2). Spray-up GRCmortar was identical to the one used for Young’s modulusdetermination, while premix GRC mortar had the following:white cement type BR I 42,5R, 100 kg; sand, 67 kg(148 pounds); polymer Primal MC 76 S, 1.8 L (110 inch3);fluidizer type Sikament: 163, 1.0 L (61 inch3); and water,29 L (1770 inch3).

The plain mortar specimens (without fiber reinforcement) hadan explosive rupture, while the GRC ones, despite the crackpattern, almost maintained the initial shape at rupture,denoting a much more ductile behavior (Fig. 3). This distincttype of GRC behavior, when compared to that of the plainmortar, is relevant for structural use and will be highlightedin the analysis of the stress–strain diagrams.

Based on the strength tests results, the average value (fm) andcharacteristic value at 95% (fk) were determined (Table 2).

The results show that GRC strength is comparable to thatobtained for good quality concrete. The compression strengthsof premix and spray-up plain mortars are greater than thecorresponding values obtained for GRC specimens. The lossof compression strength caused by the presence of fibers maybe due to a less compaction of the material associated to thespaces occupied by the glass fibers.

Stress–Strain DiagramsThe tests to determine the stress–strain behavior in compres-sion of GRC were performed according to the standard test forcompression strength but maintaining the load applicationafter the maximum forced is reached in order to assess thepostpeak behavior.

Five specimens were tested to determine the stress–strainbehavior in compression. Three of these specimens were

Fig. 1: Production of element with spray-up GRC13

Table 1—Typical values of some GRC properties12,14

PROPERTY GRC SPRAY-UP GRC PREMIX

Dry density, kN/m3 (pci) 19–21 (108–120) 19–20 (108–114)

Compression strength, MPa (psi) 50–80 (7252–11603) 40–60 (5802–8702)

Young’s modulus (compression), GPa (psi) 10–20 (1450 3 1023 to 2901 3 1023) 13–18 (1885 3 1023 to 2611 3 1023)

Impact strength, Nmm/mm2 (pound inch/inch2) 10–25 (57.1–142.8) 8–14 (45.7–79.9)

Poisson ratio 0.24 0.24

Bending—limit of linearity, MPa (psi) 7–11 (1015–1595) 5–8 (725–1160)

Bending—maximum strength, MPa (psi) 21–31 (3046–4496) 10–14 (1450–2031)

Direct tension—maximum strength, MPa (psi) 8–11 (1160–1595) 4–7 (580–1015)

Direct tension—maximum extension (%) 0.6–1.2 0.1–0.2

USE OF GRC AS A STRUCTURALMATERIAL

May/June 2007 EXPERIMENTAL TECHNIQUES 65

composed by premix GRC (series F), while the other two(series G) were made of plain mortar. All specimens of seriesF and G were produced following, respectively, the composi-tions of series A and E indicated for compression strengthevaluation.

Figure 4 shows the stress–strain diagrams obtained in thesetests, which clearly reflect the different type of collapse modedepending on whether the fibers are present or not. Greaterductility of GRC was seen when compared with plain mortar(right diagram) that collapseswhenmaximum force is reached.Although the presence of the fibers leads to a reduction of

compression strength, it ensures a better behavior in the post-peak zone, namely, preventing its fragmentation. This phe-nomenon is particularly important for thin-wall structuralelements, where crack propagation may lead to a disaggrega-tion of the elements, leading to a premature collapse, and hasto be taken into account when modeling GRC compressionbehavior.

TENSILE STRENGTH TESTS

The tensile behavior of GRC is one of the most importantparameters when considering its structural use. It has beenrecognized (Chanvillard19 and Banthia et al.20) that the stan-dard flexural tests do not provide reliable values of tensionstrength and should be usedmainly for quality control. On theother hand, pure tensile tests are not usually performedbecause of their operative difficulty. The tensile tests pre-sented in this paper were performed using a tension-testingmachine (Fig. 5) with controlled pressure hydraulic grabs.The specimens were 30 cm (11.8 inch) long, generally withcross-section of 1 3 5 cm (0.39 3 1.97 inch). A large numberof tests were carried out to analyze different aspects, namely,production techniques, compositions, aging, and continuousreinforcement.

Plain Spray-Up GRCThe composition used in the spray-up GRC specimens wasequal to that referred in Compression Behavior Tests. Thedifferent series are distinguished by the type, quantity (per-centage of total weight) and length of dispersed fibers, andtype of sand (regular or sieved).

The two different types of fibers correspond to Cem-FIL fiberroving designated, respectively, as Cem-FIL 53/76 and Cem-FIL 250/5. The first type is the most commonly used in GRChand-spray process, while Cem-FIL 250/5 presents improvedlong-term strength.

Within each series, all the specimens have identical charac-teristics. Table 3 presents the results (average [fm] and char-acteristic [fk] tension strength values) for each series withineach group.

These results show that the increase of fiber length and offiber percentage have, in general, a positive effect on the ten-sion strength of the material (series 1–8). However, the use of63 mm (2.48 inch)–long fibers imply some production difficul-ties, namely, a decrease of workability, a more difficult fiberimpregnation, and more air trapping. Sieving the sand didnot have a favorable effect on tension strength (comparisonof series 5 with series 9 and 10), although a fiber–matrix

Table 2—Compression tests specimens

SERIESNO. OF

SPECIMENSPRODUCTIONTECHNIQUE

PERCENTAGEOF FIBERS

LENGTH OFFIBERS, mm (inch) fm, MPa (psi) fk, MPa (psi)

A 9 Premix 2.5 12 (0.47) 40.9 (5932) 36.1 (5236)

B 8 Spray-up 4–5 31 or 63 (1.22 or 2.48) 37.4 (5424) 32.6 (4728)

C 10 Premix (mortar) — — 51.8 (7513) 50.6 (7339)

D 6 Spray-up (mortar) — — 58.3 (8456) 43.7 (6338)

Fig. 2: Tests to determine Young’s modulus


66 EXPERIMENTAL TECHNIQUES May/June 2007

adherence increase was expected. Substituting fibers of type53/76 by those of type 250/5 implied, in general, an increase ontension strength (comparison of series 9 with series 11 and ofseries 10 with 12).

Plain Premix GRCThe composition of premix specimens was equal to thatreferred in Compression Behavior Tests but with a fiber incor-poration of only 2.5%. This change proved to be necessary toincrease the workability and fiber dispersion regarding thethickness of the structural elements to be fabricated. Table 4shows the results obtained for the two tested series with dif-ferences in the specimens’ cross-section.

Tension strength values of premix GRC are smaller, espe-cially when compared to those obtained for spray-up GRC.However, to produce considerable quantities of GRC for struc-tural elements, this is a much more convenient method. Thetension strength, in this case, may be achieved by continuousreinforcing elements. The dispersed glass fibers still have therole of preventing premature disaggregation by microcrack-ing propagation and increase the impact strength and energydissipation capacity of GRC.

Reinforced Spray-Up GRCThe test series of reinforced spray-up specimens were dividedin two groups, being the first with carbon strands reinforce-ment and the second with glass fiber strands (Tables 5 and 6).

The carbon fiber strands type Torayca T700SC-24000-50Cused in the tests have a tension strength of 4.893 kN (1100pounds) (maximum stress of 5420 MPa [785.9 3 103 psi],cross-section of 0.928 mm2 [1.44 3 1023 inch2]), ultimate ex-tension of 2.3%, and Young’s modulus of 232 GPa21 (33.6 3106 psi). The glass fiber strands used as continuous reinforce-ment, Cem-FIL 53/76, have a tension strength of 1.554 kN(349 pounds) (maximum stress of 1700 MPa [246.5 3 103 psi],cross-section of 0.914mm2 [1.423 1023 inch2]), ultimate exten-sion of 2.4%, and Young’s modulus of 72 GPa10 (10443 3 103

psi). Different reinforcement patterns were considered,attempting to achieve optimized adherence to the matrix.The ‘‘sinusoidal’’ layout indicates a longitudinal patternwhere the same strand passes different times along the lengthof the specimen, without being cut at its ends. When ‘‘fiber at458’’ is indicated, the strands are positioned obliquely to thelongitudinal axes. In some cases, the reinforcing fibers were

0 2000 4000 6000 8000 10000

Strain (µm/m)

0

10

20

30

40

50

Stre

ss (

MPa

)

Premix GRC

0 2000 4000 6000 8000 10000

Strain (µm/m)

0

10

20

30

40

50

Stre

ss (

MPa

)

Plain Mortar

Fig. 4: Stress–strain diagrams of premix GRC and of plain mortar

Fig. 3: GRC (a) and plain mortar (b) ruptured specimens

Fig. 5: Tension tests set up



slightly wet in order to increase their adherence to the cemen-titious matrix. These patterns are illustrated in Fig. 6. Thespecimens of each type were produced together on the samesteel mold and were individualized by sewing, after curing.The fibers were positioned after projecting and compactinghalf thickness of the specimens. GRC was again projectedand compacted until the specimens’ final thickness wasachieved. In all cases, the fibers were manually tensionedwhen placed in the molds in order to ensure their efficacyfor specimens’ tension strength.

The results obtained show that the use of carbon strandsincreases the tension strength of the specimens, althoughits effectiveness strongly depends on the anchoring type adop-ted. The sinusoidal pattern proved to be the best anchoring

Table 3—Spray-up GRC tension test results

SERIESNO. OF

SPECIMENS NSPERCENTAGE

OF FIBERSTYPE OFFIBERS

LENGTH OFFIBERS, mm (inch)

SAND SIEVE,mm (inch fm, MPa (psi) fk, MPa (psi)

1 10 5.2 Cem-FIL 53/76 63 (2.48) Nonsieved, ,1.0 (,0.039) 7.6 (1102) 5.6 (812)








9 10 5.0 Cem-FIL 53/76 31 (1.22) Sieved, 0.6 (0.024) 7.9 (1146) 7.3 (1059)

10 10 5.0 Cem-FIL 53/76 31 (1.22) Sieved, 0.3 (0.012) 6.8 (986) 5.4 (783)

11 10 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.6 (0.024) 8.1 (1175) 6.4 (928)

12 10 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.3 (0.012) 7.5 (1088) 6.4 (928)

Table 4—Series of premix GRC specimens subjectedto tension tests

SERIESNO. OF

SPECIMENSCROSS-SECTION,

mm 3 mm (inch 3 inch)fm, MPa

(psi) fk, MPa (psi)

25 18 50 3 15 (1.97 3 0.59) 3.9 (566) 2.6 (377)

26 14 40 3 10 (1.57 3 0.39) 3.4 (493) 2.5 (363)

Table 5—Series of spray-up GRC specimens with carbon fiber strands reinforcement

SERIESNO. OF

SPECIMENSPERCENTAGE



SAND SIEVE,mm (inch) REINFORCEMENT fm, MPa (psi) fk, MPa (psi)

13 15 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.6 (0.024) 1 longitudinal

carbon strand

10.3 (1494) 8.7 (1262)

14 10 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.3 (0.012) 1 longitudinal

carbon strand

8.6 (1247) 6.2 (899)

15 9 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.6 (0.024) wet carbon strands 45º 7.3 (1059) 5.3 (769)

16 10 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.6 (0.024) 4 wet sinusoidal

carbon strands

13.2 (1915) 9.1 (1320)

17 9 5.0 Cem-FIL 250/5 31 (1.22) Sieved, 0.6 (0.024) 5 longitudinal wet

torsioned carbon strands

14.5 (2103) 11.9 (1726)

18 11 5.0 Cem-FIL 250/5 31 (1.22) Siliceous sand,

,0.3 (,0.012)

3 longitudinal wet

torsioned strands

5.6 (812) 4.4 (638)


,0.3 (,0.012)

3 wet sinusoidal

carbon strands

16.3 (2364) 12.6 (1827)


,0.3 (,0.012)

3 longitudinal wet torsioned

carbon strands with knots

every 5 cm

5.1 (740) 3.9 (566)



system, followed by the simple longitudinal layout, the knotarrangement, and the 458 pattern. Torsioning the strands didnot lead to noticeable increase of the strength. The totalstrength of the carbon strands was never completely mobi-lized. Tension strength is practically not affected by the typeof dispersed glass fibers.

The use of glass fiber strands showed similar effects but withlower increase in the tension strength of GRC.

Reinforced Premix GRCThe four series of reinforced premix GRC specimens (Table 7)correspond, respectively, to reinforcements with one simplecarbon strand with no special anchoring scheme, one carbonstrand with a 3 mm (0.12 inch)–diameter stainless steel bar,and one single stainless steel bar.

The results show that the reinforcement increases the speci-mens’ tension strength. Considering that the plain GRC

tension strength value is not changed by the presence of con-tinuous reinforcement and that the increment on tensionstrength of the specimens is mainly due to the reinforcement,the rupture force of these elements was determined. Based onthat force and on the tension strength of the fibers, it can be

Table 6—Series of spray-up GRC specimens with glass fiber strands reinforcement

SERIESNO. OF

SPECIMENSPERCENTAGE



SAND SIEVE,mm (inch) REINFORCEMENT

fm, MPa(psi)

fk, MPa(psi)

21 5 4.0 Cem-FIL 53/76 31 (1.22) Nonsieved 1 longitudinal glass

fiber strand

8.0 (1160) 7.3 (1059)


,0.3 (,0.012)


glass fiber strands

5.6 (812) 4.8 (696)


,0.3 (,0.012)

3 wet sinusoidal

glass fiber strands

12.3 (1784) 10.8 (1566)


,0.3 (,0.012)


glass strands with knots

every 5 cm (1.97 inch)

6.1 (885) 5.3 (769)

Continuous fiberGRC

“Sinusoidal” pattern

Fiber tendonsGRC

“Fiber at 45º” pattern

Fig. 6: Patterns of continuous reinforcement

Table 7—Series of reinforced premix GRC specimens subjected to tension tests

SERIES NO. OF SPECIMENS REINFORCEMENTCROSS-SECTION, mm 3 mm

(inch 3 inch) fm, MPa (psi) fk, MPa (psi)

27 17 1 carbon strand 50 3 15 (1.97 3 0.59) 4.2 (609) 3.3 (479)

28 13 1 carbon strand 40 3 10 (1.57 3 0.39) 5.0 (725) 3.7 (537)

29 7 1 carbon strand and

1 f3 mm–steel bar

50 3 15 (1.97 3 0.59) 7.3 (1059) 5.5 (798)

30 16 1 f3 mm–steel bar 40 3 10 (1.57 3 0.39) 6.2 (899) 5.0 (725)

Fig. 7: Slipping of continuous reinforcing elements in GRCspecimens



seen that the carbon strands are tensioned to 11–13% of theircapacity. In the case of steel bars, this value is 59%, in theseries with carbon strands, and 29% in the series withoutcarbon strands. This difference between the steel stresses inboth cases is due to a better anchoring in the series withcarbon strand, where the steel bar had hooked ends.

This effect is partially related to the reduced length of thespecimens, which prevents the adequate anchoring of thereinforcement. This fact is illustrated in Fig. 7, which showsthree specimens, with continuous reinforcement (one longitu-dinal carbon strand, one longitudinal steel bar, and both ele-ments together, respectively), tested in tension, where the slipof the reinforcement is evident.

Anchoring schemes that prevent excessive slip of reinforcingelements can be used to increase their efficiency in tensionbehavior, as demonstrated for spray-up specimens. It isexpected, however, that in real structural applications, thisproblem can be less important if the anchoring of the contin-uous elements is in a nontensioned zone.

CREEP BEHAVIOR TESTS

Because some of the structural uses of GRC include pre-stressed elements, evaluation of creep behavior was requiredto evaluate long-term losses. For this purpose, two specimenswere tested during 5 months under a constant load. To ensurethe stability of applied compressive stress, the specimenswere subjected to a gravity load of 85 kN (19,109 pounds),as shown in Fig. 8. The strain variation in a control specimenwas also measured to evaluate the strain component due toshrinkage and temperature variation.

To evaluate the creep coefficient for loads applied in differentages, two specimens were loaded, one 8 days after production(S1) and the other 28 days afterward (S3). With this proce-dure, the creep coefficient for loads applied on the 8thand 28th days was obtained. The test procedures were basedin the national standard LNEC E399,22 for creep evaluationin concrete, and LNEC E398,23 for shrinkage evaluation ofconcrete.

Creep tests were performed on standard cylindrical specimensof spray-up GRC, with the same mortar composition indicatedin Compression Behavior Tests, with 4% of 31 mm (1.22 inch)–long fibers. Figure 9 shows the tests results, where f(t) repre-sents the creep coefficient, defined as the relation betweencreep strain and instantaneous elastic strain.

It can be observed that creep coefficient values are compara-ble to those usually obtained in concrete. The type of curve isalso similar to that of concrete, where the curve’s slopedecreases with time, nearly following a logarithmic curve.The values indicate that the creep deformation decreases withthe age of the material when the load is applied.

APPLICATION TO A TOWER DESIGN

PrototypesOne of the first prototypes built with structural GRC wasa telecommunication tower (Fig. 10), 30-m (118.1 inch) high

and built with three segments, produced separately andprestressed longitudinally. The thin-walled cross-sectionis externally a polygon with 12 sides and internally circular(Fig. 11). The cross-section dimensions vary progressivelyalong the tower height. The wall thickness in the thinnestzone is 0.03 m (1.18 inch). The tower segments are builtby injecting premix GRC in a mold. The reinforcing ele-ments were previously placed in the mold connectedslightly tensioned to transverse stainless steel bars locatedat its ends.

Fig. 8: Specimens subjected to creep test

0.00 20 40 60 80 100 120 140 160

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Age (days)

φ(t)

S1 S3

Fig. 9: Creep tests results



DesignThe tower was designed with the national code for actions(INCM24), namely, considering the effects of self-weight andwind pressure. Due to the tower geometry, including anten-nas and stairs, the wind action simulation was complex and

wind tunnel tests were carried out to obtain realistic windshape factors (Ferreira5).

The strength of the pre-stressed GRC was not enough to sup-port the wind effects and supplementary reinforcing elementshad to be placed. In the prototype, the use of ordinary steelbars was avoided for durability reasons and to prevent elec-tro-magnetic interferences. Instead, carbon tendons (sametype of those used in tension specimens) were used as longi-tudinal reinforcement along the tower height, with supple-mentary stainless steel bars in the most tensioned zones.The amount of reinforcement was established based on theresults of the tests previously presented and on numericalmodels specifically developed for designing the tower cross-sections (Ferreira5).

Numerical ModelA numerical model was developed to simulate the collapsebehavior of the tower cross-sections, considering a uniaxialmaterial behavior with a parabolic-constant diagram in com-pression (with similar shape as for concrete) and by a lineardiagram in tension, based on the experimental results of smallspecimens. This numerical model allowed the evaluation ofthe M–N (bending moment versus axial load) curves consid-ering that collapse occurs when GRC ultimate strain in ten-sion or compression occurs in the outside fiber. Figure 12shows the collapse curves obtained for several cross-sections(distance to tower top indicated) along the tower height.

The model accuracy was also tested with the experimentalcollapse of tower segments and the differences between thecollapse bending moments predicted by the numerical modelsand those obtained experimentally (Fig. 13) were less than5%. Based on these results, the numerical model was adoptedfor the tower’s design.

CONCLUSIONS

An experimental test program carried out on small specimensallowed for the assessment of the main mechanical character-istics of GRC concerning its structural use. The GRC compo-sitions of the final tested specimens were achieved based onan optimization of the fabrication procedures and on previoustest results.

Fig. 10: Prototype tower

R

e

Fig. 11: Tower cross-section

-6000

-5000

-4000

-3000

-2000

-1000

00 200 400 600 800 1000 1200 1400

1000

Bending Moment (kN.m)

Axia

l Loa

d (k

N)

30,0 m

0,0 m5,5 m 6,5 m

18,5 m18,5 m

Fig. 12: M–N curves for the tower cross-sections



Although the tests performed in this study have shown thatspray-up GRC presents a better behavior than premix GRC,namely, for tension loads, this last technique is better adaptedto the production of structural elements, especially for impor-tant volumes of material. This study also analyzed the effec-tiveness of the reinforcing elements introduced in GRC forstructural elements.

The results obtained in small specimens were used ina numerical model to obtain the design bending moment ver-sus axial load collapse curves of GRC telecommunication tow-ers’ cross-sections. The results given by the numerical modelclosely match the cross-sections resistance evaluated in theexperimental collapse tests of prototype towers, and thenumerical models were then adopted for the towers’ design.

ACKNOWLEDGMENTS

The authors thank the financial support from FCT (Fundacx aopara a Ciencia e Tecnologia) and from the European Commis-sion for the research developed within project PRAXIS/P/ECM/14046/1998.

REFERENCES1. Bentur, A., and Mindess, S., Fiber Reinforced Cementitious

Composites, Elsevier Applied Science, Amsterdam, The Netherlands(1990).

2. Majumdar, A., and Ryder, J., ‘‘Glassfiber Reinforcement forCement Products,’’ Glass Technology 9(3):78–84 (1968).

3. Cem-FIL GRC Technical Data, Cem-FIL International Ltd,Vetrotex, UK (1998).

4. Liang, A., Cheng, J., Hu, Y., and Luo, H.,‘‘Improved Proper-ties of GRC Composites Using Commercial E-glass Fibers with NewCoatings,’’ Materials Research Bulletin 37(4):641–646 (2002).

5. Ferreira, J., ‘‘Structural Characterization of Glass-fiber Rein-forced Concrete (GRC). Application to Telecommunications Towers’’(available in Portuguese), PhD thesis, Instituto Superior Tecnico,Lisbon, Portugal (2002).

6. Branco, F., Ferreira, J., and Calado, L., ‘‘Structural Behaviourof Prestressed GRC Towers,’’ Proceedings of the 12th InternationalCongress of the International Glassfiber Reinforced Concrete Associ-ation, Dublin, 13–23, GRCA International, Camberley, UK (2001).

7. Branco, F., Ferreira, J., Brito, J., and Santos, J., ‘‘BuildingStructures with GRC,’’ Proceedings of CIB World Building Con-gress, Wellington, 11, CIB, Rotterdam, The Netherlands (2001).

8. Branco, F., Ferreira, J., Brito, J., and Santos, J., ‘‘The Use ofGRC as a Structural Material,’’ Proceedings of Symposium onMechanics of Composite Materials and Structures, Coimbra, Portu-gal, 12, University of Coimbra, Coimbra, Portugal (1999).

9. Branco, F., and Ferreira, J., Experimental Testing of a GRCAccess Ramp for Pedestrian Bridges, Report ICIST EP 55/01, IST,Lisbon, Portugal (2001).

10. Viegas, J., ‘‘Production Control of GFRC Structural Compo-nents in Portugal,’’ Proceedings of the 12th International Congressof the International Glassfiber Reinforced Concrete Association,Dublin, 33–40, GRCA International, Camberley, UK (2001).

11. Cian, D., and Della Bella, B., ‘‘Structural Applications of GRCfor Precast Floors,’’ Proceedings of the 12th International Congressof the International Glassfiber Reinforced Concrete Association,Dublin, 41–52, GRCA International, Camberley, UK (2001).

12. Knowles, E., Recommended Practice for Glass Fiber Rein-forced Concrete Panels, Committee on Glass Fiber Reinforced Con-crete Panels, PCI, Chicago, IL (1987).

13. CEN, EN 1169:1999, Precast Concrete Products—General Rulesfor Factory Production Control of Glass-fiber Reinforced Cement, CEN,Brussels, Belgium (1999).

14. International Glassfiber Reinforced Concrete Association,Specification for the Manufacture, Curing and Testing of GRC Prod-ucts, 2nd ed., GRCA International, Camberley, UK (2000).

15. CEN, EN 1170: 1998: Parts 1-7: Precast Concrete Products:Test Methods for Glass-fiber Reinforced Cement, CEN, Brussels,Belgium (1998).

Fig. 13: Examples of collapse tests on telecommunication towers



16. Laboratorio Nacional de Engenharia Civil, E397 Standard—Assessment of Compressive Young’s Modulus in Concrete (availablein Portuguese), Laboratorio Nacional de Engenharia Civil, Lisbon,Portugal (1993).

17. Coutinho, A., and Goncxalves, A., Production and Properties ofConcrete (available in Portuguese), Laboratorio Nacional de Engen-haria Civil—LNEC, Lisbon, Portugal (1994).

18. Laboratorio Nacional de Engenharia Civil, E226 Standard—Compression Tests in Concrete (available in Portuguese), Labora-torio Nacional de Engenharia Civil, Lisbon, Portugal (1993).

19. Chanvillard, G., ‘‘Caracterisation des performances d’unbeton renforce de fibers a partir d’un essai de flexion. Partie 1: Dela subjectivite des indices de tenacite,’’ Materials and Structures32:418–426 (1999).

20. Banthia, N., Moncef, A., Chokri, K., and Sheng, J., ‘‘UniaxialTensile Response of Microfiber Reinforced Cement Composites,’’Materials and Structures 28:507–517 (1995).

21. Toray Industries, Inc., Torayca Technical Reference Manual,Toray Industries, Tokyo, Japan (1997).

22. Laboratorio Nacional de Engenharia Civil, E399 Standard—Assessment of Creep Coefficient in Compression (available inPortuguese),Laboratorio Nacional de Engenharia Civil, Lisbon, Portugal (1993).

23. Laboratorio Nacional de Engenharia Civil, E398 Standard—Assessment of Retraction and Expansion in Concrete (available in Por-tuguese), Laboratorio Nacional de Engenharia Civil, Lisbon, Portugal.

24. Imprensa Nacional Casa da Moeda, RSA—Code for Safetyand Actions of Buildings and Bridges Structures (in Portuguese),DL 235/83, Portugal (1983). n



Seminaretrsertg

Documents

Transcript of Seminaretrsertg