FRPRCS-8 Full Paper Format

BASIC RESEARCH ON THE ANCHORAGE OF TEXTILE REINFORCEMENT IN CEMENTITIOUS MATRIX E. Lorenz 1 1 2

R. Ortlepp 2

Institute of Concrete Structures, Technische Universität Dresden, Germany Institute of Concrete Structures, Technische Universität Dresden, Germany

Keywords: strengthening, textile, TRC, bond, pull-out, anchoring

1 INTRODUCTION Textile Reinforced Concrete is a composite material consisting of two major components namely concrete and textile. While the concrete is taking the function of the matrix with a volume amount of 90 to 99 % the low carrying capacity under tensile load is being compensated by inbuilt textile reinforcement. They are arranged according to the load situation. The endless yarns being produced like textile are made out of high performance materials such as Carbon or AR-Glass and are composed of hundreds up to thousands of separate fibers. Textile reinforcement represents an excellent alternative and compliment to existing means for strengthening and repairing concrete structures today. The effectiveness of textile reinforced fine-grained concrete, relative to flexural, lateral and torsion forces, was proven by BRÜCKNER, SCHLADITZ, BRAMESHUBER AND WEILAND [1-4] Precondition for the operability of the bond units is a safe transfer and transmission of the forces. This applies especially to the end anchorage areas of the reinforcement. In these areas can occur sudden system failures when the bond is being destroyed. Concerning unit reinforcement by TRC there can be effective four different failure mechanisms in the anchorage area according to ORTLEPP ET AL.[5]. Besides a failure of the old concrete in the bond area and the bonding joint between old and fine concrete a delamination within the textile layer can emerge. Additionally there is the possibility of yarn extraction or fiber failure. This is a problem for carbon textiles in particular since very high tensile strengths are being reachable and its smooth yarn surface. In the following article are examined the influences of bond increasing modifications and allowances within the anchorage area with regard to a shortening of the required anchorage lengths of textile reinforcements. In addition to that and following the reinforced concrete construction there are experiments being carried out in order to determine the efficiency of geometrical anchorage elements such as yarn redirection and the comparison of loop-shaped and straight ends of the yarn.

2 DEVELOPMENT LENGTH OF MODIFIED TEXTILE REINFORCEMENTS The aim of the experiments has been the verification of possibilities to shorten the required anchorage length of textile structures so as to avoid extract failure within the textile reinforced layer. 2.1 Experimental program Besides checking the textile of reference the required anchorage lengths for epoxy resin coated and additionally sanded textiles are being fixed. In dependence on anchorage within the reinforced concrete construction a further examination of the influence of a increase of the reinforcement amount has been carried out. The increasing has been provided by allowances within the anchorage area. The examined parameters are displayed in figure 1.

reference textile

double layer

epoxy resin

Fig. 1 Examined influence parameters

1

epoxy resin + sand

2.2 Test set-up During the testing of the anchorage length special attention was paid to a unit suited test set-up. Test set-up:

Specimen:

lE

modification in the anchorage range

100

lE

350 - 450

F A

A F section A - A:

textile

8

F

F

reference textile

[mm]

double layer, epoxy resin and sand

Fig. 2 Test set-up and used specimens for the tests of the anchorage length of textile reinforcements As a result of the glued steel sheets in the lower extraction area a load introduction without applying lateral compression can be assured. The anchorage of the specimen at the upper end of the test setup has been provided by a clamp. There have been glued steel sheets onto both sides of the examination area. Thus the anchorage length to be tested has been determined. 2.3 Experimental results The tests showed the following results. While there can be seen a yarn crack (figure 3 b) at sufficiently bound filament yarns too short anchorage lengths result in yarn extractions (figure 3 a).

lE

10 mm

a) yarn extraction

10 mm

b) yarn crack

Fig. 3 failure modes

reference textile

double layer

epoxy resin

epoxy resin + sand

Fig. 4 Comparison of the required development lengths lE

The needed anchorage length in order to introduce the maximum fibre tensile force has been measured 80 mm for the reference textile. When doubling the reinforcement a shortening of the development length of about 55 % could be examined. The verification of the effectiveness of an epoxy resin coating revealed a decrease of the required anchorage lengths by 50 % to 40 mm. The highest reduction was achieved with the epoxy resin coated and sanded textiles namely 62 %.

2

3

DEVELOPMENT LENGTH OF DIFFERENT ANCHORAGE ELEMENTS

The tests in order to determine the effect of hook- and loop-shaped untreated filament yarn was carried out on the basis of anchorage methods in the reinforced concrete construction. 3.1 Test set-up The force was introduced into the test specimen within the upper area through a clamp arrangement, which had been connected flexibly to the path controlled testing machine. The examined transition radius of the used carbon yarns was 15 mm. lE

Test set-up:

Specimen: 350

A

F

section A - A:

F

A reference yarn

10

lE

lE

saw cut

lE

100

carbon yarn

hookshaped

loopshaped

[mm] F F Fig. 5 Test set-up and used specimens for the tests of the anchorage length of hook- and loopshaped anchorage elements

We had to develop specimen specially designed for the particular requirements. Through a selective positioning of the point of predetermined rupture by help of a two-sided saw cut the anchorage areas to be investigated have been determined. The load was introduced on lines with the fibre extraction tests. 3.2 Experimental program The bond length lE of the examined specimen has been increased starting with 20 mm as far as the failure changed into the area out of the anchorage. 3.3 Experimental results The investigated anchorage lengths are to be seen in figure 6. In general there can be seen a shortening of the required load introduction lengths through integrating hook- or loop-shaped filament yarns. According to the measurements there are 100 mm of anchorage length for straight yarn ends necessary. By using anchorage hooks this can be reduced to 70 mm at the load introduction. The usage of loop-shaped elements results in a further decrease of the area of introducing the load by 50 % to 50 mm.

reference textile

hookshaped

loopshaped

Fig. 6 Comparison of the required development lengths lE

3

4

DISCUSSION OF TEST RESULTS

The tests regarding the anchorage lengths showed a shortening of the load introduction lengths of 50 up to 60 %. An increase of the reinforcement within the anchorage area is leading to a decline of the force being able to be introduced per thread. Meanwhile shortening the anchorage lengths of the surface modified textiles can be justified by a notable improvement of the bond. Besides an enlarging of the surface through the coating the extraction resistance within the gusset is increased considerably. Within the tests concerning the efficiency of geometrical anchorage elements shortenings of the anchorage lengths of up to 50 % could be achieved. The reductions of the development length at the hook-shaped anchorage elements are only based on the geometrically enlarged bond length. In contrast to that using loop shaped anchores activates another percentage contact area. Alongside the bond between matrix and filament yarn there is to be seen a mutual anchorage of the filament threads through the radius due to the redirection effect. The maximum tension forces within the curved areas are still limited due to the selected radius no matter which shape the anchorage elements have. This is due to the shear pressure sensitivity of the carbon yarn. That leads to the conclusion that using bigger transition radiuses can lead to further shortening of the required development length.

5

CONCLUSIONS

The following conclusions are deduced from the experimental results: With the use of the described coatings as well as the enhancement of the percentage of reinforcement and the geometrical anchorage elements a significant reduction oft the development length in the anchorage range was achieved. A simple modified design of the anchorage range and the lap range in the textile production is possible by a loop-shaped positioning of the yarns. Moreover, the possibility of a increase of the reinforcement amount as well as the application of epoxy resin coatings for the specific reduction of the anchorage lengths exists also on construction sites.

6

ACKNOWLEDGEMENTS

The authors gratefully thank the German Research Foundation and their partners within the Collaborative Research Centre 528 “Textile Reinforcement for Structural Strengthening and Retrofitting” for their support.

REFERENCES [1] [2]

[3] [4]

[5]

Brückner, A.; Ortlepp, R.; Curbach, M.: “Textile Reinforced Concrete for Strengthening in Bending and Shear”, Materials and Structures, 39, 8, 2006, pp 741–748. Weiland, S.; Ortlepp, R.; Curbach, M.: “Strengthening of predeformed slabs with textile reinforced concrete”, CEB-FIP: Proceedings of the 2nd fib-Congress, Neapel, 5.–8.6.2006. – Book of Abstracts and CD-ROM, Bd. 2, pp. 428–430 – ID 14-22. Brameshuber, W., ed. (2006). “Textile Reinforced Concrete: State-of-the-Art Report of RILEM Technical Committee 201 – TRC: Textile Reinforced Concrete”, Bagneux : RILEM, Report 36. Schladitz, F.; Curbach, M.: “Increase in the torsional resistance of reinforced concrete members using Textile Reinforced Concrete (TRC)”. 2nd International Conference on Concrete Repair, Rehabilitation and Retrofitting (ICCRRR), Cape Town, 24.-26.11.2008. – Book of Abstracts and CD-ROM, pp. 391-392. Ortlepp, R., Hampel, U. and Curbach, M., “A new Approach for Evaluating Bond Capacity of TRC Strengthening”, Cem Conc Comp, 28, 7, 2006, pp 589-597.

4