Acta Polytechnica Vol. 43 No. 412009 Long-term Test Arrangement for Externally strengthened Reinforced Concrete Elements T. Variura, P. Stdp6nek, I. Svaifikov6,J. Ad:imek Melh.ods for extemal st'rengtluning of concrete use elements ofaery high tensionaL shvngth gLued on to its tensioned" surface. Tfuse 4zmmts may be of metaL carb.onfbers (CFRP), gkus fibers or others, usuntty haaing aery good iechanicat properties. Howeuei, these high*trmgth elements are normn'lly attached t.o concrete .lry epoxy resins. Epoxy resins hoot olo, Young's rnoiulis and therefore a'higher rZte of crup rnay haae an inJluence on the long-tenn.behauior of such extemal strengthening. In oid.er to uerifi this idzi experiicntatty oipu6t space+auing artangement of tests is desribed in this p-aper. Panels act as loaded beanu but simultaneiusly as a load, for the other paneis in a starul. Thc dffircnt load magnitud.e acl;ing on a ffirent layer of panek should mahe it possibte to stu"dy the loig+erm in/lience of the rlegree of shearf.orye ory the glue creep. Certainly, llrc glue creep ?nn) be dependent on ttu iype of epoxy reiin; thereiore seaeial epoxyiesin types are inclu.ded in the tests. KEuords: carbon fiber (CFRP), glass fiber GERP), extemal strengtlrcning, epoxy-resin creep, test arrangement. I Notation G weight of load g self-weight of panel Co weight of extension piece Vo vertical load acrion Vh vertical support action M bending momenr {. g span ct coeflicient y ratio of increments of moments 2Introduction Because of the durability of concrete structures, many of them were designed for lighter live loads rhan are common today. Strengthening of some their components has therefore become necessary. Certainly other reasons for such strength- ening may also arise, e.g., partial damage, erc. Steel plates, composite lamellas (plates) or glass-fabric strengthening are used for such reinforcement. They are glued by very effective adhesives on ro rensioned surface of the structure. Today's adhesives, i.e., epoxy resins mostly, enable satis- factory gluing of the strengthening elements on a construc- tion site. Howeveq climatic and humidity conditions should be taken into account. The experiments described in this paper were prepared in laboratory conditions, akhough in the case of the glass-fabric strengthening the gluing over- head without mat supporting was successfully put to the test (see [2]). There remains the separate problem of perfect bonding of the sffengthening element to the structure surface, which means no slip benveen the strengthening element and the concrete. According to the test results reported in [l] and also those achieved by ourselves (mentioned in the following text), this assumption need not be necessarily completely satisfied. A special test arrangement focused on adhesive creep moni- toring is described in this paper. 3 Conclusions from previous tests In conjunction with short-term-load tests [2], long-term- -load tests of three remaining strengthened panels were started, with the aim of evaluating the long-term behavior of glued fiberylass strengthening in nar.ural open air weather conditions under constant load. The duration of these tests was 14 months. Time [dd.mm] Fig. 1: Time dependent deflections ofthree panels strengthened with a glass-fiber mat [2] under different load magnitudes The load position of two solitary forces was in one third of the span of each panel, but the strength of the load was dif- ferent for each of them. The deflections of the rested panels grew continually, as follows from Frg. l. Due to illness there was an almost nine month gap in measurements (as shown in Fig. l). The time behavior of the deflections indicates the sus- picion of possible continuous horizontal displacement of the glass laminate course against the concrete surface. The tested l4 l2 =lo tr6 '586 a + 2 0 60c.la.l$\o€o d-Ad6odod-€a€ 27 Acta Polytechnica Vol. 43 No. 412009 panels yrr. lq months old when the long-term-load tests st4rred. Therefore concrete creeping probibly was not the main reason for the displacement growth. The problem of epoxy-resin creep in strengthening con- nectrons has come under the spotlight in tests now going ahead at the Technical University in Brno 3 Special long-term test arrangement on strengthened concrete panels Frg. 2 shows the constitutive idea of a special space-saving arrangement of tests scheduled for a minimum of three years. The panels in the stand in Fig. 2 act as loaded beams, but simultaneously act as a load for the other panels. The dif- ferent load magnitude acting on a different layer of panels should make it possible to study the long-term influence of the degree ofshear force on the glue creep. The glue creep may be dependent on the type of epoxy resin; therefori several types of epoxy resin are included in the tests. Alto- gether six stands with different combinations of adhesive and strengthening material have been built up in the open air. This arrangement should ensure a regular step-up of the bending moments and also the shear fories in each layer of the stand. For this purpose, some comparative calculations have been made to determinate the right magnitudes of the span of supports /6 and also of coefiicient o. The following relations have been used in these calculations: Vertical load action minMp =^ (vp-r* "p)? t, -ir(n -; trf $) Mps=-(vp-, +cr)lto -;rcf *roY# When evidenily lU esl