Theoretical and experimental analysis of load-carrying capacity of steel-concrete composite beams with glass-fibre-concrete slab

Transcription

1 Theoretical and experimental analysis of load-carrying capacity of steel-concrete composite beams with glass-fibre-concrete slab MARCELA KARMAZÍNOVÁ, PAVLA BUKOVSKÁ and PAVLA NEUBAUEROVÁ Faculty of Civil Engineering Brno University of Technology Veveří St. 331/95, 62 Brno CZECH REPUBLIC Abstract: - The paper deals with the problems of the theoretical and experimental investigation of load-carrying capacity of steel-concrete composite beams with glass-fibre-concrete (GFC) slab. The paper presents some selected results of the more extensive research realized on the authors workplace and oriented to the utilization of high-strength steels and high-performance concretes in steel-concrete composite structural members. This paper is directed towards one part of this research only, which represents theoretical analysis of the bending moment capacity and experimental verification of the actual bending moment capacity of steel-concrete composite beams with glass-fibre-concrete (GFC) slab in connection with their actual behaviour and corresponding relevant failure mechanism. Within the framework of the bending moment capacity analysis four basic types of beams have been (or will be, respectively) investigated, all of them composed of 3 different steel IPE cross-sections (IPE18, IPE2, IPE22) and concrete slab: (i) beams with GFC slab without usual steel reinforcement subjected to sagging bending moment, to investigate the contribution of GFC only to the sagging moment capacity; (ii) beams with GFC slab with steel reinforcement (reduced amount) subjected to sagging bending moment, to investigate the contribution of GFC slab and steel reinforcement together to the sagging moment capacity and to compare it with the first case; (iii) beams with plain concrete (PC) slab subjected to the sagging bending moment, to compare the results with the first case only; (iv) beams with GFC slab without steel reinforcement subjected to hogging bending moment, to verify the contribution of GFC to the hogging moment capacity. During the experimental parts of this research in common 27 loading tests of steel-concrete composite beams have been realized so far (but no all results are evaluated in detail so far) and other 9 specimens will be tested immediately. The attention was paid mainly to the following significant problems: the efficiency of the utilization of fibre-concrete slab in steel-concrete composite beams subjected to sagging or hogging bending moments, too; the effectiveness of the contribution of glass-fibre-concrete to the moment capacity of steel-concrete composite beams in comparison with reinforced concrete and plain concrete. Key-Words: - Composite member, steel-concrete beam, glass-fibre-concrete, load-carrying capacity, resistance, sagging bending moment, experimental verification, theoretical analysis. 1 Introduction The workplace of the paper authors is significantly focused on the usage of advanced non-traditional materials in traditional structural members. One of the topics in this research field is the application of new progressive concrete types in composite steelconcrete structural members and structures, hereto the usage of glass-fibre-concrete for slab of steelconcrete composite beams, mainly in the case of the negative (sagging) bending moment, when concrete is subjected to tension. The fibres in concrete slab can help to increase the load-carrying capacity, i.e. bending moment resistance, and also the flexure stiffness, i.e. to decrease the deflections and it also allow decrease the steel reinforcement amount. Within the framework of this problem solution experimental verification of the actual behaviour, failure mechanism and load-carrying capacity has been realized in the period (approximately) of the last year. In parallel with loading tests the structural members, geometrical and mechanical properties of which corresponded to test specimen parameters, have been subjected to the theoretical analysis oriented mainly to the numerical modelling. In this paper the particular results of the loading tests of specimens with glass-fibre-concrete slab without and with steel reinforcement subjected to sagging moment are presented especially. To obtain the effect of glass-fibres only in comparison with glass-fibres together with reduced amount of steel ISBN:

2 reinforcement also the test results of the beams with plain concrete slab are presented for the illustration. 2 Theoretical analysis determination of bending moment resistance The usual approach for the determination of the bending moment resistance is based on the plastic behaviour considering following basic assumptions: (i) constant normal stress distribution in the crosssection particular parts; (ii) not taking into account tensile concrete for bending moment resistance. In the case of hogging bending moment concrete slab or its larger part is usually compressed, while larger part of steel beam or whole one is subjected to tension. For the plastic behaviour assumption the formulas for the resistance in the hogging bending moment can be given according to the European standard EN 1994 in dependence on the neutral axis position [15]. In such a generally known case it is not necessary to describe the resistance in detail. In the case of sagging bending moment the larger part of steel beam is usually compressed, while concrete slab is subjected to tension, so that the tensile stresses in concrete must be introduced by reinforcement, not by concrete. If concrete is reinforced by dispersed fibres, those ones may be assumed to resist (partially, at least) to the tension in slab. But it is a question what is a real contribution of fibres to the resistance in the sagging moment and effectiveness of those usage. 2.1 Sagging bending moment In the case of concrete slab reinforced by usual steel reinforcement the plastic approach can be applied for the sagging bending moment resistance as given in [15]. But in the case of concrete slab reinforced by dispersed fibres the question is, whether the plastic behaviour can be decidedly considered because of the quasi-brittle character of material and because of the crack initiation and propagation. Then the elastic approach is probably more apposite and following assumptions should be considered: (i) linear normal stress distribution; (ii) taking into account tensile concrete for bending moment resistance assumed for the case of no steel reinforcement, theoretically, to compare it with the resistance of the beam with reinforced or fibrereinforced slab and subsequently, to compare it with actual resistances obtained from the tests for test specimen configurations mentioned above; actually, of course, nor in fibre-concrete steel reinforcement does not absent at all, but its amount is usually much lower than in the case of fibreless concrete. The typical configuration of steel-concrete beam cross-section is shown in Fig. 1. The beams of this cross-section type with dimensions according to Fig. 1 have been used for the investigation applying theoretical analysis and experimental verification. Fig. 2 shows the normal stress distribution in the steel-concrete beam cross-section for the following conditions: sagging moment concrete subjected to tension; elastic behaviour substitute cross-section conception applied for the calculation of bending moment resistance (see e.g. [15]); fibre-concrete tensile concrete is taken into account for the bending moment resistance. For the illustration, numerical values present the example of the predicted stresses calculated for the cross-section with steel profile of IPE 2, steel yield strength of 235 MPa and fibreconcrete tensile strength of 14,2 MPa (see below). r c r a b c b i T c T i T a z Fig. 1 Beam cross-section: IPE section (IPE 18, IPE 2, IPE 22), b c = 1 mm, h c = 1 mm -35,5 MPa 92,8 MPa fct = 14,2 MPa 92,8 / 1,66 = 8,71 MPa fy = -235, MPa 1,66 x (-35,5) = -378,43 MPa Fig. 2 Elastic stress distribution in steel-concrete cross-section: numerical example for IPE 2 3 Experimental verification The experiments should verify the correctness and justification of the theoretical calculation based on the elastic behaviour for steel-concrete beams with fibre-concrete slab subjected to sagging moment, y z 2 z 1 n h c h a ISBN:

3 and namely obtain the actual bending moment loadcarrying capacities of the beam with fibre-concrete and steel reinforcement (together) in comparison with the same beam without steel reinforcement, to investigate the difference between both beam types and to evaluate the contribution of fibres dispersed in concrete slab to the bending moment resistance. In connection with the investigation of material properties, practical usage, technology, production of glass-fibre-concrete within the framework of the co-operation with the Institute of Building Materials Inc., the part of this research was oriented just to the possibility of GFC usage (among others) in steelconcrete composite beams subjected to the sagging moment, that for the experimental verification (see above) just glass-fibre-concrete has been used. 3.1 Test arrangement and realization Within the framework of the loading tests following test specimens have been (or will be) verified: (i) steel-concrete beams with GFC slab without steel reinforcement subjected to sagging bending moment 9 tests (3 specimens for each steel crosssection IPE 18, IPE 2, IPE 22); all specimens tested, all test results evaluated so far; (ii) steel-concrete beams with GFC slab with steel reinforcement subjected to sagging bending moment 9 tests (3 specimens for each steel crosssection IPE 18, IPE 2, IPE 22); the amount of steel reinforcement was considered as the minimum given by constructional requirements and prescribed in [18], so that reinforcing bars with the diameter of 12 mm were applied and displaced in distances of 15 mm in one row; all specimens have been tested so far, but 3 test results only (one of each group) have been evaluated in this moment, because of the recent testing finish only; (iii) steel-concrete beams with plain concrete slab subjected to the sagging bending moment 9 tests (3 specimens for each steel cross-section IPE 18, IPE 2, IPE 22); all specimens tested, all test results evaluated so far; (iv) steel-concrete beams with GFC slab without steel reinforcement subjected to hogging bending moment 9 tests planned (3 specimens for each steel cross-section IPE 18, IPE 2, IPE 22); no specimen tested so far, because of the permanently continuing research. Test specimens should present sagging moment zone, i.e. zones around the internal supports of the continuous beam loaded approximately by uniform loading, so the test specimen span has been chosen to correspond with this zone in the usual beams of floor structures. Based on this assumption, the span of the test specimens was 3 m. Specimens have been loaded by force introduced in the span middle to obtain the same (similar, approximately) bending moment distribution as (actually) around the internal support of continuous beam. As written above, in common 36 specimens have been or will be tested. Material properties were (or will be) following: (I) steel steel grade of S 235 (nominal value of steel yield strength is 235 MPa in all cases of specimens); (II) glass-fibre-concrete mean value of tensile strength is 14.2 MPa, corresponding modulus of elasticity is 19.7 GPa; mean value of the cube (compression) strength is 85.8 MPa, modulus of elasticity is 24.4 GPa; (III) plain concrete because of the necessity of comparison of test results, plain concrete has been chosen to have material properties in compression in accordance with glass-fibre-concrete, but naturally, material properties in tension cannot correspond; (IV) steel reinforcement steel of the nominal value of yield strength of 45 MPa has been used. For tested specimens the material tests have been realized to obtain actual mechanical properties of investigated beams. For measured values of material properties the assumed bending moment resistances have been calculated for the beams subjected to sagging bending moment in accordance with the approach indicated above, to compare them with test results and to obtain the contribution of GFC to the bending moment load-carrying capacity. Fig. 3 Illustration of test set-up, specimen and measuring apparatus Fig. 4 Detail of the loading equipment and load introduction to the test specimen ISBN:

4 In Figures above and below the illustrations of test preparation and realization showing test specimens, test set-up, loading equipment, measuring apparatus (Fig. 3, 4), strain gauges on test specimens together with specimen failure (Fig. 5, 6), are presented. measured properties on the base of elastic approach. From the comparison of experimental values and calculated values it is seen: the resistance increases in the case of steel reinforcement added to GFC slab are 53% (IPE 18), 16% (IPE 2), 25% (IPE 22), but it is not evidently dependent on the cross-section dimension. In average the effect of reinforcement to increase the resistance can be about 3 % Fig. 5 Strain gauges on concrete slab detail Fig. 6 Strain gauges in the slab part with cracks Test 4: Mu=12. knm Test 6: Mu=112.5 knm Test 11: Mu=128. knm Test 5: Mu=97.5 knm Mu,el,ftb = 84.2 knm Mu,el,ftb,R = 11 knm Fig. 8 Relationship M w for IPE 2: GFC without reinforcement (Tests 4, 5, 6), GFC with steel reinforcement (Test 11) Test 1: Mu=6.5 knm Test 3: Mu=75.2 knm Test 1: Mu=13.9 knm Test 2: Mu=67.2 knm Mu,el,ftb = 68.7 knm Mu,el,ftb,R = 9 knm Fig. 7 Relationship M w for IPE 18: GFC without reinforcement (Tests 1, 2, 3), GFC with steel reinforcement (Test 1) The graphs in Figs. 7, 8, 9 show the relationships between bending moments M and deflections w in the span middle obtained from the tests realized for steel-concrete beams with glass-fibre-concrete slab without and with steel reinforcement for all groups of specimens. In the graphs the objective ultimate moments M u obtained from the tests in comparison with resistances M u,el,ftb (slab without reinforcement) and M u,el,ftb,r (slab with reinforcement) calculated for Test 7: Mu= knm Test 9: Mu=15.75 knm Test 12: MU=153.1 knm Test 8: Mu= knm Mu,el,ftb = 12.4 knm Mu,el,ftb,R = 13 knm Fig. 9 Relationship M w for IPE 22: GFC without reinforcement (Tests 7, 8, 9), GFC with steel reinforcement (Test 12) ISBN:

5 But as Figs. 1, 11, 12 show, the resistance increase due to glass-fibre-concrete related to the resistance of the beam with plain concrete is from about 1 % even to 19 %, i.e. the resistance with GFC is from 2 even to 2.9 times higher (for more see [1], [2], [3], [4], for example) IPE 18 + NC slab, 2,5 5, 7,5 1, 12,5 Test 1 NC Test 2 NC Test 3 NC Fig. 1 M w for IPE 18: plain concrete IPE 2 + NC slab, 2,5 5, 7,5 1, 12,5 Test 4 NC Test 5 NC Test 6 NC Fig. 11 M w for IPE 2: plain concrete IPE 22 + NC slab, 2,5 5, 7,5 1, 12,5 Test 7 NC Test 8 NC Test 9 NC Fig. 12 M w for IPE 22: plain concrete 4 Conclusion The moment resistance of steel-concrete composite bending structural members composed of steel beam and glass-fibre-concrete slab (with and without steel reinforcement) is continuously analyzed regarding other problems, namely with respect to rheological influences, i.e. creep or shrinkage. The investigated structural members are also subjected to the numerical modelling verified and calibrated with the respect to the test results. Although many design and realization problems exist in this professional field, steel-concrete composite members using fibrereinforced concrete can contribute to the reliable and economy structural design very significantly not only from the viewpoint of the limit states, but also from the viewpoint of the structural durability. On the authors workplace the high attention is paid to other topics related to the problem presented here, that means the problems of the usage of highstrength steels and high-performance concretes and fibre-reinforced concretes in load-carrying structural members (see e.g. [5], [7], [8], [1], [12]), problems of steel and concrete structures in general (see e.g. [9], [11], [13], for example) in combination with the usage of mathematical, statistic and probabilistic methods for the theoretical analysis and evaluation of test results (see [1], [2], [6], [7], [11], [12], [13], for example). Acknowledgement: The paper has been elaborated within the framework of following research projects solutions: (i) MŠMT Projects (Czech Ministry of Education, Youth and Sports) CZ.1.5/2.1./3.97 (Research Centre Project AdMaS ), FAST S-11-32/1252 (Specific Research Project); (ii) GAČR Projects (the Czech Science Foundation) 13/9/597, 13/9/H85. References: [1] M. Karmazínová, J. J. Melcher, Analysis of the resistance of steel-concrete composite members composed of high-strength materials, In Proceedings of 1 th International Conference on Steel, space and composite structures SS 11, Famagusta, CI-premier: Singapore 211. [2] M. Štrba, M. Karmazínová and J. Melcher, Reliable and effective design of composite members Steel-concrete composite members using high-strength materials, In Proc. of the 6 th European Conference on Steel and Composite Struct. EUROSTEEL 21 1, Budapest, ECCS 211, pp ISBN [3] M. Karmazínová, J. J. Melcher, Possibilities of application of glass-fibre-concrete in composite steel-concrete beams, In Proceedings of the 9th International Symposium on Fiber-Reinforced Polymer Reinforcement for Concrete Structures FRPRCS-9 held in Sydney, University of Adelaide, 29, p. 51 (book) + DVD (full version 4 pages). ISBN ISBN:

6 [4] J. Melcher, M. Karmazínová, J. Pozdíšek, Experimental verification of behaviour of composite steel and glass-fibre-concrete beam, In Proceedings of the 9th International Conference on Steel-Concrete Composite and Hybrid Structures ASCCS 29 held in Leeds, Singapore: Research Publ. Services, 29, pp ISBN [5] M. Karmazínová, M. Štrba and V. Kvočák, Steel-concrete composite members using highstrength materials in building constructions structural design, actual behaviour, application, In Proceedings of the 2 nd European Conference on Civil Engineering ( ECCIE 11 ) Recent Researchers in Engineering and Automatic Control, North Atlantic University Union, WSEAS: Puerto de la Cruz, Tenerife, 211, pp ISBN [6] Z. Kala, M. Karmazínová, J. Melcher, L. Puklický, A. Omishore, Sensitivity analysis of steel-concrete structural members, In Proceedings of the 9 th International Conference on Steel-Concrete Composite and Hybrid Structures ASCCS 29 held in Leeds, Research Publishing Services: Singapore, 29, pp ISBN [7] Z. Kala, L. Puklický, A. Omishore, M. Karmazínová, J. Melcher, Stability problems of steel-concrete members composed of highstrength materials, Journal of Civil Engineering and Management, 21, 16(3), pp doi: /jcem [8] M. Karmazínová, J. J. Melcher, V. Röder Loadcarrying capacity of steel-concrete compression members composed of high-strength materials, In Proceedings of the 9 th International Conference on Steel-Concrete Composite and Hybrid Structures ASCCS 29, Leeds, Research Publishing Services: Singapore, 29, pp ISBN [9] M. Karmazínová, J. Melcher, M. Štrba, Fastening of steel structural members to concrete using post-installed mechanical fasteners, In Proceedings of 9 th International Conference on Steel-Concrete Composite and Hybrid Structures ASCCS 29, Leeds, Research Publishing Services: Singapore 29, pp ISBN [1] M. Karmazínová and J. J. Melcher, Design assisted by testing applied to the determination of the design resistance of steel-concrete composite columns, In Proceedings of the 13 th Int. Conf. on Mathematical and Computational Methods in Science and Engineering MACMESE '11, WSEAS Press: Catania 211, pp ISBN [11] Karmazínová, M. and Melcher, J. J., Methods of the design assisted by testing applicable tools for the design resistance evaluation using test results, In Proc. of the 2 nd Int. Conference on Mathematical Models for Engineering Science Mathematical Models and Methods in Modern Science, Institute of Environment, Engineering, Economics and Applied Mathematics, WSEAS Press: Puerto de la Cruz, 211, pp ISBN [12] Karmazínová, M., Pilgr, M. and Melcher, J. J., Methods based on the approach of the design assisted by testing applied to the determination of material properties, In Proceedings of the 2 nd International Conference on Mathematical Models for Engineering Science ( MMES 11 ) Mathematical Models and Methods in Modern Science, WSEAS Press: Institute of Environment, Engineering, Economics and Applied Mathematics, Puerto de la Cruz, 211, pp ISBN [13] M. Karmazínová, J. Melcher, Z. Kala, Design of expansion anchors to concrete based on the results of experimental verification, Advanced Steel Construction, an International Journal, Vol. 5, No. 4, Hong Kong Institute of Steel Construction, December 29, pp ISSN X. [14] EN 199 Basis of Structural Design: Annex D Design assisted by testing, CEN Brussels, 24. [15] EN Design of Composite Steel and Concrete Structures Part 1-1: General Rules and Rules for Buildings, CEN Brussels, 26. [16] EN Design of Concrete Structures Part 1-1: General Rules and Rules for Buildings, CEN Brussels, 26. [17] EN Design of Steel Structures Part 1-1: General Rules and Rules for Buildings, CEN Brussels, 26. ISBN: