Theoretical and experimental analysis of load-carrying capacity of steel-concrete composite beams with glass-fibre-concrete slab
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 (IPE180, IPE200, IPE220) 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.
Actual behaviour of composite externally CFRP-reinforced timber beams – stress analysis
The paper is focused on the problems of composite CFRP-reinforced timber beams. CFRP reinforcement is represented by the lamella externally bonded on the tensile part of the beam for the strengthening the member to increase in the resistance from the viewpoint of both the ultimate and serviceability limit states. Usually for the resistance determination the concept of composite structural members based on the substitute (ideal, respectively) cross-section is applied, but the usage of this principle is depending on the efficiency of the shear connection (here bonded) between CFRP reinforcement and basic material – timber. It is mainly influenced by the glue type and also by the bonded connection quality. The practical experiences obtained from the tests oriented to the experimental verification of the actual behaviour show that the efficiency is very different in dependence on the particular structural member. The paper presents selected results of the measurement of the stresses in CFRP reinforcement and in timber base, which can give the information on the level of the mutual interaction between both materials and on the rightness of the substitute cross-section approach mentioned above in the case of timber beams. The paper deals with the verification of the actual normal stresses, mainly in the cross-section part of the contact between timber and CFRP reinforcement (here bottom tensile edge). Actual normal stresses obtained from the tests have been used for the evaluation of actual characteristics of the substitute cross-section, especially the second moment of the area. Applying those derived cross-section characteristics the effects of the longitudinal shear, that means shear forces and stresses, have been calculated aimed to the verification of the bonded shear connection. Keywords—Timber beam, composite, strengthening, CFRP reinforcement, bonded lamella, actual behaviour, elasticity, normal stress, shear connection, longitudinal shear stress, experimental verification, theoretical analysis, interaction.
Formation and Strength of Magnesia Whiskers
The formation of single-crystal magnesia whiskers during the compressive deformation of single crystals at room temperatures is described. These whiskers can have strengths of the order of millions of pounds per square inch. They are formed during fracture as a result of the discontinuous propagation of cracks which are mechanically relieving internal stresses resulting from plastic flow