Tests on composite slabs and evaluation of relevant Eurocode 4 provisions

The paper addresses some key issues related to the design of composite slabs with cold-formed profiled steel sheets. An experimental programme is first presented, involving six composite slab specimens tested with a view to evaluating Eurocode 4 (EC4) provisions on testing of composite slabs. In four specimens, the EC4-prescribed 5000 load cycles were applied using different load ranges resulting from alternative interpretations of the reference load Wt. Although the rationale of the application of cyclic loading is to induce loss of chemical bond between the concrete plate and the steel sheet, no such loss was noted in the tests for either interpretation of the range of load cycles. Using the recorded response of the specimens the values of factors m and k (related to interface shear transfer in the composite slab) were determined for the specific steel sheet used in the tests, on the basis of three alternative interpretations of the related EC4 provisions. The test results confirmed the need for a more unambiguous description of the m-k test and its interpretation in a future edition of the Code, as well as for an increase in the load amplitude range to be used in the cyclic loading tests, to make sure that the intended loss of bond between the concrete slab and the steel sheet is actually reached. The study also included the development of a special-purpose software that facilitates design of composite slabs; a parametric investigation of the importance of m-k values in slab design is presented in the last part of the paper

Test results and strength estimation of R/C beams strengthened against flexural or shear failure by the use of SRP and CFRP

The paper reports tests on three groups of reinforced concrete (R/C) beam full-scale specimens, strengthened in flexural or shear using Steel Reinforced Polymers (SRP) and Carbon Fibre Reinforced Polymers (CFRP). The first group of five specimens represents the middle part of the span of a continuous beam and specimens are flexurally strengthened. The second group represents the support region of a continuous beam and its four specimens are strengthened in flexure. The third group also represents the support region of a continuous beam and its four specimens are strengthened in shear. Four specimens in total are tested unstrengthened to allow comparisons with the response of strengthened specimens. In addition to the different part of the beam that each specimen represented and the shear or flexural strengthening, the main parameters that varied among the specimens were: the type of polymer (SRP of two different types, or CFRP), the type of steel bars (ribbed or smooth, the latter being representative of older R/C members), the type of anchorage used for the polymers, and the way loading is applied to the specimens. Low strength concrete grade is used for the specimens, again to simulate older R/C members. The recorded response of the specimens is presented and discussed, and the experimentally measured strengths of the specimens are estimated analytically on the basis of the measured deformations of the specimens. Finally conclusions are drawn regarding the relative performance and merits of SRPs and CFRPs as strengthening materials for R/C beams

Tests on RC Beams Strengthened at the Span with Externally Bonded Polymers Reinforced with Carbon or Steel Fibers

The main objective of the experimental work reported herein is the comparative evaluation of steel-reinforced polymers (SRPs) and carbon-reinforced polymers (CFRPs) used as externally-bonded reinforcement in strengthening of reinforced-concrete (RC) members. Tensile stress strain as well as bond constitutive laws for these materials were first derived from 16 tests and are summarized here. Results are then reported from four-point bending tests of five full-scale RC beams strengthened at their span using SRP and CFRP strips. The bond tests have shown that by providing a bond length greater than the effective one, neither the bond strength nor the deformation capacity are increased, whereas by increasing the width of the strip the bond strength is increased. From the bending tests of beams it was found that the use of both SRP and CFRP strips resulted in a significant increase in strength (up to 92%) with respect to the strength of the initial specimen. The experimentally measured strengths were estimated analytically using both the experimental measurements of the specimen deformations and the pertinent provisions of standards from the American Concrete Institute and the European Committee for Standardization

Experimental and numerical study of the behaviour of high dissipation metallic devices for the strengthening of existing structures

The use of steel bracing systems for the strengthening of existing reinforced concrete (RC) frames may lead to increase of both strength and stiffness. However, in most of the cases the main target is the increase of the energy dissipation capacity. This paper studies, both experimentally and numerically, the efficiency of a specific strengthening type which utilizes a small steel link element having an I-shaped cross-section connected to the RC frame through bracing elements. The energy is dissipated through the plastification of the steel link element. The case studied in this paper is a typical one bay, single storey RC frame constructed according to older code provisions, which is strengthened through two different types of steel link elements. The behaviour of the strengthened frames is studied with respect to the one of the original bare frame. The experimental study is supported by complete numerical simulations of the performed tests. To this end, detailed numerical models are formulated, which are able to follow the highly non-linear nature of the problem, involving the plastification of the steel rebars, the cracking and plastification of concrete and the plastic deformation and hysteretic response of the dissipative link elements