Peter Helincks

Bond Behaviour and Shear Capacity of Self-Compacting Concrete

In this paper the bond mechanism of steel reinforcement to concrete and the shear capacity are examined. Tests have been conducted on conventional vibrated concrete (CVC) and self-compacting concrete (SCC). The results from pull-out tests on 200 mm cube specimens show that for the same compressive strength the maximum bond stress for SCC is as high or higher than for CVC and this for all tested diameters (8, 12 or 16 mm). The bond stress increases with increasing bar diameter. The specimens were loaded at constant rate and during testing the slip of the bars and the applied load were recorded. The four-point loading tests point out a slightly decreased shear capacity of SCC in respect to CVC with the same compressive strength. The shear capacity decreases with increasing shear span-to-depth ratio a/d (2 to 3) for all the tested concrete types. During the testing the maximum applied load was recorded and the crack and failure mechanism were observed.

Experimental Investigation of the Influence of the Bond Conditions on the Shear Bond Strength between Steel and Self-Compacting Concrete Using Push-Out Tests

Steel-concrete joints are often provided with welded shear studs. However, stress concentrations are induced in the structure due to the welding. Moreover, a reduction in toughness and ductility of the steel and a decreased fatigue endurance of the construction is observed. In this paper the shear bond strength between steel and ultra-high performance concrete (UHPC) without mechanical shear connectors is evaluated through push-out tests. The test samples consist of two sandblasted steel plates with a thickness of 10 mm and a concrete core. The connection between steel and concrete is obtained by a 2-component epoxy resin. Test samples with a smooth adhesive layer are compared with those with an epoxy layer, which is applied with a toothed paddle and/or gritted with small aggregates. In this research, specimens prepared with river gravel, crushed stone, and steel grit are compared and also two different epoxy resins are used. During the tests, the ultimate shear force is recorded as well as the slip between steel and concrete. All test specimens exhibited a concrete-adhesive or concrete failure. Furthermore, test results show that the use of a more fluid epoxy resin improves the anchorage of the gritted aggregates in the adhesive layer, resulting in higher shear bond stresses. No significant difference is found between specimens, gritted with river gravel or crushed stone. Applying the adhesive layer with the toothed paddle in horizontal direction slightly improves the bond behaviour. Finally, the experimental results of the test members with a smooth epoxy layer without gritted aggregates, provide test data for a fracture mechanics approach, which uses a 2D numerical model of the test specimen, composed of steel, epoxy resin, and concrete.

Failure Conditions from Push Out Tests of a Steel-Concrete Joint: Fracture Mechanics Approach

In order to evaluate the shear bond strength of a steel-concrete joint using an epoxy adhesive interlayer, push-out tests were carried out. The test samples consisted of two sandblasted steel plates and a self-compacting concrete sample, with the epoxy layer applied on the steel plates and gritted with granulates. During testing, an external force was applied to the concrete core and continuously recorded. To investigate the failure mechanism in detail, a fracture mechanics approach is required. In this paper theoretical-numerical assessment of the push-out test is performed. Regarding the finite element calculations, the locations suitable for failure initiation match bi-material (steel-concrete) notches. The most dangerous locations are evaluated from a generalized linear elastic fracture mechanics point of view. The critical load corresponding to the conditions of failure initiation is estimated and compared with the experimental results.

Influence of Steel Fibre Reinforcement on the Shear Resistance and Crack Pattern Formation of Self-Compacting Concrete Beams

This paper presents the results of experimental tests carried out on steel fibre reinforced self-compacting concrete (SFR-SCC) beams without stirrups. Sixteen beams are cast using four mixtures of SCC with different steel fibre content, while the longitudinal reinforcement is kept constant in all test members. The beams are subjected to four point bending tests at a shear span-to-depth ratio of 2. The ultimate shear stress is recorded, as well as the crack pattern and the mid-span beam deflection. Test results show that as fibre content increases, higher ultimate shear stresses are achieved. When fibres are included, test members exhibit an increase in ductility and a more extensive crack pattern is observed. The experimental values of the ultimate shear stresses are also compared with theoretical values as given by empirical expressions in literature.

Generalised fracture mechanics approach to the interfacial failure analysis of a bonded steel-concrete joint

Steel-concrete joints are often made by welded shear studs. However, this connection reduces the fatigue strength, especially in situations where locally concentrated loads occur with a large number of load cycles e.g. in bridge decks. In this paper the shear bond strength between steel and ultra-high performance concrete (UHPC) without welded mechanical shear connectors is evaluated through push-out tests and a generalized fracture mechanics approach based on analytical and finite element analyses. The connection is achieved by an epoxy adhesive layer gritted with granules. In the tests, specimens made with various manners of preparation of the epoxy interlayer are tested experimentally. Numerical-analytical 2D and 3D modelling of a steel-concrete connection is performed without and with the epoxy interlayer. The model of a bi-material notch with various geometrical and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

Fatigue assessment of a lightweight steel-concrete bridge deck concept

This paper presents results of a constant amplitude fatigue test on a lightweight steel-concrete deck concept, in which a network of longitudinal and transverse concrete ribs transmit shear forces between thin top and bottom steel plates. In order to achieve a lightweight composite structure, the concrete volume is only 32% of the volume between the plates. In previous research the deck was tested statically, indicating that the lightweight steel-concrete sandwich bridge deck concept possesses the necessary static resistance to bridge loads. This paper describes a constant amplitude fatigue test on a full-scale bridge deck test panel (3.60 m × 1.50 m) up to 6 million cycles. During this dynamic test, the deflection of the bridge deck, and steel and concrete strains are recorded on predetermined intervals in order to evaluate the fatigue behavior of the sandwich deck as a function of the number of cycles. The results indicate that the lightweight steel-concrete sandwich bridge deck concept possesses the necessary fatigue resistance to traffic loads.

The Influence of the Epoxy Interlayer on the Assessment of Failure Conditions of Push-Out Test Specimens

Connection between steel and concrete parts is frequently required in constructions where the steel-concrete joints are often realized by welded shear studs. In order to avoid stress concentrations, corrosion proneness, and other negative consequences of the welding process, steel-concrete connection without welded mechanical shear connectors is sought nowadays. Connection can be realized via an epoxy adhesive layer and gritted with granules. In the paper, the assessment of the push-out test configuration was performed from the generalized fracture mechanics point of view. The numerical-analytical modelling of a steel-concrete connection is performed without and with the epoxy interlayer, while 2D and 3D modelling is used. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. The model of a bi-material notch with various geometry, and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Various manners of preparation of the epoxy interlayer are tested experimentally. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

Failure Conditions from Push-Out Tests of a Steel-Concrete Joint: Experimental Results

Steel-concrete joints can suffer from premature fail due to inadequate shear bond between the two surfaces. In this paper the shear bond strength between steel and self-compacting concrete (SCC) without mechanical shear connectors is evaluated through push-out tests. The test samples consist of two sandblasted steel plates (10 and 6 mm) and a concrete core, with connection between steel and concrete obtained by a 2-component epoxy resin, gritted with granulates. During the tests, the ultimate shear force is recorded as well as the slip between steel and concrete. All test members exhibited a concrete - adhesive failure, and indicate nominal shear bond stresses between 2.20 and 4.22 MPa. In addition, a substantial difference in measured shear bond stresses is found between the 6 and 10 mm steel plates, indicating unwanted secondary effects with the 6 mm plates. During testing, maximum slip values between 0.02 and 0.05 mm are recorded. In addition to the experimental tests, shear stress distribution in the epoxy – concrete interface is examined by finite element analysis (FEA). In this way, a non-uniform stress distribution between steel and concrete is found with the maximum shear value about 2.5 times higher than the nominal shear stress value. The FEA combined with the experimental results provide a reasonable understanding of the shear induced failure conditions at a steel-concrete joint, and create test data for a fracture mechanics approach.