Laboratory Tests of Two-Layer Beams Consisting of Normal and Fibered High Strength Concrete: Ductility and Technological Aspects

Holschemacher

2017

Structural Concrete

Funding informationAlexander von Humboldt Foundation.Models and full-scale statically determinate two-layer beams (TLBs) made of steel-fiber high-strength concrete (SFHSC) in the compression zone and normalstrength concrete (NSC) in the tensile zone have been tested by the authors. The present study is a further stage of these investigations, focused on testing a continuous, two-span TLB with optimal steel/fiber ratio as in the previous stages. This is the first experimental investigation of continuous TLBs (CTLBs). The study is aimed at testing the CTLB behavior under positive and negative bending moments in the span and above the middle support. An additional issue that is studied in the course of this work is the influence of bending moment redistribution on the behavior of a CTLB. As in the previous research stages, interaction of the concrete layers in a CTLB was studied to demonstrate the efficiency of such beams for real structures. No cracks between the SFHSC and NSC layers were observed up to the ultimate limit state of the tested beam, which demonstrates proper interaction between the layers. The results obtained in the present study enable the recommendation of CTLBs for practical application as effective and economical continuous bending elements. K E Y W O R D Scontinuous two-layer beams, interaction between concrete layers, steel-fiber high-strength concrete | INTRODUCTIONAs is known, the main drawback of simply supported reinforced concrete (RC) beams is the relatively large moments in the span, which leads to large deflections and extensive cracking. Moreover, in simple statically determinate RC structures there is no internal moment redistribution, so the section in which the moment is maximum determines the load-bearing capacity of the structure. A solution to this problem is the use of continuous (statically indeterminate) RC structures that allow reduction of the maximum moment and deflection. In continuous beams, the moments above the supports and those in the span are redistributed, permitting the use of typical longitudinal reinforcement.One of the first theoretical works on continuous RC beams was carried out by Gvozdev, 1 which was focused on the load-bearing capacity of such beams. According to this method, each of the beam bays is loaded and the corresponding load-bearing capacity for the loaded bay is found. An equation for the calculation of the external bending moment in a certain loaded bay was proposed. The problem was solved for a beam with constant section dimensions by maximizing the internal forces. In a more general form, the problem of maximization of the internal forces for continuous RC beams was recently solved theoretically. Two-layer high-performance RC beams can be used in the traffic (longitudinal) direction of long-span bridges. The beam section consists of two parts: a bottom part made of normal-strength concrete (NSC), and an upper one made of steel-fiber-reinforced high-strength concrete (HSC). Using two-layer beams (TLBs) is logical because, as the beam span beco...

Section: Experimental Programmentioning

confidence: 99%

Section: Research Background and Aimsmentioning

confidence: 99%

Section: Research Background and Aimsmentioning

confidence: 99%

See 1 more Smart Citation

Experimental investigation of continuous two-layer reinforced concrete beams

Holschemacher

2017

Structural Concrete

“…It was concluded that there is no experimental evidence relating Poisson's coefficient of concrete to its strength. At the same time, our experimental results demonstrate that this ratio grows after the appearance of transverse cracks [4]. However, in this case, it is not Poisson's coefficient, but a ratio between transverse and longitudinal deformations.…”

Section: Introductionmentioning

confidence: 52%

“…Experimental studies were carried out to select effective fiber contents as well as suitable fiber types, to study most efficient combination of fiber and regular steel bar reinforcement [4]. It was shown that steel fibers have little effect on beams' elastic deformations but increase the ultimate ones, due to additional energy dissipation potential of steel fibers.…”

Section: Introductionmentioning

confidence: 99%

Transverse Deformations and Structural Phenomenon as Indicators of Steel Fibred High-Strength Concrete Nonlinear Behavior

Advances in Materials Science and Engineering

2019

As known, high-strength compressed concrete elements have brittle behavior, and elastic-plastic deformations do not appear practically up to their ultimate limit state (ULS). This problem is solved in modern practice by adding fibers that allow development of nonlinear deformations in such elements. As a rule, are applied steel fibers that proved high efficiency and contribute ductile behavior of compressed high-strength concrete (HSC) elements as well as the desired effect at long-term loading (for other types of fibers, the second problem is still not enough investigated). However, accurate prediction of the ULS for abovementioned compression elements is still very important and current. With this aim, it is proposed to use transverse deformations in HSC to analyze compression elements' behavior at stages close to ultimate. It is shown that, until the appearance of nonlinear transverse deformations (cracks formation), these deformations are about 5-6 times lower than the longitudinal ones. When cracks appear, the tensile stress-strain relationship in the transverse direction becomes nonlinear. This fact enables to predict that the longitudinal deformations approach the ultimate value. Laboratory tests were carried out on 21 cylindrical HSC specimens with various steel fibers content (0, 20, 30, 40, and 60 kg/m3). As a result, dependences of transverse deformations on longitudinal ones were obtained. These dependences previously proposed by the authors’ concept of the structural phenomenon allow proper estimation of the compressed HSC state up to failure. Good agreement between experimental and theoretical results forms a basis for further development of modern steel fibered HSC theory and first of all nonlinear behavior of HSC.

Two‐layer concrete bridge beams as composite elements

2013

Structural Concrete

Two‐layer high‐performance RC beams can be used in the traffic (longitudinal) direction of long‐span bridges. The beam section consists of two parts: a bottom part made of normal‐strength concrete (NSC), which has a U‐type section, and an upper one made of steel fibre‐reinforced high‐strength concrete (HSC), which has a rectangular section. Using two‐layer beams is logical because as the beam span becomes longer and the service load increases, so a higher concrete strength is required in the beam's compression zone to withstand rather large bending moments. As concrete in the tension zone of the section contributes little to the beam's loadbearing capacity, this zone is made of NSC. This is an important economical advantage of two‐layer beams. Steel fibres are only used in the compression zone made of HSC. The addition of steel fibres results in a higher ductility for the HSC layer, allowing proper design of two‐layer bridge beams for dynamic loads. The design parameters for such beams include the HSC class, where the HSC layer depth is known and is equal to the depth of the rectangular section (above the U‐section). The bottom NSC part (U‐section) of a long‐span beam is usually prestressed. Taking into account this circumstance, the total beam section depth should be checked for the serviceability limit state.