TEST METHOD FOR HYBRID-REINFORCED TWO-ARCH CONCRETE BEAMS WITH EXPANSION ZONES

ABSTRACT

This article investigates the behavior of two-span continuous reinforced concrete beams with hybrid reinforcement under static loading. The tensile zones of the beams are partially reinforced with a combination of steel and composite (FRP) bars to improve structural performance. Experimental specimens were prepared and tested to evaluate strength, crack resistance, and deformation characteristics. The testing methodology included gradual loading, monitoring of crack formation, and measurement of displacements and strains. The results show that hybrid reinforcement enhances both the strength and serviceability of reinforced concrete beams compared to conventional reinforcement. The combination of steel and composite bars allows effective utilization of their advantages, such as corrosion resistance and stiffness. The study provides valuable experimental data and supports the development of more efficient design methods for reinforced concrete structures.

АННОТАЦИЯ

В данной статье исследуется поведение двухпролётных неразрезных железобетонных балок с гибридным армированием при статическом нагружении. Растянутые зоны балок частично армированы комбинацией стальной и композитной (FRP) арматуры с целью повышения эксплуатационных характеристик конструкции. Были изготовлены и испытаны экспериментальные образцы для оценки прочности, трещиностойкости и деформационных характеристик. Методика испытаний включала поэтапное нагружение, наблюдение за образованием трещин, а также измерение прогибов и деформаций. Полученные результаты показали, что гибридное армирование повышает как прочность, так и эксплуатационную надежность железобетонных балок по сравнению с традиционным армированием. Совмещение стальной и композитной арматуры позволяет эффективно использовать их преимущества, такие как коррозионная стойкость и жесткость. Исследование предоставляет ценные экспериментальные данные и способствует разработке более эффективных методов расчёта железобетонных конструкций.

Keywords: composite reinforcement, steel reinforcement, arch, reinforced concrete beams, crack resistance, deformation, strength.

Ключевые слова: Композитная арматура, стальная арматура, арка, железобетонные балки, трещиностойкость, деформация, прочность.

Introduction. Reinforced concrete structures are one of the types of structures widely used in the construction industry. They offer high strength, reliability and cost-effectiveness. At the same time, the performance characteristics of reinforced concrete structures are directly dependent on the type of reinforcement and its placement. Although conventional steel reinforcement has high strength, its main drawback is its susceptibility to corrosion. For this reason, research into the use of composite and steel reinforcement types has been carried out in recent years.

The use of fibre-polymer reinforcement (FRP) as longitudinal reinforcement in concrete structures has become widespread in recent years. This is primarily due to its advantages, such as high strength, light weight and corrosion resistance. However, concrete beams reinforced solely with FRP have certain drawbacks. In particular, the development of cracks and cold spots beyond the permissible limits during service limits the widespread use of FRP reinforcement to a certain extent.

To address these problems, a hybrid reinforcement method combining fibre-polymer and steel longitudinal bars in the tensile zone of concrete beams has been proposed [1]. This approach allows for the effective utilisation of the favourable properties of both materials. Specifically, the FRP reinforcement, placed in the tensile zone, increases the strength and durability of the structure, while the steel reinforcement enhances the element's stiffness, ensuring reliability during the structure's service life.

The main aim of the study is to experimentally investigate the strength and deformation characteristics of two-span concrete beams with hybrid reinforcement in the arch and central support zones (Figures 1-2).

Figure 1. Moulds for preparing the main test specimens

Figure 2. Equipping the sample with reinforcement

Three continuous beams with two spans were prepared for the experimental investigations. The dimensions of the specimens, consisting of a continuous two-span solid beam, are  b×h×l = 100×200×3700 mm (Figures 3–4). The arrangement of the reinforcements in the beams' cross-sections is shown in Figure 4. Samples fitted exclusively with steel reinforcement and those fitted exclusively with composite reinforcement were also prepared as controls.

Figure 3. Reinforced bar assembly scheme for sample beams

Figure 4. Cross-sections of the test specimens and their reinforcement

The continuous two-span concrete beam was reinforced with composite and steel reinforcement in accordance with Recommendation [1]. The characteristics of the experimental specimens are presented in Table 1.

Table 1.

The characteristics of the experimental specimens

Note: MC is a sample made of monolithic concrete.

The mechanical and deformation properties of the reinforcement and concrete were determined on auxiliary specimens in the laboratory in accordance with GOST 10180-2012 [3] and GOST 31938-2012 [4]. The test results are presented in Figures 5 and 6.

a)                                               b)

Figure 5. Concrete cube samples (a) and strength indicators (b)

a) b)

Figure 6. FRP samples prepared for testing (a) and strength indicators (b)

Methodology. The testing of two-arch beams under static loads was carried out on the apparatus shown in Figure 7. The two-arch continuous beam was loaded with four forces generated by hydraulic jacks. At each stage, the load applied was approximately 0.05 of the destructive force until cracks appeared in the specimen. After the crack appeared, the load applied at each stage amounted to approximately 0.1 of the destructive force. The longitudinal deformations occurring in the beam were measured with clock-type indicators accurate to 0.01. The vertical displacements (settlements) of the beam over the supports and between the beam arches were measured with clock-type indicators accurate to 0.01. At each stage, readings from the measuring instruments were recorded twice, both before and 5–10 minutes after the beam was loaded. Crack formation in the beam was detected visually and with an MB-24 microscope with a resolution of 0.05 mm. The tests were conducted until the beam failed.

Figure 7. Preparing samples for testing

Conclusions. Within the framework of an experimental investigation programme on two-span concrete beams reinforced with hybrid reinforcement comprising steel and basalt fibre composite bars, the authors designed the test specimens, A research methodology was developed by the authors, covering the design of the experimental specimens, the process of their fabrication, and the procedure for conducting the tests. The ongoing experimental work will allow for the acquisition of new experimental data on the in-plane behaviour of statically indeterminate reinforced concrete beam elements, hybrid-reinforced with steel and basalt fibre composite working longitudinal bars.

Furthermore, the results obtained allow for the verification of the validity of the theoretical approaches adopted for the calculation of this type of structure, as well as the assessment of the practical effectiveness of implementing the hybrid reinforcement method.

References:

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