رفتار ساختاری پانل های ساندویچی کامپوزیتی با هسته های بتنی حبابدار ساده و مسلح شده با الیاف و وجوه فولادی موجدار

This paper studies the four-point bending response and failure mechanisms of sandwich panels with corrugated steel faces and either plain or fibre-reinforced foamed concrete core. Mechanical properties of both plain and polyvinyl alcohol fibre-reinforced foamed concrete were obtained, which are needed for the design of sandwich panel and numerical modelling. It is found that the fibre-reinforcement largely enhances the mechanical behaviour of foamed concrete and composite sandwich panels. Finite element code Abaqus/Standard was employed to investigate the influence of face/core bonding and fastening on the four-point bending response of the sandwich panels. It was found that face/core bonding plays a crucial role in the structural performance while the influence of fastening is negligible.

Foamed concrete is a type of cellular solid comprised of cement mortar matrix and air-void of minimum 20% in volume. It is made by incorporating air-voids into the cement matrix using pre-formed foam. Foamed concrete is a lightweight, low cost and easy-to-manufacture material with good workability and excellent performance on thermal insulation, acoustic insulation, fire resistance, corrosion resistance and shock absorption [1], [2], [3] and [4]. However, foamed concrete is not used as structural material due to its low compressive strength. Inclusion of fine aggregates in the mortar matrix to improve the mechanical properties of foamed concrete has been investigated by several researchers [2] and [3]; however, studies of the use of fibre-reinforcement in foamed concrete are very limited. Zollo [5] and [6] reported that polypropylene fibre-reinforced cellular concrete with density of 640 kg/m3 presented a significant improvement of mechanical and impact properties. It was shown that the fibre reinforcement can change the typical brittle behaviour of cellular concrete into ductile elastic–plastic behaviour [6], which has been also observed for lightweight concrete reinforced by steel fibres [7]. Jones and McCarthy [2] reported that the compressive strength of polypropylene fibre-reinforced foamed concrete exhibited an increase of 52% when compared to the unreinforced foamed concrete. High-performance fibres have also been used to reinforce lightweight concrete. Arisoy and Wu [8] and [9] used polyvinyl alcohol fibres as reinforcement for aerated concrete with density of 800–1600 kg/m3. They found that the fibre-reinforced aerated concrete showed increases of flexural strength, flexural ductility and toughness when compared to plain aerated concrete. The capacity of foamed concrete in structural applications has not been fully investigated. Due to its low density and low strength characteristics, it is an ideal core material for composite sandwich structures. Othuman Mydin and Wang [10] studied sandwich panels made with profiled thin steel face sheets (0.4 mm thickness) and foamed concrete core under uniaxial compression. Uddin et al. [11] investigated the flexural behaviour of composite panels made with carbon fibre reinforced polymer face sheets and autoclaved aerated concrete core. It was found that the flexural strength of the panels is increased considerably when compared to the strength of the autoclaved aerated concrete. This research is motivated by the lack of knowledge in the study of fibre-reinforced foamed concrete and composite sandwich panels with foamed concrete core for structural applications. In this work, tensile and compressive properties of plain foamed concrete and polyvinyl alcohol fibre-reinforced foamed concrete are presented. Two different methods are used to obtain compressive properties of foamed concrete and their results are discussed. Sandwich panels with corrugated steel faces and either plain or fibre-reinforced foamed concrete core are studied. The behaviour of the sandwich panels in four-point bending test is described and the various failure mechanisms observed in the test are reported. Finite element method was employed to understand the influence of face/core bonding and fastening on the four-point bending response of the sandwich panels. Materials and experimental details are described in Section 2. The experimental results and discussion are presented in Section 3. Numerical simulations are described in Section 4, which is followed by conclusions in Section 5.

Compressive mechanical properties of plain foamed concrete and polyvinyl alcohol fibre-reinforced foamed concrete were obtained using uniaxial compression test and indentation test. It is found that the fibre-reinforcement enhances the compressive strength of foamed concrete, which is attributed to the increase of specimen integrity by the fibres. A densification regime was observed in the compressive test of fibre-reinforced specimens, which is also attributed to the maintenance of specimen integrity by the fibres after failure. Tensile mechanical properties were obtained using uniaxial tensile test. It is found that the fibre-reinforcement drastically increases the tensile modulus, strength and yield strain of the foamed concrete and also prevents a sudden failure of the specimens, which is in contrast to the brittle behaviour of plain foamed concrete specimens. Full-scale specimens with corrugated steel sheet faces and either plain foamed concrete core or fibre-reinforced foamed concrete core were manufactured and tested in four-point bending. It is found that the fibre-reinforcement improves the structural response of composite sandwich panels by increasing the maximum load-carrying capacity before the failure of the specimen; however, for sandwich specimens with plain foamed concrete core, the average load in the plateau regime was higher than the average peak failure load showing an apparent strengthening of the specimens after failure. For fibre-reinforced foamed concrete cored sandwich specimens, the average load in the plateau-like regime is 65.28% of the average peak failure load. Such difference should be considered when fibre-reinforced foamed concrete is used in sandwich structural constructions. Numerical simulations of foamed concrete cored sandwich panels in four-point bending were performed using Abaqus/Standard finite element code. It is found that face/core bonding plays a crucial role in the structural performance while the contribution of fastening is negligible. This indicates that improvement of the face/core bonding should be addressed when foamed concrete core is used to obtain optimum structural performance of composite sandwich panels.