Behaviour of multi-celled GFRP beam assembly with concrete infill: experimental and theoretical evaluations

Glass Fibre Reinforced Polymer composites (GFRP) have become an attractive construction material for civil engineering applications due to their excellent corrosion resistance, design flexibility, and high stiffness and strength-to-weight ratios. However, research related to the flexural behaviour of concrete filled GFRP tubes is very limited, especially with regards to developing high strength and lightweight composite beams. Therefore, this research project has developed and investigated the behaviour of a new composite beam, termed 'multi-celled GFRP beam', which was made by gluing together a number of pultruded GFRP tubes and then filled with low-strength concrete. Firstly, the effective elastic properties of the pultruded GFRP tubes were evaluated by testing full-scale specimens with different shear span-to-depth ( ) ratios. The flexural ( ) and shear ( ) moduli of the GFRP tubes were then calculated using back calculation ( ) and simultaneous ( ) methods. The results showed that the method gives a more reliable elastic properties of pultruded hollow GFRP sections compared with SM and coupon tests. In addition, the full-scale test can accurately capture the local buckling failure of the compression flange of the GFRP section and the contribution of shear deformation, which is impossible to capture using a coupon specimen due to the discontinuity of the fibres. The compression buckling failure can significantly affect the ultimate failure load of GFRP sections and result in the section utilising only half of its design capacity. Secondly, the effect of filling the pultruded GFRP single sections with concrete of different compressive strengths on the flexural behaviour was investigated. Three different compressive strengths of concrete, i.e. 10 MPa, 37 MPa, and 43.5 MPa, were used to fill the hollow pultruded tubes. These beams were then tested under 4-point static bending. The results indicated that the concrete filling improved the flexural behaviour of GFRP tubes. The beams filled with concrete of 10 MPa compressive strength showed a 100% increase in strength, while the beams filled with concrete of 43.5 MPa compressive strength exhibited a 141% increase in strength, compared to the hollow sections. However, both concrete filled beams showed an approximately similar stiffness suggesting that low-strength concrete is a practical solution to filling the GFRP tubes. Thirdly, multi-celled GFRP beams were developed, and the flexural behaviour of this new beam concept was investigated. Beams with 1, 2, 3, and 4 cells were tested in hollow and concrete-filled configurations. From the experimental outcomes, it was found that gluing the pultruded GFRP profiles together can help stabilise the section and effectively utilise the high strength of the fibre composite materials. Moreover, the provision of a concrete core in the top cells significantly enhanced the bending strength and stiffness of the GFRP sections, due to the concrete supporting the tube walls and delaying the local buckling. Similarly, the increased number of cells in the cross-section changed the failure mode from compression buckling to bearing. Finally, a simplified prediction equation, based on the maximum stresses of the GFRP materials and incorporating the shear span-to-depth ratio and local buckling, was developed. This model was used in a parametric study to evaluate the effect of the number of cells, shear span-to-depth ratio, and filling percentage on the flexural behaviour of the multi-celled GFRP beams. The results indicated that the increased number of cells enhanced the capacity of the hollow and concrete-filled beams. Similarly, the failure of the hollow beams will be governed by either the buckling failure of the compression flange of the top cell or the bearing failure, while the concrete filled beams will be affected by either bearing failure of the hollow cell under the filled cells or web buckling of the top-filled cell. It was also established that the multi-celled beams with a concrete infill at the top cell only would have a higher strength-to-weight ratio compared to their hollow beam counterparts. Furthermore, a failure mechanism map was developed to help identifying the possible failure mode for any combinations of GFRP tubes and concrete. An in-depth understanding of the behaviour of multi-celled GFRP beams, with and without concrete infill, was the significant outcome of this study. Moreover, the newly developed multi-celled GFRP section, filled with a low compressive strength concrete at the top cell only, showed high potential for structural applications that need high strength, high stiffness, and lightweight characteristics

Geopolymer concrete: the green alternative with suitable structural properties

Concrete is the most widely used building material around the world because of the availability of raw materials, the simplicity in preparation and the moulding into different shapes. One of the main ingredients in a normal concrete mixture is Portland cement. However recent literature reveals that cement industry accounts for approximately 5 % of the current man made carbon dioxide (CO2) emission worldwide. World cement demand and production are ever increasing with the expected growth is from approximately 2836 million tons in 2010 to between 3680 (low estimate) and 4380 million tons (high estimate) by 2050. Knowing that about 1.5 tons of raw materials are needed in the production of every ton of Portland cement concrete and about one ton of CO2 is released in to the environment during the production, developing alternative construction materials is required. This paper will review the utilization of geopolymer concrete as an alternative for Ordinary Portland Cement concrete. The use of new greener material instead of concrete requires two main characteristics: reduced environmental impact which is a main concern in the world and better structural performance. This paper aims at investigating these characteristics using the available literature

Testing and characterization of pultruded glass fiber reinforced polymer (GFRP) beams

Elastic properties of the fiber reinforced polymer (FRP) composite represent a significant effect on the structural behaviour of this material. Therefore, it is important to use an accurate method to determine these properties as the behaviour is often governed by deflection rather than strength. In this study, full size pultruded glass FRP (GFRP) beams were used to determine the elastic properties using static four-point bending with different shear span to depth (a/d) ratios. Two different methods -back calculation and simultaneous - were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the test using coupon specimens. The results indicate that the elastic properties determined from full scale test using back calculation method can reliably predict the load - deflection behaviour of the pultruded GFRP beams

Effects of impulsive loading and deformation damage on reinforced concrete slabs during building construction

The effects of impulsive loading and deformation damage in reinforced concrete slabs were observed for analyzing the under-construction buildings for specific period of time. To fully harvest the structural capacity of building under constrcution with reinforced slabs sections exposed to combined actions, it is necessary to leave behind the simplicity of treating the verification of structural adequacy for normal stresses separately from that of shear stresses and instead fully exploit the advantages of choosing more efficient stress distributions. By exploring the vast possibilities of other statically admissible systems using optimization routines for deformation damage reduced to 20% from 80% in the work, the longitudinal reinforcement near the neutral axis in reinforced concrete can be utilized much more efficiently. In addition, by adhering to the interdependency constraints between normal and shear stresses in reinforced concrete a much more precise picture of the actual service stress state can be determined for impulsive loading and deformation damage where the maximum deformation and impulsive loading on RC-slab were observed at strain 91s≤t≤97s on RC-slab in the total simulation steps from 0s to 398s. There is therefore a need for a one- step, automated design tool capable of addressing such verifications holistically which was performed in the simulation of this study using Matlab R2019b. In this paper the theoretical basis and a free to use open-source design tool is presented, allowing for easy access to highly optimized designs capable of observing the impulsive loading and deformation damage on reinforced concrete materials to their limit

The effect of shear span-to-depth ratio on the failure mode and strength of pultruded GFRP beams

The use of structural pultruded fibre reinforced polymers (FRP) sections have gained wide acceptance in civil engineering applications due to their favourable structural characteristics like high strength, light weight and durability in severe environmental conditions. However, due to their relatively low modulus of elasticity and thinned walls, these sections are vulnerable to local buckling which can affect their ultimate strength. This paper investigates experimentally the flexural behaviour of pultruded GFRP beams with shear span-to-depth (a/d) ratios in the range of 1.2 to 6 using full scale pultruded profiles. Failure modes, strength and crack patterns are the main parameters that were examined in this study. The study shows that shear span has a minor effect on the failure modes of the beams while it has a noticeable effect on the ultimate strength. In addition, fibre model analysis was used to validate the experimental results. Comparison between the experimental and the theoretical analysis results shows a good approximation of the moment - deflection behaviour and failure moment of pultruded GFRP beams

Flexural behavior of glued GFRP tubes filled with concrete

The corrosion of steel reinforcement is considered the greatest factor limiting the service life of reinforced concrete structures. Glass fiber reinforced polymers (GFRPs) are known as cost-effective materials offering long-term durability and less maintenance. As a result, these materials show great potential for use in the civil engineering applications. Due to the high cost of the manufacturing die, pultruded GFRP tubes are produced in specific cross-section dimensions only. For high load applications and to comply with the serviceability requirements, a number of these pultruded sections can be assembled together by gluing them appropriately. This study presents an experimental investigation onto the flexural behavior of glued GFRP tube beams with 1, 2, 3 and 4 - cells filled with concrete under four-point loading. The results show that the strength of the 4 cells glued beams increased by 150 % and 88% for hollow and filled beams, respectively, compared with its counterpart single cell beam. The filled beams failed at 42 – 88 % higher load and showed 10 – 22 % higher stiffness compared with their hollow counterparts. The results also show that gluing small section tubes to produce large section beam is a practical solution to enhance the flexural performance of the composite tubes

Behaviour of hollow pultruded GFRP square beams with different shear span-to-depth ratios

It is important to determine accurately the elastic properties of fibre-reinforced polymer composites material, considering that their member design is often governed by deflection rather than strength. In this study, the elastic properties of the pultruded glass fibre-reinforced polymer square sections were evaluated firstly using full-scale with different shear span to depth (a/d) ratios and tested under static four-point bending. Back calculation and simultaneous methods were then employed to evaluate the flexural modulus and shear stiffness and were compared with the results of the coupon tests. Secondly, the full-scale beams were tested up to failure to determine their capacity and failure mechanisms. Finally, prediction equations describing the behaviour of the pultruded glass fibre-reinforced polymer square beams were proposed and compared with the experimental results. The results indicate that the back calculation method gives more reliable values of elastic properties of glass fibre-reinforced polymer profiles. In addition, the behaviour of the beams is strongly affected by the a/d ratios. The shear was found to have a significant contribution on the behaviour of beams with lower a/d ratios while the flexural stress played a major part for higher a/d ratios. The proposed equation, which accounts for the combined effect of the shear and flexural stresses, reasonably predicted the failure load of pultruded glass fibre-reinforced polymer square beams

Modelling reinforced concrete beams for structural strengthening of buildings

Iraq has many damaged and vandalized building since it is located in the Middle East, in southwestern Asia. Reinforced concrete beams of normal weight and lightweight's beams were conducted. The study is also done on normal strength and high strength beams in each category. The reinforced concrete used were 0% and 0.75% in each category. The lengths of the concrete beams used were 35 mm and 60 mm in each category. The longitudinal reinforcement ratio in all the beams is kept at 1.46%. The effect of types of aggregates, length of concrete beams, and concrete compressive strength were studied and results were presented with regard to the shear and flexure strengths, beam load-deflection responses, mode of failure, stiffness, energy absorption, and ductility. Shear and flexural crack widths and cracking patterns of the beams were also presented. Reinforced concrete content of the beams was also discussed. The possibility of replacement of minimum concrete reinforcement for lightweight beams with reinforced concrete is discussed. The most efficient length of beams for this purpose was presented. The modeling of buildings were designed in ANSYS and the strengthening as well as reinforcement was being shown using the software tool for the buildings in Iraq

Occupational safety basics understanding in oil and gas industry: An evaluation

In project management, risk is a surprise that might be resulted in a good, or bad, impact on a project. However, people tend to consider it a threat. This study is an evaluation work to the understanding of the risk management and safety culture of the construction sector in oil and gas industry in Iraq. A survey questionnaire was prepared, tested, distributed to a sample of engineers, from several engineering specialties, who are working on different levels in the mentioned sector. A high percent of the respondents are safety engineers, and some have a higher university degree, e.g. MS an Ph.D. The collected data then analyzed using different statistical approaches. The results show that there is a good understanding of the safety in general among engineers. However, risk management and planning tools are not understood effectively among the respondents. Moreover, having a higher degree or specializing in different majors have no impact on perceptional understanding of the safety and risk. This study is one of the first steps in studying the occupational safety in Iraq construction and oil and gas industries. Since Iraq is considered for rebuilding after different wars, international firms are in need to understand how safety is managed and to what level it is applied. From this perspective, this study is one of studies that help achieving the firms’ goal regarding safety

Flexural behaviour of multi-celled GFRP composite beams with concrete infill: experiment and theoretical analysis

This research introduces multi-celled glass fibre reinforced polymer (GFRP) beam sections partially filled with concrete. Hollow pultruded GFRP square tubes (125 mm x 125 mm x 6.5 mm) were bonded together using epoxy adhesives to form the beams using 2–4 cells. Concrete with 15 and 32 MPa compressive strengths was used to fill the top cell of the multi-cell beams. These beams were then tested under static four-point bending and their behaviour was compared with hollow beams. The results showed that up to 27% increase in strength was achieved by using multi-cell beams compared to a single cell beam. Filling in the top cell of the beams with concrete enhanced the capacity as well as the stiffness of the beams. The multi-celled GFRP beams filled with concrete at the top cell failed at 38–80% higher load and exhibited 10–22% higher stiffness than their hollow counterparts. The increase in the compressive strength of the concrete infill from 15 MPa to 32 MPa resulted in up to 14% increase in the failure load but did not enhance the flexural stiffness. Finally, the proposed prediction equation which account for the combined effect of shear and flexural stresses showed a good agreement with the experimental results for hollow cells and up to 3 cells of concrete filled beams. The bearing stress equation gave a better estimation for 4-cell filled section