STUDY ON STRUCTURAL BEHAVIOUR OF STEEL SECTION USING ARAMID FIBERS

Transcription

1 STUDY ON STRUCTURAL BEHAVIOUR OF STEEL SECTION USING ARAMID FIBERS Priyanka Nagasuri P.G. Student, Department of Civil Engineering 1, SRM University, Chennai, India, P.Sriram Assistant Professor, Department of Civil Engineering 2, SRM University, Chennai, India, Abstract: This study investigate the behaviour of steel section by wrapping aramid fibre reinforced polymer (AFRP) subjected to axial compression. Two specimens wrapped with aramid fibre having different wrapping schemes were tested under axial compression using universal testing machine (UTM). Influence of a loading rate was examined by loaddeflection curve and also examined by varying the number of AFRP layer. For the analytical study, 3 steel square hollow section of a nominal dimension of 100mm x 100mm x 3mm and 700mm length were loaded under axial compression to allow a column buckling. The experimental results indicate the ultimate strain and load deflection curve and that external AFRP confinement significantly improves these properties. Keywords:- Aramid fibre reinforced polymer (AFRP), Steel square hollow section, Universal testing machine I. INTRODUCTION In the steel construction industry, Tubular structures became typically used due to of their structural efficiency and economical values. Compared to conventional steel sections, the surface and profile of hollow steel section are attractive and structural performance. Related to strengthening of steel hollow section with FRP there have been a number of studies in recent years. FRP jacketing is a technique for the enhance and strengthening of square hollow steel tubes. On further Studies it clarifies that the capability of applying external AFRP square steel hollow section delaying local buckling. The study presented valuable experimental results showed that the AFRP wraps provided better confinement of the square steel hollow section and also AFRP sheet can restraint to delay buckling of steel hollow section. A series of synthetic polymers in which repeating units containing large phenyl rings are linked together by amide groups. Amide groups (CO-NH) form strong bonds that are resistant to solvents and heat. Phenyl rings (or aromatic rings) are bulky six-sided groups of carbon and hydrogen atoms that prevent polymer chains from rotating and twisting around their chemical bonds. They are characterized by medium to ultra-high strength, medium to low elongation and moderately high to ultra-high modulus with the densities ranging from 1.38g/cm3 to 1.47g/cm3. Heat-resistant and flameresistant aramid fibres contain high proportion or meta-oriented phenylene rings, whereas ultra-high strength high-modulus fibbers contain mainly para-oriented phenylene rings. All aramids contain amide links that are hydrophilic. However, not all aramid products absorb moisture the same. The PPD-T (poly-phenylene terephthal) amide fibre has very good resistance to many organic solvents and salt, but strong acids can cause substantial loss of strength. Aramid fibres are difficult to dye due to their high Tg. Also, the aromatic nature of paraaramid is responsible for oxidative reactions when exposed to UV light that leads to a change in color and loss of some strength. Aramid fibres do not melt in the conventional sense but decompose simultaneously. They burn only with difficulty because of Limited Oxygen Index (LOI) values. It should be mentioned that at 300 degrees Celcius some aramid types can still retain about 50% of their strength. Aramids show high crystallinity which results in negligible shrinkage at high E-ISSN : Page 77

2 temperature. Aramid yarn has a breaking tenacity of 3045 MPa, in other words more than 5 times than this of steel (under water, aramid is 4 times stronger) and twice than this of glass fiber or nylon.high strength is a result of its aromatic and amide group and high crystallinity. Aramid retains strength and modulus at temperatures as high as 300 degrees Celcius. It behaves elastically under tension. When it comes to severe bending, it shows non-linear plastic deformation. With tension fatigue, no failure is observed even at impressively high loads and cycle times. Creep strain for aramid is only 0.3%. In a world where lightweight and durable composites are increasingly replacing conventional materials, aramid and para-aramid fibers play an important role. They are essential for reinforcing composites where weight reduction and excellent damage tolerance are required. Many different kinds of composite goods are reinforced with aramid because of the strength, stiffness and dimensional stability of laminates that contain it. Aramid and Kevlar fibers are compatible or can be used with many types of resin systems. The best choice of resin system is epoxy as it adheres best to the fiber surface. II. ANALYTICAL INVESTIGATION Finite element model in ANSYS is the direct generation of the finite element model creating a solid model within ANSYS by using pre-defined shapes. Direct generation is employed when the model is fairly simple and provides more control over the geometry and numbering of modes and element. Finite element analysis in structure is mainly carried out to investigate the structural behaviour of the structure due to various loading conditions. Hence accurate of the modelling is vital. There are secured way of applying the necessary loading to a structure as displacement, structural force or pressure onto either geometric entities or a set of nodes in the finite element model, if investigation is pure structural analysis. Dimensions of the specimen are shown in Table 1 and physical properties of steel section, AFRP and epoxy resin adhesive are stated in Table 2, Table 3 and Table 4 respectively. Section Square hollow steel section Table 1: Specimen Dimensions Length Width Depth Thickness Table 2: Properties of the Light Gauge Section Density 7850 kg/mm 3 Modulus Of Elasticity N/mm 2 Poisson s Ratio 0.3 Modulus of Rigidity N/mm 2 Table 3: Physical properties of Aramid fiber Fiber type Aramid fiber Density (g/cm 3 ) Ulimate Elongation (%) Tensile strength (MPa) Tensile Modulus (MPa) ,000 Table 4: Physical properties of epoxy resin adhesive Adhesive Master Brace 3500/part A Density (g/cm 3 ) 1.13 ±.03 Mixing ratio (B:H) Mixed viscosity at 25 o 2:1 4000±500 Setting time At 25 o <4 hours During the solution process, ANSYS program performs series of statistical operations using a system of simultaneous equations generated from the Finite element model and corresponding result are stored. Fig 1 represents the model of hollow square steel column(hssc), Fig 2 represents the hollow square steel column with linear wrapping of 1mm thickness with 40mm spacing and 50mm width of AFRP[HS 40-50(1)]. Fig 3 represents the linear wrapping of 2mm thickness with 40mm spacing and 50mm width of AFRP [HS 40-50(2)]. E-ISSN : Page 78

3 Fig 1: modelling of HSSC in ANSYS Table 5: Deflection values Section Load (kn) Deflection Bare steel of 1mm of 2mm III. EXPERIMENTAL INVESTIGATION Fig 2: linear wrapping [HS 40-50(1)] The section dimensions of the commercially offered hollow square steel section with thicknesses 3mm. High strength AFRP was used and applied to the outside of the hollow square steel section with epoxy. The high strength AFRP (KELVAR 29) with tensile strength of 3600MPa and elastic modulus fibre is 83,000MPa. The column was overlapped by 1mm thick layer of aramid fiber to avoid the premature failure. To roughen the surface before laying the AFRP, the surface of the hollow square section was prepared by sandblasting, and then cleaned with acetone. The specimen setup is shown below. Fig 3: linear wrapping [HS 40-50(2)] The deflections obtained from analytical studies for different wrapping conditions are shown in Table 5. Fig 4: AFRP surface preparation E-ISSN : Page 79

4 Fig 8: Test set up of HS 40-50(2) Fig 5: Applying epoxy Fig 6: AFRP wrapping At room temperature, all specimens were cured for 10 days. In a standard servo universal testing machine, the columns were tested in pure axial compression. The test set up of hollow square steel columns wrapped with horizontal AFRP [HS 40-50(1)], AFRP [HS 40-50(2)] and bare steel (CC) are shown in Figures 7,8 and 9. Fig 9: Test set up of Bare steel (CC) The deflections obtained from analytical studies for different wrapping conditions are shown in Table 5. Table 6: Deflection values Section Load (kn) Deflection Bare steel Fig 7: Test set up of HS 40-50(1) The instrumentation consists of dial gauges. The specimens were kept at the supports and loaded up to failure to grasp the influence of AFRP on their axial behaviour and also centred to confirm symmetric loading. of 1mm of 2mm E-ISSN : Page 80

5 IV. RESULTS AND DISCUSSIONS The deflection values obtained from analytical investigations are compared with experimental investigations. The experimental results are found to be precise compare with analytical results. The comparison of deflection values obtained from analytical and experimental investigations are shown in table 7. The comparison of deflection values of analytical and theoretical values are shown in fig 10. Smooth load deflection curve is exhibited from the control specimen. Failure mode observed at the end of the test and is shown in Figure 10. In both the wrapping schemes, all the columns exhibited the smooth load deflection curve throughout the entire test. Before the peak load there was no symptom of AFRP delamination or rupture of AFRP observed during the test. Table 7: Comparisons of deflection values Specimen Analytical Experimental Bare steel (CC) Linear wrapping [HS (1)] Linear wrapping [HS 40-50(2)] ANALYTICAL EXPERIMENTAL Fig 11: Failure pattern V. CONCLUSION The ultimate load carrying capacity of CC column was found to be kn. For HS 40-50(1) load carrying capacity was increased by % as compared to bare steel. By increasing the thickness of aramid fiber (HS 40-50(2)) load carrying capacity was increased by % as compared to bare steel. AFRP confinement of hollow square steel section leads to great increase in ductility with limited increases in strength. VI. Acknowledgment Fig 10: compression of deflection values I express my sincere thanks to Project Coordinator Prof G. AUGUSTINE MANIRAJ PANDIAN and Dr. N. UMAMAHESHWARI, Department of Civil Engineering, SRM University for his valuable guidance and timely suggestions during the project work. I am thankful to Class advisor Mr. N. LOKESHWARAN, Assistant Professor (O.G), for his support in successful completion of the project. E-ISSN : Page 81

6 I hereby acknowledge with deep sense of gratitude the valuable guidance, encouragement and suggestion given by my guide Mr. P. SRIRAM, Assistant Professor (O.G), who has been a constant source of inspiration throughout this project. I express my deep love and warm regards to My Parents and My Friends for their support, constant encouragement and timely help. REFERENCE [1] B. Zhang a, J.G. Teng a, T. Yub, (2015), Experimental Behavior Of Hybrid FRP- Concrete-Steel Double-Skin Tubular Columns Under Combined Axial Compression And Cyclic Lateral Loading, Engineering Structures. [2] Hui Yang, Hengwen Song, Shi Zhang, (2015), Experimental Investigation Of The Behavior Of Aramid Fiber Reinforced Polymer Confined Concrete Subjected To High Strain-Rate Compression, Construction and Building Material. [3] Tohid Ghanbari Ghazijahani, Hui Jiao, Damien Holloway, (2015), Timber Filled CFRP Jacketed Circular Steel Tubes Under Axial Compression, Construction and Building Material. [4] Tohid Ghanbari Ghazijahani, Hui Jiao, Damien Holloway, (2015), Rectangular Steel Tubes With Timber Infill And CFRP Confinement Under Compression, Journal of Constructional Steel Research. [5] Tianyu Xie, Togay Ozbakkaloglu, (2015), Behavior Of Steel Fiber Reinforced High Strength Concrete Filled FRP Tube Columns Under Axial Compression, Engineering Structures. E-ISSN : Page 82