Strengthening of the Deficient Steel Sections Using Hybrid Composites under Various Loading Scenarios

Strengthening of the Deficient Steel Sections Using Hybrid Composites under Various Loading Scenarios

Shifa Ameer

Post Graduate Student Department of Civil Engineering

Sree Narayana Guru College of Engineering and Technology

Payyannur, Kannur, Kerala, India

Shilpa Valsakumar

Assistant Professor Department of Civil Engineering

Sree Narayana Guru College of Engineering and Technology

Payyannur, Kannur, Kerala, India

Abstract Recently ,the strengthening of steel sections using various fiber reinforced polymer (FRP) has come to the attention of several researchers. For different reasons, this type of structures may be placed under combination of loads. The deficiency in steel members may be due to errors caused by construction, corrosion, fatigue cracking, and other reasons. This study investigated the behavior of deficient tubular hollow section (THS) steel members strengthened by HYBRID composite FRP under two types of combined loads. To study the effect of HYBRID composite FRP strengthening on the structural behaviour of the deficient steel members, various parametric studied were conducted by varying damage level, various strengthening methods were analysed. To analyse the steel members, three dimensional (3D) modelling and nonlinear static analysis methods were applied, using ANSYS software. The results expected that HYBRID composite FRP strengthening had an impact on raising the ultimate capacity of deficient steel members and could recover the strength lost due to deficiency.

Keywords Fiber Reinforced Polymer, Tubular Hollow Sections, Non Linear Static Analysis.

1. INTRODUCTION

   Strengthening of the steel structures can be done using Fiber-reinforced polymer (FRP) FRP, also Fibre-reinforced plastic, is a composite material made of a polymer matrix reinforced with fibres. The fibres used are usually glass, carbon, or aramid. It is actually a stronger material than steel, making it a much stronger system whilst maintaining being a very lightweight material. Hence FRP is able to maintain its high strength even being a very lightweight material. Fiber reinforced polymer (FRP) composites or advanced composite materials are very attractive for use in civil engineering applications due to their high strength-to- weight and stiffness-to-weight ratios, corrosion resistance, light weight and potentially high durability. FRP outperforms wood and concrete structures, while holding up to decades of wear and tear. Fiber-Reinforced Polymer (FRP) composites offers five major benefits for any infrastructure , faster installation time, Lightweight material, Resistance to corrosion & very little maintenance, Cost savings, Design flexibility. Fiber Reinforced Polymer (FRP) includes a system of both carbon fibres and the bonding epoxy. The carbon fibres themselves are great in fire as they will not lose strength, even while glowing red hot. One drawback of FRP materials is their relatively high cost

   compared to other materials. Other drawbacks include: The need for various saw blades and drill bits than those used with wood or steel. Attention if irritation persists, or if severe coughing or breathing difficulty occurs. This provides the raw materials used for economical alternatives to conventional construction materials such as steel and wood. Most important in the context of sustainability, FRP manufacturing represents a radically low environmental impact over the traditional material preparation methods. Fiberglass reinforced plastics (FRP), are indeed initially more overpriced than traditional materials. However, it offers huge merits over these materials and has a lower overall cost of ownership and many other benefits. FRP panels are normally 0.09 inch in thickness and weigh about 12 ounces per square foot. Variations in material removal rates and hardness between the matrix and filler materials create difficulties in preparation such as polishing relief or rounding. These problems can cause wrong measurements, disguise problems or create artificial damage. Fiber Reinforced Plastics or Fiber Reinforced Panels (FRP) are plastics that contains fiber such as glass, carbon, aramid, or basalt. The deficiency in steel members may be due to errors caused by construction, corrosion, fatigue cracking, and other reasons. The use of externally bonded FRP has become increasingly popular for civil infrastructure applications. CFRP, GFRP, AFRP, BFRP etc. are some of the types of FRP. CFRP contains carbon as the fibre component, whereas GFRP contains glass as the fiber component. Moreover, CFRP is highly expensive, which limits the use of this material in many applications. BFRP It is a composite material containing rigid polymer resin bounding unidirectional basalt fibers. Basalt Fibre Reinforced polymer bars have the advantage of corrosion resistance, high strength, light weight, good dielectric properties. AFRP- Aramid Fibre Reinforced Polymer is made up of aramid fibers, and have excellent corrosion resistance. The most common FRP systems for concrete strengthening applications are carbon based (CFRP). Carbon has high mechanical properties and higher tensile strength, stiffness, and durability compared with glass fiber based systems. Prefabricated FRP elements are typically stiff and cannot be bent on site to wrap around columns or beams. FRP fabric, on the other hand, is available in continuous unidirectional sheets supplied on rolls that can be easily tailored to fit any geometry and can be wrapped round

   almost any profile. FRP fabrics may be adhered to the tension side of structural members (e.g. slabs or beams) to provide additional tension reinforcement to increase flexural strength, wrapped around the webs of joists and beams to increase their shear strength, and wrapped around columns to increase their shear and axial strength and improve ductility and energy dissipation behavior.

2. OBJECTIVES

   • Study the properties of the tubular sections without damage and with damage by varying the damage levels and to analyse the 3D model developed using ANSYS software.

   • Various types of damage includes, surface level corrosion, local level corrosion etc. and to determine the type of damage and strength loss.

   • To propose effective method of strengthening the deficient case.

   • Hybrid composite FRP means the composition of combination of various FRP elements like GFRP, BFRP and ASRP (cost effective than CFRP).

   • By varying the thickness and combinations, best strengthening and deficiency improvement technique are introduced

   • Output parameters are Ultimate load, Ultimate deflection, Ultimate strength and strength index.

3. SUMMARY OF LITERATURE REVIEW

   The main advantages of using CFRP laminates are their light weight and their durability, which result in ease of handling and maintenance. CFRP sheet wrapping decreases the corrosion rate, the corrosion of steel reinforcement could continue to occur, eventually showing a decrease in ultimate axial compression capacity. The findings showed that a deficiency leads to reduced load-carrying capacity of steel SHS columns and the retrofitting method is responsible for the increase in the load-bearing capacity of the steel columns.

   CFRP performed better than steel plates in compensating the axial force caused by the cross-section reduction due to the problems associated with the use of steel plates, such as in welding, increased weight, thermal stress around the welding location, and the possibility of creating another deficiency by welding.

4. FINITE ELEMENT MODELLING AD MODELLING SPECIMENS

   It can be observed that many investigations were conducted on the behavior of the steel members strengthened with CFRP composite, but it seems that there is a lack of understanding about the behavior of deficient hollow steel members under combined loads. Therefore, this study explored the effect of CFRP strengthening on the structural behaviours of deficient hollow steel members under combined loads, using numerical investigations. Loading scenarios applied to the SHS steel members were five types. Loading scenario 1 (Pure Tension), loading scenario 2 (Pure Compression), loading scenario 3 (Pure

   Torsion), loading scenario 4(Combination of tension and torsion), loading scenario 5(Combination of compression and torsion). To obtain accurate results, 5 hollow steel members were analysed (one non-strengthened member without deficiency) 10 members with local corrosion and Surface corrosion were analysed. CFRP strengthened sections with deficiencies were also analysed. The coverage length and the number of CFRP layers, loading scenarios, lengths, widths and orientations of deficiency were implemented to examine the ultimate capacity of the hollow steel members. Nonlinear finite element models were prepared using ANSYS software to investigate the structural behavior of the SHS steel members strengthened with CFRP sheets in length.

   1. SECTIONAL PROPERTIES

      All models were prepared as steel members of fixed-pinned ends. The dimensions of local corrosion were 500 mm × 25 mm × 8 mm (8 mm thickness of the THS steel). Also, the dimensions of surface level corrosion were 175mm × 5 mm

      × 8 mm. In this study, three types of materials were used. Type 1 of the material used was SHS steel. The THS steel had a dimension of 80 mm × 80 mm. The length and thickness of the used SHS steel were 3000 mm and 3 mm, respectively. Also, the modulus of elasticity, the yield strength, and the ultimate tensile strength of the used SHS steel were 200000 N/mm2, 240 N/mm2, and 375 N/mm2, respectively. These values were extracted from studies conducted by Keykha A H. Type 2 of the materials used was CFRP sheet. The CFRP sheet used in the present research was SikaWrap-200C. The SikaWrap-200C is a unidirectional carbon fiber. This CFRP had a modulus of elasticity of 230000 N/mm2 and a tensile strength 3900 N/mm2. The thickness of this CFRP sheet was 0.111 mm. These values were extracted from studies conducted by Abdollahi Chahkand and Zamin umaat. The last material used in this study was adhesive used to paste CFRP sheets to SHS steel. The adhesive used in this study was suggested by the supplier of the CFRP product. The adhesive commonly used for the SikaWrap-200C, was called Sikadur-

      330. The Sikadur-330 is a two part adhesive, a hardener and a resin. The Sikadur 330 had a modulus of elasticity about 4500 N/mm2 and a tensile strength about 30 N/mm2. These values were retrieved from studies conducted by Keykha A H.

      The sectional properties of the finite element model are tabulated in table 1.

      TABLE 1. Sectional Properties of the Model

      PARAMETERS
      Thickness	8 mm
      Length	3000 mm
      Depth	80 mm
      Mesh size	100 mm
      Material	Steel

   2. MATERIAL PROPERTIES

      The material mechanical properties of the finite element model are tabulated in table 2.

      TABLE 2. Material properties of the section

      Element	Youngs modulus (GPa)	Yield stress (MPa)	Ultimate stress (MPa)
      Section	200	240	375

   3. 3D MODEL OF STEEL TUBULAR HOLLOW SECTION

      To simulate the THS steel members, the full three- dimensional modelling and nonlinear static analysis methods were applied. The THS steel member, CFRP sheet, and adhesive were simulated using the 3D solid triangle elements (ten-nodes 187). Nonlinear static analysis was carried out to achieve the characteristics of failures in the steel members. In this case, the load was incrementally applied until the plastic strain in an element reached its ultimate limit. Subsequently, linear and nonlinear properties of materials were defined. The CFRP sheet material properties were defined as linear and orthotropic because CFRP materials had linear properties which were unidirectional. Also, the adhesive was defined as linear because the adhesive used had linear properties. In addition, the SHS steel members were defined as the materials having nonlinear properties. For meshing, map meshing was used.

      Fig.1 3D Model of the Tubular Steel Section

      VALIDATION

      It was necessary to validate the software calculations. In this study, the software results were validated and calibrated by the experimental results of A.H. Keykha, Strengthening of Deficient Steel Sections using CFRP Composite under Combined Loading , MACS,2020 Department of Civil Engineering, Islamic Azad University, Zahedan Branch, and Zahedan, Iran. Model is validated using ANSYS software

      .For the analysis of the specimens, as mentioned in the previous section, the solid element of 187 with the mesh size of 25 was used. From the studies conducted by A.H. Keykha, Department of Civil Engineering, Islamic Azad University, Zahedan Branch, Zahedan, Iran The ultimate capacity of the specimens, were obtained from experimental, theoretical, and numerical analysis . As mentioned in the Introduction section, A.H. Keykha carried out an experimental and a theoretical study on the behavior of CFRP strengthened SHS steel beams in pure torsion.

      • Depth = 60 mm

      • Length= 1600 mm

      • Thickness= 6 mm

      • Modulus of elasticity= 200000 N/mm2

      • Yield strength = 240 N/mm2

      • Ultimate tensile strength= 375 N/mm2

      • End restraints= One end fixed and the other end pinned.

      • Loading scenario included tension pull and rotation

      • Tension pull = 10 mm

      • Rotation = 5 to 90 degrees

   Fig.2 3D Model of the Square Steel Section

   Fig.3. Total Deformation

   Fig.4 Equivalent stress

   Fig 5. Compression capacity

   Fig 6. Torsional capacity

   TABLE 3. Comparison of the Results obtained from software and Journal

   RESULT
   	Compression capacity(kN)	Torsional Capacity(kNm)
   Journal	68.28	0.96
   FEA	65.20	0.97
   %	4.36	4.36

5. PARAMETRIC STUDY

   The steel members included one control specimen, five non- strengthened specimens with different loading scenarios and

   10 specimens with deficiency and steel sections strengthened with two and four CFRP layers applied on all four sides of the steel members. The control specimen was analysed without strengthening to determine the rate of the ultimate capacity increase in the strengthened steel members. To easily identify each specimen, steel members were designated W TL- Without deficiency Torsion loading, W TE L Without deficiency Tension Loading -, W C L- Without deficiency Compression Loading, W TE TL- without Deficiency Tension Torsion Loading, W CTL- Without deficiency Compression Torsion Loading.

   Without deficiency, 5 models were designed and analysed using ANSYS software.

   CASE 1

   Pure Compression: By varying the values of the Compressive forces, So many models were drawn and solved and got -50 kN/m^2 as the limit force.

   Fig.6. 3D Model of the section subjected to pure Compression

   Fig.7.Deformation of the section subjected to pure Compression

   Fig.8.Compression caacity of the section subjected to pure Compression

   Fig 9 .Force reaction of the section subjected to pure Compression

   CASE 2

   Pure Tension: By varying the values of the Compressive forces, So many models were drawn and solved and got 150 kN/m^2 as the limit force.

   Fig.10. Deformation diagram for pure tension

   Fig.10. Stress diagram for pure tension

   Fig.11. Compression Capacity for Pure Tension

   Fig 14. Stress Diagram

   Fig 15. Compression Capacity

   Fig 16. Moment reaction

   CASE 4

   Compression+ Torsion:

   CASE 3

   Fig.12. Force Reaction for pure tension

   Pure Torsion: By varying the values of the Compressive forces, So many models were drawn and solved and got 40 kNm as the limit force

   Fig.13. Deformation diagram for pure Torsion

   Fig 17: Deformation

   Fig 18: Compression Capacity

   Fig 19. Force reaction

   Fig 24. Moment reaction

6. GRAPHS

   CASE 5

   Fig 20. Moment reaction

   3000

   Load(kN)

   2000

   1000

   LOAD VS DEFLECTION

   WOD-CL

   Tension+ Torsion

   Fig 21: Deformation

   0

   0 50 100

   Deflection(mm)

   Load(kN)

   Fig 25. Graph- Pure Compression

   LOAD VS DEFLECTION

   4000

   3000

   2000

   1000

   0

   WOD-TE L

   0

   100

   Deflection(mm)

   200

   Fig 26. Graph- Pure Tension

   Fig 22: Stress Diagram

   0 50 100 150

   Deflection(mm)

   Load(kN)

   Fig 23 Force reaction

   TORQUE(KNm)

   400

   300

   200

   100

   0

   TORQUE VS DEFLECTION

   0 50 100 150

   Deflection(mm)

   Fig 27. Graph- Pure Torsion

   WOD-TOR L

   LOAD VS DEFLECTION

   2500

   2000

   1500

   1000

   500

   0

   WOD-TOR C L

   400

   300

   200

   100

   0

   4000

   Load(kN)

   3000

   2000

   1000

   0

   200

   Moment(kNm)

   150

   100

   50

   0

   MOMENT VS DEFLECTION

   WOD-TOR C L

   0 50 100 150

   Deflection(mm)

   Moment(kNm)

   Fig 28. Graph- Combined Torsion and Compression LOAD VS DEFLECTION

   WOD-TE TOR L

   0 100 200 300

   Deflection(mm)

   MOMENT VS DEFLECTION

   WOD-TE TOR L

   0 100 200 300

   Deflection(mm)

   VIII. CONCLUSION

   Non-linear static analysis of Tubular Hollow steel sections under various loading scenarios are done using ANSYS software. The maximum deflection is obtained for pure torsion loading. Five models were solved effectively using ANSYS. Surface level Corrosion and Local Level Corrosion of the above fixed dimensions are to be drawn and solved, CFRP is to be wrapped and Strength Index is to be found by making appropriate number of models. From the literature review, it can be concluded that the CFRP wrapped sections have more strength and hence the gain in strength is to be measured.

   REFERENCES

   [1] Sundarraja MC, Prabhu GG. Flexural Behavior of CFST Members Strengthened using CFRP composites Steel and Composite Structures 2013; 15(6): 623-643.
   [2] Idris Y, Ozbakkaloglu T. Flexural behavior of FRP-HSC-steel composite beams. Thin-Walled Structures 2014; 80: 207-216.
   [3] Teng JG, Fernando D, Yu T. Finite element modelling of de bonding failures in steel beams flexurally strengthened with CFRP laminates Engineering Structures 2015; 86: 213-224.
   [4] Al Zand AW, Badaruzzaman WHW, Mutalib AA, Qahtan AH. Finite element analysis ofsquare CFST beam strengthened by CFRP composite material Thin-Walled Structures 2015; 96: 348-

   358..

   [5] Elchalakani M. Plastic collapse analysis of CFRP strengthened and rehabilitated degraded steel welded RHS beams subjected to combined bending and bearing. Thin- Walled Structures 2014; 82: 278-295.
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   Fig 29. Graph- Combined Torsion and Tension

7. RESULTS AND DISCUSSION

Under various loading scenarios, substantial changes in the deformation, force reaction and moment reaction are noted. The maximum deflection in the pure axial case was 49.8 mm at the load 2782.6 KN. The maximum deflection obtained in the pure torsion case was 114.7 mm at the moment 359 kNm. The maximum deflection obtained in the pure tension case was 71.03 at the load 3500 kN. In case 4 that is torsion + compression, the deflection obtained is 78.59 mm at the load 3185.5 kN and moment, 147.12 kNm. We can see that the deflection obtained is in between 49.8 mm and 114.7 mm. (deflections obtained in the pure axial and torsion cases respectively.) In the 5 th case, that is torsion + tension, the deflection obtained is 98.7 mm at the load 2061 kN and moment, 293.26 kNm. The deflection in the pure tension case was 71.30 mm at load 3500 kN and that in pure torsion case was 114.78 mm at the moment 359 kNm. The deflection is in between 71.30 mm and 114.78 mm.