Transient Thermal Analysis of Steel, CFRP & GFRP Reinforced Beams

Transient Thermal Analysis of Steel, CFRP & GFRP Reinforced Beams

Reshma Merin Roy1

1P.G Student, Department of Civil Engineering,

Amal Jyothi College of Engineering, Kerala, India

Jeena B Edayadiyil2

2Assistant Professor, Department of Civil Engineering,

Amal Jyothi College of Engineering, Kerala, India

Abstract Fibre Reinforced Polymers are used for strengthening concrete structures to eliminate cracks and damages formed as a result of environmental effects, increasing loads, natural disasters and toxics emitted. FRP are composite materials which consist of fibres in a polymer matrix. FRP materials are used in aerospace industries and construction of bridges as they offer high tensile strength, lightweight, high stiffness, high fatigue strength, excellent durability and highly versatile. FRP bars are used in concrete structures as an alternative to steel reinforcement as it has high corrosion resistance, strength to weight ratio and moderate modulus of elasticity. This paper portrays a brief study on transient thermal analysis conducted to investigate deflection behaviors on beams based on different material property of reinforcement in FEM softwares.

KeywordsFibre reinforced polymers,concrete structures, CFRP,GFRP

1. INTRODUCTION

   Fibre Reinforced Polymer (FRP) as reinforcement in concrete structures is used as an alternative to the steel reinforcement in recent years. FRP are composite materials made up of fibers and polymer matrix. FRP are of different types such as GFRP, CFRP, AFRP. FRP materials are used in construction of bridges and aerospace industries. The key factor of structural deficiency and deterioration in reinforced concrete (RC) members has been identified as the corrosion of steel reinforcement. FRP reinforcement is mainly used in bridges, its use in multistory buildings, industrial structures and parking areas have an enormous economic potential. However, the stability of FRP members to overcome the fire effects should be established before to be used to reinforce the concrete structural members. FRP materials are highly versatile as they are available as tubes, sheets, bars, tendons and many other forms.

   To strengthen structural RC members in shear, torsion and flexure, FRP bar reinforcement seems to be a promising solution [6, 14]. As compared to conventional steel reinforced concrete the behavior of FRP bar under fire exposure is quite different. The drawback of using FRP embedded bars is the tendency to change state; from solid to liquid at elevated temperatures and their low glass temperature. Hence, under elevated temperatures the performance of FRP reinforced members draws many concerns and doubts and warrants further investigation. Only few tests have been conducted in the previous years on the fire performances of RC beams reinforced with FRP bars due to the tremendous amount of preparation, high costs of such tests and shortage of specialized facilities.

   Many expressions are developed to predict the required stiffness and strength of composite bars and concrete matrix at elevated temperatures [1]. Fire exposure played a major effect on the behavior of FRP reinforced concrete and its failure load. The response of FRP reinforced beams depends mainly on the concrete cover. FRP reinforced concrete beams exhibit greater degradation in flexural resistance than the steel reinforced concrete [2]. The transient temperature distributions and the structural response analysis due to effect of mechanical and thermal load [3] and finite element analysis using the ABAQUS on FRP bars reinforced concrete columns with varied cover thickness [4] showed a good agreement by the comparison of the predicted and test results. GFRP bars as reinforcement as satisfied fire design requirements, [5]. Flexural strength and ultimate load capacity were improved by retrofitted with GFRP [10]. When worked on RC structures damaged during earthquake, the ANSYS results showed that the deflection of the retrofitted beam with CFRP was minimized about 73%, with GFRP was minimized about 65%, with KFRP was minimized about 60% when compared to controlled beam and higher load carrying capacity than the controlled RC beam specimen [11].

   This paper presents an attempt to model the nonlinear behaviour of beams at elevated temperatures. The beams were reinforced with steel, CFRP & GFRP bars. Validation is done analytically and the objectives of the project are

   • To understand the concept of FRP reinforced beams

   • To model beams with different material reinforcements

   • To conduct transient thermal analysis to determine deformations

2. NON LINEAR FINITE ELEMENT ANALYSIS

   Non-linear finite element analysis was conducted to simulate the thermal behavior of concrete beams reinforced with fully steel, fully GFRP & fully CFRP bars. In this study three beams with same geometric properties are modeled with both ends fixed. The thermal behavior of these sections is compared. Mainly, deformation of reinforcement of each section is taken into consideration. Finite element method has been extensively used to study the structural behavior of steel concrete sections. Finite element model is developed using ANSYS 16.2 version. In this study, beam of M 25 grade concrete and Fe 500 grade steel as internal reinforcement is designed. Table 1 shows the geometric properties of the beam.

   TABLE 1: Geometric properties

   Span	2.55m
   Section	0.2m X 0.3m
   Compression Reinf:	2# 10mm dia bars
   Tension Reinf: @ Midspan	4# 12mm dia bars
   Tension Reinf: @ Support	2# 12mm dia bars
   Shear Reinf:	2L 8mm dia bars @ 125mm c/c

3. VALIDATION

   For the validation of thermal analysis in ANSYS a long bar is considered which is solved analytically using thermal equations. Then the values are compared with ANSYS results. The long bar has thermal conductivity varied with temperature. The bar is constrained at both ends by frictionless surfaces. A temperature of T °C is applied at one end of the bar.

   A. Results Comparison

   Results obtained analytically and with help of ANSYS software are compared. Table 2 shows the comparison of results. Clearly, the FE model provides closer predictions of deformations and thermal strains. The close agreement between the analytical and FE results demonstrates the validity and accuracy of the proposed FE model.

   TABLE 2: Comparison of Results

   Results	Analytical value	FEM value
   Minimum Temperature (°C)	38.047	38.015
   Maximum Thermal strain (z = 20) (mm/mm)	0.0004953	0.00049523
   Maximum Thermal strain (z = 0) (mm/mm)	0.001425	0.001425
   Maximum Z Deformation (mm)	2.32	2.3459

4. TRANSIENT THERMAL ANALYSIS Temperature and all other thermal quantities are

   determined using transient thermal analyse which varys over time. Thermal analyse can be executed to find temperature gradient, deformations, temperature distribution and heat flowing in the model, heat exchanged between the model and the environment. Thermal effects such as temperatures are easy to simulate, but quite difficult to measure epecially inside parts and assemblies, or if temperatures are changing rapidly. Analysis is done with varying time (end time 2500s) and temperature (12000C) (fig.1). Transient analysis is done on the beam model with steel (fig.2), CFRP (fig.3) & GFRP (fig.4) reinforcements. Deformation variation is noted to find out the best reinforcement material to withstand thermal effects as well as to find out replacement reinforcement to conventional steel reinforcement.

   Fig. 1: Temperature Input to Beam

   Fig. 2: Total deformation in steel reinforced beam, max 5.73mm

   Fig. 3: Total deformation in CFRP reinforced beam, max 3.587mm

   Fig. 4: Total deformation in GFRP reinforced beam, max 3.2mm

5. THERMAL ANALYSIS RESULTS AND DISCUSSIONS

   From the thermal analysis of beams with different reinforcement materials the maximum deflection value for steel bars is 0.5449mm, for CFRP bar is 0.0564mm and for GFRP bars is 0.055mm and after a temperature of 12000c the values become steady state in nature. Table 3 shows the tabulated deformation results.

   TABLE 3: Tabulated Deformation Results

   Beam reinforcement material	Deformation rebar(mm)	Total deformation (mm)	Total Uy (mm)	Uy rebar (mm)
   steel	0.5449	5.73	4.799	0.0761
   CFRP	0.0564	3.587	3.749	0.0041
   GFRP	0.055	3.2	2.99	0.0034

6. CONCLUSION

   From the transient thermal analysis it is clear that GFRP reinforced beam has lesser deformation as compared with CFRP reinforced beam and steel reinforced beam. FRP can be used as a better alternative to steel reinforcement as both CFRP & GFRP bars have nearly equal deformation result which is very small compared with steel bars.

7. FUTURE SCOPE

FRP bars are made of different types of polymers with varying thermal resistance. There is a need to find out the best polymer which can withstand thermal effects. Bond behavior between concrete and FRP bars should be studied.

REFERENCES

1. Hamid Abbasi (2003) Model for Predicting Properties of Constituents of Glass Fibre Rebar Reinforced Concrete Beam at Elevated Temperature Simulating Fire Test Magazine of Concrete Research, pp 1-14

2. Ali Nadjai,Faris Ali, Didier Talamona (2005) Fire Performance of Concrete Beam Reinforced with FRP Bar International Journal on Symposium in Bond Behaviour of FRP in Structures, pp 401-410

3. W.Y.Gao, K.X. Hu, Z.D.Lu (2009) Modeling the Behaviors of Insulated FRP-Strengthened Concrete Beam Exposed to Fire Concrete Repair, Rehabilitation & Retrofitting, pp 1217-1222

4. Katy Branthwaite (2010) FEA of Fire Resistance on FRP Reinforced Concrete Members International Journal of Concrete Structures & Materials, 3(2)

5. Rami A. Hawileh (2011) Heat Transfer Analysis of Reinforced Concrete Beam with GFRP Bars Journal of Composites for Construction (ASCE), 6(2), pp 299-314

6. Esam El-Awady, Mohamed Husain, Sayed Mandour (2013) FRP- Reinforced Concrete Beams Under Combined Torsion & Flexure International Journal of Engineering Science & Innovative Technology, 2(1), pp 384-393

7. P.Jayajothi, R Kumutha, K. Vijai (2013) FEA of FRP Strengthened RC Beam Using ANSYS Asian Journal of Civil Engineering,14, pp 631-642.

8. Vinod Kumar M, Stephen Jebamalai Raj (2013) Static & Fatigue Response of High Strengthened Fibre Reinforced Concrete Beam using FRP Laminates International Journal for Engineering Research & Technology (IJERT), 2(4), pp 604-609

9. C.C. Spyrakos, I.G. Raftoyiannis, L. Credali, J.Ussia (2014) Experimental and Analytical Study in Reinforced Concrete Beam on Bending Strengthened with FRP Open Construction & Building Technology Journal, pp 153-163

10. [10] Dhanu M.N, Revathy D, Lijina Rasheed, Shanavas S (2014) Experimental & Numerical Study of Retrofitted RC Beam with FRP International Journal of Engineering Research & General Science, 2, pp 383-390

11. P.Parandaman, M.Jayaraman (2014) FEA of Reinforcement Concrete Beam Retrofitted using Different Fibre Composites Middle-East Journal of Scientific Research, pp 948-952

12. Rameshkumar U More, D.B.Kulkarni (2014) Flexural Behaviour Study on RC Beam with Externally Bonded AFRP International Journal of Research in Engineering & Technology, 3, pp 316-321

13. Ummer Farooq Pasha, N.Jeevan, Subramanya K.G (2014) Strengthening of RC Beam FRP Surface Mounted Technique International Journal of Advanced Scientific & Technical Research, 6(4), pp 29-45

14. Maher A. Adam, Mohamed Said, Ahmed A. Mahmoud, Ali S. Shanour (2015) Analytical and Experimental Flexural Behavior of Concrete Beam Reinforced with GFRP Bars Journal on Construction & Building Materials, 84, pp 354366