NEW NUMERICAL MODELS FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE

Transcription

1 COST Action TU0904 Integrated Fire Engineering and Response Training school University of Malta, Sliema, April Scientific project: Reliability of Structures and Risk Assesment to Extreme Loading, Ministry of Science and Tehnology, Croatia NEW NUMERICAL MODELS FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE Neno Torić, PhD student UNIVERSITY OF SPLIT, CROATIA FACULTY OF CIVIL ENGINEERING, ARCHITECTURE AND GEODESY Chair for steel and timber structures

2 OVERVIEW Introduction Research concept Numerical model for behaviour of steel and concrete structures exposed to fire Experimental research Numerical examples Discussion

3 INTRODUCTION Development of structural analysis models for predicting fire behaviour Current research is focused on development of structural analysis model comprised of 3D heat transfer model, model for calculating mechanical properties of the cross section and model for structural analysis Development of simplifed model for calculating mechanical properties of the cross section taking into account the additional load dependent strains that occur during heating (creep, transient-creep) Calculation of modified stress-strain curves which implicitly take into account the additional load dependent strains (strain modified curves) 3

4 RESEARCH CONCEPT Steel steady state test vs. transient state test vs. EC3 steady-state test EC3 transient-state test 4

5 RESEARCH CONCEPT Concrete steady state test vs. EC2 70 Stress [MPa] EN C EN ] C EN C EN C EN C EN C EN C STEADY S. TEST - 20 C STEADY S. TEST C STEADY S. TEST C STEADY S. TEST C STEADY S. TEST C STEADY S. TEST C STEADY S. TEST C Strain 5

6 RESEARCH CONCEPT Strain modified curve 6

7 NUMERICAL MODEL FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE 3D nonlinear heat transfer model, Model for calculating mechanical properties of the cross section Model for structural analysis D Bernoulli beam (6 D.O.F.) Cross-section discretization (0,0,0) D Cube element 7

8 NUMERICAL MODEL FOR BEHAVIOUR OF STEEL AND CONCRETE STRUCTURES EXPOSED TO FIRE Calculation procedure for strain modified curve 8

9 EXPERIMENTAL RESEARCH Material behaviour 9

10 EXPERIMENTAL RESEARCH Structure behaviour V Furnace V V V Furnace V H V H

11 EXPERIMENTAL RESEARCH Structure behaviour HE 320 A Chimney H H1 HE 200 A 1955 lvdt lvdt aerated concrete blocks oil burner oil burner oil burner 11

12 Example 1 Creep model: Dorn/Harmathy V Furnace V=200 kn Steel: S355 V V

13 Example 1 13

14 Example 1 14

15 Example 1 15

16 Example Temperature [ C] T_furnace Exp upper flange Exp lower flange 3 Model Time [min] 16

17 Example 1 Midspan deflection [mm] Exp midspan defl EC3 Exp stress-strain curves without creep Exp strain modified curves EC3 strain modified curves Time [min] 17

18 Example 2 Creep model: Dorn/Harmathy V Furnace V=200 kn H=400 kn Steel: S355 V H V H

19 Example 2 19

20 Example 2 20

21 Example 2 21

22 Example T_furnace Exp upper flange Exp lower flange Model Temperature [ C] Time [min] 22

23 Example 2 60 Midspan deflection [mm] Exp midspan defl EC3 Exp stress-strain curves without creep EC3 strain modified curves Exp strain modified curves Time [min] 23

24 Example 3 Transient-creep model: Anderberg/Thelandersson K d=20 cm K=20 kn Concrete: C 60/70 Prest. Steel - f y =1600 MPa K K K

25 Example 3 25

26 Example 3 26

27 Example 3 27

28 Example Temperature [ C] Exp cable T7 Exp cable T8 Exp cable T9 Exp void T10 Exp surface T11 Model T7 Model T8,T9 Model T10 Model T11 T_furnace Time [min] 28

29 Example Exp midspan defl LVDT3 Exp midspan defl LVDT4 Exp stress-strain curves EC2 Exp strain modified curves EC2 strain modified curves Deflection (mm) Time (min) 29

30 DISCUSSION Application of strain modifed curves in classical structural analysis calculation was presented Validity of the strain modified curves was tested on results of three different experiments conducted on testing of simply supported steel and prestressed concrete elements exposed to high temperatures Numerical results of the three presented examples show good agreement with the experiment by using strain modified curves in terms of predicting the structural stiffness Further research is required to confirm the application of the presented calculation methodology 30

31 THANK YOU FOR YOUR ATTENTION