Thermal & Compressional Analysis of circular CFDST using Abaqus software

MSc Civil and Structural Engineering. Presented by Asimina Tzempetzi. Supervised by Dr. Therese Sheehan.

2. Aims & Objectives• Conduct a thermal and a compressional analysis in order

to understand the structural behaviour in room and elevated temperatures

• Examine the effect of different geometrical parameters in the temperature distribution of the three layers.

• Analyse the mechanical behaviour of axial loaded circular CFDST columns in room and elevated temperatures by discuss the influence of different geometrical factors.

• Compare the results of axial loaded CFDST columns in room with axial loaded columns in elevated temperatures.

5. ConclusionIn total 24 circular CFDST columns were analyzed when subjected in fire, axial loading and the combination of the last two. Generally, columns with large outer steel tube dimensions prove better mechanical and fire performance. VR,(Do/to), (Di/ti) were the most important factors that have significant effect in the column’s behavior. After the comparison of the axially loaded columns in room and elevated temperatures columns exposed to fire present significant decrease in their strength as well as in the failure time. The failure modes occurred were almost in all the columns local buckling, inward for the inner tube and outward for the outer steel tube.

4. Numerical Resultsi. Thermal Analysis: By comparing different geometrical

parameters, such as VR, (Do/to), (Di/ti), it was found that different VR influence only the concrete and inner layer. The same fact was noticed when changing the (Do/to), (Di/ti). No significant influence was noticed in the temperature distribution of the outer steel tube in all cases fig3.

ii. Compressional Analysis in Room Temperature: Four different geometrical parameters including (Do/to), (Di/ti), ti ,to were analyzed. It was found that as smallest is the (Di/ti) ratio the better load resistance the columns have. On the other hand, as bigger is the (Do/to) ratio, the higher strength the columns present. As far as, the ti it was found that columns with greater inner tube thickness have greater load capacity fig3. The same outcomes were obtained for columns with grater to.

iii. Compressional Analysis in Elevated Temperatures: The same columns with the same four parameters were examined in ISO standard fire exposure while they were loaded. Again the decrease in (Di/ti) ratio and the increase in (Do/to) ratio lead to higher resistance in axial loading and fire. Similarly, the increase in the ti and to enhance the fire resistance of columns.

1. Introduction The project focuses on the thermal and mechanical behaviour of a new type of composite columns called concrete filled doubled skin tubes using software ABAQUS. This new type of innovative composite construction benefits of the sandwiched concrete between the two steel layers, outer and inner steel tube. The two materials combination contribute to the high strength resistance of the column, its light weight, improved bending, good damping, cyclic and fire performance. Fig2.Thermal and Compressional validation.

3. Methodology & ValidationIn the first steps of this research a thermal analysis took place, by exposing the circular CFDST into fire followed by a mechanical deportment investigation in room temperature. Finally, the behaviour of axial loaded circular columns at elevated temperatures was studied.

Fig 7: Outward-inward buckling in circular CFDST

Fig 5: Deformation of columns with Di/ti=4 in room temperature and fire

Fig 6: Deformation of columns with Do/to=22.5 in room temperature and fireFig.1 Methodology Steps

Fig 4: Comparison of deformation for columns with ti=2mm and 8mm.

Fig3: Graphical results of numerical analysis