The simulation of CFRP in the models will increase the stiffness locally in the bridge. As seen previously, the reduction of stiffness due to cracks had a signif-icant impact on the structure. The scope of implementing CFRP in the models is to observe the possible effects on the bridge globally and locally.
8.2.1 Influence of CFRP in Frame Model
The adjustment in the stiffness is imposed in the Abaqus model and compared to the situation without the fiber reinforcement. Both models are subjected to a temperature field equivalent to an expansion of about 200 mm. This is a fic-titious situation since the externally bonded fiber reinforcement is applied after the expansion. Even though this is a wrong assumption, it can give a picture of how an increase in stiffness can give an impact on ASR expansion.
In this case, there is only made a cracked section on the east-facing beam in field 8 and not on both of the inner beams as the other cracked sections. This reflects a realistic simulation of the situation and can indicate if the symmetry assumptions made previously are reliable.
The change in moment given in percentage after application of CFRP is shown in figure 8.10. As expected, it is some increase in the moment over the inner beam where the carbon fiber reinforcement is applied. This is shown with dif-ferent colors for span 3, span 6 and span 8. The non-strengthen span 1, 2, 4 and 5 gets a reduction, while span 7 in between two strengthened spans obtains a small increase.
Figure 8.10: Impact on moment after application of CFRP on inner beams
98 CHAPTER 8. INFLUENCE OF MODIFICATIONS IN ABAQUS The alteration in the axial force shows similar behavior. Though, a small in-crease can be seen in span 4 as well. The inin-creased stiffness seems to have a higher impact on the axial forces.
Figure 8.11: Impact on axial forces after application of CFRP
In span 8, a decrease in axial forces is observed. This could be explained by the asymmetrical crack and strengthening imposed in this span. This can be understood by comparing the inner beams to each other. Table 8.1 compares the forces in the inner beams and gives an impression of the force distribution.
Section Meast[kN m] Mwest[kN m] Neast[kN] Nwest[kN]
Support 8 1966 1966 5052 5122
ZM 8-9 2183 2085 4921 5097
Field 8 4902 4945 4808 4833
Support 9 2977 2863 4278 4141
Table 8.1: M and N for both of the inner beams
The west faced beam is not cracked and even though the crack in the east-facing beam is strengthened, it is not adequate to increase the stiffness to an uncracked state. Therefore, the moments and axial forces are expected to be re-duced in the cracked area compared to the same section in the other inner beam.
A decrease of about 170 kN in the axial force is seen in the actual cracked part and some effects are imposed to support 8 and field 8, but with less impact.
Regarding the moment it is necessary to study the forces separately in the concrete and the steel. In the cracked section the steel obtains higher stresses which makes the contribution from the reinforcement greater. This increase is greater than the observed decrease in the concrete and therefore the total moment is greater. Regarding the other sections where the steel is not yielding, the axial forces are reduced in both the steel and the concrete. The impact on the moment is therefore rather small because the negative contribution coming from the upper reinforcement is reduced as well. All in all, the effect of having one cracked inner beam is not very significant. This can justify the simplification of symmetry done previously.
99 8.2.2 Influence of CFRP in Solid Model
To understand the influence of CFRP in Elgeseter bridge, a comparison with and without CFRP is done. Both models are subjected to a temperature field equivalent to an expansion of about 50 mm and have the simulation of a crack at zero moment section 8-9. All reinforcement is active in this analysis. Results are presented in figure 8.12, 8.13 and 8.14.
Figure 8.12: Impact on axial forces in inner beams after application of CFRP
Figure 8.13: Impact on axial forces in outer beams after application of CFRP The deviations in axial forces are small. Some deviations can be explained by errors when obtaining the stresses from reinforcement in Abaqus. This shows that the application of CFRP in the model mainly does not affect the acting axial forces in the bridge globally. The exceptions occur in ZM 8-9 and field 8, where a local effect of the stiffness of the CFRP appears. An interesting aspect is that the CFRP does not affect the axial forces in the outer beam. The in-creased stiffness of the inner beams does not contribute to additional restraining forces imposed by the ASR expansion.
Until the span between axis 8 and 9, where the CFRP is placed, the moment distribution is quite similar in both models. However, in field 8 there is an increase in the acting moment. This is expected since the moment capacity and
100 CHAPTER 8. INFLUENCE OF MODIFICATIONS IN ABAQUS
Figure 8.14: Impact on total moment after application of CFRP
stiffness is increased when applying CFRP. In a statically indefinite structure where parts of the structure become stiffer, a higher moment will occur in these parts.