Chapter 5 Testing of Bridge by Hybrid Simulation
5.4 Simulation results
5.4.1 Observed distribution of damage
The damage states of both conventional concrete and HyFRC specimens of Type 1-3 at various displacement levels are shown in Figure 5.15 (a–f). At the end of test under 0.5 MCE, hairline cracks are seen near the base of the pier of the Type 1 specimen. However, a clear shift in the initial crack location from pier-foundation interface could be seen for Type 2 and 3 specimens. The hairline crack subsequently coalesced at the end of 1MCE test and became more visible for all the specimens. Multiple cracks are also observed distributed over the pier-foundation interface region mostly in Type 1 specimens. The position of first crack for specimen Type 2 is at the location 150 mm from pier-foundation interface, which is in the vicinity of the terminating point of the dowels. Interestingly, specimen Type 3 also had first crack almost at similar location, i.e. 150 mm from pier-foundation interface.
However, on further increase in the intensity of excitation, the crack location in specimen Type 3 got shifted towards pier-foundation interface region. The maximum strain corresponding to the moment for 0.5 MCE intensity level and available stiffness at 150 mm from the pier-foundation interface is likely to be higher than the cracking strain of concrete due to which the first crack appeared in that location. At the same loading stage, due to the increase in stiffness provided by the corrugated sheet near the pier-foundation interface, the imposed strain is perhaps lower than the concrete cracking strain, though the moment is maximum at that location. However, with the increase in loading, the strain in the interface zone possibly became higher than the cracking strain and cracks started appearing at that
location. This is a typical case of relative increase in moment vs increase in stiffness due to the corrugated sheet. However, when the gauge size of corrugated sheets are further increased, it may be possible that the cracks will occur only in the zone away from the pier- foundation interface. Concrete spalling occurred in the zone of initial crack in Type 1 and 2, while in Type 3 spalling occurred near the pier-foundation interface during the test under 2MCE intensity level. At the end of 3MCE intensity level test, the concrete spalling is more prominent. It may be seen that the specimen Type B consistently suffered lesser damage in comparison to specimen Type A at any stages of intensity levels. Further, amongst all the specimens, Type 2 performed relatively better with lesser damage than rest of the specimens.
The damaged specimens are further subjected to cyclic displacement after 3MCE level tests of hybrid simulation for ascertaining the reserve strength.
During cyclic test, longitudinal reinforcement C1, C5 and C6 in specimen A-1 fractured at peak displacement of 90 mm, 100 mm and 100 mm respectively. In specimen B-1 longitudinal reinforcement C1 and C5 fractured at peak displacement of 100 mm.
Crushing of the concrete near the interface zone of the pier A-1 occurred at displacement amplitude of 40 mm, however similar condition is observed at displacement amplitude of 60mm in specimen type B-1. Longitudinal reinforcement C1 and C5 of specimen A-2 and C1 of specimen B-2 fractured at peak displacement of 100 mm. Crushing of the concrete predominantly occurred at displacement amplitude of 50 mm located near the first crack of the specimen A-2, however similar condition is observed at displacement amplitude of 70 mm in specimen B-2. In specimen A-3, longitudinal reinforcement C1 and C5 fractured while in specimen B-3, C4 and C5 fractured at peak displacement of 100 mm. Crushing of the concrete near the pier-foundation interface occurred at displacement amplitude of 50 mm in specimen A-3, however similar condition is observed at displacement amplitude of 60 mm in specimen B-3. The damage in the pier-foundation interface zone became more
5.4 Simulation results
prominent after the completion of cyclic test in specimen Type 3. The enhanced ductility of the HyFRC made piers is responsible for delay in concrete crushing as well as reduced number of reinforcement rupture in all the three specimen of Type B. Specimen B-2 performed best out of all six piers. Figure 5.15 (e-f) shows the damaged states of specimen A and B type respectively, when the experiments are stopped. Reinforcement got snapped and formation of flexural hinges are observed. However, from the Figure 5.15 (e-f) it is quite evident that damage level in HyFRC made piers is much lesser than that of conventional concrete specimens.
Type 1 Type 2
Type 3
(a) Conventional concrete specimens at the end of 1st level of of Hybrid test
Type 1 Type 2
Type 3
(b) HyFRC specimens at the end of 1st level of Hybrid test
Type 1 Type 2
5.4 Simulation results
Type 3
(c) Conventional concrete specimens at the end of 4th level of of Hybrid test
Type 1 Type 2
Type 3
(d) HyFRC specimens at the end of 4th level of Hybrid test
Type 1 Type 2
Type 3
(e) Conventional concrete specimens at the end of Cyclic test
Type 1 Type 2
5.4 Simulation results
Type 3
(f) HyFRC specimens at the end of Cyclic test Figure 5.15. Damage states of the six test specimens
Fibres bridging cracks is the prime cause of this lesser observed in piers of Type B.
Structural rehabilitation of HyFRC specimens will be much easier compared to specimens made of conventional concrete.