Publication
Study of the damage indices of concrete members reinforced with high-strength steel
doi: 10.1680/jstbu.20.00165
What is it about?
The effects of high-strength steel (HSS) on the damage indices (DIs) of four special moment frames and three beam–column connection (BCC) specimens under cyclical loading were experimentally studied. The specimens with HSS rebars (with yield strengths of 500 MPa and 580 MPa) were designed and constructed based on the special seismic provisions of ACI 318-19. Several types of DIs (from single DIs to combined DIs based on parameters such as displacement, absorbed energy and stiffness) were calculated according to the experimental results. The results showed that the application of the higher strength steel expedited the failure process of the specimens. Moreover, the DIs indicated that the specimen fitted with HSS for both the longitudinal and transverse rebars had the greatest damage propagation speed of the frames. For the BCCs, the specimen with HSS as just the longitudinal rebars showed the greatest damage propagation speed. The results also showed that the displacement-based DIs were less accurate than the other types of DIs for studying the damage behaviour of both the frame and the BCC specimens. The combined DIs were found to be more accurate than the other DIs.
Why is it important?
With recent technological advancements, the production of higher strength materials such as high-strength steel (HSS) and high-strength concrete (HSC) is more feasible. Nowadays, steel rebars with a yield strength of 500 MPa are generally considered to be HSS rebars. The application of HSS has considerable benefits, such as decreases in material costs and construction time, thus facilitating construction procedures (Kheyroddin et al., 2021). However, there are also considerable disadvantages related to HSS applications, such as crack widening, brittle failure, possible increase in stiffness loss and possible decrease in structural ductility. The progress of non-linear structural performance can be monitored through the damaged area using damage indices (DIs), and various DIs have been suggested based on different structural properties (strain, stress, displacement, dissipated energy, stiffness, ductility etc.) (Arshadi et al., 2020a, 2020b). All these DIs can are either cumulative or non-cumulative in nature: the cumulative ones evaluate damage sensitivity to both the loading amount and the number of loading cycles, whereas the non-cumulative DIs are evaluated using maximum mechanical criteria (displacement, rotation etc.). DIs are generally categorised into different types: local DIs (if loads are dependent on motion and the number of cycles), global DIs (by the merging of local DIs) and individual DIs (which are related to a subset of structural elements).
Perspectives
Considering the research gaps, in this study, the effects of HSS rebars on the damage process of four concrete special frames and three BCCs were investigated using different types of DIs. These specimens were constructed based on the special seismic suggestions of ACI 318-19 (ACI, 2019). As a first step, frames with the same geometric specifications and equivalent amounts of steel rebars, but with different yield strengths (500 MPa and 580 MPa) for both the longitudinal and transverse rebars were constructed. The BCCs were also constructed with the same geometry and equivalent amounts of steel rebars. The specimens were tested under cyclic loading. The results showed that the application of HSS generally accelerated the damage process of the specimens. The DIs of the specimens were calculated using several methods. These DIs were based on different parameters (displacement, energy absorption and stiffness). At attempt was thus made to find the most appropriate DIs for frames and BCCs fitted with HSS rebars. The reason for this is that most DIs in previous studies were proposed for single members such as short columns with NSS, and not whole frames or BCCs with HSS rebars. The results showed that all the methods produced DIs close to each other, except the displacementbased DIs. Moreover, the calculated DIs indicated that the experimental specimen using HSS as both the longitudinal and transverse rebars had the greatest damage distribution speed among the frames. For the BCCs, the specimen with HSS as just the longitudinal bars had the greatest damage distribution speed.
Dr.
Hamed
Arshadi
Semnan University of Medical Sciences and Health Services