Influence of Loading Ratio on Quantified Visible Damages of R/C Structural Members

Abstract eng:
The information such as repair cost and downtime is useful for a decision-making in a performance-based seismic design, but the more intuitive information such as the visible damage propagation is assumed to be useful for a decision-making of building owners in the next-generation performance-based seismic design. Therefore the evaluation methods of visible seismic damage for reinforced concrete (R/C) members have been developed in recent years. One of the developed method estimates the propagation of crack length in a very simple way. It is basically combining the empirical and mechanical models, and the models are originally verified under static service load level in CEB-FIP model code for concrete structure (1978). In this paper, this simple method of estimating the crack propagation under seismic load level with large deformation and under dynamic load is verified. Firstly, to verify the proposed model estimating the crack propagation in a simple way, three R/C beam specimens (F-60, F90, and FS-90) proportioned to approximately 1/2 of full scale were tested under monotonic static loading. During the service load level (before rebar yielding), estimated total crack length approximates the observed total crack length in each specimen. After rebar yielding (in seismic load level with large deformation), estimated crack lengths of specimen F-60 and F-90 approximates the experimental results. But estimated crack lengths of specimen FS-90 is underestimated the experimental result. Although there is the tendency of underestimating a shear crack length, some accuracy of the simple estimation method for crack length propagation under the static load with large deformation is shown in this case. Secondly, to verify the proposed model estimating the crack propagation in a quick and easy way under dynamic load, R/C beam dynamic and static test results are employed. The specimen S-5, S-6, S-7, and S-8 are tested under static load (0.1 mm/sec), and the specimen D-5, D-6, D-7, and D-8 are tested under dynamic load (100 mm/sec). Specimens, which ratio of shear strength to flexural strength are around 1.8~1.9, show the almost same damage propagation under static and dynamic load in experimental results. But specimens, which ratio of shear strength to flexural strength are around 2.5~2.6, show the difference of their damage propagation between static loading and dynamic loading, where the dynamic loading results shows the damage around 30% less than that of the static loading. In the proposed simple method, the strain rate effect on the material strength affects slightly the estimation crack length as with experimental results. But an effect of the ratio of shear strength to flexural strength on the crack length difference between static loading and dynamic loading doesn’t follow the tendency of experimental result. It is the future issues how to consider key factors like the ratio of shear strength to flexural strength in the proposed simple method.

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