Introduction: One of the important steps in determining and improving the seismic performance and behavior of the existing structures is to determine the displacement demands. In seismic codes, it is desirable to limit the displacement demands. Since the increase of displacement demands in the structures will result in increased structural damage, displacement boundary conditions have been specified in the seismic codes. Displacement demand is a function of the seismic load or seismic acceleration acting on the structure. The DD-2 earthquake ground motion describes a rare earthquake ground motion which has a probability of exceedance of 10% in 50 years and a return period of 475 years. This earthquake ground motion is also referred to as the standard design earthquake ground motion. With the changed seismic code and the acceleration spectrum, the expected spectral displacement values also change. Aim: Determining the displacement demands for reinforced concrete structures, according to Turkish Seismic Code 2007 (TSC 2007) and Turkish Building Seismic Code 2018 (TBSC 2018). Scope: For the province of Kocaeli located in the 1st degree seismic zone according to TSC 2007, in the view of the changed code's criteria, the spectral displacements to be formed in reinforced concrete buildings with different soil classes and different periods were found and compared between the codes. Limitations: 5 different building models having 3 spans with a span length of 5m and 5 different numbers of storeys (5, 7, 9, 11, 13) with a storey height of 3m were designed. These models were analyzed under the design earthquake (DD-2) for five different soil classes according to TBSC 2018 and their spectral displacement values were calculated according to both the codes. Method: The 25 building models were analyzed by the ETABS structural analysis program and the natural periods of the buildings were determined. Using these periods, based on the displacement spectrum equations defined in TBSC 2018 code, spectral displacement values of uncracked section according to TSC 2007 and cracked section according to TBSC 2018 were obtained. Obtained spectral displacements were compared using tables and graphs and interpreted taking into account the displacement limits given in the related codes. Results: When the obtained tables and graphs were examined, the dimensionless spectral displacement values differ at certain ratios between TBSC 2018 that adopts the cracked section and TSC 2007 that adopts the uncracked section. As expected, it was observed that the displacement values of the cracked section increased with respect to the uncracked section. When the values of the cracked sections were compared to those of the uncracked sections, increase of 48.3%, 50.1%, 51%, 51.3% and 51% was observed in the building models with total heights of 15m, 21m, 27m, 33m and 39m, respectively. Generally, as the heights of the building models increased, the increase ratios also increased; only the model with the height of 39m showed a lower increase ratio than the one with 33m height. For the same building height, these ratios were found to be the same for the five soil classes. It was also observed that as the soil class gets softer, the amount of displacement increases. However, in each of the codes, it was observed that the spectral displacement values in the soil classes ZA and ZB for each building height were the same. Conclusion: Displacement increase ratios between the codes were not affected by the soil class. When all the results were evaluated, the increase ratio of the displacement demand that is about 50% shows that in order to design a building according to TBSC 2018 that has the same displacement values of a building designed according to TSC 2007, the cross-sections of the load bearing elements must be enlarged seriously. Although this situation shows that TBSC 2018 is in a safer area when compared to TSC 2007, it will also cause a considerable raise in the cost of the building.
Anahtar Kelimeler: Cracked Section, Displacement Demand, Spectral Displacement, TBSC 2018, TSC 2007, Uncracked Section
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