# Shear Performance for Prestressed Concrete Hollow Core Slabs
## 5 Conclusions  
To evaluate the shear performance of HCS, this study conducted shear experiments with cross-sectional height and presence of topping concrete as variables. Comparing the experimental results to the analytical results based on the design codes and previous studies, the following conclusions were derived.  
1. Regardless of the presence of topping concrete, HCS exhibited linear shear behavior of a constant gradient, and experienced typical web shear failure with decreased stress due to diagonal cracks formed in webs during peak stress.
2. Such tendencies were observed in the comparison of S and CS series. The effective depths of S and CS series increase with the increase in cross-sectional height and inclusion of topping concrete, and the resulting decrease in shear span-to-depth ratio significantly enhances shear resistance. S and CS series having the same experimental sections showed increases in shear force and deflection with increasing cross-sectional height.
3. Comparing shear strength values to analytical results based on KCI 2017 and ACI 318-19, the average ratios of analytical to experimental shear strength were 1.14-1.69 for S series and 1.73-2.18 for CS series. That is, shear strength conditions were satisfied regardless of cross-sectional height or presence of topping concrete. In particular, CS series had ratios 29-52% higher than those of the S series. Prediction equations that allow more rational calculation of shear strength of HCS with topping concrete should be developed.
4. The experimental results of HCS were found to be similar to the results of previous studies. Among the key influence factors, web-shear strength was most influenced by compressive strength of concrete due to prestress at the cross-sectional centroid. Web-shear strength was partly influenced by concrete compressive strength and shear span-to-depth ratio, but the extent of that influence was insignificant compared to the key influence factors.  
Conceptualization, Y.-J.L. and K.-H.K.; methodology, Y.-J.L.; validation, H.-G.K. and M.-J.K.; formal analysis, Y.-J.L.; investigation, D.-H.K.; data curation, H.-G.K. and M.-J.K.; writing--Original draft preparation, Y.-J.L.; writing--Review and editing, H.-G.K., M.-J.K. and K.-H.K.; supervision, K.-H.K.; project administration, K.-H.K. All authors have read and agreed to the published version of the manuscript.  
Figure 11: Analysis of key influence factors on the web-shear capacity: (**a**) Concrete compressive strength; (**b**) shear span-to-depth ratio; (**c**) Prestress introduced in centroid of section; (**d**) Height of member.  
**Funding:** The research was supported by the International Science and Business Belt Program through the Ministry of Science and ICT (2015-DD-RD-0068-05) and this work was supported by the Priority Research Centers Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2019R1A6A1A03032988). This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2018R1A2B3001656).  
**Acknowledgments:** The authors would like to give sincere thanks to Duksan GS Corporation for supporting this work.  
**Conflicts of Interest:** The authors declare no conflict of interest.