One of the attractiveness of flat slab structures and flat plate structures is that the structural types without beams have the advantage of a high degree of freedom to use of indoor spaces. The new construction method that we will describe in this study is a flat slab mixed structure with steel capitals in RC slab. The distinctive of this construction is that the columns are generally designed in RC but changed to small diameter steel round bars. In addition, by replacing the RC drop panel and the RC capital with a steel capital in RC slab, the structure will provide a space with a high degree of freedom as well as flexibility.
The purpose of this research was to experimentally grasp the failure in RC slab by punching shear, the strength and the deformation capacity under lateral load. Furthermore, it is a characteristic of this structure that the decrease in the rigidity of RC slab due to cracking has a great effect on the properties of the structure. Therefore, we will also describe the serviceability and reparability limits by the observation of the residual crack width of the specimens.
The following conclusions were obtained from this study.
1) If the circumference obtained by adding the effective depth of RC slab to the capital plate diameter is taken as the critical section for shear in RC slab, it is confirmed that the ultimate vertical force when only the vertical force is transmitted can be calculated with a safety factor of about 10% by using the AIJ standard for RC structure6). Here, we use the effective depth is calculated by subtracting the capital plate thickness from the effective depth of the AIJ standard.
2) By setting the long-term allowable load to about 1/3 of the ultimate vertical force when only the vertical force, it was confirmed from the observation of the crack width that there is no problem in the serviceability of RC slab under the long-term load.
3) Under the 1/3 (inner column) or 1/6 (outer column) of ultimate vertical force on RC slab, in the lateral loading test, regardless of the inner and outer columns in all the loading directions, it was confirmed that the resistance for lateral force did not decrease up to the story drift angle (“R”) become 20×10-3 rad, and it was confirmed the high deformation capacity.
4) The lateral initial stiffness of this method was almost equal when the inner column and outer column specimens were applied in the positive direction. Then the outer column was applied in the negative direction, it was about half that of the positive direction. Furthermore, as the story drift angle increased, the lateral stiffness further reduced due to the damage of RC slab. We also confirmed that the story drift angles of all the specimens were about 10 to 20% of the initial stiffness at R=40×10-3 rad.
5) At the story drift angles (R=10×10-3 rad) often used as the design criteria for large earthquakes, high reparability of this structure was confirmed from the observation of the residual crack width.
6) The shear failure strength around the column was verified that the correlation equation Vu/Vo+ Mu/Mo≧1.0 of the AIJ standard using RC column is established when punching failure occurs.