A STUDY ON DESTRUCTION PROPERTIES OF PILE CAPS WITH ECCENTRIC COLUMNS AS FRAMES

Pile-cap is an important structural joint member. Its function is to transfer the stresses occurring on the columns through a group of piles to the ground, occurring on the complex stresses that occur under earthquake loading. It is difficult to identify if the pile-caps were damaged by the earthquake. It is hard to observe the seismic behaviour under earthquake loading. It is very important to clarify pile-cap failure mechanism of reinforced concrete (RC) structures. However, failure mechanism of a pile, exterior column-beam pile-cap in RC structure is not resolved yet under bi-lateral loading. Currently, there is no research and few valid experiments, regarding the study of pile-caps. As a result, the stress mechanism has not been defined. Looking at actual cases, when pillars are placed at the edge of the site due to site conditions and design factors, pile caps are sometimes planned in which the center of the upper column and the center of the pile are misaligned. Therefore, the purpose of this study was to clarify the failure characteristics of pile caps in which the columns are eccentric to the outside of the piles. The specimens which were the exterior subassemblages of a precast pile, foundation beam and column, were half scale to actual frames. The eccentric distance was set to 100 mm so that the surface of the side column and the surface of the pile cap were aligned. The depth and width of the column and beam section were same, respectively. The length from the center of the column to the pin-roller support of a beam end was 1600mm. The height from the center of the beam to the loading point on the top of the column or to the bottom support was 1415mm, respectively. Reversed lateral horizontal loads at the top of a column and constant axial load were applied to all specimens. Concrete compressive strength was 24MPa. All specimens were designed to fail in pile-cap. The properties of pile caps with eccentric columns differed from those without eccentricity in terms of cracking properties, and the final fracture properties were such that the column bases were crushed, and the axial force could not be maintained. In the case of eccentric columns, the yield strength increased by increasing the amount of vertical and tie-downs in the pile cap. Within the scope of this experiment, the axial force could be maintained.