Numerical and analytical study of pinned column base plate connections

Abstract

Gravity system column base plate connections are generally classified as pinned connections with no to minimal moment capacities. A low rotational stiffness value is recommended by the New Zealand Steel Structures Standard, NZS 3404, to represent pinned connections. However, numerous past research studies have shown that these so-call pinned connections possess significant rotational stiffness which could attract large moment demand and potentially lead to yielding of the column base. Furthermore, the constant axial load on the gravity column in conjunction with column base yielding could result in axial shortening of the column, which would significantly increase the cost and difficulty of post-earthquake rehabilitation. With the aim to minimize column base yielding and column axial shortening, a numerical parametric study was conducted to examine the influences of various parameters, including base plate thickness, anchor rod diameter, axial load magnitude, foundation depth and anchor rod pitch distance, on the connection behaviour. It was found that the applied axial load greatly affected the moment resistance as well as the rotational stiffness of the connection. Results also showed that the rotational stiffness of pinned column base plate connections was significantly higher than the value suggested in NZS 3404. An analytical model was developed and validated against numerical and experimental studies to predict moment-rotation response of pinned column base plate connections. Satisfactory results were observed.