Moment Restraint and Second-Order Analysis of a Cantilevered Precast Column Supported by an Isolated Footing

摘要

This paper presents criteria for determining the base rotational spring restraint and the second-order analysis of a cantilevered precast concrete column supported by an isolated reinforced concrete footing and its anchorages bearing on elastic soil or on piling. The column-base-footing system is analyzed; as well as the relative importance of its two interfaces: the column base plate to footing and the footing to soil. This issue is of major importance in the analysis and design of framed structures and in the determination of their deflections, stability, and second-order effects. This paper extends the procedure presented in Sections 3.8.2 through 3.8.4 of the PCI Design Handbook, Fifth Edition, and provides a practical tool for calculating the degree of fixity at the base of precast and monolithic columns on isolated footings bearing directly on soil or supported by piling. The steps for calculating the total overturning moment, overall stability, and stresses in the different materials and supporting soil, in accordance with the ACI Building Code (ACI 318-99), are presented. The proposed model is limited to rigid footings and short-term behavior. Further research is ongoing to determine the effects of secondary settlements in the soil, creep and shrinkage of the concrete, bond slippage in the anchor bolts, and other factors.