Structural design of isolated column footings

• Published in: Alexandria engineering journal 2016-09, Vol.55 (3), p.2665-2678
• Main Authors: Abdrabbo, Fathi, Mahmoud, Zaki I., Ebrahim, Mariana
• Format: Article
• Language: English
• Subjects: Codes; Contact stress; Correlation; Footing; Punching shear; Shear span
• ISSN: 1110-0168
• DOI: 10.1016/j.aej.2016.06.016

Superstructure loads are transmitted to the underlying soil strata through a suitably designed foundation. Therefore, the foundation of a structure is considered the most crucial structural element in a building. The foundation may be classified into two main categories, shallow and deep foundations. Shallow foundation comprises isolated column footings, combined footings and reinforced concrete mat. The design of isolated column footing is accomplished through the application of geotechnical and structural analysis concepts. So that, the input research into isolated column footings comes from two different disciplines, geotechnical and structural. This may be one of the main causes that attributed to the limited research input to the subject. Therefore, the structural design of isolated column footings is based on empirical rules and the calculations of bending moments (BM) and shearing forces (SF) induced in a footing are based on the rules of beam theory, which is questionable. On the other hand, punching theory was developed on relatively thin floor slab, even though the theory is implemented for the calculation of punching shear in relatively thick footings. Also experimental research on isolated column footings is scarce, due to the difficulties involved in the setup of the laboratory models and the cost of experiments. The work presented in this article deals with the correlation between failure loads predicted by different code provisions, ECP203-11, ACI318-08, BS 8110.1-1997 and EC2-2004, of isolated column footings, and the corresponding measured values. The study showed that shear span to depth ratio of a footing and distributions of contact stress at footing–soil interface are key factors in the structural design of the footing. ECP203-11, ACI318-08, and EC2-2004 code provisions, underestimate the structural failure loads of isolated column footings, while BS 8110.1-1997 overpredicts the failure loads of isolated column footings, if punching provisions at perimeter of column are pulled out from the code.