11
Behavior of Piles Supporting
Offshore Structures
Lymon C. Reese
As discussed in detail in other chapters, the behavior of structures under dynamic loading dépends on the geometry and mass of the particular unit, the
nature of embedment into soil, and the relevant characteristics of the soil itself.
Each of these features is discussed herein.
Offshore structures maintain their stability under loading due to the mass
of the structure, a gravity foundation, or due to embedded piles. The piles, of
course, can be considered as an extended portion of the structure, or the piles
can be analyzed separately. In the latter case, a free body is selected at the pile
heads or at the top of a pile cap and methods of analysis achieve compatibility
between the piles and the superstructure. In the case of a gravity foundation.
the mass of the structure is sufficient that environmental loads do not cause a
lift off or excessive soil deformation. Whatever the concept of foundation design,
the engineer must make a study of the soil supporting the structure. The nature
of the response of soil under loading is discussed and methods of obtaining t e
needed properties of the soil at offshore locations are presented briefly.
With regard to the loading of a pile, four types can occur: short-term static,
cyclic, dynamic, and sustained. Static loading can be assumed m many
with an appropriate factor of safety. However, cyclic loading must e a
in detail for latéral loading. Dynamic loading is discussed brie y m t e a.
section. Sustained loading usually needs addressing only if the supporting
is a soft, saturated clay. Methods of analyzing piles under axial an at r
>ng are presented because pile-supported structures dominate t ose at
locations. The analytical methods relate specifically to short term an
loadings. An example problem involving a single pile and an actu s°*
from the Gulf of Mexico is solved by two analytical metho an
e r
compared.
289
Behavior of Piles Supporting
Offshore Structures
Lymon C. Reese
As discussed in detail in other chapters, the behavior of structures under dynamic loading dépends on the geometry and mass of the particular unit, the
nature of embedment into soil, and the relevant characteristics of the soil itself.
Each of these features is discussed herein.
Offshore structures maintain their stability under loading due to the mass
of the structure, a gravity foundation, or due to embedded piles. The piles, of
course, can be considered as an extended portion of the structure, or the piles
can be analyzed separately. In the latter case, a free body is selected at the pile
heads or at the top of a pile cap and methods of analysis achieve compatibility
between the piles and the superstructure. In the case of a gravity foundation.
the mass of the structure is sufficient that environmental loads do not cause a
lift off or excessive soil deformation. Whatever the concept of foundation design,
the engineer must make a study of the soil supporting the structure. The nature
of the response of soil under loading is discussed and methods of obtaining t e
needed properties of the soil at offshore locations are presented briefly.
With regard to the loading of a pile, four types can occur: short-term static,
cyclic, dynamic, and sustained. Static loading can be assumed m many
with an appropriate factor of safety. However, cyclic loading must e a
in detail for latéral loading. Dynamic loading is discussed brie y m t e a.
section. Sustained loading usually needs addressing only if the supporting
is a soft, saturated clay. Methods of analyzing piles under axial an at r
>ng are presented because pile-supported structures dominate t ose at
locations. The analytical methods relate specifically to short term an
loadings. An example problem involving a single pile and an actu s°*
from the Gulf of Mexico is solved by two analytical metho an
e r
compared.
289