Random Response of Offshore Towers With Pile-Soil-Pile Interaction

1990 ◽  
Vol 112 (1) ◽  
pp. 35-41 ◽  
Author(s):  
M. Novak ◽  
H. Mitwally
Keyword(s):  
Closed Form ◽  
Dynamic Interaction ◽  
Random Wave ◽  
Wave Forces ◽  
Vibration Modes ◽  
Random Response ◽  
Pile Groups ◽  
Stiffness Matrices ◽  
Interaction Factors ◽  
Pile Interaction

Dynamic pile-soil-pile interaction is analyzed using dynamic interaction factors. For pile groups, complex stiffness matrices are formulated in closed form for excitation in all vibration modes and introduced into the analysis of an offshore tower. The effects of dynamic pile-soil-pile interaction on tower response to random wave forces are demonstrated. Temporal as well as spatial randomness of wave forces are considered.

Dynamic Interaction Factors for Floating Pile Groups

1991 ◽  
Vol 117 (10) ◽  
pp. 1531-1548 ◽  
Author(s):  
George Gazetas ◽  
Ke Fan ◽  
Amir Kaynia ◽  
Eduardo Kausel
Keyword(s):  
Dynamic Interaction ◽  
Pile Groups ◽  
Floating Pile ◽  
Interaction Factors

Seismic Analysis of a Double-Hinged Articulated Offshore Tower

2008 ◽  
Author(s):  
Syed Danish Hasan ◽  
Nazrul Islam ◽  
Khalid Moin
Keyword(s):  
Seismic Analysis ◽  
Offshore Structures ◽  
Random Wave ◽  
Wave Forces ◽  
Offshore Structure ◽  
Concentrated Mass ◽  
Energy Principle ◽  
Rotational Angle ◽  
Sea Bed ◽  
Time Histories

The response of offshore structures under seismic excitation in deep water conditions is an extremely complex phenomenon. Under such harsh environmental conditions, special offshore structures called articulated structures are feasible owing to reduced structural weight. Whereas, conventional offshore structure requires huge physical dimensions to meet the desired strength and stability criteria, therefore, are uneconomical. Articulated offshore towers are among the compliant offshore structures. These structures consist of a ballast chamber near the bottom hinge and a buoyancy chamber just below the mean sea level, imparting controlled movement against the environmental loads (wave, currents, and wind/earthquake). The present study deals with the seismic compliance of a double-hinged articulated offshore tower to three real earthquakes by solving the governing equations of motion in time domain using Newmark’s-β technique. For this purpose Elcentro 1940, Taft 1952 and Northridge 1994 earthquake time histories are considered. The tower is modeled as an upright flexible pendulum supported to the sea-bed by a mass-less rotational spring of zero stiffness while the top of it rigidly supports a deck in the air (a concentrated mass above water level). The computation of seismic and hydrodynamic loads are performed by dividing the tower into finite elements with masses lumped at the nodes. The earthquake response is carried out by random vibration analysis, in which, seismic excitations are assumed to be a broadband stationary process. Effects of horizontal ground motions are considered in the present study. Monte Carlo simulation technique is used to model long crested random wave forces. Effect of sea-bed shaking on hydrodynamic modeling is considered. The dynamic equation of motion is formulated using Lagrangian approach, which is based on energy principle. Nonlinearities due to variable submergence and buoyancy, added mass associated with the geometrical non-linearities of the system are considered. The results are expressed in the form of time-histories and PSDFs of deck displacement, rotational angle, base and hinge shear, and the bending moment. The outcome of the response establishes that seismic sea environment is an important design consideration for successful performance of hinges, particularly, if these structures are situated in seismically active zones of the world’s ocean.

Analysis for Axial Vibration and Internal Forces of Totally and Partially Embedded Pile Groups with Flexible Caps

2010 ◽  
Vol 163-167 ◽  
pp. 3860-3867
Author(s):  
Qing Ren ◽  
Mao Song Huang
Keyword(s):  
Wind Farm ◽  
Mass Density ◽  
Offshore Wind ◽  
Parameter Study ◽  
Pile Groups ◽  
Inertial Interaction ◽  
Soil Deposits ◽  
Pile Interaction ◽  
Internal Forces ◽  
Dynamics Response

In this paper, a simplified analytical method is developed for the axial harmonic response of totally and partially embedded pile groups in homogeneous and layered soil deposits. Based on BDWF model, finite element sub-structure method is used to setup the dynamic model of cap-pile groups which can precisely simulate kinetic interaction and inertial interaction. A comprehensive parameter study focuses on the influence of caps’ elastic modulus and mass density on pile groups’ dynamic response, and then points out the limition of rigid cap in practical design. An approximate solution is finally presented for the internal forces distributed on pile heads due to pile-to-pile interaction. The solution of above approach was compared with that of traditional simplified model (rigid and massless cap solution) in simulating an in-site experiment and dynamics response of partially embedded pile groups for offshore wind farm.

scholarly journals Numerical modelling of perimeter pile groups in clay

2013 ◽  
Vol 50 (3) ◽  
pp. 250-258 ◽  
Author(s):  
A.V. Rose ◽  
R.N. Taylor ◽  
M.H. El Naggar
Keyword(s):  
Load Distribution ◽  
Load Capacity ◽  
Relative Effectiveness ◽  
Pile Group ◽  
Block Type ◽  
Pile Groups ◽  
Total Load ◽  
Group Behaviour ◽  
Pile Interaction ◽  
Spacing Length

The load distribution among piles in a group varies such that the inner piles often carry a smaller share of the total load compared to the outer piles, which is a result of increased soil–pile interaction. The main objective of this paper is to establish the relative effectiveness of pile groups with no inner piles (perimeter group), when compared to the more common grid configuration. The numerical investigation utilized the finite element programme ABAQUS and considered a range of variables that affect pile group behaviour including number of piles, pile spacing, length/diameter ratio, and soil strength. It was demonstrated that a complete grid group is less efficient than a perimeter group, where efficiency is defined as the load capacity of the whole group expressed as a ratio of the number of piles in the group multiplied by the load capacity of a single isolated pile. Efficiencies close to unity were observed for some perimeter groups. Perimeter groups also showed that a “block” type group failure could occur, where piles were placed at a spacing of less than 2.0 pile diameters,d, centre-to-centre. This often, but not always, led to a reduction in the efficiency of the pile group.

scholarly journals Flexible Pile Group Interaction Factors under Arbitrary Lateral Loading in Sand

2020 ◽  
Vol 8 (10) ◽  
pp. 800
Author(s):  
Miloš Marjanović ◽  
Mirjana Vukićević ◽  
Diethard König
Keyword(s):  
Numerical Study ◽  
Group Interaction ◽  
Pile Group ◽  
Lateral Loading ◽  
Soil Conditions ◽  
Offshore Platforms ◽  
Lateral Loads ◽  
Pile Groups ◽  
Main Hypothesis ◽  
Interaction Factors

Marine and harbor structures, wind turbines, bridges, offshore platforms, industrial chimneys, retaining structures etc. can be subjected to significant lateral loads from various sources. Appropriate assessment of the foundations capacity of these structures is thus necessary, especially when these structures are supported by pile groups. The pile group interaction effects under lateral loading have been investigated intensively in past decades, and the most of the conducted studies have considered lateral loading that acts along one of the two orthogonal directions, parallel to the edge of pile group. However, because of the stochastic nature of its source, the horizontal loading on the pile group may have arbitrary direction. The number of studies dealing with the pile groups under arbitrary loading is very limited. The aim of this paper is to investigate the influence of the arbitrary lateral loading on the pile group response, in order to improve (extend) the current design approach for laterally loaded pile groups. Free head, flexible bored piles in sand were analyzed through the extensive numerical study. The main hypothesis of the research is that some critical pile group configurations, loading directions, and soil conditions exist, which can lead to the unsafe structural design. Critical pile positions inside the commonly used pile group configurations are identified with respect to loading directions. The influence of different soil conditions was discussed.

Symmetry transformation matrices for structures

2007 ◽  
Vol 463 (2082) ◽  
pp. 1563-1583 ◽  
Author(s):  
Markus Pagitz ◽  
Jonathan James
Keyword(s):  
Fourier Series ◽  
Closed Form ◽  
Symmetry Transformation ◽  
Symmetry Groups ◽  
Vector Spherical Harmonics ◽  
Alternative Derivation ◽  
Closed Form Solutions ◽  
Transformation Matrices ◽  
Displacement Vectors ◽  
Stiffness Matrices

Many structures in nature and engineering are symmetric. Depending on the degree of symmetry, it is possible to simplify the computations considerably by block diagonalizing the stiffness matrices. Closed-form solutions of transformation matrices for such block diagonalizations can be derived using group theory for arbitrary symmetry groups. This paper presents closed-form solutions of transformation matrices based on an alternative derivation. It is shown that transformation matrices for C nv and D nh groups can be obtained from a finite Fourier series decomposition of load and displacement vectors. Furthermore, it is shown that structures with tetrahedral, octahedral and icosahedral symmetries can be block diagonalized in an elegant way using vector spherical harmonics.

scholarly journals An Experimental Study on Pile Spacing Effects under Lateral Loading in Sand

2013 ◽  
Vol 2013 ◽  
pp. 1-8 ◽  
Author(s):  
Mahdy Khari ◽  
Khairul Anuar Kassim ◽  
Azlan Adnan
Keyword(s):  
Pile Group ◽  
Experimental Investigations ◽  
Pile Groups ◽  
Dense Sand ◽  
Spacing Effects ◽  
Pile Diameter ◽  
Lateral Resistance ◽  
Model Pile ◽  
Pile Interaction ◽  
Subgrade Modulus

Grouped and single pile behavior differs owing to the impacts of the pile-to-pile interaction. Ultimate lateral resistance and lateral subgrade modulus within a pile group are known as the key parameters in the soil-pile interaction phenomenon. In this study, a series of experimental investigation was carried out on single and group pile subjected to monotonic lateral loadings. Experimental investigations were conducted on twelve model pile groups of configurations 1 × 2, 1 × 3, 2 × 2, 3 × 3, and 3 × 2 for embedded length-to-diameter ratiol/d= 32 into loose and dense sand, spacing from 3 to 6 pile diameter, in parallel and series arrangement. The tests were performed in dry sand from Johor Bahru, Malaysia. To reconstruct the sand samples, the new designed apparatus, Mobile Pluviator, was adopted. The ultimate lateral load is increased 53% in increasing ofs/dfrom 3 to 6 owing to effects of sand relative density. An increasing of the number of piles in-group decreases the group efficiency owing to the increasing of overlapped stress zones and active wedges. A ratio ofs/dmore than6dis large enough to eliminate the pile-to-pile interaction and the group effects. It may be more in the loose sand.

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