K-Factor Solution for Combined Braced–Unbraced Offshore Jacket Frames

2019 ◽  
Vol 142 (2) ◽  
Author(s):  
Albert Ku ◽  
Jieyan Chen ◽  
Stephen Gunzelman
Keyword(s):  
Finite Element Method ◽  
Wave Loads ◽  
Braced Frames ◽  
American Institute ◽  
Moment Frame ◽  
Factor Solution ◽  
Frame Alignment ◽  
Entire Structure ◽  
K Factor ◽  
Portal Frame

Abstract Many offshore jackets have no braces between the top of jacket and the bottom of topsides deck. This can be either due to the installation requirement and/or an effort to reduce wave loads. This kind of jacket bay is a portal frame. For the design of portal frame columns, the current offshore standards point to the unbraced frame alignment chart solution from onshore standards such as the American Institute of Steel Construction (AISC). In this paper, we will show that the AISC alignment chart unbraced frame K-factor solution is conservative for offshore applications, and perhaps too conservative. This is because the traditional alignment chart assumes that the entire structure is a moment frame. In offshore applications, the unbraced frame is almost always combined with braced frames from above and/or below. In this paper, we will derive a K-factor solution that is suitable for a braced/unbraced frame combination. This solution is validated with structural buckling finite element method (FEM) analyses of typical offshore frames. Design implications from using the traditional alignment chart versus current new K-factor solution are also discussed.

scholarly journals IMPACT OF INTRODUCING SEMI-RIGID MOMENT FRAMES ON SEISMIC RESPONSE OF BRACED FRAMES

2019 ◽  
Vol 6 (1) ◽  
Author(s):  
Mahmoud Faytarouni ◽  
Onur Seker ◽  
Bulent Akbas ◽  
Jay Shen
Keyword(s):  
Braced Frames ◽  
Seismic Evaluation ◽  
Moment Frames ◽  
Moment Frame ◽  
Braced Frame ◽  
Shear Connections ◽  
Seismic Force ◽  
Steel Building ◽  
Story Drift ◽  
Moment Resisting

Maximum seismic inelastic drift demand in a steel building with braced frames as primary seismic-force-resisting (SFR) system tends to concentrate in few stories without considering inherent participation of designed gravity-force-resisting (GFR) system in actual structural stiffness and strength. The influence of GFR system on stiffness and strength can be taken into account by considering the composite action in beam-to-column shear connections that exist in modern steel building construction to form actual semi-rigid moment-resisting frames. Therefore, modeling semi-rigid moment frames as an equivalent to the GFR system in braced frame buildings could be utilized as a representative to the strength provided by gravity frames. This paper presents a seismic evaluation of a six-story chevron braced frame, with and without semi-rigid moment frame. Four different cases are investigated under a set of ground motions and results are discussed in terms of story drift distribution along the height. The results pointed out that the current findings lay a foundation to conduct further investigation on the seismic performance of braced frames as designed SFR system together with GFR system.

Analysis of Octagonal Pile Supporting Offshore Wind Turbines Under Wave Loads

2014 ◽  
Author(s):  
Serena Lim ◽  
Longbin Tao
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Computational Cost ◽  
Offshore Wind ◽  
Computational Time ◽  
Offshore Wind Turbine ◽  
Wave Loads ◽  
Element Method

Offshore wind energy development has gained considerable momentum around the world as wind is stronger and steadier offshore compared to land. This has led to a significant increase in production in recent years, especially offshore wind turbine embedded in shallow waters, such as the recent large scale offshore wind farms in the Northern Europe region. Being at the offshore waters, the wind turbines are subjected to harsh environment. The pile supporting the wind turbine must be reliable and able to withstand such sea condition. It is an important part of the design to study the structural behaviour of the piles under the wave loads. Due to the significant capital cost associated with the fabrication of the large circular cylinders, a new recommended innovative design to overcome such problem is to substitute the circular cylinder with a vertical monopile of octagonal cross-sectional shape. This paper describes the development of an efficient numerical model for structural analysis of wave interaction with octagonal pile using a modified semi analytical Scaled Boundary Finite Element Method (SBFEM). In contrast to the existing solutions obtained using the traditional methods such as the Finite Element Method (FEM) which typically suffer from high computational cost and the Boundary Element Method (BEM) which faces limitation from fundamental equations and problems with singularities. The most prominent advantage that SBFEM has over the FEM is in terms of the number of elements used for calculation and hence a reduction in computational time. When compared with BEM, the SBFEM does not suffer from computational stability problems.

scholarly journals The effect of number and position of braced frames on column behavior of the dual steel structural system (MRF and EBF) (With a view on amplified seismic load)

2015 ◽  
Vol 37 ◽  
pp. 277
Author(s):  
Sajjad Mohammadi ◽  
Abd-ol-Reza Sarvghad Moghaddam ◽  
Alireza Faroughi
Keyword(s):  
Seismic Design ◽  
Structural Model ◽  
Seismic Load ◽  
Structural System ◽  
Braced Frames ◽  
Moment Frame ◽  
Moment Capacity ◽  
Moment Resisting Frame ◽  
Moment Resisting

In seismic design of structures, determination of number and position of braced frames, considering the architectural scheme of projects, is usually confronted by obstacles. Due to this fact, in some cases, selecting the best location and number of braced bays has led to mistakes in determination of their adjacent members (columns) design loads. One of the seismic design requirements of lateral resisting system is to control the columns adjacent to braced bays for load combinations of amplified seismic load, which is a function of over-strength factor of the structure. This research aims to present and introduce the best structural model of number and position of braced frames in a structural system, such as steel moment resisting frame and eccentric braces dual system; because in 3rd revision of Iranian 2800 standard of seismic provision, there are statements and criteria provided only for capacity of moment frame, not for braces. Though the amplified seismic load function is controlled in models which columns are connected to braces in 2 directions, and seismic loads are applied in those 2 directions, number of damage hinges (Exceeding CP) is significantly increased in comparison to the models with straggly braces. As the increase in axial force of these columns leads to decrease in their moment capacity (despite controlling the amplified seismic load provision), columns in dual systems that resist flexure, would be damaged and exceed the collapse threshold much sooner than other columns. This important fact is not presented in Iranian or even American codes and provisions.

scholarly journals STRESS-STRAIN BEHAVIOR OF BLADES WITH NON-ENTIRE STRUCTURE FOR MINE AXIS FLOW FAN

2019 ◽  
Vol 2 (4) ◽  
pp. 282-289
Author(s):  
Evgeny Russky ◽  
Pavel Kosykh
Keyword(s):  
Finite Element Method ◽  
Aluminum Alloy ◽  
Rotational Speed ◽  
Honeycomb Structure ◽  
Stress And Strain ◽  
Light Weight ◽  
Strain Behavior ◽  
Entire Structure ◽  
Increase Productivity ◽  
Core Rod

The work is devoted to development issue of construction of working wheel blades satisfying conditions of strength when peripheral speed at end of the blades is more than 140 m/s. Due to high rotational speeds cast blades do not have required strength, therefore it is important to develop light-weight construction allowing to increase rotational speed of fan rotor. The calculations of strength of blades with various honeycomb structure are carried out with finite-element method at software. Dependences of stress and strain distributions on rotational speed of the rotor. Development of core rod of working wheel blade of axis flow fan of VOD series in form of honeycomb structure from aluminum alloy AK7 allows to increase rotational speed of the fan in 1.8 times. Consequently, it allows to increase productivity of the fan in the same times.

scholarly journals Inelastic dynamic analysis of steel structures

1975 ◽  
Vol 8 (4) ◽  
pp. 273-277
Author(s):  
J. Lord ◽  
J. B. Hoerner ◽  
M. Zayed
Keyword(s):  
Bending Moment ◽  
Steel Structures ◽  
Braced Frames ◽  
Moment Frames ◽  
Moment Frame ◽  
Braced Frame ◽  
Panel Zone ◽  
Aspect Ratios ◽  
Linear Behaviour ◽  
Zone Deformation

This paper updates a previously described analytical approach (1,2) using computer technology to investigate the time-dependent material non-linear behaviour of two dimensional moment-frame, truss-frame, and braced-frame steel structures during significant excursions into the post-elastic range. The approach includes considerations for energy analysis; element buckling; stable or unstable mechanism formation; yield capacity reduction resulting from interaction of axial load and bending moment; stiffness degradation; P-δ effects; viscous damping; joint panel zone deformation; and also incorporates a suitable element load-deformation relationship. The computer program NLDYN2 which incorporates this approach has been implemented successfully on many steel structures ranging from 60-story moment frames to braced frames having aspect ratios of up to 10.

Study of Bracing Force Acting at Mid-Span of Beam of Single-Span Portal Frame

2013 ◽  
Vol 405-408 ◽  
pp. 869-872 ◽  
Author(s):  
Wen Wen Jia ◽  
Deng Feng Wang
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Ultimate Load ◽  
Structural Parameters ◽  
Research Work ◽  
Nonlinear Finite Element ◽  
Nonlinear Finite Element Method ◽  
Portal Frame ◽  
Overall Stability ◽  
Lateral Constraint

The brace at the mid-span of beam of portal frame provides lateral constraint and improves its overall stability. By the nonlinear finite element method, the influences of structural parameters on the required bracing force for the beam bearing ultimate load were investigated when only one brace acting on the upper flange of beam at mid-span. The bracing force is correlated to the failure mode and configuration of beam of portal frame. The failure of beam trends to be controlled by the strength and the required bracing force increases when the stiffness of column increases. The required bracing force corresponding to the beam subjected to the ultimate load increases when the span of beam or the width of beam flange increases. The research work can be used as reference for the brace design for beam of portal frame.

scholarly journals Impacts of Mooring-Lines Hysteresis on Dynamic Response of Spar Floating Wind Turbine

Energies ◽  
2021 ◽  
Vol 14 (8) ◽  
pp. 2109
Author(s):  
Weimin Chen ◽  
Shuangxi Guo ◽  
Yilun Li ◽  
Yijun Shen
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Wave Loads ◽  
Mooring Lines ◽  
Hysteresis Behavior ◽  
Floating Wind Turbine ◽  
Motion Responses ◽  
Element Method

Floating wind turbines often experience larger-amplitude motions caused by wind and ocean wave loads, while mooring-lines, such as catenary and taut mooring-lines, make the structure configurations along with an analysis of the global response more complicated compared to a fixed support foundation. Moreover, the restoring performance of dynamic mooring-lines exhibits a significant hysteresis behavior, and this hysteresis behavior may have profound impacts on the structural response of floating wind turbines under environmental loads. In this study, using the coupled finite element method, a dynamic simulation model is developed to study the motion responses of a spar floating wind turbine under consideration of mooring-lines hysteresis. In order to consider large-amplitude motion and nonlinear behaviors of catenary mooring-lines, a FEM (finite element method) model is developed based on a combination of 3D nonlinear beam elements and the super-element approach, and the interaction between mooring-lines and seabed is also included. Using our FEM numerical simulations, firstly, the restoring performance of mooring-lines and its hysteresis behavior are studied. Then, the motion responses, e.g., the displacements of the spar float undergoing various wave loads, are examined. The numerical results show that: the restoring stiffness of mooring-lines exhibits significant hysteresis behavior, and the restoring force is directionally dependent. Due to the hysteresis of restoring performance, for a case of regular wave conditions, little change of the spar surge in a steady-state is seen; however, for a case of extreme wave loads, the motion response gets about 14.4% smaller, compared with the quasi-static cases.

Practical design (aseismic) of steel structures

1979 ◽  
Vol 6 (2) ◽  
pp. 292-307
Author(s):  
Henry J. Degenkolb
Keyword(s):  
Structural Design ◽  
Shear Walls ◽  
Steel Structures ◽  
Braced Frames ◽  
Moment Frame ◽  
Steel Moment Resisting Frames ◽  
Elastic Resistance ◽  
Moment Resisting ◽  
The Stability ◽  
Stability Of Structures

Structural design to resist earthquakes is different from structural design for the more usual forces in that the loads are uncertain but much larger than the elastic resistance of the structure; consequently, the engineer must be concerned with cyclic postelastic performance of materials and systems, ductility, and the stability of structures near ultimate loads.Cyclical tests on members and connections for steel moment-resisting frames indicate very stable hysteresis in the plastic range, a very desirable characteristic. Moment-frame structures, however, are subject to large deflections with consequent damage to the point where secondary effects such as P-delta may become critical. Some observations have indicated that better performance can be obtained by combining the ductile steel frame with concrete shear walls or with steel-braced frames. Tests, both in Japan and California, suggest that large amounts of energy can be absorbed and large ductilities can be achieved by using eccentric connections with steel-braced frames.

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