scholarly journals Analysis of Offshore Structures Based on Response Spectrum of Ice Force

2019 ◽  
Vol 7 (11) ◽  
pp. 417 ◽  
Author(s):  
Liu ◽  
Li ◽  
Zhang
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Response Spectrum ◽  
Time History ◽  
Offshore Structures ◽  
Potential Threat ◽  
Influence Coefficients ◽  
Design Response Spectrum ◽  
Ice Force ◽  
Bending Failure

With the development of large-scale offshore projects, sea ice is a potential threat to the safety of offshore structures. The main forms of damage to bottom-fixed offshore structures under sea ice are crushing failure and bending failure. Referred to as the concept of seismic response spectrums, the design response spectrum of offshore structures induced by the crushing and bending ice failure is presented. Selecting the Bohai Sea in China as an example, the sea areas were divided into different ice zones due to the different sea ice parameters. Based on the crushing and bending failure power spectral densities of ice force, a large amount of ice force time-history samples are firstly generated for each ice zone. The time-history of the maximum responses of a series of single degree of freedom systems with different natural frequencies under the ice force are calculated and subsequently, a response spectrum curve is obtained. Finally, by fitting all the response spectrum curves from different samples, the design response spectrum is generated for each ice zone. The ice force influence coefficients for crushing and bending failure are obtained, which can be used to estimate the stochastic sea ice force acting on a structure conveniently in a static way. A comparison of the proposed response spectrum method with the Monte Carlo method by a numerical example shows good agreement.

scholarly journals Implementation of the structural performance factor (Sp) within a displacement-based design framework

2018 ◽  
Vol 51 (3) ◽  
pp. 159-165 ◽  
Author(s):  
Dion Marriott
Keyword(s):  
Response Spectrum ◽  
Time History ◽  
Structural Performance ◽  
Integration Time ◽  
Design Framework ◽  
Base Shear ◽  
Structural Behaviour ◽  
Performance Factor ◽  
Design Response Spectrum ◽  
Displacement Based

This paper discusses the application of the Structural Performance factor (SP) within a Direct Displacement-Based Design framework (Direct-DBD). As stated within the New Zealand loadings standard, NZS1170.5:2004 [1], the SP factor is a base shear multiplier (reduction factor) for ductile structures, i.e. as the design ductility increases, the SP factor reduces. The SP factor is intended to acknowledge the better-than-expected structural behaviour of ductile systems (both strength, and ductility capacity) by accounting for attributes of response that designers are unable to reliably estimate. The SP factor also recognizes the less dependable seismic performance of non-ductile structures, by permitting less of a reduction (a larger SP factor) for non-ductile structures. Within a traditional force-based design framework the SP factor can be applied to either the design response spectrum (a seismic hazard/demand multiplier), or as a base shear multiplier at the end of design (structural capacity multiplier) – either of these two approaches will yield an identical design in terms of the required design base shear and computed ULS displacement/drift demands. However, these two approaches yield very different outcomes within a Direct-DBD framework – in particular, if SP is applied to the seismic demand, the design base shear is effectively multiplied by (SP)2 (i.e. a two-fold reduction). This paper presents a “DBD-corrected” SP factor to be applied to the design response spectrum in Direct-DBD in order to achieve the intent of the SP factor as it applies to force-based design. The proposed DBD-corrected SP factor is attractive in that it is identical to the SP relationship applied to the elastic site hazard spectrum C(T) for numerical integration time history method of analysis within NZS 1170.5:2004 [1], SP,DDBD = (1+SP)/2.

Post-Yielding Behavior of Hinge-Supported Wall with Buckling-Restrained Braces in Base

2019 ◽  
Vol 13 (03n04) ◽  
pp. 1940003 ◽  
Author(s):  
Xiaoyan Yang ◽  
Jing Wu ◽  
Jian Zhang ◽  
Yulong Feng
Keyword(s):  
Response Spectrum ◽  
Time History ◽  
Shear Wall ◽  
Seismic Intensity ◽  
Nonlinear Time History Analysis ◽  
Wall Structure ◽  
Superposition Method ◽  
Structural Wall ◽  
Design Response Spectrum ◽  
Buckling Restrained Braces

A novel structural wall with hinge support and buckling restrained braces (BRBs) set in the base (HWBB) is studied. HWBB can be applied to precast manufacturing due to its considerable ductility and the separate loading mechanism in HWBB–frame structure. In elastic stage, BRBs play a brace role to make the hinged wall resist horizontal forces like a shear wall. BRBs dissipate seismic energy through plastic and hysteresis effects after yielding and the damage is only concentrated in BRBs. The performance of an HWBB is equivalent to a shear wall structure with excellent ductility and stable energy dissipation capacity. Numerical analysis indicates that the hinged wall body in the HWBB well controls the deformation mode of the structure, avoiding the concentration of story drifts, thereby protecting the remaining parts of the structure. It is revealed that the moments of the wall body will generate significant increments after BRBs yielding, and the Seismic Intensity Superposition Method is proposed to calculate the moments. In this method, nonlinear response of an HWBB can be regarded as the sum of the responses of two elastic corresponding structures excited with two parts of the seismic intensity, respectively. Modes and moments equations of the hinged wall with uniform distribution of stiffness and mass are derived, and calculation results coincide with that of the nonlinear time history analysis (NHA). For a more general case, the white noise scan method is proposed to solve the structure’s natural characteristics and to further calculate the response. Finally, the post-yielding moment calculation method and the process based on design response spectrum are proposed. It is proved that the moments from proposed Seismic Intensity Superposition Method can envelop most of the moments from NHA, and it is a good estimate of the response of HWBB in nonlinear stage.

Improved Model for Ice Force on Conical Structure

2005 ◽  
Author(s):  
W. Feng ◽  
Z. M. Shi ◽  
L. M. Liu
Keyword(s):  
Ice Sheet ◽  
Bending Moment ◽  
Offshore Structures ◽  
Structure Design ◽  
Offshore Structure ◽  
Conical Structure ◽  
Offshore Structure Design ◽  
Improved Model ◽  
Ice Force ◽  
Bending Failure

Ice force is an important factor to be taken into account for offshore structures in cold region, and the calculation method of the ice force is meaningful for the offshore structure design. Cone is now used as optimal ice-resistant structure because it can cause bending failure of the ice sheet. The interaction between ice sheet and conical structure is studied in this paper and Croasdale’s model is modified based on the field observations. The newly built model separates the ice sheet into emersed part and floating part, and the equilibrium analyses are carried out respectively. The bending moment distribution of the ice sheet is analyzed to determine the position of bending failure, which serves as a supplementary restriction. Analytic solution of ice force on conical structure is got and it is verified by the experimental data of previous researches.

Ice Forces due to Changes in Water Level and Adfreeze Bond Strength Between Sea Ice and Various Materials

1988 ◽  
Vol 110 (1) ◽  
pp. 74-80 ◽  
Author(s):  
N. Nakazawa ◽  
H. Saeki ◽  
T. Ono ◽  
T. Takeuchi ◽  
S. Kanie
Keyword(s):  
Bond Strength ◽  
Sea Ice ◽  
Water Level ◽  
Bending Strength ◽  
Construction Materials ◽  
Ice Cover ◽  
Offshore Structures ◽  
Method Of Calculation ◽  
Bending Failure ◽  
Ice Forces

In cold regions, changes in water level can induce vertical forces on offshore structures (such as caisson and tower types) when sea ice cover to structure adfreeze bonding is present. This paper summarized the theoretical analyses of vertical ice forces as well as the results of experiments which identified the parameters required when estimating sea ice adfreeze bond strength. 1) Vertical Ice Forces. The authors have proposed a method of calculation that estimates the vertical ice forces taking the following into account: bending failure of the ice cover and adfreeze bond failure (shear induced). Calculation of vertical ice forces by this method requires the following information: bending strength of ice. Young’s modulus of ice, Poisson’s ratio of ice, and adfreeze bond strength to various materials. 2) Adfreeze Bond Strength of Sea Ice. The authors have been conducting, for 6 yr, adfreeze bond strength experiments between sea ice and various common construction materials for offshore structures such as concrete and steel. The following conclusions have been drawn from this study: (i) under certain conditions, the adfreeze bond strength of sea ice greatly depends on the surface roughness of construction materials; (ii) adfreeze bond strength increases with decreasing sea ice temperature; (iii) adfreeze bond strength decreases, approaching a constant, with increasing structure diameter; (iv) adfreeze bond strength increases, approaching a constant, with increasing ice thickness; (v) adfreeze bond strength is not greatly affected by push out velocity and stress rate.

Design Ground Motion Library: An Interactive Tool for Selecting Earthquake Ground Motions

2015 ◽  
Vol 31 (2) ◽  
pp. 617-635 ◽  
Author(s):  
Gang Wang ◽  
Robert Youngs ◽  
Maurice Power ◽  
Zhihua Li
Keyword(s):  
Ground Motion ◽  
Earthquake Engineering ◽  
Response Spectrum ◽  
Time History ◽  
Earthquake Ground Motion ◽  
Engineering Practice ◽  
Period Range ◽  
Engineering Research ◽  
Interactive Tool ◽  
Design Response Spectrum

The Design Ground Motion Library (DGML) is an interactive tool for selecting earthquake ground motion time histories based on contemporary knowledge and engineering practice. It was created from a ground motion database that consists of 3,182 records from shallow crustal earthquakes in active tectonic regions rotated to fault-normal and fault-parallel directions. The DGML enables users to construct design response spectra based on Next-Generation Attenuation (NGA) relationships, including conditional mean spectra, code spectra, and user-specified spectra. It has the broad capability of searching for time history record sets in the database on the basis of the similarity of a record's response spectral shape to a design response spectrum over a user-defined period range. Selection criteria considering other ground motion characteristics and user needs are also provided. The DGML has been adapted for online application by the Pacific Earthquake Engineering Research Center (PEER) and incorporated as a beta version on the PEER database website.

scholarly journals Modified Partial Capacity Design (M-PCD): achieving partial sidesway mechanism by using two steps design approach

2021 ◽  
Vol 907 (1) ◽  
pp. 012003
Author(s):  
L S Tanaya ◽  
H Herryanto ◽  
P Pudjisuryadi
Keyword(s):  
Response Spectrum ◽  
Pushover Analysis ◽  
Structural Models ◽  
Time History ◽  
Soil Classification ◽  
Seismic Load ◽  
Capacity Design ◽  
History Analysis ◽  
Design Response Spectrum ◽  
Non Linear

Abstract Partial Capacity Design (PCD) has been developed by using magnification factor to keep some columns undamaged during major earthquake. By doing so, the structures will experience the partial side sway mechanism which is also stable, instead of the beam sidesway mechanism. However, in some cases, structures designed by PCD method failed to show the partial side sway mechanism since unexpected damages were still occurred at some columns. In this research, modification of PCD method is proposed by using two structural models in the design process. The first model is used to design beams and columns which are allowed to experience plastic damages, while the second model is used to design columns which are intended to remain elastic when the structure is subjected to a target earthquake. Two nominal earthquakes corresponding to Elastic Design Response Spectrum (EDRS) level with seismic modification factors (R) of 8.0 and 1.6 are used in the first and second structural models, respectively. It should be noted that the second model is identical to the first model except that the stiffnesses are reduced for elements to simulate potential plastic damages. This proposed method is applied to symmetrical 6 and 10 storey buildings with seismic load according SNI 1726:2012 and with soil classification of SE in Surabaya city. A Non-linear Static Procedure (NSP) or pushover analysis and Non-linear Dynamic Procedure (NDP) or time history analysis are employed to evaluate the performance of the structure. The evaluation is conducted at three earthquake levels which are nominal earthquake that is used in second model, earthquake corresponding to EDRS level, and maximum considered earthquake (MCER) specified by the code (50% higher than EDRS level). The building performances satisfy the drift criteria in accordance with FEMA 273. However, the partial side sway mechanism was not achieved at NDP analysis at maximum seismic load, MCER.

Mechanics of Ice Rubble Over Multiple Scales

2015 ◽  
Author(s):  
E. Bailey ◽  
R. Taylor ◽  
K. R. Croasdale
Keyword(s):  
Sea Ice ◽  
Large Scale ◽  
Oil And Gas ◽  
Multiple Scales ◽  
Offshore Structures ◽  
Composition And Structure ◽  
Block Level ◽  
Design Loads ◽  
The One ◽  
Sintering Processes

The mechanics of ice rubble plays an important role in many different engineering applications, including ice-structure interactions with oil and gas infrastructure, river and lake engineering, and ship-ice interactions in northern shipping lanes. Of particular interest are the massive accumulations of rubble formed by shear or compression in the ice cover, which consolidate to form sea ice ridges that can be hazards to such structures. These are common ice features in Arctic and sub-Arctic environments and as a result often govern the design loads for ships, coastal and offshore structures operating in these environments. In addition, ridge keels can scour the seafloor in relatively shallow waters posing a threat to pipelines and other subsea facilities. It is not clear what load an ice rubble feature can exert on a given structure and how it will deform. It will depend on a number of parameters including the age of the feature, its composition and structure, and its strength and failure behaviour. This paper will examine the mechanical properties of ice rubble over multiple scales. The paper will begin at the one block level, describing how ice block properties vary over time, before advancing to look at the bonding/sintering processes that occur between two ice blocks and eventually the processes that take place between multiple ice blocks (i.e., ice rubble) and large scale sea ice ridges. Particular attention will be paid to the effects temperature and pressure have on ice rubble, as these parameters are believed to be important to our understanding of its behavior.

scholarly journals Development of equivalent linear systems for single-degree-of-freedom structures with magneto-rheological dampers for seismic design application

2017 ◽  
Vol 28 (19) ◽  
pp. 2675-2687 ◽  
Author(s):  
Yunbyeong Chae ◽  
James M Ricles ◽  
Richard Sause
Keyword(s):  
Response Spectrum ◽  
Damping Ratio ◽  
Time History ◽  
Analysis Procedure ◽  
Degree Of Freedom ◽  
Single Degree Of Freedom ◽  
Single Degree ◽  
Design Response Spectrum ◽  
Simplified Analysis ◽  
Magneto Rheological

Numerous studies have been conducted for magneto-rheological dampers, but the application of magneto-rheological dampers in seismic design is limited due to the lack of a systematical design procedure. In this article, a simplified analysis procedure is proposed to estimate the response of a single-degree-of-freedom structure with diagonal bracing and a magneto-rheological damper without performing the time history analysis. The proposed simplified analysis procedure is based on the equivalent linear system of a magneto-rheological damper. The equivalent damping ratio and the effective period of the single-degree-of-freedom system are determined from the loss factor and the effective stiffness of the magneto-rheological damper based on the quasi-static model. Design response spectrum is utilized to calculate the displacement of the single-degree-of-freedom system. The equivalent damping ratio and the effective stiffness of the single-degree-of-freedom system are dependent on the displacement of the system; thus, the proposed procedure is iterated until the displacement from the design response spectrum converges. The accuracy of the simplified analysis procedure is evaluated by comparing the estimated response from this procedure with the response from the time history analysis. The results show a good agreement between two methods, demonstrating the robustness of the proposed simplified analysis procedure.

OPTIMUM DESIGN OF SPACE FRAMES UNDER SEISMIC LOADING

2001 ◽  
Vol 01 (01) ◽  
pp. 105-123 ◽  
Author(s):  
MANOLIS PAPADRAKAKIS ◽  
NIKOS D. LAGAROS ◽  
VAGELIS PLEVRIS
Keyword(s):  
Structural Optimization ◽  
Optimum Design ◽  
Large Scale ◽  
Optimization Problems ◽  
Response Spectrum ◽  
Minimum Weight ◽  
Optimization Procedure ◽  
Seismic Loading ◽  
Approximate Design ◽  
Design Response Spectrum

The objective of this paper is to perform structural optimization under seismic loading. Combinatorial optimization methods and in particular algorithms based on Evolution Strategies are implemented for the solution of large-scale structural optimization problems under seismic loading. In this work the efficiency of a rigorous approach in treating dynamic loading is investigated and compared with a simplified dynamic analysis in the framework of finding the optimum design of structures with minimum weight. In this context a number of accelerograms are produced from the elastic design response spectrum of the region. These accelerograms constitute the multiple loading conditions under which the structures are optimally designed. This approach is compared with an approximate design approach based on simplifications adopted by the seismic codes. The results obtained for a characteristic test problem indicate a substantial improvement in the final design when the proposed optimization procedure is implemented.

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