Torsionally coupled dynamic performance analysis of asymmetric offshore platforms subjected to wave and earthquake loadings

The dynamic equations of motion of asymmetric offshore platforms under three different environmental conditions:seismic action,wave action and their combination are established in this paper. In establishing these motion equations,three typical eccentricity types including mass eccentricity,rigidity eccentricity and their combination were considered,as are eccentricities that occur un-idirectionally and bi-directionally. The effects of the eccentricity type,the dynamic characteristics and the environmental conditions on the torsional coupling response of platforms are investigated and compared. An effort has also been made to analyze the inffluence of accidental eccentricity on asymmetric platforms with different eccentricity in two horizontally orthogonal directions. The results are given in terms of non-dimensional parameters,accounting for the uncoupled torsional to lateral frequency ratio. Numerical results reveal that the eccentricity type has a great inffluence on the torsionally coupled response under different environmental conditions. Therefore,it is necessary to consider the combination of earthquake and wave action in the seismic response analysis of some offshore platforms.

Optimal seismic design of reinforced concrete structures under timehistory earthquake loads using an intelligent hybrid algorithm

A reliable seismic-resistant design of structures is achieved in accordance with the seismic design codes by designing structures under seven or more pairs of earthquake records. Based on the recommendations of seismic design codes, the average time-history responses （ATHR） of structure is required. This paper focuses on the optimal seismic design of reinforced concrete （RC） structures against ten earthquake records using a hybrid of particle swarm optimization algorithm and an intelligent regression model （IRM）. In order to reduce the computational time of optimization procedure due to the computational efforts of time-history analyses, IRM is proposed to accurately predict ATHR of structures. The proposed IRM consists of the combination of the subtractive algorithm （SA）, K-means clustering approach and wavelet weighted least squares support vector machine （WWLS-SVM）. To predict ATHR of structures, first, the input-output samples of structures are classified by SA and K-means clustering approach. Then, WWLS-SVM is trained with few samples and high accuracy for each cluster. 9- and 18-storey RC frames are designed optimally to illustrate the effectiveness and practicality of the proposed IRM. The numerical results demonstrate the efficiency and computational advantages of IRM for optimal design of structures subjected to time-history earthquake loads.

Factors Affecting Vulnerability of Ready-Made Garment Factory Buildings in Bangladesh: An Assessment Under Vertical and Earthquake Loads

The importance of workplace safety in the ready-made garment(RMG) industry in Bangladesh came to the forefront after a series of disastrous events in recent years. In order to reduce the loss of lives and to ensure sustainable development, an in-depth understanding of the determining factors governing structural vulnerability in the RMG industry is needed. This research explores the key factors influencing the vulnerability of factory buildings under both vertical and earthquake loads. For this purpose,an ordered probit model was applied to 3746 RMG factory buildings to determine the key factors that influenced their vertical load vulnerability. A smaller subset of the original sample, 478 buildings, was examined by the same modeling method in greater detail to assess the key factors that influenced their earthquake load vulnerability. This research reveals that column capacity, structural system,and construction materials are the most influential factors for both types of vulnerabilities. Among other factors, soil liquefaction and irregular internal frame affect earthquake load vulnerability significantly. These findings are expected to enable factory owners and designers to better weigh the appropriate vulnerability factors in order to make informed decision that increase workplace safety. Theresearch findings will also help the designated authorities to conduct successful inspections of factory buildings and take actions that reduce vulnerability to both vertical and earthquake loads.

Behaviour of Earth Dam under Seismic Load Considering Nonlinearity of the Soil

The stability and safety are very important issues for the dam structure which are built in seismic regions. The dam body consists of soil materials that behave nonlinearly modelled with finite elements. The numerical investigation employs a fully nonlinear finite element analysis considering linear and elastic-plastic constitutive model to describe the material properties of the soil. In this paper, seismic analysis of an earthen dam is carried out using Geo-Studio software based on finite element method. Initially, the in-situ stress state analysis has been done before the earthquake established, and then its results are used in the seismic analysis as a parent analysis. A complete parametric study is carried out to identify the effects of input motion characteristics, soil behaviour and strength of the shell and core materials on the dynamic response of earthen dams. The real earthquake record is used as input motions. The analysis gives the overall pattern of the dam behaviour in terms of contours of displacements and stresses.

Dynamic Response Analysis and Vibration Control for A Fixed-Bottom Offshore Wind Turbine Subjected to Multiple External Excitations

For the offshore wind turbines installed in earthquake areas,their operation is affected by seismic loads in addition to wind and wave loads.Therefore,it is necessary to study the dynamic responses and vibration control of the wind turbines.In previous studies,the structural responses of offshore wind turbines are usually investigated in the parked case,while the blade rotation effect is usually not considered.The evaluation on the structural responses may be inaccurate under this condition,further affecting the evaluation on the vibration control performance of a control system.In view of it,this paper established a complete multi-body model of a fixed-bottom offshore wind turbine considering pile-soil interaction,and then performed simulations when the wind turbine was subjected to multiple external excitations.Continued,a single tuned mass damper(STMD)system and a multiple tuned mass dampers(MTMDs)system were applied to control structural vibrations of the wind turbine.Then,based on the construction of a simplified main structure-TMD system,TMD parameters were optimized.Finally,twelve load cases including operating and parked conditions were selected to perform simulations.Results show that the influence of the seismic excitation on blade responses is greater under the parked condition than that under the operating condition.Moreover,STMD/MTMDS exhibit better performance under the parked condition than that under the operating condition.Compared with STMD,MTMDS can better suppress the vibrations at both the fundamental and high-order modes,and exhibits significant robustness under the condition of changing soil parameters.

Seismic bearing capacity of a strip footing on rock media

The bearing capacity factors for a rough strip footing placed on rock media,which is subjected to pseudostatic horizontal earthquake body forces,have been determined using the lower bound finite element limit analysis in conjunction with the power cone programming(PCP).The rock mass is assumed to follow the generalized Hoek-Brown(GHB)yield criterion.No assumption needs to be made to smoothen the GHB yield criterion and the convergence is found to achieve quite rapidly while performing the optimization with the usage of the PCP.While incorporating the variation in horizontal earthquake acceleration coefficient(kh),the effect of changes in unit weight of rock mass(γ),ground surcharge pressure(q0)and the associated GHB material shear strength parameters(geological strength index(GSI),yield parameter(mi),uniaxial compressive strength(σci))on the bearing capacity factors has been thoroughly assessed.Non-dimensional charts have been developed for design purpose.The accuracy of the present analysis has been duly checked by comparing the obtained results with the different solutions reported in the literature.The failure patterns have also been examined in detail.