High-precision nonlinear comprehensive analysis of curved beams with shear effects under extreme loads via advanced mixed finite elements

This paper investigates the progressive collapse behaviour of steel concrete composite buildings subject to ground blast explosion using nonlinear dynamic analysis and conventional alternate path approach. The alternate path approach, which is a threat independent methodology, is commonly used as a design guide for minimising the potential for progressive collapse. This method may not be always conservative in assessing the robustness of the structure, especially for building subject to heavy blast loads and thus nonlinear analysis is often needed to investigate the building response under such extreme load. In the present paper, composite slab model based on equivalent area approach and composite joint model based on Eurocode's component method are proposed for nonlinear analysis of building framework. The analysis results show that a heavy blast load may wipe out a series of columns/beams at once instead of a single one. High blast pressure may also induce large lateral drift and lead to significant damage to structural elements spreading over several storeys of the building. Generally, such extensive damage cannot be captured using the alternate path approach. The present investigation recommends that nonlinear analysis should be performed in order to capture the true behaviour of such buildings subject to extreme blast loads.

The dynamic performance of simply-supported rigid-plastic circular steel plates subjected to localised blast loading

A procedure is presented for nonlinear design of offshore structures subjected to extreme loads such as strong motion earthquakes. It is proposed that the design be based on the Safety Level Earthquake (SLE) and should be checked for the Operating Level Earthquake (OLE). A reduced inelastic response spectrum should be used for the SLE. It is recommended that the preliminary design be obtained using a response spectrum approach. Nonlinear analyses should then be performed using one or more artificial time histories of ground motion compatible with the inelastic spectrum. The preliminary design could be modified as necessary to obtain the final design. The reliability of the final design could then be estimated using a deterministic-cum-probabilistic procedure. INTRODUCTION The design of an offshore platform structure for extreme loading conditions such as earthquakes, ocean waves, and high winds, as well as their combinations, is a very complex problem. This is mainly because the problem of extreme loads, when combined with critical structures such as offshore platforms requiring significant economic investment and safety considerations, warrants inclusion of additional technical considerations for the analyses and design of these structures. These include:the high magnitude and associated uncertainties in extreme loadings and the necessity to determine realistic combinations of these loadings for design purposes,the possible nonlinear behavior of structures and components due to the extreme nature of these loadings,the uncertainties involved in the material properties and the behavior of structures and components,influence of structure-water interaction including severe hydrodynamic effects,influence of soil-pile-structure interaction,modeling of novel and complex structural systems, andsevere stress and fatigue check requirements. The most important of all the above considerations is the potential nonlinear behavior of structures, including material as well as geometric nonlinearities. Nonlinear analysis and design techniques are, therefore, required for a realistic determination of the behavior of structures and to obtain an economical and rational structural design in the ult1mate-strength range. In addition, it is also important to employ a combination of deterministic and probabilistic techniques to effectively include the considerations described above, especially the uncertainties in the loadings and material properties. A design methodology is presented below, in view of the above discussion, with the main objective of being able to obtain a rational, economical, and reliable design. The procedure is mainly oriented toward seismic design, although it can be easily extended to other extreme load designs. SPECIFICATION OF DESIGN EARTHQUAKES The Design Earthquakes are specified in the form of response spectra corresponding to Operating Level (OLE) and Safety Level (SLE) Earthquakes, as recommended by American Petroleum Institute (API).I,2 For the SLE, API now specifically recommends that an investigation of the inelastic response of the platform be performed to obtain estimates of ductility demands in the structure. The OLE is intended to represent a condition of ground shaking which has a reasonable likelihood of occurring once during the lifetime of the structure. The structure should be designed to resist this earthquake in the elastic range with no or minor damage.

Simulation of buckling-driven progressive damage in composite wind turbine blade under extreme wind loads

The structural components failure of wind turbine pitch bearing system under extreme multiaxial loading conditions significantly affects operational safety and reliability. In this regard, this paper presents a method for safety performance assessment of pitch bearing structural components. Firstly, finite element mesh model and fatigue analysis model of pitch bearing structural components were established. The contact characteristics of the pitch bearing’s rolling element and raceway under various extreme combined load conditions were investigated, and the safety performance of the sealing structure was evaluated. Finally, the fatigue life assessment of the pitch bearing structural components under extreme loads ranges was accomplished using the Markov matrix of the overturning moment at various angles. The results show that the accuracy of the pitch bearing finite element mesh model are validated. Under the overturning moment Markov matrix over the entire angular range, the cumulative fatigue damage indices of the pitch bearing structural components are less than 1, no fatigue failure occurs during the 20-year design life cycle. The pitch bearing inner ring bolts are highly susceptible to damage under extreme loading and should be designed with particular concern.

Nonlinear analysis, optimization, and testing of the bridge-type compliant displacement amplification mechanism with a single input force for microgrippers

Large deflection and postbuckling behavior of Timoshenko beam–columns with semi-rigid connections including shear and axial effects

Failure probability of a jack-up under environmental loading in the central North Sea

This paper presents a theoretical analysis for determining the transverse deflection of simply supported battened beams subjected to a uniformly distributed transverse quasi-static load. The analysis considers not only the shear effect but also the discrete effect of battens on the transverse deflection of the battened beam. The analytical solution is obtained using the principle of minimum potential energy. Numerical validation of the present analytical solution is accomplished using finite element methods. The present analytical solution shows that the shear effect on the transverse deflection of battened beams increases with the cross-section area of the main member but decreases with the cross-section area of the batten. The longer the battened beam is, or the larger the moment of inertia of the main member is, the smaller the shear effect will be.

Due to increased frequency of terrorist attacks and blast threats all over the world, safety of personnel and structural integrity under blast loading is most important. This necessitates immediate research intervention to understand the behavior of various structures and structural components under such extreme loadings. In the present investigation, non-linear dynamic finite element (FE) analysis of sacrificial curved steel wall is carried out with varying angle of curvature (i.e. 0°–180°). Herein, non-linear dynamic analysis is carried out using ABAQUS ® finite element package. ConWep formulation is used for defining blast loading and performance of the wall, in terms of peak deflection, is compared to understand the effect on curvature on peak deflection. For this purpose, three-dimensional deformable 4-node, reduced integration, hourglass control with finite membrane strains elements are employed for non-linear FE analysis of curved wall. Non-linear dynamic analysis is carried out with varying angle of curvature along top one-fourth length of the wall. Further, performance of curved walls is compared with that of straight vertical wall in terms of peak deflection. Deflection at various points along the height of wall is computed and analyzed. Based on this analysis, it is observed that a simple change in curvature of wall results in considerable improvement in blast resistance with all other conditions being same.

Flexible riser tensile armour stress assessment in the bend stiffener region

PurposeThis study delineates the effect of cover thickness on reinforced concrete (RC) columns and beams under an elevated fire scenario. Columns and beams are important load-carrying structural members of buildings. Under all circumstances, the columns and beams were set to be free from damage to avoid structural failure. Under the high-temperature scenario, the RC element may fail because of the material deterioration that occurs owing to the thermal effect. This study attempts to determine the optimum cover thickness for beams and columns under extreme loads and fire conditions.Design/methodology/approachCover thicknesses of 30, 40, 45, 50, 60 and 70 mm for the columns and 10, 20, 25, 30, 35, 40, 50, 60 and 70 mm for the beams were adopted in this study. Both steady-state and transient-state conditions under thermomechanical analysis were performed using the finite element method to determine the heat transfer through the RC section and to determine the effect of thermal stresses.FindingsThe results show that the RC elements have a greater influence on the additional cover thickness at extreme temperatures and higher load ratios than at the service stages. The safe limits of the structural members were obtained under the combined effects of elevated temperatures and structural loads. The results also indicate that the compression members have a better thermal performance than the flexural members.Research limitations/implicationsNumerical investigations concerning the high-temperature behavior of structural elements are useful. The lack of an experimental setup encourages researchers to perform numerical investigations. In this study, the finite element models were validated with existing finite element models and experimental results.Practical implicationsThe obtained safe limit for the structural members could help to understand their resistance to fire in a real-time scenario. From the safe limit, a suitable design can be preferred while designing the structural members. This could probably save the structure from collapse.Originality/valueThere is a lack of both numerical and experimental research works. In numerical modeling, the research works found in the literature had difficulties in developing a numerical model that satisfactorily represents the structural members under fire, not being able to adequately understand their behavior at high temperatures. None of them considered the influence of the cover thickness under extreme fire and loading conditions. In this paper, this influence was evaluated and discussed.

Full-scale test and numerical failure analysis of a latticed steel tubular transmission tower

Design and analyses of porous concrete for safety applications

The mechanical performance of lap welded joints is essential for safeguarding the structural integrity of steel water pipelines, after a severe earthquake or other geohazard loadings. Over the past 4 years, an extensive experimental project was launched to determine the structural performance of lap welded joints under the most severe ground deformations. The research consisted of full-scale physical experiments, supported, and validated by rigorous numerical finite element simulations. The experimental results have indicated a remarkable strength and deformation capacity of the standard lap welded joints without loss of water containment. In addition questions related to local lap weld joint deformation were elucidated and the corresponding strains developed under extreme tensile or compressive loads at critical locations were quantified, demonstrating the ability of those joints to sustain a significant amount of local strain at critical locations. The latest phase of the research focuses on the behavior, analysis, and design of a new seismic resistant lap welded joint. Results of a series of additional full-scale experiments, supported by finite element numerical simulations, on the mechanical performance of the new lap welded joints under severe structural (axial and bending) loading conditions are presented herein. The new lap weld joint comprises the standard lap weld configuration but contains a small geometric projection introduced at a specific location near the field applied fillet weld. Based on current research results, a modification of the standard lap welded joint is proven to result in consistent buckling of the steel pipe cylinder and not the lap weld joint, during severe or extreme loading. The proposed joint, referred to as “Atlas Seismic Resilient or ATLAS SR-joint”, effectively allows steel pipe to not be limited by the capacity of the standard lap welded joint during strong seismic or geohazard events, and offers an efficient, reliable, yet economical solution for welded joints in steel water pipelines in geohazard areas.