Optimisation of cold-formed steel (CFS) structures can be challenging due to the complex behaviour of thin-walled CFS sections affected by different buckling modes. In this paper, a coupled framework ...is presented for element and structural level optimisation of CFS portal frames, under serviceability limit state (SLS) and ultimate limit state (ULS) conditions, using Genetic Algorithm. First, CFS lipped-channel beam sections are optimised with respect to their flexural capacity determined in accordance with the effective width method specified in Eurocode 3 (EC3). The relative dimensions of the cross-section are considered as the main design variables, while the EC3 plate dimensions and slenderness limits and a number of manufacturing and end-use constraints are taken into account in the optimisation process. The results show that the optimum CFS sections exhibit significantly higher (up to 84%) ultimate capacity compared to the standard lipped channel sections with the same plate width and thickness. The structural level optimisation is then carried out to obtain the optimal design solution for a long-span CFS portal frame with knee braces under SLS and ULS conditions. Compared to conventional optimisation using standard cross-sections, it is shown that the proposed coupled framework leads to more cost-effective solutions (up to 20% less structural material) by using the more efficient CFS cross-sectional shapes optimised for generic applications. The results also indicate that optimising the frame geometry and knee brace configuration can noticeably improve the structural performance and reduce the required structural weight, especially when both ULS and SLS conditions are considered.
•A coupled element and structural level optimisation framework is proposed for CFS portal frames.•Real-Coded GA is adopted by considering manufacturing and EC3 design constraints under SLS and ULS.•Optimised sections possess up to 84% higher flexural capacity compared to their standard counterparts.•Coupled framework reduced the structural weight up to 20% by using sections optimised for generic applications.•Optimising frame geometry and knee brace configuration further reduced the structural weight up to 17%.
The assessment of ship structural reliability involves the quantification of hull girder ultimate bending capacity. Traditionally, Smith’s method is employed for the probabilistic modeling of ...capacity. The modeling uncertainty associated with Smith’s method is considered by an independent multiplicative random variable Xr. As real-scale data from hull collapses are not available, the quantification of Xr is usually based on the combination of engineering judgment with more objective information, such as non-linear finite element analysis (NLFEA). In this paper, we propose a Bayesian analysis for the determination of Xr. Specifically, we use Bayesian statistical inference to estimate the parameters that characterize the probabilistic model of Xr based on expert judgment and a limited number of high-fidelity NLFEA data. We demonstrate the applicability of the method on container ships, for which two typical load scenarios are considered: (i) pure hogging moment and (ii) combined hogging moment with local bottom loads. For each load scenario, the corresponding Xr is determined. For cases where specific information from a target ship is available, a classical Bayesian updating scheme is proposed to adjust the distribution of Xr based on the individual ship’s structural characteristics. We present a numerical demonstration for the case of the MOL Comfort at the time of the accident. Finally, the impact of the proposed Xr on the failure probability estimate of a 4,400 TEU and a 9,400 TEU container ship is investigated. We show that using the proposed Xr the estimate of the uncertainty in Smith’s model prediction in pure hogging condition is considerably reduced. In addition, we demonstrate that the action of bottom local loads, which considerably decreases the hull girder ultimate strength and the reliability level of container ships in hogging, can be captured by the proposed Xr without any intervention in the conventional Smith method.
•Bayesian statistical inference is used to estimate the uncertainty in Smith’s model.•Engineering judgment and FEA data are formally combined through Bayesian analysis.•We explicitly account for the uncertainty in FEA data through likelihood formulation.•We provide new probabilistic models to estimate Smith’s model uncertainty on container ships.•The failure probability of two container ships in ultimate limit state is reassessed.
A riser conveys fluids from a subsea system to a host floater; however, oil and gas phases may alternate, increasing pipe's stress and damaging downstream facilities. This paper studies the nonlinear ...planar vibrations of a steel lazy wave riser excited by slug flow. The employed formulations comprise the Euler-Bernoulli beam model and the steady plug-flow model with a time-space-varying mass per unit length in the form of a rectangular pulse train. The equations are solved by a Runge-Kutta finite difference scheme and frequency-response curves are constructed for effective tension, curvature, usage factor and fatigue damage. The results offer a useful insight of the slugging frequencies and slug lengths that may receive attention during the design of risers.
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•Influence of two-phase flow induced vibration (2-FIV) on structural limit states for a marine riser.•The governing equations of motion are solved by Runge-Kutta-finite difference numerical analysis.•Large amplitude motions are observed at the bottom end of a steel lazy wave riser.•2-FIV can consume substantial percentage of the ULS usage factor, and cause serious fatigue damage.
•Full-scale tests on mechanical behavior of the longitudinal joint are conducted.•A progressive model is proposed to simulate mechanical behavior of the joint.•Joint opening is highly dependent on ...the axial stress level.•Upper limit of joint opening for different axial loads are reported.•Opening of the joint in hogging moment case is larger than in sagging moment case.
Longitudinal joint opening is a common distress in shield tunnel operation. Existing longitudinal joint models are mainly developed for the design of segmental lining, but the real behavior of longitudinal joints in operational tunnels may exceed the normal design range. The aims of this paper are to study the development of longitudinal joint opening with bending moment under different axial stress levels, and investigate the longitudinal joint opening in the Ultimate Limit State (ULS). Firstly, full-scale tests on the longitudinal joints that are adopted in the Shanghai Metro Line No. 13 are conducted. The longitudinal joints are continuously loaded until completely damaged. Secondly, based on the test observations, a progressive model is proposed to predict the mechanical behavior of the joint. The proposed model is then verified by the test results. Lastly, using the proposed model, the influences of the axial stress level, bolt pretightening force, concrete delamination depth and bolt corrosion depth on the mechanical behavior of the joint are investigated. The following conclusions are drawn from the analysis: (1) Longitudinal joint opening is highly dependent on the axial stress level. For the joint subjected to the same bending moment, the larger the axial load, the smaller the joint opening. (2) Generally, the joint opening decreases with the increasing of bolt pretightening force, and increases with the increasing of concrete delamination depth and bolt corrosion depth. (3) The joint opening in the ULS increases with the increasing of axial load for the sagging moment case, and decreases for the hogging moment case. The structural state based on joint opening and the effects of joint configuration are also discussed.
Summarized in this article are the major findings from a detailed damage investigation of an instrumented ductile reinforced concrete moment frame building subjected to a design-level earthquake. The ...building sustained widespread damage during the 2016 M-7.8 Kaikoura earthquake and was subsequently demolished. Prior to demolition, the structural system was extensively surveyed to document the severity and distribution of the damage sustained in the reinforced concrete frames and the flooring system. Furthermore, the building response during the earthquake was reconstructed from the acceleration records obtained from instruments installed throughout the building. The site seismic demands were also obtained from a local free-field instrument. The data collected from this damage investigation provide a high-quality dataset that is valuable to researchers investigating different parameters related to the seismic performance of reinforced concrete moment frame buildings. The dataset is published and publicly available on DesignSafe-CI (project PRJ-3444); https://www.designsafe-ci.org/data/browser/public/designsafe.storage.published/PRJ-3444v2 . The data collection methodology is described, and a roadmap for navigating the dataset is presented to support future use of the archived dataset.
Offshore Wind Turbines are increasingly being constructed in seismically liquefiable zones and monopile is one of the main foundation types for water depths of up to about 40 m. Due to the nature of ...the loading history from wind, wave, and machine loading (1P and 2P/3P), the governing loading on the monopile foundation is asymmetric cyclic overturning moment defined by maximum moment (Mmax) and minimum moment (Mmin). During earthquakes, additional lateral loads will be experienced by the foundation due to inertia as well as kinematic interaction. In addition, if the ground is liquefiable, the foundation will also lose moment carrying capacity. One of the design challenges is therefore the prediction of the long-term tilt during earthquake liquefaction. The paper proposes a framework to predict the permanent tilt for monopiles in seismically liquefiable soils. A 5 MW turbine is taken to show the applicability of the method. Parametric studies are also carried out to show the influence of different parameters affecting the tilt.
•A comprehensive review of seismic loading on monopiles.•A framework to predict the permanent tilt for monopiles in seismically liquefiable soils.•Parametric studies to understand the influence of different parameters affecting the tilt.•Flowchart of the methodology which can be coded.
A multi-purpose platform is an offshore system designed to serve the purposes of more than one offshore industry. Within the context of “The Blue Growth Farm” project, an innovative multi-purpose ...configuration, comprising a wind turbine, wave energy converters, and an internal pool to accommodate aquaculture fish cages, has been proposed. The present work proposes a framework to assess the coupled dynamic response of the multi-purpose platform in realistic environmental conditions. A simplified parametric analysis of the structure is first carried out to propose a preliminary design of the platform. The preliminary design is subsequently investigated through hydro-elastic and aero-hydro-servo-elastic coupled analyses. Modal analysis is performed through a 3D finite-element structural model. It confirms the feasibility of rigid-body hypothesis for the dynamic analysis of the support structure and manifests that the vibration modes of the structure are not excited by wave or wind loads. In order to assess the coupled dynamic responses, an aero-hydro-servo-elastic coupled numerical model is developed. The motion and structural responses in operational and survival states are investigated. A modified mean up-crossing rate method has been employed to assess the ultimate limit state. The results obtained from the present research confirm the technical feasibility of the proposed configuration and provide a reference for further studies on similar concepts.
•A novel offshore multi-purpose platform concept is proposed.•The structure design is preliminarily optimized using a parametric analysis model.•Hydroelasticity of the preliminary design is investigated.•An aero-hydro-servo-elastic coupled model is developed to simulate the coupled dynamic response of the multi-purpose platform.
•Review of experimental push-off investigations of notched connections in TCC-deck.•Establishment of a novel database with 413 tests from 25 different push-off series.•Review and discussion of ...different experimental push-off test setups.•Quantitative and qualitative study of the five connection failure modes.
This paper presents a comprehensive literature review on experimental push-off investigations of notched connections in Timber-Concrete Composite deck structures. The study has established a novel database with 413 specimens from 25 different push-off series, and includes a detailed examination of the applied push-off test setups. The results from the database are used to investigate the five known failure modes and evaluate quantitative and qualitative findings, such as influence of fasteners and material strengths, across the experimental series. This review aims to contribute to a better understanding of the notched connection and can ultimately allow for improved experimental understanding and design approaches.
At present, offshore wind turbine jacket structures are generally modeled with beam elements. The local joint flexibility and stress concentration of the joints are hardly considered. In this work, ...one jacket model is developed to consider joint stress concentration by using super-elements. Another jacket model is also developed with pure beam elements. The stress concentration is investigated between the two jacket models. Moreover, a general framework is proposed to conduct the reliability analysis with active learning Kriging approaches and one typical ultimate limit state is studied. At first, the developed jacket models are validated with the numerical simulation results of National Renewable Energy Laboratory (NREL) technical reports. Secondly, global sensitivity analysis is carried out to reduce the random parameters for the reliability analysis. In the end, the reliability analysis is conducted with active learning Kriging approaches. The results show the probabilities of failure of the beam model are very sensitive to the assumed stress concentration factors. More importantly, it is noticed that active learning Kriging approaches can efficiently and accurately assess the probabilities of failure. Compared with the traditional Monte Carlo simulation approach, active learning Kriging approaches can reduce computational loads by hundreds of times and have the same accuracy.
•Sensitivity analysis of an offshore wind turbine (OWT) jacket.•Stress concentration study of the joints in the OWT jacket.•Reliability analysis of the OWT jacket with active learning approaches.•The influence of stress concentration factors on the probability of failure.
Ultimate capacity of large-span soil-steel structures Embaby, Kareem; Hesham El Naggar, M.; El-Sharnouby, Meckkey
Tunnelling and underground space technology,
February 2023, 2023-02-00, Volume:
132
Journal Article
Peer reviewed
•Evaluating the ultimate capacity of large-span soil-steel structures.•Calculating the actual straining actions induced in buried steel structures.•Comparing the ultimate capacity with ultimate limit ...state provided by current design codes.•Providing design guidelines for soil-steel structures under ultimate limit state.
The ultimate limit states provided by current design codes and standards were based on full-scale field and laboratory tests performed on soil-steel structures (SSS) of spans less than 10.0 m. Recently, the spans of SSS have increased up to 32.4 m with the tendency to exceed this record. The ultimate capacity of SSS utilizing the deepest corrugation profile, i.e., 237 mm depth and 500 mm pitch, has not been yet investigated under earth and truck loading. The current study evaluates the ultimate capacity of the world’s largest-span SSS with 32.4 m span and 9.57 m rise, using three-dimensional (3D) nonlinear finite element simulation. The investigation covered both the maximum backfill height and ultimate truck loading conditions. The 3D finite element modelling technique under ultimate loading was validated by full-scale test measurements of 10.0 m span soil-steel structure subjected to tandem axle loading. The critical straining actions obtained from the steel structure at ultimate condition was used to evaluate the ultimate limit states provided by the Canadian Highway Bridge Design Code (CHBDC, 2019) and AASHTO (AASHTO LRFD, 2019). The results revealed that the ultimate capacity of the SSS was reached without conforming to all ultimate bounds provided by the current design codes. Finally, a limit state function was proposed to account for the structure instability that may occur to the steel structure under ultimate loading condition. The proposed function successfully predicted failure in the steel structure under all cases considered in the current analysis before failure occurred in the numerical results.
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