Compartment level progressive collapse analysis of lightweight ship structures

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads part 1: Nonlinear finite element analysis

FEM analysis using fine-mesh shell models has been increasingly applied to the ultimate longitudinal strength analysis of ship's hull girder. However, the cost and elapsed time necessary for FEM analyses including FE modelling are still large for the design stage. Therefore, it is a common procedure to apply the Smith's method and to evaluate approximately the maximum longitudinal bending strength of a specified cross section. In this case, the effect of shear and warping stresses, which is significant in very large container ships, is not considered. The objective of this study is to propose a method of the analysis of ultimate hull girder strength under combined bending and torsion. The hull girder is modelled by a series of thin-walled beam elements and the average stress-average strain relationship of plate and stiffened panel segments under axial loads considering the effect of shear stress is implemented in the beam elements. The shift of instantaneous neutral axis and shear center can be automatically considered by introducing axial degree of freedom as well as the bending ones in the beam elements, and keeping the zero axial load condition. The proposed simplified method is applied to the test model explained in the 1st report. First, bending and torsional moment is applied to the beam model for a whole model within the elastic range. Then, the ultimate bending strength of cross sections is calculated applying the Smith's method to a beam element considering the warping and shear stresses. On the other hand, nonlinear explicit finite element analyses are adopted for analysis of the test model by using LS-DYNA. The effectiveness of present simplified analysis method of ultimate hull girder strength under combined loads is discussed comparing with the results of experiments and LS-DYNA analyses.

With the expectation of hull girder asymmetry and corresponding shift in elastic neutral axis resulting from collision damages and other forms of structural deteriorations, the interaction of vertical and horizontal hull girder capacities become quite significant in the assessment of ship structural safety. This paper therefore extends the application of a previously proposed interactive-numerical probabilistic based methodology for structural safety to assess the hull girder ultimate strength reliability of a damaged ship by means of a user-defined numerical framework. Hull girder capacity is calculated using the NS94D ultimate strength code, which is based on the Smith’s progressive collapse method. The resulting deterministic responses have been interactively linked to the NESSUS probabilistic framework so that the reliability of the damaged hull girder is predicted using an implicit limit state function defined based on a transformation of coordinates to appropriately account for any shift in the neutral axis. Random deviations of the constituent variables are directly applied to calculate the ultimate strength deterministic responses, thereby circumventing the need to characterize any correlated strength variable, which is at best subjective. The conventional approach of characterizing ultimate strength by an assumed coefficient of variation and distribution type was found to be conservative in predicting structural safety of ships relative to the proposed method. Application of the interactive-numerical technique for structural reliability is therefore considered significant for problems involving correlated random variables with unknown statistical characteristics. The method is being considered to predict the safety of cracked hull girders by accounting for the residual strength and further load bearing capabilities of deteriorated and adjacent elements.

Optimal risk-based design of reinforced concrete beams against progressive collapse

Investigations on the torsional failure characteristics of the global hull girder with large deck openings

Objectives: This nonlinear three-dimensional finite element analysis (FEA) study evaluated the effect of the number of implants, distal implant inclination, and use of angled abutments on stress magnitude and distribution in cortical bone (CB), abutment screw (AS), and prosthetic screw (PS) of implant-supported fixed complete dentures. Methods: Nonlinear 3D FEA models of mandibular fixed complete dentures were created with five, four, or three parallel straight implants (5S, 4S, 3S) and with tilted distal implants (5T, 4T, 3T). In addition, the 5T model was tested using angled abutments over the tilted distal implants to re-align the implant inclination. A 100-N axial load was applied over the first molar region (cantilever) to analyze the von Mises stresses in selected points (CB, AS, and PS). Results: The implant adjacent to the load showed the highest stresses in CB, AS, and PS. The model with three implants showed higher stresses than the ones with four and five implants. Peak stresses in the AS increased 40% from five to four implants and 100% from five to three implants. Tilting the distal implants increased stresses in CB. Peak stress in the PS increased 150% from 5S to 5T models and 100% from 4S to 4T models. Angled abutments generated lower stresses on CB and AS but higher stresses on PS. Conclusions: The results suggest that stresses in the cortical bone, abutment screw, and prosthetic screw increase when tilting the posterior implants and reducing the number of implants. The use of angled abutments decreased stresses at the bone-implant interface and in abutment screws but increased stresses on prosthetic screws.

Ultimate load capacities of mooring bollards and hull foundation structures

Design of CFRP-strengthened aluminium alloy tubular sections subjected to web crippling

The design shear resistance of an existing structure can be evaluated with analytical design procedures and numerical procedures provided by non‐linear finite element analyses. The new fib Model Code 2010 proposes different calculation methods that fall into four different levels of approximation. As the level of approximation rises, so the complexity and the accuracy of the calculated shear resistance increases. Non‐linear finite element analyses belong to the highest level of approximation, but although they are more and more becoming a customary tool in the daily design process, building codes do not provide guidance on how to perform these analyses.This paper describes non‐linear finite element analyses performed on prestressed beams, which underwent shear failure during experimental loading, in order to assess and criticize the finite element approaches. The aim of this work is to propose guidelines for numerical simulations in order to reduce model and user factors. The results obtained from the non‐linear finite element analyses have been compared with the analytical results using different levels of approximation. The design shear resistance obtained with the highest level of approximation, level IV, derived from non‐linear finite element analyses, turned out to be higher than the design shear resistance obtained with analytical procedures (levels I/II/III).

Progressive collapse is characterized by disproportionate structural failure triggered by localized damage, such as column loss under extreme loading conditions. The objective of this study is to develop a simplified analytical model that is applicable in engineering practice without the need for high-fidelity nonlinear finite element analysis. Although current design guidelines (GSA and DoD) provide analytical procedures and acceptance criteria, they do not explicitly address the tensile resistance of girders after the acceptance criteria are satisfied, particularly under large deformation and connection failure. To address this limitation, this study proposes a simplified theoretical load–displacement model for a fixed-end girder subjected to three concentrated loads, considering the effects of secondary beams and focusing on the local girder response under a column-removal scenario. The proposed model incorporates moment–axial force interactions at plastic sections in the large-deformation range. Based on one-dimensional finite element analysis results, an early-developed axial force of 0.15Fₚ at the onset of the transition stage and a residual bending moment of 0.3Mₚ during the catenary action stage are explicitly introduced to better represent actual structural behavior. The girder response is idealized using five characteristic points: yielding (Y), full plasticity (P), transition initiation (T), pure catenary action initiation (C), and collapse governed by connection failure (Fconn). Stress distributions at plastic sections are analyzed using three-dimensional finite element models to establish stress-based formulations and a rational procedure for estimating axial force at collapse. The validity of the proposed model is verified through comparisons with finite element analysis results for girders with different span-to-depth ratios. The results demonstrate reasonable agreement in terms of collapse load and displacement, particularly for slender girders, confirming the applicability of the proposed model for progressive collapse assessment.

The seismic vulnerability of a historical Basilica church located in Italy is studied by means of limit analysis and nonlinear finite element (FE) analysis. Attention is posed to the failure mechanisms involving the façade of the church and its interaction with the lateral walls. In particular, the limit analysis and the nonlinear FE analysis provide an estimate of the load collapse multiplier of the failure mechanisms. Results obtained from both approaches are in agreement and can support the selection of possible retrofitting measures to decrease the vulnerability of the church under seismic loads.

Ultimate strength of composite ships’ hull girders in the presence of composite superstructures

Simplified nonlinear progressive collapse analysis of welded steel moment frames

The initial geometric imperfection is recognized as substantially influential on the buckling behaviour and ultimate strength of stiffened plated structures. Conventionally, the initial geometric imperfection is defined in a deterministic manner, such as a hungry-horse mode, ARE mode or critical buckling mode with characteristic magnitudes. However, due to the uncertainty in manufacturing and in-service effects, the initial geometric imperfection should be better described as a random field. This paper aims to assess the effects of the stochastic nature of geometric imperfection on the ultimate strength of stiffened panel in compression. A probabilistically-based imperfection model developed by spectral representation method is applied to an orthogonally stiffened panel. A Monte-Carlo Simulation enhanced by a Latin-Hypercube Scheme (LHS) is utilized to sample the initial geometric imperfection. A series of nonlinear finite element analyses are completed to calculate the ultimate compressive strength of the case study model. With reference to the deterministic representations, the impact of the stochastic imperfection model is discussed. The present work may provide useful insights for the reliability-based ship structural assessment regarding the uncertainty due to geometric imperfection.

Importance of ‘DAF’ in evaluating structural adequacy of gravity-load designed RC buildings