Preliminary Structural Design Research Articles

Multi-level Pareto supported design methodology- application to RO-PAX structural design

A novel decision support methodology for concept and preliminary design of a complex ship structure is described together with its application to the structural design of large a RO-PAX ship. The multi-criteria, multi-stakeholder design problem was solved using the suggested methodology with the support of a ship-owner, Classification Society and a shipyard. Developed methodology combines three design steps for the fast generation of a different design variants regarding topological (no. of decks), geometrical (bulkhead and deck positions) and scantlings variables. For each design step different structural FEM models, load models and optimization models have been established. In the final step the full ship 3D FEM model was developed to validate and synthesize the optimal design variant using safety, weight, cost and fatigue criteria. Decision making implied multi-objective decision making (MODM) and multi-attribute decision making (MADM) procedures based on dual SLP and MOPSO optimization algorithms all combined with the stakeholders' subjective decision making (selection) on the generated Pareto frontiers. The procedure resulted in the optimal structural design of the RO-PAX ship with two superstructure decks, increased parking area on lower decks, lower VCG position, etc., combined with the considerable savings in the ship lightweight and related savings in the fuel and other operational costs.

Evaluating Structural Failure of Load-Carrying Composite Box Beams with Different Geometries and Load Conditions

The load-carrying component of wind turbine blades is a composite box beam that often consists of two spar caps and two shear webs. Local buckling of such beams usually leads to failure of spar caps and/or shear webs. As the failure modes change with cross-sectional geometries and load conditions, it is of interest to develop a method for efficient structural failure evaluation. As a correlation exists between linear buckling response and the potential structural failure, this study presents comprehensive numerical studies on the box beams with different external shapes and layer thicknesses to establish buckling mode maps that can be useful for the preliminary structural design. The results show that the changes of cross-sectional aspect ratio affect the buckling strength more than the change of the weight or the material usage when the spar cap buckling dominates the failure. Larger curvature of spar caps can significantly improve the buckling strength due to better resistance to the cross-sectional flattening. The evaluation method only uses the modeling techniques readily available in common commercial FE software, and no in-house user subroutines is needed, thus allowing the failure evaluation to be performed efficiently in the early design of the load-carrying box beams in wind turbine blades.

Development of lightweight emergency bridge using GFRP–metal composite plate-truss girder

Design of a lightweight emergency vehicular bridge comprising a GFRP–metal composite plate-truss girder and measuring 24 m in span is reported. The said bridge was designed based on optimization of an original 12-m bridge specimen. The bridge, so developed, is intended to be lightweight, structurally sound with modular feasibility, and representative of a construction that is less time consuming overall and fully exploits advantages offered by the use of inherent and complementary pultruded GFRP materials. Conceptual design and considerations of the large-scale structure were first described in detail. Subsequently, full-scale nondestructive tests were performed under on- and off-axis static loadings to evaluate the actual linearly elastic mechanical behavior of the prototype. Experimental results demonstrated that the bridge satisfactorily met the requirements of strength, overall bending stiffness, and torsional rigidity with regards to emergency-bridge applications. Being recognized as the most critical loading case for emergency bridges with major influence on load distribution among truss girders, the lateral live-loading distribution was assigned great importance during design of the unique bridge. Extrusion-type unidirectional GFRP profiles with high-longitudinal but low shear strengths are predominantly suitable for structures subjected to large axial forces, and are, therefore, appropriate for application in the proposed hybrid structural system. Favorable testing results demonstrated that the proposed improved version of the original conceptual design can appropriately be used as a truss girder for a new lightweight emergency bridge with a longer measured span. It is suggested that such a hybrid bridge, which demonstrates reasonably good linearly elastic behavior under service live loads, must also be designed in accordance with a stiffness criterion. Corresponding finite element and analytical analyses were performed and compared against experimental results whilst demonstrating good agreement. The elicited comparisons indicated that the established simplified analytical models and the finite element model (FEM) were both equally applicable for use in preliminary structural calculations and design of the improved bridge under states within its serviceability limit. Results reported herein are expected to make a valuable initial contribution, which in turn, could further lead to development of similar lightweight structural systems.

Pressure−impulse diagram method – a fundamental review

Accidental and deliberate explosions stemming from catastrophic events in the petroleum industry, incidents during complex manufacturing processes, mishandling or failure of domestic gas appliances or installations, terrorist attacks and military engagements, are becoming increasingly relevant in structural design. Pressure−impulse (P–I) diagrams are widely used for the preliminary assessment and design of structures subjected to such extreme loading conditions. A typical P–I diagram provides information concerning the level of damage sustained by a specific structural member when subjected to a blast load. This paper presents a state-of-the-art review describing the development of the P–I diagram method over the past 70 years, the main assumptions on which its development is based and the framework through which such a method is applied in practice. The structural analysis methods used for the derivation of P–I curves are discussed and the existing approaches are categorised according to algorithms used. A review of the P–I curve formulae proposed to date is performed, where the formulae are classified according to the formulation methods.

Sectional strength design of concrete-infilled double steel corrugated-plate walls with T-section

This paper presents the sectional strength design method of concrete-infilled double steel corrugated-plate walls with T-section (T-CDSCWs). The T-CDSCW is composed of flange and web wall elements and concrete-filled steel tubes, where the former are formed by bolt-connected steel corrugated-plates and infilled concrete while the latter behave as vertical boundary elements. Load bearing capacities of T-CDSCWs are significantly improved by the favorable combination effect between bolt-connected steel corrugated-plates and infilled concrete in the wall elements. The failure mechanism and the sectional strength design of T-CDSCWs under combined axial compression and bending moment are focused analytically, experimentally and numerically, with an assumption of no consideration of overall instability of T-CDSCWs and local buckling of the steel corrugated-plates in the wall elements. An experiment of the T-CDSCW for sectional strength prediction was carried out, and a refined finite element (FE) model of the T-CDSCW was validated by the experimental results. Based on the FE model, parametric analyses of T-CDSCWs are performed to further investigate the effects of steel ratio and sectional geometry on the load-bearing capacities. It is found that T-CDSCWs under axial compression have completely different values of load-bearing capacities when they incorporate different bending direction moments. Based on experimental and numerical results, design formulas for predicting the sectional strength of T-CDSCWs under axial compression and bending moments are proposed, providing a preliminary structural design method of T-CDSCWs.

A Numerical–Analytical Approach for the Preliminary Design of Thin-Walled Cylindrical Shell Structures with Elliptical Cut-Outs

The presence of cut-outs within thin-walled shell structures is unavoidable, holes being needed for the passage of electrical cables, fuel, or just to reduce the weight of the components. Nevertheless, the high stress concentration can lead to a premature collapse of the structure. For this reason, the preliminary design of cylindrical shell structures with holes needs a profound knowledge of the stress distribution for different loading conditions and constraints. In this paper, a parametric study of a fiber-reinforced composite shell cylinder with an elliptical cut-out has been performed. Three different loading conditions were analyzed: Tension, bending, and torsion. Ansys® script, capable of easily generating and analyzing different geometrical configurations, was used to study the dependence of the geometry on the stress distribution near the cut-out. Finally, graphical and analytical relationships were tentatively extrapolated from numerical results, aimed at linking the geometrical parameters of the cut-out to the maximum stress near the cut-out.

An efficient technique for simultaneous local and overall buckling analysis of stiffened panels

The overall buckling and local buckling of stiffened panels are two possible failure modes and thus should be concerned by engineers in the preliminary design of lightweight structures. In this paper, an efficient technique is proposed to solve the local and overall buckling problem of stiffened panels simultaneously. A weak form quadrature plate element with stiffeners located anywhere in the plates other than along the nodal lines of the plate element is formulated. Explicit formulations with an arbitrary number of nodes are given. Improvement of solution accuracy can be easily done by increasing the number of element nodes if necessary. A convergence study is performed. Several numerical examples are given. Results are compared with either existing analytic solutions or finite element data for verification. It is shown that high accuracy can be achieved with a small number of nodes. In addition, the proposed method can allow a quick analysis of simultaneous overall and local buckling behavior of stiffened panels and thus may be suitable for optimization routines in preliminary design of stiffened panels.

Design With SADSF Method and Analyses of Elastic Properties of Torsion-Loaded Double-Tee Section With Torsional Box

The work presents the results of preliminary strength design of a thin-walled structure based on double-tee section loaded with a torsion moment. One of the solutions to this problem is considered, in which the torsional box is introduced in the central part. Then, one constructs a series of solution variants that differ in the torsional box length. In the design one uses the method of statically admissible discontinuous stress fields (SADSF) assuming the condition of equalized equivalent stress in the limit state. The work is complemented with elastic FEM analyses of one of the solution variants. Using this example, one shows good load-carrying properties of structures designed with the SADSF method, and proves that they could be several times better than the properties of structures designed with traditional or intuitive ways.

Correction to: Bird-Strike Damage Analysis and Preliminary Design of Composite Radome Structure Using Smoothed Particle Hydrodynamics

The original version of this article unfortunately contained a mistake. Fig 2 was captured incorrectly. Since the analysis of bird-strike in the paper was carried out with Abaqus, it was replaced by a picture of the analysis process of Abaqus' bird-strike. The corrected Fig 2 is now given

Simplified calculation of shear lag effect for high-rise diagrid tube structures

A high-rise diagrid tube structure is a new type of building structural system that can provide greater lateral stiffness. Simplified calculation methods for diagrid tube structures have been studied by scholars in recent years, but the shear lag effects in such structures have not been reviewed. The shear lag effect will affect the lateral stiffness and stress distribution of a tube structure, so it is necessary to propose a simplified calculation method that can consider the shear lag effect of diagrid tube structures. This paper adopts the principle of stiffness equivalence to equate a high-rise diagrid tube structure to an elastic orthotropic membrane, constructs the stress function considering the shear lag effect under the action of typical horizontal loads, and obtains the stress function through the principle of energy variation. A simplified calculation method is achieved; calculation formulas for the components internal forces and structural displacements are deduced and compared with a detailed finite element program calculation to verify the method. Further, through the simplified calculation method proposed in this paper, two key issues (angle optimization of diagonal columns and evaluation of the shear lag effect at any aspect ratio) are solved in the preliminary design of this kind of structure. Results of this paper can provide a theoretical reference for the preliminary design of a diagrid tube structure. Under the basic condition that only the aspect ratio of the structure is known, the optimal angle of diagonal column can be determined, and the shear lag effect of the diagrid structure can be quickly estimated by the proposed simplified method.

Seismic performance of an existing low-rise RC building considering the addition of a new storey

DOI: 10.7764/RDLC.18.3.459 In low-rise reinforced concrete (RC) buildings, structural design is generally performed considering the seismic effects as well as the vertical loads. However, there may be situations where the additional or unpredicted loads may be encountered during the service life of the buildings. The loads that are governed from a new storey addition during the service life is a good example for these additional loads. Since the reconstruction permits and building height limits specified by the authorities may vary in life-cycle of the structures, it is critical to decide the addition of a storey to an existing building considering the structural safety concerns. In this study, an existing low-rise RC building is modelled with an added storey (subsequently planned for construction), and numerical analyses are carried out considering the extra loads of this additional storey. The aim is to evaluate the seismic performance of the structure considering this unpredicted situation which was not taken into account in the original structural design. The suitability of the preliminary structural design project to the existing building was checked by the site investigations. The results of the numerical analysis were compared with the seismic code requirements, and the seismic performance level of the building is determined. The study is intended to be useful in determining the path to be followed for the determination of the seismic capacity if existing buildings are subjected to additional loads.

Applying several soft computing techniques for prediction of bearing capacity of driven piles

Pile as a type of foundation is a structure which can transfer heavy structural loads into the ground. Determination and proper prediction of pile bearing capacity are considered as a very important issue in preliminary design of geotechnical structures. This study attempts to develop several intelligent techniques for prediction of pile bearing capacity in cohesionless soil. To show the effects of fuzzy inference system and imperialism competitive algorithm (ICA) on a pre-developed artificial neural network (ANN), two hybrid ANN models namely ICA-ANN and adoptive neuro-fuzzy inference system (ANFIS) were considered and developed to estimate pile bearing capacity. Then, results of these techniques were compared with those of ANN model and the best one among them was chosen according to the results of performance indices. Several parameters (i.e., internal friction angle of soil located in shaft and tip, effective vertical stress at pile toe, pile area, and pile length) were set as model inputs, while the output is the total driven pile bearing capacity. As a result of the developed models, coefficient of determination (R2) values of (0.895, 0.905), (0.945, 0.958), and (0.967, 0.975) were obtained for training and testing data sets of ANN, ICA-ANN, and ANFIS models, respectively. The results showed that both hybrid models are able to predict bearing capacity with high degree of accuracy; however, ANFIS receives more applicable based on used performance indices and it can be utilized for further researchers and engineers in practice.

Appraisal of historical maritime structures at Clydebank, Scotland

The site at Queens Quay, Clydebank, features maritime structures built (most recently) in 1954, 62 years ago. The land site is currently being developed for commercial and residential purposes and the maritime structures are being appraised to meet a further 60-year design life. The structures comprise a suspended concrete deck supported on driven concrete piles, which forms the basin deck structure. Within the concrete structure, a sheet pile wall retains soil from approximately +1·5 m chart datum (CD) to a historical dredged depth of around −8·0 m CD. The unique arrangement of the structure and the scant records have demanded challenging investigative engineering work to appraise the structure and determine whether remedial work is required. This paper describes the activities that were carried out to appraise the structures: desktop study, diver inspections, archive researching, preliminary structural assessments, finite-element analyses and design concept solutions.

Exploitation of a Multifunctional Twistable Wing Trailing-Edge for Performance Improvement of a Turboprop 90-Seats Regional Aircraft

Modern transport aircraft wings have reached near-peak levels of energy-efficiency and there is still margin for further relevant improvements. A promising strategy for improving aircraft efficiency is to change the shape of the aircraft wing in flight in order to maximize its aerodynamic performance under all operative conditions. In the present work, this has been developed in the framework of the Clean Sky 2 (REG-IADP) European research project, where the authors focused on the design of a multifunctional twistable trailing-edge for a Natural Laminar Flow (NLF) wing. A multifunctional wing trailing-edge is used to improve aircraft performance during climb and off-design cruise conditions in response to variations in speed, altitude and other flight parameters. The investigation domain of the novel full-scale device covers 5.15 m along the wing span and the 10% of the local wing chord. Concerning the wing trailing-edge, the preliminary structural and kinematic design process of the actuation system is completely addressed: three rotary brushless motors (placed in root, central and tip sections) are required to activate the inner mechanisms enabling different trailing-edge morphing modes. The structural layout of the thin-walled closed-section composite trailing-edge represents a promising concept, meeting both the conflicting requirements of load-carrying capability and shape adaptivity. Actuation system performances and aeroelastic deformations, considering both operative aerodynamic and limit load conditions, prove the potential of the proposed structural concept to be energy efficient and lightweight for real aircraft implementation. Finally, the performance assessment of the outer natural laminar flow (NLF) wing retrofitted with the multifunctional trailing-edge is performed by high-fidelity aerodynamic analyses. For such an NLF wing, this device can improve airplane aerodynamic efficiency during high speed climb conditions.

Membrane effect of geosynthetic reinforcement subjected to localized sinkholes

A membrane effect often occurs in geosynthetic-reinforced structures, where subsoil may have voids or sinkholes. An analytical model is proposed to estimate membrane effect of a geosynthetic reinforcement subjected to localized sinkholes. The upper interface friction in the subsided area and vertical deformation of supporting soil in the anchorage area are considered simultaneously. The maximum geosynthetic strain and maximum surface settlement, serving as key design points, can be determined. Based on the proposed method verified using a full-scale experiment, a parametric study is conducted. The results show that ignoring upper interface friction results in significant undervaluation of maximum geosynthetic strain, and ignoring vertical deformation of supporting soil leads to obvious undervaluation of maximum surface settlement. A practical design framework is also proposed and it is an applicable tool for preliminary design of geosynthetic-reinforced structures, especially for cases with soft ground.

A “direct five-step procedure” for the preliminary seismic design of buildings with added viscous dampers

In the present work a direct procedure for the preliminary seismic design of building structures with added dampers is described which represents the simplification of the so-called “five-step procedure” originally developed in 2010 by some of the authors. The procedure is applicable to yielding frame structures with a generic along-the-height distribution of inter-storey viscous dampers. It is aimed at guiding the structural engineer through the sizing of both viscous dampers and structural elements making use of an equivalent static analysis approach. First, the peak structural response under earthquake excitation is reduced by imposing an overall reduction factor accounting for both the ductility demand and the viscous damping provided by the added dampers. Second, linear damping coefficients are calculated in order to reduce the structural response according to the selected target damping ratio. Then, analytical formulas allow the estimation of peak velocities and forces in the dissipative devices, and an energy criterion is used to identify the non-linear mechanical characteristics of the actual manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA). At this initial stage of the research, the procedure appears suitable for the preliminary design phase, while correction factors for the higher modes contributions need to be applied to improve its accuracy, especially for high-rise buildings. A numerical verification of the final behaviour of the system by means of non-linear time-history analyses is recommended. An applicative example is finally developed to highlight the soundness of the procedure.

Ellipsoidal Solid Flame Model for Structures Under Localized Fire

This paper presents a model to evaluate the thermal energy transfer between a localized fire and the surfaces exposed to it, without the flame impinging the ceiling of the semi-open compartment. Although this type of fire may not have significant consequences for the structure as a whole, it is capable of triggering other disasters such as explosions and larger fires, which is why its study becomes increasingly important. Currently, this accident is analyzed using either sophisticated or semi-empirical numerical models available in the literature. The former uses computational fluid dynamics (CFD), which acceptably reproduces the fire, although with high computational cost. In turn, the semi-empirical models generally present conservative results. The proposed model presents variants in classic simple models available in the literature with the aim of being a tool that allows designers to estimate the thermal fields resulting from this type of fires at the preliminary structure design stage. In this model, the thermal analysis is performed using a finite element program, considering relevant parameters that characterize the fire such as: heat release rate, location and equivalent diameter of the fire source, among others. Through subroutines, the finite element model considers (a) a modification of hot gases temperature field based in a classic simple model and (b) proposition of a new geometry of the flame. The estimated radiative heat flux employs a solid ellipsoidal flame whose height changes according to the heat release rate. The convective heat flux is evaluated using a model for localized fire. Efficiency and accuracy of the methodology are checked by comparing the simulation results with those obtained by sophisticated models developed in fire dynamic simulator (FDS). The cases studied consider: (a) the replication of the experimental test conducted at Lulea University and (b) an offshore platform deck under localized fire action. The results of the first case confirm that the FDS replicates the experimental measurements with high accuracy. Finally, the results show that the proposed model allows to realistically represent the temperature fields generated by the fire, with relatively low computational cost compared to the CFD models for cases (a) and (b), therefore it is possible to use it to develop preliminary analyses in other fire scenarios.

A zonal safety analysis methodology for preliminary aircraft systems and structural design

ABSTRACTZonal Safety Analysis (ZSA) is a major part of the civil aircraft safety assessment process described in Aerospace Recommended Practice 4761 (ARP4761). It considers safety effects that systems/items installed in the same zone (i.e. a defined area within the aircraft body) may have on each other. Although the ZSA may be conducted at any design stage, it would be most cost-effective to do it during preliminary design, due to the greater opportunity for influence on system and structural designs and architecture. The existing ZSA methodology of ARP4761 was analysed, but it was found to be more suitable for detail design rather than preliminary design. The authors therefore developed a methodology that would be more suitable for preliminary design and named it the Preliminary Zonal Safety Analysis (PZSA). This new methodology was verified by means of the use of a case study, based on the NASA N3-X project. Several lessons were learnt from the case study, leading to refinement of the proposed method. These lessons included focusing on the positional layout of major components for the zonal safety inspection, and using the Functional Hazard Analysis (FHA)/Fault Tree Analysis (FTA) to identify system external failure modes. The resulting PZSA needs further refinement, but should prove to be a useful design tool for the preliminary design process.

Design, analysis and optimization of anisogrid composite lattice conical shells

Abstract A methodology for structural analysis and optimal design of conical anisogrid composite lattice shell structures subject to different external loads concurrently applied and multiple stiffness constraints is presented. The critical buckling load of the anisogrid lattice conical structure is exactly assessed, independently of the buckling failure mode, by means of a discrete approach. The method makes use of a full FE parametric modeling technique able to manage all the geometrical parameters of the anisogrid composite lattice structure. Additionally, the genetic algorithm NSGA-II is employed to set up an optimization procedure which allows to analyze different sets of geometrical variables, both continuous and discrete, to reach the optimal solution in terms of mass amount and fulfilling of structural and stiffness requirements, aiming at the preliminary design of an actual structure. Numerical case-studies are outlined in order to demonstrate the practical usefulness and versatility of the proposed procedure to industrial cases where the anisogrid lattice conical structure undergoes multiple external loads and various stiffness constraints must be satisfied.

Automated layout design of multi-span reinforced concrete beams using charged system search algorithm

PurposeThe preliminary layout design of structures impacts upon the entire design process and, consequently, the total cost. The purpose of this paper is to select the most economical layouts that satisfy structural and architectural requirements, while considering the reciprocal effects of cost factors and layout variables at the preliminary stages of design.Design/methodology/approachThis paper presents an automated method for cost optimization of geometric layout design of multi-span reinforced concrete (RC) beams subjected to dynamic loading by using the charged system search (CSS) algorithm. First, a novel cost optimization approach for geometric layout problems is introduced, in which both cost parameters and dynamic responses are considered in the preliminary layout design of beams. The proposed structural optimization problem with constraints on the static and dynamic equilibrium, architectural dimensions and structural action effects is solved using the CSS algorithm.FindingsThe proposed CSS algorithm for solving the cost optimization problem can be easily used for optimizing the span lengths and is also capable of working with various cost functions. The presented examples show that the proposed algorithm using the new cost optimization function provides satisfactory results and can result in over 7 per cent cost saving.Originality/valueThis is an original paper proposing a novel methodology for preliminary layout design of concrete beams.