Preliminary Structural Design Research Articles

High-Rise Structures with Belt Bracing Subject to Lateral Load

This paper presents simple methods of analysis for preliminary design of high-rise structures comprising reinforced concrete shear walls or steel trussed frames with a perimeter belt bracing structure consisting of steel trusses, subjected to horizontal loading. The methods are based on the analysis of facade rigger braced structures where horizontal steel trusses (web riggers), located in the two end facades (web frames), are positioned in a direction parallel to the lateral loading on the building. Perpendicular to the horizontal load additional horizontal steel trusses in the wind and lee sides of the building, “flange trusses”, complete the belt bracing structure. The method is focused on the contribution of the flange trusses to the lateral stiffness of the structure. The shear-lag due to differential strain in the flange frame columns along the wind and leeward facades is caused by bending and racking shear deformations in the flange trusses and is taken into account. In an approximate method the flange columns are replaced by a continuous medium of equivalent axial stiffness, i.e. a beam on an elastic foundation. The proposed methods of analysis, for use in the initial stages of the structural design of proposed tall buildings, offer simple and rapid means of establishing the influence of belt structures on horizontal deformations of the high-rise structure and internal forces.

Multi-objective optimization of a composite wing subject to strength and aeroelastic constraints

This article presents a multi-objective optimization of a large aircraft composite wing subject to multiple constraints including strength, damage tolerance, and aeroelastic stability. Based on a preliminary design of the wing structure, the investigation demonstrated a multi-disciplinary design optimization process to replace the usual manual iteration of finite element analysis in the detailed design phase. For potential application, the optimization process was performed by making the full use of the commercial software MSC Nastran, which is widely employed in aerospace industry. The optimization procedure was divided into two stages according to the design objectives. This allows the designer to interact and make decision in the design process. The first stage was focused on the minimum weight optimization subject to the multiple constraints. The laminate ply thickness and orientation of the wing skins were taken as design variables. The optimized structure weight was reduced by 44.6 per cent. The second stage was focused on aeroelastic tailoring to reduce the wing gust response to the same level as the original value of the preliminary design with a minimum weight penalty. This led to the final optimized structure weight saving by 34.5 per cent. A post-process was performed to trim the optimized skin laminate layup and ply thickness under the manufacturing constraint. For a conservative design, an option of increasing the skin laminate thickness was made and led to a slight increase of the structure weight. However, the final weight saving is still over 30 per cent. A practical optimum design of the composite wing structure with significant weight saving can be achieved by a practical approach.

FRP 보강재의 최적 단면 형상 결정 및 평가에 관한 연구

Abstract This paper deals with the structural assessment of metallic and non-metallic stiffened/monocoque plated marine structures unde r a lateral pressure load to identify appropriate combination of ma terial and section configuration, especially at the preliminary marine structural design stage. A generic rectangular plated structure is exemplified from the metallic superstructure of a marine ve ssel and itsstructural topology is varied for the structural assessment. In total 13 different structural t opologies are proposed and assessed using appropriate elastic solutions in conjunction with a set of stre ss and deflection limits obtained from practice. The geometry dimensions and weights of the structural topologies are calculated, and su bsequently, the costs of the materials used in the structural topologies are reviewed to discuss the cost-effectiveness of the materials . Finally, conclusions are made with the aim of suggesting suitable structural topology for the marine structural member considered in this paper.Keywords :Metallic stiffener section shape(금속재료 보강재 단면 형상), FRP stiffene r section shape(복합재료 보강재 단면 형상), Optimal sectionshape(최적 단면 형상), Structural assessment(구조적 평가), Weight effectiveness(중량 효율성), Cost effectiveness(비용 효율성)

A knowledge-based software for the preliminary design of seismically isolated bridges

Seismic design of isolated bridges involves conceptual, preliminary and detailed structural design. However, despite the variety of commercial software currently available for the analysis and design of such systems, conceptual and preliminary design can prove to be a non-straightforward procedure because of the sensitivity of bridge response on the initial decisions made by the designer of the location, number and characteristics of the bearings placed, as well as on a series of broader criteria such as serviceability, target performance level and cost-effectiveness of the various design alternatives. Given the lack of detailed design guidelines to ensure, at this preliminary stage, compliance with the above requirements, a “trial and error” procedure is typically followed in the design office to decide on the most appropriate design scheme in the number and location of the bearing systems; the latter typically based on engineering judgment to balance performance with cost. To this end, the particular research effort aims to develop a decision-making system for the optimal preliminary design of seismically isolated bridges, assumed to respond as single degree of freedom (SDOF) systems. The proposed decision-making process is based on the current design provisions of Eurocode 8, but is complemented by additional criteria set according to expert judgment, laboratory testing and recent research findings, while using a combined cost/performance criterion to select from a database of bearings available on the international market. Software is also developed for the implementation of the system. The paper concludes with the application, and essentially the validation of the methodology and software developed through more rigorous MDOF numerical analysis for the case of a real bridge.

Preliminary design of composite fuselage structures using analytical rapid sizing methods

The increasing use of composite materials in aircraft structures aims in reducing the structural weight significantly. In order to exploit the advantages of composite materials especially within a large-scale optimization calculation, a model for a computationally efficient structural analysis needs to be developed. In this regard, algorithms need to be developed to rapidly compute stress distribution and critical loads for both strength and stability of the composite aircraft fuselage. Therefore, sizing methods for metallic and composite orthotropically stiffened fuselage structures have been reviewed. For critical load computation, fibre fracture and inter-fibre fracture need to be taken into consideration with respect to strength. Regarding stability, the critical buckling loads of skins and stringers as well as the critical crippling load need to be taken into account. The buckling of stringers often occurs after the skin buckling load is exceeded. Hence, the postbuckling behaviour needs to be analyzed and load redistributions in the postbuckling range have to be taken into consideration. These load redistributions can generally be calculated numerically using either the finite element method or the finite strip method (Mocker and Reimerdes in Compos Struct 73:237–243, 2006) as well as analytically. In order to minimize the computational time, the postbuckling behaviour of the skins regarded as composite plates is computed analytically within this work by means of a computation of effective stiffnesses for global analysis and local failure load computation. Even though the postbuckling behaviour of metallic and composite plates has been widely studied in literature, only few work has been spent on the analytical or semi-analytical derivation of methods for the common load case of combined compression and shear loading. As the preliminary design of an aircraft fuselage requires a rapid and sufficiently accurate description of the postbuckling behaviour, the postbuckling behaviour of an orthotropic composite plate under combined compression and shear loading is analytically analyzed within the present work. The derived rapid sizing method for postbuckling significantly reduces the computational time when compared to the computational time needed for a nonlinear finite element computation. In this regard, it even allows for the consideration of postbuckling behaviour within a large-scale optimization computation of complete fuselage structures.

Input to the application of the convergence confinement method with time-dependent material behaviour of the support

The convergence confinement method is a two-dimensional, analytical method used in the design of subsurface structures and for the description of ground and system behaviour. Its purpose is to derive the required support measures from the combination of the following values: the ground characteristic curve; a model of the development of the radial deformations of the excavation surface in the axial direction of the tunnel; the support characteristic curve; and the installation time and location of the support measures. The convergence confinement method is usually employed in the preliminary design of underground structures. This article investigates the various methods of the convergence confinement method and includes comments on possible application scenarios. One point of focus considers the system-bolting of rock mass as a supporting as well as a reinforcement measure. Another view is taken on the time-dependent material behaviour of shotcrete and its adaptation to the convergence confinement method.

Explicit local buckling analysis of rotationally-restrained orthotropic plates under uniform shear

The explicit closed-form local buckling solution of in-plane shear-loaded orthotropic plates with two opposite edges simply supported and other two opposite edges either both rotationally restrained or one rotationally restrained and the other free is presented. Based on the boundary condition of the other two opposite edges, two types of plates are considered: the RR (both the edges rotationally restrained) and RF (one edge restrained and the other free) plate elements. Different plate buckled shape functions are proposed, and the approximate explicit expressions for the buckling loads are derived using the Rayleigh–Ritz method for the plate with the generic rotationally-restrained (R) boundary conditions which can be reduced to two extreme cases, i.e., simply supported (S) and clamped (C). The accuracy of the derived explicit solutions is verified by comparing the predictions with the existing solutions and numerical finite element analysis, and excellent agreements are obtained. The effects of material and boundary restraining parameters on the local shear buckling behavior of the plate elements are discussed. The derived explicit formulas for the shear buckling loads are straightforward, efficient and reliable for preliminary engineering design and analysis of composite structures under primarily shear-dominant loading conditions.

The ITER EC H&CD upper launcher: Structural design

Four ITER EC H&CD (Electron Cyclotron Heating and Current Drive) Upper Launchers will be installed in the ITER Tokamak to counteract plasma instabilities by injection of up to 20 MW of millimeter-wave power at 170 GHz. Each Launcher features a structural system which is equipped with eight beam lines in a Front-Steering arrangement. The Launcher development has reached the status of a preliminary design, since the corresponding review meeting was held in November 2009 at the ITER site in Cadarache. All design work is performed by several EU associations being contracted by Fusion for Energy (F4E). The structural design of the Upper Launcher consists of three sub-components: First of all the Blanket Shield Module (BSM), which fills the gap between the regular blankets. The BSM dissipates about 80% of the nuclear heating and envelopes the front mirrors of the mm-wave system. Further the Launcher Mainframe, which provides a rigid structure for precise and secure integration of the mm-wave system to guarantee reliable operation under all potential scenarios. Finally the internals, such as dedicated support structures for the mm-wave system, shielding elements and components for gas and coolant supply. The most challenging design aspects are proper dissipation of nuclear heating in zones of high heat flux, the mechanical integrity during plasma disruptions, the integration of sufficient shielding material and the precise alignment of the mm-wave system under tight space conditions. Furthermore the definition of efficient manufacturing routes with respect to tolerance compliance requires substantial investigation and, though the Launcher is designed for ITER lifetime, potential repair by adequate remote handling procedures must be considered. This paper presents the recent status of the preliminary structural design and outlines future design approaches with the main focus on manufacturing methods, remote handling capability of the sub-components and optimum integration of the internals to bring the EC Launcher towards the final design.

Design and Finite Element Analysis on Crown Gear Coupling of High Torque Considering Radial Restriction

In order to meet the requirements of high torque and small center distance of the twin screw pulping extruder, an improved design method of the crown gear coupling (CGC) was studied. Based on the preliminary structural design, the paper selected parameters of tooth form of the crown gear firstly, and according to the contact strength solved the tooth width, then the discussed influences of radius of displacement circle and unilateral thinning amount on tooth thickness, finally through the finite element analysis verified the design results. The results show that under the condition of radial restriction the most effective ways to increase load-bearing capability of the CGC are to improve the tooth stiffness and increase the tooth width, and the increasing of tooth width should consider the tip strength of the crown gear and avoid over-cutting. The CGC design method of the paper can meet the requirements of the twin screw extruder.

Transmission loss of orthogonally rib-stiffened double-panel structures with cavity absorption

The transmission loss of sound through infinite orthogonally rib-stiffened double-panel structures having cavity-filling fibrous sound absorptive materials is theoretically investigated. The propagation of sound across the fibrous material is characterized using an equivalent fluid model, and the motions of the rib-stiffeners are described by including all possible vibrations, i.e., flexural displacements, bending, and torsional rotations. The effects of fluid-structure coupling are account for by enforcing velocity continuity conditions at fluid-panel interfaces. By taking full advantage of the periodic nature of the double-panel, the space-harmonic approach and virtual work principle are applied to solve the sets of resultant governing equations, which are eventually truncated as a finite system of simultaneous algebraic equations and numerically solved insofar as the solution converges. To validate the proposed model, a comparison between the present model predictions and existing numerical and experimental results for a simplified version of the double-panel structure is carried out, with overall agreement achieved. The model is subsequently employed to explore the influence of the fluid-structure coupling between fluid in the cavity and the two panels on sound transmission across the orthogonally rib-stiffened double-panel structure. Obtained results demonstrate that this fluid-structure coupling affects significantly sound transmission loss (STL) at low frequencies and cannot be ignored when the rib-stiffeners are sparsely distributed. As a highlight of this research, an integrated optimal algorithm toward lightweight, high-stiffness and superior sound insulation capability is proposed, based on which a preliminary optimal design of the double-panel structure is performed.

A new approach for estimation of properties of metamorphic rocks

Rock properties play an important role in the preliminary design of structures. This research focuses on developing empirical models using multiple regression technique for prediction of physical properties of metamorphic rocks. The model considers the following parameters: drill bit diameter, bit speed, penetration rate and equivalent sound level produced during drilling. The F-test was used to check the validity of the developed models. The experimentally measured rock property values and the values calculated from the developed regression model were fairly close which indicates that the developed models could be efficiently used in prediction of intact metamorphic rock properties.

Multicriteria optimization of lightweight bridge structures with a constrained force density method

This paper deals with the preliminary shape design of three-dimensional bridge structures. For crossing wide spans, lightweight truss structures are well-suited. Due to their complex equilibrium state involving a geometrically nonlinear behaviour, the generation of an equilibrated system requires numerical form finding methods, namely the force density method for truss structures. To enforce geometric restrictions, a constrained force density method is developed. Then, the scope of the form finding method is extended to the search of optimal configurations by combining the force density method with multiobjective genetic algorithms within an integrated design process. Large scale applications illustrate the proposed strategy.

Hydrogen fuel tanks for subsonic transport aircraft

Hydrogen is since long seen as an outstanding candidate for an environmentally acceptable, future aviation fuel. Since the first studies, the design of light yet highly insulated tanks for cryogenic liquid hydrogen has been identified as one of the key enabling technologies. Despite this early recognition, the design of the tanks is nowadays still seen as crucial as aircraft tanks differ significantly from existing tanks in the automotive or aerospace sector. To enable system level feasibility studies of hydrogen fueled aircraft, a preliminary design model for aircraft liquid hydrogen tanks is developed for both foam and multilayer insulations. This model is then used to design tanks for a small regional airliner as well as a large long range transport aircraft. Foam based and multilayer insulations are compared and the sensitivity of the tank weight to the fuselage diameter and the mission fuel load is assessed. The influence of a ‘hold’ period before take-off is analyzed too. As the developed model is intended for use in the preliminary aircraft design phase, structural design or attachment issues are not addressed.

Stiffness-based design methodology for steel braced tube structures: A sustainable approach

Braced tubes are efficient structural systems for tall buildings and have been continuously used for major tall buildings since their emergence in the late 1960s. This paper presents a stiffness-based design methodology for determining preliminary member sizes of braced tubes for tall buildings. The methodology is applied to a set of buildings ranging from 40 to 80 stories tall, and parameters for the most economic design in terms of material usage are generated for representative design loadings. The impact of different geometric configurations of the structural members on the economic design is also discussed, and recommendations for the optimal geometries are made. The stiffness-based methodology, with a less iterative process, is very efficient for the preliminary design of braced tube structures, and will contribute to constructing built environments using minimum amounts of resources.

Multilevel Structural Optimization for Preliminary Wing-Box Weight Estimation

This paper deals with the weight estimation of the wing box of a commercial aircraft by means of a procedure suitable for very large liners and/or unconventional configurations for which statistical data and empirical formulas may not be sufficiently reliable. Attention is focused on the need to account for aeroelastic interaction from a very preliminary stage of the design cycle. The procedure exploits the first of three levels of a multilevel structural optimization system conceived for the preliminary design of the wing primary structure and a simplified evaluation of the cross-sectional properties. The comparison between weight estimates obtained with the present procedure and predictions supplied by available literature shows a satisfactory agreement.

The development of a preliminary structural design optimization method of an aircraft wing-box skin-stringer panels

In the current paper a methodology for the design optimization of a skin-stringer panel of an aircraft wing-box is presented. The ability to resist the compressive load is assessed through a stability study to compute the critical buckling load of the stiffened panel while the ability to resist the tensile load is assessed through damage tolerance analysis of the lower wing panels. The design methodology of the compression panel included general and local failure modes as well as panel beam column analysis that are common in aerospace compression structures. Linear Elastic Fracture Mechanics theory is applied for the design of the tension panels where the Boundary Element Method is used to perform numerical crack growth analysis. Optimization routines have been developed and the design methodology is validated by comparison with several existing skin-stringer panels from four jet aircrafts and showed a good agreement. Finally, the developed design methodology has been used to design the skin-stringer panels of one complete bay in the wing-box of a DLR-F6 aircraft.

PASSIVE CONTROL DESIGN METHOD FOR ELASTO-PLASTIC FRAME ADDED WITH VISCO-ELASTIC DAMPERS

Simplified theories are proposed for seismic response evaluation and preliminary design of elasto-plastic building structures added with visco-elastic dampers. They are based on the single-degree-of-freedom (SDOF) idealization of multistory building, and produce the control performance curve expressing the peak responses as a function of stiffness of all components, based on spectral characteristics of the earthquake. Against the target peak response, a rule to convert the SDOF design to multistory design, with consideration to distribute damper stiffness over the building height, is also presented. Accuracy of the approach is demonstrated by time history simulations over a wide range of parameters.

PASSIVE CONTROL DESIGN METHOD FOR MDOF SLIP-HYSTERETIC STRUCTURE ADDED WITH VISCO-ELASTIC DAMPER

Vicso-elastic dampers are increasingly used to reduce earthquake-induced vibration of building structures, including wood house structures which show slip hysteresis under earthquake loading. In this paper, simplified theories are proposed for seismic response evaluation and preliminary design of slip-hysteretic structures combined with visco-elastic dampers. They are based on the single-degree-of-freedom (SDOF) idealization of multistory structure, and produce the control performance curve expressing the peak responses as a function of stiffness of all components, based on spectral characteristics of the earthquake. Against the target peak response, a rule to convert the SDOF design to multistory design, with consideration to distribute damper stiffness over the height of structure, is also presented. Accuracy of the approach is demonstrated by time history simulations over a wide range of parameters.

Preliminary Thermal and Hydraulic Analysis on the ITER Upper Diagnostic Port Plug During Normal Operation and Baking

A preliminary thermo-hydraulic analysis was performed on the ITER diagnostic upper port plug. Relevant thermal and hydraulic parameters, such as coolant pressure drop, maximum structure temperature and bake-out time, were calculated for normal operation and baking. The upper port plug considered is based on the preliminary generic structure design of Princeton Plasma Physics Laboratory and the Blanket Shield Module (BSM) developed in Europe. The diagnostic shield modules are modeled so that the Korean diagnostic procurement package, which includes Vacuum Ultra-Violet (VUV) spectrometer and neutron activation system, can be integrated. The analysis provides design inputs to optimize flow in the cooling channels of the plug. The conjugated heat transfer analysis for the port plug confirms that it is important to secure accurate nuclear heat and accurate electro-magnetic (EM) force for the design of the joining flange between the BSM and the main body. Thermal analysis shows that it will take ten hours for the port plug to reach the bake-out temperature (240°C), if the window plate is heated additionally from the rear side.

Design of a ${\rm Nb}_{3}{\rm Sn}$ Magnet for a 4th Generation ECR Ion Source

The next generation of Electron Cyclotron Resonant (ECR) ion sources are expected to operate at a heating radio frequency greater than 40 GHz. The existing 3rd generation systems, exemplified by the state of the art system VENUS, operate in the 10-28 GHz range, and use NbTi superconductors for the confinement coils. The magnetic field needed to confine the plasma scales with the rf frequency, resulting in peak fields on the magnets of the 4th generation system in excess of 10 T. High field superconductors such as Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn must therefore be considered. The magnetic design of a 4th. generation ECR ion source operating at an rf frequency of 56 GHz is considered. The analysis considers both internal and external sextupole configurations, assuming commercially available Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn material properties. Preliminary structural design issues are discussed based on the forces and margins associated with the coils in the different configurations, leading to quantitative data for the determination of a final magnet design.