Preliminary Structural Design Research Articles

Some aspects of the genesis of structures

Bendsoe and Kikuchi (1988) introduced a novel approach of distributing mass within a specified design domain utilizing a stiffness-density relation obtained by homogenization of a cellular microstructure. This approach was extended to multiple loading cases and three-dimensional applications by the author and his associates (Mlejnek and Schirrmacher 1989; Mlejnek 1990). Moreover the well-known concept of explicit convex behaviour approximation together with a dual solution scheme (Fleury and Smaoui 1988) was successfully introduced to this problem. Further objectives such as eigenvalues and displacements generalized the range of application. It is the aim of this paper, to develop a simplified procedure that can be easily integrated into a FEM-analysis package. Its application requires essentially not much more than the usual FEM-technology. Nevertheless a traceable mathematical base is still maintained. A series of examples demonstrates the suitability of this approach to the preliminary design of minimal compliance structures made of isotropic materials.

Identification of flexible joints in vehicle structures

A method for identification of flexible joints in vehicle structures is presented. The method identifies the most important parameters of a joint model and estimates their values by using displacement measurements of the overall structure. Thus, the method can be used to develop simple, design-oriented joint models that are suitable for preliminary structural design. The viability of the proposed method is demonstrated by applying it to plane frame structures with flexible joints. Nomenclature b = vector of parameter estimates bj = vector of parameter estimates obtained by using the y'th data subset C — covariance matrix Cjb — covariance matrix of parameters obtained by the jth data subset / = force vector K = global stiffness matrix Kj = stiffness matrix of a joint KR = stiffness matrix of the vehicle structure without joints u = vector of displacements um = vector of measured displacements u = vector of estimated displacements jc = vector of regressor variables Z = matrix of sensitivity derivatives of the displacements with respect to the parameters of the joints j8 = vector of parameters of a joint model y = the vector of transformed joint parameters in principal direction analysis e = vector of measurement errors (n) = combinations of n objects taken m at a time Subscripts b = vector of parameter estimates s = vector of measurement errors

Decision-making in preliminary engineering design

A designer often has to deal with complex and ill-structured situations during specification synthesis and preliminary engineering design. To assist in the development of computer-aided design systems, it is desirable to capture the designers decision-making process during these design states. The research presented in this paper is towards this direction. Based on the conceptual understanding of the process, three postulates are presented. The following two postulates; (1) the decisions are neither optimum nor just satisfying but retain certain characteristics of both, (2) the design is driven by the important objective(s) among all the specified objectives, at the preliminary design, although the remaining objectives do have a weak influence on the preliminary design; are used to develop a compensatory and a non-compensatory model of the decision-making. These models are formulated with the help of fuzzy set theory and they implicitly or explicitly follow the two postulates. These models are suitable for discrete decision situations where the above mentioned postulates apply. Examples of material selection during a preliminary structural design are used to illustrate the effectiveness of these models.

Stability formulae for shear-wall frame structures

For preliminary design of shear-wall frame structures, the lowest buckling load has to be estimated, preferably using a simple and accurate formula. A simple formula is presented by modeling the structure as a shear-restrained column and solving the associated total energy functional or the governing differential equation by means of the energy approach. The formula is applicable for fixed as well as elastic support conditions and the results agree with the exact analytical transcendental solutions.

An expert system for the preliminary design of offshore topside superstructures

In this article, we discuss a knowledge-based expert system, IPDOTS, implemented for the preliminary design of offshore topside superstructures. This study is an extension of the study, described in our earlier article [1], into using an expert system for the preliminary design of offshore jacket structures. As we have already introduced the concept of knowledge–based expert systems and their application to the design of offshore structures in our earlier article, this article concentrates on the architecture of IPDOTS and how it can assist in the design of offshore topside superstructures.

Implementation of generalized optimality criteria in a multidisciplinary environment

Generalized optimally criteria methods can alleviate the computational burden of designing for many hundreds or thousands of design variables. The implementation in an Automated Structural Optimization System (ASTROS) for preliminary design of aerospace structures is described. A dual mathematical programming method is used in conjuction with a compound scaling technique. Both are applied together to minimize structural weight in example problems, including a wing model with constraints on its structural behavior and aerodynamic performance.

A Knowledge-Based Approach to Preliminary Design of Structures

Computers have been used extensively for the analysis, detailed design and drawing production of structures. However, they have not been utilized effectively in the preliminary design stage. During this stage, the structural framing schemes that are likely to offer an optimum solution for the given design constraints are identified. Once an appropriate framing scheme is selected, an analytical model which requires initial member sizes is developed to investigate the behavior and performance of the structure under the design loads. An engineer may have to perform an approximate analysis to select the preliminary member sizes; however, experienced engineers may be able to make a reasonable estimate of the required sizes using their past experience with similar structures. A prototype computer-based design tool that utilizes past engineering experience for selecting initial member sizes of structures has been developed and is described in this paper. This tool is applicable to the design of various types of structures through the use of knowledge base techniques.

ASTROS - A multidisciplinary automated structural design tool

ASTROS (Automated Structural Optimization System) is a finite-element-based multidisciplinary structural optimization procedure developed under Air Force sponsorship to perform automated preliminary structural design. The design task is the determination of the structural sizes that provide an optimal structure while satisfying numerous constraints from many disciplines. In addition to its automated design features, ASTROS provides a general transient and frequency response capability, as well as a special feature to perform a transient analysis of a vehicle subjected to a nuclear blast. The motivation for the development of a single multidisciplinary design tool is that such a tool can provide improved structural designs in less time than is currently needed. The role of such a tool is even more apparent as modern materials come into widespread use. Balancing conflicting requirements for the structure's strength and stiffness while exploiting the benefits of material anisotropy is perhaps an impossible task without assistance from an automated design tool. Finally, the use of a single tool can bring the design task into better focus among design team members, thereby improving their insight into the overall task.

Development of a PC-based expert system for the design of offshore topside structures

This paper describes the development of an integrated system, AIDOCS, for the preliminary design and analysis of fixed steel offshore topside structures. Within the framework of AIDOCS, an artificial intelligence technique is employed in the subsystem, PREDES, to assist designers in preliminary structural design. This includes the selection of topside configuration and computation of primary member sizes. The preliminary design, in symbolic representation, is converted by an interface Data Generator program to mathematical models which can be analysed by a conventional structural analysis package. A Graphic Editor has been implemented in the system to allow the designer to modify the mathematical models prior to structural analysis. A post-analysis subsystem in which optimization of structural members is carried out, based on member stress ratios and displacement per span, has also been developed.

A knowledge-based approach to the design of offshore jacket structures

A discussion is given on an alternative approach, using a knowledge-based expert system, to the design of offshore structures. The implemented expert system can assist engineers in the preliminary design of shallow-water offshore jacket structures. The system is capable of configuring and automatically generating the basic structural model of a fixed template-type steel jacket structure for analysis and design. In addition, the system allows the user to alter any of the inferred recommendations. The system is called IPDOJS (interactive preliminary design of offshore jacket structures). >

Flexural Stiffness of Rectangular Reinforced Concrete Columns

The ACI Building Code permits a moment magnifier approach for design of slender reinforced concrete (RC) columns. This approach is strongly influenced by the effective flexural stiffness EI of the column which varies due to cracking, creep, and nonlinearity of the concrete stress-strain curve, among other factors. However, the EI expressions given in the ACI Building Code are quite approximate when compared with the values of EI derived from thrust-moment-curvature relationships. This study was undertaken to determine the influence of a full range of variables on EI of slender tied rectangular RC columns bent in symmetrical single curvature under short-time loads. Approximately 9500 columns, each with a different combination of variables, were used to generate the stiffness data. The EI expresions were then statistically developed for use in slender column designs. Two sets of equations are proposed in this paper; (a) Eq. 21 through 23 for initial sizing and preliminary design of structures; and (b) Eq. 18 through 20 for use in final more accurate structural designs.

Mathematical optimization in multi-disciplinary design

This paper presents a brief discussion of mathematical optimization and the motivation for the development of more recent numerical research procedures. A review of recent developments and issues in multi-disciplinary optimization are also presented. These developments are discussed in the context of preliminary design of aircraft structures. A capability description of programs FASTOP, TSO, STARS, LAGRANGE, ELFINI and ASTROS is included.

Hibernia geotechnical investigation and site characterization

A detailed offshore site investigation was conducted in the Hibernia field in 1983 to provide engineering data for the preliminary design of a gravity base structure (GBS) for use as an oil production platform. Reliable information regarding the strength and variability of near-surface soils was needed to verify that the foundation would be capable of resisting large environmental design loads, including those induced by iceberg impacts and storm waves. This paper presents an overview of the geotechnical equipment and methods that were successfully used to complete the investigation, major results of the field and laboratory program, and an interpretation of soil strength parameters needed for analysis of GBS stability under the design loads. Results are presented that confirm that the preshear density and effective confining pressure, or "state," of underlying sand elements are major factors that must be considered when establishing design parameters for GBS structures. It is demonstrated that consideration of state changes resulting from GBS installation is important in the analysis of granular soil resistance under both drained and undrained loading conditions. Failure to account for this effect could lead to an unconservative design. Key words: Hibernia, offshore site investigation, CPT, sand strength, state parameter.

Transverse vibrations of a trapezoidal cantilever plate of variable thickness

N ATURAL frequencies of a trapezoidal cantilever plate of variable thickness, which model an aircraft wing structure approximately, are determined using energy techniques. Characteristic orthogonal polynomials in two variables are constructed to describe the structural deflections, which are used in the Rayleigh-Ritz method to obtain the natural frequencies. The fundamental natural frequencies for different parameter values are also obtained using a deflection function containing an optimized exponent. The first technique can be used to obtain the natural frequencies and corresponding mode shapes for the preliminary design of aircraft wing structures.

Finite-surface spline

'Wilkinson, K., Lerner, E., and Taylor, R. F., ''Practical Design of Minimum Weight Aircraft Structures for Strength and Flutter Requirements, Journal of Aircraft, Vol. 13, Aug. 1976, pp. 614-624. Wilkinson, K., Markowitz, J., Lerner, E., George, D., and Batill, S. M., FASTOP: A Flutter and Strength Optimization Program for Lifting-Surface Structures, Journal of Aircraft, Vol. 14, June 1977, pp. 581-587. Isakson, G., Pardo, H., Lerner, E., and Venkayya, V., ASOP-3: A Program for the Optimum Design of Metallic and Composite Structures Subjected to Strength and Deflection Constraints, Journal of Aircraft, Vol. 15, July 1978, pp. 422-428. Lerner, E. and Markowitz, J., An Efficient Structural Resizing Procedure for Meeting Design Objectives, Journal of Aircraft, Vol. 16, Feb. 1979, pp. 65-71. Lerner, E., The Application of Practical Optimization Techniques in the Preliminary Structural Design of a Forward-Swept Wing, Collected Papers of the Second International Symposium on Aeroelasticity and Structural Dynamics, DGLR Bericht 85-02, Aachen, West Germany, April 1985, pp. 381-393. Stirk, M. H., Hertz, T. J., and Weisshaar, T. A., Aeroelastic Tailoring—Theory, Practice, Promise, Journal of Aircraft, Vol. 23, Jan. 1986, pp. 6-18. Sheena, Z. and Karpel, M., Static Analysis Using Aircraft Vibration Modes, Collected Papers of the Second International Symposium on Aeroelasticity and Structural Dynamics, DGLR Bericht 85-02, Aachen, West Germany, April 1985, pp. 229-232.

A knowledge-based assistant for preliminary design of framework structure. An approach based on multiple candidates.

A knowledge-based assistant for preliminary design of framework structure. An approach based on multiple candidates.

An interactive computer-aided system for preliminary structural design of plane frames. (1st report. Expression of shapes, constraints and remodeling procedure).

The present paper describes the first step in building an interactive computer-aided system for preliminary structural design of plane frames. This system is such that if an initial shape which partially satisfies design specifications is inputted by a designer, the system will automatically modify the shape so as to fulfill all specifications, or tell the designer to input an alternative shape with reference to knowledge bases. To make remodeling feasible, the design specifications are resolved into shape design variables, geometric constraints and mechanical constraints. Free design variables are determined by the forward reasoning system to fulfill constraint relations. During remodeling, the system checks inconsistency between design variables with constraint relations and generates alternative plans satisfying the constraints. Some examples of remodeling processes are given.

Combining Expert Systems and Cad Techniques

Drawings provide a medium for communicating design decisions. The dtask of preparing and changing design drawings has been simplified by various packages available for computer aided drafting (CAD). Recently, expert‐systems techniques are being used to aid the design process by monitoring and refining design decisions. Combining expert systems and CAD techniques raises issues concerning representation of the design. An expert system for evaluation of the design. An expert system for evaluation of preliminary structural designs has been implemented using an expert system shell and a CAD package. This and other similar implementations illustrate different approaces to the integration problems

Expert Systems for Structural Design

This paper considers the role the computer can have in less‐formalized phases of the structural design process, particularly during preliminary design. Since preliminary design is based largely on the designers experience, an expert systems approach to developing computer aids is appropriate. Four expert systems are presented HI‐RISE, FLODER, LOCATOR, and STRUPLE. HI‐RISE was the first system developed and serves as the basis for current research. HI‐RISE identifies a formalization for preliminary structural design as a synthesize, analyze, and evaluate paradigm. HI‐RISE illustrates that although computer aids can be developed for preliminary design, much work needs to be done before such aids can be practical. FLODER is an expert system that addresses the decisions made in generating a structural grid for a building. LOCATOR proposes a methodology for generating alternative placement schemes for a lateral load resisting system on a given grid. STRUPLE serves as a preprocessor to the synthesis part of the preliminary design by using past experience to identify the structural subsystems and materials relevant to the current design.

A parameter study of the full-range axisymmetric response of uniformly loaded circular plates

Incremental elasto-plastic large deflection equations and their solution via a finite-difference version of the DR-algorithm are outlined as background to a parametric study of the axisymmetric full-range response of uniformly loaded circular plates. Stocky and slender plates with four combinations of flexural and extensional edge conditions are studied. The parametric results for deflections etc. illustrate the limits on the response variation in the full-range regime due to changes in the slenderness as well as the flexural and extensional edge conditions. The results of the study are presented in dimensionless graphical format and, therefore, may be useful in the preliminary design of circular plate structures.