摘要:

Abstract:This paper illustrates the application of an effective optimization procedure for the design of prestressed concrete cellular bridge decks consisting of single‐ and two‐cell box girders or voided slab systems. An approximate live load moment analysis using the finite‐strip method and finite‐difference techniques that determines moment sensitivities to changes in the deck depth and flange thickness is proposed for box girder decks. The optimization process is much simplified by eliminating the need of finite‐strip reanalysis at each iteration. The optimal design is formulated as a nonlinear programming problem and solved by the projected lagrangian method. The resulting solutions may be used as preliminary designs for short‐ and medium‐span highway bridges, for which cellular decks represent competitive solutions. Optimization results show that voided slab decks are more economical than box girder decks for the short span range and wide decks, and single‐cell box girders are a cost‐effective alternative for medium span range

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00381.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:In the past, implementation of active structural control strategies employing PC‐based hardware has often been problematic, and there seems to be a need to improve the understanding of the issues associated with implementation of digital control, as well as to reduce the excessive computational times required for I/O processes and calculation of control forces. Recently developed hardware based on dedicated digital signal processing (DSP) chips has offered new possibilities for control algorithm implementation. This paper discusses digital control system concepts and specific practical aspects of digital control implementation, including the use of supervision. Details regarding active structural control using the Texas Instruments TMS32OC30 DSP chip and experimental verification of the hardware performance are give

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00382.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:An efficient and robust finite‐element‐based method for estimating nonlinear responses of complex three‐dimensional structures with partially restrained connections under dynamic and seismic loading is presented. The method is developed using the assumed stress‐based finite‐element method in which the tangent stiffness can be expressed in explicit form and fewer elements are needed to model a structure. Geometric and material nonlinearities and the nonlinear behavior of partially restrained connections are considered. For the dynamic and seismic analyses, three major sources of damping are considered. They are viscous damping, hysteretic damping in the PR connections, and the hysteretic damping at the plastic hinges, if plastic hinges are developed in the structure. It is observed from the examples considered in this study that proper consideration of PR connections is essential in modeling the realistic dynamic and seismic behavior of structures. Numerical results show that the presence of partially restrained connections may not cause failure of a structure due to insufficient strength but may make serviceability constraints, e.g., the lateral deformation, more

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:In a previous study, we presented an efficient optimal structural synthesis method for truss structures in which the design variables are coordinates of the panel points, cross‐sectional areas, and discrete material kinds subjected to stress and displacement constraints. In this paper, the synthesis method is extended to solve design problems subject to stress, displacement, and fundamental natural‐frequency constraints. The design problem is formulated in terms of discrete material kinds and continuous shape and sizing variables and which are approximated by a convex and separable subproblem. The approximate subproblem is expressed in direct and/or reciprocal design variables and shape, material, and sizing sensitivities. Each subproblem is solved by a two‐stage minimization process. In the first stage, the continuous shape and sizing variables are optimized by a dual method. Second, the discrete material and continuous sizing variables are improved by a discrete sensitivity analysis. Using the proposed two‐stage minimization procedure, both the discrete material kinds and the continuous shape and sizing variables can be systematically improved to obtain an optimal solution. The rigorousness, reliability, and efficiency of the method are illustrated by applying it to the minimum cost design of truss structures subject to stress, displacement, and fundamental natural‐frequency co

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:A methodology for the geometric and material nonlinear analysis of plane steel frames suitable for implementation in a microcomputer or personal computer platform is presented. The proposed procedure takes into consideration both geometric and material nonlinearities in its formulation. Geometric nonlinearity in the form of member and frame instabilities is accounted for by the use of pseudo‐joint loads derived from the geometric stiffness matrix of the structure. Material nonlinearity in the form of cross‐sectional plastification and progressive member yielding is accounted for by the use of a cross‐sectional plastification model and the concept of effective member stiffness. Since both cross‐sectional plastification and spread of yield along member length are considered in the analysis, the proposed approach is regarded as a plastic zone model. Unlike conventional plastic zone models in which intensive computations are required to obtain solutions, the proposed model employs simplified procedures by which spread of plasticity in the structural frame is accounted for in an approximate manner. Despite its simplicity, the proposed model gives reasonably accurate results when compared with other more rigorous approaches. To verify the applicability of the approach in predicting inelastic frame behavior, the proposed method was used to analyze a variety of frame structures. The results, expressed in terms of load‐deflection responses, member forces, and moments, compared well with those obtained using other more elaborate inelastic analysi

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract:Some structures are capable of being proportioned in several different ways such that each one is a fully stressed design. This paper investigates the nature of these multiple fully stressed designs, the relationships that exist between them, and the behavior of the stress ratio method when applied to the sizing of such structures. “Basins of attraction” constructions are used to graphically portray the behavior of the stress ratio method and to compare it with those of alternative design techniques. It is shown that both attracting and repelling fully stressed designs coexist in the design space under the action of the stress ratio method. A simple modification of the stress ratio method is suggested for transforming repellers into attractors. Instances of limit cycle and chaotic behavior of the stress ratio method are also presen

ISSN:1093-9687    

DOI:10.1111/j.1467-8667.1995.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY