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Linear quadratic regulator (LQR) formulation has been used extensively in many control systems designed for structural control applications due to its stability and robustness. However, recent results obtained from simulation, laboratory experiments, and full-scale structural applications show that it is difficult to use linear feedback-control laws to produce a significant peak-response reduction when the peak response occurs during the first few cycles of the time history. On the other hand, although another class of well-known optimal control laws, so called 'bang-bang' control, has been investigated for several decades, their potential in civil engineering structural control has not yet been exploited. The purpose of this paper is to present a new implementable control law for response control of civil engineering structures, based on the optimal bang-bang control principle. Through a series of simulation studies and experimental verification in the laboratory using a model structure, it is shown that the proposed new control law can significantly improve peak-response reduction under the same constraints imposed on the control resources as in the LQR case.

Soil is composed of particles of various sizes. Once some particles are removed in a physical or chemical process, the particle contacts and soil microstructure will change, leading to irreversible soil deformations and changes in soil behavior. Understanding soil deformation characteristics caused by particle removal under realistic stress conditions is of great importance to the safety of earth structures. In this study, soil deformations induced by particle removal under complex stress states were investigated through a series of tests on a triaxial internal erosion test apparatus in which fine soil particles were removed through salt dissolution. These tests were performed under common realistic stress conditions: isotropic stress state, triaxial compression stress state, and triaxial extension stress state. Soil deformations, both local and global, were systematically measured using a photographic method. With a gradual loss of soil particles, both the axial and radial strains and the void ratio increased. Greater soil deformations developed under a larger shear stress ratio or a higher mean effective stress. The test results provide solid evidence for verifying numerical analyses of particulate materials. [ABSTRACT FROM AUTHOR]

A genetic algorithm has been applied to the optimal design and rehabilitation of a water distribution system. Many of the previous applications have been limited to small water distribution systems, where the computer time used for solving the problem has been relatively small. In order to apply genetic and evolutionary optimization technique to a large-scale water distribution system, this paper employs one of competent genetic-evolutionary algorithms--a messy genetic algorithm to enhance the efficiency of an optimization procedure. A maximum flexibility is ensured by the formulation of a string and solution representation scheme, a fitness definition, and the integration of a well-developed hydraulic network solver that facilitate the application of a genetic algorithm to the optimization of a water distribution system. Two benchmark problems of water pipeline design and a real water distribution system are presented to demonstrate the application of the improved technique. The results obtained show that the number of the design trials required by the messy genetic algorithm is consistently fewer than the other genetic algorithms.

Development of the long-gauge fiber-optic sensor provides an excellent opportunity for structural-change localization, because it measures averaged strains over a long gauge length. A practical structural-change localization, procedure using long-gauge dynamic strains in the modal space is proposed to process the ambient vibration data of a steel-stringer bridge. The proposed procedure is easy to execute by general bridge engineers; meanwhile, it has a solid theoretical basis, thus guaranteeing its effectiveness. By theoretically deriving the magnitude ratios between the analytical strain frequency response functions (FRFs) and the estimated strain FRFs from ambient vibration data, it is proved that the proposed procedure is the same as using long-gauge strain mode shapes for change location; therefore, it is effective and much simpler for general bridge engineers to use. An ambient vibration test of a steel-stringer bridge using long-gauge fiber-optic sensors has been performed. The results of applying the proposed method to the measured and simulated data of the bridge have successfully verified its effectiveness for structural-change localization. [ABSTRACT FROM AUTHOR]

Optimal design and rehabilitation of a water distribution system is a constrained nonlinear optimization problem. A penalty function is often employed to transform a constrained into a nonconstrained optimization problem within the framework of a genetic algorithm search. A penalty factor is used for defining the penalty function and calculating the penalty cost for the solutions with constraint violation. Effective penalty factors vary from one optimization model to another. This paper introduces a self-adaptive penalty approach to artificially evolve both the penalty factor and the design solutions. Solution robustness is proposed and quantified, along with solution fitness, for representing the boundary between the infeasible and feasible solutions of a high-dimension optimization problem. The solution space of multiple dimensions is mapped onto a 2D space, providing significant insight into the self-adaptive penalty approach, which is compared with other constraint-handling techniques tested on a benchmark example. The results show that this approach is more effective than other penalty methods used for searching for optimal and near-optimal solutions. The self-adaptive penalty approach relieves modelers from tuning the penalty function and facilitates a practical optimization modeling for water distribution design. [ABSTRACT FROM AUTHOR]

Existing research on semirigid jointed frame includes only the rotational flexibility of the joint without consideration of the flexibility in the direction of the transverse shear force. This omission would lead to inaccuracies in the dynamic response of structures, especially in the nonlinear analysis. This paper investigates the dynamic behavior of a bolted joint which has flexibility in both the tangential and rotational directions. The joint is prestressed with axial tension in the bolt shank. It is represented as a virtual connection spring element at the intersection between the beam and the supporting member. The formulation of the hybrid beam–column element including the end springs is presented, and the dynamic behavior of a cantilever beam with this nonlinear semirigid joint is studied. The natural frequencies and mode shapes remain relatively unchanged only for a limited range of the joint stiffnesses, and the eigenpair is influenced by the instantaneous stiffness of the joint defined at a point on the hysteretic loop, particularly when the initial moment stiffness is small. [ABSTRACT FROM AUTHOR]

The system identification and vibration control of a cable-stayed bridge are considered difficult to achieve due to the bridge's structural complexity and system uncertainties. In this paper, based on the concept of decentralized information structures, a decentralized, nonparametric identification and control algorithm with neural networks is proposed for the purpose of suppressing the vibration of a documented six-cable-stayed bridge model induced by earthquake excitations. The control strategy proposed here uses the stay cables as active tendons to provide control forces through appropriate actuators. Each individual actuator is controlled by a decentralized neuro-controller that only uses local information. The feature of decentralized control simplifies the implementation of the control algorithms and makes decentralized control easy to practice and cost effective. The effectiveness of the decentralized identification and control algorithm based on neural networks is evaluated through numerical simulations. And the adaptability of the decentralized neurocontrollers for different kinds of earthquake excitations and for a damaged cable-stayed bridge model is demonstrated via numerical simulations. [ABSTRACT FROM AUTHOR]

Most research on semirigid jointed frames include only the rotational flexibility of the joint without consideration of the flexibility in the direction of the shear force. This paper investigates the nonlinear frictional behavior of a bolted slotted joint which includes flexibility in the tangential direction. The contact behavior at the end of the slot is also studied. The joint is prestressed with axial tension in the bolt shank. A virtual connection spring element is included at the intersection point between the beam and the column members. The formulation of the hybrid beam-column element including the end springs is presented, and the elemental matrices are also given for easy and direct implementation into finite-element analysis for static and/or dynamic loading. [ABSTRACT FROM AUTHOR]