Journal of Engineering Mechanics

Predicting the response of restrained beams under fire conditions is complex owing to the development of fire-induced forces and requires finite-element or finite-differences analysis. In this paper, a simplified approach is proposed for predicting the fire-induced forces and deflections of restrained steel beams. The method applies equilibrium equations for obtaining critical fire-induced forces and then utilizes compatibility principles for obtaining temperature-deflection history of the beam. Effect of end restraints, thermal gradient, location of axial restraint force, span length, and load intensity are accounted for in the proposed approach. The validation of the approach is established by comparing the predictions from the proposed approach with results obtained from rigorous finite-element analysis. The applicability of the proposed approach to practical design situations is illustrated through a numerical example.

This paper proposes a wavelet neurocontroller capable of self-adaptation and self-organization for uncertain systems controlled with semiactive devices that are ideal candidates for control of large-scale civil structures. A condition on the sliding surface for cantilever-like structures is defined. The issue of applicability of the control solution to large-scale civil structures is made the central theme throughout the text, as this topic has not been extensively discussed in the literature. Stability and convergence of the proposed neurocontroller are assessed through various numerical simulations for harmonic, earthquake, and wind excitations. The simulations consist of semiactive dampers installed as a replacement for the current viscous damping system in an existing structure. The controller uses only localized measurements. Results show that the controller is stable for both active and semiactive control using limited measurements and that it is capable of outperforming passive control strategies for earthquake and wind loads. In the case of wind loads, the neurocontroller is found to also outperform a linear quadratic regulator (LQR) controller designed using full knowledge of the states and system dynamics.

This paper proposes a close-range digital photogrammetric system based on edge detection for structural deformation measurement. Different from traditional photogrammetric applications using discrete points, continuous edges in digital images are used here as the controlling feature in this new system. This makes it possible to acquire spatially intensive information. The system uses several digital images of the structure, taken from a number of different stations before and after the deformation is induced. Then, an image-matching algorithm based on the coplanarity condition developed here is applied to establish spatial relationships of the interested edges, identified by using a new high-precision method. These relationships are subsequently employed to acquire full-field deformation measurement of the structure. A series of experiments was conducted in the laboratory to investigate the capability of the new photogrammetric system. Results show that the system is highly accurate and suitable for structural deformation measurement. It offers noncontact, full-field, and spatially intensive measurement, in contrast with conventional contact and point-measurement.

A new method using neural networks for the transformation of results from dam models to prototypes has been proposed and validated through application to Koyna and Pine-Flat Dams, which have also been investigated by other researchers. The neural network has been called the neurotransformer. The common method for building a suitable experimental model for a dam to be tested on a shaking table is linear dimensional analysis or simply linear scaling (LS). However, because LS is theoretically applicable to linear systems, it generally provides imprecise results of transformation for extreme loading when the model or the prototype experiences noticeable nonlinearity. In this paper, it is shown through numerical simulation of the dynamic behaviour of Koyna Dam and its $1/50$ model under strong earthquakes, which cause nonlinear behavior in both the dam and its model, that transformation by neural networks is considerably more precise than LS. To show the method can also be applied to other dams, the same procedure was successfully applied to Pine-Flat Dam; again, the neurotransformer outperformed the LS.

The design of shape memory alloys (SMAs) structures against fatigue requires the computation of the stabilized mechanical state. The classical computation method, based on a plasticity-like algorithm, requires a step-by-step calculation, leading to prohibitive computation time to reach this stabilized state. To overcome this issue, we propose to extend the direct cyclic method (DCM), for elastoplastic structures, for use with the Zaki-Moumni (ZM) model for SMAs. DCM is a large time increment method in which a periodicity condition is enforced on the state variables. Comparison with the classical incremental approach shows considerable reduction in computation time.

Orthotropic plates are widely used in bridge deck systems. However, these are not commonly treated as such within design specifications, and semianalytical solutions are not presently available for all deck types. This paper develops deflection equations for infinitely wide and simply supported thin plates considering each of the three cases of orthotropy: (1) relatively torsionally stiff, flexurally soft; (2) uniformly thick plate; and (3) torsionally soft, flexurally stiff; subjected to arbitrary patch loading. These are common boundary and loading conditions encountered for bridge deck applications. The reported analytical solutions enable rapid evaluation of multiple moving patch loads to determine maximum design load effects and permit validation of numerical and finite-element methods. Application of the solutions will produce guidelines that can prescribe design demands and establish practical design simplifications for treatment of different bridge deck and slab systems in a uniform and consistent manner.

This paper presents the corrected development of viscous boundary efficiency initially proposed by Lysmer and Kuhlemeyer. The expressions of the energy ratio are given, in accordance with the original numerical results, and confirm the authors’ recommendations to minimize the reflected energy of body waves that impinge on the artificial boundary.

The influence of linear elastic support on the damper effectiveness of a cable-damper system was investigated by modeling the system as a taut string, an intermediate damper, and a spring in series. Two types of damper were analyzed in this study: (1) the linear elastic damper; and (2) the friction threshold. An exact formulation for the free vibration of the system was developed for the linear viscous damping system, and a complex eigenfrequencies equation was worked to obtain the explicit solution for the frequency shift. A damping ratio equation for different modes, which depicts the effect of the spring, was developed from the frequency shift. An effective flexibility coefficient was introduced to investigate the effect of different values of support stiffness on the effectiveness of the linear viscous damper. A universal curve family diagram was constructed, which indicated that linear elastic support reduces the effectiveness of the linear viscous damper. The universal curve obtained previously by Main and Jones was a special case of this universal curve family for the case in which the stiffness of the support approached infinity. The equation of maximum force introduced to the spring was also derived and was shown to be positively related to the cable tension force and the cable vibration amplitude at the damper attachment location. The influence of the linear elastic support on a cable-damper system with a friction threshold was also investigated by using the result of the linear viscous damper and the equivalent energy method. The result showed that the linear elastic support also reduces the effectiveness of the friction threshold. An equation showing how to select an optimal friction threshold for a stay cable was also proposed.