On the Vibrational Damping of Structural Steel Beams

In this paper, experimental results and their considerations on the vibrational damping characteristics of model beams and of actual steel highway bridges are presented. The fundamental characteristics of damping due to internal frictions of the steel beam and the friction of bearing are clarified by using three kinds of beams. Also, the damping characteristics of several actual bridges have been investigated and they are compared in this paper with the results obtained by the experiments on model beams. These results are useful for analysis of the dynamic problems of bridges

Elastic-Plastic Analysis of Suspension Bridge Towers Subjected to Earthquake Ground Motions

This paper deals theoretically with the elastic-plastic analysis of suspension bridge towers subjected to ground motions. In a previous theoretical study it was concluded that the response of the towers of a long span suspension bridge was more significant than that of suspended structures. For convenience of analysis a simplified structural system for a suspension bridge tower with finite degrees of freedom of motion was adopted, and ground disturbances of a simple shape and of an actual earthquake were used. The numerical computation were done on the Kyoto University High Speed Digital Computer, KDC-I. In this investigation some remarkable conclusions on the elastic-plastic response of the system were obtained

Random Response Analysis of a Long-span Suspension Bridge Tower and Pier with Consideration of Nonlinear Foundation

The nonlinear foundation effect upon the response of the tower and pier system of a long-span suspension bridge is investigated by the random vibration theory. As the equivalent linearlization yields the nonproportional damping matrix, the exact response is evaluated both through the frequency domain analysis and the complex mode analysis. Also discussed is the approximate response analysis using classical normal modes for the practical design procedure

Fundamental Studies on Earthquake Response of a Long Span Suspension Bridge

This paper deals theoretically with the earthquake response of a long span suspension bridge. An exact solution of this problem is seldom possible because of the complexity of the structure and the earthquake motions. For the convenience of the analysis a simplified structural system of the suspension bridge with finite degrees of freedom of motion is adopted, and the ground disturbances are assumed to be a simple shape. To simplify the problem, linearized deflection theory of suspension bridges is employed. Some parts of numerical calculation, natural frequencies and modes of the system, had been done on a high speed digital computer. On this investigation some response spectra are given, and the fundamental earthquake response characteristics of the suspension bridge are made clear

Studies on the Responses of Multi-degrees of Freedom Systems Subjected to Random Excitation with Applications to the Tower and Pier Systems of Long Span Suspension Bridges

In this paper the responses of multi-degrees of freedom systems with applications to the pier and tower systems of long span suspension bridges due to earthquake motions are studied by the stochastic process theory and the results are compared with the direct-integration. For the present system, foundation conditon coupled with the pier dimensions has significant effects on the structural dynamic characteristics. The response behaviors and then their evaluation become complex for some foundation ranges. Here, on the assumption that the normal mode analysis can be applied, the direct-effects of individual modes and their cross-effects to the dynamic response characteristics are investigated by simulating earthquake motions to a suitable form

On the Experimental Stress Analysis of a Composite Box Girder Bridge

Experimental researches on composite box girders have been carried out on several bridges and test models and their structural behaviors are gradually becoming clear. The results of the measured stresses obtained at the Yamasu Bridge built in Kyoto in 1955 and the considerations of these results are described in this report. There is good agreement between the theoretical predictions and the actual behavior

Three-Dimensional Response Spectra for Multiple-Support Input Motions

New response spectra for multiple-support input motions are presented to study the seismic responses of long-span bridges. Three-dimensional response spectra are defined using the response of simple beams with various natural periods. These spectra clearly verify the dominant vibration mode and the critical location of the maximum response. Numerical examples using the earthquake records observed by a newly-installed array at the Akashi Kaikyo bridge construction site in Japan show that the different input motions to each support produce different predominant vibration modes compared with the identical excitation case. It has also been observed that response usually decreases when multiple-support input motions with phase lags are considered. The ordinary response spectra method is also examined and it has been found that the approximated values using the RMS method overestimated the maximum response

Seismic Damage Assessment of RC Structures using Different Hysteretic Models

Estimation of seismic damage of a structure varies depending on the assumed hysteretic rules and input excitations due to indices being calculated from earthquake response time histories. In this study, effects of the different hysteretic models on damage indices were studied. First, the response of RC bridge piers during earthquakes was calculated using different hysteretic models and input motions. Then, seismic damage was evaluated by 1) a damage index based on a linear combination of the maximum deformation ratio and the energy dissipation during cyclic loadings, and 2) damage spectra of damage index, ductility and absorbed hysteretic energy for structures with various natural periods. Results showed that the non-degrading maximum value directed model was accurate enough for seismic damage analysis while the bilinear model underestimated damage because of its linear response to the low intensity cyclic loadings. The maximum value directed model was also needed to predict the damage index from the maximum velocity or the spectral intensity of the input motions