Seismic Design and Retrofit of Bridges

https://dr.ntu.edu.sg/bitstream/10220/8634/1/173%20Residual%20strength%20of%20blast%20damaged%20reinforced%20concrete%20columns%20-%20ongoing%20Yichi.pdf

Residual strength of blast damaged reinforced concrete columns

The extended N2 method has been developed, which takes into account higher mode effects both in plan and in elevation. The extension is based on the assumption that the structure remains in the elastic range when vibrating in higher modes. The seismic demand in terms of displacements and storey drift can be obtained by combining the results of basic pushover analysis and those of standard elastic modal analysis. In the paper, the proposed procedure was summarized and applied to a test example which represents an actual 8-storey reinforced concrete building. The results obtained by the extended N2 method were compared with the results of nonlinear response history analysis and basic N2 analysis without the consideration of higher modes. The extended N2 method was able to provide fair, conservative estimates of response in the case of the test example. In comparison to the basic N2 method, the prediction of seismic demand was greatly improved in the upper part of the building and at the flexible edges.

The extended N2 method considering higher mode effects in both plan and elevation

This paper is intended to review the main causes and mechanisms of bridge collapse. The common factors resulting in bridge collapse are first reviewed. These factors are classified into two broad categories, namely, natural factors (including flood, scour, earthquake, landslide, debris flow, hurricane, typhoon, wind, etc.) and human factors (including imperfect design and construction method, collision, vehicle overloading, fire, terrorist attack, lack of inspection and maintenance, etc.). Then the collapse modes of a few major types of bridges are reviewed and some relevant measures adopted in the current practices are discussed. It is hoped that this paper will provide a concise but comprehensive summary of information needed by researchers and engineers to understand the collapse mechanisms of the major bridge types and how the current practices deal with these issues. Meanwhile, much effort is made to identify future research needed to better understand this topic and to find better solutions ...

State-of-the-Art Review on the Causes and Mechanisms of Bridge Collapse

This paper presents analytical assessment of the effect of vertical earthquake ground motion on RC bridge piers. A bridge structure damaged during the Northridge Earthquake and a Federal Highway concept bridge design are examined. The effects of a suite of earthquake ground motion records with different vertical-to-horizontal peak acceleration ratios on the two bridges are presented and the results are compared with the case of horizontal-only excitation. The effects of arrival time interval between horizontal and vertical acceleration peaks are also reported and compared to the case of coincident motion. It is observed that the inclusion of the vertical component of ground motion has an important effect on the response at all levels and components. It is therefore concluded that vertical motion should be included in analysis for assessment and design, especially that there are no particular challenges impeding its inclusion.

Analytical assessment of the effect of vertical earthquake motion on RC bridge piers

Results of comprehensive nonlinear response history analyses on a range of configurations representing typical highway overcrossings subjected to combined effects of vertical and horizontal components of near-fault ground motions are reported. Current seismic design guidelines in California neglect the vertical components of ground motions for peak ground accelerations less than 0.6 g and provide rather simplistic measures to account for vertical effects when they need to be incorporated in the design. Results from the numerical simulations show that the vertical components of ground motions cause significant amplification in the axial force demand in the columns and moment demands in the girder at both the midspan and at the face of the bent cap. Axial capacity of the columns and moment capacity of the girder at the face of the bent cap were generally found to be sufficient to resist the amplification in the respective demands due to vertical effects. However, midspan moments in negative bending due to vertical motions are found to exceed the capacity of the girder. The amplified midspan moments lead to yielding of the top reinforcement resulting in average peak strains on the order of 1%. It is concluded that seismic demand analysis of ordinary highway bridges in general and overcrossings in particular should incorporate provisions for considering the adverse vertical effects of near-fault ground motions.

Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings

Drift based damage functions for reinforced concrete columns

In this study, the multi-intensity seismic response of code-designed conventional and base-isolated steel frame buildings is evaluated using nonlinear response history analysis. The results of hazard and structural response analysis for three-story braced-frame buildings are presented in this paper. Three-dimensional models for both buildings are created and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the design objectives are met and the performance of the isolated building is superior to the conventional building in the design event. For the Maximum Considered Earthquake, isolation leads to reductions in story drifts and floor accelerations relative to the conventional building. However, the extremely high displacement demands of the isolation system could not be accommodated under normal circumstances, and creative approaches should be developed to control displacements in the MCE. Copyright © 2010 John Wiley & Sons, Ltd.

Comparative response assessment of minimally compliant low‐rise conventional and base‐isolated steel frames

Evaluation of Rayleigh damping and its influence on engineering demand parameter estimates

In this study, the multihazard response of code-designed conventional and base-isolated steel frame buildings is evaluated using nonlinear response history analysis. The results of hazard and structural response analysis for 3-story moment-resisting frame buildings are presented in this paper. Three-dimensional models for both buildings are created, and seismic response is assessed for three scenario earthquakes. The response history analysis results indicate that the performance of the isolated building is superior to the conventional building in the design event. However, for the Maximum Considered Earthquake, the presence of outliers in the response data reduces confidence that the isolated building provides superior performance to its conventional counterpart. The potential causes of the outliers have been carefully evaluated.

Emrah Erduran

Papers

Effect of Near-Fault Vertical Ground Motions on Seismic Response of Highway Overcrossings

Drift based damage functions for reinforced concrete columns

Comparative response assessment of minimally compliant low‐rise conventional and base‐isolated steel frames

Evaluation of Rayleigh damping and its influence on engineering demand parameter estimates

Comparative Response Assessment of Minimally Compliant Low-Rise Base-Isolated and Conventional Steel Moment-Resisting Frame Buildings