Muhammad Fiaz Tahir

Past bridge failures due to earthquakes have been found to be due to inadequate seismic design of the bridge piers. It is thus essential to investigate the effect of lateral confinement on the seismic behaviour of bridge piers. The aim of this study was to evaluate, experimentally and numerically, the seismic performance of reinforced concrete bridge piers with various types of transverse reinforcement. For this purpose, three scaled-down (1 : 4) circular bridge pier specimens were tested under constant axial and quasi-static cyclic loading (QSCL). A control specimen was made with spiral lateral reinforcement, while the other two specimens were made with stirrups with cross-ties and strips with cross-ties. The hysteresis loops, envelope curves, energy dissipation and stiffness degradation of all three specimens were determined in order to evaluate their seismic behaviour. Compared with the control specimen, the specimen with strips and cross-ties showed increased lateral load capacity, cumulative energy dissipation and higher initial stiffness due to the effect of increased confinement. The results of finite-element analysis showed good agreement with the experimental results. The findings of this study indicate that strips with cross-ties can be used in bridge piers when a high lateral load carrying capacity and energy dissipation are required.

Dynamic properties such as natural frequencies and mode shapes are directly affected by damage in structures. In this paper, changes in natural frequencies and mode shapes were used as the input to various objective functions for damage detection. Objective functions related to natural frequencies, mode shapes, modal flexibility and modal strain energy have been used, and their performances have been analyzed in varying noise conditions. Three beams were analyzed: two of which were simulated beams with single and multiple damage scenarios and one was an experimental beam. In order to do this, SAP 2000 (v14, Computers and Structures Inc., Berkeley, CA, United States, 2009) is linked with MATLAB (r2015, The MathWorks, Inc., Natick, MA, United States, 2015). The genetic algorithm (GA), an evolutionary algorithm (EA), was used to update the damaged structure for damage detection. Due to the degradation of the performance of objective functions in varying noisy conditions, a modified objective function based on the concept of regularization has been proposed, which can be effectively used in combination with EA. All three beams were used to validate the proposed procedure. It has been found that the modified objective function gives better results even in noisy and actual experimental conditions.

Three case studies of bridge‐pier‐related problems are presented. The first two concern problems during the construction of new bridge piers, while the third examines the reconstruction of an existing bridge. The first case is associated with an error in a construction drawing, the second involves inadequate pier survey, and the third is related to poor judgment in the inspection of the bridge‐pier base. The enabling causes of these problems were poor planning and supervision prior to and during construction stages. As design and construction of bridges becomes more and more complex, component details can be easily overlooked without adequate planning and supervision. Despite their significance for pier performance, such problems are generally unreported, and even if they are investigated, the results are seldom publicized. These problems, which cause project cost overruns and delays, can be avoided by emphasizing stricter quality‐control measures.