Nawawi Chouw

Multi-Sided Pounding Response of Bridge Structures with Non-Linear Bearings to Spatially Varying Ground Excitation

Considerable research of pounding effect on adjacent structures has been conducted in the past. However, most of them neglected the effect of multi-sided poundings. In bridges multiple adjacent bridge structures are common. Consequently, restraint due to additional neighbouring bridge structures cannot be avoided. This study addresses the effect of multi-sided pounding on structural responses due to spatially varying ground movements. Additional effect of non-linear bearing supports of the girders is also considered. The ground motions were simulated stochastically according to the Newmark-Hall spectrum. The result shows that in order to estimate the pounding and bearing forces as well as unseating potential of the girders realistically a consideration of non-uniform ground motions, end-restraint effect and non-linear girder bearings is necessary.

Vibration-based damage identification of an unreinforced masonry house model

Non-destructive vibration-based damage identification techniques are especially attractive for assessing damage in structures of high historical and architectural value. So far, most studies have focused on slender structures built using relatively homogeneous materials. In this study, global damage identification methods based on vibration response parameters were applied for identifying damage in an unreinforced masonry full-scale house model (non-homogeneous material and non-slender structure). The house model was dynamically loaded using an eccentric-mass shaker. Structural damage to the walls was initiated by increasing the amplitude of the applied load. At each damage state, a modal test was performed by impacting the walls with a calibrated hammer. Statistically significant variations of modal frequencies and the modal assurance criteria were considered as suitable parameters to identify damage. It was concluded that different sets of modes can be found for different states of damage because of material degradation, change in the support and connectivity conditions, and breaks in the members continuity generated by damage. All these changes are reflected in variations of modal frequencies and modal assurance criteria. It was also established that prior to identifying the damage distribution on the entire building, it was necessary to determine how the modal frequencies were related to each wall.

Damage Identification of Unreinforced Masonry Panels Using Vibration-Based Techniques

Several damage indicators based on changes in modal properties validated for homogeneous materials were applied to detect damage in an unreinforced masonry cantilever panel. Damage was created by a “clean diagonal cut” at the center of the specimen which length was progressively extended towards the specimen’s corners. Numerical simulations were employed to determine the modal response at several damage states and this data was used to calculate the damage indicators. Those indicators presenting a good performance were then applied to identify damage on a physical specimen tested in the laboratory. The outcomes of this study demonstrated that vibration-based damage detection in unreinforced masonry structures can be satisfactorily performed. However, the identification of the damage spatial distribution using vibration-based methods in unreinforced masonry structures is still difficult. To improve the prediction of damage distribution, a large number of measurement points need to be considered to obtain an acceptable level of resolution.

Significance of Soil-Structure Interaction and Near-Source Earthquakes in Causing Pounding of Bridge Girders

The study addresses the influence of near-source earthquakes and soil-structure interaction on the pounding response of two adjacent bridge frames. In the study the bridge frames and the foundations are described by a finite element method, and the subsoil by a boundary element method. The result reveals that the subsoil together with the long-period pulses in the ground motions can significantly increase the pounding potential of the structure.