Ufuk Yazgan

Field testing of substandard RC buildings through forced vibration tests

In this study, forced vibration tests were conducted on two full-scale substandard reinforced concrete (RC) buildings to obtain the dynamic characteristics (modal frequencies and damping ratios) of these buildings. These tests were carried out before and after quasi-static lateral loading cycles. Through quasi-static cyclic loading, which was applied only in x direction of the buildings, the buildings were forced to experience specific damage states in a controlled manner. The original aspect of the study is investigating the rates of changes of the dynamic characteristics with the increasing damage. According to the test results, it was observed that modal frequencies tend to decrease while damping ratios for different modes tend to increase with the increasing levels of damage. In addition, finite element models of the buildings were established and modal analyses were performed for the undamaged state. Model updating was carried out in order to determine the optimal means of improving the accuracies of the finite element models of the test buildings. Experimentally identified modal frequencies of the buildings and those computed using finite element model were found to be consistent. Since the buildings tested in this study represent most of the existing substandard RC buildings in Turkey, determining the changes in dynamic characteristics with the increasing damage would be useful in the decision of demolishing/retrofitting of these types of buildings after potential future earthquakes.

Seismic performance of buildings during 2011 Van earthquakes and rebuilding efforts

The October 23, 2011 M7.2 Tabanli - Van and November 9, 2011 M5.2 Edremit–Van earthquakes caused damage in a widespread area across the Van province in Turkey. The ground motions, the damage caused by these earthquakes and the recent progress related to recovery efforts are presented herein. First, the key properties of the recorded strong ground motions like spectral amplitudes and directionality are evaluated. The observed damage in the affected reinforced concrete and masonry structures are discussed. The set of common structural damage mechanisms (i.e., soft story failure, torsional response due to plan irregularity, short column failure, pull out failure, pounding) observed in the damaged buildings were identified. The relationship between the key structural properties and the extent of damage is investigated. The primary loss drivers across the region were identified to be the poor quality of workmanship and improper use of building materials. The results from the investigation suggest that a large portion of the loss could have been prevented if sufficient attention and care were given to the implementation of the design regulations and in particular to the construction practice. Lastly, the recent progress in the ongoing rebuilding activities is presented.

Quantifying the value of SHM for emergency management of bridges at-risk from seismic damage based on their performance indicators

This paper proposes a framework for quantifying the value of information that can be derived from a structural health monitoring (SHM) system installed on a bridge which may sustain damage in the mainshock of an earthquake and further damage in an aftershock. The pre-posterior Bayesian analysis and the decision tree are the two main tools employed. The evolution of the damage state of the bridge with an SHM system is cast as a time-dependent, stochastic, discrete-state, observable dynamical system. An optimality problem is then formulated how to decide on the adoption of SHM and how to manage traffic and usage of a possibly damaged structure using the information from SHM. The objective function is the expected total cost or risk. The paper then discusses how to quantify bridge damage probability through stochastic seismic hazard and fragility analysis, how to update these probabilities using SHM technologies, and how to quantify bridge failure consequences.

Quantifying the value of seismic structural health monitoring of buildings

The decision to adopt a monitoring system for a structure should be based on sound appraisal of the expected economic benefits of such decisions. These benefits can be quantified in terms of the reduction of the risks posed by the failure of the structure versus the cost of monitoring. This paper discusses a framework for rationalising the adoption of monitoring for buildings subjected to seismic risks. The approach adopted is that of the preposterior decision analysis. Methods for automatic damage detection and joint utilisation of monitoring and visual inspection data are considered from a point of view of how they can be used in the pre-posterior analysis. Two short numerical examples are included to illustrate the proposed conceptual developments.

Post-Earthquake Risk-Based Decision Making Methodology for Turkish School Buildings

Safety assessment of damaged school buildings is one of the challenging tasks after damaging earthquakes. In this study, a new post-earthquake safety assessment method is proposed for school buildings. The method enables researchers to evaluate the level of risk and to judge the safety of the school building by taking into account the observed level of structural and non-structural damage. First, the vulnerability of the building is identified by considering the relevant damage indicators. Subsequently, the likely consequences of the various performance levels of the school building are identified. The likelihood of a specific consequence is evaluated by jointly considering all failure mechanisms that can lead to the considered consequence. Critical decisions regarding the school are made based on the level of risk and the available resources for risk mitigation. The methodology is expected to be a useful supporting tool for the post-earthquake decision-making process. Using the proposed method, critical decisions, such as continued use, strengthening or decommissioning school buildings can be handled in a rational and consistent way.