Ozan Celik

Dynamic Testing of a Laboratory Stadium Structure

Studies with large physical models are a vital link between the theoretical work and field applications provided that these models are designed to represent real structures where various types and ...

Sensing and Monitoring for Stadium Structures: A Review of Recent Advances and a Forward Look

Stadiums like those used for sporting or concert events, are distinct from other civil engineering structures due to several different characteristics. Some challenges mainly originate from the interaction with the human factor, as stadiums are subjected to both synchronized and random motion of large crowds. The investigations in the literature on this topic clearly state that stadiums designs are in urgent need of more reliable load quantification and modeling strategies, deeper understanding of structural response, generation of simple but efficient human-structure interaction models and more accurate criteria for vibration acceptability. Although many aesthetically pleasing and technologically advanced stadiums have been designed and constructed using structurally innovative methods, recent research on this field still calls for less conservative and more realistic designs. This article aims to highlight the recent advances in this field and to provide a follow up to the 2008 literature review on vibration serviceability of stadiums structures. The article will also discuss new sensing and monitoring techniques on load-time history measurements and their regeneration, as well as crowd motion, stadium health monitoring, and human comfort analysis. Operational effects of crowds on the dynamic properties are also discussed. The paper concludes with a forward look on the recommended work and research for dynamic assessment of stadiums.

Recent Issues on Stadium Monitoring and Serviceability: A Review

Unlike most of civil engineering structures whose static and dynamic responses are estimated accurately through several codes and guidance, stadiums reserve a distinctive place especially when it comes to their dynamic behavior. This difference takes its source from several factors such as influence of crowd size, motion and slenderness of the structure. The most noticeable form of this difference shows itself as excessive vibration levels which is actually a threat to the serviceability of these structures. Eventually, it becomes essential to carefully evaluate several steps of this particular problem starting from correct representation of crowd activity through accurate loadings and human-structure interaction models to arranging acceptable vibration serviceability limits. This publication intends to point out the newly developed techniques and discovered issues on several stages of the problem during the last decade.

Quantification of Structural Damage with Self-Organizing Maps

One of the main tasks in structural health monitoring process is to create reliable algorithms that are capable of translating the measured response into meaningful information reflecting the actual condition of the monitored structure. The authors have recently introduced a novel unsupervised vibration-based damage detection algorithm that utilizes self-organizing maps to quantify structural damage and assess the overall condition of structures. Previously, this algorithm had been tested using the experimental data of Phase II Experimental Benchmark Problem of Structural Health Monitoring, introduced by the IASC (International Association for Structural Control) and ASCE (American Society of Civil Engineers). In this paper, the ability of this algorithm to quantify structural damage is tested analytically using an experimentally validated finite element model of a laboratory structure constructed at Qatar University.

Damage detection of a bridge model based on operational dynamic strain measurements

Vibration data analysis reserves a significant place in structural health monitoring practice since it can be employed for certain engineering problems such as locating damage and assessing damage severity by means of vibration signature interpretation. In this study, a damage detection study is carried out in light of vibration data analysis methods on a four-span bridge model by exploiting strain measurements. The concept of strain operating deflection shape along with an extraction method based on frequency and spatial domain decomposition is proposed. The damage-induced state of the bridge model is compared with the baseline state to detect and locate the damage. The result of strain analysis is also compared with acceleration analysis by simultaneous measurements of strain and acceleration. The power spectrum matrix of responses is estimated using digital signal processing principles. Besides the operating deflection shape analysis, operational modal analysis and correlation analysis of strain modes are conducted to identify and locate the damage.

Practical Calibration Techniques for the Modal Impact Hammer

Modal impact hammer comprised of a force transducer, a hammer body and different impact tips, is widely used in structural dynamic testing. Users might usually overlook the sensitivity of the impact hammer since it has no influence on the estimation of modal frequency, damping, and mode shape in a Multiple Reference Impact Test (MRIT). However, for the reason of accurate measurement and analysis for estimating the modal scaling factor or measuring the inertial mass of the structure, the calibration process has to be performed in advance. For the majority of off-the-shelf impact hammers, the force transducer cannot be detached. Moreover, the sensitivity of the integrated force transducer is not identical with the hammer because the force is transferred from the sensor to the structure via the impact tip. Therefore, the calibration method for common force transducers is not suitable for the impact hammer. In this paper, on the basis of drop calibration, two practical methods using an accelerometer and a load cell are presented respectively to calibrate the impact hammer and findings are compared with each other. The influence of different impact tips to the sensitivity of the hammer is also discussed.

Measurement of Human Loads Using Computer Vision

The applications of computer vision techniques in civil engineering are becoming increasingly popular with their promising capabilities such as easy and low-cost deployment, contactless measurement solutions and accurate reconstruction of structural finite element models. This paper aims to explore the possibilities of using several computer vision techniques on the reconstruction of load time histories. The motivation is to find a suitable method that could be applied both in the laboratory environment and in the field for the prediction of excessive loads that are exerted upon assembly type structures and specifically on stadiums. Virtual feature extraction and tracking methods are applied on the video recordings of test subjects while jumping and bobbing on structures instrumented with load cells and accelerometers. The results are compared with the sensor based measurements to assess the accuracy levels and feasibility of the methods.