Key Engineering Materials Vols. 569-570

Abstract: The concept of the buildings stability, based on experimental methodology consists of objective monitoring of the parameters defined by modelling and control using hardware tools, i.e. systems monitoring and diagnostics, which allows generating appropriate response to emerging defects, their fixing and prognosis of their location. In the framework of the problem of buildings stability the complex research was done in which mathematical models of buildings construction were created, defects identification method developed and also monitoring concept was composed according which automated monitoring system and software prototypes and structures were implemented. The strategic aim of the development of buildings monitoring system was realized by mathematical and physical modelling of the damages (e.g. defects like crack or destroy of linkage); analysis of characteristics sensitive to defects; selection of stability parameters and measurements; creation of automated system prototype; investigation of the methods applied for the monitoring system and diagnostics; development of software and separate elements of the system and approbation of the whole complex. Thorough evaluation of the technical state of the buildings numerical is executed using physical models and natural objects which support reliable state identification of the building and also helps to track changes.

Abstract: Recent studies have proved that there is no fatigue limit for metallic materials; the stress life curve continuously drops even after 10⁷ cycles. However, existing design codes assume that there is a fatigue limit. Therefore, it is important to use appropriate safety factors if existing codes are used for life evaluations. This paper first describes a method to extend high cycle fatigue stress life curves which are developed using tests on small scale specimens, to the gigacycle regime. Then the difference between the stress life curves of small scale specimens and full scale tests related to steel bridges are explained. Finally, the paper presents a case study on a fatigue critical element of a steel railway bridge to show the significance of the gigacycle regime for fatigue life evaluation.

Abstract: Bridges are considered as vital components that require a high degree of protection to guarantee their functionality, even after significant earthquakes. So, the damage evaluation of current conditions of these structures is considered a necessary tool for inspection, maintenance and rehabilitation. Seismic fragility curves of a common highway bridge structure, with simple-supported girders, for different seismic scenarios, are evaluated in this paper. The selected bridge is a RC system with rectangular piers, forming a frame substructure; the bridge piers reinforcement is designed using steel jackets. Damage fragility curves are again evaluated for the reinforced system and compared with the initial condition; for that, a non-linear analyses with Ruaumoko program are accomplished, using a Takeda constitutive model and the damage index proposed by Park et al. As an external seismic action, artificial accelerograms are obtained based on signals registered in the most hazardous earthquake zone of Mexico. The probability changes of a certain damage level are verified for the obtained results.

Abstract: Many of the bridges currently in use worldwide are approaching the end of their design lives. However, rehabilitating and extending the lives of these structures raises important safety issues. There is also a need for increased monitoring which has considerable cost implications for bridge management systems. Existing structural health monitoring (SHM) techniques include vibration-based approaches which typically involve direct instrumentation of the bridge and are important as they can indicate the deterioration of the bridge condition. However, they can be labour intensive and expensive. In the past decade, alternative indirect vibration-based approaches which utilise the response of a vehicle passing over a bridge have been developed. This paper investigates such an approach; a low-cost approach for the monitoring of bridge structures which consists of the use of a vehicle fitted with accelerometers on its axles. The approach aims to detect damage in the bridge while obviating the need for direct instrumentation of the bridge. Here, the effectiveness of the approach in detecting damage in a bridge is investigated using a simplified vehicle-bridge interaction (VBI) model in theoretical simulations and a scaled VBI model in a laboratory experiment. In order to identify the existence and location of damage, the vehicle accelerations are recorded and processed using a continuous Morlet wavelet transform and a damage index is established. A parametric study is carried out to investigate the effect of parameters such as the bridge span length, vehicle speed, vehicle mass, damage level and road surface roughness on the accuracy of results.

Abstract: The post-earthquake function of elevated water tank structures so as respond to the civil water requirements is of extreme significance. These structures are, however, extremely vulnerable to seismic conditions and there has been substantial damage/failure of several such structures during major earthquakes. A review of the damage and performance of some elevated water tanks subjected to earthquakes is presented in this paper. An investigation is also made on the seismic vibration control of elevated water tank structures by using Tuned Liquid Dampers (TLDs). A frequency domain formulation for the transfer function of the elevated water tank with attached TLDs is developed. Numerical studies on a reinforced concrete elevated water tank with shaft type support are carried out. The effect of detuning on the performance of the TLDs due to the change in the structural frequencies resulting from the fluctuating water level in the water tank is also examined. Results indicate that it is possible to design a fairly robust and effective TLD system for the seismic vibration mitigation of the considered elevated water tank.

Abstract: Safety ofhealth facilities (hospitals) is only partially related to the performance ofprimary structural members. Modern seismic codes provide strict requirements toboth structural and non-structural components, since the latterare alsocritical to ensure that the system remains fully operational in the case offrequent earthquakes. Thus, performance and safety checks apply also to electro-mechanicaland medical equipment,elevators, tanks, power supply systems, distributionsystems, heating, ventilation and air-conditioning systems.In the present paperattention is focusedon the analysis of the factors which make health facilities vulnerable and onthe issues related to a rational and objective assessment of performance andhealth state of structural and non-structural components. This is not a trivialtask, since functions and resilience of the system as a whole depend also onthe ability of inspectors and managers to integrate theoretical evaluationswith field measurements and their physical meaning.In this context, strategies and recommendations for a sustainableimplementation of Smart Health Facilities, which fulfilAtoE characteristics (Accuracy, Budget compliance, Computational burden,Durability, Ease of use)on a long term basis, are discussed, taking into account the specific requirementsand characteristics of the different subsystems in a hospital.

Abstract: Rapid assessment of large, short-period structures is extremely important for establishing structural integrity. This paper demonstrates experimental non-contact detection of consistent frequency peaks from the ambient vibration of a range of large buildings. Long distance, remote Laser Doppler Vibrometry is employed to estimate the dominant response frequencies of these large building structures from their ambient vibration. These dominant frequencies were reproducible in the frequency domain. The results demonstrate potential field applications of this method in a number of important applications. Such applications include model-free and rapid assessment or monitoring of historical structures, strategically important structures, lifelines, assessment and monitoring of structures such as nuclear facilities and rapid evaluation of large scale structures following disasters. Empirical formulas specified in codes do not cover such special structures and experimental determination of periods employing the method proposed may thus become essential.

Abstract: During the past earthquakes, different low ductile failure modes are observed in the gravity design structures and thus, the most of existing damage indices may fail to assess the damage of gravity design structures accurately in referring to the two main performance levels: immediate occupancy and ultimate limit state. Therefore, this study investigates the possible damage indices for the damage assessment of gravity design frames. For this purpose, among the existing damage indices in the literature, this study considers the inter-story drift and the natural period based damage indices. In addition, two new damage indices based on the wavelet based energy and the dominant inelastic period of a building are also considered in this study. Furthermore, the damage assessment results from the four damage indices for three gravity design buildings are compared and discussed. From the comparison, linear correlations between the inter-storey drift based damage index and the wavelet energy based index, and dominant inelastic period based damage index are observed. Finally, this study concludes based on the observations that no significant effects of number of inelastic cycles to the damage assessment results for low ductile structures. However, this study also highlights the effects of number of inelastic cycles to the damage for medium and high ductile structures.

Abstract: Many post-tensioned concrete bridges have been reported to have ruptured tendons due to corrosion [1] and the assessment of their residual structural capacity has to account for the possibility of re-anchorage of failed tendons. This paper presents an experimental programme to validate a numerical model developed by the authors for the re-anchorage of a ruptured tendon in post-tensioned concrete [2]. The experimental programme considered 33 post-tensioned concrete prisms, in which the rupture of tendon was simulated by releasing the tendon at one end. The full field displacement at concrete surface after release was measured using 3D Electronic Speckle Pattern Interferometry (ESPI). A wide range of parameters: tendon diameter, duct material, grout strength, concrete strength and shear reinforcement were investigated to validate the proposed model, which is found to be suitable for use in assessing post-tensioned concrete bridges with damaged tendons.

Abstract: This paper presents the current post-earthquake damage assessment procedure in Turkey, and is based on the authors experience in the province of Van after the earthquakes in late 2011. The damage assessments were conducted mainly by the state with the collaboration of the Chamber of Architects in Turkey. It is aimed at explaining how the damage surveys are conducted and what problems occurred during and after the completion of the assessments. The differences and similarities between other countries post-earthquake damage assessment practices are also examined by comparing them and giving some examples.