Experimental and Numerical Investigation on Dynamic Properties and Human-Induced Vibrations of an Asymmetric Steel-Plated Stress-Ribbon Footbridge

This paper presents a comprehensive study on dynamic properties and human-induced vibrations of a slender asymmetric steel-plated stress-ribbon footbridge via both experimental and analytical methods. Bridge modal test was conducted using both ambient vibration testing and impact methods. Modal properties of the bridge were identified based on stochastic subspace identification and peak-pick techniques. Results show that the bridge is characterized by closely spaced modes with low natural frequencies and small damping ratios (<0.002). A sophisticated finite element model that incorporates pretension of the stress ribbon and contribution of deck panels is developed and proven to be capable of reflecting the main dynamic characteristics of the bridge. Human-induced vibrations were measured considering synchronization cases, including single-person and small group walking as well as random walking cases. A theoretical model that takes into account human-structure interaction was developed, treating the single walking person as an SDOF system with biomechanical excited force. The validity of the model was further verified by measurement results.

Ambient vibration testing and operational modal analysis of monopole telecoms structures

A structural health monitoring (SHM) system was developed to study the ambient response of monopole communication structures in the UK operated by Arqiva Ltd. The exercise had several purposes that included the evaluation of the SHM system itself and the system identification procedures applied to the data, followed by analysis of the evaluated modal properties to validate the current analytical models, structural assessments and standardised design procedures advising on dynamics actions. This paper describes the instrumentation and procedures used during monitoring of a lightweight flexible 14.5 m tubular tapered monopole supporting an array of mobile telecoms antennas. A Bayesian OMA (BAYOMA) approach is implemented to identify structural modal properties under different time windows as comparison for further assessments. Results from stochastic subspace identification are also obtained and compared. The correlation between modal properties and monitoring wind-response data reveals specific tendencies such as nonlinear stiffness behaviour, the existence of aerodynamic damping and typical directionality of the mode shapes with future implications for reformulation of current methods of assessing dynamics on monopole.

Dynamic Characteristics Evaluation on Portable Steel Frame due to Mass Irregularities

Application of irregular mass configuration in modern design era of buildings is unavoidable in order to serve various building functionality. The effect of mass irregularities was investigated on 5-storey portable moment resisting steel tower (PostFrame), against its dynamic behaviour. PostFrame was designed at five meter height and assembled on the strong floor in Jamilus Research Centre laboratory, UTHM. The predominant frequencies and mode shapes were determined on bare frame, uniform mass frame and mass irregularities’ frames. A total of four steel blocks at 800 kg were placed in uniform, ascending and alternating orientations on the first to fourth level of the PostFrame. Ambient vibration testing (AVT) was conducted using uni-axial accelerometer sensors. The sensors were aligned in bi-axial horizontal directions with respect to the North-South (NS) and East-West (EW) directions. ARTeMIS processing tool and Frequency Domain Decomposition (FDD) methods were used in the analysis of dynamic behaviour. Comparative findings were made between bare frame and mass action frame. Two translation mode shapes and torsional mode were illustrated by respective three predominant frequencies. Significant reduction of predominant frequency showed up to 37.79% between bare frame and frame with ascending mass orientation.Uniform mass orientation shows at the lowest percentage discrepancy percentage compared to others. Even though some changes have be found in predominant frequencies, but comparable mode shapes illustration were observed from all three predominant frequencies from all frame configurations.

Developing a Feature Extraction of Existing Structures Using an Ambient Vibration Test

The paper aims to extract the dynamic properties of existing structures without utilizing the analytical models. The ambient vibration testing could be used on any type of frame such as concrete, steeland masonry to investigate the structural vulnerability.The method could bethe first stage and necessarily forthe retrofit process. To achieve this aim, the ambient vibration testing can also be employed. The experimental data obtained from the methodcan be used to monitor the health, evaluating, and damage detection structures at present. The achieved datacan be comparedin future with the recorded signals at different times.

Developing a Feature Extraction of Existing Structures Using an Ambient Vibration Test

The paper aims to extract the dynamic properties of existing structures without utilizing the analytical models. The ambient vibration testing could be used on any type of frame such as concrete, steel and masonry to investigate the structural vulnerability. The method could be the first stage and necessarily for the retrofit process. To achieve this aim, the ambient vibration testing can also be employed. The experimental data obtained from the method can be used to monitor the health, evaluating, and damage detection structures at present. The achieved data can be compared in future with the recorded signals at different times. So, the ambient vibration test was carried out on the building of Imam Hossein Hospital at Mashhad. Then, its dynamic characteristics of the acceleration records are obtained by using Data Acquisition System with three accelerometers in two perpendicular coordinates. The method is more accurate and practical compare with analytical models of the existing buildings. The ambient vibration test prevents of several points such as destructive testing or may irreparable damage to the building as well as high cost. Even, the ambient vibration test maybe required for every couple of decayed, when noticed of any changes in the condition of buildings after construction. These type of changes could be quality of concrete or welding or some changes in the location of walls that can be affected the dynamic specifications of the building. The method provides real lateral load pattern and actual modes that can evaluate existing condition of the building compare with the time of construction.

Structural health assessment of Puente del Inca natural monument using the integration of instruments and technologies

Puente del Inca is a natural monument standing over the Cuevas river in Mendoza, Argentina. The bridge currently exhibits structural deterioration due to natural and anthropic factors. This article seeks to offer a contribution to the conservation and restoration works of Puente del Inca by integrating instruments and technologies that allow the assessment of the health state of the natural bridge. The study relied on visual inspection, accretion-erosion rate measurements, hydrothermal flow characterization, ground-penetrating radar, soil dielectric sensor, Global Navigation Satellite System, laboratory testing, Structure from Motion, the Finite Element Method and ambient vibration testing. The results show that the morphology and health of the natural bridge depend on the dynamic balance between the erosion and the geobiological system intervening in the formation of the travertine constituting the natural bridge. The computational structural modeling demonstrates that there is a controversy between the benefit of irrigating the geological formation with thermal water and the loss of stability of the bridge under saturation conditions. Nevertheless, a continuous monitoring and an efficient administration of thermal water may ensure the deceleration of most of the erosive processes as well as the improvement of the geobiological system health.

Ambient Vibration as a Basis for Determining the Structural Behaviour of Watchtowers against Horizontal Loads in Southeast Spain

The Kingdom of Granada occupied the southeast of the Iberian Peninsula, what today would be the current Spanish provinces of Granada, Malaga and Almeria. Having succeeded the Nasrid kingdom of Granada (1238–1492), it remained a geographical and administrative unit until 1834, defended from the advancement of Castilian troops by means of a large network of watchtowers located principally along its inland border. Following the Castilian conquest of Granada, the extensive coastline was also strengthened with a network of towers and fortifications that were progressively adapted to house artillery. A technical survey focusing on the characteristics of their geometrics and construction, as well as their performance in a series of non-destructive tests, such as ambient vibration testing, was undertaken to study the towers’ mechanical strength against both gravitational and seismic loads. The results propose a numerical estimate that defines the fundamental frequency of this type of structure, which in turn can be used to approximate the mechanical properties of the masonry. Such a precise definition based on objective data enables accurate and rigorous numerical analysis of this defensive architecture, thus reducing uncertainties. Furthermore, slenderness is found to be a relevant parameter for adjusting fundamental frequency and for analysing the towers’ historical evolution, enabling their initial height and number of levels to be estimated.