Paul J. Fanning

Vibration Based Condition Monitoring: A Review:

Vibration based condition monitoring refers to the use of in situ non-destructive sensing and analysis of system characteristics –in the time, frequency or modal domains –for the purpose of detecting changes, which may indicate damage or degradation. In the field of civil engineering, monitoring systems have the potential to facilitate the more economical management and maintenance of modern infrastructure. This paper reviews the state of the art in vibration based condition monitoring with particular emphasis on structural engineering applications.

Three-dimensional modelling and full-scale testing of stone arch bridges

Abstract Existing test results of full-scale in-service masonry arch bridges are analysed to determine appropriate material properties for the modelling of this structural type. Three-dimensional nonlinear finite element models of three masonry arch bridges are generated using a commercially available finite element package. The behaviour of the masonry is replicated by use of a solid element that can have its stiffness modified by the development of cracks and crushing. The fill is modelled as a Drucker–Prager material, and the interface between the masonry and the fill is characterised as a frictional contact surface. The bridges are modelled under service loads, and the model results are compared to the results of a program of field testing of the structures. It is found that the assumption of a reasonable set of material properties, based on visual observations of the material and construction of the structure, implemented through a program of three-dimensional nonlinear finite element analysis enable good predictions of the actual behaviour of a masonry arch bridge.

Longitudinal and transverse effects in masonry arch assessment

Abstract Recent advances in the analysis of masonry arch bridges, substantiated by extensive testing programs in the United States and Europe, provide bridge engineers and inspectors with increasing confidence that reasonable estimates can be made of the capacity of these structures. Observations of ultimate strength testing indicate that spandrel walls and fill contribute greatly to the strength and stiffness of these structures, and that loads approaching the plastic collapse load can often be obtained. Observations from service load testing indicate that the development of cracking and non-linearity under service loads can be a significant indicator of the capacity of the structure. Modeling of these structures has shown the importance of restraint of the abutment to the overall resistance of the structure, and has recently shown the importance of transverse effects in diminishing the strength of structures with high spandrel walls or thin arch rings.

Characteristic vertical response of a footbridge due to crowd loading

The characteristic vertical vibration of a flexible footbridge subject to crowd loading is examined in this paper. Typically, bridge vibrations produced from a crowd of pedestrians are estimated by using an enhancement factor applied to the effect caused by a single pedestrian. In this paper, a single pedestrian model, represented by a spring mass damper, which incorporates variables such as pedestrian mass and body stiffness, is used to calibrate a computationally efficient moving force model. This calibrated moving force model is further used in Monte Carlo simulations of non-homogenous crowds to estimate characteristic vertical vibration levels. Enhancement factors, which could be applied to simple single pedestrian moving force models in estimating the response due to a crowd are thus derived. Such enhancement factors are then compared to previously published values. It is found that the greatest difference between the spring mass damper and moving force models respectively occurs when the bridge frequency is at the mean crowd pacing frequency. For bridges with frequencies even slightly removed from this mean, moving force models appear adequate.

Load testing and model simulations for a stone arch bridge

Service and high level load tests on a typical single span stone arch bridge in the south of Ireland and an associated set of three-dimensional nonlinear numerical analyses are discussed in this paper. The three-dimensional finite element models, which were generated using a commercially available finite element package, include the arch fill and a frictionless contact interface between this fill and the spandrel walls modelled with a nonlinear smeared crack material model. While this modelling strategy has been previously corroborated for service load levels, the results of the numerical model (which are compared with results from the experimental tests) also demonstrate the suitability of this modelling strategy at higher load levels. Finally, the suitability of three-dimensional solid models in the context of stone arch bridge assessment is discussed.

The Deployment Analysis of a Large Space Antenna

The volume constraints imposed by current launch modules and the desirability of large reflectors and communication booms for space applications has given rise to active research in the field of deployable systems. These systems are stowed in a compact package for launch before being deployed into their operating configurations in orbit. A new concept for a deployable antenna is presented. The deployment of one such 5.0 m antenna is investigated. The antenna is deployed by a number of mechanical joints. The energy stored in these joints is quantified and the deployment times and stresses at ‘latch-up’ are predicted.

A Parametric Study of Pedestrian Vertical Force Models for Dynamic Analysis of Footbridges

Footbridge vibration has received much attention in recent years. However, stochastic models for crowd loading are not common, and estimation of crowd-induced vibration is typically done through enhancement factors applied to single pedestrian loading models. This work compares two such models, a moving force model and a spring-mass-damper model (SMD). Typical ranges for various pedestrian parameters are examined, and it is found that the pacing frequency has by far the greatest influence on bridge vibration response. It is also found that the magnitude of the response for pacing frequencies near the bridge natural frequency is lower for the SMD model, but otherwise the results prove similar. This suggests that moving SMD models may be more suitable than moving force models when the bridge natural frequency is in the critical frequency range. 2 EVACES 2011 – Experimental Vibration Analysis for Civil Engineering Structures (2011) noted that several recently published design guidelines, while adopting a similar general approach, all differed in the input parameters used even for these moving force models and that the results derived from applying each of the guides to a benchmark structure varied by a factor of approximately four. It has further been acknowledged for a long time that there is a need for a probabilistic approach to pedestrian loading (Matsumoto et al, 1978; Wheeler, 1982). Despite this, design codes such as BS 5400 (1978, 2006) and Eurocode 5 (EN 1995-2:2004) use deterministic moving force models to predict the response of a single pedestrian. Zivanovic (2006) stated that these models are commonly unable to accurately predict the response of a bridge due to a single pedestrian and usually overestimate it significantly. This inevitably leads to overestimation of the crowd response if enhancement factors are used in conjunction with moving force models. Archbold (2008) also found the moving force model to be conservative as it does not consider interaction between the pedestrian and the moving bridge surface, while Clemente et al (2010) added that if the interaction between the pedestrian and the bridge is to be considered, the pedestrians should be modelled as ‘biological oscillators’. 1.2 Approach of this work In order to model the interaction between a pedestrian and the bridge surface, the authors have employed a moving spring mass damper (SMD) model to represent a single pedestrian (Caprani et al, 2011). This single degree of freedom SMD model captures changes in vertical forces applied to vibrating bridge surfaces. This SMD model is then moved across an idealized bridge at a velocity derived from a combination of pacing frequency and step length. The bridge used in the model is a simply-supported beam, chosen to be susceptible to excitation from typical pedestrian pacing rates. To model the footfall force, a time-varying harmonic force is applied to the pedestrian mass, as proposed by Fanning et al (2005). Input parameters for this model include pedestrian mass, step length, pacing frequency, pedestrian stiffness and damping properties associated with the pedestrian model. The aim of the work reported herein is to determine the sensitivity of the numerical models and estimated acceleration levels induced in the bridge to a range of input parameters related to the movement of the crossing pedestrians. The results from the SMD pedestrian model are thus compared to those estimated using the conventional moving force model. 2 USE OF SMD MODELS TO REPRESENT HUMAN LOADING 2.1 Human leg stiffness Rapoport et al (2003) stated that in repetitive physical activity, such as running, hopping and trotting, a subject bounces on the ground in a spring-like manner. Geyer et al (2006) state that walking is also a bouncing gait. This is due to knee, ankle and hip flexure throughout the gait cycle (Rapoport et al, 2003; Lebiedowska et al, 2009). Blum et al (2009) stated that leg stiffness is a key parameter of modelling legged locomotion. Lee and Farley (1998) and Geyer et al (2006) represented the human leg as a compliant spring-mass model while running and walking, respectively. Rapoport et al (2003) stated that constant mechanical stiffness may not be applicable to the human leg as joint stiffness is nonlinear in nature as damping may be present and as a result, a model which accounts for this damping may improve the model predictions Lee and Farley (1998) acknowledged that spring and damping elements have been incorporated into the legs of some models of walking in order to match ground reaction force (GRF) patterns observed in human walking. They report that the values used in these models are generally higher (kP =12-35.5 kN/m) than the leg stiffness values reported for normal walking (kP ≈11 kN/m). Geyer et al (2006) stated that these models are too complex to serve as conceptual models. The authors reference Dickinson et al (2000) and Srinivasan and Ruina (2005) as stating that, despite being inaccurate, the stiff-legged motion remains the mechanical concept for a walking gait. Geyer et al (2006) themselves state that not stiff but compliant legs are fundamental to the walking gait.

Investigation of the Rail-Induced Vibrations on a Masonry Historical Building

Increasingly historic masonry buildings are subjected to higher levels of traffic and rail vibrations due to urbanization and population growth. Deterioration and destabilisation of these buildings may result, especially if they were previously damaged (e.g. earthquakes or settlement problems). To better understand building response, vibration measurements were conducted on the Little Hagia Sophia Mosque, located adjacent to Istanbul’s Sirkeci-Halkali railway line. Transport-induced vibrations were recorded at several points on the ground and building. Attenuation characteristics in the ground and amplification features on the building were examined. Peak particle velocities often exceeded previously established thresholds for human perception and in some cases for structural damage. These are evaluated with respect to the building’s condition.

The Evolving Dynamic Response of a Four Storey Reinforced Concrete Structure During Construction

Structures include elements designated as load bearing and non-load bearing. While non-load bearing elements, such as facades and internal partitions, are acknowledged to add mass to the system, the structural stiffness and strength is generally attributed to load bearing elements only. This paper investigates the contribution of non-load bearing elements to the dynamic response of a new structure, the Charles Institute, in the grounds of University College Dublin (UCD) Ireland. The vertical vibration response of the first floor and the lateral response at each floor level were recorded at different construction stages. The evolution of the structural response as well as the generation of a finite element (FE) model is discussed. It was found that the addition of the non-load bearing facades increased the first floor natural frequency from 10.7 Hz to 11.4 Hz, a change of ap- proximately +6.5%. Similarly these external facades resulted in the first sway mode having its frequency increased by 6%. The subsequent addition of internal partitions, mechanical services and furnishings resulted in the floor natural frequency reducing to 9.2 Hz. It is concluded that external facades have the net effect of adding stiffness and the effect of internal partitions and fur- nishings is to add mass. In the context of finite element modelling of structures there is a significant challenge to represent these non-structural elements correctly so as to enable the generation of truly predictive FE models.

Nonstructural Partitions and Floor Vibration Serviceability

AbstractNonstructural vertical partitions and cladding can have a significant effect on the vibration serviceability of floor systems. A typical modern office building, consisting of steel–concrete composite floor systems, was created to investigate the potential beneficial effects of integrating nonstructural partitions into structural floor systems to reduce floor vibrations due to walking excitation. Two models of this building are presented: one to represent the completed building with an open-plan layout and another with partitions added in a beneficial pattern to enhance the floor’s vibration performance. The addition of nonstructural partitions successfully reduced floor accelerations due to walking excitation and helped the floor to satisfy the vibration serviceability criterion for office floors. The potential of vertical full-height nonstructural partitions and cladding to transmit vibrations between floors was also investigated. A vibration transmission simulation was conducted on the finite-el...