Ambient Vibration Tests Research Articles

Influence of the ground on the structural identification of a bell-tower by ambient vibration testing

The article revolves around the structural identification technique through dynamic in situ tests trying to unravel the contribution of Soil Structure Interaction (SSI). The issue is addressed by considering the bell tower of Santa Sofia in Benevento (Italy) as a case study. Together with the homonymous church, the monastery and the fountain, the bell tower is part of a monumental complex included in the UNESCO World Heritage List since 2011. As the tower is completely separated from the other buildings of the complex, from a structural viewpoint it is quite a simple structure but likely to be affected by SSI. The latter phenomenon in some way could dictate the tower static and dynamic response, thus affecting the overall structural dynamic identification process. Invasive investigations are not usually allowed on cultural heritage due to preservation requirements. Thus, the paper proposes a simple but effective procedure for obtaining the data set required for both structure and soil characterization through noninvasive in-situ tests. The dynamic response of the subsoil at the tower site was firstly identified by reproducing the experimental amplification function provided by geophysical tests. Later, the results of an ambient vibration test performed on the bell tower have been interpreted and used to calibrate two refined 3D finite element models of the tower, one having the structure with a restrained base and another with a base compliant with the reality found. In the latter case, a suitable portion of the soil below the tower was included in the analysis domain. The contribution of the ground has been ascertained to move towards a reliable dynamic identification of the built cultural heritage. • Procedure for structure and soil data set characterization by noninvasive in-situ tests. • The importance of SSI on the correct identification of the structure behavior. • Combined geotechnical and structural optimization procedure to validate a FE model.

Radar Interferometric Experimental Reconstruction of Three-Dimensional Displacement Vectors and Mode Shapes for Masonry Constructions

Abstract Radar interferometry is an innovative measurement technique capable of remotely measuring vibrations in terms of displacement history. It apparently allows overcoming some major drawbacks of the plodding and time-consuming conventional accelerometric experimental setup for vibration testing. Indeed, radar interferometry does not require any access to the structure; moreover, its use is simpler and faster. Therefore, this technique appears very appealing for ambient vibration testing on structures, and in particular on architectural heritage masonry constructions. However, radar interferometry is still affected by some relevant limitations, that currently outweigh the advantages. One of the most important limitations is that displacements are measured only along the line-of-sight; therefore, it is not possible to determine the whole three-dimensional displacement vector for moving structural points and, consequently, to reconstruct three-dimensional mode shapes of structures, whose knowledge is crucial for characterizing the dynamic behavior of structures and for detecting eventual damages. In this paper, a theoretical and experimental approach for reconstructing both three-dimensional displacement vectors and mode shapes of masonry constructions is proposed. This approach is based on the simultaneous use of two synchronized radar interferometers, and on the application of a theoretical model assuming a specific kinematical constraint, which is generally plausible in the case of masonry constructions. The proposed approach has been validated through in-situ experimental tests on a masonry bell tower.

Ambient vibration testing and seismic fragility analysis of masonry building aggregates

Ambient vibration testing and seismic fragility analysis of masonry building aggregates

Dynamic Characterization of a Reinforcement Rammed Wall for the Earthen Ruins

In recent years, the earthen ruins’ cultural relics have aroused people’s extensive attention, and the protection of them is more and more urgent. The aim of the paper is to present the essential results of an ongoing research on a reinforced rammed earthen wall in the Suoyang ancient city (Guazhou, China). A variety of methods to combining aerial survey, dynamic test, and numerical model is provided with the purpose of estimating the structural characteristics of the ancient rammed wall. An aerial geometric survey based on high-resolution images made by unmanned aerial vehicle (UAV) has been approached to acquiring a 3D model. An ambient vibration test has been adopted by using vibration pick-ups. The experimental data were dealt with the operational modal analysis (OMA) followed by comparing with the numerical results delivered by the model. Meanwhile, the results showed the maximum displacements and corresponding positions of the structure under the three modes by the finite element model (FEM).

Application of a Non-Invasive Technique for the Preservation of a Fortified Masonry Tower

The Cultural heritage spread all over the World needs to be preserved with systems that do not compromise its architectural and historical value. Nowadays, the most advanced technology available is the ambient vibration test. It allows to obtain the current frequencies, modal shapes, and damping of structures, without being invasive. The comparison between different monitoring campaigns and their use in combination with Finite Element models can give an insight into the state of structures’ health. This paper presents two ambient vibration tests performed on a fortified masonry tower in the Marche region of Italy, carried out after one year each other, with different temperature and humidity conditions. To extract the structure’s dynamic parameters both a time and a frequency domain approaches were used. The comparison between the parameters obtained during the two experimental campaigns showed similar frequencies and modal shapes underlining that no damage occurred and that the dynamic response of the tower does not suffer temperature and humidity variations. In addition, the steps carried out for a first attempt manual calibration of the tower’s Finite Element model are shown. The match between the numerical model and the experimental data is evaluated through the absolute frequencies’ errors and the Modal Assurance Criteria between the modal vectors. The calibrated numerical model can be used for future and accurate assessment of the tower’s structural capacity.

Design, fabrication, and dynamic testing of a large-scale outdoor aeroelastic model of a long-span cable-stayed bridge

To overcome the limitations of existing experimental methods (including wind tunnel tests and field measurement experiments) for the study of bridge wind engineering, the research group at the Dalian University of Technology recently proposed to study the wind-resistance behaviours of long-span bridges through large-scale outdoor full-bridge aeroelastic models in natural wind. Several full-bridge aeroelastic models have been constructed, including a 1:50 model of a long-span cable-stayed bridge, which had a total length of 41.76 m and a height of 6.0 m. This paper systematically introduces the design, fabrication, and dynamic testing of the aeroelastic model. Taking the safety, adjustability, durability, and cost of the aeroelastic model into account, new approaches for the design of the main girder envelope, core beam of the bridge tower, and connections of the aeroelastic model are proposed. Free vibration tests and ambient vibration tests were utilised to measure the modal parameters of the aeroelastic model. The identified modal parameters were consistent with those calculated by finite element analysis, suggesting that the design and fabrication of the model were valid. The representative wind field data and measured buffeting responses of the aeroelastic model were presented.

Model updating of a masonry tower based on operational modal analysis: The role of soil-structure interaction

Vibration-based finite element model (FEM) updating of cultural heritage assets is gaining so much attraction these days since destructive tests are usually not allowed to be performed. In this study, a framework for developing three-dimensional (3D) FEMs is proposed using 3D laser scanners and applied on Slottsfjell tower, a stone masonry tower in Tønsberg, Norway. Operational modal analysis (OMA) was done based on the ambient vibration testing (AVT) data to define the frequency values and corresponding mode shapes of the tower. Mechanical properties of the tønsbergite stone were utilized to derive the base values of the material properties of the homogenized masonry for performing sensitivity analysis and FEM updating. To investigate the effect of the soil-structure interaction (SSI) on the FEM updating results, three FEMs are developed. The fixed-base model is the FEM without considering the SSI effects, and two other FEMs are developed using the substructure and direct methods for simulating the SSI effects. Sensitivity analysis was performed to investigate the effective parameters on the dynamic characteristics of the models. FEM updating was conducted on the three FEMs, and results are compared to each other to show the role of the SSI on the FEM updating results. The resonance effect can cause damages to buildings located even in low seismicity zones. For this aim, the risk of resonance effect has been evaluated for the tower. Finally, linear dynamic analysis was performed on the three calibrated models, and the results were compared to each other.

A methodology for the identification of physical parameters of soil-foundation-bridge pier systems from identified state-space models

A methodology for the identification of the physical parameters of a model describing the transverse dynamics of soil-foundation-pier systems founded on piles is presented in this paper, starting from identified state-space models of the systems obtained from results of dynamic experimental tests and identification techniques available in the literature. By assuming the order of the model to be compliant with that of a numerical one suitably developed to capture the dynamics of the bridge pier, the procedure allows the identification of the stiffness, mass and damping matrices of the analytical model from which the physical parameters of the real system (e.g. masses, pier stiffness matrix and soil-foundation impedance) can be extracted by directly comparing the components of the identified and analytical matrices. The procedure allows the direct definition of the numerical model that best fits the experimental data without the need of any model calibration, and permits the identification of the soil-foundation compliance taking into account its intrinsic frequency-dependent behaviour. Firstly, the dynamics of the analytical model is formulated adopting the continuous-time first-order state-space form. The model includes the frequency-dependent behaviour of the soil-foundation system through the introduction of a lumped parameter model able to reproduce the typical soil-foundation impedances of pile foundations. Then, an identification strategy of the physical parameters of a generic realistic soil-foundation-pier system is proposed starting from the discrete-time state-space model identified from dynamic tests. The procedure is illustrated with some applications, simulating results of forced vibration and ambient vibration tests executed on a known system whose parameters are then identified according to the proposed approach. The procedure revealed to be effective to identify the stiffness, mass and damping matrixes of the known system, and consequently its physical parameters.

Vehicle Bump Testing Parameters Influencing Modal Identification of Long-Span Segmental Prestressed Concrete Bridges.

In-service prestressed concrete box girder bridges have received increasing attention in recent years due to a large number of bridges reaching decades in service. Therefore, the ageing of infrastructure demands the development of robust condition assessment methodologies based on affordable technology such as vehicle-induced vibration tests (VITs) in contrast with more expensive existing technologies such as tests using hammers or shakers. Ambient vibration tests (AVTs) have been widely used worldwide, taking advantage of freely available ambient excitation sources. However, the literature has commonly reported insufficient input energy to excite the structure to obtain satisfactory modal identification results, especially in long-span concrete bridges. On the other hand, the use of forced vibration tests (FVTs) requires more economic resources. This paper presents the results of field measurements at optimally selected locations in VITs consisting of a 32-ton truck and a springboard with a height of 50 mm. AVTs using optimal sensor placement (OSP) provide similar results to VITs without considering OSP locations. Additionally, the VIT/AVT cost ratio is reduced to 2 since a shorter data collection time is achieved within a one-day (8 h) test framework, which minimizes temperature effects, thus leading to improvements in AVT identification results, especially in vertical modes.

Model updating using causal information: a case study in coupled slab

Problems like improper sampling (sampling on unnecessary variables) and undefined prior distribution (or taking random priors) often occur in model updating. Any such limitations on model parameters can lead to lower accuracy and higher experimental costs (due to more iterations) of structural optimisation. In this work, we explored the effective dimensionality of the model updating problem by leveraging the causal information. In order to utilise the causal structure between the parameters, we used Causal Bayesian Optimisation (CBO), a recent variant of Bayesian Optimisation, to integrate observational and intervention data. We also employed generative models to generate synthetic observational data, which helps in creating a better prior for surrogate models. This case study of a coupled slab structure in a recreational building resulted in the modal updated frequencies which were extracted from the finite element of the structure and compared to measured frequencies from ambient vibration tests found in the literature. The results of mode shapes between experimental and predicted values were also compared using modal assurance criterion (MAC) percentages. The updated frequency and MAC number that was obtained using the proposed model was found in least number of iterations (impacts experimental budget) as compared to previous approaches which optimise the same parameters using same data. This also shows how the causal information has impact on experimental budget.

Unveiling the complexity of twin church bells dynamics using ambient vibration tests

Unveiling the complexity of twin church bells dynamics using ambient vibration tests

Numerical evaluation of the seismic performance of thin reinforced concrete wall buildings representative of the industrialized building system

The industrialized building system has specific characteristics that set it apart from the conventional concrete wall system, namely, a reduced wall thickness, the use of electro-welded wire mesh, and a lack of boundary element confinement. These conditions have attracted the interest of researchers, who have developed various experimental programs to evaluate the behavior of these walls. However, evidence on the seismic performance of buildings remains scarce. In this study, the performance of 5-, 8- and 12-story buildings was evaluated by nonlinear chronological analysis. Numerical models were constructed using the Shell Layered element of the ETABS software and adjusted based on the results from tests of isolated walls and the periods of one of the buildings identified in an ambient vibration test. The findings suggest that these buildings may fail to meet the life safety performance level in high seismic hazard areas.

Optimal sensor placement techniques for modal identification of historical masonry structures

Since destructive tests are not allowed for historical structures, numerical model updating using accelerometers has gained a lot of attraction in the last decade. Furthermore, another application of structural health monitoring is damage detection for near-real-time monitoring of cultural heritage assets of infrastructures such as masonry bridges. However, high cost is the main problem that discourages the use of large-scale structural health monitoring systems, and a modal pretest analysis is required to plan and optimize the modal tests procedure. For this purpose, various optimal sensor placement (OSP) techniques have been developed to derive the operational modal analysis results with a minimum number of sensors, leading to a lower cost. In this study, various OSP techniques have been applied to optimize sensor placement in two selected case studies. The first case study is a two-span masonry arch bridge in Rhodes, Greece and the second is a stone masonry tower located in Tønsberg, Norway. Baseline finite element models were developed before performing the ambient vibration tests and model updating process. The optimum sensor locations were detected using various techniques, and a comparative study was conducted on the results. Furthermore, the effect of considering soil-structure interaction on the OSP results was investigated.

Dynamic performance investigation of a long-span suspension bridge using a Bayesian approach

In the past few decades, many large-scale bridges have been built to meet the different needs of styles and characteristics. Large bridges usually carry heavy traffic, and some bridges work in harsh environments. All these make the condition assessment of bridges very significant. On-site vibration testing is a general way to obtain the real response of the structure. Among a variety of measurements, the ambient vibration test has become popular due to its convenient usage and better economics. Based on the vibration data, modal identification can be used to identify the modal parameters that represent the dynamic characteristics of a structure. In this study, before being opened to traffic, a short-term non-destructive field vibration test was conducted on a newly-built long-span suspension bridge. Due to the limited number of sensors, multiple setups were designed to complete the entire measurement. For the measurement locations on the bridge deck, three-dimensional coordinates were determined using an electronic level. Analysis was performed based on the fast Bayesian FFT method, which can provide theoretical estimates for the posterior uncertainty and the most probable values of modal parameters. Nine modes of the bridge deck and four modes of the bridge tower were determined. The analysis results are discussed, and the posterior coefficient of variations (COVs) and sample COVs in different setups are compared. The analysis results in a healthy state can be used to verify the finite element model built in the design stage. It can also provide a benchmark for the future SHM of the bridge and improve the decision-making during usage and maintenance.

Dynamic Characterization of Timber Floor Subassemblies: Sensitivity Analysis and Modeling Issues

AbstractTimber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years, ambient vibration tests have become very popular due to the many adv...

Dynamic monitoring of buildings as a diagnostic tool during construction phases

The paper discusses the usefulness of the dynamic characterization of buildings based on the use of ambient vibration tests at different construction phases. The proposed experimental procedure, integrated with more conventional non-destructive in-situ tests for the estimation of the material mechanical properties, foresees the monitoring of the evolution of the building modal properties during the main construction phases. The monitoring makes it possible to assess the correctness of the construction through comparison with expected trends, and to consider possible countermeasures in case of unexpected behaviours. A case study, monitored during its construction, is presented to show the additional value of information obtained from the proposed experimental approach: (i) tests on the bare frame can be adopted to validate the design numerical model of the structure, in which non-structural elements are neglected in performing ultimate limit state verifications, (ii) the proposed monitoring allows the identification of the infills contribution on the building dynamics, providing useful information to address the interaction problem between structural and non-structural elements that may be detrimental at ultimates, and (iii) trends of resonance frequencies during the construction, validated through numerical applications, constitute an important tool for interpreting data from structural health monitoring system, as well as to establish alert thresholds of demand parameters (e.g. relevant to the building occupancy or structural damage).

Estimation of Live Load Distribution Factor for a PSC I Girder Bridge in an Ambient Vibration Test

Maintenance of bridges in use is essential and measuring the live load distribution factor (LLDF) of a bridge to examine bridge integrity and safety is important. A vehicle loading test has been used to measure the LLDF of a bridge. To carry this out on a bridge in use, traffic control is required because loading must be performed at designated positions using vehicles whose details are known. This makes it difficult to measure LLDF. This study proposed a method of estimating the LLDF of a bridge using the vertical displacement response caused by traveling vehicles under ambient vibration conditions in the absence of vehicle control. Since the displacement response measured from a bridge included both static and dynamic components, the static component required for the estimation of LLDF was extracted using empirical mode decomposition (EMD). The vehicle loading and ambient vibration tests were conducted to verify the validity of the proposed method. It was confirmed that the proposed method can effectively estimate the LLDF of a bridge if the vehicle type and driving lane on the bridge are identified in the ambient vibration test.

Seismic vulnerability assessment and fragility analysis of Iranian historical mosques in Kermanshah city

Kermanshah is a city in Iran's Zagros seismotectonic region regarded as one of the cradles of prehistoric and historic cultures. This novel study investigates the quantitative assessment of the seismic vulnerability of historical buildings in Kermanshah using numerical modeling. This study uses the hybrid method to estimate seismic vulnerability for seven mosques in Kermanshah's historical heritage. The structures are modeled by macro-elements. The material properties for the numerical models of the mosques are calibrated through ambient vibration tests. Furthermore, the efficiency and accuracy of Italian indirect method in evaluating the damage probability in Iranian historical buildings could be determined by the comparison with the hybrid method results. Moreover, it provides the knowledge for developing these methods by the architecture and structural specifications of Iranian historical structures. In the indirect method, the aggregate effect of mosques interacting with other structures is taken into account. Finally, considering local site effects, the fragility curves of both methods are developed and compared to each other at the probable design acceleration acquired from the Iranian seismic standard. The results show the seismic vulnerability of investigated mosques and the necessity to provide some parameters for the type of ceiling and configuration of the aggregates to evaluate the Iranian historical structures by indirect method more effectively.

Control performance of active tuned mass damper for mitigating wind-induced vibrations of a 600-m-tall skyscraper

Based on the field measurements on a 600-m-tall skyscraper equiped with an active tuned mass damper (ATMD) system, this paper investigates the control performance of the world's largest ATMD system to suppress the building vibrations. On-site forced vibration tests on the skyscraper were first conducted and the results showed that the ATMD system can increase the damping ratios of the fundamental sway modes up to about 11 times. Accordingly, ambient vibration tests on the building during Super Typhoon Hato were carried out, and the measured building acceleration responses showed that the ATMD system can effectively suppress the wind-induced vibrations of the skyscraper. Moreover, the structural damping ratios of the building with and without the operation of the ATMD system were identified, which showed that the ATMD system can significantly boost the damping ratios of the fundamental sway modes of the building for suppressing wind-induced vibrations, while it had limited effects on higher modal responses. The paper aims to provide useful information for the design of active vibration control systems and the wind-resistant design of high-rise buildings.

Methods for the vibration analysis of reinforced concrete precast one-way joist slab floor systems under human walking

An assessment of analytical methods for the vibration analysis of reinforced concrete (RC) precast one-way joist slab floor systems under human walking is presented. This study consists of a comparative analysis between analytical, numerical and experimental results. Firstly, an assessment of an existing analytical method for such evaluations is done, since it has not been validated. Subsequently, an efficient finite element model for the vibration analysis of this type of floor system under human walking is proposed. In the experimental program, two slabs specimens were tested under free and forced vibration . One test specimen was done in a laboratory and the other test in an apartment building of confined masonry. Ambient vibration tests were carried out to determine natural frequencies, and forced vibration tests to compute peak accelerations under people walking as induced loads. The experimental results were used as a reference for assessing the analytical and numerical results. It is observed that, in some cases, the analytical procedure underestimates the peak acceleration of the floor systems, while the numerical models yield satisfactory results, which are in agreement with experimental findings. In the assessment of the response of the two specimens with the current serviceability criteria for vertical vibrations, resultant accelerations are greater that permissible acceleration. Consequently, people may experience annoyance and discomfort in this type of floor system under vibrations caused by human walking. • An experimental, analytical and numerical dynamic investigation of two reinforced concrete precast one-way joist slabs with different boundary conditions is developed. • Vibration tests on two reinforced concrete precast one-way joist slabs with two different human-induced excitations are performed. • A practical modelling technique to accurately and efficiently simulate reinforced concrete precast one-way joist slabs under human-induced vibrations is proposed. • An analytical method is evaluated for the analysis of reinforced concrete precast one-way joist slabs under human walking.