Abstract: Noise generated from modular bridge expansion joints during vehicle pass-bys has caused localized environmental problems in Japan and elsewhere. The objective of this study was to understand the mechanism of noise generation and radiation from a modular expansion joint installed in an expressway bridge. A numerical investigation was conducted in order to understand the dynamic characteristics of the joint and the acoustic characteristics of the sound field around the joint that measurements cannot reveal due to their limitations, such as the number of measurement locations that are required. Vibro-acoustic analysis was conducted by using the finite element method–boundary element method (FEM–BEM) approach: dynamic analysis of the joint was carried out by FEM and the sound fields inside the cavity located beneath the joint and outside of the cavity were analyzed by BEM. It was concluded that dominant frequency components in the sound pressure inside the cavity were due to excitation of the structural modes of the joint and/or acoustic modes of the cavity. For the expansion joint investigated, the sound field farther than about 35 m from the joint–cavity center could be considered as far field in the range 50–400 Hz.

Abstract: Noises generated from modular bridge expansion joints during vehicle pass-bys have been causing local environmental problems recently. Previous experimental studies showed that possible causes of dominant noise components generated from the bottom side of the joint might be different from those from the top side. The objective of this study was to obtain theoretical insights into the mechanism of noise generation from the bottom side of the joint for which a main noise source might be structural vibration of the joint. Vibro-acoustic analysis was conducted based on the information from a full-scale model of modular expansion joint obtained in previous experimental studies. The dynamic behavior of the joint model was investigated by using the finite element method (FEM) and the sound field inside the cavity located beneath the joint model was analyzed by using the boundary element method (BEM). Indirect BEM was used to calculate the sound pressure inside the cavity with the velocity response obtained by the FE analysis as a boundary condition. The frequency range considered in the analysis was 20–400 Hz where dominant frequency components were observed in the noise measured in the cavity beneath the joint in the previous experiment. It was intended to interpret numerical results obtained by a model developed with available mechanical properties of the joint components to seek a general understanding of the noise generation mechanism of the modular expansion joint. It was observed that the peaks in the spectrum of noise inside the cavity were due to resonances of structural vibration modes of the joint and/or resonances of acoustic modes of the cavity. There was evidence that showed possible interaction between structural modes of the joint and the acoustic modes of the cavity.

Abstract: Finite element software, SW_FEAD has been developed for the structural analysis and design of multi-storeyed buildings. Two dimensional (2D) as well as three dimensional (3D) finite element models of the buildings can be created using the graphical user interface (GUI) of the software. Seismic Analysis of the buildings can be carried out according to Nepal National Building Code (NBC) . Automatic calculation of earthquake loads from both (1) Seismic Coefficient Method and (2) Modal Response Spectrum Method, defined by Nepal National Building Code is one of the most important capabilities of this software. The different types of loads and their combinations can be applied and analyzed for the evaluation of internal forces in the structural members of the building. Earthquake resistant design of different structural components of the buildings like columns, beams, slabs, footing etc. can be carried out according to NBC. The detail structural design drawings of the building can be produced automatically in other CAD software like AutoCAD and therefore work load of design team can be reduced considerably. Results of SW_FEAD are validated by comparing the results from other well established software like SAP2000 and STAADPro.

Abstract: The applicability of the sensitivity-based model updating technique to the identification of structural changes made in an existing structure was investigated with a pile supported reinforced concrete building undergoing major renovation. Seven different renovation stages which represented the different states of the building during the renovation were considered. The modal properties, i.e., natural frequencies and mode shapes, identified from the ambient vibration measurement of the building were used in the identification of structural changes. The sensitivity-based model updating technique was used to update the mathematical models of the building for all renovation stages. Structural change made in the building during renovation was quantified in terms of structural parameters identified from the model updating. More than 50 % reduction in stiffness in the longitudinal direction of the building was found significant in all four storey of the building, which may be attributed to the removal of shear walls. The storey stiffness obtained from model updating was compared between before and after the renovation.

Abstract: Noises generated from modular bridge expansion joints during vehicle passages have been causing environmental problems recently in Japan. The objective of this study was to investigate the mechanism of noise generation from the joint by carrying out vibro-acoustic analysis of a full scale test model of modular expansion joint. Numerical analysis of the dynamic behavior of the joint model was conducted by using the finite element method and the boundary element method was used to analyze sound field inside a cavity located below the joint model. Velocity response of the joint was calculated by applying point loads at the locations where dynamic loads might be applied during vehicle passage. Acoustic modal analysis of the cavity below the joint model was carried out by using FEM also. Indirect Boundary element method was then applied to calculate the sound pressure inside the cavity by using the velocity response obtained by the FEM analysis as a boundary condition. The frequency range considered for the analysis was 20-400 Hz. The numerical results were compared with experimental results obtained from impact testing. It was shown that the peaks in the spectrum of noise inside the cavity was due to either resonances of structural member of the joint and/or resonances of acoustic modes of the cavity. The interaction of structural modes of the joint with the acoustic modes of the cavity was observed.

Abstract: Noises generated from modular bridge expansion joints during vehicle passage have been causing environmental problems recently in Japan and elsewhere. The objective of this study was to investigate the characteristics of noise generation and radiation from a joint installed in a real bridge. Vibro-acoustic analysis was conducted: the dynamic behavior of the joint was analyzed by the finite element method and the sound field around the joint was analyzed by the boundary element method. Velocity response of the joint was calculated by applying point loads at locations where external loads might be applied during vehicle passage. Indirect boundary element method was then applied to calculate sound field around the joint by using the velocity responses of the joint as boundary conditions. The directivity patterns of sound field around the joint were calculated at radial field points at different distances from the joint. The frequency range considered in the analysis was 20-400 Hz. It was shown that dominant frequency components in the sound pressure response were due to vibration mode of joint structure and/or acoustic mode of the cavity below the joint. The directivity pattern appeared to depend on the frequency of the sound and the distance from the joint.

Abstract: The building of Civil and Environmental Engineering Department of Saitama University was renovated and major structural changes were made. Different finite element models of this four-storey reinforced concrete building, supported on prestressed concrete pile foundation, were developed so as to identify the dynamic characteristics at different stages of the renovation. Significant changes in the dynamic characteristics were observed from the results of ambient vibration measurements conducted before and after each major renovation stage as well as from the results of analytical models, developed to represent the different renovation stages. Soil-structure interaction was observed from the measurement in which first vibration mode obtained was a rigid body mode, where the mass of whole building was lumped as a single mass, and stiffness was contributed by the piles and surrounding soil. This soil-structure interaction was incorporated in the analytical model by considering one additional storey in the model. Modal properties obtained from the models developed showed reasonable agreement with experimental results.

Abstract: In this study, model validation and updating for vibration-based structural change identification was investigated with an existing pile supported four-storey reinforced concrete building undergoing major renovation. Seven different renovation stages, which represented the different states of the building during the renovation, were considered. The modal properties, i.e., natural frequencies and mode shapes, identified from ambient vibration measurement of the building in a separate study were used for the identification of structural changes. Structural changes made in the building during the renovation were identified: (1) by comparing the dynamic characteristics of the building at different renovation stages, identified from finite element models and (2) by comparing the updated structural parameters of different renovation stages identified from sensitivity-based model updating technique. Three dimensional finite element models of the building were developed for all renovation stages and their dynamic characteristics were identified. Soil-structure interaction was observed from the experimental results, in which significant displacement at the base of the building in fundamental vibration was observed in both longitudinal and transverse directions of the building. The soil-structure interaction was incorporated in the models developed by considering one additional storey. Significant reduction in natural frequencies at second stage of renovation at which shear walls were removed in longitudinal direction of the building, and increase in natural frequencies at later stages at which new frames were added to the building, were observed from the experimental results as well as from the results of finite element models. Sensitivity-based model updating technique, in which structural parameters of analytical model sensitive to natural frequencies and mode shapes are updated using experimental results, was used to update the building models. Since, the significant changes in dynamic characteristics of the building during the renovation were identified in longitudinal direction of the building, two-dimensional model of the building was considered for updating. The initial two-dimensional models of the building for updating were developed from least squares method by using natural frequencies and mode shapes identified from the three-dimensional finite element models. The initial model of each stage of renovation was updated by using the natural frequencies and mode shapes of corresponding stage identified from the experiment. Effect of weighting factor used for updating parameters in the updating algorithm was found significant to the updated results. The natural frequencies identified from the updated models were in good agreement with the experimental values and the correlation between experimental and analytical mode shapes was improved after updating the model parameters. Structural changes made in the building during the renovation were not only identified but also located and quantified in terms of structural parameters. Stiffness reduction in longitudinal direction of the building from shear walls removal was significant in all four storeys of the building. Stiffening of the building was identified when new frames were added to the building. Stiffness loss of building storeys from shear wall removal was regained at the end of renovation by adding new frames. The updated stiffness results were interpreted with the help of the stiffness values evaluated by considering size and number of columns in the building before and after renovation.

Abstract: Modular expansion joint is commonly used for large expansion joint movement. Because of the several advantages over other types of expansion joint, use of modular expansion joint has been increased recently. However, the noise generated and radiated from the modular joint has been a localized environmental problem in Japan and elsewhere. Understanding of noise generation and radiation is important from noise control point of view. Noise from modular expansion joint is mainly generated and radiated from the top of the joint on carriageway surface and from the bottom part of the joint which has a cavity beneath it for the maintenance purpose. From the previous studies, noise generation and radiation mechanism inside the cavity beneath the joint is not fully understood. There have been no reported studies on the noise radiation from the joint to the outside environment, which is necessary to be understood from noise control point of view. The vibration power of the joint during vehicle impact can be transmitted to the connected bridge. No reported studies were found on possible vibration power flow from the joint to the connected bridge and noise contribution from the bridge. The objectives of this study have been: (i) to understand the noise generation and radiation mechanism inside the cavity beneath the joint; (ii) to understand the characteristics and mechanism of noise radiation from the joint to the outside environment and (iii) to understand the possible vibration power flow from the joint to the bridge and noise radiation from the bridge. A full scale model of modular expansion joint was considered to fulfill the first objective. Vibro-acoustic analysis was conducted by considering the joint and cavity which was underground as one system. Finite element method (FEM) - boundary element method (BEM) approach was used for the analysis. FEM was utilized for the dynamic response estimation of the joint structure and BEM was used to analyze the sound field inside the cavity of the joint-cavity system in the frequency range of 20-400 Hz. FE modal analysis was also conducted to obtain the acoustic modal parameters of the cavity beneath the joint. Impact testing experiment of noise and vibration were used to interpret the numerical results. It was concluded that dominant frequency components in the sound pressure response inside the cavity was due to vibration modes of the joint structure and/or acoustic modes of the cavity. In lower frequencies, peaks in the sound pressure response inside the cavity were mainly due to the vibration modes of the joint structure with possible interaction with acoustic modes of the cavity. At higher frequencies where the modal density of the acoustic modes was high, effect of acoustic resonance of cavity on sound pressure response was significant. A modular expansion joint installed between prestressed concrete bridges was considered to fulfill the second objective. The cavity beneath the joint had openings at both ends along its length. Noise generated inside the cavity could radiate to the outside environment from these openings. FEM-BEM approach as in the previous study of full scale model joint was utilized to analyze the sound field inside as well as outside of the joint-cavity system. FE modal analysis was also conducted to obtain the acoustic modal properties of the cavity beneath the joint. Measurement of noise and vibration of expansion joint during vehicle pass-bys were also carried out. Sound field was analyzed in the frequency range of 50-400 Hz. It was concluded that the noise from the bottom side of the joint was caused by the excitation of structural modes of the expansion joint and/or acoustic modes of the cavity beneath the joint, which is consistent with a conclusion derived in a previous study with a full scale model joint. The sound radiation efficiency of the joint-cavity system appeared to be high at natural frequencies of vibration modes of the joint with significant vertical vibration of middle beams and support beams (coupled modes). Sound radiation efficiency of lateral modes of the joint appeared to be low. Noise from the joint–cavity system may be propagated most effectively at radiation angles of acoustic modes of the cavity, which can be predicted roughly from the fundamental theory of sound radiation from cavities and waveguides. The sound field around the joint-cavity system investigated in this study could be considered near field within 35 m from the joint-cavity center and far field at farther distances. A modular expansion joint installed in a steel-concrete non-composite bridge was considered to fulfill the third objective. A simplified analytical approach using FEM and statistical energy analysis (SEA) was considered. FE model of the joint was used to estimate the dynamic response of the joint. SEA was used to estimate vibration response of the bridge. Measurement results of noise and vibration of expansion joint and bridge during vehicle pass-bys were used to interpret the analytical results. It was found that the simplified approach was able to predict the flow of vibration power from the expansion joint to the bridge and noise radiation from the bridge during vehicle pass-bys. This approach can be utilized to reduce the vibration power flow from the joint to the bridge.