Dynamic analysis of 'smart' pin-frame system using timefrequency representation of earthquakes

This paper presents the dynamic analysis of a 'smart' pin-frame system employing instantaneous frequency (IF) extracted using Time-Frequency Representations (TFR) of earthquake records. The study is, therefore, aimed to demonstrate the applicability of real-time modal frequency shift technique for the non-linear 'smart' pin-frame model, but it is also used to numerically assess the performance of the proposed frequency shift strategy. The results showed the potential use of this approach for vibration mitigation of structures. © 2006 by School of Engineering and Technology, Asian Institute of Technology

Lateral seismic response of building frames considering dynamic soil-structure interaction effects

In this study, to have a better judgment on the structural performance, the effects of dynamic Soil-Structure Interaction (SSI) on seismic behaviour and lateral structural response of mid-rise moment resisting building frames are studied using Finite Difference Method. Three types of mid-rise structures, including 5, 10, and 15 storey buildings are selected in conjunction with three soil types with the shear wave velocities less than 600m/s, representing soil classes Ce, De and Ee, according to Australian Standard AS 1170.4. The above mentioned frames have been analysed under two different boundary conditions: (i) fixed-base (no soil-structure interaction), and (ii) flexible-base (considering soil-structure interaction). The results of the analyses in terms of structural lateral displacements and drifts for the above mentioned boundary conditions have been compared and discussed. It is concluded that the dynamic soil-structure interaction plays a considerable role in seismic behaviour of mid-rise building frames including substantial increase in the lateral deflections and inter-storey drifts and changing the performance level of the structures from life safe to near collapse or total collapse. Thus, considering soil-structure interaction effects in the seismic design of mid-rise moment resisting building frames, particularly when resting on soft soil deposit, is essential

Effects of Dynamic Soil-Structure Interaction on Performance Level of Moment Resisting Buildings Resting on Different Types of Soil

In this study, two structural models comprising five and fifteen storey moment resisting building frames are selected in conjunction with three different soil deposits with shear wave velocity less than 600m/s. The design sections are defined after applying dynamic nonlinear time history analysis based on inelastic design procedure using elastic-perfectly plastic behaviour of structural elements. These frames are modelled and analysed employing Finite Difference approach using FLAC 2D software under two different boundary conditions namely fixed-base (no soil-structure interaction), and considering soil-structure interaction. Fully nonlinear dynamic analyses under the influence of different earthquake records are conducted and the results of inelastic behaviour of the structural models are compared. The results indicate that the inter-storey drifts of the structural models resting on soil types De and Ee (according to the Australian standard) substantially increase when soil-structure interaction is considered for the above mentioned soil types. Performance levels of the structures change from life safe to near collapse when dynamic soil-structure interaction is incorporated. Therefore, the conventional inelastic design procedure excluding SSI is no longer adequate to guarantee the structural safety for the building frames resting on soft soil deposits

Seismic behavior of building frames considering dynamic soil-structure interaction

The seismic excitation experienced by structures is a function of the earthquake source, travel path effects, local site effects, and soilstructure interaction (SSI) influences. The result of the first three of these factors is referred to as free-field ground motion. The structural response to free-field motion is influenced by the SSI. In particular, accelerations within structures are affected by the flexibility of the foundation support and variations between the foundation and free-field motions. Consequently, an accurate assessment of inertial forces and displacements in structures can require a rational treatment of SSI effects. In the current study, to depict these effects on the seismic response of moment-resisting building frames, a 10-story moment-resisting building frame resting on a shallow foundation was selected in conjunction with three soil types with shear-wave velocities of less than 600 m/s, representing Soil Classes Ce, De, and Ee according to an existing Australian Standard. The structural sections were designed after applying dynamic nonlinear time-history analysis, based on both the elastic method, and inelastic procedure using the elastic-perfectly plastic behavior of the structural elements. The frame sections were modeled and analyzed using the finite-difference method andthe FLAC 2D software under two different boundary conditions: (1) fixed-base (no SSI) and (2) considering the SSI. Fully nonlinear dynamic analysis under the influence of various earthquake records was conducted and the results of the two different cases for elastic and inelastic behavior of the structuralmodel were extracted, compared, and discussed. The results indicate that the performance level of themodel resting on Soil Class Ce does not change substantially and remains in the life safe level while the performance level of themodel resting on Soil Classes De and Ee substantially increase from the life safe level to near collapse for both elastic and inelastic cases. Thus, considering SSI effects in the elastic and inelastic seismic design of concrete moment-resisting building frames resting on Soil Classes De and Ee is essential. Generally, by decreasing the dynamic properties of the subsoil such as the shear-wave velocity and shear modulus, the base shear ratios decrease while interstory drifts of the moment-resisting building frames increase relatively. In brief, the conventional elastic and inelastic design procedure excluding the SSI is not adequate to guarantee structural safety for moment-resisting building frames resting on Soil Classes De and Ee. © 2013 American Society of Civil Engineers

Numerical and experimental investigations on seismic response of building frames under influence of soil-structure interaction

In this study, an enhanced numerical soil-structure model has been developed which treats the behaviour of soil and structure with equal rigour. The proposed numerical soil-structure model has been verified and validated by performing experimental shaking table tests. To achieve this goal, a series of experimental shaking table tests were performed on the physical fixed based (structure directly fixed on top of the shaking table) and flexible base (considering soil and structure) models under the influence of four scaled earthquake acceleration records and the results were measured. Comparing the experimental results with the numerical analysis predictions, it is noted that the numerical predictions and laboratory measurements are in a good agreement. Thus, the proposed numerical soil-structure model is a valid and qualified method of simulation with sufficient accuracy which can be employed for further numerical soil-structure interaction investigation studies. Based on the predicted and observed values of lateral deflections of fixed base and flexible base models, lateral deflections of the flexible base model have noticeably amplified in comparison to the fixed base model. As a result of the lateral deflection amplifications, it is observed that the performance level of the scaled structural model changed significantly which could be safety threatening

Damage localization based on symbolic time series analysis

Copyright © 2014 John Wiley & Sons, Ltd. The objective of this paper is to localize damage in a single or multiple state at early stages of development on the basis of the principles of symbolic dynamics. Symbolic time series analysis (STSA) of noise-contaminated responses is used for feature extraction to detect and localize a gradually evolving deterioration in the structure according to the changes in the statistical behaviour of symbol sequences. Basically, in STSA, statistical features of the symbol sequence can be used to describe the dynamic status of the system. Symbolic dynamics has some useful characteristics making it highly demanded for implementation in real-time observation application such as SHM. First, it significantly reduces the dimension of information and provides information-rich representation of the underlying data. Second, symbolic dynamics and the set of statistical measures built upon it represent a solid framework to address the main challenges of the analysis of nonstationary time data. Finally, STSA often allows capturing the main features of the underlying system whilst alleviating the effects of harmful noise. The method presented in this paper consists of four primary steps: (i) acquisition of the time series data; (ii) creating the symbol space to produce symbol sequences on the basis of the wavelet transformed version of time series data; (iii) developing the symbol probability vectors to achieve anomaly measures; and (iv) localizing damage on the basis of any sudden variation in anomaly measure of different locations. The method was applied on a flexural beam and a 2-D planar truss bridge subjected to varying Gaussian excitation in presence of 2% white noise to examine the efficiency and limitations of the method. Simulation results under various damage conditions confi rmed the efficiency of the proposed approach for localization of gradually evolving deterioration in the structure; however, for the future work, the method needs to be verified by experimental data

Flexural toughness and ductility characteristics of polyvinyl-alcohol fibre reinforced concrete (PVA-FRC)

This paper presents the results of an experimental study investigating the effect of un-coated polyvinyl alcohol (PVA) fibres on the properties of hardened concrete. PVA fibre of varying lengths, 6 and 12 mm and aspect ratio (l/d) of 430 and 860, respectively, was utilised in different volume fractions of 0.125%, 0.25%, and 0.5%. In addition, 30% fly ash was also used as partial replacement of Portland cement in all fibre reinforced concrete (FRC) mixes. Uniaxial compression, splitting tensile, modulus of rupture (MOR) and modulus of elasticity (MOE) tests were performed following the Australian Standards to evaluate the mechanical properties of PVA-FRCs. Fracture test is also conducted in accordance with European Standard in order to evaluate the residual flexural tensile strength and limit of proportionality of PVA-FRCs. Furthermore, the structural properties of reinforced concrete (RC) beams incorporating PVA fibres are investigated for their load-deflection behaviour using 4-point loading. Flexural toughness of the test specimens and peak load deflection were measured and discussed indicating to what extent the un-coated PVA fibre can enhance the brittle-like behaviour of concrete. Results show that adding PVA fibres to the mix generally improves the mechanical properties of concrete. Regarding the strength, the optimum fibre content goes to 0.25% for both fibre lengths and in the case of toughness and ultimate deflection 0.5% shows the highest values. An increase of 30% in ductility is noted for the RC beam incorporating 0.5% by volume fraction of 12 mm PVA fibre

On the magnetic field and temperature monitoring of a solenoid coil for a novel magnetorheological elastomer base isolator

Following a successful experimental validation of a magnetorheological elastomer (MRE) base isolator, this study presents one of the major concerns, the heating of the magnetic coil, in the design and development of the adaptive MRE based isolator. In this research, the MRE materials, with a total thickness of nearly 150 mm, are placed as the magnetic core of the device to best utilize the magnetic energy provided by the coil. A series of tests are undertaken to investigate the magnetic fields inside the coil with or without the MRE materials. Thermocouples are used to monitoring the surface temperature of the coil when it is applied with various currents for 10 min. It is shown that the measurement of field inside the solenoid when no MRE is placed inside agrees with the theoretical analysis. It is also shown that the temperature of the coil increase dramatically when a current is applied. Cooling of the coil may takes even longer, about 4 h, till down to the room temperature. Dropping of the magnetic field is observed when the temperature goes high. © Published under licence by IOP Publishing Ltd

Pushover testing of circular adobe structure

Many unreinforced adobe or mud-brick structures have in the past suffered severe damage from seismic forces and have caused a vast number of deaths. In contrast, some adobe buildings located in seismic regions have performed well under several seismic events. Researchers noticed that most existing circular adobe houses performed well in withstanding earthquakes even though some did not have any additional ductile reinforcement. This paper presents the investigation of seismic performance of unreinforced circular adobe buildings using static pushover testing. A scaled model (1:3 scale) of adobe circular structure were built and tested by static lateral load and pushed to total collapse. The results presented in the form of capacity curves, are compared with the expected lateral loading obtained from the static tilt testing carried out in earlier research. The outcome of this research can be used to evaluate the existing circular adobe houses and can give design recommendations of suitable configurations for new circular adobe buildings. © (2011) Trans Tech Publications

Transmissibility function analysis for boundary damage identification of a two-storey framed structure using artificial neural networks

This paper presents a damage identification technique that uses output-only scalar transmissibility measurements of a structure to identify boundary conditions. A damage index is formulated based on output-only acceleration response measurements from ambient floor vibration. The damage index is analysed by a system of artificial neural networks (ANNs) to predict boundary condition changes of the structure. Using the data compression and noise filtering capabilities of principal component analysis (PCA), the size of the damage index is reduced in order to obtain suitable patterns for ANN training. To test the proposed method, it is applied to different models of a numerical two-storey framed structure with varying boundary conditions. Boundary damage is simulated by changing the condition of individual joint elements of the structure from fixed to pinned. The results of the investigation show that the proposed method is effective in identifying boundary damage in structures based on output-only response measurements. © 2013 Taylor & Francis Group