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One-part alkali-activated materials (AAMs) are developed to improve conventional two-part systems. One-part AAMs technology has been used in cement binders to produce concrete, mortar, and paste. Current research mainly focuses on synthesizing raw materials obtained from industrial and agricultural waste as the main aluminosilicate precursors of the cement binder for a concrete application. The one-part AAMs were reported to have higher early compressive strength at 7 days of age, contributed by its fast-setting time, mainly when the binder activates by a higher dosage of alkaline activator and containing OPC-rich. Due to bonding issues, single or combination, FA/GGBFS/MK precursors were reported as unsuitable for use as a concrete repair material. They were the reason for the lack of one-part AAMs application of mortar compared to concrete usage. This study was conducted to determine the potential of one-part AAMs used as concrete patch mortar by investigating its rheology and mechanical properties. The compressive strength of the mortar was tested under lab ambient temperature in the tropical climate country of Malaysia. The setting time of fresh mortar and bonding strength were set under controlled lab temperature. The one-part alkali-activated mortar was composed of hybrid aluminosilicate precursors between fly ash (FA), Ground Granulated Blast Furnace Slag (GGBFS) and ordinary Portland cement (OPC). A low alkaline activator of solid potassium carbonate was used for the geopolymerization process. Three types of solid admixtures were added to complete the composition of the new mix design. The experiment's outcome showed that the mortar composed with the combination of conventional Portland cement and industrial waste products has compressive and pull-off adherence strength that meets with Class R3—EN1504-3 standard for structural concrete repair materials requirement.

One-part alkali-activated materials (AAMs) are an alternative material to respond to the shortcoming of the conventional two-part systems. One-part AAMs are more practical and safer to handle from transporting to the casting stage on site. It can be applied in the form of paste, mortar, and concrete, providing more options than an ordinary cement binder. The most common aluminosilicate precursors sources for the one-part AAMs are the combination or single raw material of fly ash, ground granulated blast furnace slag and metakaolin. However, it was found that the one-part AAMs experienced high porosity levels primarily due to their inconsistent pore structures that affect their long-term performance. One-part AAMs mortar is one of the cementitious products used as concrete repair materials that may be affected by these weaknesses. Nevertheless, the combination of aluminosilicate precursor by-products with the ordinary Portland cement or hybrid AAMs help to develop a robust performance mainly used as a patching product for concrete repair materials. This hybrid one-part AAMs mortar can be composed with other admixtures with a suitable mix design to ensure its stability and useable in the form of a fresh and hardened state. Unlike the ordinary concrete, hybrid one-part AAMs have significantly strengthened growth beyond the 28th day. In this study, the mechanical strength of the mortar increased over time up to 63 N/mm2 at 56 days of curing age, shorter setting time and workable comparable to the control samples. In addition, the water to binder ratio of 3.0 activated the dry mixes and significantly improved the physical and microstructure of the hybrid one-part AAMs mortar.

This paper introduces a wireless smart sensor network to meet the requirements for measuring low-amplitude ambient and sudden event monitoring of civil structures. The developed sensor platform con...

This paper uses the results of experimental and finite element analyses of the Campbell Creek Bridge in Alaska to highlight the effect of seasonal freezing on bridge dynamic response and the structural and geotechnical parameters controlling the changes in response. The experimental modal characteristics of the bridge were defined using dynamic monitoring data collected over 1 year by means of several frequency and time domain system identification techniques. Good agreement was shown across the range of techniques and clear modal characteristics were defined, suggesting a significant increase in natural frequency and change in mode shape of the bridge due to seasonal freezing effects. Elastic finite element models of the bridge, utilizing a Winkler spring approach, were able to effectively capture the experimental dynamic response, with the natural frequencies and mode shapes of the bridge in the transverse direction shown to be controlled by the changes in the stiffness of the foundation soil and the bearings. The significant shift in bridge dynamic characteristics and change in boundary conditions due to seasonal freezing demonstrates the need for seismic assessment of the bridge stock across potential temperature ranges in seismically active regions that experience seasonal freezing.

In this paper, the condition of a full-scale concrete bridge subjected to strong earthquakes is evaluated using vibration-based analyses. A new computational toolkit is developed in MATLAB environment for damage identification and long-term monitoring. Two types of parametric and non-parametric analysis methods are carried out on monitoring data. Moreover, a dynamic performance index is proposed based on an AutoRegressive Moving Average with eXogenous excitation (ARMAX) model. This index utilises the response predicted from an ARMAX model to evaluate bridge behaviour during strong earthquakes. Based on the results, a minor but permanent drop of 0.05 Hz in natural frequency of the first transverse and vertical modes is observed after the first strong earthquake. Also, a significant drop in frequency of the first transverse mode is observed during the two strong earthquakes. The results of the index show that the bridge did not follow linear behaviour during the two strong earthquakes as expected fr...

The challenges of accurately identifying the dynamic characteristics of bridge structures from ambient vibration responses persist because, unlike in the ideal laboratory environment, elevated levels of noise in data are unavoidable at any in-situ testing site and may have detrimental effects on the modal parameter identification process and results. This is especially true for vibration tests conducted under weak ambient excitation sources resulting in poorer signal-to-noise ratios (SNRs). This paper presents an investigation into the feasibility and reliability of modal identification using operational modal analysis (OMA) techniques under such weak excitation circumstances and with responses measured by inexpensive stand-alone accelerometers/data recorders. An eleven-span concrete motorway off-ramp bridge, closed to traffic, was excited only by ground vibrations generated by traffic on the motorway passing underneath the bridge as well as on nearby motorway on- and off-ramps, weak winds, and possible micro tremors. A high spatial resolution of measuring points on the bridge deck was used to collect vibration responses. Three output-only modal parameter identification algorithms were utilised to extract the modal properties, namely the peak picking (PP), the frequency domain decomposition (FDD) and the data driven stochastic subspace identification (SSI) method. Nine lateral and three vertical modal frequencies below 10 Hz could be identified despite the weakness of the environmental excitations and noise in sensors. The identified experimental natural frequencies were stable, damping ratios, however, had a marked scatter. A comparison with the results of a numerical modal analysis using a finite element model revealed, however, that several higher order vertical modes were missing from the experimental results altogether, and some of the OMA methods missed the fundamental lateral mode. Overall the PP method was the most successful in finding the largest number of frequencies but the SSI method yielded the highest quality mode shapes. The SSI method is, however, computationally more expensive that the remaining two methods. For quick, preliminary results, the PP and FDD methods can still be useful and detailed analyses could use SSI and FDD. Overall, the study argues that output-only system identification can provide useful quantitative insights into the modal properties of stiff bridges even under weak environmental excitations, or poorer SNRs, but its limitations need to be acknowledged.

This study investigates factors affecting tsunami-borne debris impact force on structures. Debris collision accelerations were measured at the contact point on the structure's seaward wall using disc- and box-shaped smart debris devices; the equation of motion was used to estimate the debris impact forces from the measured accelerations. Also, the impact force was measured at the base of the structure using a multi-axis load cell, and compared with the forces determined using the smart debris devices. The basic impulse-momentum formula was modified by the addition of coefficients, taking into account the added mass and the debris velocity. Debris shape also influenced the impact force. Deformability of the debris and flexibility of the structure both reduced the debris impact force.

This paper presents new experimental techniques utilizing a smart debris device for direct measurement of the impact acceleration forces associated with tsunami-borne debris that impact inland structures. The resulting experimental data will lead to advanced predictive capabilities of such forces for use in design guidelines. The measured debris acceleration data were used to calculate impact forces (mass × acceleration). An image processing technique was used to detect the debris impact angle. The debris impact tests were conducted using a disc-shaped smart debris device with masses of 550, 800 and 1000 g. For calculation of the debris force it was found necessary to include the mass of entrained water. The impact acceleration was found to be a function of debris mass, velocity, and contact duration. An equation is developed to allow estimation of the debris velocity for a known distance between the debris pick-up location by a tsunami and the structure.

This paper addresses and evaluates the influence of different types of dynamic excitation sources on identifiability and reliability of modal parameter identification of an eleven-span, post-tensioned, curved concrete motorway off-ramp bridge. The excitation sources included ground vibration waves generated by traffic on nearby motorways, people jumping on the bridge deck, broad-band linear chirp excitation induced by two light electro-dynamic shakers, and stepped sinusoidal sweeping forcing induced by a rotating eccentric mass shaker. Experimental modal analysis, operational modal analysis (OMA) and OMA with exogenous input system identification by a subspace state-space identification algorithm were carried out to extract the modal characteristics of the bridge. Numerical frequencies and mode shapes were also calculated from a detailed shell-element bridge model with the purpose of serving for the corroboration of the experimental modal properties. Through comprehensive cross-comparisons, it was revealed that the natural frequency discrepancies across different excitation methods were small (within ±1.5% relative difference), whist the consistency of the estimated damping ratios was poorer (up to 1.4% absolute difference). Eccentric mass shaker testing enabled identification of all modes predicted by the numerical model but used very heavy equipment. On the other hand, in ambient testing about one-third of the modes were missed, including the fundamental lateral mode. Electrodynamic shaker testing proved attractive as it only missed one mode and achieved its good performance with shakers that could be moved on site with relative ease.

New Zealand is one of the seismically active countries on the planet and it’s tectonic setting has featured many active faults. Strong motion monitoring has been carried out for about 40 years in New Zealand and recorded data on ground shaking as well as structural response. While the ground motion monitoring has been growing in scale over the years, just over a decade ago, a nationally significant structural monitoring program was established to record seismic response of typical structures that are representative of New Zealand building inventory. Monitoring with permanent instrumentation and continuous recording of data enable to perform short-term damage detection after an event as well as long-term effects in the health of the structure. The chapter will further discuss on the damage detection methods that were proposed and adopted using the records from instrumented structures in New Zealand. It will include a description around the new computational tools for damage identification and long-term dynamic monitoring. The toolkits provide functions for automated dynamic parameters and response amplitudes monitoring. The potential of these toolkits is illustrated using data collected by the continuous dynamic monitoring system installed on a full scale reinforced concrete bridge in Wellington, New Zealand.

This paper presents a unique study of dynamic behaviour of a full-scale 13-story reinforced concrete building under forced vibration, ambient vibration, and distal earthquake-induced excitation. Initially, an eccentric mass shaker located on the upper floor of the building was used to excite the building while instrumented with eight accelerometers. Then, ambient vibrations induced by traffic and wind were recorded over a period of two weeks, utilizing over 40 tri-axial accelerometers. During the sampling period, the building was excited by a M6.5 earthquake and high-quality vibration data sets were recorded. Modal parameters of the building were identified with a range of frequency and time domain system identification (SI) methods, and the influence of excitation force characteristics on performance of various techniques was also investigated. A finite element model of the building was developed using SAP2000 to compare modal properties to the identified counterparts from experiments. Results showed a strong correlation between modal parameters identified by different SI methods, and all techniques provided accurate estimation of modal parameters when used with output-only data. Modal parameters determined from ambient vibrations were comparable to their forced vibration counterparts, providing evidence that ambient vibration testing can be as effective as forced vibration testing in determining modal parameters for similar size structures. The near stationary vibration data can produce accurate estimation of modal parameters. However, further study is required to facilitate application of output-only SI techniques with non-stationary data. There was a good match between peak displacement amplitudes obtained by the numerical model and those experimentally measured at different excitation frequencies. This match demonstrated the accuracy of the finite element model to predict realistic dynamic behaviour of the building under various harmonic excitation forces.

This paper examines experimentally the effect of forcing and response amplitude on the variability of modal parameters of a bridge. An eleven-span prestressed concrete motorway off-ramp bridge was subjected to multiple dynamic tests with varying excitation levels by using eccentric mass shakers exerting forces in the vertical and lateral direction. The frequency sweeping technique with small increment steps in the vicinity of resonant frequencies was employed to construct frequency response functions at different shaking levels from which the natural frequencies, damping ratios and mode shapes were identified for several vertical, mixed vertical–torsional and lateral modes. Softening dynamic force–displacement relationships were observed for all the modes, and the natural frequencies showed clear and consistent decreasing trends with increasing response amplitude. Modal damping ratios initially increased with increasing response amplitude, but later, for the modes where experimental data were available, stabilised at elevated levels. A finite element (FE) model of the bridge was also created and the experimental modal properties compared to the numerical ones. A good agreement was generally noticed for the lower modes but the higher modes had more error. The FE model was used to assess the likely levels of structural damage that would have a similar effect on the natural frequencies as the amplitude dependence. One numerical damage scenario indicated that a reduction of 20% of stiffness in the middle of the main span would cause larger frequency shifts of some modes but amplitude dependent effects will dominate in other modes. Another numerical damage scenario was a reduction by 50% of stiffness at the bottom of the highest pier, and it was shown this type of damage would result in only one third of the frequency drop caused by the amplitude effects in a single, most affected mode.

With the recent high level of earthquake activity throughout New Zealand there is growing awareness of the need for quick and reliable determination of whether buildings are safe. In parallel, on-going advances in sensors and computing technology have resulted in the potential for new and innovative sensing systems which could change the way that civil infrastructure is monitored, controlled and maintained. Following the 21 July 2013, MW 6.5 Cook Strait earthquakes, seven buildings in the Wellington region were instrumented with low-cost accelerometers to record building response data sets during aftershock excitations. A summary of the data analyses and insightful information obtained through processing and interpretation of the raw data is presented. Key challenges and considerations of installing a permanent structural monitoring system into buildings in New Zealand are discussed. The goal was to relate building performance indicators to decision making processes regarding the safety and resilience of structures post-earthquake. The information obtained was sufficiently reliable and valuable to the decision making process and New Zealand can expect more permanently instrumented buildings in the future.

By using a piezoelectric actuator, a real steel bridge can be accelerated locally to detect the effect of small damage like fatigue crack and connection damage as a response to change of vibration. Power spectrum density (PSD) function of the response can give us the indication of the extent of damage before and after the damage. Detailed analysis of PSD before and after damage can give us the location and size (area) of damage. This paper shows the experimental result of damage detection by using local excitation method on a real bridge.

The Bridge Engineering Laboratory in Kitami Institute of Technology, Japan has introduced a number of different damage identification techniques to detect structural damage and identify its location utilizing piezoelectric actuators as a localized excitation source. Several spectral functions, such as cross spectral density, power spectral density, phase angle and transfer function estimate, were used to estimate the dynamic response of the structure. Each function’s magnitude, measured in a specified frequency range, is used in the damage identification methods. The change of the spectral function magnitude between the baseline state and the current state is then used to identify the location of possible damage in the structure. It is then necessary to determine which spectral function is best able to estimate the dynamic response and which algorithm is best able to identify the damage. The first part of this paper compares the performance of different spectral functions when their magnitude is used in one damage identification algorithm using experimental data from a railway steel bridge. The second part of this paper compares the performance of different damage identification algorithms using the same data.

Because of the critical importance of bridges in land transport networks and broader economy, an increasing interest in permanent observation of their dynamic behavior under traffic, seismic and other live loads has been observed during the past decade. In addition, recent technological advances have made the installation and operation of permanent dynamic monitoring systems much more practical and economical. A multi-channel dynamic monitoring system is being installed in the 12 span pre-cast, post-tensioned Newmarket Viaduct, recently built using the balanced cantilever method and situated in Auckland, New Zealand. This paper first describes the preliminary studies including extensive one-off ambient vibration tests using wireless sensors that provided important information for the design of the monitoring system shortly after construction of the bridge. Then the designed monitoring system is characterized and proposed research that will be undertaken using the monitoring data is outlined.

There has been little full-scale physical experimentation to support the findings of numerous computational studies regarding the contribution of various substructure components to overall bridge-foundation system behavior. In response to this lack of experimental data, a field testing program was undertaken to investigate the in situ dynamic characteristics of a 27-m-long, three-span, precast-concrete bridge. Forced vibration testing and system identification were used to characterize the dominant modal behavior of the bridge-foundation system in each loading direction, leading to identification of the likely force-transfer mechanisms between the structure and the substructure components. It was determined that both the transverse and longitudinal responses of the bridge were dominated by the abutment stiffness, with the passive resistance of the buried settlement slab contributing significantly to the transverse response and the backfill passive resistance dominating the longitudinal response.

During the 2010 Mw7.1 Darfield earthquake, the single span Davis Road Bridge located 5 km southeast of Lincoln, New Zealand, sustained significant lateral spreading damage to the western approach. While lateral spreading resulted in up to 450 mm of approach settlement and evidence of damage to the pile foundations, the bridge superstructure sustained no significant damage. Prior to reinstating traffic, the bridge was used for full scale dynamic testing to characterise the influence of different substructure components on the lateral dynamic behaviour of the bridge superstructure. The bridge was characterised using an eccentric mass shaker and an array of accelerometers to perform lateral forced vibration testing in both the transverse and longitudinal directions. Modal properties were extracted from these tests using multiple system identification algorithms. The experimental testing and system identification methodology are described here. Forced vibration testing was able to detect one mode in each principal direction of the bridge, with the fundamental modes for the transverse and longitudinal direction occurring at a period of 0.118 s and 0.092 s respectively. The torsional response found during the transverse direction shaking was most likely due to the effect of gap opening around the piles on the western abutment, while the longitudinal response was dominated by the approach soil.

SUMMARY Vibration-based damage detection (VBDD) comprises a promising set of techniques for damage detection and health monitoring of civil engineering structures. However, the successful application of these methods to real structures is still a challenging task, due primarily to the large size of such structures and the relatively high levels of variability in their dynamic response under operational load conditions. In this paper, a new methodology is introduced for the application of VBDD techniques, with the goal of enhancing their effectiveness for identifying and locating low damage levels and improving their applicability to the continuous or periodic health monitoring of structures. The basic features of the methodology include the use of a controlled and consistent excitation force, the use of operational deflection shapes (ODSs) at all measured frequency increments rather than only at natural frequencies, the use of a logarithmic scale for representing the ODS amplitudes at each frequency increment and the establishment of a threshold level for damage detection that accounts for experimental variability. The performance of the proposed methodology is verified and demonstrated by applying several Level 1 (damage detection) and Level 2 (damage localization) VBDD techniques using experimental data measured on a steel girder taken from a railway bridge. The proposed approach is shown to perform very well at detecting, locating and monitoring the growth of damage. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, a new approach for damage detection in beam-like structures is presented. The method can be used without the need for baseline modal parameters of the undamaged structure. Another advantage of the proposed method is that it can be implemented using a small number of sensors. In the proposed technique, the measured dynamic signals are decomposed into the wavelet packet decomposition (WPD) components, the power spectrum density (PSD) of each component is estimated and then a damage localisation indicator is computed to indicate the structural damage. The proposed method is firstly illustrated with a simulated beam and the identified damage is satisfactory with assumed damage. Then, the method is applied to a steel beam. The effect of damage location and the effects of wavelet type and the decomposition level are examined. The results show that the proposed method has great potential in crack detection of beam-like structures.

This paper presents structural damage detection method based on changes in Transfer Function Estimate (TFE) for detecting damage, predicting its location and monitoring the growth in damage. This method assumes that the displacement or the acceleration response time histories at various locations along the structure both before and after damage are available for damage assessment These responses are used to estimate TFE. The change of TFE between the baseline state and the current state is then used to identify the location of possible damage in the structure. TI1e method is applied to the experimental and numerical data obtained from a railway steel bridge that is no longer in service. Several damage scenarios were introduced to the main girder of the test structure. Results show the method can be used to detect the damage, determine the exact location and measure the growth in damage with very good accuracy. The use of piezoelectric actuators as a local excitation source for large structures such as steel bridges is also presented. Experimental and numerical results show that the proposed approach may be successfully implemented on-line to detect the damage and to locate regions where damage occurred., application/pdf

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Impact of tsunami-borne debris causes a significant force on coastal structures. Tsunami bores can carry different geometrical shapes of floating debris, which are often the greatest cause of damage to inland structures. Despite such a serious threat, the impact of floating debris on structures has received limited attention. The objective of this paper is to introduce a new method for measuring the impact force of floating debris on the seaward wall of structures during tsunami events. This will improve the understanding of tsunami-borne debris impact forces on structures and increase the predictive capabilities required for estimates of such forces in design guidelines. The debris impact tests were conducted using two smart debris devices with different geometrical shapes. Impact accelerations and forces in the horizontal and vertical planes were investigated.

The identification of structural damage is an essential goal of health monitoring for civil infrastructures. Damage of a structure reflects on a change of modal parameters, such as natural frequencies, mode shapes and modal damping. A method of damage identification for civil infrastructures based on strain energy is proposed in this paper. The method is described theoretically and applied to the experimental data from a steel bridge. Several damage scenarios were introduced to the members of the test structure. Experimental results show that the proposed approach may be successfully implemented to detect damage and to locate regions where damage occurred.This research also aims at establishment of experimental environment to enable the verification of applicability and the effective evaluation of the structural health monitoring (SHM) technology that uses the high performance sensor system on real bridges. The primary goal of the project is the development of test beds that meet wider requests for SHM experiments. Several steel bridges on an abolished railway in Hokkaido, Japan will be available for the establishment of the test beds. The test beds can be utilized by not only researchers of this project but also other researchers. The final goal of the project is international contribution by means of cooperative utilization of the test beds.

A wavelet-based technique is proposed for structural damage detection and health monitoring. In this technique, characteristics of representative vibration signals under the wavelet transformation are examined for damage identification. The proposed method is based on only the output data without the need for measuring the excitation forces, any modal identification or numerical models. The method is described theoretically and verified both experimentally and numerically using a railway steel bridge. The applicability of utilizing piezoelectric actuators for exciting large structures such as steel bridges is also investigated in this paper. Several damage scenarios were introduced to the test structure by removing bolts from some stiffeners located on the web of the main girder. Similar damage scenarios were introduced to the finite element model of the test structure. The results indicate that the current approach can identify the location of small damage effectively. The proposed method combined with the use of piezoelectric actuators is shown to be very suitable for continuous health monitoring of steel bridges. Copyright © 2009 John Wiley & Sons, Ltd.