Our goal was to develop a long life, low cost, scalable wireless sensing network, which collects and distributes data from a wide variety of sensors over the internet. Time division multiple access was employed with RF transmitter nodes (each w/unique16 bit address) to communicate digital data to a single receiver (range 1/3 mile). One thousand five channel nodes can communicate to one receiver (30 minute update). Current draw (sleep) is 20 microamps, allowing 5 year battery life w/one 3.6 volt Li-Ion AA size battery. The network nodes include sensor excitation (AC or DC), multiplexer, instrumentation amplifier, 16 bit A/D converter, microprocessor, and RF link. They are compatible with thermocouples, strain gauges, load/torque transducers, inductive/capacitive sensors. The receiver (418 MHz) includes a single board computer (SBC) with Ethernet capability, internet file transfer protocols (XML/HTML), and data storage. The receiver detects data from specific nodes, performs error checking, records the data. The web server interrogates the SBC (from Microsoft's Internet Explorer or Netscape's Navigator) to distribute data. This system can collect data from thousands of remote sensors on a smart structure, and be shared by an unlimited number of users.

The permanent or regular monitoring of structures with sensors of any type can generate a consistent volume of data. Furthermore, it is often necessary to store additional information that is useful for the analysis of the measurements. This data should be comprehensible even after tens of years. Our experience has shown that the use of relational database structures can greatly simplify the handling of this large data-flow. With an appropriate data structure, the measurement data and other related information on the monitoring network, the structure and its environment can be organized in a single file that will follow the structure's life in the years. The standardization of a database structure for storing monitoring data also allows the development of re-usable components for data acquisition, data analysis and representation. The use of relational database structures greatly simplifies the quality management and can help in the certification of monitoring systems. This contribution presents a new open and free standard for database structures aiming to the archival of long-term monitoring data. The implementation of this standard in data acquisition, analysis and representation software modules will also be described.

Working towards full implementation of semi-active MR dampers to over 200 cables in the cable-stayed Dongting Lake Bridge, a few selected stay cables were installed with both MR dampers and vibration sensors for trial testing before full implementation. This paper reports the field vibration tests of a typical stay cable of 115 m long before and after being installed with MR dampers. The field vibration tests were conducted by using ambient vibration excitation, and sinusoidal excitation followed by free vibration decay, respectively. The resonant frequencies and equivalent modal damping of the first twenty in-plane modes of the cable with and without MR dampers are identified. The relationship between the equivalent modal damping ratio and the applied voltage strength to MR dampers is experimentally determined. The test results show that the modal damping ratios of the free cable without dampers conform to a combined Rayleigh and frequency-independent damping model, and are almost unvaried with vibration amplitude within the tested range. Installation of MR dampers results in a slight change of resonant frequencies in comparison with the free cable, but variation in applied voltage almost does not affect the resonant frequencies. The equivalent modal damping ratios of the cable-damper system are found to be dependent on the installation location of MR dampers, voltage strength applied to the dampers, and the cable vibration level. The optimal voltage input, which achieves maximum system damping, is obtained for different modes under different vibration amplitudes. With optimal voltage applied to the dampers, the resulting system damping should be high enough to suppress both wind-rain-induced vibration and wake galloping of cables.

The newly built cable-stayed Dongting Lake Bridge in Hunan, China has experienced wind-rain-induced cable vibration several times during the past months. A research/implementation project on using semi-active magneto-rheological (MR) dampers for cable vibration control of the bridge is in progress. As part of this ongoing project, one typical stay cable with 115 m length was installed with two MR dampers near the lower anchorage, and accelerometers were deployed on the damped cable and its two neighboring cables for long-term monitoring. After installing the dampers and sensors, wind-rain-induced cable oscillations were observed two times. This paper aims to investigate the vibration characteristics and to identify the equivalent modal damping of the cables with and without MR dampers in one wind-rain-excited event based on in-situ monitoring. In this wind-rain-excited event, the in-plane and out-of-plane responses of the damped cable and its two neighboring free cables were monitored. Equivalent modal damping ratios of the cables in both in-plane and out-of-plane motions are identified by means of spectral analysis of the measured data in conjunction with a curve-fitting technique. Such observed and identified results are beneficial to understanding the coupled motion of cables in wind-rain-excited conditions and the damping contribution of MR dampers to both in-plane and out-of-plane motions. The frequency-domain analysis of the wind-rain-excited responses of the damped and undamped cables also reveals the response characteristics under wind-rain excitation and the damping mechanism of MR dampers in suppressing such oscillation.

In this paper, the effects of using semi-active control strategy (such as MR dampers) in vehicle suspensions on the coupled vibrations of a vehicle traversing a bridge are examined in order to develop various designs of smart suspension systems for bridge-friendly vehicles. The bridge-vehicle coupled system is modeled as a simply supported beam traversed by a two-degree-of-freedom quarter-car model. The surface unevenness on the bridge deck is modeled as a deterministic profile of a sinusoidal wave. As the vehicle travels along the bridge, the system is excited as a result of the surface unevenness and this excitation is characterized by a frequency defined by the speed of travel and the wavelength of the profile. The dynamic interactions between the bridge and the vehicle due to surface deck irregularities are obtained by solving the coupled equations of motion. Numerical results of a passive control strategy show that, when the lower natural frequency of the vehicle matches with a natural frequency (usually the first frequency) of the bridge and the excitation frequency, the maximum response of the bridge is large while the response of the vehicle is relatively smaller, meaning that the bridge behaves like a vibration absorber. This is undesirable from a bridge design viewpoint. Comparative studies of passive and semi-active controls for the vehicle suspension are performed. It is demonstrated that skyhook control can significantly mitigate the response of the bridge, while ground-hook control reduces the tire force impacted onto the bridge.

Steel strands are widely used in civil structures as pre- stressing tendons and stay-cables. The structural criticality of strands has led to an increasing interest in developing methods able to monitor applied loads as well as detect potential defects. In this paper ultrasonic guided waves, generated and detected via magnetostrictive sensors, are exploited to address this need. The sensors were developed in collaboration with the US Federal Highway Administration NDE Validation Center. An acousto elastic formulation of the Pochhammer-Chree longitudinal vibrations in cylindrical waveguides is proposed to predict the change of ultrasonic velocity as a function of applied stress. Results from acousto elastic experiments performed on seven- wire strands and on single wires are presented and compared to the theoretical predictions. Ways to enhance the inhernetly-low sensitivity of the acousto elastic measurements are proposed and investigated. The different behavior exhibited by the strand when compared to the single wire suggests the need for widening the theory governing the acousto elastic phenomenon in multi-wire members. The role of the strand anchorages is examined in the context of wave attenuation. The suitability of the guided wave method for the detection of defects is demonstrated including the possibility of inspecting the critical anchored regions.

In Germany, a group of researchers from four universities has developed an advanced experimental supported objective condition assessment method for concrete bridges, called 'EXTRA'. This method is useable preferably in cases where conventional assessment methods cannot be applied successfully. In the past more than 250 bridges and buildings were evaluated regarding their real actual load bearing capacity using this objective assessment method. In Germany, an authorized guideline for the practical application of concrete structures is available. Because in the past the process of mounting and dismantling the loading equipment did require the most time of the test duration and also the traffic interruption, the same researchers developed the loading truck BELFA, suitable for bridges with single spans 1 <EQ 18 m. The main aim was to reduce the test duration on less than two days. Since March 2001 the truck prototype with a maximum total loading capacity of 150 t now has been used for testing of more than 10 pilot objects. Operational areas, technical and economical experiences, but also aspects of acceptance are the main subjects, presented in connection with different practice examples. Besides this the truck structure and his flexible applicability for structure control and assessment tasks will be short illustrated. Experiences with the employment of the truck including costs and future possibilities for a cooperation with consulting offices, owners and authorities will be explained.

The goal of this project is to obtain structural health monitoring data using optical fiber Bragg grating sensors embedded in the filament-wound composite tube of a load carrying pile. This technology has applications for structural health monitoring of bridges, piers, and other post-supported infrastructure. These sensors provide strain data for the life history of the pile including pre-installation, installation, residual strains due to the installation process, and health monitoring for the lifetime of the pile. This paper describes the embedding process for the multiplexed fiber Bragg grating sensors into a 2-ft diameter, 60-ft long composite shell including composite manufacturing lay-up, sensor orientation, and ingress/egress of the optical fiber lead from the composite shell. The paper then discusses in-field tests of the monitoring system. Results from the sensor system will provide civil engineers with a greater understanding of load transfer in the composite pile system. Long term structural monitoring of the composite piles will also be demonstrated with this technology. The purposes of these tests are to: 1) determine the survivability of the sensor arrays during a pile driving process, 2) measure strains on the filament wound composite shell following the pile driving process, and 3) determine if structural integrity issues are observed from the strain data.

Simple and inexpensive passive sensors that can monitor the peak strain or displacement of a critical structural member were developed. The developed sensors have an ability to quickly assess the degree of damage in a structure when a checkup is needed. The sensors need no power supply for monitoring. The peak values can be retrieved wirelessly if desired. In addition, they can be easily modified to measure other damage indexes such as maximum acceleration and force. The mechanism to memorize the peak strain or displacement values relies on the pure plastic extension of sensing section. The pure plastic extension of the sensing section is made possible by introducing elastic buckling. The peak value is detected by measuring a change in electric resistance, inductance or capacitance. In addition, introduction of an LC circuit into the sensor enabled wireless retrieval of the data. Theoretical and experimental studies exhibit the feasibility of the developed sensors for structural health monitoring of smart structures.

Damage diagnosis is a problem that can be addressed at many levels. Stated in its most basic form, the objective is to ascertain simply if damage is present or not. In a statistical pattern recognition paradigm of this problem, the philosophy is to collect baseline signatures from a system to be monitored and to compare subsequent data to see if the new 'pattern' deviates significantly from the baseline data. Unfortunately, matters are seldom as simple as this. In reality, structures will be subjected to changing environmental and operational conditions that will affect measured signals. In this case, there may be a wide range of normal conditions, and it is clearly undesirable to signal damage simply because of a change in the environment. In this paper, a unique combination of time series analysis, neural networks, and statistical inference techniques is developed for damage classification explicitly taking into account these natural variations of the system in order to minimize false positive indication of true system changes.

Vibratory compaction is a proven and commonly adopted densification technique applicable for a wide variety of soil types and compositions. There is a clear need to develop performance-based intelligent vibratory soil compaction techniques wherein the state of the soil is determined during compaction (i.e., health monitoring, continuous quality control). The application of vibration-based structural health monitoring strategies utilized in damage detection applications to the problem of soil compaction appears promising. A vibratory compactor (plate or drum) operating on a soil mass constitutes a coupled dynamic system. As the soil densifies and its mechanical properties change, the dynamic response of the compactor will change. This paper examines the changes in dynamic response of a vibratory plate during compaction. The analysis of vibration data taken from sensors on the plate and embedded within the soil reveals clear changes in both amplitude and frequency components that provide insight into the evolving nonlinear response of the system.

A wireless sensing unit for use in a Wireless Modular Monitoring System (WiMMS) has been designed and constructed. Drawing upon advanced technological developments in the areas of wireless communications, low-power microprocessors and micro-electro mechanical system (MEMS) sensing transducers, the wireless sensing unit represents a high-performance yet low-cost solution to monitoring the short-term and long-term performance of structures. A sophisticated reduced instruction set computer (RISC) microcontroller is placed at the core of the unit to accommodate on-board computations, measurement filtering and data interrogation algorithms. The functionality of the wireless sensing unit is validated through various experiments involving multiple sensing transducers interfaced to the sensing unit. In particular, MEMS-based accelerometers are used as the primary sensing transducer in this study's validation experiments. A five degree of freedom scaled test structure mounted upon a shaking table is employed for system validation.

In order to restore damaged buildings affected by earthquake excitations, it is important to identify damaged elements in terms of their dynamic properties; stiffness, mass and damping coefficients. In this paper, a simple method is proposed for identification of the damaged part. By considering all unknown dynamic properties of structure as variables of a target function f in nonlinear programming problem, the damage identification problem can be replaced by a typical unconstrained minimization problem. The target function is defined as f equals (Sigma) [ (y_n,i) - (y_n*) ]² where (y_n,i) is structural response at the time of t equals (Delta) X n derived from i-th trial variable (X_i), and (y_n*) means observed response, respectively. In order to achieve quick convergence, quasi- Newton method and BFGS formulae are adopted for minimizing the target function. Two decision problems are discussed. One is the choice of structural response; displacement, velocity or acceleration. The second is the kind of external excitations that should be adopted. By observing three dimensional graphics. It appeared that good convergence can be achieved by adopting displacement response and sinusoidal excitation. Furthermore, it appeared that we should not evaluate the identified properties only from the response diagrams.

The Siggenthal Bridge is a concrete arch bridge with an arch span of 117 m, being built over the Limmat River in Baden, Switzerland. This bridge has been instrumented with 58 long- gage SOFO fiber optic deformation sensors, 2 inclinometers and 8 temperature sensors to monitor its deformations, curvatures and displacements during construction and int eh long-term. The sensor have been built installed successfully and the arch was monitored during the removal of the formwork and supports. It was therefore possible to observe the deformations of the arch wen being loaded by its dead load and by the daily temperature fluctuations. The measurements have shown that the temperature changes produce deformations of the same order of magnitude as the dead loads. The out-of-plain displacements obtained by double- integration of the measured curvatures are in good agreement with the direct triangulation measurements. Monitoring was also carried out during the construction of the superstructure, with the associated change of the load distribution in the arch. This paper briefly introduces the functional principle of the long-gage sensors used in this application, illustrates their installation and discusses the measurement results obtained during the bridge construction.

This paper uses a damage detection approach based on de- reverberated transfer functions to detect multiple damage locations in a building structure model. De-reverberated transfer functions (DTFs) can be obtained by applying virtual wave controllers to eliminate wave reflections at structural discontinuities and boundaries. The ratio of DTFs between two successive degrees of freedoms (DOFs) represents local structural dynamics. Multiple damage locations in a structure result in phase differences of DTFs before and after damage. Damage occurring in multiple locations can be determined by introducing the concept of phase damage index. However, one can identify multiple damage locations one by one along the traveling wave path. The downstream damage is identified and corrected until all damage elements are repaired. In this study, a three-story building model is tested under sine sweep wave excitation. Experimental results show that this approach can be used to locate the presence, determine the type, and quantify the extent of multiple damage conditions in a structure.

Thirty years ago, automotive engineers perfected real-time damping for vehicle suspension systems prior to hitting bumps in the road. In the near future, architects and structural engineers may be able to use the same philosophy for tuning structures to withstand earthquakes as their waves impinge on the structure. Coupled with seismic monitors and a reliable communications systems such as California's TriNet real-time seismic monitoring system which can relay specific ground motions to buildings, we can expect that-we will be able to tune building frames to reduce both motion and damage in an economic manner. Most materials respond to heat by expanding in volume. Nitinol is a shape memory alloy (SMA) that has the peculiar quality ofcontracting when heated. By variably heating a system ofnitinol wires designed within a building structure, the frequency response ofthe structure, torsion and percent ofcritical damping could be altered as the structure experiences an earthquake. Nitinol is a nickel-titanium-based metal that has seen use in robotics for return control that resembles the bioenergetics ofmuscles and tendons. Small electrical currents can be placed into the nitinol where the resulting resistance causes rapid heating and consequent reduction in volume. By lacing steel buildings with a series ofnitinol wires in cross directions and coupling them with both an energy source and communications receiving systems from TriNet, the response ofthe building structure can be altered. This could improve damping ratios with respect to any particular earthquake in a similar fashion to forward looking automotive suspension systems. This paper shows examples by using building models.

The thermoelastic martensitic transformation is the origin of the peculiar properties of Cu-based SMA. One of the potential uses consists on taking advantage of their hysteresis cycle to smooth the oscillations induced by wind or quakes. The experimental study at mesoscale level of the Cu-based alloys and in preliminary level of TiNi allows the development of a one-dimensional model that describes their response to the external thermodynamic forces. The evolution associated to diffusion effects (phase coexistence and temperature-time on parent phase) is also included. The results furnished by the model establish the appropriate guarantee of the alloy properties for series of working cycles separated by long times in austenite phase as the scarce events (as in earthquakes). Using a simple case, the simulation determines the boundaries of the suitable fluctuation zone related to the diffusive effects (summer, winter and coexistence effects). The results establish a way to guarantee the damper behavior for several years.

Advanced and innovative materials and structures are increasingly used in civil infrastructure applications. By combining the advantages of composites and smart sensors and actuators, active or smart composite structures can be created and be efficiently adopted in practical structural applications. This paper presents results of active vibration control of a pultruded fiber-reinforced polymer (FRP) composites thin-walled I-beams using smart sensors and actuators. The FRP I-beams are made of E-glass fibers and polyester resins. The FRP I-beam is in a cantilevered configuration. PZT (Lead zirconate titanate) type of piezoelectric ceramic patches are used as smart sensors and actuators. These patches are surface-bonded near the cantilevered end of the I-beam. Utilizing results from modal analyses and experimental modal testing, several active vibration control methods, such as position feedback control, strain rate feedback control and lead compensator, are investigated. Experimental results demonstrate that the proposed methods achieve effective vibration control of FRP I-beams. For instance, the modal damping ratio of the strong direction first bending mode increases by more than 1000 percent with a positive position feedback control.

A stochastic optimal control strategy for randomly excited nonlinear systems using semi-active electro-rheological/magneto-rheological (ER/MR) dampers is developed based on the stochastic averaging method, stochastic dynamical programming, and variational principle. The control force of ER/MR dampers is separated into passive part and controllable part. The passive part is incorporated into the uncontrollable terms and the stochastic averaging method is applied to the system with controllable damping force to yield a diffusion process of system energy along with It* stochastic differential equations. Then the stochastic dynamical programming principle is applied to the controlled energy process to establish a dynamical programming equation. According to the variational principle, optimal control force is obtained from the dynamical programming equation under the constraint that ER/MR dampers are only able to exert dissipative forces. Because the requirement of dissipative control force is directly enforced as a constraint condition in the variational formula, the resulting control force is a generalized damping force and always implementable by ER/MR dampers without clipping. An example is given to illustrate the application and effectiveness of the proposed non-clipping semi-active control method.

This paper presents a semi-active vibration control of a scaled two-span bridge structure. Magneto-rheological fluid dampers are utilized as the semi-active energy absorbing deices and a bridge vibration control system is developed. Closed-loop control system based on fuzzy logic is used to suppress the bridge deck motion under random excitations. The sufficient condition for the closed-loop stability of the fuzzy control system is derived from the variable structure system theory. It is demonstrated that this stable fuzzy control system can significantly reduce the relative deck displacement using about 55 percent less power compared to passive-on state, while the absolute deck acceleration is relatively unaffected.

In this effort, long gage fiber Bragg grating sensors are used to provide dynamic strain measurements in conjunction with a damage detection algorithm to provide a real-time assessment of the health of a civil structure such as a abridge or a building.

Previous studies have shown the capability of fiber Bragg gratings (FBGs) to monitor components of strain on bridges and structures. In past months, Blue Road Research and the Oregon Department of Transportation embedded long-gage FBG sensors into the Interstate 84 freeway east of Portland, Oregon to determine the feasibility of retro-install and for use of these sensors in monitoring freeway traffic speeds under conditions similar to loop inductors, piezo-ceramic weigh-in-motion (WIM) systems, and other vehicle monitoring devices. The objective of the study was to develop a working traffic sensor system with the potential to be more durable, reliable, informative, and cost-effective than currently available traffic sensors. A primary purpose of the freeway installation was to test the sensors for vehicle classifier and counter applications. In addition to discussion of the advantages of using FBGs for traffic classifiers and systems over conventional sensing methods, this paper overviews the installation and summarizes the use of FBG traffic sensors for vehicle counting and classification.

The optimal design and placement of controllers at discrete locations on civil engineering structures is an important control problem that will have impact on the earthquake engineering community. Though algorithms exist for the placement of sensor/actuator systems on continuous structures, the placement of controllers on discrete civil structures is a very difficult problem. Because of the nature of civil structures, it is not possible to place sensors and actuators at any location in the structure. This usually creates a nonlinear constrained mixed integer problem that can be very difficult to solve. However, genetic algorithms have been found to be a powerful too in solving such problems. The introduction of algorithms based on genetic search procedures should increase the rate of convergence and thus reduce the computational time for solving the difficult control problem. In this research task, a real coded genetic algorithm will be used to simultaneously place and design a control system for a civil engineering structure. The proposed method of simultaneously placing and designing sensor/actuators will be compared to a similar work that used a hybrid method. The hybrid method involves using a genetic algorithm to place the sensor/actuators, followed by a gradient-based method to determine the optimal controller gains. The proposed method is more convenient, in that both placement and design is done in the same algorithm, and as such it has a better convergence rate than the hybrid method.

Ultrasonic methods can be used to monitor crack propagation, weld failure, or section loss at critical locations in steel structures. However, ultrasonic inspection requires a skilled technician, and most commonly the signal obtained at any inspection is not preserved for later use. A preferred technology would use a MEMS device permanently installed at a critical location, polled remotely, and capable of on-chip signal processing using a signal history. We review questions related to wave geometry, signal levels, flaw localization, and electromechanical design issues for microscale transducers, and then describe the design, characterization, and initial testing of a MEMS transducer to function as a detector array. The device is approximately 1-cm square and was fabricated by the MUMPS process. The chip has 23 sensor elements to function in a phased array geometry, each element containing 180 hexagonal polysilicon diaphragms with a typical leg length of 49 microns and an unloaded natural frequency near 3.5 MHz. We first report characterization studies including capacitance-voltage measurements and admittance measurements, and then report initial experiments using a conventional piezoelectric transducer for excitation, with successful detection of signals in an on-axis transmission experiment and successful source localization from phased array performance in an off-axis transmission experiment.

We are developing the rocking structural systems that can reduce earthquake responses of buildings by causing rocking vibration. This paper aims to examine the effects of the rocking system. To cause rocking vibration under appropriate control, weak base plates are attached at the bottom of each steel column at the first story. When the weak base plates yield during a strong earthquake, the building causes rocking vibration. In this paper, the earthquake responses of this rocking system (the base plate yielding system) are examined comparing with those of the simple rocking system and the fixed-base system by nonlinear time history analyses. The results are summarized as follows: 1) Story shear forces of the base plate yielding systems are reduced as much as those of the simple rocking system. The roof displacements and axial forces are less than those of the simple rocking system. 2) The roof displacements and axial forces of the base plate yielding systems are almost similar to those of the fixed-base system under a certain input level. It is concluded that the rocking system with weak base plates can reduce earthquake responses of buildings.

We have focused on the development of a fiber optic BOTDA (Brillouin Optical Time Domain Analysis) sensor system in order to measure temperature distributed on large structures. Also, we present a feasibility study of the fiber optic sensor to monitor the distributed temperature on a building construction. A fiber optic BOTDA sensor system, which has a capability of measuring the temperature distribution, attempted over several kilometers of long fiber paths. This simple fiber optic sensor system employs a laser diode and two electro-optic modulators. The optical fiber of the length of 1400 m was installed on the surfaces of the building. The change of the distributed temperature on the building construction was well measured by this fiber optic sensor. The temperature changed normally up to 4 degrees C through one day.

A high-speed measurement system has been successfully developed to measure the pavement surface texture. This device is based on the laser triangulation measurement using a position sensitive device (PSD) as detector. In this paper we will discuss the basic design and implementation of the system. This system has a sampling rate of 175kHz, which greatly increases the ability of texture profiling and provides more quantitative information for the pavement measurement. The proper accuracy of dynamic measurement (0.02mm) guarantees correct detection in the particular applications on the pavement surface quality inspection. The flexible-hardware design enhances the system's performance under various practical situations, especially the high-response frequency, which makes the system control more prompt in handling the suddenly changed slopes and colors. The resolution in both static and dynamic measurement, the temperature shifting, the noise level, and the good repeatability indicates that the system has a good functionality at a very low cost. The experiment results illustrate that the system not only facilitates the high-speed macro/micro texture profiling, but also provides great potential to the wide industrial applications that need fast measurement.

A highway crack monitoring system (HCMS) has been successfully developed to measure the pavement crack and its coverage of the road. A road-image processing algorithm is presented in this paper. Recurring thresholding (RT) segmentation is developed to extract crack objects from a complicated background on an estimation-verification process. A connect component object identification (CCOI) identifies the binary image object according to its connectivity with other objects. A boundary contour convolution (BCC) is applied in the binary-image object analysis to achieve fast processing and reduce computational complexity. The experiment results are provided to illustrate the performance of the system scheme.

The response of the simplified moment resisting frame structure discussed in this paper is characterized by relatively large elastic deflection capacity with reduced residual deflections, auto-adaptive system stiffness modification, and considerable energy dissipation. The suggested structural system is assembled from particular column and beam elements with elastic and elastic/plastic load-deformation characteristics utilizing advanced composite materials and common construction technology without use of mechanical devices. Conventional frame structures, exclusively utilizing steel reinforced concrete members, ultimately form a collapse mechanism upon formation of plastic hinges in the beam and column members. While the flexural strength of the columns in the proposed system exceeds that of the beam as required in seismic design provisions, the relative stiffness of the frame members changes upon formation of plastic hinges in the beam element. This switching mechanism and the resulting modification of frame stiffness are inherent structural properties of the system, which can be adjusted to specific requirements in the design process. Although extensive inelastic rotation occurs in the beam element, plastic hinges at the column base are not required in order to initiate and utilize the energy dissipation potential of the beam element. In this frame configuration, the auto-adaptive stiffness modification is expected to reduce structural demand in terms of base shear forces under dynamic excitations while the formation of a kinemetic mechanism is prevented.

Monitoring chloride concentration and transport in concrete structures susceptible to corrosion of embedded steel reinforcement is a challenge as difficult as it is important. An embedded sensor based on nuclear magnetic resonance (NMR) would be a good solution to the problem because it would make a non-destructive atom-specific measurement of the presence and concentration of chloride. The important question is the scale of the device required to detect the chloride. Laboratory experiments to detect chloride in a cement matrix using pulse-NMR were conducted to assess the potential of this application; they provided a basis for projecting the scale of a device that would have a good chance of success. The coils were cm-scale and the magnetic field was 2.35 T. NMR signals were obtained from both aqueous chloride solution and samples of both regular and white portland cement. The experiments demonstrated that the signal-to-noise ratio (SNR) for a cm-scale cement sample volume is so small, even after averaging, that sample volumes much lower than that are unlikely to produce measurable signals at fields of 1 T or below. Thus the potential for realizing an embedded NMR-based sensor including the magnet is low. Parametric studies identify feasible alternative coil diameters and magnetic field strengths for detecting chloride ion concentrations in hardened concrete.

It has been well demonstrated that the structural performance of reinforced concrete (RC) columns can be enhanced by retrofitting using fiber reinforced polymer (FRP) composite jackets. Therefore, an increasingly large number of bridges and building columns have been retrofitted with such jackets. The authors developed a microwave imaging technology for detecting such damage as voids and debonding between the jacket and the column, which may significantly weaken the structural performance of the column. The authors developed surface imaging technology using focused microwave in previous works. In this paper, extending the earlier analytical and experimental works, a microwave sub-surface imaging system using antenna array was developed and verified for its capabilities to assess the damage of concrete structures. The proposed imaging system uses an arrangement consisting of several cylindrical or planar arrayed antennas for transmitting and receiving signals, and a numerical focusing operator is applied to the external signals both in transmitting and in receiving fields. This paper describes a numerical focusing procedure and numerical simulations demonstrated that the sub-surface image can be successfully reconstructed by using the proposed sub-surface imaging technology. For the experimental verification, the prototype of planar antenna array was fabricated and tested on the concrete block, in which the artificial voids were inserted.

This paper reports an experimental study on semi-active seismic response control of adjacent building structures using magneto-rheological (MR) dampers. A 1:15 scaled adjacent structural system consisting of a 12-story building model and an 8-story building model was tested on shaking table with MR damper passive and semi-active control. An MR damper with large stroke is specifically designed for this study. After experimentally identifying dynamic characteristics of the individual MR damper and the uncontrolled structural models, the two building models are interconnected with the MR damper at different floors and semi-active control is implemented using the dSPACE DS1005 real-time control system. The structures are excited on their base by a shaking table imposing sweep sine excitation and El Centro earthquake excitation. A stochastic optimal control strategy proposed by the authors is applied through the dSPACE system and its MATLAB environment to accomplish real-time semi-active control from the measurement of displacement and velocity responses at each floor. This control strategy results in a dissipative energy control with its feedback control force being a nonlinear generalized damping force. The structural response under semi-active control is compared with that by using the MR damper as a passive device without voltage input. Different MR damper installation locations are addressed in the experimental study to search for maximum response mitigation capability.

This paper presents experimental results for a novel external by-pass, fail-safe, magneto-rheological fluid (MRF) damper. A fail-safe MRF damper is referred to as a device which retains a minimum required damping capacity in the event of a power supply or electronic system failure. The new MRF device has a simple design, is compact, can generate a considerable dynamic force range, and can be sized for specific vibration control applications. As an example of the performance of this by-pass valve, a MRF damper is presented that can be used for vibration mitigation in cable stay bridges under strong storms. Performance characteristics of the by-pass valve and the MRF damper are discussed.

This paper presents a comprehensive study on the application of the MR damper to base-isolated building structures. It first proposes a simple semi-active control algorithm for a base-isolated structure with an MR damper. The algorithm, in which the MR damper's hysteresis shape is controlled, aims to reduce the isolator's displacement without increasing the acceleration responses of the upper structures. The second part of this paper covers the properties of an MR fluid and an MR damper developed for a base-isolated model structure. The damper has a nominal capacity of 40kN, which can be adjusted in accordance with the applied magnetic fields. In the test, the damper is subjected to cyclic sinusoidal displacements with different amplitudes, velocities and magnetic field intensities. The last part describes shaking table tests carried out using the MR damper and the base-isolated model structure. It is confirmed that the proposed semi-active control method is effective in reducing the isolator's displacement without increasing the acceleration responses.

This paper explores the status and techniques of post-tensioning and splicing precast concrete I-beams in bridge applications. It will look at the current practices that have been used in the United States and comment on the advantages of these techniques. Representative projects are presented to demonstrate the application and success of specific methods used. To demonstrate the benefits of using post-tensioning and splicing to extend spans, multiple analysis of simple span post-tensioned I-beams were performed varying such characteristics as beam spacing, beam sections, beam depth and concrete strength. Tables were then developed to compare the maximum span length of a prestressed I-beam versus a one segment or a spliced three segment post-tensioned I-beam. The lateral stability of the beam during fabrication, transportation and erection is also examined and discussed. These tables are intended to aid designers and owners in preliminary project studies to determine if post-tensioning can be beneficial to their situation. AASHTO Standard Specifications(2) will be used as basic guidelines and specifications. In many cases, post-tensioning was found to extend the maximum span length of a typical 72-inch precast I-beam more than 40 feet over conventional prestress.

Significance of effectively managing civil infrastructure systems (CIS) throughout CIS life-cycles, and especially during and after natural or man-made disasters is well recognized. Disaster mitigation includes preparedness for hazards to avoid casualties and human suffering, as well as to ensure that critical CIS components can become operational within a short amount of time following a disaster. It follows that mitigating risk due to disasters and CIS managementare intersecting and interacting societal concerns. A coordinated, multi-disciplinary approach that integrates field, theoretical and laboratory research is necessary for innovating both hazard mitigation and infrastructure management. Health monitoring (HM) of CIS is an emerging paradigm for effective management, including emergency response and recovery management. Challenges and opportunities in health monitoring enabled by recent advances in information technology are discussed in this paper. An example of HM research on an actual CIS test-bed is presented.

Civil infrastructures are generally the most expensive investments in a country. Concrete has been used extensively in the construction of most of the civil infrastructures. Structures made of concrete have long life span and are rarely replaced once they are erected. During the service life, the concrete ages and deteriorates leading to the loss of structural integrity. One of the major factors for the deterioration of concrete is the attack from environmental factors such as sulfate and acid. This paper presents some experimental results on the effects of environmental attacks on the system performance of impedance-based structural health monitoring. Two types of environmental factors are investigated - sulfate attack and acid attack. The experimental results show that impedance-based health monitoring technique is capable of identifying the change in the material property of concrete due to chemical attacks. Another interesting observation is that the impedance-based monitoring technique appears to be sensitive to the moisture contents in the concrete cube.