This paper focuses on a theoretical model that predicts the temperature increase of Magneto-rheological (MR) fluid dampers experiencing a sinusoidal input motion. A theoretical model is developed to estimate the temperature rise based on the non-linear behavior of the MR fluid damper. This model is solved numerically, and the numerical solution is compared with a known linear solution and experimental result in order to validate the accuracy of the model. Also, a non-dimensional form of the governing equations are developed to examine the key parameters. The non-dimensional terms show the effect of external and internal parameters on the trends of heat dissipation as well as heat generation within the MR fluid damper.
Recent earthquakes in the US and Japan have highlighted the vulnerability of bridges to collapse due to excessive movement at the hinges as a result of bearing and restrainer failure. Conventional hinge restrainers used in the US and Japan do not provide adequate protection from unseating, which can lead to collapse of bridges. This paper investigates the efficacy of using 'smart restrainers' to reduce the seismic vulnerability of bridges. The use of shape memory alloy devices as replacements for conventional restrainers are investigated as a method of improving the seismic response of bridges. Analytical studies show that these deices, used as passive dampers, are effective in both limiting the relative displacement between frames, and reducing the negative effects of pounding of bridge decks. In addition, by concentrating damage and energy dissipation in controlled locations, these devices can be used to reduce the demand on individual frames in multiple-frame bridges. Comparisons with conventional restrainers show that the 'smart restrainers' are more effective for a wide range of ground motions and bridge types than current restrainers.
The proposed toggle vibration controller is an excellent vibration-controlling device that efficiently absorbs seismic energy input into a building by amplifying small relative story displacements using a lever mechanism. And we tried to adopt the toggle mechanism as a lever mechanism. This is a brace-shaped passive response-controller installed in a column-beam frame of a building. It can minimize the response displacement and response acceleration by earthquakes, and is applicable independently of the type of construction, including steel-framed structures and reinforced concrete structures. The response-controlling effect is excellent for both newly built structures and seismic retrofit. This paper reports on seismic retrofit of existing reinforced concrete buildings using these devices.
The application of intelligent materials with self-diagnosis functions will provide more efficient and effective earthquake protective system to bridge structures. Shape memory alloys are possible candidates of intelligent materials that are applicable to bridge structures. The damping device made of shape memory alloys that can absorb seismic energy and reduce the seismic force by its pseudo yield effect was proposed. The device also enables the bridge to set again to the original position by its shape memory effects or self-centering effect even if residually displaced. This study focuses on the damping effect of shape memory alloys and verified its effect. First, the experiment to obtain the force-displacement relationship of the propose damping device was carried out in the Martensite and Austenite phases so that the effects were verified in the shape memory phase and super elastic phase. A series of shaking table test were also carried out in order to verify the effect under earthquake type shaking. As a result of this study, the shape memory alloy damper device performs its function more efficient and effective when designed in shape memory phase.
This paper describes the modifications in the dynamic behavior of a building structure when devices with variable stiffness and damping are installed in parallel with a low- damping isolation system. The results of eigen-value analyses of linear-elastic structural models with varying degrees of isolation stiffness and damping direct the subsequent design of a semi-active deice. A hydraulic semi- active actuator is designed to minimize an H2 norm of the closed loop system. Details regarding the energy storage mechanisms of the device are retained in the device model. The energy dissipation mechanisms are idealized to be viscous in nature. The actuator behaves essentially as a visco-elastic Maxwell element with a variable damping coefficient. The response time of the control-valve mechanism in this actuator is studied to reveal the relative benefits of a valve that is fast to open and valve that is fast to close. Device parameters that result in a variable damping and variable damping and variable stiffness properties are given. A model-independent, bang-bang, control rule is employed to illustrate the closed loop control system when variable damping and variable stiffness embodiments are deployed. Rules governing the placement of device with this control rule are given when the device is primarily dissipative.
The development of magnetorheological (MR) fluid damping devices has made it reasonable to consider incorporating controllable dampers to increase structural reliability by limiting seismic structural response. Several properties experimental studies have focused on characterizing the dynamic behavior of the MR dampers and have illustrated that significant changes in the quite nonlinear force-velocity relationship can be achieved by controlling the magnetic field of such devices. There have also been previous studies of control algorithms for this type of smart damper based on adjustments to techniques from nonlinear optimal/active control. This leads to a relatively complicated structure for the nonlinear control algorithm. This paper investigates the possibility of developing a much simpler nonlinear control algorithm for seismic control of civil structure using the smart MR dampers. The control philosophy is based on consideration of the energy balance in the structure of suing the unique, controllable characteristics of the MR dampers to minimize the distortional energy in the structure. Numerical results for response to random excitations illustrate that this simplified nonlinear control algorithm may provide additional reductions of building structural distortions, particularly in the top story.
Large scale implementation of smart materials and smart technology to engineered structures in any particular location requires the demonstration of cost effective applicability to the construction, repairs/upgrades and in- service inspections required by that site. The potential for using smart materials/technology at the Savannah River Site can be demonstrated through the repair, upgrade and construction of two bridges. The design and construction philosophy for one of the bridges will incorporate smart materials and technologies while the other parallel bridge has already been constructed using standard construction practices. This demonstration of smart materials/technology at the Savannah River Site is still in the planning stage and will advance quickly as funding is acquired.
Smart structures can be subdivided into two general categories. The first is structures that would perform 'smartly' during a specific event, e.g. earthquake events. The second category is the structures that would perform 'smartly' during any normal and/or abnormal event. The second category includes structures sensitive to vibration levels, structures which are exposed to wind, since wind can affect the structure from numerous directions and bridges, since loads on a bridge can have an arbitrary location at a given time. the distinction between the two structural types will have an important effect on both the optimal sensor number and locations. Recently, researchers have presented several methods for optimal number and location of sensors. These methods are based on different optimization techniques. In most of these published studies, many variable shave been investigated. These include the number and location of sensors, number of structural degrees of freedom, number of tests, and number of structural modes. All these studies assume that the location and the magnitude of damage are known a priori, before locating the sensors. In addition, in most of the published studies, the variability of the location of the loading source has not been well studied. This paper present a simple approach, which address the above issues. First, the stress ratio concept is used to logically estimate the expected location and magnitude of structural damage. Second, the load factor approach in combination with the goal programming algorithm will be presented as a means to find the optimal sensor location when dealing with structures with multiple loading conditions. The examples in this study demonstrate these techniques.
Development of a health monitoring system is of vital importance for all civil infrastructures. However, this effort has been stymied in part by the lack of suitable low priced sensors and associated signal conditioning. Very often the requirement of a controlled stable power supply to the sensor itself poses another challenge. Piezoelectric polymer films offer an excellent alternative to the ubiquitous strain gage technology. The PVDF film generates an electrical charge when mechanically deformed. The PVDF film is typically a high impedance source with a capacitance in the nanofarad range and measurement of low frequency event can pose a challenge. The authors have utilized a charge mode amplification scheme for measuring quasi-static processes. The processed signal can be transmitted to a data acquisition system via a RF microelectronic circuit. The PVDF film as a transducer can be cut to very small size and are very affordable at around 50 cents per sensor. The whole circuitry can be integrated into one single unit. It would require very low power to function and could be embedded in the structure for a large number of remote applications. In this article the authors have reported the result of the various characterization test that have been carried out to determine the suitability of the basic film as the core of an autoadaptive sensor system to be designed for infrastructure monitoring.
A strain gage is being developed, based on optical modulation that is capable of gage factors on the order of 500 for stains in excess of 2000 (mu) (epsilon) . The strain sensing element is a coated, hollow, glass waveguide of dimensions 0.5 mm ID X 1mm X OD X 100mm long. Since the geometry is compatible with standard telecommunication optical fiber such gages it can be readily incorporated into smart system arrays for damage assessment in structure such as buildings, roads and bridges. Optical fibers bring the excitation light signal to and the response signal for the sensing element. The small diameter glass tubes act as the substrate for a multiple thin film layers which can be optimized to provide the maximum dynamic range for a predetermined strain excursion. The sensor respond to bending strain by attenuation the optical intensity of the excitation signal. The gage elements exhibit little or no hysteresis and are insensitive to temperature. Also, they are environmentally stable and are not affected by factors such as corrosion or electromagnetic fields. The preliminary experimental result will be presented for this type of strain gage system operating to 2000 (mu) (epsilon) . Also, the model for the physical process will be discussed.
There are several applications in the area of traffic monitoring and control as well as road condition monitoring where fiber optic based sensor systems are advantageous. This study focuses on the use of fiber optic sensors to monitor the strain state in structures. This monitoring accomplishes two main tasks: it assesses the health of the structure and provides useful data for traffic monitoring/control applications.
In certain applications, such as microelectronic manufacturing, monitoring and controlling small floor vibrations can be essential. This paper describes how an array of distributed fiber optic sensor can be used to monitor micro floor vibrations as part of an adaptive control strategy. The performance target is to limit vibrations in 'the 10 Hz frequency range to less than 10 microinches peak to peak. The distributed fiber optic sensor are of an interferometric design that uses a single mode to multi mode to single mode configuration. The fibers are laid in an orthogonal grid so as to localize vibration hot spots. Data comparing the performance of the vibration sensing array with that of conventional point piezoelectric accelerometers, as well as sensing and control strategies will be presented.
Twenty-eight fiber-grating sensors were used to instrument two reinforced concrete beams that were externally strengthened with composites on the historic Horsetail Falls Bridge in the Columbia River Gorge. Sensor assemblies were placed in the beams and mounted on the outside of the composite to provide performance data.
The objective of this paper is to present and discuss the most critical issues the writers have identified as needing resolution in order to implement meaningful and beneficial applications of health-monitoring. The challenges in the integration of intelligent transportation and structural systems concepts within an optimum integrated asset management framework will be overviewed. Examples from ongoing research on the health-monitoring of short-span bridge families and long-span bridges will be offered to illustrate the issues.
A long-term, structural health monitoring system has been designed and installed on the firs polymer composite bridge to be built in Delaware. The system is designed to monitor and record strains and deflections of the bridge, and the temperature and humidity of the surrounding area. Two types of information are gathered, 'monitor' data and 'event' data. The monitor data records very slow gradual changes in the bridge behavior, while the event data captures the bridge response due to truck loads. The system has been on- line since June, 1998. Sample result are presented in the paper of event and monitor data. The event data shows that the transverse strain of the deck is greater than the longitudinal strain, by a factor of about 1.5, and that the absolute deflection of the deck at mid-span is due mostly to the deflection of the edge girder. Monitor data from a one month period is presented that shows the thermal variations in strain due to daily temperature changes, and the gradual, changes due to the average daily temperature. The long-term monitoring system should provide valuable data for assessing the long-term performance and durability of this unique polymer composite bridge.
Sensors are currently available and used to monitor structural performance and loads incurred by bridges already in service. However, there has been limited research concerning the stresses that steel bridge girders endure during transport from the manufacturer to the job site and during the installation process. This paper reports the measured stresses on steel bridge girders during transportation from Lancaster, PA to Hanover, NH and during construction of the Ledyard Bridge on the New Hampshire - Vermont border. Two different monitoring system were developed for this data acquisition in a mobile environment. The first, a fiber optic strain monitoring system, utilizing Bragg grating technology. The second utilized an electrical- resistive foil strain gage network, in conjunction with wireless telemetry equipment. Together, these two systems formed a smart structure system for monitoring bridge girders while confirming the accuracy of data gathered through redundancy. Result conclusively demonstrated for the first time, that stresses in beams during transportation are significant and approach the factor of safety margin in girder design.
A sophisticated instrumentation system, called Wind and Structural Health Monitoring System (WASHMS), is devised by the Hong Kong Highways Department to monitor the structural health and performance of three long-span cable-supported bridges in Hong Kong. This system consists of about 900 sensors including accelerometers. Strain gauges, displacement transducers, level sensing stations, anemometers, temperature sensors and wight-in-motion sensors. The Hong Kong Polytechnic University is commissioned to investigate the feasibility of using measured dynamic characteristics for structural damage detection in these bridges. Explored in this paper are some key issues related to developing a viable vibration-based damage assessment strategy for these bridges: (a) Evaluation of possible damage likely to occur in the three bridges - the detectibility of damage to structural components by using global or local dynamic characteristics is discussed; (b) Concept and rules of damage detection oriented modeling for large-scale structures - a super-element formulation for complicated two-tier bridge deck is developed within this framework; (c) System identification methodology for heavily redundant structures - a neural network based hierarchical identification strategy is pose for successively detecting the occurrence, type, location and extent of the damage.
Electronic hardware has been developed to telemetrically transmit temperature and strain measurements from within a public highway in the UK. These measurements provide an important health check for monitoring fatigue damage in pavements. Previous attempts at measuring strain and temperature have required lengths of cable to be installed in the highway. The installation of these cables is both expensive and damaging to the pavement and provides potentially unreliable electrical connections. The new systems consist of a retrofitted instrumented asphalt core which is bonded into the pavement structure. The core contains all the electronics necessary to record two temperatures and two strains. An analogue front end provides signal conditioning which is digitized and passed to microcontroller for endcoding. From there the data is transmitted via a low power radio link to a receiver and data logger positioned by the side of the road. The system has an in-situ operating life of 6 months on AA alkaline batteries. Results are presented of power management and fault tolerant radio protocol techniques, long term temperature variations, dynamic strain measurements within the highway, and RF transmission capabilities through a layer of asphalt.
In deep waters scenarios Tension Leg Platforms (TLP), under severe sea/wind conditions, may experience large response amplitudes of the hull motion. Large heave amplitudes caused by random dynamic loads appear as one of the most deleterious effects to the structural safety and integrity of the most critical components: mooring system and the handing risers. In a preliminary design reduction of these amplitudes is in general tentatively sought by compromised measures and concurrent design criteria like: high flutuability and deck payload vs. tendons and risers submerged weight; deck hydrodynamic vs. length variation of pretension tendons, etc. This paper shows that active control system may be installed inside the hull to attenuate dynamic amplitudes in heave motion. Optimal control theory are applicated for the idealization of mechanism to reduce the dynamic response amplitude, improving the safety conditions and increasing service life of tendons and risers, insuring the system functioning at all. The uncontrolled and controlled dynamic behaviors of a TLP prototype are investigated by using simplified mathematical models. The numerical results lead to the conclusion that active systems have good performance and efficiency in reducing and controlling the heave motion amplitudes and consequently the stress variations in tendons and risers of a TLP.
This study explores the use of a linear PMDC machine as a regenerative force actuator for the mitigation of earthquake disturbances in civil structures. Unlike previous studies of this kind, the control system developed is purely active, meaning no 'hybrid' control techniques are used, such as the combination of active force actuation and passive tuned mass dampers. Modeling methods for the machine as well as its associate drive electronics are briefly described. It is shown that for this purely active system, it is possible and feasible to develop regenerative excitation schemes which drive the machine primarily by absorbing power from the excited building. Such regenerative excitation makes it possible to isolate the actuator from the external power grid, which is necessary during earthquakes, where the quality, or even the mere availability of external power is questionable. Furthermore, results are presented which find the minimum reservoir of energy necessary to excite the machine during the beginning of the earthquake, and it is shown that the actuator local power supply will see a gain in energy across the duration of the disturbance. The control system design methods presented employ position feedback. Then, force limiting techniques are employed to regulate power flow in the machine. The effectiveness of this control design is evaluated on a 3-story building, and performance is briefly compared to that of semi-active control designs proposed elsewhere.
Natural hazards such as earthquakes and strong wind events place large forces on tall, slender structures and also on long bridges. The structural system usually can be described by a Lagrangian model. In view of numerous uncertainties due to model errors, stress calculations, material properties, and load environments, the system is uncertain. Here, the Lagrangian structural systems is modeled as an uncertain state space model. The paper develops a robust active control approach with uncertainties in the system, control input, and disturbance input matrices. Robust active control provides both robust stability and H(infinity ) disturbance attenuation. The H(infinity ) norm of the transfer function from the external disturbance forces to the observed system states is restricted by a prescribed attenuation index. Considered uncertainties are norm-bounded to robust control analysis and design of structural systems.
A new procedure is presented for determining dynamic characteristics and seismic response of adjacent buildings linked by active tendon devices. Dynamic characteristics of active tendon-linked adjacent buildings are obtained by a generalized modal analysis approach. Random seismic response of adjacent buildings linked by active tendon devices is determined by a combination of the generalized modal analysis approach and a pseudo-excitation method. Based on the derived formula, a computer program is written and extensive parametric studies are performed to assess the effectiveness of active tendon devices and to identify optimal type of sensor and beneficial parameters of devices. It is showed that using active tendon devices of proper sensors and parameters to link adjacent buildings can increase the modal damping ratios and reduce the seismic response of both buildings significantly.
An active 6-DOF microvibration control system using giant magnetostrictive actuators is developed in order to realize microvibration-free space for precision instruments which hate vibration. A giant magnetostrictive actuator is suitable as a displacement actuator for active microvibration control, because it is both compact and durable and also its response against input is fast and reliable. The developed device consists of a table, six air springs, eight magnetostrictive actuators and six accelerometers on the table. Four actuators are set in the horizontal directions, and another four in the vertical direction. Since air springs and actuators as a unit of vertical support system are arranged in parallel, readjustment of the system is quite easy, even when operating load on the table is changed. The dimension of table is 2000mm in length and 1400mm in width and 230mm in height and the weight of about 2 tons. Operating load on the table is 2 tons. A giant magnetostrictive rod is 6mm in diameter and 50mm in length. The actuators operate within the stroke range of +/- 25 micrometers . Feedback, control strategy using only six components of table acceleration on the table is adopted and the controller is designed by a model matching model. The obtained control performance of the system through two vibration control test can be summarized as follows: (1) Root-mean-square values of the table accelerations under micro-tremor are reduced to 1/3 to 1/10 of the floor accelerations, and kept less than 0.008cm/s2. (2) Induced vibrations by impacts acting on the table disappear in less than 0.05sec.
Accelerated aging research on samples of composite materials and candidate UV protective coatings is determining the effects of six environmental factors on material durability. Candidate fastener materials are being evaluated to determine corrosion rates and crevice corrosion effects at load-bearing joints. This work supports field testing of a 30-ft long, 18-ft wide polymer matrix composite (PMC) bridge at the Idaho National Engineering and Environmental Laboratory. Durability results and sensor data form test with live loads provide information required for determining the cost/benefit measures to use in life-cycle planning, determining a maintenance strategy, establishing applicable inspection techniques, and establishing guidelines, standards and acceptance criteria for PMC bridges for use in the transportation infrastructure.
Transverse shrinkage cracking of bridge decks occurs during and shortly after construction. It allows cracks to form and later allows water and other elements to enter the concrete matrix of the deck and most importantly to fall onto the supporting structure below. This leads to significantly damage of that support structure. This paper describes a field application of the design for an in-situ means of controlling and repairing transverse shrinkage cracking, by utilizing brittle tubes with sealants in the concrete deck.
This paper addresses constructing appropriate input vectors to neural networks for hierarchical identification of damage location and extent from measured modal properties. Hierarchical use of neural networks is feasible for damage detection of large-scale civil structures such as cable- supported bridges and tall buildings. The neural network is first trained using one-level damage samples to locate the position of damage. After the damage location is determined, the network is re-trained by an incremental weight update method using additional sample corresponding to different damage degrees but only at the identified location. The re- trained network offers an accurate evaluation of the damage extent. The input vectors selected for this purpose fulfil the conditions: (a) most parameters of the input vectors are arguably independent of damage extent and only depend on damage location; (b) all parameters of the input vectors can be computed from several natural frequencies and a few incomplete modal vectors. The damage detection capacity of such constructed networks is experimentally verified on a steel frame with extent-unknown damage inflicted at its connections.
Hybrid laminates typically consist of alternate layers of fiber-reinforced polymer and aluminium alloy. Developed primarily for fatigue critical aerospace applications, the hybrid laminates are orthotropic materials with lower density and higher strength compared to the aluminium alloy monolith. One of the damage mechanism of particular interest is that of fatigue crack growth, which for hybrid laminates is a relatively complex process that includes a combination of delamination and fiber bridging. To facilitate the development of a unified model for both crack and damage growth processes, a remote sensing system, reliant upon fiber optic sensor technology, has been utilized to monitor strain within the composite layer. The fiber optic system, with capacity for sub microstrain resolution, combines time domain multiplexing with line switching to monitor continuously an array of Bragg grating sensors. Herein are detailed the findings from a study performed using an array of 40 sensors distributed across a small area of a test price containing a fatigue crack initiated at a through- thickness fastener hole. Together with details of system operation, sensor measurements of the strain profiles associated with the developing delamination zone are reported.
The objective of this paper is to perform damage detection utilizing the coefficients obtained from an ARMA model. The Damage Index Method has been proven to be one of the better modal based damage detection methods currently in use. One major drawback to this method is the need to determine mode shapes from the frequency response function (FRF) data. Extracting mode shapes from FRF data can be extremely time consuming and the result at times can be highly dependent on the users knowledge and the application of the software package being utilized to extract the modal parameters. In an attempt to minimize user interaction in the damage detection process and to eliminate the need to determine modal parameters, we will develop a method which is capable of providing damage detection results from accelerometer time histories. This will be accomplished by utilizing the parameters of an ARMA model as damage indicators. Expressions for classification is attempted for a simply supported beam which contains damage of various degrees at several locations. The damage detection result will then be compared to the damage detection results obtained by the Damage Index Method.
Electrical time domain reflectometry (ETDR) stress/strain sensing technique has been successfully used in geotechnical applications to detect rock deformation and longwall movement. Since durable sensor media that can survive harsh construction environment and has long service life can be used, the ETDR sensing method appears to be a practical technique for health monitoring applications of civil concrete structures. In this paper, the applicability of using an embedded coaxial ETDR cable to sense structural deformation and detect load-induced crack damages of a concrete structure is investigated. Bending test were performed on small-scale concrete specimens with embedded coaxial ETDR sensors. The test results show that the deformation patterns of the concrete specimens are clearly represented and the location and magnitude of load-induced crack damages that pass the sensing line are evidently shown in the ETDR signal response of the sensor. The results of the current study demonstrate the great potentials of the ETDR technique for the health monitoring application of large civil concrete structures.
Interest in infrastructure health monitoring and damage detection has received a considerable amount of attention over the past two decades. Previous approaches to non- destructive evaluation of structures to assess their integrity typically involved some form of human interaction. Recent advances in smart materials and structures technology has resulted in a renewed interest in developing advanced self-diagnostic capability for assessing the state of a structure without any human interaction. The goal is to reduce human interaction while at the same time monitor the integrity of a structure. With this goal in mind, many researchers have made significant strides in developing damage detection methods for civil structures based on traditional modal analysis techniques. These techniques are of the well suited for structures which can be modeled by discrete lumped-parameter elements where the presence of damage leads to some low frequency change in the global behavior of the system. On the other hand small defects such as cracks are obscured by modal approaches since such phenomena are high frequency effects not easily discovered by examining changes in modal mass, stiffness or damping parameters. This is because at high frequency modal structural models are subject to uncertainty. This uncertainty can be reduced by increasing the spatial order of discrete model, however, this increases the computational effort of modal-based damage detection schemes. On the other hand, wave propagation models of structures have higher spatial order model fidelity. Thus, they are better suited for detecting and global wave propagation models to detect damage in a discrete model of a farmed building structure, consisting of discrete structural elements. Simulated damage in the form of mass or stiffness loss is used to determine the effect on the resonant and incident wave response of the structure. Examination of the incident transfer function response of the structure reveals the loading path of the damaged element.
This study develops a method of detecting the damage of jacketed RC columns measured in terms of stiffness degradation by horizontally exciting the damaged bridge and by identifying the change in its vibration characteristics including frequencies and mode shapes from those of the undamaged bridge. The method combines neural network techniques with finite element analysis to establish a reliable relationship, a well trained neural network, between the vibration characteristics and the stiffness degradation. The unknown stiffness degradation is then identified by inputting the vibration characteristics obtained from the vibration test into the neural network. This method was verified in an earlier study by the present authors on the basis of experiments performed on two half- scale bridge columns wrapped respectively with carbon and glass fiber jackets. The present study validates the usefulness of this method for the assessment of column damage on the basis of the vibration test involving an entire bridge. Specifically, the validation is carried out by comparing damage scenario with the stiffness degradation computed from the vibration characteristics of a three-span bridge model with jacketed columns. It is identification of the stiffness degradation at jacketed columns. This fact indicates that the proposed damage assessment method of combining horizontal vibration test with neural network- based identification is practical and effective because of the ease with which the first mode vibration can ge induced in the field.
Continuous segmental prestressed concrete bridges have been used extensively all over the world since the late 1960's. In this case the authors are investigating one such bridge in the state of Illinois. The bridge has developed extensive cracks on the webs of the segments. Yet, it is very difficult to assess the safety of this bridge. One of the possible ways of coming up with some quantification involves the estimation of the structural dynamic properties, such as modal frequencies and mode shapes. This approach is especially useful if a previous baseline has already been established for that structure. Such a baseline does exist for the structure. This paper is a summary of the ongoing of experimental investigations and Finite Element simulations that have been conducted on the bridge. In particular, three experimental modes have been identified using both forced vibration and ambient vibration excitation at two different seasons of the year and the results have been compared to results that were obtained by CTL twelve years ago.
A system identification (SI) procedure to identify structural parameters is proposed in this paper. Instead of identifying parameters in the physical domain, which involves search in a large-dimensional parameter space, the search is made easier computationally in sub-domains orders. Modal decomposition technique is employed. The objective function is the minimization of error of modal response history. Physical parameters are then recovered by making use of modal orthogonality properties. The genetic algorithm is employed based on the principle of natural selection whereby better genes survive and propagate and therefore increase the change of converging to the best parameter set. For numerical study, a 10-story shear building is considered to illustrate the efficiency of the proposed procedure.
Rigid pavement structures have uncertainties and variability in their structural layers and components. These variations and uncertainties are seldomly included in performance assessment and evaluation in pavement systems. This paper proposes to use Stochastic Finite Element Method (SFEM) in rigid pavement faulting and load transfer efficiency. The SFEM uses random parameters, as stochastic process namely random fields. These random fields are characterized, quantitatively by spatial functions of statistical moment like the mean, variance and covariance.
A large number of relatively long bridges have been constructed using prestressed segmental box girder technology and are currently in service around the world, This article purports to report the investigation of one such structure. The structure has been operational since the late 1970's and has innumerable visible shear cracks originating from the shear keys of the individual segments. The present investigation, a non-linear finite element model of the structure has been developed and analyzed under dead load, live load and thermal gradients. Results from a preliminary crack propagation investigation have also been reported. To validate and upgrade the finite element model a long term monitoring system has been installed on the bridge for monitoring temperature changes, crack growth and strain cycling due to traffic and temperature variations.