Expanding with a Lofty Goal

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Categories: Computing in Civil Engineering (Journal)

A Decentralized Control Algorithm for Large-Scale Building Structures

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Abstract: Decentralized control strategy is more suitable for structural control of large-scale structural systems as it increases in the feasibility of control implementation and decreases the risk on the failure of the control system compared with the conventional centralized control approach. In this article, a decentralized control algorithm is proposed for large-scale linear building structures. A large-scale building structure is divided into a set of smaller substructures based on its finite element model. Interconnections between adjacent substructures are treated as disturbances to the individual substructure. Each substructure is controlled by its own local controller using linear quadratic Gaussian control scheme with acceleration measurements as feedback signals. A computational procedure is developed for the recursive estimation of the unknown disturbances to each substructure. Two cases, with substructure interface measurement and without substructure interface measurement respectively, are considered. A numerical example of the decentralized control of the 20-story Structural Engineers Association of California (SAC) benchmark linear building under seismic excitation is studied to evaluate the performance of the proposed algorithm. Simulation results demonstrate that the decentralized control algorithm has quite good control performance compared with the conventional centralized control approach. Therefore, the proposed decentralized control algorithm is viable for structural control of large-scale linear structural systems.

Categories: Computing in Civil Engineering (Journal)

Comparing Ant Colony Optimization and Genetic Algorithm Approaches for Solving Traffic Signal Coordination under Oversaturation Conditions

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Abstract: This article proposes to solve the oversaturated network traffic signal coordination problem using the Ant Colony Optimization (ACO) algorithm. The traffic networks used are discrete time models which use green times at all the intersections throughout the considered period of oversaturation as the decision variables. The ACO algorithm finds intelligent timing plans which take care of dissipation of queues and removal of blockages as opposed to the sole cost minimization usually performed for undersaturation conditions. Two scenarios are considered and results are rigorously compared with solutions obtained using the genetic algorithm (GA), traditionally employed to solve oversaturated conditions. ACO is shown to be consistently more effective for a larger number of trials and to provide more reliable solutions. Further, as a master-slave parallelism is possible for the nature of ACO algorithm, its implementation is suggested to reduce the overall execution time allowing the opportunity to solve real-time signal control systems.

Categories: Computing in Civil Engineering (Journal)

Concrete Crack Detection by Multiple Sequential Image Filtering

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Abstract: This article presents a new robust automated image processing method for detecting cracks in surface images of concrete structures. This method involves two steps: (1) development of an image filter for detecting major cracks using genetic programming (GP), and (2) elimination of residual noise after filtering and detection of indistinct cracks by iterative applications of the image filter to the local regions surrounding the cracks. The proposed method can be used for the accurate detection of cracks in surface images recorded under various conditions. Moreover, the widths of the detected cracks can be quantified on the basis of the spatial derivatives of the brightness patterns. The estimated crack widths are in good agreement with those measured manually.

Categories: Computing in Civil Engineering (Journal)

Active and Semi-active Adaptive Control for Undamaged and Damaged Building Structures Under Seismic Load

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Abstract: During the lifetime of a structural system, many severe events such as earthquakes and strong winds may impact the system and result in potential damage. To mitigate the structural vibration and damage during these extreme events, control devices such as active and semi-active devices have received considerable attention because of their attractive characteristics. Active control devices are adaptable to any change and semi-active devices have the capability of offering the reliability of passive devices and the versatility and adaptability of active devices. In this research, a direct-adaptive-control method is used to control the behavior of an undamaged and a damaged structure using semi-active and active devices. In the adaptive control method, the controlled system is forced to behave like the model system which exhibits the desired behavior. The model of the adaptive control method is defined in a way to optimize the response of the controlled structure. The controller developed using this method can deal with changes that occur in the characteristics of the structure because it can modify its parameters during the control process. A magnetorheological (MR) damper is used as the semi-active device in this study, whereas a hydraulic actuator is utilized as the active device to control the behavior of the structure. The performance of a three-story building from the SAC project for the third generation of the control benchmark problem is studied by performing time–history analyses. The structure is subjected to different earthquakes and controlled by the direct adaptive control method. In the analysis of the structure, some stiffness reduction is assumed as a result of potential damage in the first story of the building. Also, the direct adaptive control strategy is used to optimize the response of the undamaged structure and to mitigate the damage impact on the performance of the controlled structure in the presence of noise for output measurements. The results of adaptive control method are compared with those of other control strategies. It is shown that the performance of the three-story building is improved using the adaptive control method. By assessing the results of different control approaches, it is found that the adaptive control method works more effectively than other methods and semi-active devices can provide reliable results.

Categories: Computing in Civil Engineering (Journal)

Using Numerical Simulations and Engineering Reasoning under Uncertainty: Studying the Collapse of WTC-1

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Sun, 01/01/2012 - 12:00am

Abstract: A series of numerical aircraft crash simulations and thermal behavior analyses were made at Purdue University to study the response of the World Trade Center Tower 1 (WTC-1) on September 11, 2001. The process included accuracy verification for the computational tools using available experiment data. Numerical models for the Boeing 767–200ER aircraft and the structural system for the top 20 stories of WTC-1 were developed for the simulations. A second aircraft model, simpler yet comparable in effect, was developed and used for a parametric sensitivity analysis. Results from these simulations and published by other researchers indicate that while the observed impact damage to tower exterior framing can be estimated accurately, the unseen impact damage to the core structure of the tower could not be estimated with high confidence. Although the computational tools helped in developing an understanding as to what might have happened as the aircraft penetrated and disintegrated into the structure, they were not able to reduce the uncertainty in the core damage estimate. However, reflecting insight from the behavior of the Pentagon building under the impact loads it received on the same day and studying the effects of elevated temperature on mechanical properties of steel in light of experimental data, the uncertainty in the core structural damage estimate was found to be of negligible importance with regards to the ultimate fate of the tower. It is demonstrated that through use of numerical simulations and engineering reasoning, a dominant factor in the collapse of the tower could be proposed with confidence. It was the loss of fire-proofing in the tower core during aircraft impact that left the core vulnerable to ensuing thermal loads and resulted in the eventual collapse of the tower.

Categories: Computing in Civil Engineering (Journal)

Optical Analysis of Strength Tests Based on Block-Matching Techniques

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 17/11/2011 - 3:06pm

Abstract: One of the main issues in civil engineering is to analyze the behavior of materials in strength tests. Traditionally, information about displacements and strains in the materials is carried out from these tests using physical devices such as strain gauges or other transducers.

Although these devices provide accurate and robust measurements in a wide range of situations, they are limited to obtaining measurements in a single point of the material and in a single direction of the movement, thus, the global behavior of the material cannot be analyzed.

The proposed technique consists of the integration of a calibration process with a block-matching algorithm to measure displacements from images. This algorithm uses the similarity between regions in the images to extract the 2D vector displacement field from each point, and to quantify the strain on the surface of the material.

The proposed algorithm has been designed to measure displacements from real images of material surfaces taken during strength tests, and it has the advantages of being robust with long-range displacements, of performing the analysis on the image space domain (avoiding the problems related to the use of Fourier Transforms), and of measurements in long sequences related to a real point of the material and not to a pixel position.

Categories: Computing in Civil Engineering (Journal)

Consistent Point Clouds of Narrow Spaces Using Multiscan Domain Mapping

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Tue, 08/11/2011 - 10:13am

Abstract: Three-dimensional (3D) range scanning of large spaces, such as civil structures, generates an immense cloud of 3D points with inconsistent data densities due to the limited positions of the stationary scanner, inaccessible surfaces, and narrow pathways. This density variation is the dominant detrimental factor in extracting accurate scanned shapes. This article introduces an effective scan planning methodology for capturing accurate geometry from long and narrow spaces, which minimizes the need for subsequent data approximations. The technique computes an optimum scanning range for each stationary position of the scanner that limits the density variation to a user-defined value. Three cases are proposed to define the “limited data density” and a FARO®-LS880 laser scanner is used to illustrate the proposed approach that achieves acceptable scanning results in terms of its critical shape capturing capability, overall point cloud density, and accurate point-based visualization. The experimental observations confirm that the accuracy of the scanned data can be improved by registering multiple partial scans with restricted density and positioning the data acquisition device close to the critical features. The latter recommended step decreases the incident angle to the world domain, which, in turn, reduces the surface occlusions and data density variations.

Categories: Computing in Civil Engineering (Journal)

Modeling of Tension Stiffening Behavior in FRP-Strengthened RC Members Based on Rigid Body Spring Networks

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Tue, 08/11/2011 - 10:12am

Abstract: Allowing for the tension stiffening effects resulting from the bond between steel reinforcement and surrounding concrete leads to effective deformation analysis of reinforced concrete (RC) members when using a nonlinear finite element analysis modeled on the smeared crack concept. Nowadays, externally bonded fiber reinforced polymer (FRP) composites are widely used for strengthening existing RC structures. However, it remains unclear to what extent the tension stiffening of postcracking concrete is quantitatively influenced by the addition of FRP composites, as a result of the bond between the FRP and the concrete substrate. This article presents a discrete model, which is based on rigid body spring networks (RBSN), for investigating the tension stiffening behavior of concrete in FRP-strengthened RC tensile members. A two-parameter fracture energy-based model was deployed to represent the bond-slip behavior of the FRP-to-concrete interface. The reliability of the RBSN model was verified through comparisons with previous test results. Further parametric analysis indicates that the tension stiffening of concrete is hardly influenced by the addition of FRP composites before the yield of steel reinforcement has occurred although concrete crack patterns and crack widths may be influenced by the bond-slip behavior of the FRP-to-concrete interface.

Categories: Computing in Civil Engineering (Journal)

Determining an Optimal Maintenance Period for Infrastructure Systems

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Tue, 25/10/2011 - 9:16am

Abstract: This article proposes a maintenance policy that sets a limit to the cumulative failure rate over the life cycle of an infrastructure system. Under this policy, there are three maintenance scenarios in an arbitrary period of the life cycle: a maintenance action will be implemented in scenario 1 in which the failure rate limit has not been reached and the system does not fail; a preventive replacement will be implemented to renew the system in scenario 2 where the failure rate limit has been reached and the system does not fail; and a corrective replacement will be implemented at the time of failure to renew the system in scenario 3 where the system fails no matter whether the failure rate limit has been reached or not. The maintenance effect is measured by the type 1 effective age model. An optimization model is developed to determine the optimal length of the maintenance period on the basis of the proposed maintenance policy, with an objective to minimize the system's life cycle cost per unit time that includes maintenance cost, failure loss, and the cost of system unavailability. This optimization model and the search algorithm that is consequently formulated are applied to the maintenance of bridge decks. Weibull distribution is used to model the deterioration process of the bridge deck.

Categories: Computing in Civil Engineering (Journal)

Dynamic Parameter Identification of Secondary Mass Dampers Based on Full-Scale Tests

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Tue, 25/10/2011 - 8:38am

Abstract: For a secondary mass damper such as tuned liquid damper (TLD) or tuned liquid column damper (TLCD), whose moving mass is liquid, it is impossible to prefabricate the damper in a factory for the identification of dynamic properties. Also, it is not easy to prefabricate a concrete tuned mass damper (TMD), whose moving mass is made of concrete, in a factory. In this article, an identification method for finding dynamic properties of secondary mass dampers based on the full-scale field test is presented. Decoupled equations of motion are derived from a coupled equation of motion of building and damper. The decoupled equations of motion are then used for system identification using the response of the damper as an input and the response of the building as an output. The proposed method is applied to numerical examples and an actual TMD and TLCD installed in buildings.

Categories: Computing in Civil Engineering (Journal)

Operational Modal Parameter Identification from Power Spectrum Density Transmissibility

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Mon, 24/10/2011 - 11:46am

Abstract: Operational modal analysis subjected to ambient or natural excitation under operational conditions has recently drawn great attention. In this article, the power spectrum density transmissibility (PSDT) is proposed to extract the operational modal parameters of a structure. It is proven that the PSDT is independent of the applied excitations and transferring outputs at the system poles. As a result, the modal frequencies and mode shapes can be extracted by combing the PSDTs with different transferring outputs instead of different load conditions where the outputs from only one load condition are needed. A five-story shear building subjected to a set of uncorrelated forces at different floors is adopted to verify the property of PSDTs and illustrate the accuracy of the proposed method. Furthermore, a concrete-filled steel tubular half-through arch bridge tested in the field under operational conditions is used as a real case study. The identification results obtained from currently developed method have been compared with those extracted from peak-picking method, stochastic subspace identification, and finite element analysis. It is demonstrated that the operational modal parameters identified by the current technique agree well with other independent methods. The real application to the field operational vibration measurements of a full-sized bridge has shown that the proposed PSDTs are capable of identifying the operational modal parameters (natural frequencies and mode shapes) of a structure.

Categories: Computing in Civil Engineering (Journal)

Automatic Road Defect Detection by Textural Pattern Recognition Based on AdaBoost

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 22/09/2011 - 11:07pm

Abstract: The state of roads is continuously degrading due to meteorological conditions, ground movements, and traffic, leading to the formation of defects, such as grabbing, holes, and cracks. In this article, a method to automatically distinguish images of road surfaces with defects from road surfaces without defects is presented. This method, based on supervised learning, is generic and may be applied to all type of defects present in those images. They typically present strong textural information with patterns that show fluctuations at small scales and some uniformity at larger scales. The textural information is described by applying a large set of linear and nonlinear filters. To select the most pertinent ones for the current application, a supervised learning based on AdaBoost is performed. The whole process is tested both on a textural recognition task based on the VisTex image database and on road images collected by a dedicated road imaging system. A comparison with a recent cracks detection algorithm from Oliveira and Correia demonstrates the proposed method's efficiency.

Categories: Computing in Civil Engineering (Journal)

Crack Detection from the Slope of the Mode Shape Using Complex Continuous Wavelet Transform

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 22/09/2011 - 9:36pm

Abstract: A new method for cracks detection in beams is proposed by using the slope of the mode shape to detect cracks, and by introducing the angle coefficients of complex continuous wavelet transform. This study is aimed at detecting the location of the nonpropagating transverse crack. A series of beams with cracks that are simulated by rotational springs with equivalent stiffness are analyzed. The mode shape and the slope of this lumped crack model are calculated. Through complex continuous wavelet transform of the slope of the mode shape using Complex Gaus1 wavelet (CGau1), the locations of cracks are detected from the modulus line and the angle line of wavelet coefficients. By comparison, the singularity is much more apparent from the angle line of complex continuous wavelet transform. This demonstrates that the proposed method outperforms the existing method of wavelet transform of the mode shape with real wavelets. Also, this method can detect cracks in beams with different boundary conditions. The influence of crack locations and crack depth on crack detection is discussed. Finally, the noise effect is studied. Through the multiscale analysis, the locations of cracks may be detected from the angle of wavelet coefficients.

Categories: Computing in Civil Engineering (Journal)

Network-Level Road Pavement Maintenance and Rehabilitation Scheduling for Optimal Performance Improvement and Budget Utilization

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 22/09/2011 - 8:29pm

Abstract: This article discusses how to efficiently and completely solve a bi-objective pavement maintenance and rehabilitation-scheduling problem, which aims at optimizing two objectives of pavement condition improvement and budget utilization in a simultaneous manner. This problem may be addressed by the weighting method, constraint method, ranking method, and various metaheuristic methods. However, none of these methods can guarantee the complete Pareto-optimal solution set, which would potentially lead to suboptimal decisions. In this article, a parametric method is suggested to solve the bi-objective pavement maintenance and rehabilitation-scheduling problem. The effectiveness and efficiency of the parametric method is investigated and demonstrated through a case study using the real-world data set from the Dallas District's Pavement Management Information System. A performance comparison between the widely used weighting method and the parametric method clearly justifies the computational advantages of the parametric method.

Categories: Computing in Civil Engineering (Journal)

Hybrid Time-Frequency Blind Source Separation Towards Ambient System Identification of Structures

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 22/09/2011 - 8:16pm

Abstract: Ambient system identification in noisy environments, in the presence of low-energy modes or closely-spaced modes, is a challenging task. Conventional blind source separation techniques such as second-order blind identification (SOBI) and Independent Component Analysis (ICA) do not perform satisfactorily under these conditions. Furthermore, structural system identification for flexible structures require the extraction of more modes than the available number of independent sensor measurements. This results in the estimation of a non-square modal matrix that is spatially sparse. To overcome these challenges, methods that integrate blind identification with time-frequency decomposition of signals have been previously presented. The basic idea of these methods is to exploit the resolution and sparsity provided by time-frequency decomposition of signals, while retaining the advantages of second-order source separation methods. These hybrid methods integrate two powerful time-frequency decompositions—wavelet transforms and empirical mode decomposition—into the framework of SOBI. In the first case, the measurements are transformed into the time-frequency domain, followed by the identification using a SOBI-based method in the transformed domain. In the second case, a subset of the operations are performed in the transformed domain, while the remaining procedure is conducted using the traditional SOBI method. A new method to address the under-determined case arising from sparse measurements is proposed. Each of these methods serve to address a particular situation: closely-spaced modes or low-energy modes. The proposed methods are verified by applying them to extract the modal information of an airport control tower structure located near Toronto in Canada.

Categories: Computing in Civil Engineering (Journal)

Influence of the Tunnel Shape on Shotcrete Lining Stresses

Computer-Aided Civil and Infrastructure Engineering (Wiley InterScience) - Thu, 22/09/2011 - 7:36pm

Abstract:

Tunnel excavation is frequently carried out in rock masses by the drill and blast method and the final shape of the tunnel boundary can be irregular due to overbreaks. In order to investigate the effects of overbreaks a study of the effect of tunnel boundary irregularity has been carried out. This is done developing a computational tool able to take into account fuzzy variables (i.e., thickness of the beams of the bedded spring approach used for the model). The obtained results show that irregularity effects should be considered when a shotcrete lining is used as the final tunnel lining (for the case where the tunneling procedure does not permit a smooth surface to be obtained). This is crucial to obtain a durable lining.

Categories: Computing in Civil Engineering (Journal)