Structures Congress 2010: 19th Analysis and Computation Specialty Conference

Continued aging and deterioration of bridges poses a threat to bridge performance not only under regular service loads, but also results in pronounced vulnerability under extreme dynamic loads, such as seismic or hurricane induced surge and wave loading. In fact, aging of bridges in the form of corrosion attacks load paths critical under dynamic loads, including the superstructure-substructure connection elements and the reinforcing steel in column plastic hinge zones. This paper investigates the effect of aging on the dynamic response of multiple span concrete girder bridges when subjected to seismic as well as coupled surge and wave loading induced by hurricanes. The paper highlights the key differences and similarities in the nature of loads under the two natural hazards, the demand placed on key components, and the resulting dynamic response and failure modes of aging bridges. Nonlinear dynamic analysis is conducted using 3-dimensional bridge models with time-varying model parameters due to corrosion of reinforcing bars in decks and columns and degradation of elastomeric bearings with steel dowels. The sensitivity of component response, such as column demands, bearing deformations, or deck displacement, to variation in aging parameters is investigated in the study. Findings indicate that while the nonlinear dynamic behavior and select failure modes of the bridges may differ between the seismic and surge/wave loading cases, there is some consistency in the impact and criticality of aging parameters affecting dynamic response under the extreme loading cases, such as corrosion of bearing dowels and column reinforcement. These results form the foundation for multi-hazard vulnerability assessment of bridges considering the present in field condition.

The implementation of a probabilistic approach to quantify peak component acceleration (PCA) demands for acceleration-sensitive nonstructural components attached to structural wall models is presented. The proposed approach is useful to estimate PCA hazard curves and generate component uniform hazard spectra (CUHS) based on various structural and nonstructural parameters. CUHS are obtained for a family of structural wall structures with various characteristics for a site located in Los Angeles, CA. The results demonstrate that probabilistic estimates of PCA demands depend significantly on parameters such as the ratio of the period of the component to the fundamental period of the structure, the location of the component within the supporting structure, and the strength and stiffness of the supporting structure. In addition, the results from this study indicate that ASCE-7 estimates of component accelerations do not provide a consistent reliability level for NSCs with various periods that are attached to the structure at different locations. This highlights the importance of probabilistic seismic demand quantification approaches for the design and evaluation of nonstructural components.

Most current modeling methods for damping assume global linear viscous damping, even when nonlinear behavior is present in the structural system. While this analysis is simple, the results do not accurately model the damping behavior, in particular for yielding or damaged members, nonstructural components and connections. This work presents two methods for modeling damping that can account for the nonlinearity of damping behavior across the system. In the first method, the evolutionary approach, damping is added to each individual element through rotational dampers attached by a rigid-link ghost element. The second method, the instantaneous viscous damping approach, assumes that damping at any time is dependent on stresses the system. Both these methods allow for calculation of damping based on the changing displaced shape and behavior of the element and can be modeled at every location in the structure. Although these methods increase computational demands for the analysis of damping, the results provide realistic behavior not seen in global linear viscous damping models. Finally a modification to the Newmark time integration method is presented to specifically handle the analysis of systems in which the only nonlinearity is associated with damping.

Reinforced concrete shear walls are often used to resist the lateral loads imposed by earthquakes. This paper presents the probabilistic seismic demand analysis of typical shear walls with flexible foundations to evaluate the significance of soil-structure interaction (SSI) effects. Utilizing the realistic numerical models for shear wall and foundation elements, the nonlinear time history analyses are conducted with a large number of recorded ground motions. Response quantities in terms of drift ratio and base shear are monitored and related to the intensity measure of ground motions for the cases with and without considering the SSI effects. The fragility functions of shear walls are derived and the impact of SSI effects is discussed.

The research presented herein describes the findings and conclusions thus far in an experimental and analytical study of the behavior of woodframe shear walls sheathed with OSB combined with drywall and/or stucco subjected to cyclic loading. Eight, 8 ft square shear wall specimens were constructed and tested using the CUREE-Caltech pseudo-static loading protocol. A total of four different configurations were investigated to quantify the performance characteristics of conventional woodframe shear walls sheathed with OSB finished with either drywall and/or stucco. Currently, ASCE 41 provisions suggest no increase in capacity, nor difference in acceptance criteria for plywood sheathed walls clad with non-structural finishes (drywall and/or stucco) citing that stucco/drywall are brittle and fail at low levels of seismicity. However, data collected from research conducted as part of an ongoing study show that there are large differences in the backbone curves. Furthermore, using the Type 1 curve (as put forth by FEMA 356/ASCE 41) for establishing the acceptance criteria of ductile subassemblies may not be a good match for the recorded data from wood sheathed walls (both with/without cladding of drywall/stucco). Lastly, when a Type 1 component behavior is fit to test data consistent with the ASCE 41 Alternative Modeling Parameters and Acceptance Criterion, the suggested Life Safety and Collapse Prevention acceptance criteria vary greatly for each of the four configurations tested.

This paper proposes an alternative algorithm for estimating structural resistance to earthquake-induced collapse. The method utilizes nonlinear static (pushover) analysis to obtain an initial estimate of collapse resistance. This estimate serves as the starting point for dynamic analysis. Analyses presented demonstrate that the proposed algorithm is more computationally efficient than a standard incremental dynamic analysis approach, reducing analysis time by approximately 90%. Accuracy of the proposed approach is demonstrated through comparison with results obtained from incremental dynamic analysis, indicating good agreement between the two methods.

This paper develops a simple yet reliable demand model for estimating the inelastic displacement and ductility of RC bridge columns considering their shear-flexure interactive behavior. Utilizing a coupled hysteretic model to realistically simulate the nonlinear behavior of columns and the rigorous dimensional analysis, the study revealed strong correlation between the normalized inelastic displacement and the dimensionless structure-to-pulse frequency, a proposed dimensionless nonlinearity index as well as the aspect ratio of columns. Two regressive equations are proposed and validated against the simulation results. The inelastic displacement of columns can therefore be estimated directly from structural and ground motion characteristics using the proposed model.

Seismic behavior of an inelastic beam resting on a nonlinear soil bed is analyzed with the development of fiber beam element. The Winkler approach models the soil as a single layer, and assumes that the foundation reaction at a particular point is proportional to the soil displacement. In this paper a new finite element formulation was developed to simulate the seismic performance in which the soil can be viewed as a semi-infinite inelastic element that can resist bending, in addition to the well-known Winkler effect. The non linear response of structures resting on this improved foundation model is analyzed following a Vlasov approach with soil parameters based on a plane strain assumption. The tensionless character of the foundation results in the creation of lift-offs between the beam and foundation is also being considered. Effect of the earthquake intensity on drift demands is investigated. Parametric analysis of the reinforced concrete and steel foundation elements are carried out and comparisons were made with the simple Winkler model. The presented solutions and applications show the superiority of the element in simulating the seismic response of foundation structures.

In the context of performance-based earthquake engineering, we aim to better quantify the seismic demand on structures. This is usually done through the use of ground motion intensity measures (IM) such as PGA and elastic spectral acceleration (Sa). Unfortunately, these peak-valued IMs are often not sufficient to characterize the seismic demand or to predict the structural response. For stiffness-degrading and strength-degrading structural components and systems, the number of cycles of inelastic response determines the degree of degradation. In soil liquefaction, the number of cycles of loading above a strength threshold is critical. At present we have no simple and convenient way to estimate the number of response cycles that a given ground motion may induce above a given threshold. In this paper, we introduce a new ground motion IM we call "peak exceedance spectra" or "n-Spectra". For a given excitation motion, n-Spectra quantify how many times an elastic single-degree-of-freedom (SDOF) oscillator will exceed any given amplitude of response (e.g., Sa). The n=1 spectrum is the conventional elastic response spectrum. At any period, the n-Spectra plot serves as a cumulative histogram of spectral response peak amplitudes. By quantifying the number of demand peaks (and hence cycles) above a level of interest, n-Spectra provide a more complete estimator of the potential damage due to earthquake ground motions. n-Spectra are easy to compute, they complement conventional elastic response spectra, and have many practical applications. Because of this, n-Spectra have the potential to become a very useful tool in earthquake engineering. This paper presents an introduction to n-Spectra, their computation and interpretation and a list of potential applications for this new IM.

The earthquake engineering community has made significant progress in developing design-oriented finite element methods that can systematically simulate nonlinear foundation-building behavior. This paper presents a parametric investigation using one such widely used method, namely the Beam-on-Nonlinear-Winkler-Foundation (BNWF) model. The focus herein is on characterizing the effects of foundation configuration variation on seismic response of moment-frame buildings. For this purpose, a large suite of nonlinear time history analyses are conducted, adopting the incremental dynamic analysis approach, while evaluating the resulting engineering demand parameters. The paper concludes with findings regarding the effects of varying basementmat levels on several key engineering demand parameters.

Piezoelectric materials have been widely adopted for sensing, actuation, and energy harvesting in structural health monitoring applications. To date, most of the piezoelectric materials employed are piezoceramics such as lead zirconate titanate (PZT) or piezoelectric polymers such as poly(vinylidene fluoride) (PVDF). Although PZTs exhibit high piezoelectricity, they are extremely brittle; on the other hand, PVDF and their copolymers are inherently very flexible but cannot generate large actuation forces due to their low stiffness. Thus, the main objective of this research is to develop a piezoelectric zinc oxide nanoparticle-based thin film that possesses high piezoelectricity with enhanced mechanical properties (i.e., high stiffness, strength, and flexibility). In order to explore the influence of film fabrication parameters on the bulk nanocomposite's piezoelectric and mechanical performance, different concentrations of zinc oxide nanoparticles are dispersed in polyelectrolyte solutions. These solutions are then employed for fabricating thin films via a simple thermal evaporation procedure to evaporate the excess solvent. Upon nanocomposite fabrication, these prototype films are surface-mounted to cantilevered beam specimens. Piezoelectric response is validated by measuring the thin film's generated voltages during free vibration of the cantilever due to an applied initial displacement at the free end. Evaluation of mechanical performance is then conducted by mechanically cutting the nanocomposites to small rectangular specimens. Then, these films are loaded in monotonic uniaxial tension to extract their stress-strain response for determining the films' Young's modulus, ultimate tensile strength, and ultimate failure strain.

Due to the complexity of monitoring the integrity of existing structures, current research in the area of structural health monitoring (SHM) has highlighted the need for more effective damage detection methodologies and efficient sensing devices. The development in nanotechnology in terms of precision, sensitivity, energy harvesting, and wireless capability will provide an unprecedented generation of sensors to the field of structural health monitoring. While several biosensors are in use for industrial applications, ongoing research in the area of biosensing has great potential to bring in a new generation of sensors with multifunctional and integration capabilities. This work will shed light on the possibility of combining some of the global and local SHM methodologies with different sensors for maximum efficiency and minimal cost for damage detection of civil engineering structures.

Structural health monitoring is an important issue for the maintenance of large-scale civil infrastructure, especially for bridge columns. In this paper, an innovative piezoceramic-based approach is developed for the structural health monitoring of reinforced concrete columns. An innovative piezoceramic-based device, smart aggregate, is utilized as a transducer for health monitoring purposes. To investigate the seismic behavior of RC bridge columns, structural health monitoring tests were performed on two bridge columns under combined reversed cyclic loading at Missouri University of Science and Technology. Experimental results show that the proposed smart aggregate-based approach successfully evaluated the health status of concrete columns during the loading procedure.

In this paper, a new approach using mobile sensor networks is proposed for structural health monitoring. Compared with static sensors, mobile sensor networks offer flexible system architectures with adaptive spatial resolutions. The paper describes the design concept of a flexure-based mechatronic (flexonic) mobile sensing node and its application in structural health monitoring. The flexonic mobile sensing node is capable of maneuvering on structures built with ferromagnetic materials, as well as attaching/detaching an accelerometer onto/from a steel structural surface. The performance of the prototype mobile sensor network has been validated through laboratory experiments, where two flexonic mobile sensing nodes are adopted for maneuvering on a steel portal frame. Transmissibility function analysis is then conducted to identify structural damage using data collected by the mobile sensing nodes. This preliminary work is expected to spawn transformative changes of using mobile sensors for future structural health monitoring.

In this study, the real time strain response of the Multiwalled Carbon Nanotube (MWCNT) film to different kinds of tensile loading and response of the MWCNT film to temperature changes at macroscale is studied experimentally. The strain is applied to the MWCNT film by attaching it to a brass specimen using vacuum bonding, and subjecting it to tensile loading. Voltage output from MWCNT film is obtained using four-point probe in conjunction with a sensitive voltage measurement device. Experimental results demonstrate a linear relationship between change in voltage across the film and change in strain in the brass specimen when subjected to tensile load. The observed electromechanical characteristics also exhibit excellent reversibility evident from the way the voltage of the MWCNT film recovers to its unstressed state upon unloading. The MWCNT film exhibited a stable and linear response to changes in temperature with the resistance observed to be decreasing as temperature is increased. The study of MWCNT response to changes in temperature was done over a limited range. The experimental results presented in this paper demonstrate the effectiveness of MWCNT thin film in strain sensing as well as highlight the effect of temperature on it.

This paper proposes a new signal processing method for non-stationary signals based on a new concept called intrinsic frequency. Intrinsic frequency, as derived in this paper, is an inherent characteristic of a signal, which has clear physical meanings and describes the local waveform of the data. This new method actually corresponds to a completely adaptive local fitting of the signal data into harmonic functions. Compared with short-time Fourier transform, it allows for non-integer numbers of complete sinusoidal waves, thus is not subjected to uncertainty principle. Unlike wavelet transform, it does not use any preset functional forms, thus is very adaptive to data. It does not have the problems of HHT due to Bedrosan and Nuttul theorem. This paper gives the mathematic derivation of intrinsic frequency, followed by five examples of continuous signals. The results are compared with theoretical frequencies, Fourier transform, instantaneous frequencies based on Hilbert transform, and instantaneous frequencies based on Hilbert Huang Transform. The advantages and physical meanings are clearly shown. Numerical algorithm for discrete signals and the difficulties of the method are also discussed. This new analysis method can be applied to a wide spectrum of challenging engineering problems. In structural engineering, the applications include analysis of ground motion characteristics, nonlinear structural responses, structural health monitoring, and damage detection.

Post-earthquake repair costs and repair times are important for evaluating the performance of bridges in a fundamentally different way than the traditional component-level metrics such as bearing displacements and column ductility demands. Repair costs and times are metrics that address the system-level response of bridges to a suite of seismic events, especially when cast probabilistically in the form of fragility curves. As with any vulnerability assessment that is comprised of numerous components, each with their own individual vulnerability, there is a potential for greater uncertainty in the resulting system-level metrics, or conflicting contributions from different components to obscure the principal importance measures in the process. A typical multi-span reinforced concrete highway overpass bridge in California is used to investigate sensitivity of the probabilistic repair cost and time metrics to changes in repair quantities, unit costs, production rates, and correlation at the demand and damage levels. Results show the definition of the discrete damage states and the uncertainties in certain repair quantities and production rates to be critical parameters.

Bridge level failure event definitions per limit state have evolved from failure of one key component as representative of the system, to failure of at least one of many components. In practice, this and similar definitions limit the inclusion of joint failures of several components in a previous limit state, whose effects on repair cost and functionality can equate to system failure in the next limit state. This paper explores a closed form combinatorial method to evaluate all possible ways in which components can fail and argues that typical system failure definitions per limit state can incorporate joint failures of multiple important components in a previous limit state. Other failure events can be considered for the augmentation of typical system events, but this work focuses on the most influential components because they can be visually identified through conditional importance measures as a by-product of the combinatorial approach. Bridges in as-built circumstances and retrofitted with elastomeric bearings are used to illustrate the augmentation calculation, which increases the median system fragility at moderate limit states in the range of 4% to 20%. This methodology to connect bridge component to system reliability can readily support infrastructure stakeholder decision making and risk management.

Most of the past seismic fragility studies on typical highway bridges in the Central and Southeastern United States (CSUS) have focused on regular three-span bridges with little to no skew. However, past earthquakes and studies have shown that skewed multi-span simply supported bridges may also be susceptible to earthquake damage, specifically causing coupled responses (longitudinal and transverse) that place more demand on individual components. With over 27 percent of simply supported steel girder highway bridges in the CSUS having a skew angle over 15 degrees, there is a specific need to further quantify the vulnerability of such bridges exposed to seismic hazard. This study seeks to add to the current knowledge base of the seismic fragility of multi-span steel girder bridges in the CSUS by specifically addressing the issue of skew in the assessment. A sensitivity study for each of the column, abutment, and bearing components along with the system as a function of skew angle is presented. This comparison indicates that bridge vulnerability appears to be largely unaffected by skew angles under fifteen degrees, but larger skew angles do indeed result in more fragile bridge systems. Within this system the longitudinal components of the bridge become less fragile with increasing skew, but to a lesser degree than the transverse components become more fragile. Understanding the impact skew plays on seismic bridge fragilities will facilitate more robust regional risk analyses of highway systems.

This paper examines the eigenvalues of multi-span seismically isolated bridges in which the transverse displacement of the deck at the end-abutments is restricted. For moderate long bridges the first natural period of the bridge is the first longitudinal period, while the first transverse period is the second period, given that the flexural rigidity of the deck along the transverse direction shortens the isolation period offered by the bearings in that direction. This paper shows that for isolated bridges longer than a certain critical length, the first transverse period becomes longer than the first longitudinal period despite the presence of the flexural rigidity of the deck. This critical length depends on whether the bridge is isolated on elastomeric bearings or on spherical sliding bearings. On the other hand this result can not be captured with the limiting idealization of a beam on continuous distributed springs (beam on Wrinkler foundation) — a finding that has practical significance in design and system identification studies. The paper discusses the implications of this finding in design.

For a long time, erectors have been using simplified rules of thumb to assess the stability of single cantilevers or simply-supported girders under erection by the L/b ratio, where L is the unbraced length and b is the compression flange width. Certain limits on the L/b ratio exist, which determine if a girder under erection with a specific L/b ratio would remain stable, need temporary support or need stability check. Those rules of thumb, although convenient for on site check, were purely based on experiences and therefore need to be checked for accuracy and applicability with the current design code. Formulae for the maximum allowable girder span L_max as well as the maximum (L/b) ratio have been developed following the current AASHTO LRFD code. Parametric studies were conducted on various girder sections in order to 1) calculate the maximum L/b ratio for each girder section and check the rules of thumb; 2) determine the dominant section parameters on girder stability under erection. Finite element analyses (FEA) were also conducted in order to 1) further understand the behavior of girder instability; 2) compared the maximum L/b ratio obtained from FEA with the ratio obtained from AASHTO LRFD code.

A benchmark model of seismically excited bridge has been proposed in 2004. The benchmark problem package consists of dynamical model of the bridge with designs of sample controllers in MATLAB environment with prescribed evaluation criteria and ground motions. Research contributions to the benchmark study by researchers around the world have been published in as special issue (vol. 16, issues; 5–6, year; 2009) of Structural Control and Health Monitoring. This paper presents a review of contributions to the benchmark study and analysis of competing control strategies in the benchmark study.

The nonlinear benchmark problem for seismically excited buildings was published in 2004, along with MATLAB code for the associated nonlinear evaluation model. The benchmark problem focused on three typical steel structures, 3-, 9-, and 20-story buildings designed for the SAC project for the Los Angeles, California region. The goal of the benchmark was to provide a clear basis to evaluate the relative merits of various passive, active or semiactive structural control strategies on fixed-based seismically excited buildings. With 75 archived publications citing this benchmark problem and over 17 studies conducted using the nonlinear seismically excited benchmark problem the lessons learned from these studies can be examined. This paper presents an overview of the studies conducted on the set of benchmark control problems for seismically excited nonlinear buildings and identifies key findings resulting from these studies.

A benchmark problem for the response control of a 76-story building was established in December 1997. The problem package consisted of a model of the 76-story tall building with a height to width ratio of 7.3, a paper describing the problem and computer programs to perform stochastic and deterministic response analysis. For the deterministic response analysis, wind loading time histories through a wind tunnel testing were generated. The response control performance criterions were formulated in terms of both stochastic and deterministic response quantities. Participation in the benchmark study was completed in 2004 with the publication of the special issue of the Journal of Engineering Mechanics (vol. 130, issue; 4). This paper presents a critical analysis, impact and summary of contributions by researchers in the benchmark study.

Two phases of the benchmark problem on base-isolated buildings concluded recently, culminating in two separate special issues in the Journal of Structural Control and Health Monitoring. The base-isolated building considered in the benchmark problem is based on the USC hospital building in Southern California. The goal of this benchmark is to provide a common computational test-bed to analyze competing control strategies on base-isolated buildings, including devices, algorithms and sensors. To achieve this goal, a 3-D finite-element model was developed in MATLAB to represent the complex behavior of the full-scale base-isolated building with lateral-torsional behavior. The model allows users to model both linear and nonlinear isolation systems. A nonlinear structural analysis tool was developed in Matlab^TM and distributed to the participants for nonlinear dynamic analysis. Over twenty papers in two special issues in the Journal of Structural Control and Health Monitoring were published as a result of this effort. This paper presents an overview of this benchmark effort.

This paper presents two sets of test bed structures for structural control researches. One is the 6-story steel frame (scale down model) and the other is the 3-story steel frame (almost full scale). The system matrix including the mass, stiffness and damping matrices of these two structures were identified using stochastic subspace identification technique by adopting the response data of white noise excitation. The 6-story steel frame (Floor: 1.5m*1m / Height: 1m *6) was designed for testing the developed structural control algorithm. Different control algorithms can be used and apply to this test bed structure to examine the effectiveness of the developed control algorithms. The 3kN MR damper (Lord Co.) was selected as the control devices for this 6-story structure. Performance test of the 3kN MR damper was also conducted to obtain the mathematical model of the damper. All these data (including the original test data) were collected in the control test bed data bank. Researchers can use this data bank to design the controller. Different from the 6-story steel structure, an almost full-scale 3-story steel frame (Floor: 3m*2m / Height: 3m *3) is constructed for testing the control devices. This paper will introduce these two test beds and demonstrates different test that had been applied to these two test-bed structures. Researchers can use these two test beds to develop the control algorithms as well as the control devices and test it on the NCREE shaking table The proposed structural models and data banks can support the development of structural control researches.

In this paper, experimental and simulation results on the control of structural vibrations using a newly proposed adaptive pendulum mass damper with real-time tuning capability are presented. The adaptive pendulum mass damper is a spherical pendulum augmented with a tuning frame to adjust its length and two adjustable air dampers connected to the mass for achieving the damping adjustment. The mechanical adjustments are implemented using three independent stepper motors, one micro-controller and three drives. The mass damper is used to control the vibration responses of a bench-scale two-story model structure with sufficiently long fundamental period representative of flexible structures such as towers. The basic architecture of the system proposed consists of two components; identification and control, one followed by the other in that order. The identification is carried out using traditional Fourier methods and a second-order blind identification method in the time-domain. The control phase consists of position control based on the identified frequency from the identification phase. The paper focuses on the hardware and software aspects of the real-time implementation of this adaptive mass damper. The identification methods used in this study rely only on acceleration measurements collected from high accuracy-low frequency accelerometers mounted on the structure, and do not utilize the excitation information. This study is primarily intended to demonstrate the feasibility of employing adaptive pendulum mass damper designs to enhance the robustness of passive tuned mass dampers to structural, environmental and design changes.

Tuned mass dampers (TMD), active mass dampers (AMD) and hybrid mass dampers (HMD) have been widely applied for vibration control of tall buildings and bridges in the past decade. Recently, the first author and his coworkers have developed semiactive or smart tuned mass dampers (STMD) using semiactive variable stiffness systems. STMD's are superior then TMD's in reducing the response of the primary structure. In case the fundamental frequency of the primary structure changes due to damage or deterioration, then the TMD will be off-tune; hence, it will lose its effectiveness significantly, whereas the STMD is robust against such changes as it is always tuned. The author and his coworkers have shown that STMD can provide performance similar to AMD/HMD, but with an order of magnitude less power consumption. This paper presents the development of a new STMD to reduce the vibrations of structures. The new STMD is an adaptive length pendulum (ALP) damper. It is essentially an Adaptive Stiffness Device (ASD); wherein, the length of the pendulum is varied in real time to achieve the change in frequency or stiffness (with mass remaining constant) of the pendulum. The Two different control approaches to adjust the length of pendulum of the ALP-STMD are developed (1) a shape memory alloy (SMA) actuator, and (2) servomotor. In both the mechanisms the length of the pendulum is adjusted semi-actively based on the feedback signal displacement of the top floor of the structure. Experimental studies are carried on a two-storey scaled model building with ALP-STMD. Effectiveness of the proposed ALP-STMD in controlling the fundamental mode of the structure is validated experimentally using both the SMA and servomotor to change its length. Off-tuned ALP-STMD results are presented to demonstrate the importance of tuning the length of pendulum.

During the past decade numerous researchers have investigated the dynamic behavior of structures with magnetorheological (MR) dampers using various semi-active control laws. A majority of the conclusions focused on the superiority of semi-active controllers over passive control. Large-scale MR dampers have not been studied extensively in conjunction with semi-active control laws since only a few experiments have been conducted with large-scale dampers. The assessment of semi-active controllers however needs to be verified more rigorously by using large-scale MR dampers. In this paper, real-time hybrid simulations using large-scale MR dampers are conducted to evaluate the effectiveness of various structural control strategies in enabling the seismic performance objectives of a building structure to be achieved. A prototype structure of a 3-story building is designed in accordance with the ICC code to satisfy the strength requirement, and an MR damper is installed to control the drift of the structure. Three different control strategies are considered: (1) passive control; (2) linear quadratic regulator (semi-active control); and (3) sliding mode control (semi-active control). Six ground motions scaled to the same design basis earthquake are used for the real-time hybrid simulations and statistical responses of the structure are obtained to compare the performance of each controller.

There exists a current need in our nation to address the deteriorating integrity of our infrastructure. Highway bridges in particular are continuously approaching or exceeding their design life and are increasingly being classified as structurally deficient. The service life of highway bridges can be extended through the innovative application of structural control to reduce the peak stress in the critical elements of the bridge due to heavy truck traffic. A promising class of controllable hardware, the Magneto-Rheological (MR) damper, is proposed to reduce the dynamic response of bridges and extend the service life. The inherent stability, robust performance, and low power requirements of MR dampers make them an attractive type of controllable hardware for highway bridges. In this paper the large-scale real-time experimental verification of a typical highway bridge excited by a crossing truck and controlled with MR dampers using hybrid testing at the Lehigh University Network for Earthquake Engineering Simulation (NEES) facility is described. Preliminary simulation results indicate that peak and dynamic responses can be effectively reduced to increase the fatigue life of the structure. Initial experimental tests validate the simulations and indicate the potential of using MR dampers to reduce traffic induced vibration of bridge structures.

This paper describes a study-abroad capstone experience for civil engineering students at Brigham Young University. Students gather information about assigned megastructures in China, and then take a two-week trip to China to see these megastructures, visit construction sites, and interact with design professionals. The paper describes the operation and outcomes of the program. It also discusses the experiential learning that takes place in the program.

Internet era has faced us with new challenges in every aspect of our lives. Knowledge and information sharing is one of these areas that have significantly affected students learning process. 21st century education is not immune to these challenges. Traditional method of teaching in which the professor was the leading figure on the stage and students had to follow step-by-step the wise man's instructions, has lost its appeal. 21^st century students' demand highly supported learning environment. In this environment, computers can play an important supporting role. It is important to realise that most of the processing and number-crunching activities, which was a dominant learning activity in the past can be more efficiently performed by the computer and instead students can focus on conceptual thinking and problem solving activities. This paper proposes a new method of teaching in which conceptual thinking is a core activity. In this approach, students are actively involved in taking responsibility for their learning and using computers, as a necessary supporting tool, can greatly enhance their learning.

Assessment of the nation's aging infrastructure has become one of the most important problems in civil engineering. The infrastructure of the United States increasingly deteriorates, but due to the limited resource, maintenance schedule has to be prioritized carefully based on the rigorous assessment. Currently, for the assessment, the decision-makers have to refer to various types of heterogeneous data, such as condition of a bridge, traffic, and societal impact of the structure. It is difficult, and sometimes impossible, to make an objective decision due to the heterogeneous nature of the data. In this paper, we propose to adopt and improve data-mining techniques based on self-organizing maps (SOM), to visualize and analyze the nation's aging infrastructure. SOM is widely used in computer science, but its application to the assessment of aging infrastructure has not been studied before. By using SOM, data points that share similar characteristics will be clustered together in 2D space. Therefore, we can gain further insight into the problem that was not possible in the original high-dimensional data space. Another important study using SOM is to seek the possibility of prioritizing different clusters, which requires quantification of reduced-dimensional space. Numerical examples are provided to illustrate the proposed approach.

Strategies for design-oriented structural engineering education are presented. The discussion is based on tall building design projects carried out by the graduate students at the schools of architecture, Yale University as well as University of Illinois at Urbana-Champaign, where the author instructed the design projects. The importance of integrated design approach in executing multidisciplinary design projects is presented with a particular emphasis on structural engineering. The aesthetic potential of structural engineering in contemporary architectural design projects is discussed. Further, sustainable structural engineering strategies are discussed. By presenting what have been learned from the design-oriented structural engineering education based on the experience of the author, the contribution of this paper is to help create more constructive relationships between structural engineers and other related disciplines to produce higher quality built environments.

Modern Design Build groups face an turbulent environment with constant proliferation of unstructured electronic data. Every office member generates shocking and expanding amounts of unstructured content every hour of every workday. Word documents, PDFs, spreadsheets, e-mail, CAD/CAE files, pictures, etc. - this is only a small listing of data generated daily. Numerous existing generic software packages efficiently handle metadata, workflows, CAD/CAE, ERP and databases. Yet, high acquisition and implementation costs coupled with generic packaged software solutions offer minimal impact to the total problem of data management. Today's shrinking economic environment requires efficient answers to managing information. Lean principles have been applied successfully to manufacturing and operations processes in many companies over the last two decades, but their application to engineering or new product introduction processes has been minimal. Design Build is only beginning to benefit from the lessons learned in other industry sectors. This paper deals with the development of the methodology and consequent deployment of the integrated "assembly to order" product development and fabrication document delivery automated system. The integration of a seamless product processes workflow brings a completely new approach to handling customer needs and requirements. Customizing unique product architecture and verifying code and specification requirements into a uniquely organized set of design parameters had been fulfilled. Managing these factors along with the project life cycle, 3D CAD/CAM model generation, digital simulation and construction planning provides a homogenous organizational mechanism for the entire turnkey solution. The present document provides a brief review of a successful implementation of the hybrid assembly-to-order business strategies at GlenMartin, Inc. The implementation of product architecture, families, classes and designs brought the increased value for the entire enterprise. Data driven processes management coupled with highly parameterized 3D CAD models are the basics to efficient product control. Utilizing lean engineering principles allowed the creation of value throughout the product lifecycle and the enterprise. Moreover, the application of lean thinking provided a perfect opportunity to eliminate waste and improve cycle time without sacrificing quality. Understanding the strategy, priorities and operational actions helped GlenMartin Inc. service their customers in the manner they deserve.

The definition of Management Information Systems (MIS) is a planned system of the collecting, processing, storing and disseminating data in the form of information needed to carry out the functions of management. The term usually refers to business operations not engineering. However, over the past several years engineers have started to develop systems that not only convey basic design (2 dimensional) data but multi-dimensional data. The foray into multi-dimensional data systems is allowing engineers to see their projects and decisions in ways that were never possible or dreamed of. The reason for these efforts is that amount of data that an engineer generates for any given project has grown far beyond what the normal human brain can grasp and make decisions on in a reasonable amount of time. So there is an attempt to filter, organize, store, manipulate and manage data down to a level understandable by humans, in other words MIS in Structural Engineering. My presentation will introduce MIS concepts and provide an example of a MIS in structural engineering. The example is the design of an edge girder for a cable-stayed bridge. The girder design contained millions of records of forces, moments, lengths, etc. for every half floor-beam spacing point along the length of the girder. This pile of data was collected, organized and filtered down to only a few thousand lines that captured the essential information for a thorough design effort.

Topology optimization is a structural design approach in which material and voids are distributed within a prescribed volume referred to as the design domain. Due to the large number of design variables and the computational cost of the structural analysis, classical optimization methods are usually impractical. This has motivated the implementation of specialized numerical methods. Moreover, as there is an increased need to design robust and resilient structural systems that can withstand extreme event such as blast and impact loading, it is also required to account for nonlinearities in design optimization process. In this paper a novel formulation for topology optimization of nonlinear structures is presented. The proposed formulation is applied for minimum compliance design of nonlinear structures. Representative examples presented in this paper include classic Mitchell-type structures.

The world is experiencing an upsurge of tall building construction. Recent trends toward developing increasingly taller and irregularly-shaped complex buildings imply that these structures are potentially more sensitive to wind excitation. Structural engineers are facing the challenge of striving for the most efficient and economical design solution while ensuring that the final design of a building must be serviceable for its intended function, habitable for its occupants and safe over its design life-time. Performance-based design (PBD) is a modern approach to the design of building structures. While PBD is still under active development primarily in seismic engineering, the concept of performance-based wind engineering should be extended to the design of wind sensitive tall buildings. This paper presents a computer based technique for optimal wind resistant performance-based design of tall buildings under various levels of wind hazards. Once the wind-induced loads and responses of a tall building structure under multiple levels of wind events are accurately determined, the optimal performance-based design problem can then be explicitly formulated. A rigorously derived Optimality Criteria (OC) method is to be developed to solve the optimal structural solution satisfying the strength (life-safety), drift (damage) and acceleration (occupant comfort) design performance constraints. The effectiveness and practicality of the optimal design technique are illustrated through an actual 40-story building with complex 3D mode shapes.

Topology optimization techniques are employed to automate the design of reinforced concrete members. Truss models are derived with maximum stiffness (minimum total strain energy) from an initial ground structure defined over a general concrete member. The optimization routine, implemented with a freely available computer program, produces strut and tie geometries consistent with elastic tensile and compressive stress trajectories, resulting in steel reinforcement layouts with the potential to minimize crack widths and improve member performance over traditional strut and tie models. Ongoing work in continuum topology optimization of reinforced concrete members is summarized, including consideration of constructability in the optimized solution and the development of solutions with curved compressive struts which are more consistent with elastic stress trajectories than traditional strut-and-tie models derived by hand.

In 1981, the Optimal Structural Design Committee of ASCE identified impediments preventing structural engineers from adopting widespread application of optimization techniques in design. Almost 30 years later, many of the structural optimization algorithms that have been developed are still being tested on simplistic models proposed in the 70s and 80s. There is a need for new realistic system benchmarks that could serve as testbed application and verification of novel methods of structural optimization. We discuss the advancements of the past and present a venue for development of future benchmark problems. This paper serves three purposes: it challenges developers of optimization techniques to tackle larger scale problems by posing new yet practical problems; it encourages practitioners to realize the strength of structural optimization techniques in developing safe and cost effective designs; and it seeks to persuade design professionals and academicians to efficiently utilize available computational power and paradigms in solving today's engineering design and optimization problems. In an upcoming paper, review of performance of emerging design optimization techniques in handling the newly proposed optimization benchmarks will be studies. Future research and development needs will be discussed.

Most benchmarks in structural optimization have limited their design criteria to aspects of safety such as strength, stiffness and reliability. However, good practical designs must also consider design criteria based on cost. Therefore, structural optimization formulations must expand benchmarks to include design criteria relating to cost such as constructability, repetition of design and material procurement. This presentation will discuss what design constraints of practical design warrant inclusion in structural optimization techniques and possible challenges to expanding optimization techniques into using such criteria. The presentation will also facilitate a discussion with practitioners to prioritize what building systems can benefit from improvements in practical design techniques, and how structural optimization formulations can solve those challenges. The feedback from this presentation will help establish a prioritization of optimization benchmarks for future research. While much optimization research to date has focused on structural steel systems, this presentation will consider both reinforced concrete as well as structural steel systems.

Recently, the authors have been making research efforts to overcome technical challenges in applying design/topology optimization techniques to large-scale structural systems with uncertainties. First, in order to evaluate the probability of a system failure event and its parameter sensitivities accurately and efficiently during reliability-based design optimization, a system reliability-based design optimization (SRBDO) approach using the matrix-based system reliability (MSR) method was developed. In this approach, the MSR method utilizes matrix calculations to evaluate the system failure probability and its parameter sensitivities. The SRBDO/MSR approach is applicable to general systems including series, parallel, cut-set and link-set systems consisting of statistically dependent component events. Second, the material distribution method used for topology optimization often requires a large number of design variables, especially in three-dimensional applications. A multiresolution topology optimization (MTOP) scheme is thus developed to obtain high resolution optimal topologies with relatively low computational cost. These technical advances enable system reliability-based optimization of large-scale structural topology with low computational cost. This paper presents the SRBDO/MSR approach and MTOP scheme, respectively, and demonstrates these technological advances through numerical examples of system reliability-based optimization of structural topology.

This paper presents an integrated thermomechanical method for modeling the behavior of fiber reinforced polymer (FRP) composite structures subject to simultaneous fire and mechanical load. The model includes heat transfer modeling to calculate temperature history of the structure and structural modeling to predict the mechanical performance of the structure. Heat transfer modeling assumes that heat and mass transfer of volatile by decomposition are one dimensional through thickness. With the temperature profile calculated by heat transfer modeling, structural modeling analyzes the deformation and failure. Both thermal and mechanical properties in modeling are temperature dependent. Arrhenius equation is used to describe decomposition reaction of resin and a concept of shift temperature is introduced to account for heating rate's effect on the decomposition temperature. The integrated model is validated with experimental data from structural fire tests.

This paper presents a new finite element-based model for analysis of reinforce concrete (RC) frames subjected to combined loading conditions. The proposed model is formulated to address the interaction between the axial force, biaxial shear, biaxial bending, and torsion. The shear mechanism along the beam is modeled by using the Timoshenko beam approach with curved three dimensional (3-D) frame elements with arbitrary cross-section geometry. The problem consists of solving a system of equations by combining the equilibrium conditions, compatibility conditions and constitutive laws of materials at the section and structural level. The concrete constitutive model follows the Softened Membrane Model (SMM) with a tangent-stiffness formulation. The validity of the model is established by correlation of analytical results with experimental tests of RC specimens. The result shows that the flexural capacity and ductility of the RC members decreased significantly under the effect of combined bending and torsion.

In structural elements made up of two or more materials, such as steel-concrete composite beams and columns, reinforced and prestressed concrete elements, and members with FRP reinforcement, the relative slip between material components plays an important role in the strength and energy dissipation capacity of the composite element. Frame finite elements proposed to date that include the relative slip between components are limited to 2d members and, furthermore, lack a framework that permits large displacement cyclic analysis of structures. This paper formulates a new 3d frame element for the inelastic response of structural members that includes the relative slip among components. The formulation is based on the three field Hu-Washizu variational principle with the interface slip among components as one of the independent variables. The proposed element is validated with two correlation studies. They showcase the advantages of the proposed formulation which allows for the relative slip discontinuity at the interface between the element and the joint or foundation.

The present study extends a multi-hazard methodology presented previously by the authors for evaluating performance of moment resisting frames subject to extreme lateral loads such as earthquake and blast. After increasing resistance based on hazard specific analysis, relative benefits are assessed in order to obtain a better appreciation of safety and economy in multi-hazardous regions. The present study examines the influence of damage on the overall stability of a system based on analysis of a beam-column subsystem. First floor columns affected by external ground level blasts may effectively lose all load carrying capacity thereby transferring gravity and live loads to adjacent parts of the subsystem, which may have reduced capacity as a result of the loading event. A mapping procedure is performed correlating reflected pressures at varying distances from the source to varying degrees of loss of load carrying capacity and stiffness. The subsystem loss is established using both analytical and computational simulations. The present study uses a 3-story steel moment resisting frame building for performance evaluation. Nonlinear material and geometric analysis are used to estimate the damage and stability, respectively, of various column subsystems around the affected area.