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Tunnelling under the York University Schulich Building was one of the milestones of the Toronto-York Spadina Subway Extension Project. The challenge was to bore the tunnel under a flagship building only one diameter below the foundation without a compensation grouting process. Intensive finite element structural and geotechnical analyses of the building and the tunnel were performed, together with monitoring field measurements. The results showed that compensation, included in the initial design, was not necessary to ensure the building's structural integrity. The tunnel monitoring during crossing confirmed the results of the performed analyses. The paper highlights the difficulty of deciding whether a compensation grouting is necessary or not when tunnelling under buildings and explains the procedure that was followed in this particular case.Key words: tunnels, monitoring, buildings, settlements.Le creusement d'un tunnel sous l'edifice Schulich de l'Universite York etait un des jalons du projet de prolongement de la ligne de metro de Toronto-York Spadina. Le defi etait de forer le tunnel sous un immeuble de prestige seulement un diametre au-dessous de la fondation sans une compensation par injection de coulis. D'intensifs calculs des structures et d'analyses geotechniques par elements finis de l'edifice et du tunnel ont ete effectues, ainsi que des mesures sur le terrain pour faire un suivi. Les resultats ont montre que la compensation, faisant partie de la conception initiale, n'etait pas necessaire pour assurer l'integrite structurale de l'edifice. La surveillance du tunnel pendant le croisement a confirme les resultats des analyses effectuees. Cette etude met en evidence la difficulte de prendre une decision a savoir si la compensation par injection de coulis est necessaire ou non dans le cas de creusement de tunnel sous des edifices et explique la procedure qui a ete suivie dans ce cas particulier. [Traduit par la Redaction]Mots-cles: tunnels, surveillance, edifices, tassements., 1. IntroductionTunnelling under existing structures is a challenge that engineers often face in urban underground projects. Therefore, great efforts were devoted in the past to predict the impact of tunnelling [...]

To identify and calibrate the finite element model for multi-story buildings, a simplified approach is being introduced in this paper; this methodology is based on interferometric imaging and encompasses spectral ratio (SR) method. Interferometric imaging provides a new set of seismic data free of coupling between structures to its subsurface and independent of the excitation of the building. The SR method, on the other hand, is the ratio of Fourier amplitude spectra of the roof- deconvolved records on two adjacent stories. The newly introduced methodology enables each story to be identified uniquely for its stiffness since the SR of a particular story is dependent only on the properties of itself and the stories above. Key words: finite element model calibration, interferometric imaging, spectral ratio of a story. Dans le but d'identifier et de calibrer le modele d'elements finis de batiments a multiples etages, on presente dans cet article une approche simplifiee; la methodologie repose sur l'imagerie interferometrique et englobe la methode du rapport spectral (SR). L'imagerie interferometrique produit un nouvel ensemble de donnees seismiques libre du couplage entre la structure et le sous-sol et independant de l'excitation du batiment. La methode du SR, d'un autre cote, est le ratio du spectre d'amplitude de Fourier des enregistrements du toit deconvolue pour deux etages adjacents. La methode nouvellement presentee permet d'identifier chaque etage distinctement pour sa rigidite puisque le SR d'un etage en particulier est dependant uniquement des proprietes propres a l'etage et de celles des etages au-dessus. [Traduit par la Redaction] Mots-cles: calibrage du modele d'elements finis, imagerie interferometrique, rapport spectral de l'etage., Introduction To develop effective, reliable tools and techniques to maintain the safety and integrity of multi-story buildings, scientists and engineers have conducted substantial research in vibration-based damage identification. A broader [...]

The joined wing is a new concept of the airplane wing. The forewing and the aft wing are joined together in a joined wing. The range and loiter are longer than those of a conventional wing. The joined wing can lead to increased aerodynamic performance and reduction of the structural weight. In this research, dynamic response optimization of a joined wing is carried out by using equivalent static loads. Equivalent static loads are made to generate the same displacement field as that from dynamic loads at each time step of dynamic analysis. The gust loads are considered as critical loading conditions and they dynamically act on the structure of the aircraft. It is difficult to identify the exact gust-load profile; therefore, the dynamic loads are assumed to be a one-cosine function. Static response optimization is performed for the two cases: one uses the same design variable definition as dynamic response optimization, and the other uses the thicknesses of all elements as design variables; the results are then compared.

This paper proposes a methodology based on the gust response factor (GRF) for evaluating the along-wind response of wind turbine towers. The approach presented differs from conventional GRF methods as the GRF contains contributions from two resonant modes, mainly due to blade/tower interaction effects. The wind turbine tower model considered contains two interconnected flexible subsystems, representing the tower and the rotor system. Each component is initially modeled as a separate degree-of-freedom (DOF), and these are coupled together to form a two DOF reduced order model of the coupled tower/rotor system. Thus, the resonant component of the response contains energy output from the two modes of the coupled system. The GRF is obtained for both tower tip displacement and base bending moment through numerical integration, with a closed form expression included for the former. A series of numerical examples are included to investigate the magnitude of GRFs obtained for the two DOF assembly which allows for blade/tower interaction, and these are compared with GRF values obtained from an equivalent singe DOF model which ignores blade/tower interaction by lumping the mass of the blades in with that of the nacelle. DOI: 10.1061/(ASCE)0733-9445(2007)133:1(139) CE Database subject headings: Vibration; Wind forces; Structural response; Methodology; Wind gusts.

In structural design of steel structures in fire, the failure criterion needs to be checked for all members under individual design actions or a combination of them. For space frames, combined design actions usually include forces due to bending, axial, shear, and torsion. An increase in temperature will result in changes to these forces as well as the diminution of the failure criterion due to reduced member capacities as a result of these combined design actions. This paper presents an elastic method for the prediction of limiting temperature of members in space steel frames. Since the critical temperature of the structure corresponds to the ultimate failure of the member with the lowest limiting temperature, this elastic method is equivalent to finding the location of the first plastic hinge in a general plastic analysis. By considering the degradation of the mechanical properties of steel in fire, a formulation based on the failure criterion of combined design actions including torsion is presented for limiting temperature calculation. The fundamentals of the solution strategy are also explained. CE Database subject headings: Torsion; Temperature; Steel structures; Fire hazards; Fire resistance.

In the past two decades, the development of algorithms for structural engineering applications has received a boost due to the advent of parallel computers. Considerable research is being done in order to rewrite algorithms originally designed to run on sequential machines as well as to develop new methods that take advantage of the parallelism offered by the multiprocessing computers. This work is concerned with some of the parallel algorithms that have been developed in this field. More specifically, it is a survey of parallel algorithms that are of interest to structural engineering. Such algorithms include parallel solvers (direct and iterative) for linear systems of algebraic equations, techniques for the parallelization of the finite element method, and concurrent time-stepping algorithms for the solution of the equations of evolution arising in structural dynamic problems. One should keep in mind that parallel processing is a rapidly evolving field and it is the focus of intensive research worldwide. Extensive research on new methodologies for the development of concurrent algorithm is underway in universities and industry. CE Database subject headings: Parallel processing; Finite element method; Structural engineering; Algorithms.

Civil engineering structures are part of our cultural heritage. The story of who we are can be told, in part, by what we have built. There have been pivotal moments in civil engineering design history wherein a master engineer creates a pioneering structure. One major example is Anton Tedesko's 1936 Hershey Ice Arena, the first large-scale thin shell concrete roof in the United States. Tedesko left all his papers, including the original design and analysis calculations of the Hershey shell, to the Princeton Maillart Archives. These documents, as well as other archival materials and photographs, provide insight into the design history of Hershey, and the transfer of thin shell technology to America. In this paper, we retrace the design and analysis calculations performed by Tedesko, and compare them to modern computer models. We show that the hand calculations are sufficiently accurate, and in fact are necessary for initial form finding. We close by pointing out the enormous impact that this design had in thin shell concrete construction, and argue for the preservation of this remarkable structure. CE Database keywords: Thin shell structures; Technology transfer; Conceptual design; Historic sites; Roofs; Structural engineering.

A new approach is presented for the calculation of moments on top slab in single-cell box girders. Using the classic thin plate theory, trigonometric series solutions for bending moments of the top slab under local distributed load and concentrated load with elastically clamped boundary conditions are derived. A numerical example is given to demonstrate the application of the proposed method. DOI: 10.1061/(ASCE)0733-9445(2003)129:1(130) CE Database keywords: Box girders; Finite strip method; Bending moments; Plates.

A method of global nondestructive evaluation for identifying local damage and decay in timber beams was developed in previous analytical studies and verified experimentally using simply supported beams in the laboratory. The method employs experimental modal analysis and an algorithm that monitors changes in modal strain energy between the mode shapes of a damaged structure with respect to the undamaged structure. A simple three-girder bridge was built and tested in a laboratory to investigate the capability and limitations of the method for detecting damage in a multimember timber structure. The laboratory tests showed that the method can correctly detect and locate a simulated pocket of decay inflicted at the end of a girder as well as detect a notch removed from the midspan of a girder. The tests showed that the method can correctly detect damage simultaneously at two locations within the bridge, but also that large magnitudes of damage at one location can mask smaller magnitudes of damage at another location. When a calibrated baseline model is used to represent the undamaged state of the bridge, the results show that the method of nondestructive evaluation is able to detect each case of inflicted damage, but with some increase in localization error. DOI: 10.1061/(ASCE)0733-9445(2003)129:1(116) CE Database keywords: Bridges, wooden; Vibration tests; Nondestructive tests; Damage.

The procedures described in this paper for determining a limit load is based on Mura extended variational formulation. Used in conjunction with linear elastic finite element analyses, the approach provides a robust method to estimate limit loads of mechanical components and structures. The secant modulus of the various elements in a finite element discretization scheme is prescribed in order to simulate the distributed effect of the plastic flow parameter, [[mu].sup.0]. The upper and lower-bound multipliers [m.sup.0] and m' obtained using this formulation converge to near exact values. By using the notion of 'leap-frogging' to limit state, an improved lower-bound multiplier, [m.sub.[alpha]], can be obtained. The condition for which [m.sub.[alpha]] is a reasonable lower bound is discussed in this paper. The method is applied to component configurations such as cylinder, torispherical head, indeterminate beam, and a cracked specimen. [DOI: 10.1115/1.1499960]

Wavelet transform (WT) is a mathematical tool that can decompose a temporal signal into a summation of time-domain basis functions of various frequency resolutions. This simultaneous time-frequency decomposition gives the WT a special advantage over the traditional Fourier transform in analyzing nonstationary signals. One drawback of the WT is that its resolution is rather poor in the high-frequency region. Since structural damage is typically a local phenomenon captured most likely by high frequency modes, this potential drawback can affect the application of the wavelet-based damage assessment techniques. The wavelet packet transform (WPT) adopts redundant basis functions and hence can provide an arbitrary time-frequency resolution. In this study, a WPT-based method is proposed for the damage assessment of structures. Dynamic signals measured from a structure are first decomposed into wavelet packet components. Component energies are then calculated and used as inputs into neural network models for damage assessment. Numerical simulations are performed on a three-span continuous bridge under impact excitation. The results show that the WPT-based component energies are good candidate indices that are sensitive to structural damage. These component energies can be used for various levels of damage assessment including identifying damage occurrence, location, and severity. DOI: 10.1061/(ASCE)0733-9445(2002)128:10(1354) CE Database keywords: Damage assessment; Neural networks; Decomposition.

A two-story, single-family woodframe house, designed according to current engineered code seismic design requirements, was tested on a uniaxial shake table. The main objectives of this experimental study were to determine the dynamic characteristics and the seismic performance of the test structure under various base input intensities representative of both ordinary and near-field ground motions in southern California. The structure was tested with and without interior (gypsum wall board) and exterior (stucco) wall finish materials. The test results revealed good performance of the engineered woodframe structure. Wall finish materials are usually considered in design as nonstructural elements. However, the structure incorporating wall finish materials exhibited a substantial increase in its lateral stiffness and a dramatic reduction in its seismic displacement response. Furthermore, the seismic acceleration response of the structure was only moderately increased by the presence of wall finish materials. These shake table test results provide the motivation for further studies on the evaluation of the long-term effectiveness of wall finish materials as potential structural components of lateral load-resisting systems of woodframe structures. DOI: 10.1061/(ASCE)0733-9445(2002)128:10(1.337) CE Database keywords: Seismic tests; Gypsum; Wooden structures; Buildings, multistory; Construction materials.

A probability-based reliability assessment methodology for single flexible piles and pile groups under stochastic lateral loads is developed. The methodology was based on state-of-the-art techniques for the analysis of single piles and pile groups as well as reliability assessment methods. Critical strength and serviceability modes of failure for flexible piles in sandy soil under lateral loads were defined. The reliability of a pile-group system was assessed by accounting for system redundancy with the occurrence of partial failures of the system components. Reliability indices and failure probabilities were used as relative measures for the performance of piles. A case study was presented to illustrate the proposed methodology. DOI: 10.1061/(ASCE)0733-9445(2002)128:10(1346) CE Database keywords: Pile foundation; Pile groups; Reliability; Limit states; Limit analysis; Failure modes.

A simplified method for the analysis and design of membrane elements subjected to in-plane shearing and normal stresses is presented. The method proposed is capable of calculating the ultimate strength and the mode of failure of membrane elements. The strength curves in the method are also cast in a tabular format to further simplify the method. The results of the proposed method compare well with experimental results of 14 membrane elements reported in the literature and with the results of the modified compression field theory. Comparisons with the general method and the American Concrete Institute code are also presented. Use of the method is illustrated by two examples, one for design and the other for capacity calculation. DOI: 10.1061/(ASCE)0733-9445(2002)128:8(1064) CE Database keywords: Beams; Building codes; Failure; Prestressing; Concrete, reinforced; Compression.

This study examines the fragility curves of a bridge by two different analytical approaches; one utilizes the time-history analysis and the other uses the capacity spectrum method. The latter approach is one of the simplified nonlinear static procedures recently developed for buildings. In this respect, a sample of 10 nominally identical but statistically different bridges and 80 ground-motion time histories are considered to account for the uncertainties related to the structural capacity and ground motion, respectively. The comparison of fragility curves by the nonlinear static procedure with those by time-history analysis indicates that the agreement is excellent for the state of at least minor damage, but not as good for the state of major damage where nonlinear effects clearly play a crucial role. Overall, however, the agreement is adequate even in the state of major damage considering the large number of typical assumptions under which the analyses of fragility characteristics are performed.

Issues discussed concern the design and construction of a 1.5 mil square foot conference facility in Salt Lake City, Utah. Topics addressed include designing theater space, acoustical engineering, earthquake resistance, foundation engineering, and the aesthetic design of space used for religious purposes.

Issues discussed concern the design and construction of roller coasters, focusing on coaster engineers' use of height, speed, and curvature to design innovative amusement rides. Topics addressed include the race to design the tallest and fastest coasters, technological advances in design software, the design history of thrill rides, and engineering and safety concerns.

A continuum-based design sensitivity analysis (DSA) and optimization procedure for hyperelastic structures using reproducing kernel particle method has been developed. Shape DSA and optimization using the meshless methods, which have been tested in an engine mount example, have the potential to eliminate mesh distortion problems that are associated with conventional finite element methodologies. A CAD-based optimization and three-dimensional extension applications are under development.

The proposed octree-based agglomeration multigrid method, which uses the naturally well-ordered intergrid relationship between a tetrahedral mesh and its dual mesh for steady Euler equations, is capable of generating high-quality coarse cells with minimal effort. The implicit agglomeration technique is also capable of converging at a speed that is three to five times faster than the single grid computation in terms of CPU time.

Knowledge-based systems (KBS) are being widely used for risk analysis of structures. The KBS make use of various types of observations made during postdisaster damage surveys and also the expertise of various domain engineers. Consolidation of all the observations to form the knowledge base (KB) is a difficult task. Each of the observations consists of various parameters. Establishing parameter interdependencies is important for creating a KB. The use of a graph theoretic technique is proposed in this paper to determine the interdependencies among various parameters useful in the creation of a KB. This approach helps in identifying necessary and sufficient data required to develop an effective KBS for risk analysis of structures. Using the proposed approach, an example problem of establishing parameter interdependencies for risk analysis of roof structure against damage due to cyclonic winds is solved. This example also demonstrates how sufficiency and consistency of the observations can be checked.

The objectives of control of structures in earthquakes are to prevent injury to occupants and damage to contents and to protect the integrity of the structure. Both objectives can be achieved through base isolation and feedback control, whereby the structure is stabilized relative to the inertial space. Nonlinear on-off control with a dead zone in conjunction with direct feedback has the advantages of economy and simplicity of implementation. Indeed, the actuators operate only when the velocity exceeds certain threshold values and only in response to sensor signals at the same location. An example using two actuators, one on the base and the other at the top of the structure, shows very good performance of the control design.

In structural optimization problems, conventional approximations are often used. For this type of approximations, move limits are usually defined as allowable changes in design variables during optimization of the approximate problem. This paper shows that these common move limit constraints, which are suitable for first-order series approximations, might not be effective for various improved approximations. The improved approximations, developed in recent years and used extensively in various applications, require more effective constraints. Such alternative move limits, proposed in this paper, include angle move limits, which are explicit nonlinear constraints on the angle between the initial and the modified design lines and error move limits, which are implicit nonlinear constraints on the errors in the equilibrium equations. The effectiveness of the aforementioned types of move limit constraints is demonstrated by various numerical examples. It is shown that, for improved approximations, the proposed move limits provide more reasonable results than the common approach.

Dynamic deformation monitoring of structures such as long bridges, towers, and tall buildings, for the purpose of determining structural vibrations, is now possible using global-positioning-system (GPS) technology. Current non-GPS techniques for measuring structural vibrations (these include vibration measurement with accelerometers, vibration measurement with a laser interferometer, and vibration measurement with an electronic distance measurement instrument) are first briefly outlined, with advantages and disadvantages noted. The specific application, measurement of structural vibrations in the Calgary Tower, Calgary, Alberta, Canada, using GPS receivers in differential mode, is then described. The results show that the Calgary Tower, under wind loading, vibrates with a frequency of about 0.3 Hz in both north-south and east-west directions. The 0.3 Hz vibration frequency measured on the Calgary Tower is within the range of 0.1 Hz to 10 Hz expected for structures of this type. When the capability of GPS to monitor structural vibrations is verified by further tests, it could be adopted as a standard technique.

A theoretical method uses internal translational actuators to regulate static shapes of flexible structures. Finite element analysis of an adaptive rib model demonstrates the efficiency of the method in providing a close fit to any desired shape. Open- and close-loop studies of unloaded and loaded structures, respectively, help produce commanded shapes. The method, on application to the problem of keeping maximum airfoil shapes, reduces wind drag.

The mining techniques adapted by engineers for IBM's expansion of its semiconductor manufacturing operations on an underutilized basement space are discussed. This creative approach was used to satisfy building codes requirements on horizontal emergency access and egress without disturbing the vibration-sensitive operations aboveground. A series of contiguous soil dowels to presupport the ground, jet-grouted columns for underpining the existing structure and staged mined excavation with installation of steel rib assemblieswere used as the project was finished in less than a year.

Construction of the National Law Enforcement Officers Memorial in Washington, DC, was a feat in civil engineering. Built in honor of Americans who died in line of duty since 1794, the memorial features the names of 12,561 officers engraved on two 304 ft long and 3.5 ft high marble walls. Architect Davis Buckley designed the memorial which required over 12,000 pieces of granite and marble. The design and construction of the memorial's foundations posed the most challenging undertaking as the site's soil mechanics and underground subway structures presented difficulties.