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The article comments on a study which describes approaches for generating initial ground structures in fields of discrete structural topology optimization including macroelement and macropatch methods. Topics include information on finite-element method (FEM); information on numerical topology optimization which depends on problem specification, and evolutionary structural optimization; and determination of arch bridge as an application of macroelement approach to structural engineering design.

Timber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years , ambient vibration tests have become very popular due to the many advantages they have over traditional forced vibration tests when dealing with civil engineering structures. Furthermore, sensitivity analyses and black-box" optimization algorithms can support the development of refined finite-element models that accurately predict the structures' responses based on the experimental modal parameters. However, applications of these methods and techniques to timber structures are scarce compared with traditional materials. This paper presents and discusses the findings of an experimental testing campaign on a lightweight timber floor. At first, each component of the assembly was tested separately under different boundary conditions. Then, the authors evaluated the behavior of the whole floor assembly. In a second step, the authors carried out a covariance-based sensitivity analysis of finite element (FE) models representative of the tested structures by varying the different members' mechanical properties. The results of the sensitivity analysis highlighted the most influential parameters and supported the comparison among diverse FE models. As expected, the longitudinal modulus of elasticity is the most critical parameter, although the results are very dependent on the boundary conditions. Then automatic modal updating algorithms tuned the numerical model to test results. As a concluding remark, the experimental and numerical results were compared with the outcomes of a simplified analytical approach for the floor's first natural frequency estimate based on current European standards. [ABSTRACT FROM AUTHOR]

The paper addresses the lateral-torsional buckling for a special steel truss structure which is adopted to reinforce a particular class of composite steel-concrete beams. The investigated instability phenomenon deals with a transitory ultimate limit state that may occur when the truss structure is being assembled and is bearing the precast floor system, before the concrete has hardened. During this transitory stage the truss beam works as a steel structure and may exhibit local or global instability phenomena. It provides the reinforcement of the final composite steel-concrete beam once the concrete has hardened. The main result of this paper is an analytical approach for the estimation of the elastic critical moment which is required to calculate the final design lateral-torsional buckling resistance moment in accordance with the technical code in force (the European standard for steel structures is considered in this paper). The simplified analysis this paper presents leads to a closed-form solution for the elastic critical moment, thus providing a simple and rapid tool for the calculation of the lateral-torsional buckling resistance moment. A comparison to a finite element analysis has been performed to demonstrate the correctness of the proposed analytical formulation. [ABSTRACT FROM AUTHOR]

In the companion paper, a total Lagrangian finite element (FE) model was formulated for the second order nonlinear inelastic analysis of steel–concrete composite members. This paper describes the implementation of the incremental–iterative procedure for the FE model. It has been found that using the standard tangent modulus matrix in an incremental–iterative solution procedure may cause error accumulations. These errors in turn lead to an unsafe drift from the yield surfaces, and the yield criteria may be violated. Consequently, the quadratic asymptotic rate of convergence of the Newton–Raphson method is lost. To solve this problem, a consistent tangent modulus matrix is needed in the incremental–iteration solution process, and this is described. This paper presents the implementation of the FE model and shows how to use the constitutive models in the companion paper in association with the uniaxial stress–strain relations including that for confined concrete. Some of the applications of the FE model to various problems are also shown in this paper. The comparisons between numerical and experimental results demonstrate that the FE model provides excellent numerical performance for the nonlinear inelastic analysis of steel–concrete composite members. [ABSTRACT FROM AUTHOR]

The aims of this study are to generate experimental data and develop numerical models for aluminum alloy continuous beams, and to utilize the results to underpin the development of revised design methods for indeterminate structures. This paper presents an experimental program and finite-element (FE) analyses for two-span continuous beams (i.e., five-point bending) of square and rectangular hollow sections (SHSs and RHSs). The experimental program comprised 27 five-point bending tests with three different positioning of loads. The testing procedures and key results are reported. The test specimens were manufactured by extrusion, with 18 of grade 6061-T6 and 9 of grade 6063- T5 heat-treated aluminum alloys. The test specimens were nonslender sections, and mostly of Class 1 proportions. Generally, the specimens failed by the formation of a collapse mechanism comprising three plastic hinges. The distances between the supports and the loading points were varied in order to form the first plastic hinge in different locations, to achieve different load levels between the first hinge and collapse, and to change the rotation demands on the first hinge that formed. The FE models were developed and failure was defined as either when a plastic collapse mechanism was formed or the material fracture strain was reached on the tension flange, whichever occurred first. The numerical models were first validated against the experimentally obtained load-deflection responses, as well as the failure modes. The experimental and FE ultimate loads were both found to be beyond the theoretical loads corresponding to the formation of the first hinge as well as the calculated plastic collapse loads. A key characteristic of aluminum alloy, strain hardening, is shown to be particularly significant in both the experimental program and the numerical investigation. The validated FE models are used to generate numerical results through parametric studies in the companion paper. The development of design rules for indeterminate aluminum alloy structural systems is then described. [ABSTRACT FROM AUTHOR]

This paper presents an extension to an algorithm called HYST to develop the hysteresis characteristics of a nail connection. The paper also discusses the implementation of the algorithm in a finite-element model of a wood shear wall, called WALL2D, to study the hysteretic wall response. The HYST algorithm is a protocol-independent and mechanics-based procedure that considers the nail shank as steel beam elements and the wood embedment medium as compression-only spring elements smeared along the nail shank. By accounting for the stiffness degradation of the wood embedment medium under cyclic loading, HYST can fully address strength/stiffness degradation and the pinching effect in the hysteresis of typical nail connections. HYST was verified by the load-slip hystereses from nail connections tested with two different loading protocols. The WALL2D application model consists of linear elastic beam elements for framing members, orthotropic plate elements for sheathing panels, linear springs for framing connections, and oriented nonlinear springs for panel-frame nail connections. The hysteretic behavior of the nonlinear springs is represented by the HYST algorithm. The wall model was verified by reversed cyclic test results of two types of shear walls. [ABSTRACT FROM AUTHOR]

This paper introduces an innovative structural system consisting of four-sided hyperbolic-paraboloid (hypar) roof umbrellas as hard countermeasures against nearshore hazards. The umbrellas line the coast and remain upright during normal operation, providing shade and shelter along the waterfront while not limiting access to the shore. A hinge at the hypar-column interface permits tilting to form a physical barrier against surge-induced coastal inundation. Analytical equations based on idealized boundary conditions are formulated in the hydrostatic regime. The equations provide insight into optimal geometric parameters and are used to validate a decoupled numerical scheme constituting smoothed particle hydrodynamics (SPH) and the finite element method (FEM). All numerical reactions concur with the analytical solutions for water inundation matching the total deployed height. A proof-of-concept study was employed to successfully illustrate the applicability of deployable hypar umbrellas as coastal armor from a structural engineering perspective. This work ultimately demonstrates the feasibility of decoupled SPH-FEM methods in modeling fluid-structure interaction involving hypar forms, while establishing a foundation for their analysis and design for coastal hazard adaptation. [ABSTRACT FROM AUTHOR]

The seismic performance of segmental precast unbonded posttensioned bridge columns with hollow cross sections is investigated in this paper. Bonded longitudinal mild steel reinforcement crossing the column segment joints is provided to enhance the hysteretic energy dissipation of the columns, also referred to as energy dissipation (ED) bars in this paper. The ED bars are detailed to provide energy dissipation without premature fracture at the critical column segment joint. For design purposes, a simplified analytical model to predict the lateral force-displacement response (pushover curve) is proposed. Moreover, a detailed three-dimensional (3D) finite-element (FE) model is developed and utilized to predict the behavior of segmental columns under cyclic loading. Parametric studies using the simplified analytical model and the 3D FE model are conducted to investigate the seismic behavior of this type of column construction. At the end of this paper, the comparisons of the results of the response-history analyses between the segmental columns with flag-shape hysteretic behavior and their comparable conventional counterparts are given. [ABSTRACT FROM AUTHOR]

Different methods are proposed in literature using experimental modal information to detect possible damage. In this paper a finite-element (FE) model updating technique is applied. The unknown properties of a FE model are adapted, such that the differences between experimental modal data (modal curvature in combination with eigenfrequencies and mode shapes) and the corresponding analytical predictions are minimized. An iterative sensitivity based algorithm is used for solving this optimization problem. The method is applied to the damage assessment of a gradually damaged prestressed concrete beam. It is assumed, that damage can be characterized by reducing the bending stiffness. The main focus of this paper is to analyze the influence of using modal curvatures. In contrast to eigenfrequencies and mode shapes, modal curvatures are very sensitive to local changes of the bending stiffness nearby the sensor location, but insensitive to local changes far from the measurement location. [ABSTRACT FROM AUTHOR]

This paper presents the test results of three steel-reinforced concrete (SRC) columns to SRC beam joints under combined loading and fire. Simulated fires, including heating and cooling phases with different heating times, were applied to the lower part of the three composite joint specimens. Failure modes, concrete cracking, concrete spalling, and deformation development were observed or measured. The test results indicate that heating time affects the postfire residual bearing capacity significantly. A finite-element analysis (FEA) model was developed to simulate the response of SRC beam-to-column joints in whole loading sequences, including initial loading, heating, cooling, and postfire loading. Some key influencing factors, such as the creep of steel at high temperatures, slippage between the steel and concrete, and residual stresses in the H-shaped steel, were considered in the model. On the basis of the verified FEA model, the development of the rotation angle between the beam and column, which cannot be measured by testing, was calculated and discussed. [ABSTRACT FROM AUTHOR]

This second-part article presents applications of advanced nonlinear finite-element analysis for the design of large reinforcedconcrete structures. Because shear and the size effect are fundamental aspects of these structures, the first section of this paper is devoted to the prediction of shear failure for very large members more than 3 m deep. It is shown that the tendency of shear strength is much less sensitive to size effects for very large members than the predictions of some design code equations. Applications to the draft tube complex structure are then presented in a second part. A comparison of cracking patterns with an existing powerhouse is performed at the service level. It is shown that thermal effects have an important effect on the final cracking pattern. The draft tube model is then analyzed up to failure. Following a new design methodology proposed by the authors in a previous paper, and using the model error properties computed in part 1, the global resistance factor is computed for the ultimate level. The effects of temperature, nominal shear reinforcement, and lateral confinement are discussed. [ABSTRACT FROM AUTHOR]

This paper presents the development of a lumped-parameter model of multistory framed shear buildings supporting rigid blocks with the possibility to slide. After favorably comparing with results from finite-element analyses and shake table tests, the model was used to assess design provisions in regard to the treatment of live load as seismic weight. It was found that using the minimum live load percentage in current design standards may lead to unconservative drift estimates for buildings supporting heavy and nearly permanent live load objects and structures that are (1) designed for higher R values, (2) located in regions of low-to-moderate seismic risk, or (3) base isolated. Results from a parametric study led to a design expression that allows determining the portion of the expected live load that is effective as seismic weight on the structure as a function of the object/floor interface's friction coefficient and the maximum floor acceleration of the building alone. The adequacy of the design expression was confirmed through three-dimensional finite-element analyses of two- and four-story buildings supporting live load objects that could slide. [ABSTRACT FROM AUTHOR]

Current seismic design of bridges is based on 'one-time' performance of the bridges during the design seismic event. However, there might be a considerable probability of observing more than one damaging earthquakes in a bridge's service life. Bridge components are known to accumulate seismic damage and deterioration in their structural properties. In such a scenario, design criteria that account for the cumulative seismic damage of bridges over time and performance objectives that span more than one seismic event are needed. This paper computes the probability of occurrence of more than one damaging earthquake during a bridge's service life. Furthermore, it investigates the importance of accounting for cumulative seismic damage in seismic design. This paper develops a probabilistic model to compute the degraded deformation capacity of flexural reinforced concrete (RC) bridge columns as a function of cumulative low-cycle fatigue damage incurred in the past earthquakes. The model is developed for flexural RC columns because low-cycle fatigue is most significant for such columns. The proposed model accounts for the degradation in the ultimate curvature capacity and deformation capacity of RC columns associated to low-cycle fatigue. The proposed model is calibrated by using data from cyclic-load analyses of RC columns performed by using the finite element method (FEM). The FEM model accounts for the cracking and pinching of RC sections to properly simulate the degradation process. Finally, the proposed model is used to assess the fragilities of RC bridge columns conditioning on the values of low-cycle fatigue damage and deformation demand. It is found that in seismically active regions there is a significant probability of observing more than one damaging earthquake in a bridge's service life. Therefore, accounting for the cumulative seismic damage in the seismic design is important. It is also found that the cumulative seismic damage can significantly affect the reliability of bridge columns. The developed models are useful for a seismic design that properly accounts for long-term safety and reliability of bridges. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study on the compressive behavior of timber columns with longitudinal cracks. Material property tests and full-scale compression tests were conducted to investigate the failure modes and the recovery in the load-carrying capacity of cracked timber columns with the use of fiber-reinforced polymer (FRP) sheet wrapping. Different combinations of column geometries, crack dimensions, and types and spacing of FRP sheets were considered. A finite-element method (FEM)-based model was developed and verified on the basis of the test results. A parametric study was also conducted by using the verified model to further quantify the influences of crack dimensions and types and spacing of the FRP sheets. It was found that wrapping FRP sheets around cracked timber columns can recover their load-carrying capacity by up to 20%. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element (FE) modeling approach to predict the deformation, softening, and failure of compression-loaded aluminum structures exposed to fire. A fully coupled thermal-mechanical FE model is outlined. The FE model can analyze the thermal profile and deformation as well as the initial and final plastic collapse of aluminum structures in fire. It calculates the temperature profile of an aluminum structure exposed to unsteady-state heating conditions representative of fire. Using the temperature profile, the elastic and plastic deformations together with the loss in the compression load capacity of an aluminum structure caused by elastic softening, time-independent plastic (yield) softening, and time-dependent plastic (creep) softening effects are analyzed by using a mechanics-based FE solution. The modeling approach is validated by structural tests on an aluminum alloy (5083 Al) plate supporting an applied compression load while locally heated at different radiant heat flux (temperature) levels. The modeling approach can estimate the deformations, initiation of plastic collapse, and final failure of the aluminum test article for heat flux levels representative of different fire types. The FE model described in this paper can be used as the basis for performing complex deformation and failure analysis of compression-loaded aluminum (and other metallic) structures in fire. [ABSTRACT FROM AUTHOR]

Recent terrorist events have underscored the importance of designing glass curtain walls as engineered systems. For most building owners, however, it is usually an unjustifiable expense to have a curtain wall designed to provide a high level of blast resistance. This paper investigates the serviceability of an economical, nearly conventional, glass curtain wall system that provides a low level of blast resistance in appropriate applications. A conventional, split screw spline mullion system is utilized with laminated glass lites properly attached to the mullions with structural silicone sealant. The response of this system to service load conditions is first explored through static and dynamic experimental testing. A simple finite-element model of the system is then calibrated to low-amplitude static test results. Finally, the calibrated model is used to perform modal and transient analyses that are compared to experimental free vibration responses. The model was found to provide results that agree well with experimental responses, indicating that the primary properties have been adequately defined for reliable serviceability investigations. [ABSTRACT FROM AUTHOR]

Lightweight, portable air-pressurized beams and arches serve as primary load-carrying members for a number of civilian and military structures. These members are made from synthetic fibers that are woven or braided into a circular cross section. The pressurized air provides structural capacity by pretensioning the fabric and through its behavior as a confined gas. In this paper, a beam finite element is developed for the analysis of pressurized fabric beams based on virtual work principles. Work done by internal pressure due to deformation-induced volume changes is included in the formulation. A nonlinear moment-curvature relationship accounts for fabric wrinkling, and shear deformations are incorporated. A mixed-interpolation Timoshenko beam element is used to discretize the virtual work expression. A numerical method for determining the moment-curvature relationship of an inflated beam made from a fabric obeying a nonlinear stress–strain relationship is developed. Results of experiments on pressurized fabric beams loaded in three- and four-point bending are presented, and the finite-element model is shown to accurately predict experimentally observed load-deflection response for a range of pressures. Simulations demonstrate that in addition to prestressing the fabric, the pressurized air significantly increases beam capacity as the beam volume decreases due to deformation. [ABSTRACT FROM AUTHOR]

Unstiffened, unbraced steel beams used in bridge falsework are subjected to patch loads from timber or steel posts. This paper investigates the critical web limit states in these types of beams experimentally and through finite-element analysis. Existing equations were appropriate for calculating the web yielding and crippling capacity, as observed in experiments, except that a 1:1 stress gradient through the flange and fillet of the web is found to be more appropriate and conservative for web yielding than the 2. 5:1 gradient assumed in the current AISC specifications. Lateral deformation of a beam flange, due to buckling of the web, was also observed experimentally. The capacity of the web for resisting lateral buckling can be calculated assuming that the web of the beam acts like a column with an appropriate effective area and length factor. The effect of accidental eccentricity between the flange and post is not significant if limited to three times the web thickness. Blocking is approximately 50% effective in increasing the web yielding and crippling capacity. Bracing or stiffeners should be used to prevent lateral buckling of a web where necessary. [ABSTRACT FROM AUTHOR]

This paper presents a study on the strength and behavior of cold-formed steel Z-sections with simple and complex stiffeners subjected to major axis bending. The study involved both experimental and numerical investigations, in which a series of specimens were examined. All specimens were failed by the combined mode of shear and moment. The results from the investigations were analyzed and compared with the combined moment and shear strengths predicted by international design rules. The suitability of the design rules in predicting the combined capacity of Z-section with complex stiffeners was assessed through a reliability analysis. [ABSTRACT FROM AUTHOR]

This paper addresses the usage of a simplified homogenization technique for the analysis of masonry subjected to out-of-plane loading. The anisotropic failure surface, based on the definition of a polynomial representation of the stress tensor components in a finite number of subdomains, is combined with finite element triangular elements employed for the upper and lower bound limit analyses. Several comparisons between the proposed model and experimental data available in the literature are presented, for wallettes subjected to bending at different orientations and for different panels loaded out of plane. The limit analysis results allow us to identify the distribution of internal forces at critical sections and to obtain the collapse modes, as well as the failure loads. Excellent results are found in all cases, indicating that the proposed simple tool is adequate for the safety assessment of out-of-plane loaded masonry panels. The combined usage of upper and lower bound approaches, and their respective simplifications, allow us to define a narrow interval for the real collapse load. [ABSTRACT FROM AUTHOR]

This paper presents a parametric study aimed at uncovering general design principles that govern the structural performance of honeycomb-type rigidified inflatable structures (RIS) as load-bearing wall systems for use in residential housing. This study involves the use of finite element modeling and optimization. A series of honeycomb-type RIS wall systems, each comprising different honeycomb cell sizes, are examined. The problem at hand is stated in the form of minimizing material volume subject to: permissible stress, maximum allowable deflection, and membrane thickness. The optimization results help identify optimal design configurations for given sets of loading conditions and material properties. The effects of various design parameters, such as cell size, material properties, and membrane thicknesses, are discussed. The performance of honeycomb-type RIS wall systems is compared with that of rectilinear-type RIS wall systems, which were studied previously. The work presented makes a significant step in establishing the feasibility of RIS for housing applications. [ABSTRACT FROM AUTHOR]

This paper presents a nondestructive global damage detection and assessment methodology based on the changes in frequencies and mode shapes of vibration of a structural system. The method is applied at an element level using a finite-element model. According to continuum damage mechanics, damage is represented by a reduction factor of the element bending stiffness. A nonclassical optimization approach involving the use of genetic algorithms (GAs) is proposed to localize damaged areas of the structure. The method has been verified by a number of damage scenarios for simulated beams and by using directly experimental data from the vibration tests of a beam. It is shown that the proposed GA yields a suitable damage location and severity detection while introducing numerous advantages compared to classical methods. The influence of noise in the modal data has also been considered. [ABSTRACT FROM AUTHOR]

For assessing the integrity of damaged hollow section joints, the plastic collapse loads of the joints containing cracks is an important parameter. Very little published information is available in the literature concerning the residual strength of square hollow section (SHS) joints containing defects or cracks. In this paper, an accurate numerical modeling of SHS T joints with cracks is proposed, whereby the entire finite element mesh is generated automatically. To validate this numerical model, several T joint models are studied and compared with the experimental data. A good agreement is obtained on the ultimate loads. Based on this model, the plastic collapse loads under different geometrical ratios are studied, and they are compared with the results calculated from the yield line theory. It is found that the yield line theory can give a reasonable prediction of the plastic collapse loads when the brace width to chord width ratio β is less than 0.8. The failure assessment diagrams (FAD), constructed using the J-integral predictions, have confirmed that the standard BS7910 Level 2A FAD is appropriate for determining limits of safe loading of cracked SHS T joints, provided the plastic collapse load is calculated using the yield line formulae neglecting the influence of the welds. [ABSTRACT FROM AUTHOR]

Response sensitivities with respect to the parameters of a finite element model are useful in many applications. The direct differentiation method (DDM) is commonly utilized to obtain such results. In recent years, the DDM has been extended to include sensitivities of inelastic response with respect to material, load, and geometry parameters. While the DDM is more efficient and accurate than finite difference methods, considerable cost is still associated with the computation of response sensitivities for inelastic problems. In this paper it is demonstrated that the computational cost can be significantly reduced for certain types of problems that are common in structural engineering. A novel event-based computation strategy is suggested, whereby sensitivities of the final response are obtained more efficiently than in the ordinary DDM. It is also demonstrated that sensitivity contributions from all inelastic material points are not needed for statically determinate structures. Numerical examples involving a truss structure, a steel frame structure, and a reinforced concrete frame structure are presented to demonstrate the efficiency of the presented developments. [ABSTRACT FROM AUTHOR]

This paper presents a numerical formulation for the nonlinear analysis of slender steel-concrete composite columns of generic cross-sectional shape, subjected to axial force and biaxial bending. The cross section is defined in terms of a number of closed polygonal loops of a specific material, each one with its own stress-strain relation, with reinforcement bars embedded in the polygons. The material and geometrically nonlinear equlibrium problem is solved by the finite element method, with displacement-based stress resultant beam-column elements. The proposed scheme turns possible, with a unified treatment, to perform analyses of concrete-filled steel tubes, fully or partially encased steel profiles, or less usual cross sections present on composite construction. The robustness and accuracy of the formulation is verified against numerical and experimental results available in the literature. [ABSTRACT FROM AUTHOR]

Assessing the structural response and vulnerability of bridge piers to collisions by barges typically involves either the use of static pier analysis codes and design-specification-stipulated equivalent static loading conditions, or a lengthy model development process followed by use of general-purpose finite-element codes. In this paper, an alternative approach is proposed that leverages the capabilities of existing nonlinear dynamic pier analysis programs by adding dynamic barge behavior in a computationally efficient and modular manner. By coupling nonlinear barge and pier responses together through a shared collision impact force and employing numerical procedures for accelerating convergence of the coupled system, dynamic barge collision analyses may be conducted for bridge piers efficiently and rapidly. The influence of impact parameters such as barge type and mass, impact speed and angle, and pier configuration can then be efficiently evaluated using dynamic collision analyses. For demonstration purposes, the method is implemented in an existing pier analysis program, validated, and used to conduct selected case studies. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to provide an efficient and accurate finite element model to understand the behavior of cold-formed steel plain angle columns. The effects of initial local and overall geometric imperfections have been taken into consideration in the analysis. The material nonlinearities of flat and corner portions of the angle sections were incorporated in the model. Failure loads and buckling modes as well as load-shortening curves of plain angle columns were investigated in this study. Furthermore, the residual stresses of a column test specimen were measured and plotted. The effect of residual stresses on the buckling behavior was studied using the finite element model. The nonlinear finite element model was verified against experimental results. The finite element analysis was performed on plain angles compressed between fixed ends over different column lengths, and column curves were obtained. An extensive parametric study was carried out using the finite element model to study the effects of cross-section geometries on the strength and behavior of angle columns. The column strengths predicted from the finite element model were compared with the design strengths calculated using the American Specification and Australian/New Zealand Standard for cold-formed steel structures. In addition, the results obtained from the finite element model were also compared with the design strengths obtained from the design rules proposed by other researchers. [ABSTRACT FROM AUTHOR]

A new analytical model for sheathing-to-framing connections in wood shear walls and diaphragms is discussed in this paper. The model represents sheathing-to-framing connections using an oriented pair of nonlinear springs. Unlike previous models, the new analytical model is suitable for both monotonic and cyclic analyses and does not need to be scaled or adjusted. Furthermore, the analytical model may be implemented in a general purpose finite element program, such as ABAQUS, or in a specialized structural analysis program, such as CASHEW. To illustrate, the responses of a 4.88×14.6 m plywood diaphragm and a 2.44×2.44 m oriented strand board shear wall are predicted using the new analytical model. [ABSTRACT FROM AUTHOR]

In routine design of steel storage rack frames, it is far more common to perform two dimensional (2D) rather than three dimensional (3D) linear buckling analyses. In this paper, it is demonstrated that the global buckling behavior of high-rise steel storage rack frames may not be revealed by 2D buckling analyses as 3D interaction modes are involved. It is shown that the monosymmetric upright columns of a high-rise rack frame fail in a flexural–torsional mode due to the shear-center eccentricity of the sections, and that the 3D frame buckling analysis is more reliable in determining the critical members of a rack frame. Current steel storage rack design standards combine independent 2D flexural buckling analyses and simplified flexural–torsional buckling analysis of individual columns to account for 3D behavior. Comparisons between the buckling stresses of the rack columns determined from 3D buckling analyses and the buckling stresses determined in accordance with the steel storage racking standards are presented. It is concluded that the use of 2D analysis based procedures can lead to poorly proportioned pallet rack structures in terms of safety or economy. By comparing the buckling analysis results using 3D beam elements of varying degrees of refinement to each other, it is also demonstrated that the beam elements available in most commercial frame analysis programs are not sufficiently refined for accurate 3D buckling analyses of high-rise rack frames composed of monosymmetric thin-walled open sections. [ABSTRACT FROM AUTHOR]

Lateral reinforcements can enhance serviceability of wood-based floor systems. However, because of a lack of proper analysis models, the benefit from installing these components has not been fully recognized in floor design. In this paper, a finite-element model for predicting static and dynamic characteristics of wood-based floor structures with various types of lateral reinforcements is presented. In this model, shell elements were employed to represent floor decking and ceiling, and beam elements were utilized to model joists and structural members in the lateral reinforcements. Special connector elements were developed to model the fasteners connecting various structural components. Other structural features, such as gaps perpendicular to joists in the subfloor, additional objects on floor and flexible supports, were also considered. A computer model incorporating these new features has been developed. For verification and validation purposes, the predicted deflections and natural frequencies for a number of full-size floors were compared with experimental values. Good agreement has been observed. These numerical test results indicated that the present finite-element model is reliable and unique, particularly in modeling floors with lateral reinforcements. [ABSTRACT FROM AUTHOR]

The design of cold-formed steel (CFS) C-sections that have bearing stiffeners installed between their flanges is a challenging task because complex interactions occur between the stiffener and the C-section when the assembly is loaded to failure. These interactions make it impractical to derive design expressions from first principles. Described in this paper is the application of a finite element (FE) model of a stiffened CFS C-section that was used to carry out parametric studies of the behavior of the stiffened joist assembly. Based on the results of these FE studies and experimental work, design expressions are proposed for the web crippling capacity of a stiffened C-section; the magnitude of the forces that develop in the fasteners connecting the joist to the stiffener; and the equivalent stiffness of the fasteners. These design expressions are fundamental components in the development of practical design expressions for the ultimate strength of stiffened C-sections. [ABSTRACT FROM AUTHOR]

This paper presents the experimental findings of high-strength concrete (HSC) interior beam-column joints under column axial compressive loading. Eight full-scale interior beam-column joints with varying degrees of reinforcement detailing were subjected to a constant column axial compressive load and quasi-static horizontal cyclic load. The test revealed that HSC improved the bond condition of bars with a larger diameter due to the higher achievable bond stress, thereby allowing for the use of longitudinal beams of a larger diameter. Parametric studies via finite-element (FE) modeling were performed to study the influence of various parameters on the strength and bond of HSC beam-column joints. The study confirmed that reinforcement of larger diameter can be used in HSC beams with the improvement in the bond condition. The presence of axial compressive load improved the bond stress of HSC beam-column joint but a threshold limit should be applied. Last, two standards were reviewed and improvements to the design equations were proposed. [ABSTRACT FROM AUTHOR]

This paper describes a newly developed Levy form adaptive cable dome, which has the ability to alter its stiffness configuration and stress properties to adapt its behavior to current loading conditions. This novel structure contains sensors that detect forces in the system and an action member that adjusts its stiffness and stress state, making the structure more rigid or flexible, depending upon the actual load applied. This system consists of 42 tensioned cables, 6 compressed struts, and a central strut that is designed to function as an actuator. Results of the experimental and theoretical analyses are compared. Tests are aimed at verifying the cable dome's ability to adapt its state of stress to changing load cases to maintain the reliability of the system. Tests confirmed the functionality of the developed adaptive system and the applicability of the proposed equipment, software, computational models, and control commands. Results demonstrate that the behavior of the adaptive cable dome obtained by tests generally can be closely predicted numerically with nonlinear finite element analyses. [ABSTRACT FROM AUTHOR]

This paper describes a new framework for the assessment of potential damage caused by tunneling-induced settlement to surface masonry buildings. Finite element models in two and three dimensions, validated through comparison with experimental results and field observations, are used to investigate the main factors governing the structural response to settlement. Parametric analyses are performed on the effect of geometrical and structural features, like the building dimensions, the nonlinear behavior of masonry, and soil-structure interactions. These results are used to create a framework of an overall damage model that correlates the analyzed parameters with the risk of the building being damaged by a given level of settlement. The proposed vulnerability framework has the potential to be developed as a decision and management tool for the evaluation of the risk associated with underground excavations in urban areas. [ABSTRACT FROM AUTHOR]

This paper presented a modeling study on force transfer around openings (FTAO) in wood-frame shear walls detailed for FTAO. To understand the load transfer in the walls, this study used a finite-element model WALL2D, which is able to model individual wall components, including framing members, sheathing panels, oriented panel-frame nailed connections, framing connections, hold-down connections, and strap connections for reinforcing the corners of openings. The various wall models were validated through laboratory testing of 12 full-scale shear wall configurations, which included a variety of opening types and sizes. At the wall design load level, the predicted strap forces around openings also agreed well with the test results, in contrast with four simplified analytical methods commonly used in designing shear walls with openings detailed for FTAO. This wall model thus presents a useful tool to check the accuracy of the simplified methods and develop a better understanding of the behavior of wood-frame shear walls with openings. [ABSTRACT FROM AUTHOR]

This paper presents a numerical finite-element parametric study on the behavior of transverse or longitudinal X-type plate-to-circular hollow section connections loaded under branch plate tension or compression, to evaluate the suitability of present international (CIDECT) design recommendations, the effect of boundary conditions and chord length, and the influence of applied chord normal stress. A total of 449 connections with wide-ranging values of geometric properties and chord normal stress levels were modeled and analyzed using commercially available software. An analysis of the effect of chord length determined that, to exclude the influence of chord end boundary conditions, an effective chord length of at least 10 times the chord diameter should be used for experimental and numerical studies. Further, the present CIDECT chord stress functions () provide an acceptable lower bound for all connections examined. Evaluation of present CIDECT partial design strength functions () indicated general conservatism, lack of plate thickness incorporation, and underutilization of tension-only connections. Partial design strength functions, determined through regression analysis, are hence proposed with lower-bound reduction (resistance) factors. [ABSTRACT FROM AUTHOR]

This paper presents development of a simplified procedure for seismic evaluation of piles with partial-moment connection typically used in marine oil terminals. The current seismic evaluation procedure of the piles in marine oil terminals includes monitoring material strains specified in the Marine Oil Terminal Engineering and Maintenance Standard (MOTEMS) during the nonlinear static pushover analysis to estimate the displacement capacity of piles. This investigation developed closed-form formulas for estimating the displacement capacity of piles by using a simple pile-deck connection system. The displacement capacity estimated from these formulas ensures that the material stain limits specified in the MOTEMS is not exceeded. These formulas are demonstrated to be “accurate” by comparing results from these formulas against those from the nonlinear finite-element analysis. The formulas developed in this investigation utilize the curvature ductility capacity of the pile section and rotation ductility capacity of the connection at the selected seismic design level, along with the parameter β which depends on the relative stiffness of the pile and the connection and the parameter η which depends on the relative strength of the connection and the pile. [ABSTRACT FROM AUTHOR]

The need to identify the physical properties of a structure given its force-response (input-output) relationship is driven primarily by the need to validate the approximate solution models, such as finite-element models. This paper proposes a method, which combines the structural system identification and model updating techniques, for the damage detection of a steel frame structure and a RC frame. The damage detection procedure consists of two steps: (1) identifying the system dynamic characteristics using the subspace identification (SI) technique from input/output measurements and (2) developing a damage assessment method for structural members (including joints) based on a progressive finite-element model updating and a large-scale optimization using a nonlinear least-square technique. The proposed method was verified through a shaking table experimental study using: (1) a 1/4-scale six-story steel frame structure by loosening the connection bolts for damage simulations and (2) a two-story RC frame subject to different levels of ground excitations back to back. As demonstrated by experimental results, the proposed damage detection method, based on the combination of SI technique and the model updating approach, is very effective for the damage assessment of frame structures. The method not only can detect the damage locations but also can quantify the damage severities. [ABSTRACT FROM AUTHOR]

This paper proposes the concept of “equivalent load for stiffness” (ELS) and presents the applicability of this concept to a variety of structural problems. ELS is a set of additional forces applied to an original structure to produce the same response as that of a modified structure. That is, ELS is equivalent to the changes of stiffness in the original structure. The novelty of the proposed algorithm is that it requires computational operations of an order of qmn, as compared to the full analysis requiring m2n, where m=half-bandwidth of the global stiffness matrix; q=number of degrees of freedom (DOF) associated with the modified members, and n=number of DOFs. Therefore, the proposed algorithm is particularly efficient for such situations as a limited number of members are modified. In addition, the algorithm involves a clear physical concept based on static condensation and is applicable to a variety of problems, including sensitivity analysis, nonlinear analysis, dynamic analysis, and so forth. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation conducted in Woomera, South Australia in May 2004 on the blast-resistance of concrete panels made of ultrahigh-strength concrete (UHSC) material. A special concrete supporting frame was designed for testing concrete panel targets against blast loading. Four 2 m×1 m panels with various thicknesses and reinforcement details were tested under a 6 t TNT equivalent explosion at standoff distances of 30 and 40 m. Data collected from each specimen included blast pressures and deflections of panels. The test data were analyzed to assess the performance of UHSC and normal-strength concrete (NSC) panels. The test results and observations showed that the 100-mm-thick UHSC panels performed extremely well surviving the blast with minor cracks. The 75-mm-thick UHSC panel suffered moderate damage while the 100-mm-thick NSC panel was breached. Test results from this experimental program were used to validate a finite-element computer code that was developed by the writers to analyze concrete structures subjected to blast and impact loading. [ABSTRACT FROM AUTHOR]

This paper discusses the design and modeling of a welded chord connection commonly used in pretopped precast double tee panels. In conventional design, the chord is intended to achieve its tension strength based on the axial capacity of the anchorage bars. An experimental study has shown that premature failure of the weld and flexure of the bar may occur, significantly reducing the tension capacity of the connection. A detailed finite-element model is developed and verified with experimental data and used for a parametric investigation. The results indicate that a ductile chord connection, with predictable capacity, can be achieved through concentric placement of the welds relative to the anchorage bar. Variations in faceplate thickness and weld throat are found to alter the load path but do not prevent premature failure. Mechanical debonding of the anchorage bars is found to significantly enhance the deformability of the connection. These findings are incorporated in a force and displacement based design procedure for the chord connection; an example is included for illustration. [ABSTRACT FROM AUTHOR]

This paper presents finite-element (FE) modeling and nonlinear analysis of steel-concrete composite frames subjected to very large cyclic loading. A three-dimensional FE model is developed to carry out the nonlinear analysis. Modeling details of the steel frame, the reinforced concrete (RC) slab, the interactions between the RC slab and the frame beams, and the associated constitutive relationships for cyclic loading are presented. A composite frame previously tested by the writers is analyzed using the proposed FE model. Good correlation is observed between the experimental and analytical hysteresis curves up to rotation amplitude of 0.04 rad. One of the notable observations during the loading to large rotations is the fracture at steel beam ends. To simulate such behavior, a simplified fractured steel connection model is introduced. The proposed nonlinear model is found to be capable of capturing the fracture behavior of beam ends to an acceptable accuracy. [ABSTRACT FROM AUTHOR]

Tests conducted in the 1980s showed that well-detailed short shear links can exhibit stable and ductile cyclic behavior. Recent tests of prevailing A992 rolled shapes revealed that shear links designed according to current seismic specifications can fail by ductile fracture in the link web, a mode of failure that was not observed in earlier tests. This paper investigates the observed ductile fractures through computational structural simulation. An existing criterion for judging the propensity for ductile fracture initiation in steel is modified based on published tests results for notched bars to better pinpoint the location of ductile fracture initiation. Validated finite- element analyses of previously tested shear links are conducted and the results postprocessed to evaluate the potential for ductile fracture of specimens with several different types of details. Reasons for the occurrence of web fractures in new A992 steel beams as opposed to older links are discussed. An alternative stiffener configuration that mitigates ductile fracture and is at the same time practical to construct is proposed. [ABSTRACT FROM AUTHOR]

This study deals with a method to identify structural damage using the combined finite element method and the advanced uniform microgenetic algorithm. The novelty of this study is the use of dynamic loading and its response due to the anomalies in a structure under testing. The technique described in this paper may allow us not only to detect the damaged elements but also to find their numbers, locations, and the extent of damage. To demonstrate the feasibility of the method, the algorithm is applied to a cantilever beam and plate structures with defects. In addition, a laminated composite plate is tested numerically using the first shear deformation theory, and the effect of noise is simulated to study the influence of measurement errors and uncertainty of the method. The results demonstrate the excellencies of the method from the standpoints of computation efficiency as well as its ability to avoid premature convergence. [ABSTRACT FROM AUTHOR]

In light of recent terrorist attacks on facilities throughout the world, designers, planners, architects, and engineers are beginning to re-visit conventional approaches in the design of military and high-security facilities. Many existing buildings, structures and facilities should be better protected against man-made explosive hazards. For this reason the designs of public/private structures and facilities are getting much more attention in recent years. This paper presents the results of experimental and numerical investigations that were conducted in order to examine the capabilities of aluminum foams in mitigating the effect of blast waves acting on reinforced concrete (RC) beams and plates. Numerical simulations of the behavior of the investigated RC beams and plates under the dynamic loads support the experimental investigation results. The numerical simulations are based on finite element commercial and in-house codes. The experimental and numerical results for both the protected and unprotected RC beams and the conclusions obtained from these experiments and simulations are presented. [ABSTRACT FROM AUTHOR]

The paper presents the experimental and analytical modal analysis of a steel-girder arch bridge. The field test is carried out by ambient vibration testing under traffic and wind-induced excitations. Both the peak picking method in the frequency domain and the stochastic subspace identification method in the time domain are used for the output-only modal identification. A good agreement in identified frequencies has been found between the two methods. It is further demonstrated that the stochastic subspace identification method provides better mode shapes. The three-dimensional finite element models are constructed and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the three-orthogonal directions. The finite element models are validated to match the field natural frequencies and mode shapes. It is observed that the finite element Model-2 with the concrete slab provides the greater stiffness in the transverse direction of the bridge. The finite element Model-1 with the lumped masses agrees well with the field tests and can serve as a baseline model of the bridge. [ABSTRACT FROM AUTHOR]

Genetic algorithms (GAs), based on a multipoint search method and a crossover operation, are useful search procedures for combinatorial optimization problems. They also are applied to many kinds of practical optimization problem. However, in general, the GAs have a tendency to decrease rapidly of population diversities in processes of searching. In order to address this drawback, some researchers have proposed new algorithms for maintaining the population diversity. On the other hand, immune algorithms (IAs) are optimization techniques that imitate immune systems in an organism. The IAs are able to obtain a multiple quasi-optimum solution while maintaining the population diversity compared with GAs. In this paper, in order to consider the application of the IAs to optimum structural design problems, we developed a useful design support system for reinforced concrete (RC) slabs by combining a three-dimensional (3D) nonlinear dynamic finite element method (FEM) and an improved immune algorithm (IA). For the analysis of impact failure behavior of RC slabs, layered nonlinear FEM models with thin plate bending elements, and 3D elastoplastic FEM models with eight-node isoparametric hexahedral elements were used. First, an existing IA was modified to make it suitable for RC slab design, and both genetic and immune algorithms were applied to optimization problems with multiple optimum solutions. This modified IA was also applied to quasi-optimization problems with multiple maximum values. By comparing the above two approaches, the usefulness of the IA for design problems with discrete parameters was verified. Next, indices for evaluating impact resistance were discussed, and design simulation was conducted, based on these indices, by combining the layered nonlinear FEM and the IA. From results obtained, the accuracy and usefulness of the IA-based design support system were discussed. For obtaining a more practical design support system, shear reinforcement will be taken into account by combining the IA with the 3D elastoplastic FEM. Furthermore, the effectiveness and future potential of the design support system were confirmed by investigating an effect of introducing a database of design plans. [ABSTRACT FROM AUTHOR]

This paper describes the closed-form and discrete computational models for a geometrically nonlinear and linear static analysis of the adaptive tensegrity module presented in the companion paper. Due to the symmetry of the spatial tensegrity system, a simplified closed-form analysis is based on a two-dimensional (2D) solution of an equivalent prestressed triangular cable truss acting under a vertical point load. Novel concrete forms of the cable and deflection equations are derived. The analytical models serve to determine the response, i.e., horizontal components of cable forces and deflections as the basis for control commands. A three-dimensional (3D) discrete geometrically nonlinear analysis of the adaptive tensegrity module is based on the application of a nonlinear finite-element method. The results obtained by the nonlinear finite-element analysis are compared with those obtained by using both the simplified linear and nonlinear closed-form solutions. Physical relevance and mathematical correctness of the applied theoretical approaches were confirmed by the results. Finally, the numerical model is applied to assess the response of the prestressed tensegrity module considering the effects of large deformations and slackening of cables. [ABSTRACT FROM AUTHOR]

Aluminum alloys are employed in a range of structural engineering applications, supported by many international design standards, but plastic design methods are generally not permitted. In the second part of this study, an extensive numerical parametric study is conducted to assess the effect of key parameters, such as cross section slenderness, cross section aspect ratio, and moment gradient on the strength, strain hardening, and moment redistribution behavior of aluminum alloy continuous beams. The key input parameters and findings are reported herein. Based on both the experimental and parametric numerical results, the design provisions of the American, Australian/New Zealand, and European specifications as well as the traditional plastic design method, the plastic hinge method, and the continuous strength method (CSM) for indeterminate structures, the scope of which is extended in the present study, have been evaluated. The design strengths predicted by the three specifications were found to be rather conservative, while the predications of the latter three methods are more precise and consistent. The results reveal that strain hardening at the cross-sectional level and moment redistribution at the global system level have significant influence on the performance of stocky (plastic and compact sections) aluminum alloy members, which should be accounted for in design. Following reliability analysis, proposals are made for revised design provisions. [ABSTRACT FROM AUTHOR]

Performance of steel reinforced concrete (SRC) columns under fire is investigated in this paper. A three-dimensional finite-element analysis (FEA) modeling is developed for sequentially coupled heat transfer and structural analysis, in which the classical creep strain and the transient strain of concrete together with thermal strain are included explicitly by subroutines. Four SRC columns with H-shaped steel and cross-shaped steel are experimentally investigated, and the test results are adopted to verify the FEA modeling. The FEA modeling is then used to construct the model of a typical full-scale SRC column and perform analysis to the behavior of the column in fire. Extensive parametric studies are performed to investigate the fire resistance of the SRC column, and the key influencing parameters are identified. Finally, a simplified calculation method is proposed to predict the fire resistance of the SRC column. [ABSTRACT FROM AUTHOR]