Nonlinear Analysis Program Research Articles

Development of integrated system for progressive collapse analysis of building structures considering dynamic effects

In this study the integrated system for progressive collapse analysis, which can evaluate the damage level of every member and automatically construct the modified structural model for the next analysis step, has been developed. The existing nonlinear analysis program code OpenSees was used as a finite element solver in the integrated system for progressive collapse analysis. The developed integrated system includes a pre-processor with intuitive graphic user interfaces and a post-processor that can simulate the progressive collapse by 3D graphic animation. Using the developed integrated system, example structures subjected to a column failure were analyzed, and the behavior of the structures was investigated in the context of how to model the failed members and whether the dynamic effects are considered or not. The analysis results show that the dynamic amplification can be larger than two which is recommended by the GSA and DoD guidelines and the collapse mechanism depends greatly on the modeling technique for failed members.

Importance of shear assessment of concrete structures detailed to different capacity design requirements

Shear failure of RC structures signifies rapid strength degradation and significant loss of energy dissipation capacity. It is thus necessary to avoid this failure mode by insuring that the shear supply exceeds the capacity corresponding to the maximum realistic flexural strength. A realistic and versatile approach is proposed in the current study and implemented in a general nonlinear dynamic analysis program to allow for the prediction of shear failure in structural member. The shear demand-supply response is monitored through employing two shear strength approaches. The first is based on extensive experimental results and has proven to be effective in representing the reduction of shear supply with the degradation in concrete strength. A design code shear strength model is also selected for comparison after eliminating the safety factors used by the code. The analytical models are implemented in a time-step fashion to allow for shear–axial interaction and to account for the instantaneous ductility demand imposed during the analysis. The investigated structures were realistically designed and detailed to different design ground accelerations and capacity design requirements to represent a wide range of contemporary buildings with variations in longitudinal (flexure) and transverse (shear and confinement) reinforcement. A series of inelastic response history analyses is conducted using a set of earthquake records scaled to increasing intensities up to collapse. The significance of including shear as a failure criterion in seismic assessment is confirmed in this study. Variations of axial forces lead to high fluctuation in shear supply and decrease the contribution of the concrete compression zone to shear resistance. The improved response of structural members designed to the modern seismic provisions is confirmed. Shear failure may be the controlling limit state in buildings designed for low-to-medium ductility capacity. This suggests improvements in the design provisions, particularly those related to beam critical regions.

GEOMETRIC NONLINEAR ANALYSIS OF CABLE STRUCTURES WITH A TWO-NODE CABLE ELEMENT BY GENERALIZED DISPLACEMENT CONTROL METHOD

This paper presents a two-node catenary cable element for the analysis of three-dimensional cable-supported structures. The stiffness matrix of the catenary cable element was derived as the inverse of the flexibility matrix, with allowances for selfweight and pretension effects. The element was then included, along with the beam and truss elements, in a geometric nonlinear analysis program, for which the procedure for computing the stiffness matrix and for performing iterations was clearly outlined. With the present element, each cable with no internal joints can be modeled by a single element, even for cables with large sags, as encountered in cable nets, suspension bridges and long-span cable-stayed bridges. The solutions obtained for all the examples are in good agreement with the existing ones, which indicates the accuracy and applicability of the element presented.

On the effect of large deflection on nonlinear behavior of an eccentric bracing system

AbstractIn this article, a particular off‐center bracing system is introduced. In this system, the tensile diagonal strut is not straight. When the load is applied, the original geometry changes and thus causes the system to harden. Based on this behavior, a step‐by‐step analytical method is developed. Using this method, a Geometrically Nonlinear Analysis Program (GNAP) is designed to analyze the elastic force–displacement relation. Extension of this program to dynamic analysis led to a Dynamic Nonlinear Analysis Program (DNAP). The object of this article is to show that such bracing systems will lead to less seismic force on such structures compared to classic concentric bracing systems. On the other hand, it will be shown that the bracing system causes semi‐uncoupling of structure, and that the probable excursions in the nonlinear range during severe earthquakes will not cause significant deterioration in its strength and stiffness. Copyright © 2007 John Wiley & Sons, Ltd.

Behaviour of High Strength Concrete-Filled Slender RHS Steel Tubes

An experimental study of the behaviour of high strength concrete-filled slender rectangular hollow section (RHS) tubes under the combined actions of axial compression and bending moment is presented. A total of 26 specimens were tested. The main parameters considered in the test were slenderness ratio, depth-to-breadth ratio, steel-to-concrete area ratio and eccentricity-to-depth ratio. The experimental results showed that the ultimate capacity of test specimens decreased rapidly with increase of slenderness ratio and eccentricity-to-depth ratio. For the specimens with depth-to-thickness ratio larger than 50, local buckling failure occurred prior to the ultimate capacity. A nonlinear analysis program, BC, was developed to analyze the behaviour of high strength concrete-filled RHS tubes. A comparison for ultimate capacity showed that the theoretical results agreed very well with the experimental results. The depth-to-breadth ratio (varying from 1.0 to 1.6) showed little influence on the stability capacity of the specimens. The comparison of the experimental results with the results calculated by the design equations in the codes, such as LRFD, EC4 and AIJ showed that EC4 closely predicts the ultimate capacity of the specimens.

Seismic damage estimation through measurable dynamic characteristics

Ductility based design of reinforced concrete structures implicitly assumes certain damage under the action of a design basis earthquake. The damage undergone by a structure needs to be quantified, so as to assess the post-seismic reparability and functionality of the structure. The paper presents an analytical method of quantification and location of seismic damage, through system identification methods. It may be noted that soft ground storied buildings are the major casualties in any earthquake and hence the example structure is a soft or weak first storied one, whose seismic response and temporal variation of damage are computed using a non-linear dynamic analysis program (IDARC) and compared with a normal structure. Time period based damage identification model is used and suitably calibrated with classic damage models. Regenerated stiffness of the three degrees of freedom model (for the three storied frame) is used to locate the damage, both on-line as well as after the seismic event. Multi resolution analysis using wavelets is also used for localized damage identification for soft storey columns.

Integrated Graphical Environment for Support Nonlinear Dynamic Software for the Analysis of Plane Frames

Nonlinear structural analyses allow reproducing in a more realistic sense the behaviour of structures subjected to several types of complex loading conditions, e.g. earthquakes. However, it is largely recognized that these analyses normally generate a considerable amount of results, being difficult its interpretation. Over the last years considerable progresses have been made in structural nonlinear behaviour modelling, associated to the fast growing development of numerical algorithms for structural analysis and computer capacities. However, a similar growth in the development of graphical results visualization tools has not been witnessed. To face this, a graphical processor called VISUALANL was developed for an existing nonlinear dynamic analysis program for plane frame structures, PORANL.

Correlation between Analytic and Experimental Results on Inelastic Behavior of Reinforced Concrete Frame

The objectives of this study are to evaluate the reliability of an existing nonlinear analysis program for predicting the inelastic behavior of reinforced concrete frame with seismic details and to observe the redistribution of the internal forces, which can not be easily measured by an experiment. In order to carry out this task, the nonlinear analysis program of IDARC 2D(3) was run on a 2-bay, 2-story moment-resisting reinforced concrete plane frame with seismic details. (1) The effort to obtain the results of the analysis similar to those of experiment was made by determining the appropriate values of model parameters. The comparison of the analysis results with those of experiment and the observation of the distribution of internal forces obtained through nonlinear analysis points to the following conclusions. (1) The overall relationship between lateral load and lateral displacement given by the analysis is similar to that of experiment. However, the values of initial stiffness and the amount of energy dissipation in the initial displacement steps given by the analysis show larger values than those of experiment. (2) The analysis provided detailed information on the distribution and redistribution of internal forces and proved useful in elucidating the crack pattern, the sequence of the occurrence of plastic hinges, and the failure or yielding mechanism for the whole structure. (3) In spite of the similarity in overall behavior of analysis and experiment, there exists a significant discrepancy in some local behaviors. Furthermore, the hysteresis in the relationship between moment and curvature in some column ends have shown sudden deteriorations in strength, which can not be interpreted satisfactorily at the present time. Therefore, it is necessary to develop a better analytical model to fill this knowledge gap.

Nonlinear Analysis of Reinforced Concrete Beam–Columns with Bond-Slip

This paper presents a new model for nonlinear analysis of reinforced concrete beam–columns with bond–slip. The model is derived from a two-field mixed formulation with independent approximation of forces and displacements. The state determination algorithm for the implementation of the model in a general purpose nonlinear finite-element analysis program is presented and its stability characteristics are discussed. Both, bond–slip and pull-out effects, are represented in the model. The paper concludes with a correlation study to investigate the validity of the model. The study confirmed the accuracy of the model in representing global and particularly local parameters.

Conformational Mobility in the Active Site of a Heme Peroxidase

Conformational mobility of the distal histidine residue has been implicated for several different heme peroxidase enzymes, but unambiguous structural evidence is not available. In this work, we present mechanistic, spectroscopic, and structural evidence for peroxide- and ligand-induced conformational mobility of the distal histidine residue (His-42) in a site-directed variant of ascorbate peroxidase (W41A). In this variant, His-42 binds "on" to the heme in the oxidized form, duplicating the active site structure of the cytochromes b but, in contrast to the cytochromes b, is able to swing "off" the iron during catalysis. This conformational flexibility between the on and off forms is fully reversible and is used as a means to overcome the inherently unreactive nature of the on form toward peroxide, so that essentially complete catalytic activity is maintained. Contrary to the widely adopted view of heme enzyme catalysis, these data indicate that strong coordination of the distal histidine to the heme iron does not automatically undermine catalytic activity. The data add a new dimension to our wider appreciation of structure/activity correlations in other heme enzymes.

설계변수에 따른 플랫플레이트-기둥 접합부의 강도산정모형

In the present study, a numerical analysis was performed for interior connections of continuous flat plate to analyze the effect of design parameters such as column section shape, gravity load and slab span on the behavioral characteristics of the connections. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases and gravity load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. And as the slab span loaded with relatively large gravity load increases, the negative moment around the connection increases and therefore the strength of connection against unbalanced moment decreases. By considering the effect of design parameters on the strength of the connections, the effective shear strength to calculate the torsional moment capacity of connection was proposed and the effectiveness of the proposed shear strength was verified.

Wall Column을 적용한 플랫플레이트 접합부 강도발현에 관한 연구

Flat-plate building systems are utilized extensively for construction of apartments, hotels and office buildings because of short construction period, low floor-to-floor height and flexibility in plan design. Recently, to increase lateral seismic resistance of flat-plate building systems, wall-columns are used frequently. Therefore, to estimate strength of flat-plate column connection accurately, the effect of column section shape on the behavior of flat-plate column connection should be considered properly, In the present study, a numerical analysis was performed for interior connections of continuous flat-plate to analyze the effect of column section shape. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. Therefore, these effects should be considered properly to estimate the strength of flat-plate connection accurately.

Layer IV of the primary somatosensory cortex has the highest complexity under anesthesia and cortical complexity is modulated by specific thalamic inputs

The system complexity, as calculated from correlation dimension, embedded in each layer and its modulation by specific inputs and general excitatory state are not yet known. The aims of present study were to estimate the system complexity across the cortical layers by analyzing intracortical EEG signals using a nonlinear analytical method, and to identify how layer-related complexity varies with the alteration of thalamic input and brain state. Male Sprague–Dawley rats were anesthetized under l% halothane. Sixteen channels of evoked or spontaneous EEG signals were recorded simultaneously across the six cortical layers in the somatosensory cortex with a single Michigan probe. The system complexity was assessed by computing correlation dimension, D 2, based on the Nonlinear Time Series Analysis data analysis program. Cortical layer IV exhibited a D 2 value, 3.24, that was significantly higher than that of the other cortical layers. The D 2 values in layers IV and II/III were significantly reduced after reversible deactivation of the ventral posterior lateral thalamic nucleus. D 2 decreased with increases in administered halothane concentration from 0.75% to 2.0%, particularly in layer IV. The present findings suggest that cortical layer IV maintains a higher complexity than the other layers and that the complexity of the mid-cortical layers is subject to regulation from specific thalamic inputs and more sensitive to changes in the general state of brain excitation.

Smart base-isolated benchmark building. Part I: problem definition

This paper presents the benchmark problem definition for seismically excited base-isolated buildings. The objective of this benchmark study is to provide a well-defined base-isolated building with a broad set of carefully chosen parameter sets, performance measures and guidelines to the participants, so that they can evaluate their control algorithms. The control algorithms may be passive, active or semi-active. The benchmark structure considered is an eight-storey base-isolated building similar to existing buildings in Los Angeles, California. The base isolation system includes both linear and nonlinear bearings and control devices. The superstructure is considered to be a linear elastic system with lateral–torsional behavior. A new nonlinear dynamic analysis program has been developed and made available to facilitate direct comparison of results of different control algorithms. Copyright © 2005 John Wiley & Sons, Ltd.

Smart base-isolated benchmark building part IV: Phase II sample controllers for nonlinear isolation systems

The first phase of the seismically excited base-isolated benchmark building was received well by the structural control community, culminating in the March 2006 journal special issue. The special issue contained contributions from over dozen participants world-wide. While the focus of the Phase I effort was on linear isolation systems, Phase II attempts to galvanize research efforts on control of base-isolated buildings with nonlinear isolation systems. Primarily, friction and hysteretic lead–rubber-bearing (LRB) isolation systems are included in this effort. The superstructure and the control framework remains the same as the Phase I benchmark. The main difference will be in the nonlinear isolation systems used, and consequently the controllers necessary to control such systems. The primary objective of this paper is to present the Phase II benchmark problem definition along with a sample controller for friction isolation system. A sample controller for the LRB isolation system was presented earlier as a part of the Phase I special issue. Included in this paper is a broad set of carefully chosen performance measures, which remain the same as Phase I, so that the participants may evaluate their respective control designs. The control algorithms may be passive, active or semiactive. The benchmark structure considered in the Phase II study is an eight-story base-isolated building that is identical to the one considered for the Phase I study. The base isolation system consists of a combination of linear, nonlinear bearings and control devices. The superstructure is considered to be a linear elastic system with lateral–torsional behavior. The nonlinearities due to the isolators and control devices are limited to the isolation level only. A nonlinear dynamic analysis program and sample controllers are made available to the participants to facilitate direct comparison of results of different control algorithms. Copyright © 2008 John Wiley & Sons, Ltd.

Nonlinear seismic response analysis of reinforced concrete tube in tube structure

Super-highly reinforced concrete tube in tube structure is a developing structure system of high-rise building. The more reasonable derivation process of the multi-vertical-line-element model stiffness matrix is given. On the premise of pointing out the problems of present multi-spring element model, combined with present multivertical-line-element model for analyzing on shear wall, the model is expanded to spatial one, and the stiffness matrix of which is derived. Combined with hysteretic axial model and hysteretic shear model, it is suitable for columns, wall limbs and beams with all kinds of section form. Some examples are calculated and compared with test results, which shows that the models have relatively good accuracy. On the base of the experimental phenomenon and failure mechanism for tube in tube structure specimen, nonlinear seismic responses analysis program on the basis of the advantaged element model for tube in tube structure is developed. Calculation results are in good agreement with those of the pseudo-dynamic tests and the failure mechanism can be well reflected.

Frictional effects on the cyclic response of laterally loaded timber fasteners

Foschi's connector model is used as a basic component in the development of nonlinear analysis programs for timber structures. This paper presents the extension of the model to include the effect of shaft frictional forces. The wood medium is modeled using the Foschi embedment model, while shaft friction is modeled using an elastic Coulomb-type friction model. The initial confining pressure for the case of driven fasteners is accounted for by a lateral shift of the load-embedment curve. The model is used to compute the cyclic response of both driven and inserted fasteners. The results obtained from the cases studied indicate that initial confining pressure and friction do not have a significant effect on the computed hysteretic response, however, they significantly affect the computed amount of fastener withdrawal. This model is particularly well-suited for modeling the hysteretic response of shear walls with moderate fastener withdrawal under lateral cyclic or earthquake loading.

Numerically Efficient Dynamic Analysis of Barge Collisions with Bridge Piers

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.

Performance evaluation of masonry-infilled RC frames under cyclic loading based on damage mechanics

Based on the equivalent strut approach (simplified model), a damage model is proposed in this paper for the characterization of masonry walls submitted to lateral cyclic loads. The model, developed along the lines of the Continuum Damage Mechanics, has the advantage of including explicitly the coupling between damage and mechanical behaviour and so is consistent with the definition of damage as a phenomenon with mechanical consequences. The model includes the simulation of phenomena such as stiffness and strength degradation and pinching behaviour. The macromodel has been incorporated in a nonlinear structural analysis program for analysis of masonry-infilled RC frames. The model has been validated with some experimental tests. An evaluation of the structural performance of the analysed masonry-infilled frames has been performed based on the calculated damage values and the storey drifts.

A general and versatile nonlinear analysis program for concrete bridge structure

To meet the application of nonlinear FEM analysis to the real bridge structure, a general and versatile nonlinear analysis program for concrete bridge structures is presented in this paper. The structural effects such as material nonlinear behavior, prestress effect, construction process, temperature, creep of concrete and so on, which are concerned in practical engineering, are covered. To simulate the nonlinear behaviors, an efficient 3D degenerated beam element is adopted. The step-by-step analysis method allows one to comprehend the structural behaviors of the bridges during the construction, service, and failure periods, respectively. Finally, two examples are studied to verify the accuracy of the program and demonstrate its application in practical bridge engineering.