Simulation Of Structural Response Research Articles

A Quantitative Basis for Building Instrumentation Specifications

A quantitative basis for key building instrumentation specifications—namely, sample rate, system resolution, and time synchronization—is established by quantifying the sensitivities of engineering demand parameters of peak floor acceleration and peak interstory drift to the errors associated with data acquisition. Details of the realistic simulation and digitization of structural responses are provided and automation of the seemingly signal-dependent procedure of high-pass digital filtering of relative displacements obtained by double numerical integration of accelerations is presented. Results from these studies, along with prior results from similar sensitivity analyses with respect to intensity measures of peak ground acceleration, peak ground velocity, and peak spectral acceleration, are used to recommend potential updates to structural instrumentation specifications of major strong-motion instrumentation programs.

Seismic Collapse Safety of Reinforced Concrete Buildings. II: Comparative Assessment of Nonductile and Ductile Moment Frames

This study is the second of two companion papers to examine the seismic collapse safety of reinforced concrete frame buildings, and examines nonductile moment frames that are representative of those built before the mid-1970s in California. The probabilistic assessment relies on nonlinear dynamic simulation of structural response to calculate the collapse risk, accounting for uncertainties in ground-motion characteristics and structural modeling. The evaluation considers a set of archetypical nonductile RC frame structures of varying height that are designed according to the seismic provisions of the 1967 Uniform Building Code. The results indicate that nonductile RC frame structures have a mean annual frequency of collapse ranging from 5 to 14×10-3 at a typical high-seismic California site, which is approximately 40 times higher than corresponding results for modern code-conforming special RC moment frames. These metrics demonstrate the effectiveness of ductile detailing and capacity design requirements, which have been introduced over the past 30 years to improve the safety of RC buildings. Data on comparative safety between nonductile and ductile frames may also inform the development of policies for appraising and mitigating seismic collapse risk of existing RC frame buildings.

Air-blast-loaded, high-strength concrete beams. Part II: Numerical non-linear analysis

The results from this investigation demonstrate the ability to perform numerical simulations of dynamic structural response of concrete elements subjected to air blast loading. Beams of both high-strength concrete (HSC) and normal-strength concrete (NSC) were studied. Also beams with two concrete layers of different strength were simulated. It is of particular interest to investigate the use of material models for implementation with software for the explicit analysis of non-linear dynamic events. The influences of concrete strength, amounts of reinforcement, the bond between concrete and reinforcement, bi-linear strain softening of concrete, the strain rate dependence of reinforcement and boundary conditions at the supports were studied. The simulations were performed with the text data as reference through comparison between numerical examples and experimental test results. It was possible numerically to analyse the dynamic behaviour of beams tested in situ and to describe the observed failure modes of these beams. The analysis tool will be used for evaluating the dynamic strength of future protective structures of HSC, possibly with parts consisting of NSC elements.

Numerical simulation of structure response outfitted with a tuned liquid damper

An integrated fluid–structure numerical model has been developed to simulate the response of a single degree of freedom (SDOF) structure outfitted with a Tuned Liquid Damper (TLD). The structure is exposed to random external excitations. A non-linear, two-dimensional, flow model has been developed using the finite-difference method. Unlike most existing flow models, the present model does not include any linearization assumptions; it rather solves the entire nonlinear, moving boundary, flow problem under conditions leading to large interfacial deformations. The free surface has been reconstructed using the volume of fluid method and the donor–acceptor algorithm. The Duhamel integral method has been used to determine the response of the structure. The effectiveness and accuracy of the flow model has been validated using a set of benchmark problems and experimental data. The numerical results of this model have been compared with results of an equivalent TMD model. The present fluid–structure model can be used as a valuable tool for performance evaluation and design of more effective tuned liquid dampers.

Technology Focus: Offshore Facilities (February 2009)

Technology Focus After many years of development work, as well as many unsuccessful attempts, the first liquefied-natural-gas (LNG) floating production, storage, and offloading (FPSO) initiative was launched in 1976 by Linde, Technigaz, et al. under the name Consortium 76—offshore LNG now is a reality. The first LNG receiving terminal installed on a gravity-based structure offshore Rovigo, Italy, will be commissioned soon. The first floating storage and regasification unit (FSRU) permanently moored in open sea offshore Livorno, Italy, is under construction, and several LNG carriers equipped with regasification facilities are able to deliver gas at several offshore ports in North America. Offshore liquefaction also seems close to materialization, with several participants (including oil companies; engineering, procurement, and construction contractors; ship owners; and others) developing LNG FPSO solutions for stand-alone gas fields or for associated-gas developments. Two main ways to approach these facilities seem to be pursued by the various participants. The "big way" is followed mainly by major oil companies: It aims at developing large-capacity liquefaction units (3×106 tonnes/a and larger) by use of processes generally derived from latest-generation onshore liquefaction cycles. A second trend, which could be called the "small way," targets smaller capacities, by use of less-efficient processes often based on nitrogen cycles, but having better suitability for use on board a floater. While the latter probably has a wider range of potential application cases and would ease topside layout and safety concerns for a lower overall capital expenditure, the former will provide higher liquefaction efficiency and will target economies of scale. In turn, it might be applicable to only a limited number of relatively large gasfield developments. Today, both approaches have equal chances to open the way for offshore floating liquefaction, but, certainly, both will need to rely on experienced companies that can gather and leverage experience in offshore regasification gained from the first FSRUs, combined with experience in large oil FPSOs and in onshore liquefaction. All the industry needs now is a good gas field! Offshore Facilities additional reading available at OnePetro: www.onepetro.org OTC 19429 • "A Coupled FE-SPH Approach for Simulation of Structural Response to Extreme Wave and Green Water Loading" by J.C. Campbell, Cranfield University, et al. OTC 19239 • "Innovative Pipe System for Offshore LNG Transfer" by Ing. C. Frohne, Nexans Deutschland Industries, et al. OTC 19315 • "Deepwater Moorings With High-Stiffness Polyester and PEN-Fiber Ropes" by P. Davies, IFREMER Brest, et al.

Critical comparisons of responses between side impact MDB and pole test modes

This paper describes in detail the comparison of structural responses and their effect on occupant responses between the moving deformable barrier and oblique pole test modes, including the test protocol, dummies and injury metrics. The temporal sequence of events that takes place in each of these test modes are presented in light of the primary momentum exchanges and the underlying physics. Furthermore, the key factors that affect dummy responses in each of these test modes are identified and summarised. Additionally, a brief conceptual framework to understand overall vehicle and occupant dynamics is presented. Vehicle crash dynamics covers the analyses of vehicle effective mass, vehicle lateral stiffness and structural analysis using momentum and energy conservation, for design and development of vehicle structure and simulation of structural responses using sub-system test/CAE methodology. Occupant dynamics focuses on analysis of dummy's body regions including head, neck, thorax, pelvis and upper leg to develop countermeasures and better understand the effectiveness of side restraints such as airbags.

Evaluation of cyclic plasticity models in ratcheting simulation of straight pipes under cyclic bending and steady internal pressure

This paper evaluates seven cyclic plasticity models for structural ratcheting response simulations. The models evaluated are bilinear (Prager), multilinear (Besseling), Chaboche, Ohno–Wang, Abdel Karim–Ohno, modified Chaboche (Bari and Hassan) and modified Ohno–Wang (Chen and Jiao). The first three models are already available in the ANSYS finite element package, whereas the last four were implemented into ANSYS for this study. Experimental responses of straight steel pipes under cyclic bending with symmetric end rotation history and steady internal pressure were recorded for the model evaluation study. It is demonstrated that when the model parameters are determined from the material response data, none of the models evaluated perform satisfactorily in simulating the straight pipe diameter change and circumferential strain ratcheting responses. A detailed parameter sensitivity study with the modified Chaboche model was conducted to identify the parameters that influence the ratcheting simulations and to determine the ranges of the parameter values over which a genetic algorithm can search for refinement of these values. The refined parameter values improved the simulations of straight pipe ratcheting responses, but the simulations still are not acceptable. Further, improvement in cyclic plasticity modeling and incorporation of structural features, like residual stresses and anisotropy of materials in the analysis will be essential for advancement of low-cycle fatigue response simulations of structures.

Evaluation of the seismic performance of a code‐conforming reinforced‐concrete frame building—from seismic hazard to collapse safety and economic losses

AbstractA state‐of‐the‐art seismic performance assessment is illustrated through application to a reinforced‐concrete moment‐frame building designed per current (2003) building code provisions. Performance is quantified in terms of economic losses and collapse safety. The assessment includes site‐specific seismic hazard analyses, nonlinear dynamic structural response simulations to collapse, damage analyses, and loss estimation. When selecting ground motion records for nonlinear dynamic analyses that are consistent with a target hazard level expressed in terms of a response spectral value at the building's fundamental period, it is important to consider the response spectral shape, especially when considering higher hazard levels. This was done through the parameter commonly denoted by ε. Neglecting these effects during record selection is shown to lead to a factor of 5–10 overestimation of mean annual collapse rate. Structural response simulations, which properly account for uncertainties in ground motions and structural modelling, indicate a 2–7% probability of collapse for buildings subjected to motions scaled to a hazard level equivalent to a 2% probability of exceedance in 50 years. The probabilities of component damage and the means and coefficients of variation of the repair costs are calculated using fragility functions and repair‐cost probability distributions. The calculated expected annual losses for various building design variants range from 0.6 to 1.1% of the replacement value, where the smaller losses are for above‐code design variants and the larger losses are for buildings designed with minimum‐code compliance. Sensitivity studies highlight the impact of key modelling assumptions on the accurate calculation of damage and the associated repair costs. Copyright © 2007 John Wiley & Sons, Ltd.

Numerical simulation of structural response and damage to simultaneous ground shock and airblast loads

Current practice in analysis and design of structures to withhold surface explosions considers only airblast forces on structures. A surface explosion, in fact, generates both ground shock and airblast pressure on a nearby structure. In this paper, the influences of simultaneous ground shock and airblast forces on structural responses are investigated. Blast-induced surface ground motions and airblast pressures estimated in a previous study are employed as input in the analysis. A previously developed three-dimensional homogenized material model for a masonry wall including the equivalent elastic properties, strength envelope and damage threshold is used to model masonry wall. Another material damage model developed for reinforced concrete structures is used for modelling RC behavior due to explosive loads. These material models are programmed and linked to an available computer program LS-DYNA3D through its user subroutine capability. A one-story masonry infilled RC frame is used as an example in the study. Dynamic response and damage of the example structure to simultaneous ground shock and airblast forces, or separately to ground shock only or airblast forces only are calculated. It is found that in general, airblast load governs structural response and damage when the scaled distance is small. However, under certain conditions, structural damage will be critically underestimated if ground shock is neglected. When the scale distance increases, the relative importance of the ground shock on structure response increases, and ground shock will dominate the surface explosion effects on structures at large scaled distance. At large scaled distance, the ground shock and airblast force effects on structures decoupled and structure response and damage to ground shock and airblast force can be analyzed separately.

RATIONAL POLYNOMIAL APPROXIMATION MODELLING FOR ANALYSIS OF STRUCTURES WITH VE DAMPERS

The objective of this paper is to introduce a Rational Polynomial Approximation (RPA) method for modelling the response of structures that contain discrete elements with linear frequency-dependent stiffness and damping characteristics. The RPA method consists of two steps: First, system identification is performed to obtain a rational polynomial approximation for the system's transfer functions. Then, a time-domain model for the system is realised. The main advantage of the RPA method is that the resulting model is a system of ordinary differential equations, facilitating time history analysis of both linear and nonlinear structures using standard time-step integration algorithms and procedures. Viscoelastic (VE) dampers comprise one of the primary classes of frequency-dependent dampers with both frequency-dependent stiffness and damping. VE dampers are used for mitigation of seismic- and wind-induced structural vibration. When using VE dampers in analysis, effective modelling of the frequency-dependent characteristics of the VE damper plays a key role in accurate simulation of structural responses. Following a description of the theory behind the RPA method, the efficacy of the method is verified through several numerical examples employing VE damped structures. The results are compared with Kasai's fractional derivative model for VE dampers. Application of the RPA method to nonlinear structures is also given. The RPA method is shewn to be effective and efficient for modelling VE damped structure.

Structural reliability software at the University of California, Berkeley

The paper provides an overview of three software for structural reliability analysis developed at the University of California, Berkeley. These are CalREL, which is a general-purpose structural reliability code written in FORTRAN; FERUM, which is a collection of Matlab ® files that can be used for structural reliability analysis in conjunction with simple finite element models; and OpenSees, which is an object-oriented code for nonlinear structural response simulation with reliability capabilities. Reliability analysis methods featured by these software include FORM, SORM, Monte Carlo simulation, and various importance sampling methods. In addition, variable importance and sensitivity measures are provided.

Numerical simulation of structural responses on a sand layer to blast induced ground excitations

Intense underground explosions may cause severe damage to nearby residential, industrial and public structures. The available empirical allowable ground vibration levels to prevent damage to surface structures are usually given in terms of peak velocities (PV). There may be many ways to mitigate the ground shock effects on structures. Among the economical methods, providing a layer of a sand base is expected to effectively filter out high frequency stress waves and thereby reduce the response and damage of structures. However, very few publications are available in the unclassified literature discussing the responses of structures with a layer of a sand base subjected to blast excitations. This study performs the dynamic response analyses of structures resting on a layer of a sand base subjected to blast induced ground excitations. A previously calibrated numerical model for stress wave propagation in a rock mass is used to generate the input ground motions to the structural model. A granular material model for sand and a damage model for reinforced concrete structure are implemented into the commercial software Autodyn3D as its user subroutines for the analysis. Numerical results demonstrate that using a sand base is effective to reduce the structural response and damage to blast induced ground motions in both high and relatively low frequency ranges, even though the isolation effects tend to reduce with decrease of the ground motion principal frequency.

A spectral density approach for modelling continuous vertical forces on pedestrian structures due to walking

Existing walking models used for vibration serviceability assessment of structures carrying pedestrians are typically based on measurements of single footfalls replicated at precise intervals. This assumed perfect periodicity allows walking forces to be modelled as a Fourier series based on the walking pace and its integer multiples. This paper examines real continuous walking forces obtained from an instrumented treadmill and the effect of their random imperfections through time simulations of structural response and shows that there are significant differences between responses due to the imperfect real walking forces and the equivalent perfectly periodic simulation. These differences are most significant for higher harmonics where the simulated vibration response is overestimated. As a realistic representation of imperfect walking is an auto-spectral density function, the random character naturally leads to a stochastic approach to treatment of pedestrian loading applied in the frequency domain. The approach can be used for single pedestrians as well as crowd loading where correlation between pedestrians as well as statistics of their pacing rates is used.Key words: vibration, coherence, loading, footbridges, gait, floors, pedestrians, spectral density.

Finite Element Simulation of a Full-Scale Crash Test of a Composite Helicopter

Finite Element Simulation of a Full-Scale Crash Test of a Composite Helicopter

Simulation of structural response under high‐frequency ground excitation

AbstractThe structural response to high‐frequency ground motions is complicated due to the involvement of local‐mode vibration. At present such a characteristic is not well recognized and this can cause confusion over the analytical and experimental modelling of the corresponding response and damage. The fact that most existing regulatory guides for limits on allowable construction vibrations are necessarily simplified for administrative reasons calls upon the derivation of more sophisticated approaches for special cases. This requires accumulation of pertinent experimental evidence. This paper attempts to provide some insights into the local‐mode dynamic response characteristics, with emphasis on appropriate modelling techniques and experimental measurements. A preliminary testing program is reported, in which efforts were made to reproduce high‐frequency response with a reduced scale reinforced concrete model with shaking table facilities. The results demonstrate the dependence of the response amplitudes with the excitation frequency. On a ppv‐basis, the current test results indicate that a substantial increase of the allowable ppv value from those specified by various standards may be considered for structural damage to reinforced concrete building structures. More analytical and experimental data are needed for further evaluation of the local‐mode effects and to quantify their impact on the structural damage process. Copyright © 2001 John Wiley & Sons, Ltd.

A Reinforced Concrete Structure UnderImpact: Response To High Rate Loads

In recent years, responses of reinforced concrete (RC) structures subjected to loading from high-energy (HE) sources in their vicinity have been reported in the literature. Moreover, intensified terrorist activities have rekindled an interest in studying the response of these structures subjected to loads from both airblast and fragments. Numerical approaches for simulating structural response due to airblast loads have been addressed by many authors. Limited literature discussing numerical simulations of structural response due to fragment loads is available. Approaches simulating the response of RC structures subjected to multiple fragment impact are addressed in this study. A number of finite-element analyses using scalable hardware and software was carried out. The fragments are modeled both explicitly (actual geometric representation) and implicitly, using an equivalent loading function. Rate effects are incorporated in the constitutive models used for these analyses. Their importance is addressed in the discussion that follows. This paper discusses comparison of numerical simulation results with the experiments.

The simulation of structural response to sonic booms using structural acoustic techniques

Structural damage from sonic booms is one of the potential environmental impacts of supersonic flight. This paper illustrates how structural acoustic techniques may be used to assess the potential for such damage in the absence of actual flyovers. Procedures are described whereby transfer functions relating structural response to sonic boom signature may be obtained with a stationary acoustic source and appropriate data processing. Further, by invoking structural acoustic reciprocity, these transfer functions may also be acquired by measuring the radiated sound from a structure that is mechanically driven. The approach is based on the fundamental assumption of linearity, both with regard to the (acoustic) propagation of the boom in the vicinity of the structure and to the structure’s response. Practical issues revolve around acoustic far field, source strength, and directivity requirements. The technique was evaluated on a specially fabricated test structure at Edwards AFB, CA. Blank shots from a cannon served as the acoustic source and taps from an instrumented hammer generated the mechanical drive. Simulated response functions were constructed. Results of comparisons with corresponding measurements recorded during dedicated supersonic flyovers with F-15 aircraft are presented for a number of sensor placements. Using the prediction of peak structural response as a metric, it was found that the direct and reciprocal simulation techniques produced ensemble-averaged mean percent errors of −4% and −26%, respectively. The corresponding standard deviations of these errors were 18% and 16%. Also, it was concluded that these uncertainties are consistent with that connected to the representation of the sonic boom itself.

Friction‐Controllable Sliding Isolation System

This paper describes the experimental and analytical study of a friction‐controllable sliding base isolation system. To overcome the problems associated with conventional passive sliding isolation systems that have hindered their practical effectiveness, a hybrid sliding base isolation system is developed using friction‐controllable bearings. This innovative hybrid system uses a variable friction force that is computer controlled by changing the pressure in the fluid chamber of the bearing. The variable friction force makes the sliding isolation system more effective in controlling the structural response under earthquakes with a broad range of intensity. A prototype hybrid sliding isolation system is physically developed and tested on a shaking table using a structural model equipped with this system. Control algorithms specially developed for controlling the frictional force that has an inherent nonlinear feature are used in this study, and their effectiveness is verified. Simulation of structural response under passive or hybrid control technique shows good agreement with the experimental results.

Advances and trends in computational structural mechanics

Recent developments in computational structural mechanics are reviewed with reference to computational needs for future structures technology, advances in computational models for material behavior, discrete element technology, assessment and control of numerical simulations of structural response, hybrid analysis, and techniques for large-scale optimization. Research areas in computational structural mechanics which have high potential for meeting future technological needs are identified. These include prediction and analysis of the failure of structural components made of new materials, development of computational strategies and solution methodologies for large-scale structural calculations, and assessment of reliability and adaptive improvement of response predictions.

R/C Structures Under Impulsive Loading

A finite element method is presented to analyze the effects of airblast‐induced ground shock on shallow‐buried, flat‐roofed, reinforced concrete structures. A finite element based on Timoshenko beam theory is adopted. Material properties are defined in terms of nonlinear stress‐strain relations in each of several layers through the thickness of the element. Elastic, ideally‐plastic constitutive properties for plain concrete are cast in terms of shear‐stress/normal‐stress variables. Elastic, strain‐hardening constitutive properties are assumed for steel. Dynamic explicit and implicit and static solution algorithms are available. General two‐dimensional structures, such as rings and arches as well as boxes, can be represented. This analysis method is applied to simulation of static beam‐column tests reported by ACI Committee 318‐77. It is then applied to simulation of structural response in FOAM HEST Events 2, 3 and 4 in which shear, flexure and combined shear‐flexure damage was observed. In these post‐test...