Dynamic Analysis Procedure Research Articles

Dynamic Response of a Long-Span Concrete-Filled Steel Tube Tied Arch Bridge and the Riding Comfort of Monorail Trains

In this study, a dynamic response analysis procedure is proposed and applied to investigate the dynamic responses of a straddle-type concrete-filled steel tube tied arch bridge under train and truck loadings. A numerical model of the coupled monorail train–bridge system is established to investigate the dynamic behaviors of the bridge under moving trains. A refined three-dimensional finite element model is built for the bridge and a 15 degrees-of-freedom vehicle model is presented for the train. The numerical model is validated using in-situ test results and then used to analyze the dynamic displacement and acceleration of the bridge and the trains on the bridge. Based on the simulation results, the impact factor of the bridge is investigated and the riding comfort of the trains is evaluated. The investigation results show that the impact factor of vehicle loads reaches the maximum value when the resonance of the bridge is induced by the moving vehicles. The effect of train braking predominates the longitudinal vibration of the bridge but is negligible in the transverse and vertical directions. The vehicle speed is the dominating factor for the riding comfort of the train.

A New Procedure for Nonlinear Dynamic Analysis of Structures Under Seismic Loading Based on Equivalent Nodal Secant Stiffness

This paper presents a dynamic analysis procedure for predicting the responses of large, highly nonlinear, discontinuous structural systems subjected to seismic loading. The concept of equivalent nodal secant stiffness is adopted to diagonalize the conventional stiffness matrix of the structure. With the lumped-mass idealization, the decoupled equilibrium equations of the structure are then solved by the implicit Newmark integration method. Additionally, an incremental-iterative procedure is performed to ensure that the equilibrium conditions are satisfied at the end of each time step. The proposed analysis procedure has the advantages of both the conventional explicit and implicit integration procedures, but with their disadvantages removed. Through extensive applications, the results demonstrate that the proposed procedure is simple and robust for analyzing practical structural systems in terms of computational efficiency and stability.

A Simplified Modal Pushover Analysis-based Method for Incremental Dynamic Analysis of Regular RC Moment-resisting Frames

Incremental Dynamic Analysis (IDA) procedure is now considered as a robust tool for estimating the seismic sidesway collapse capacity of structures. However, the procedure is time-consuming and requires numerous nonlinear response-history analyses. This paper proposes a simplified Modal Pushover Analysis (MPA) procedure for IDA of RC moment-resisting frames. The proposed method uses the dynamic response of an equivalent single-degree-of-freedom (SDOF) system, characterized by a bilinear relationship between the lateral force (F) and roof-displacement (D). The F-D relationship is determined by the ‘first-mode’ pushover analysis of the structure. Four regular RC moment-resisting frames designed based on the current US building codes are selected and subjected to the proposed method. The analysis results obtained from the original MPA-based IDA method, SPO2IDA and the method proposed by Shafei et al are also presented for comparison. The performance of the proposed method is then evaluated through comparisons with the results obtained from IDAs. The results show that the proposed method is able to efficiently estimate the dynamic capacity of the example buildings for different seismic performance levels. Nonetheless like to MPA-based IDA and SPO2IDA methods less accueate results are obtained by the proposed procedure for 16% and 84% IDA fractiles in most case studies.

Evaluation of seismic collapse capacity of regular RC frames using nonlinear static procedure

The Incremental Dynamic Analysis (IDA) procedure is currently known as a robust tool for estimation of seismic collapse capacity. However, the procedure is time-consuming and requires significant computational efforts. Recently some simplified methods have been developed for rapid estimation of seismic collapse capacity using pushover analysis. However, a comparative review and assessment of these methods is necessary to point out their relative advantages and shortcomings, and to pave the way for their practical use. In this paper, four simplified pushover analysis-based methods are selected and applied on four regular RC intermediate moment-resisting frames with 3, 6, 9 and 12 stories. The accuracy and performance of the different simplified methods in estimating the median seismic collapse capacity are evaluated through comparisons with the results obtained from IDAs. The results show that reliable estimations of the summarized 50% fractile IDA curve are produced using SPO2IDA and MPA-based IDA methods; however, the accuracy of the results for 16% and 84% fractiles is relatively low. The method proposed by Shafei et al. appears to be the most simple and straightforward method which gives rise to good estimates of the median sidesway collapse capacity with minimum computational efforts.

Recursive thoughts on the simulation of the flexible multibody dynamics of slender offshore structures

In this work, the floating frame of reference formulation is used to create a flexible multibody model of slender offshore structures such as pipelines and risers. It is shown that due to the chain-like topology of the considered structures, the equation of motion can be expressed in terms of absolute interface coordinates. In the presented form, kinematic constraint equations are satisfied explicitly and the Lagrange multipliers are eliminated from the equations. Hence, the structures can be conveniently coupled to finite element or multibody models of for example seabed and vessel. The chain-like topology enables the efficient use of recursive solution procedures for both transient dynamic analysis and equilibrium analysis. For this, the transfer matrix method is used. In order to improve the convergence of the equilibrium analysis, the analytical solution of an ideal catenary is used as an initial configuration, reducing the number of required iterations.

Evaluation of Performance Levels of Zipper-Braced Frames Using Structural Damage Index

The determination of structural and nonstructural damage under earthquake excitations is usually considered as a key factor in performance-based seismic design (PBSD) methods is In this regard, various damage indices have been developed in recent years to quantitatively estimate structural damage. The aim of this study is to develop a simple method to evaluate performance levels of zipper-braced frame (ZBF) structures by using damage indices based on the results of nonlinear static and dynamic analyses. To this end, 5, 7, 10, 12 and 15 story zipper-braced frames (ZBF) are modeled and undergone to twenty different synthetic ground motion records and their damage values have been computed. In dynamic damage analysis procedure, the performance levels of the ZBF models have been computed based on the FEMA-356 standard. Considering the results of the nonlinear dynamic analyses, the correlation between FEMA-356 performance levels and damage indices has been investigated and some simplified formula is presented. On the other side, in static damage analysis approach, by using pushover analysis the performance points of ZBF models have been estimated based on capacity spectrum method (CSM) provided by ATC-40 standard. Then, the correlation between ATC-40 performance levels and some static damage indices has been investigated and some simple equations have been proposed. These relations can be utilized to estimate the performance levels of structures from damage indices. Finally, tables are represented for determination of the structural damage index values for assumed performance levels of the ZBF structures based on static and dynamic damage analysis.

Analysis and Dynamic Performance Improvement of Grid-Connected Voltage–Source Converters Under Unbalanced Network Conditions

The energy sector is moving toward an extensive utilization of distributed and renewable energy resources. Such resources are usually interfaced to power grids via voltage–source converters (VSCs). Due to the increased penetration level of VSC-interfaced resources, the utilization of interfacing VSCs to support host grids under unbalanced conditions (e.g., due to grid voltage unbalance, unbalanced load conditions and unsymmetrical faults) becomes essential. However, detailed dynamic analysis and systematic design procedure to enhance the dynamic performance of grid-connected VSCs equipped with grid-support controllers are not reported in the literature. To fill in this gap, this paper presents a detailed small-signal model and analysis of the dynamics of a grid-connected VSC equipped with the recently developed balanced positive-sequence control and positive/negative-sequence control methods to support the grid under unbalanced conditions. The effects of the short-circuit ratio, angle of the ac system impedance, and phase-locked-loop parameters on the transient behavior of the VSC are thoroughly studied and characterized. Furthermore, to improve the dynamic performance of grid-connected VSCs, a simple yet effective current-control-based compensator is developed to mitigate possible instabilities associated with the low-voltage operation. Comparative simulation and experimental results validate the theoretical analysis and the effectiveness of the proposed compensation scheme.

A combined boundary-finite element procedure for dynamic analysis of plates with fluid and foundation interaction considering free surface effect

This study combines a mixed finite element formulation and a boundary element procedure for the free vibration analysis of Mindlin plates resting on Pasternak foundation and interacting with a quiescent fluid with a free surface on the other side. The plate-foundation system is represented by a two field mixed finite element formulation, based on the Hellinger-Reissner variational principle, and the fluid-structure interaction is incorporated into the analysis through a boundary element solution. The proposed formulation provides the added mass matrix in terms of the plate deflection, which is appended into the plate equation of motion. The method is applied to the free vibration problem of circular and elliptical bottom plates of rigid fluid storage tanks supported by elastic foundation. Effects of system parameters, such as thickness to width and fluid depth ratios, foundation parameters and plate ellipticity, are extensively studied.

11.29: Updates to the ASCE‐41‐13 provisions for the nonlinear modeling of steel wide‐flange columns for performance‐based earthquake engineering

ABSTRACTPerformance‐based earthquake engineering requires numerical models that are able to reliably predict the expected component behavior of buildings under seismic excitations. The nonlinear modeling guidelines provided in ASCE‐41‐13 have historically been used in this context by practicing engineers. However, for steel wide‐flange columns, the recommendations are primarily based on experimental data that was fairly limited until recently. This paper addresses many of the limitations present in ASCE‐41‐13 for the modeling of steel wide‐flange columns. Recent experimental data from large‐ and full‐scale tests on wide‐flange steel columns, supplemented with detailed finite element studies, has been collected for a wide range of column cross‐sections and applied compressive axial loads. Multiple regression analysis is utilized to develop multivariate predictive equations for the seismic response of steel wide‐flange columns. It is found that the primary contributors that dominate the column response are the local web slenderness, member slenderness and the applied axial load ratio due to gravity loading. Guidelines for developing nonlinear component models for steel columns that can be directly used in both nonlinear static and dynamic analysis procedures are provided. The predicted responses are validated against test data that was not part of the original database. Furthermore, recommendations are proposed for modeling wide‐flange columns subjected to varying axial loads as well as bidirectional loading; and a new limit for force‐controlled elements is proposed for columns under high axial compressive loading and lateral drift demands.

A new implicit dynamic finite element analysis procedure with damping included

Abstract The concept of equivalent nodal secant damping coefficients is proposed to diagonalize the stiffness-proportional damping matrix. Additionally, a novel method is proposed to rapidly evaluate stiffness-proportional damping nodal forces for nonlinear elements on the element level. With the assumption of lumped-mass idealization an incremental-iterative procedure is performed to solve the decoupled equilibrium equations for damped systems using the implicit Newmark integration method. The proposed analysis procedure has the advantages of both traditional explicit and implicit integration methods without their disadvantages. Through extensive practical implementations, the results demonstrate that the proposed procedure is simple and robust for analyzing practical damped systems with excellent computational efficiency and stability.

Analysis of the Dynamic Characteristics of the Distillation Column of Plate Type

The relevance of the study related to the necessity to convert to “unmanned” production in a refinery and, as a consequence, we must derive a mathematical model of the high-octane gasoline process. This paper introduces a calculation procedure for modelling and dynamic analysis of a condensate disti

Behaviour factor (q) evaluation the CFS braced structures according to FEMA P695

An upgrade of the construction standards is required to promote the use of lightweight steel structures in seismic areas of Europe. European earthquake standard EN1998-1 does not provide seismic design guidelines for the energy dissipative structural typologies in lightweight steel constructions. CFS strap-braced stud wall is an all-steel solution to dissipate the seismic energy in lightweight steel constructions. In this regard, a numerical study is performed to provide suitable value of the behaviour factor (q) for CFS strap-braced stud wall following the procedures of FEMA P695. A set of fourteen archetypes, which represented the range of design parameters and building configurations are designed following the capacity design approach. Numerical models with the ability to simulate the non-linear response of archetype buildings are then developed and analysed using non-linear static and dynamic analysis procedures. A suite of 44 normalized and scaled earthquake records, representing the probable seismic hazard to the buildings, is used for the incremental dynamic analysis. Performance of archetypes is evaluated by measuring their collapse fragility. Based on the results, it is concluded that the design method used in this study and a behaviour factor (q) of 2.5 for CFS strap-braced stud wall are appropriate to be include in next edition of the Eurocodes.

Analytical fragility assessment using unscaled ground motion records

SummaryIt is desirable that nonlinear dynamic analyses for structural fragility assessment are performed using unscaled ground motions. The widespread use of a simple dynamic analysis procedure known as Cloud Analysis, which uses unscaled records and linear regression, has been impeded by its alleged inaccuracies. This paper investigates fragility assessment based on Cloud Analysis by adopting, as the performance variable, a scalar demand to capacity ratio that is equal to unity at the onset of limit state. It is shown that the Cloud Analysis, performed based on a careful choice of records, leads to reasonable and efficient fragility estimates. There are 2 main rules to keep in mind for record selection: to make sure that a good portion of the records leads to a demand to capacity ratio greater than unity and that the dispersion in records' seismic intensity is considerable. An inevitable consequence of implementing these rules is that one often needs to deal with the so‐called collapse cases. To formally consider the collapse cases, a 5‐parameter fragility model is proposed that mixes the simple regression in the logarithmic scale with logistic regression. The joint distribution of fragility parameters can be obtained by adopting a Markov Chain Monte Carlo simulation scheme leading directly to the fragility and its confidence intervals. The resulting fragility curves compare reasonably with those obtained from the Incremental Dynamic Analysis and Multiple Stripe Analysis with (variable) conditional spectrum–compatible suites of records at different intensity levels for 3 older reinforced concrete frames with shear‐, shear‐flexure‐, and flexure‐dominant behavior.

CO2 emissions and economic growth in sub-Saharan African countries: A panel data analysis

This paper examines the causal relationship between CO2 emissions and economic growth in 10 sub-Saharan African (SSA) countries. This study attempts to answer one critical question: does economic growth Granger-cause CO2 emissions in SSA countries? Unlike some of the previous studies, this paper uses a dynamic panel data analysis procedure to examine this linkage. The results of the error-correction model (ECM)-based panel causality show that there is a unidirectional causal flow from economic growth to CO2 emissions in the 10 studied countries. This applies irrespective of whether the causality is tested in the short run or in the long run. These findings have important implications. They demonstrate that CO2 emissions mitigation policies are unlikely to have any adverse effects on these countries’ long-term growth paths. This implies that these countries can pursue CO2 emission reduction policies without necessarily compromising their quest for a long-term positive growth trajectory.

Seismic assessment of concrete buildings reinforced with shape memory alloy materials in different stories

SummaryShape memory alloy (SMA) is a unique material with many beneficial characteristics such as superelasticity and excellent resistance against corrosion. However, the high expenses related to the material costs and difficulties associated with implementation of SMAs in reinforced concrete (RC) structures may limit their usage. To decrease the costs related to SMA installation, this paper investigates the seismic performance of RC moment‐resisting frames with the intention of specifying the optimal stories for SMA utilization. To this end, RC frames with 3, 5, 7, and 9 stories are modeled and various cases are considered for SMA locations in different story levels. For each building, 4 different cases are considered including a frame with regular steel reinforcement (Steel), a frame with SMAs in all story levels (full SMA), and 2 remaining cases consist of frames with SMAs in bottom and middle story levels only. In the first part, nonlinear dynamic time history analyses are conducted to evaluate the base shear, roof displacement, interstory, and residual drift demands of the structures using 10 ground‐motion records. In the second part, the incremental dynamic analysis is employed to assess the entire range of structural dynamic behavior. By using the generated data from incremental dynamic analysis procedure, fragility evaluation is conducted on multiple limit states to provide a comprehensive performance assessment for each case. The results indicate that frames with SMA in their lower story levels performed similar to frames equipped with SMA in all story levels. However, the fragility assessments show the better performance of frames with SMA in their bottom stories versus other cases. On this basis, the costs associated with SMA fabrication could be reduced noticeably (nearly two‐thirds) without sacrificing the overall performance of the frame and its post‐earthquake serviceability.

Seismic evaluation of a steel braced frame using NBCC and ASCE 41

The article presents the seismic evaluation and retrofit of a 10-storey steel building located in Vancouver, British Columbia, designed following the provisions of the 1980 NBCC and the CSA-S16.1-M78 steel design standard. Lateral resistance is achieved by tension-only X-bracing with back-to-back double angle members. Seismic evaluation is first performed in accordance with the recommendations of the User's Guide to NBCC 2010 using response spectrum analysis. A Tier 3 systematic evaluation according to ASCE 41-13 is then carried out using both linear and nonlinear dynamic analysis procedures. The performance objectives are set same as those implied in NBCC 2010. The ASCE 41 approach results in much less corrections to the structure. Using the mean results from 10 ground motions is also less stringent than using the maximum of three records. For this structure, nonlinear dynamic analysis permitted to identify the concentration of inelastic deformations demands on the braces along the frame height. This behaviour induced considerable bending moment demands on the columns not captured by linear dynamic analysis. Finite element analysis of the structure columns showed that columns of braced steel frames can exhibit higher ductility compared to acceptance criteria specified in ASCE 41.

Behaviour during seismic aftershocks of r.c. base-isolated framed structure with fire-induced damage

Fire following strong earthquakes is considered a very high-risk event and a fire-damaged structure could be subjected to seismic aftershocks. Most probably damage produced by the main shock will be absent in case a base-isolation system is adopted. To study the post-fire seismic performance a numerical study is presented on six-storey reinforced concrete (r.c.) framed structures, composed of a basement with elastomeric bearings and five storeys above the ground level. Three fire scenarios are compared, selecting the base-isolated level (i.e. F0) and first (i.e. F1) and fifth (i.e. F5) levels of the superstructure as fire compartments. A reduction of the mechanical properties of the fire-damaged elastomeric bearings is considered in accordance with a proposed 200°C isotherm method. To this end, transient response of the elastomeric bearings corresponding to the Eurocode 1 time-temperature curve, is compared with steady response, defined as a heat conduction problem of a constant flux in an infinite circular cylinder. Reduced mechanical properties of r.c. cross-sections are considered by means of a thermal-mechanical mapping analysis, in accordance with the 500°C isotherm method in the Eurocode 2. The nonlinear seismic analysis is performed by using a lumped plasticity model to describe the inelastic behaviour of the r.c. frame members; a nonlinear force-displacement law is considered for the elastomeric bearings, with coupling of horizontal and vertical motions. Near-fault seismic aftershocks, inducing severe demand in base-isolated buildings, are scaled within an incremental dynamic analysis procedure.

Cyclic characterization of wave-induced oscillatory and residual response of liquefiable seabed

The paper presents a robust modeling method for a fully coupled effective stress analysis of the wave-induced liquefaction scenarios, based on the Biot consolidation theory. In this context, emphasis is placed on the implementation of a well-calibrated cyclic soil model and an empirical shear-volume coupling equation, which links the increment of volumetric strain per cycle of wave with the shear strain occurring during that particular cycle. Unlike most of the previous investigations using the amplitude of shear stress over the wave period (or the phase-resolved oscillatory shear stresses) as the source term for calculating the residual pore pressure, in this study, the source term is related to the rate of plastic volumetric deformation and implemented into the Biot consolidation equation to consider both generation and partial dissipation of excess pore pressure during wave propagation. Then, the proposed modeling method is incorporated into a dynamic finite difference analysis procedure. Model calibrations are carried out in terms of individual soil element behavior and seabed response under progressive waves, respectively. Overall good agreement demonstrates the reliability of the modeling method for the prediction of wave-induced seabed response. Finally, the paper highlights the potentials of proposed modeling framework to simulate the basic features of wave-induced seabed response (i.e., the coupling of progressive buildup of pore pressure and cyclic softening of soil skeleton), by means of numerical examples. The obtained results show that the cyclic behavior of liquefiable seabed under wave actions can be well captured by the proposed model.

Seismic behavior of two monumental buildings in historical Cappadocia region of Turkey

This study focuses on a displacement-based approach for the investigation of seismic behavior of two monumental buildings constructed in the historical Cappadocia region of Turkey. The first historic building is located in the town of Konakli, which is 27 km away from the city of Nigde and is situated in north-east of the city. It was built in 1844 and has served as a temple. The second building is located in the town of Fertek, 2 km from the city of Nigde. It has been used as a temple since it was built in 1835. These two buildings are seen as representative of many similar temple buildings constructed in the Cappadocia region during the same era. The seismic behavior of these two monumental buildings is investigated using dynamic analysis procedures. The buildings are subjected to ground motion records obtained during recent earthquakes in Turkey. These ground motions were recorded during the Ceyhan earthquake of 1998, which occurred close to Nigde; the Marmara earthquake of 1999 and the Duzce earthquake of 1999. Dynamic analyses are conducted for two cases with and without walls, as this helps in identification of the effect of structural walls on the seismic behaviors of these buildings. In the light of the dynamic analyses results, the expected level of damage and structural irregularities of the monumental buildings are examined. It is observed that slab discontinuities on the first floors constitute a major element in the expected structural damage for both buildings. Destructive levels of deformation are observed at Konakli in the roof domes of the building. In addition, upon application of certain ground motions, destructive levels of drift are observed, another element contributing to the expected damage.

Economic losses due to earthquake - induced structural damages in RC SMRF structures

AbstractThis study presents the seismic performance assessment of reinforced concrete frame structures designed to modern buildings codes, for calculating the economic losses due to earthquake-induced structural damages. The structures investigated in the present research considered four (3, 5, 8, and 10 storeys) prototype special moment resisting frame (SMRF) structures designed to Uniform Building Code–97/Building Code of Pakistan. Quasi-static cyclic tests were carried out herein on special moment resisting beams in order to develop damage scale and beam reparability cost ratio. The considered structures were analyzed in a calibrated FE based software SeismoStruct using incremental dynamic analysis procedure employing a set of seven natural design spectrum compatible ground motion records. Damage to structural components was identified for each intensity level and integrated over the whole structure, with the required repair cost, to calculate the structure repair cost ratio (RCR). The structure RCR is...