Results Of Incremental Dynamic Analysis Research Articles

Seismic reliability assessment of steel moment-resisting frames using Bayes estimators

The aim of this study was to develop an efficient probability-based seismic fragility assessment method for steel moment-resisting frames (MRFs). In this method, Bayes estimators are used to improve the accuracy of the results based on new analyses or experimental observations. The efficiency of Bayes estimators in the updating process of fragility curves is demonstrated based on the results of incremental dynamic analysis of three-, five- and seven-storey steel MRFs under a set of 40 spectrum-compatible earthquake ground motions. The results indicate that the constant-hazard-level (engineering demand parameter based) fragility analysis approach leads to less than 6% error in the prediction of performance levels and therefore can be considered a competent alternative to the more computationally expensive constant-performance (intensity measure based) approach. While the earthquake duration can considerably affect the results of fragility analysis, the prediction errors can be reduced to an acceptable level through selection of four different time intervals with at least three records in each group. It is also concluded that Bayes estimators can generally provide a very good level of accuracy in updating fragility curves by reducing the maximum errors to less than 2.5% compared with the exact values.

Behavior factor of concrete portal frames with dissipative devices based on carbon-wrapped steel tubes

The key element characterizing the seismic vulnerability of existing prefabricated RC structures, not designed for earthquake actions, are friction-based connections between structural members; mainly those between beams and columns and beams and roofing beams. The paper discusses the effectiveness of dissipative connectors made of carbon wrapped steel tubes. In particular, it presents the results of Incremental Dynamic Analyses on portal frames, aimed at evaluating behavior factor values to be used in design. A simplified formula for estimating the behavior factor is also proposed. Results of nonlinear IDAs suggest that the introduction of these dissipative devices in friction-based beam-column joints provides an effective connection between structural members and, in addition, reduces the forces transmitted to columns, improving the seismic behavior of the entire structure.

Performance-based wind design of tall buildings: concepts, frameworks, and opportunities

One of the next frontiers in structural wind engineering is the design of tall buildings using performance-based approaches. Currently, tall buildings are being designed using provisions in the building codes and standards to meet an acceptable level of public safety and serviceability. However, recent studies in wind and earthquake engineering have highlighted the conceptual and practical limitations of the code-oriented design methods. Performance-based wind design (PBWD) is the logical extension of the current wind design approaches to overcome these limitations. Towards the development of PBWD, in this paper, we systematically review the advances made in this field, highlight the research gaps, and provide a basis for future research. Initially, the anatomy of the Wind Loading Chain is presented, in which emphasis was given to the early works of Alan G. Davenport. Next, the current state of practice to design tall buildings for wind load is presented, and its limitations are highlighted. Following this, we critically review the state of development of PBWD. Our review on PBWD covers the existing design frameworks and studies conducted on the nonlinear response of structures under wind loads. Thereafter, to provide a basis for future research, the nonlinear response of simple yielding systems under long-duration turbulent wind loads is studied in two phases. The first phase investigates the issue of damage accumulation in conventional structural systems characterized by elastic-plastic, bilinear, pinching, degrading, and deteriorating hysteretic models. The second phase introduces methods to develop new performance objectives for PBWD based on joint peak and residual deformation demands. In this context, the utility of multi-variate demand modeling using copulas and kernel density estimation techniques is presented. This paper also presents joined fragility curves based on the results of incremental dynamic analysis. Subsequently, the efficiency of tuned mass dampers and self-centering systems in controlling the accumulation of damage in wind-excited structural systems are investigated. The role and the need for explicit modeling of uncertainties in PBWD are also discussed with a case study example. Lastly, two unified PBWD frameworks are proposed by adapting and revisiting the Wind Loading Chain. This paper concludes with a summary and a proposal for future research.

Life-cycle seismic resilience assessment of highway bridges with fiber-reinforced concrete piers in the corrosive environment

The benefit of fiber-reinforced concrete (FRC) to the life-cycle seismic performance of the bridge has not yet been fully studied. A probabilistic methodology was proposed in this study for the life-cycle performance assessment of deteriorating bridges constructed with FRC piers. The effect of the corrosive environment on the seismic performance of FRC bridges was evaluated under uncertainty through the seismic resilience analysis. The time-variant seismic capacity from different limit states was employed to estimate the functionality loss before the occurrence of the seismic event in order to improve the estimate of seismic resilience. A method was proposed to improve the accuracy of Cloud Analysis for the seismic fragility analysis, which was validated by the results of Incremental Dynamic Analysis (IDA). Seismic fragility analysis was then conducted by the improved Cloud Analysis based on numerical finite element models for simulating the behavior of FRC to obtain the reliable fragility estimates. The whole methodology in this paper was illustrated using a two-span highway bridge with conventional RC and FRC piers considering both diffusion process and seismic hazards. It can be concluded from the results that the FRC can improve the life-cycle seismic performance and resilience of highway bridges by around 25%. The performance benefit from the FRC can be underestimated if not considering the life-cycle effect. The improved Cloud Analysis is proved to be efficient and reliable in the seismic fragility analysis of bridges.

Seismic vulnerability assessment of RC buildings according to the 2007and 2018 Turkish seismic codes

Fragility curves are useful tools to estimate the damage probability of buildings owing to seismic actions. The purpose of this study is to investigate seismic vulnerability of reinforced concrete (RC) buildings, according to the 2007 and 2018 Turkish Seismic Codes, using fragility curves. For the numerical analyses, typical five- and seven-storey RC buildings were selected and incremental dynamic analyses (IDA) were performed. To complete the IDAs, eleven earthquake acceleration records multiplied by various scaling factors from 0.2g to 0.8g were used. To predict nonlinearity, a distributed hinge model that involves material and geometric nonlinearity of the structural members was used. Damages to confined concrete and reinforcement bar of structural members were obtained by considering the unit deformation demands of the 2007 Turkish Seismic Code (TSC-2007) and the 2018 Turkey Building Earthquake Code (TBEC-2018). Vulnerability evaluation of these buildings was performed using fragility curves based on the results of incremental dynamic analyses. Fragility curves were generated in terms of damage levels occurring in confined concrete and reinforcement bar of structural members with a lognormal distribution assumption. The fragility curves show that the probability of damage occurring is more according to TBEC-2018 than according to TSC-2007 for selected buildings.

Seismic collapse capacity assessment of SDOF systems incorporating duration and instability effects

This paper presents a detailed investigation into the seismic response of non-deteriorating and deteriorating single degree-of-freedom systems controlled by P -Delta effects, with due account for the influence of earthquake duration. In order to isolate the effect of duration from other ground motion characteristics, 77 pairs of records with equivalent spectral shapes are considered in the study. The structural characteristics examined include the structural period, applied gravity loading, post-yield stiffness, viscous damping, material hysteretic behaviour, as well as the level of cyclic deterioration within the pinching systems. Detailed incremental dynamic analyses are carried out, considering an intensity measure corresponding to the spectral acceleration at the structural period of vibration of the system. Based on the incremental dynamic analysis results, predictive relationships are proposed for determining the structural collapse capacity, accounting for the influence of key parameters including instability and duration effects. The median and dispersion of the collapse capacity distribution embedded in the predictive models are also presented. The effect of duration is shown to increase with longer structural periods and to decrease with higher P -Delta levels. The more rapid instigation of dynamic instability in relatively stiff systems is also shown to reduce their comparative sensitivity to variations in ground motion characteristics. Overall, it is indicated that disregarding the influence of duration could lead to over-estimations of up to 50% in the collapse capacity. The paper concludes with a discussion of other sources of structural damage that instigate collapse when using records with equivalent spectral shape but without especial consideration for duration effects.

Value based seismic design of structures using performance assessment by the endurance time method

A framework for optimal seismic design of structures, considering maximum value as the design objective, is introduced. In this framework, the value parameter incorporates a comprehensive set of performance indicators. Decision indicators are mapped into equivalent economic values and are directly involved in the design process. This approach leads to optimal assignment of the available resources to meet infrastructure requirements. The construction cost and the risk of seismic consequences are considered as the value components. FEMA-P58 methodology is utilized in estimation of the seismic consequences including the repair cost, repair time, injuries and casualties. Endurance Time method is employed as an efficient procedure for estimating the engineering demand parameters at different seismic hazard levels. The applicability of the Endurance Time method is verified and compared to the results of Incremental Dynamic Analysis. The proposed design procedure is employed in design optimization of two multi-story buildings. Design outcomes are compared to the outcome of the conventional code-based design procedure minimizing the structural construction cost, in terms of seismic response and consequences. The value-based design approach considerably increases the total economic value of the studied structures. The code-based design in the studied cases is found substantially sub-optimal considering the maximum achievable value.

Artificial Ground Motions and Nonlinear Response of RC Structures

The selection of seismic inputs for nonlinear dynamic analysis is widely debated, mainly focusing on the advantages and disadvantages provided by the choice of natural, simulated, or artificial records. This work proves the differences in the structural behavior of RC buildings when using accelerograms with different levels of stationarity. Initially, nonlinear response under three sets of accelerograms equivalent in terms of pseudo acceleration spectrum is evaluated and compared. Then, the results of incremental dynamic analyses are compared by the statistical point of view considering different levels of irregularity for the reference structure.

Soil-pile-superstructure interaction effects in seismically isolated bridges under combined vertical and horizontal strong ground motions

This paper presents a deterministic analysis carried out to study the influence of coupled vertical and horizontal ground motions on the response of an isolated bridge (or soil-pile-bridge system) considering soil-pile-superstructure effects. Towards this end, an advanced 3D finite element model is developed to evaluate the effects of combined Vertical Component (VC) and Horizontal Component (HC) of ground motion on the structural elements of the bridge including Soil Structure Interaction (SSI). Non-linear time-history analysis is carried out under strong ground motions using an advanced soil plasticity model for non-liquefiable soil. Three different bridge configurations consisting of (i) simply-supported girders (SSERB), (ii) continuous girder with fixed bearing (CFB) and (iii) continuous girder with elastomeric bearing (CERB) are considered. Ground motion selection procedure was applied among 21,000 records to select suitable ground motions for nonlinear time-history analysis. Critical damage parameters in the structural elements under the combined HC and VC of the ground motion are compared with those under only the HC of the ground excitation. Results indicate that the vertical components produce significant amplification in the pier's axial load with different lower and upper bounds for different seismic isolation systems. The Influence of higher modes on results of Incremental Dynamic Analysis (IDA) are presented for the different structural elements in a deterministic framework. The variations of shear capacity and demand are presented by IDA and the combined spectral acceleration is implemented as an Intensity Measure (IM) due to the inclusion of higher order modes. The simply-supported and continuous girder with elastomeric bearings have a trend for a higher drift ratio than the continuous girder with the fixed-bearings system under vertical excitation. Furthermore, the variation of axial loads and pile-cap displacements are highlighted with and without VC for piles at piers and abutments. In addition, pile-cap displacements, influence of bridge higher modes and VC effects on Soil-Pile-Superstructure Interaction (SPSI) relations are investigated with respect to frequency content of the ground motion. The kinematic and inertial SPSI effects on seismic isolation systems including VC are also explored comparatively. The influence of elastomeric bearing on SSI reduction was investigated by comparing the relative response of the superstructure, Free-Field and Foundation Input Motion (FIM) at the pile head in the frequency domain. The new information presented in this paper will be useful for realistic design of bridges in seismic areas considering coupled HC and VC of the seismic excitation.

Seismic capacity of steel frames braced with cross-concentric rectangular plates: Non-linear analyses

The use of cross-concentric braced steel frames is still an effective way to realize earthquake-resistant buildings, thanks to the simplicity in the design and realization, assuring good strength, stiffness and ductility, provided that capacity design be fulfilled. Results from non-linear static and dynamic analyses of steel frames braced with cross-concentric rectangular plates are presented to discuss some significant design aspects that play a key-role in the definition of the hysteretic dissipative response of such structures. Parametric cyclic analyses were performed to assess the peak- and post-buckling lateral strength and the dissipative capacity of a small- and a full-scale frame, varying the non-dimensional slenderness of the bracing plates. Then, results of incremental dynamic analyses of a one-, three-, six- and ten-storey building are discussed to evaluate the behaviour factor for this structural typology, as function of inter-storey drift. Results from the parametric and incremental analyses give the optimal range of non-dimensional slenderness of the bracing plates as a compromise between limited overstrength and good dissipative capacity and confirm the behaviour factor currently provided by Eurocode, relating it with an expected inter-storey lateral drift.

Seismic Fragility Assessment of Steel SMRF Structures under Various Types of Near and Far Fault Ground Motions

In this paper, the seismic collapse probability of special steel moment-resisting frame (SSMRF) structures, designed to 4th edition of Iranian seismic design code, under near fault pulse-like and far fault ordinary ground motions is evaluated through fragility analysis. For this purpose, five sample frames with 3 to 15 stories are designed and imposed to the ground motion excitations with different characteristics. Fragility curves are derived for the sample frames using the results of incremental dynamic analyses. Three sets of near fault ground motion records with different range of pulse period and one set of far fault ordinary records are used in dynamic analyses. Each record set involves ten acceleration time histories on soil type III. Based on the obtained results, it was found that pulse-like motions with medium- and long-period pulses are significantly more destructive than other types of ground motions. Fragility analysis reveals that the average collapse probability for the case study frames under the far and near fault ground motions at the intensity of 0.35g equals to 4.3% and 10.3%, respectively. These values are 15.9%and 38.6%, for PGA of 0.53g. It is also found that the increase in the height, leads to increase in higher modes effect to transfer drift demands toward upper stories.

Seismic fragility assessment of a multi-span RC bridge in Bangladesh considering near-fault, far-field and long duration ground motions

Seismic vulnerability of a three-span continuous highway bridge located in Kishoreganj, Bangladesh is assessed numerically in this study. Fragility curves have been derived from the nonlinear incremental dynamic analysis results of the bridge subjected to medium to strong near-fault, far-field and long duration ground motions. This study aims to investigate the damage probability of bridge components (piers and isolation bearings) and the bridge system under different types of ground motions. A total of 48 near-fault, far-field, and long duration ground motion records with peak ground acceleration values ranging from 0.08 g to 2.31 g are used in the nonlinear dynamic analysis of the bridge. A 3-D finite element model scheme is used in this study considering nonlinearity in the bridge piers and the elastomeric isolation bearings. The fragility curves are constructed for two bridge components (i.e., piers and isolation bearings), and the system as well. The numerical results show that both component levels and bridge system failure probabilities are dominated by long duration ground motions than those of near-fault and far-field ground motions.

Seismic Performance Evaluation of Liquid Storage Tanks Using Nonlinear Static Procedures

A simplified approach is presented for the seismic performance assessment of liquid storage tanks. The proposed methodology relies on a nonlinear static analysis, in conjunction with suitable “strength ratio-ductility-period” relationships, to derive the associated structural demand for the desired range of seismic intensities. In the absence of available relationships that are deemed fit to represent the nonlinear-elastic response of liquid storage tanks, several incremental dynamic analyses are performed for variable post-yield hardening ratios and periods in order to form a set of data that enables the fitting of the response. Following the identification of common modes of failure such as elephant's foot buckling (EFB), base plate plastic rotation, and sloshing wave damage, the aforementioned relationships are employed to derive the 16%, 50%, and 84% percentiles for each of the respective response parameters. Fragility curves are extracted for the considered failure modes, taking special care to appropriately quantify both the median and the dispersion of capacity and demand. A comparison with the corresponding results of incremental dynamic analysis (IDA) reveals that the pushover approach offers a reasonable agreement for the majority of failure modes and limit states considered.

Seismic Reliability Analysis of Offshore Fixed Platforms Using Incremental Dynamic Analysis

It is generally accepted that performance-based design has to be reliability-based. Seismic performance evaluation is based on nonlinear dynamics and reliability theory taking into account uncertainties during analysis. Considering the economic importance of jacket type offshore platforms, the present research aims to assess the seismic performance of offshore steel platforms. In this study, three platforms located in the Persian Gulf were modeled using three dimensional structural modeling tools. Each platform was modeled and analyzed using both rigid and pinned connections. Reliability analysis was performed in accordance with Federal Emergency Management Agency (FEMA) guidelines using the results of incremental dynamic analysis for the three platforms. The results showed that platforms possessing rigid connections provide the desired confidence level of FEMA for the performance level of collapse prevention while only one platform with pinned connections was able to provide the desired confidence level.

Development of hysteretic energy compatible endurance time excitations and its application

The aim of this study is to develop a new simulation procedure of endurance time excitations in which hysteretic energy compatibility is included. Existing methods for simulating excitations consider only amplitude and frequency content of motions and disregard parameters related to cumulative damage of structures. Hysteretic energy consistency, as a cumulative damage-related parameter, is included in the process. The proposed method is applied to generate new excitations. Efficiency of the proposed method is examined in two ways: (1) comparing damage spectra of simulated excitations with recorded ground motions; (2) applying simulated excitations in seismic assessment of three concrete special moment frame structures. Results show considerable compatibility of damage spectra with time history analysis as compared to previous excitations and, therefore, imply an improvement in the simulation process. In the second examination, engineering demand parameters in terms of maximum values and distribution of responses over structural height are predicted by the endurance time analysis and, then, are compared with incremental dynamic analysis results. These comparisons show that the endurance time method can successfully predict seismic demands of structures using the new generated excitations in comparison with existing ones. Finally, it is deduced from results that the proposed method can be employed as an alternative simulation approach for new applications.

Seismic fragility analysis of pre-1975 conventional concrete frame buildings in Canada

Fragility analysis was conducted for reinforced concrete frame buildings in Canada designed based on the 1965 National Building Code of Canada as representative of pre-1975 era of seismic design practice. Two-, five-, and ten-storey buildings were designed for Vancouver and Ottawa, representing buildings in high and medium seismic regions. They were modelled for inelastic response time history analysis, with respective inelastic hysteretic models for flexure and shear. Software PERFORM-3D was used to conduct incremental dynamic analysis under incrementally increasing earthquake intensity. Probabilistic analysis of the results of incremental dynamic analysis led to the development of fragility functions, which can be used as seismic vulnerability assessment tools. The results are compared with those generated for frame buildings designed on the basis of the 2010 NBCC. The comparison indicates that the probabilities of exceeding performance levels are significantly higher for older buildings relative to recently built fully ductile and moderately ductile buildings, respectively.

The Effects of Viscous Damping Modeling Methods on Seismic Performance of RC Moment Frames Using Different Nonlinear Formulations

Nonlinear response history analysis, contributing to seismic performance assessment, is a constructive tool for evaluating buildings' behavior and damages due to the earthquake. Applying an accurate viscous damping model constitutes a crucial part in this regard. The seismic response and performance of two reinforced concrete moment frames considering various damping modeling techniques and nonlinear elements are investigated. Two basic approaches to consider nonlinearity are selected: distributed and concentrated plasticity, using force and displacement-based fiber elements and elements that contain two end springs and elastic parts to which zero and modified initial stiffness proportional damping are allocated respectively. Rayleigh damping with mass and four different stiffness matrices are applied in fiber elements. The results of Incremental Dynamic Analysis and loss estimation, considering performance-based earthquake engineering methodology, indicate that Rayleigh damping with mass and initial stiffness overestimates collapse capacity and underestimates performance parameters, while, the model with mass and tangent stiffness with updated proportionality terms shows the opposite trend. In concentrated plasticity models, the more flexible the springs, the more conservative the evaluation of building performance.

Sensitivity of Seismic Response and Fragility to Parameter Uncertainty of Single-Layer Reticulated Domes

Quantitatively modeling and propagating all sources of uncertainty stand at the core of seismic fragility assessment of structures. This paper investigates the effects of various sources of uncertainty on seismic responses and seismic fragility estimates of single-layer reticulated domes. Sensitivity analyses are performed to examine the sensitivity of typical seismic responses to uncertainties in structural modeling parameters, and the results suggest that the variability in structural damping, yielding strength, steel ultimate strain, dead load and snow load has significant effects on the seismic responses, and these five parameters should be taken as random variables in the seismic fragility assessment. Based on this, fragility estimates and fragility curves incorporating different levels of uncertainty are obtained on the basis of the results of incremental dynamic analyses on the corresponding set of 40 sample models generated by Latin Hypercube Sampling method. The comparisons of these fragility curves illustrate that, the inclusion of only ground motion uncertainty is inappropriate and inadequate, and the appropriate way is incorporating the variability in the five identified structural modeling parameters as well into the seismic fragility assessment of single-layer reticulated domes.

Damage states of yielding and collapse for elevated water tanks supported on RC frame staging

Elevated water tanks are inverted pendulum type structures where drift limit is an important criterion for seismic design and performance evaluation. Explicit drift criteria for elevated water tanks are not available in the literature. In this study, probabilistic approach is used to determine maximum drift limit for damage state of yielding and damage state of collapse for the elevated water tanks supported on RC frame staging. The two damage states are defined using results of incremental dynamic analysis wherein a total of 2160 nonlinear time history analyses are performed using twelve artificial spectrum compatible ground motions. Analytical fragility curves are developed using two-parameter lognormal distribution. The maximum allowable drifts corresponding to yield and collapse level requirements are estimated for different tank capacities. Finally, a single fragility curve is developed which provides maximum drift values for the different probability of damage. Further, for rational consideration of the uncertainties in design, three confidence levels are selected and corresponding drift limits for damage states of yielding and collapse are proposed. These values of maximum drift can be used in performance-based seismic design for a particular damage state depending on the level of confidence.

Seismic collapse assessment of self‐centering hybrid precast walls and conventional reinforced concrete walls

The past studies have demonstrated the superior performance of self‐centering hybrid precast (SCHP) walls in terms of reducing structural damage and residual drifts compared with conventional reinforced concrete (RC) walls following an earthquake. This study evaluates the collapse performance of SCHP walls through numerical analyses, and compares the results with that of RC walls. For this purpose, analytical models of code compliant four‐story and six‐story prototype SCHP and RC wall structures designed with varying structural and seismic parameters were developed. Based on the results of incremental dynamic analysis, the adjusted collapse margin ratio (ACMR) of each prototype structure was determined and compared to the established limits specified in the FEMA P695 procedure. The results reveal that the collapse capacities for the SCHP walls are comparable to that of RC walls. The slightly larger collapse margin ratio for the six‐story RC wall over the six‐story SCHP wall might be attributed to the less sufficient energy‐dissipating capacity of the SCHP wall as demonstrated by the cyclic pushover analyses. It is found that the computed ACMRs (ranging from 3.13 to 3.79) are more than twice the accepted ACMR limit (1.56), indicating that all the structures have enough seismic collapse safety against maximum considered earthquakes.