Nonlinear Dynamic Time History Analyses Research Articles

Determination of dynamic collapse limit states using the energy-based method for multi-story RC frames subjected to column removal scenarios

The Alternative Load Path method is widely adopted to perform progressive collapse analyses for reinforced concrete (RC) frame structures subjected to column removal scenarios. Considering that the progressive collapses are usually dynamic phenomena, nonlinear dynamic analyses can yield the most accurate results. However, the associated computational cost is high. Alternatively, the energy-based method (EBM) can be employed to efficiently calculate the maximum dynamic responses. Unfortunately, collapse or dynamic limit states (DLS) cannot be directly determined when the EBM is adopted for the progressive collapse analyses, because it is essentially a quasi-static approach. To tackle this issue, in this paper an EBM-Intersection Point-based (EBM-IP-based) method is proposed to effectively determine the DLS. The method is considering that the dynamic instability will occur once the dynamic capacity curve exceeds the corresponding static capacity curve. Hence, it is possible to determine the DLS by making a correction on the intersection point of the aforementioned two curves without performing nonlinear dynamic time-history analyses. Compared with the other energy components, the kinetic energy at the moment of the peak displacement response is relatively small and the effectiveness of the EBM is verified. Through both static pushdown analyses and incremental dynamic analyses for 48 column removal scenarios of six different multi-story RC frames, the effectiveness of the proposed EBM-IP-based method is verified and the associated coefficients are calibrated. Statistical information and (joint) probabilistic density functions (PDF) of the coefficients are identified. Further, stochastic analyses are carried out in order to quantify the model uncertainties when adopting the EBM-IP-based method. On the basis of all the calculation results, a Gumbel distribution is adopted to capture the PDF of the model uncertainty in relation to displacements, while a lognormal distribution is adopted to fit the PDF of the model uncertainty in terms of resistances. Moreover, a multi-variate Gaussian distribution model with two components is employed to fit the joint PDF.

Seismic performance of recentering energy dissipation bracing with pendulum in prefabricated steel frame structure systems

This research introduces the recentering energy dissipation bracing with a pendulum in prefabricated steel frame (REBP-PSF) structures. The primary objective of this study is to mitigate potential severe damage to steel frames during seismic events and to expedite postearthquake rehabilitation. This innovative system harnesses energy dissipation through friction between structural members and facilitates recentering through the cable pretensioning force. Consequently, this may make postearthquake repairs minimal or even unnecessary. Three REBP-PSF structures and a prefabricated steel frame with cantilever beam splices (PSF-CBS) were meticulously modeled using the ABAQUS finite element method to evaluate the seismic performance of this novel system. The study investigated the effects of pretensioning parameters and varied structural morphologies on seismic performance metrics, including failure modes, hysteresis performance, energy dissipation capacity, and residual displacements. This paper introduced a simplified method to simulate the restoring force model of REBP using the connection element method. Subsequently, a model for the REBP-RSF overall structure was established, enabling nonlinear dynamic time-history analysis, which was then compared with the rigid steel frame (RSF) structure. The results showed that the REBP-PSF structure outperformed the PSF-CBS in terms of initial stiffness, yield load, ultimate load, and energy dissipation capability. The bearing and energy dissipation capacities of the REBP-PSF structure were enhanced by augmenting the cable pretensioning force within this structure. The proposed connection element method could accurately simulate the hysteretic behavior of REBP. Compared with the RSF structure, the REBP-RSF demonstrated superior seismic performance, characterized by small story drift and residual displacements during seismic activities. Furthermore, a notable augmentation was observed in the lateral stiffness and torsional rigidity of the proposed structure.

Study on the mechanical properties of a viscoelastic self-centering brace with rotational displacement amplification and its application in RC frames

This paper introduces a novel viscoelastic self-centering brace with a rotational displacement amplification function (VSB-RA), developed to address the issue of limited energy dissipation in traditional self-centering braces. The basic structure and working mechanism of the VSB-RA are detailed. Low-cycle reciprocating loading tests were performed on two types of VSB-RA specimens with different initial amplification angles, and a comprehensive analysis was conducted on their bearing capacity, energy dissipation performance, self-centering capability, and frequency correlation. A refined finite element model was developed in ABAQUS software to simulate the complete test loading process. Nonlinear dynamic time history analysis is then performed on an 8-story reinforced concrete (RC) frame structure with the VSB-RAs using different initial amplification angles. The results demonstrate that the hysteresis curves of the VSB-RA exhibit distinct flag-shaped characteristics and excellent self-centering performance, and its energy dissipation capacity increases exponentially with the decrease of the initial amplification angle. The numerical simulation results of the hysteresis curves align well with experimental findings. The inter-story drift, residual inter-story drift, floor acceleration, and base shear force are effectively controlled in the VSB-RA frame structures compared to the uncontrolled structure. Under rare earthquake actions, the base shear forces of the structure are reduced by 27.2 %, 27.9 %, and 30.7 % at initial amplification angles of 45°, 37.5°, and 30°, respectively.

Fragility Analysis and Resilience Assessment of the Single-Column Pier Steel-Concrete Composite Bridge Subjected to Seismic Loads

Abstract With the advantages of a small footprint, wide under-bridge view, and beautiful appearance, single-column pier bridges are widely used in urban bridge networks. However, single-column pier bridges are prone to damage during earthquakes or heavy vehicle use, which can seriously affect normal operations and postdisaster recoveries. Therefore, there is an urgent need to carry out seismic resilience assessments of single-column pier bridges and formulate disaster prevention and mitigation measures from the aspects of design, maintenance, and postearthquake recovery. This paper first establishes a resilience assessment framework for the single-column pier bridge and optimizes a functionality recovery model after an earthquake. Then, a numerical model of a sample bridge is built for resilience fragility analysis. Nonlinear dynamic time history analysis is performed to build a probabilistic seismic demand model, and moment–curvature analysis is performed to build a probabilistic seismic capacity model. Finally, a seismic resilience assessment of the single-column pier bridge is obtained based on the seismic fragility, and a sensitivity analysis is carried out for the pier height, pier section dimension, span and vehicle load level to improve the resilience of the single-column pier bridge.

Effects of Inclination of Longitudinal and Vertical Acceleration Components of Near-Field Earthquake Records on Seismic Responses of Pile Foundation-Superstructure Systems in Liquefiable Soil Bed

The inclination angle of such components with respect to the principal orthogonal axes cannot be neglected in the direct seismic analysis of soil-foundation-superstructure systems, specifically in a piled liquefiable soil bed. This study validated numerical simulations and numerically modeled a concrete moment frame on a pile foundation within a liquefiable soil bed. The direct seismic analysis of the superstructure-foundation-soil system was carried out in a single step (through nonlinear dynamic time-history analysis) under longitudinal and vertical near-field seismic acceleration component records. The effects of the inclination of longitudinal and vertical acceleration components on the seismic responses of the soil-foundation-superstructure system in the liquefiable soil bed were explored, evaluating the critical inclination based on the near-field earthquake magnitude. It was observed that the simultaneous application of longitudinal and vertical near-field seismic acceleration components substantially changed the liquefiable soil bed drift of the pile foundation-superstructure system, significantly altering [Formula: see text] in depth, particularly in the middle of the pile depth. The change in [Formula: see text] and its effects on the seismic responses of the superstructure and piles (interstory drift and pile shear force and bending moment) were different upon a 30° change (rotation) in the acceleration records from 0 to 90° with respect to the orthogonal principal axes.

Numerical study on optimized application of engineered cementitious composites in RC coupled shear wall structures

Due to the superior tensile strain-hardening and multi-cracking properties, engineered cementitious composites (ECC) can be adopted in reinforced concrete (RC) shear walls and coupling beams to improve the seismic performance and damage tolerance with simplified reinforcement details. This study numerically investigates the optimized application of ECC in coupled RC shear wall structures based on refined two-dimensional finite element models incorporating constitutive models of ECC and concrete for nonlinear shear behaviors. The balance between cost and performance is adequately considered from the material, member, and structural levels. At the material level, the reasonable tensile properties of ECC are suggested based on the parametric analysis of coupling beam and shear wall specimens. At the member level, the effect of diagonal bar ratios on the seismic performance of coupled walls is investigated to propose reasonable diagonal bar ratio of ECC coupling beams. Finally, at the structural level, nonlinear dynamic time-history analysis of a typical 11-story coupled wall structure based on practical engineering is conducted to investigate the influence of the application ranges of ECC on the seismic performance of the wall system. The damage indexes, including story curvature and crack width, are analyzed and compared. Based on the analytical results, recommendations related to some key issues on the application of ECC in traditional RC structures are provided, including the application range and tensile properties of ECC, as well as the reinforcement details.

Study on the Influence and Optimization Design of Viscous Damper Parameters on the Damping Efficiency of Frame Shear Wall Structure

This study investigates the influence of viscous damper parameters on the damping efficiency of frame shear wall structures. Taking a specific frame shear wall structure as the background, a three-dimensional finite element model is established using a nonlinear dynamic time–history analysis method. The damping ratio, reduction in vertex displacement, reduction in base shear, and inter-story drift utilization rate are selected as the damping performance indicators. Firstly, a sensitivity analysis is conducted to study the influence of different viscous damper parameters on these indicators. Then, the relationship models between the viscous damper parameters and the indicators are fitted using the response surface method, and the fitting effect is evaluated through an F-test and determination coefficient R2. Finally, an objective function based on key damping performance indicators is established to solve for the optimal parameters. The results show that the traditional sensitivity analysis method is unable to comprehensively consider the combined effects of different damping efficiency indicators. The response surface method has high fitting accuracy and good predictability and can serve as an optimization model. Considering the stiffness of supporting components matched with the viscous damper parameters, the feasibility of the optimal damping parameters is demonstrated from an engineering application perspective. A simple and easy-to-operate damping design flowchart is proposed, providing important guidance and reference for designers in frame shear wall structure damping design in the future.

Effect of Ground Motion Time–Frequency Non-Stationarity on Seismic Response of High-Speed Railway Simply Supported Bridge Based on Wavelet Packet Transform

Time–frequency non-stationarity is a ground motion characteristic which is frequently neglected in current seismic design and research. This paper studies its impact on the seismic response of high-speed railway simply supported bridge (HSRSSB). A method for generating time–frequency stationary earthquakes (TFSEs) and time–frequency non-stationary earthquakes (TFNSEs) using wavelet packet transform is proposed. A finite element model of a three-span HSRSSB is established using OpenSees. The seismic response is obtained through non-linear dynamic time history analysis, and the fragility curves of bridge components and system are calculated through incremental dynamic analysis. Finally, the reasons for the differences are analyzed by comparing the differences in seismic response of bridge, component fragility and system fragility under two groups of ground motion. The results show that the time–frequency non-stationarity of ground motion has an effect on the bridge response and fragility under strong earthquakes. TFNSE will lead to larger ground motion response, and the damage probability of bridge components and systems is higher. The reason is related to the damage and period extension of bridges under ground motion. Structures with prolonged period anti-seismic measures need to pay attention to this effect.

Effects of important characteristics of earthquake ground motions on probabilistic seismic demand assessment of long-span cable-stayed bridges

The uncertainties of earthquake ground motions have the most important effects on seismic responses of bridge structures, especially long-span bridges, because of complex and special dynamic properties. The nonlinear dynamic time-history analysis is conducted for a two-pylon long-span cable-stayed highway bridge by using real earthquake ground motions rationally selected. The correlation between the important characteristics of earthquake ground motions and the probabilistic seismic demand assessment of the cable-stayed bridge reveals that the geometric means and dispersions of response spectra from selected ground motions have very significant effects on mean values, dispersions and probabilistic distributions of seismic demands of long-span bridges. The spectral shape of geometric mean spectra in the period ranges with large cumulative modal mass participation factors that should be well matched to the target spectrum to improve the precision and computational efficiency of probabilistic seismic demand assessment. If earthquake ground motions are rationally selected, response spectral values at the periods with comparatively large modal participation mass ratios or PGA can be used as intensity measures and even provide more precise probabilistic seismic demand assessment than response spectral values at the fundamental periods.

Seismic performance and vulnerability analysis for bifurcated tunnels in soft soil

This paper investigates the seismic performance of complex comprehensive interchange underground structures. As an example, the seismic performance of Nanjing underground bifurcated tunnels constructed in soft soil is analyzed. A three-dimensional (3D) numerical finite element analysis model is established considering soil-tunnel interaction to analyze the seismic response characteristics and failure mechanism of the bifurcated tunnels. The results show that the tunnel damage degree is closely associated with the deformation response, and that the inter-story drift ratio of the lower layer is significantly greater than that of the upper layer. The pushover analysis method is used to obtain the seismic performance curve of the tunnel, and inter-story drift ratio limits are defined. The IDA procedure is then used to conduct multiple non-linear dynamic time history analyses based on the 3D finite element model, and IDA curve clusters are drawn with peak ground acceleration (PGA) as the earthquake intensity measures and the peak inter-story drift ratio as the damage measures of tunnels. The corresponding IDA percentiles lines are calculated, and the seismic fragility curves of the bifurcated tunnels are established. The post-earthquake functional failure probability of the bifurcated tunnels is obtained under different seismic fortification performance level.

Interference effects on the wind loads and wind-induced responses of parallel-arranged rectangular-planed air-supported membrane structures

In many practical projects, two air-supported membrane structures are parallel-arranged. The interference effects of parallel-arranged rectangular-planed air-supported membrane structures are important in the wind-resistant design. In order to address this issue, the wind pressures on isolated and parallel-arranged structures are obtained through pressure measurement wind tunnel tests. The wind-induced responses are calculated via nonlinear dynamic time–history analysis. Consequently, the interference effects on wind loads and wind-induced responses are analyzed. The results show that the wind suctions of downstream structures are amplified by the interferences of parallel-arranged structures particularly under oblique wind directions. The mean wind loads on the most disturbed zone are amplified up to about 65 %. The interference characteristics of wind-induced displacement are basically similar to mean wind loads. The membrane stresses and cable forces are significantly interfered only in oblique wind directions, which are amplified up to about 15 % in all zones of downstream structures. The strongest interference effects can be observed with a spacing-span ratio of 0.2 when the wind direction is oblique or parallel to the gap between neighboring structures. The interference factors for zones are provided to analyze the interference characteristics. In addition, recommendation values of the overall response interference factors are summarized for design reference. The overall response interference factors for displacement, membrane stress, and cable force should be considered as 1.21, 1.33, and 1.20, respectively.

Seismic performance assessment of deficient RC structures retrofitted with different steel bracing systems

This paper discusses the use of concentric steel bracing systems as a global technique for retrofitting RC structures. A case study building with a five-story RC structure was retrofitted and tested using different types of bracing systems with different arrangements namely diagonal, X, and a combination between diagonal and X steel braces with tow arrangements. The main objective of the current study is to find out the most effective bracing system to upgrading the seismic behavior of deficient RC structures. The nonlinear static pushover and dynamic time-history analyses were carried out. The first method was applied by pushing the models until they arriving at a predefined target roof displacement. In the second method, a set of three natural earthquakes was employed to perform a dynamic time history analysis. The results indicate that the combined system of the diagonal and X braces using the second arrangement has the highest base shear and reaches the target roof displacement under pushover analysis. On the other hand, when using the response history analysis, it is the best system to reduce roof displacement compared to other techniques. However, steel braces cannot reduce the acceleration of the structure. The proposed combined system with the second arrangement is an effective retrofitting technique that has a much better seismic behavior and improves the ability to withstand even larger earthquake forces compared to other techniques.

Study on the Influence of a Rubber-Modified Soil Isolation Layer on the Isolation Performance of Frame Structures with Different Foundation Forms

In order to investigate the seismic performance of a rubber-modified soil isolation layer, a three-dimensional finite element model was constructed using finite element analysis software, utilizing a two-story frame structure as the engineering background. Nonlinear dynamic time history analysis and comparisons were performed against the seismic performance of the structure. The evaluation was based on several parameters, including the contact area of the base, the thickness of the rubber-particle-modified soil isolation layer, ground motion records with varying amplitudes, and seismic frequency spectrum characteristics. The research findings indicate that the implementation of a rubber-modified soil isolation layer effectively mitigates the peak acceleration, horizontal displacement, and shear stress of the frame structure. This not only enhances the seismic performance of the structure but also enlarges the contact area of the base. Increasing the thickness of the rubber-modified soil isolation layer will effectively decrease the peak acceleration, horizontal displacement, and shear stress of the structure during seismic events. The effectiveness of the isolation provided by the rubber-modified soil layer improves as the intensity of the ground motion record increases.

Rapid damage assessment of regional beam bridges after earthquake based on simplified models and different seismic inputs

As the hub of the traffic network, the rapid damage assessment of bridges after earthquake is of great significance for post-disaster rescue. Traditional vulnerability-based method can only provide the probability of different damage states of structures under different earthquake intensity indicators, which confuses the selection of post-disaster rescue routes. Therefore, this paper proposes a post earthquake damage assessment technique for regional bridges based on nonlinear dynamic time-history response analysis. First, a simplified mechanical model for a single pier was established for a large number of beam bridges in the region, achieving standardized and batch rapid finite element model establishment. Secondly, using Kriging interpolation method and continuous wavelet transform technology, the surface seismic response of geological drilling points is calculated to obtain the seismic motion history of any bridge site in the region. Finally, using parallel computing technology, nonlinear dynamic time-history response analysis was conducted on the simplified beam bridge model, and the bridge damage status was quantitatively evaluated based on the calculation results. Eighty-five bridges in a specific area are considered as an example to verify the proposed method. The results show that the proposed method has high calculation efficiency and can consider the site characteristics and structural design parameters. Also, the calculation results can better reflect the actual earthquake damage distribution, providing strong technical support for post-disaster rescue.

Seismic Performance of Precast Concrete Special Moment Frames with Hybrid Connection System in Five and Ten Story Buildings

Precast concrete has been widely implemented in various construction projects due to shorter construction duration and consistent quality. In a previous study, Solberg et al. (2008) conducted an experiment on hybrid beam-column connections with Damage Avoidance Design concept to improve the seismic performance of precast concrete special moment frames. The objective of this study is to further evaluate the seismic performance of precast concrete special moment frames with the hybrid beam-column connections in five and ten story buildings. The evaluation was done through non-linear dynamic time history analysis using OpenSees. The analysis results show that precast concrete frame buildings exhibit insignificant difference in maximum interstory drift ratios and roof displacements as compared to conventional concrete frame buildings. However, with significantly smaller residual displacements which indicates less structural damage, precast concrete frame buildings could be preferred in the long run as they require less structural repairs after a strong earthquake event.

Improving aerodynamic response of tall buildings using smart morphing facades

Slender buildings are prone to vortex-induced vibrations and turbulence-induced buffeting. Usually, vortex-induced vibrations govern the strength and serviceability design criteria. The building's shape determines the aerodynamics of it; therefore, optimizing building shape can greatly reduce wind-induced vibrations. With a growing industry in adaptive and double-skin facades—mainly for energy saving purposes—there is an opportunity to innovate and implement smart, morphing facade modules (which we refer as Smorphacades) that actively modify their aerodynamic shape to alleviate flow-induced vibrations during high winds. This paper evaluates the performance of a 44-story tall building with the different configurations of the developed Smorphacade module system in mitigating building vibrations. Dynamic nonlinear time history analysis of the building under varying wind speeds ranging between 35 and 75 m/s are performed to evaluate the performance of building equipped with Smorphacade at low and high wind speeds. The performance measures chosen in the study are displacements and accelerations. Structural responses of building equipped with Smorphacade are compared against the bare building model responses to evaluate improvements in performance. Acceleration response comparisons at lower wind speeds provide insights into Smorphacade contributions to improving occupant comfort. Displacement comparisons at high wind speeds help understand the improvements in overall structural performance by reducing nonlinear response.

Nonlinear analysis of reinforced concrete buildings with different heights and floor systems

Most civil structures exhibit nonlinear behavior during moderate to severe earthquakes. Consequently, inelastic analysis is needed for seismic design. Several dynamic and static analysis methods are available for the assessment and design of engineering structures. Two of the available methods in terms of nonlinear dynamic time history analysis and nonlinear static analysis, which is known as pushover analysis, are employed herein to comprehensively study and investigate the seismic performance of multi-story building structures with different floor systems. Moreover, the study is extended to assess the actual values of the response reduction/modification factor (R-factor) for each building model, then evaluate the values with the code-recommended design values. Three-dimensional finite element building models with 5, 10 and 15 stories are developed for the evaluation process. The advanced computer program ETABS is used for developing and analyzing the buildings considering material and geometrical nonlinearity. A suit of seven earthquake records is considered and scaled according to the ASCE-16 seismic design code to excite the building models. The obtained results evidently reveal that the type of floor slab significantly impacts the seismic response of the building. More specifically, the effects of floor slabs on seismic demands are more evident in low- and mid-rise buildings. In addition, the type of slab system and height of the building have more influence on the response modification factors, especially for low-rise building models.

Nonlinear Dynamic Analyses Utilising Macro-Models of Reinforced Concrete Building Structures and Site-Specific Accelerograms

This paper aims to guide structural engineers on how to apply the rapid nonlinear time history analysis (RNLTHA) procedure effectively to predict seismic demand, taking into account ductility and overstrength, and effects of dynamic phenomena including cyclic degradation of strength and stiffness in structures, in a direct and expedient manner. The shortcoming of the conventional force-based approach of design involving the use of a force reduction factor to account for nonlinear effects is well recognised. Nonlinear static (pushover) analysis and dynamic nonlinear time history analysis (NLTHA) are offered as alternative methods of analysis by major codes of practices to achieve better optimisation in the use of materials. NLTHA has advantages over pushover analysis in being more direct and capable of capturing cyclic response behaviour. Despite the merits of NLTHA, its adoption in the industry has been limited, mainly because of the complexity and the higher analysis cost involved. RNLTHA proposed in this article uses a macroscopic model of the building to fulfil the purpose of NLTHA, whilst saving computational time and achieving a good degree of accuracy, as verified by comparison with results generated from SeismoStruct.

Seismic Fragility Analysis of a High-Pier Bridge under Pulse-like Ground Motion, Based on a PCA and K-Means Approach

The objective of this study is to present a novel fragility analysis method that combines principal component analysis (PCA) and the K-means clustering algorithm for a probability assessment of seismic damage in high-pier bridges undergoing pulse-like ground motions. Firstly, the method uses the correlation coefficient and the condition number as judgment indices to eliminate those seismic intensity measures (IMs) with weak correlation and multicollinearity from all 29 of the initial candidate seismic IMs, the optimal combination of IMs that satisfies the requirements for the PCA method is determined. Secondly, the method utilizes PCA to reduce the dimensionality of the optimal combination of IMs to obtain the principal components, after which the K-means algorithm is applied to classify the original group of selected pulse-like ground motions into four classes. Thirdly, a 3D finite element model of the exemplary high-pier bridge is developed via OpenSees, while incremental nonlinear dynamic time-history analyses are conducted to record the maximum cross-section curvatures of high piers under the influence of various categories of ground motions. Finally, based on the analytical procedures used in the increment dynamic analysis (IDA) method, this study develops and compares the fragility curves for the various classes of pulse-like ground motions. The results indicate the necessity of utilizing the PCA and K-means approach for classifying pulse-like ground motions in the seismic fragility analysis of high-pier bridges. This approach also significantly improves the precision and accuracy of damage probability analysis.

Seismic performance of isolated buildings with friction spring damper

The main objective of this paper is to introduce a new combination of passive seismic response control devices containing Friction Spring Damper (FSD) and Pot Bearing (PB) for buildings and compare this system with conventional seismic isolators such as Lead Rubber Bearing (LRB) and Friction Pendulum System (FPS). For this purpose, two benchmark buildings with different structural systems have been considered for implementing the devices. To capture the flag-shaped and self-centered behavior of FSD, new uniaxial material has been developed for OpenSees, and numerical verification of the material has been done based on a past experimental study. Nonlinear dynamic time-history analyses have been used to extract the seismic responses of models, including fixed-base structures, and isolated structures by FSD along with PB, LRB, and FPS. The results show that not only the proposed isolation system has the capability of reducing base shear and inter-story drift as well as both conventional seismic isolation systems compared to fixed-base structures, but also the system has even better performance than the isolated structures with LRB. Moreover, due to the self-centered behavior of FSD, the residual displacement of the proposed system is much lower than conventional isolation systems, which can lead to lower maintenance costs of isolators.