Showing papers on "OpenSees published in 2022"

Theoretical analysis on the lateral drift of precast concrete frame with replaceable artificial controllable plastic hinges

Abstract: This research proposed a calculation method for the deformation of the frame system with the artificial controllable plastic hinges (APHF). The lateral deformation amplification coefficient was introduced to regulate the deformation value of APHF. Based on the equivalent system method, the relation between the rotational stiffness of the artificial controllable plastic hinge and the lateral deformation amplification coefficient was analyzed. According to the structural performance requirements, the rotational stiffness limit of the artificial controllable plastic hinge can be obtained to avoid the APHF deformation exceeding the demand limits. Based on the APHF experiment, the APHF model was developed using Opensees. Subsequently, the dynamic response analysis was performed to further explore the deformation mechanism of APHF. The seismic response analysis results indicated that the inter-story drift of APHF was more evenly distributed, which avoided the formation of vulnerable structural layers, compared with RC frame. The artificial controllable plastic hinge effectively reduced the base shear of the frame structures.

Seismic reliability of structures equipped with LIR‐DCFP bearings in terms of superstructure ductility and isolator displacement

Abstract: This research deals with the seismic reliability of non‐linear base‐isolated structures equipped with Lateral Impact Resilient Double Concave Friction Pendulum (LIR‐DCFP) devices. Specifically, exceeding probabilities within the reference lifetime are assessed with respect to both superstructure ductility and isolator displacement demand. The innovative LIR‐DCFP bearing has an improved inner slider with an internal gap and is capable to reduce adverse effects of the lateral impact between the inner slider and the restraining rims. The dynamic behavior of the superstructure is represented by a simplified one‐degree‐of‐freedom model describing its lateral response. The isolation system is characterized by a model based on rigid body dynamics also including the lateral impact behavior. A wide parametric analysis is developed for several system properties considering the friction coefficients as relevant random variables. Different sets of natural seismic records able to match conditional spectra for a site in Riverside (California) were selected to consider the aleatory uncertainties of the seismic input. Incremental dynamic analyses were performed to determine the statistics of significant engineering demand parameters and compute probabilities exceeding specific limit states to define fragility curves. Finally, employing seismic hazard curves, the seismic reliability of isolated structures was evaluated. For increasing values of the internal gap, structures equipped with LIR‐DCFP devices exhibit better seismic performance with respect to classical DCFP bearings with same size, especially, if the superstructure is designed to behave essentially elastic when the lateral capacity of the isolation level is not reached, or the hardening post‐yield stiffness of the superstructure is relatively high. Reductions up to 20% in the exceeding probabilities within 50 years related to the ductility demand are achievable using the suggested LIR‐DCFP isolator.

Seismic fragility assessment of geotechnical seismic isolation (GSI) for bridge configuration

Abstract: Abstract The seismic vulnerability of bridges may be reduced by the application of Geotechnical Seismic Isolation (GSI) below the foundations of the columns and the abutments. However, the role of GSI on the seismic response of bridges has been limitedly examined in literature. Therefore, this research has been conducted to study the effect of applying GSI on the seismic response of bridges to address the aforementioned gap in knowledge. Advanced nonlinear dynamic three-dimensional finite element analyses have been conducted using OpenSees to study the influence of the GSI. The cases of traditional and isolated bridges subjected to earthquakes have been considered to assess the GSI effects. The results showed that the GSI reduces the seismic effect on the column while its effect seems to be less significant for the abutments. In addition, fragility curves for the traditional and isolated cases have been developed and compared to provide insights with a probabilistic-based approach. The results of this paper provide a useful benchmark for design considerations regarding the use of GSI for bridges.

Investigation of 3D effects on dynamic progressive collapse resistance of RC structures considering slabs and infill walls

Abstract: In recent years, the occurrence of a series of extreme events has raised awareness of what progressive collapse of mainstream reinforced concrete frame structures can cause in terms of damage and direct/indirect losses. Even though these low-probability/high-consequence events, which are triggered by accidental loads not necessarily considered at the design stage, have attracted growing attention, less consideration has been given to spatial effects caused by floor slabs and infill walls in the progressive collapse simulation of RC frame structures. A large number of research studies have proposed multifarious methods, the correctness and simplicity of which are characterized by different levels that are theory- and/or method-specific. Therefore, in order to assess and quantify the influence of floor slabs and infill walls on progressive collapse resistance of 3D RC frame structures, an efficient numerical modeling approach was first developed using OpenSees software. Then, the modeling strategy was validated by simulating different experimental test results. The numerical investigation was further expanded by performing incremental dynamic analysis on both 2D and 3D structural models. The results show that secondary and/or non-structural components such as floor slabs and infill walls produce a significant improvement in the capacity of the structure to resist progressive collapse, and that the respective characteristics of the two are magnified due to the coupling effect in the space frame.

A novel macroelement for seismic analysis of unreinforced masonry buildings based on MVLEM in OpenSees

Abstract: Unreinforced masonry (URM) buildings are susceptible to extraordinary actions such as earthquakes compared to steel or reinforced concrete buildings. Various methods have been developed for the computational analysis of URM buildings in the last few decades. The equivalent frame method (EFM) is one of the numerical modeling approaches widely used for the nonlinear analyses of URM buildings. Different macroelements in the context of the EFM have been proposed. However, there is still a need for an efficient modeling approach in the computational effort that can predict the real behavior of URM structural components with sufficient agreement and available in opensource structural analyses software packages. For this purpose, a new macroelement based on the multiple vertical line element method (MVLEM) element has been developed in this study. The MVLEM is available in the OpenSees software platform comprising vertical uniaxial macro-fibers and a shear spring as an efficient macroelement for nonlinear analysis of flexure-dominated reinforced concrete walls. The novel macroelement, double modified MVLEM (DM-MVELM) element has been proposed consisting of two modified MVLEM elements tied with a nonlinear shear spring at the middle with a trilinear backbone behavior. DM-MVLEM can capture the axial-flexural interaction with lower computational effort than finite element models and fiber beam-column elements. The DM-MVLEM has been validated against the test results at the structural components level and a full-scale perforated URM wall. Unified method (UM) and composite spring method (CSM) are two existing EFMs that are presented in this study. A study is performed by comparing the seismic behavior of the perforated URM walls modeled using the UM, CSM, and DM-MVLEM modeling strategies. Results show that the DM-MVLEM can predict the damage patterns, and nonlinear behavior of spandrels can be simulated that was usually modeled with linear behavior in EFMs.

Effective placement of self‐centering damage‐free connections for seismic‐resilient steel moment resisting frames

Abstract: In recent years, significant advancements have been made in the definition of innovative “minimal‐damage structures,” chasing the need for more resilient societies against extreme seismic events. In this context, moment resisting frames (MRFs) equipped with self‐centering damage‐free (SCDF) devices in column bases and beam‐to‐column joints represent a viable solution to improve structural resilience and damage reduction. However, the extensive use of these devices significantly increases complexity and costs compared to conventional structures, thus limiting their practical application. To overcome this drawback, current research works are focusing on the definition of effective placement for SCDF devices, maximizing their beneficial effect on the seismic response and controlling their impact on the overall structural complexity. Within this context, the present study investigates the influence of the placement of SCDF devices in a steel MRF. An eight‐story MRF is designed, and 50 configurations with different locations of SCDF joints are considered. Numerical models are developed in OpenSees, and non‐linear static push–pull and incremental dynamic analyses (IDAs) are carried out. The influence of the placement of SCDF devices is assessed by considering residual and peak interstory drifts, residual top story drifts, peak story accelerations, and the total dissipated energy as performance parameters. The results of IDAs for a seismic intensity corresponding to the ultimate limit state (ULS) are analyzed and compared, and fragility curves are successively derived for some relevant configurations. The paper provides insights and observations to understand how including a different number of SCDF BCJs at different stories affects the seismic response.

Determination of optimal behavior of self-centering multiple-rocking walls subjected to far-field and near-field ground motions

Abstract: In recent years, innovative seismic resistant systems have been introduced based on the Damage Avoidance Design (DAD) philosophy rather than the conventional plastic design-based methods to reduce damages to buildings and to decrease post-earthquake repair costs. Self-centering multiple-rocking walls are amongst these innovative systems. This study aims to determine the optimum number of rocking sections in self-centering concrete multiple rocking walls. To this aim, the seismic behavior of self-centering (SC) concrete rocking walls of 8, 12, 16, and 20 stories with different numbers of rocking sections were examined. Several non-linear time-history analyses were carried out via OpenSEES software in a two-¬dimensional framework. Three sets of ground motions were considered including 22 Far-Field (FF), 14 Near-Field-Pulse (NFP), and 14 Near-Field-no Pulse (NFnP). Five types of quad-rocking walls and one type of dual-rocking walls were specified and compared with base-rocking walls and fixed-base walls. To perform this comparison, a set of utility coefficients was defined to integrate different response aspects including shear and moment demands as well as the residual drifts. The results showed that the effects of higher modes (shear and moment demand) increase with the increase in the height of the rocking structures. Furthermore, NFnP and FF records produced higher mode effects in rocking systems as compared to NFP records. The results suggested that the quad-rocking walls with the reduced tendon area in the first block (R4-S1) are highly effective in reducing the effects of higher modes in NFP and NFnP records. They showed maximum utility coefficients of 67% and 65%, respectively. Also, quad-rocking walls with the reduced tendon area in the third block (R4-S3) were more effective under FF records and their maximum utility coefficient was 65%. The residual roof drift of rocking walls was so negligible that its maximum value in the 8-story structure under NFP records was 0.0008.

Determination of optimal behavior of self-centering multiple-rocking walls subjected to far-field and near-field ground motions

Abstract: In recent years, innovative seismic resistant systems have been introduced based on the Damage Avoidance Design (DAD) philosophy rather than the conventional plastic design-based methods to reduce damages to buildings and to decrease post-earthquake repair costs. Self-centering multiple-rocking walls are amongst these innovative systems. This study aims to determine the optimum number of rocking sections in self-centering concrete multiple rocking walls. To this aim, the seismic behavior of self-centering (SC) concrete rocking walls of 8, 12, 16, and 20 stories with different numbers of rocking sections were examined. Several non-linear time-history analyses were carried out via OpenSEES software in a two-¬dimensional framework. Three sets of ground motions were considered including 22 Far-Field (FF), 14 Near-Field-Pulse (NFP), and 14 Near-Field-no Pulse (NFnP). Five types of quad-rocking walls and one type of dual-rocking walls were specified and compared with base-rocking walls and fixed-base walls. To perform this comparison, a set of utility coefficients was defined to integrate different response aspects including shear and moment demands as well as the residual drifts. The results showed that the effects of higher modes (shear and moment demand) increase with the increase in the height of the rocking structures. Furthermore, NFnP and FF records produced higher mode effects in rocking systems as compared to NFP records. The results suggested that the quad-rocking walls with the reduced tendon area in the first block (R4-S1) are highly effective in reducing the effects of higher modes in NFP and NFnP records. They showed maximum utility coefficients of 67% and 65%, respectively. Also, quad-rocking walls with the reduced tendon area in the third block (R4-S3) were more effective under FF records and their maximum utility coefficient was 65%. The residual roof drift of rocking walls was so negligible that its maximum value in the 8-story structure under NFP records was 0.0008.

Investigating an Optimal Computational Strategy to Retrofit Buildings with Implementing Viscous Dampers

Abstract: Civil engineering structures may seriously suffer from different damage states result of earthquakes. Nowadays, retrofitting the existing buildings is a serious need among designers. Two important factors of required performance level and cost of retrofitting play a crucial role in the retrofitting approach. In this study, a new optimal computational strategy to retrofit structures by implementing linear Viscous Dampers (VDs) is investigated to achieve a higher performance level with lower implementation cost. Regarding this goal, a Tcl programming code was developed with the capability of considering damaged structure due to earthquake-induced structural pounding. The code allows us to improve structural models to take into account the real condition of buildings using both MATLAB and Opensees software simultaneously. To present the capability of this strategy, the 3-, and 6-story colliding Steel Moment-Resisting Frames (SMRFs) were selected. Incremental Dynamic Analysis (IDA) was performed based on the interstory drift ratio of floor levels as engineering demand parameter, and Sa(T1) as intensity measure. Interstory median IDAs of floor levels of colliding SMRFs were plotted to find out the floor level prone to damage and to retrofit only this floor level instead of all stories. The results show that implementing only two linear VDs with a cost of two units can achieve a higher life safety performance level in the case of 3-, and 6-story SMRFs. Moreover, the proposed computational strategy can be used for any structure (with and without pounding conditions), and in all performance levels prescribed in FEMA 356 code.

Modeling of seismic actions in squat reinforced concrete walls exposed to acid deposition

Abstract: Acid deposition has a noticeable influence on reinforced concrete (RC) buildings which could cause catastrophic injuries and safety risks accompanied by loss of life and property. This study aims to establish a modeling method for predicting the nonlinear response of corroded squat reinforced concrete (RC) walls caused by the acidic attack. Compression tests on corroded confined concrete are performed to provide the stress-strain relationship of concrete after erosion. Quasi-static experiments on corroded RC walls with different corrosion levels and design parameters were conducted, and the test results were used for calibration and verification. Then, a numerical simulation method of corroded squat RC walls is proposed based on the fiber-based element SFI-MVELM in the OpenSees platform, considering the influence of corrosion on three main aspects, i.e., material mechanical properties, shear mechanism, and bond-slip effect. The comparison results show that the proposed model captures the cyclic responses of the tested wall specimens with reasonable accuracy in terms of hysteresis curves, indicating that the modeling method is suitable for investigating the seismic behavior of corroded RC walls and can meet the needs of a lifecycle seismic performance evaluation of RC structure in an acidic environment.

Optimization of the structural coupling between RC frames, CLT shear walls and asymmetric friction connections

Abstract: Abstract This paper focuses on the optimum design of the e-CLT technology. The e-CLT technology consists in adding cross laminated timber (CLT) walls to an existing reinforced concrete (RC) infilled frame via asymmetric friction connection (AFC). The authors carried out quasi-static and nonlinear dynamic analyses. The RC frame is modeled in OpenSees by fiber-section-based elements with force-based formulation. The contribution of the infill is simulated using a degrading data-driven Bouc–Wen model with a slip-lock element while the AFC is modelled with a modified Coulomb model. Different types of infill, aspect ratio, scaling, and member size are considered. The benefits of using e-CLT technology are discussed and the ranges of optimum performance of the AFC are estimated. A comparison of the performance of traditional infills with the e-CLT system is presented. The authors provide optimum intervals of the ratio between slip force and in-plane stiffness of the CLT panel, following energy and displacement-based criteria. The seismic displacement demand under various seismic scenario is investigated. Correlations between the RC characteristics and the optimum design ratios bestow possible criteria for the design of the AFC.

Damping enhanced novel re-centering seismic isolator incorporating superelastic SMA for response control of bridges under near-fault earthquakes

Abstract: Abstract To enhance the bridge resilient performance, a novel re-centering seismic isolator (RSI) is developed by incorporating damping enhanced (DE)-sliding-lead rubber bearing (LRB) with superelastic shape memory alloy (SMA), which functions with the yielding-sliding hysteretic mode. The numerical model of the novel RSI is developed in OpenSees platform and validated by comparing the numerical and experimental hysteretic loops of the superelastic SMA and DE-sliding-LRB. A parametric design procedure is proposed to determine the optimum parameters of the novel RSI system. A three-span continuous girder bridge is selected to investigate the response mitigation efficiency of the novel RSI system compared with LRB system under near-fault ground motions. A systematic parametric study is conducted to design the optimal parameters of the novel RSI system for bridges. Case study is conducted to investigate the effectiveness of the proposed design procedure and the novel RSI system for response mitigation of bridges. Results show that the damping capability is effectively enhanced by designing the friction coefficient of the sliding element. The novel RSI system can achieve dual mitigation of the displacement responses and base force in piers for bridges. Case study demonstrates the effectiveness of the novel RSI and parametric design procedure.

Seismic damage state predictions of reinforced concrete structures using stacked long short-term memory neural networks

Abstract: Early and accurate damage evaluation after earthquakes is critical for planning an efficient and timely emergency response. State-of-the-art rapid evaluation techniques of structural damage include the use of fragility or vulnerability curves. However, fragility-based damage functions may vary significantly, depending on the ground motion characteristics, soil conditions, and structural geometric properties. A novel stacked long short-term memory (LSTM) network with overlapping data was developed in this study to overcome this issue. The ground motion time histories are divided into several stacks and feed to the LSTM network, and the data are overlapped with the preceding stack to link each stack. The stacked LSTM reduces the temporal dimension by stacking and generating new features, and shortens the time required for training. The proposed network significantly reduces the training time required (approximately 97%) and enhances the test accuracies (80%–95%) as the number of stacks increases. OpenSees is utilized for the creation of the numerical model of ductile frames (using concentrated plasticity modeling approach) and nonductile frames (using distributed plasticity modeling approach). Although these structures have different response mechanisms, the proposed LSTM network shows the diversity in predicting the earthquake-induced damage with a high degree of accuracy (80%–95%). The performance of the proposed model on different types of structures (nonductile and ductile building frames and a non-ductile bridge) with the same network shows the flexibility of the model.

Seismic assessment of steel frame subjected to simulated directivity earthquakes: The unilaterality of fault normal component at various rupture distances

Abstract: Directionality is prominent in the fault normal component of ground motion. It has a different effect on stations in the rupture direction on the tectonic fault than it does on stations in the opposite direction. Such pulse-like features observed in forward and backward directivity stations affect both low-rise and high-rise structures, depending on their fundamental period and the pulse period of ground motion. However, systematic availability of both forward and backward directivity ground motion for unilateral and bilateral earthquakes of the same magnitude at a similar rupture distance for a given fault is rare. So, multiple directivity scenarios are simulated using fracture mechanics-based principles. Using OpenSees, steel moment-resisting frames of 1, 5, and 9 stories, well designed according to building codes, are modeled, and their non-linear response is evaluated. Stations at constant rupture distances are used to compute fragility for each scenario separately. Variation inter-storey drift and peak floor acceleration, along with the hysteretic behavior of panel-zone springs, have also been studied for each of the directivity scenarios. Finally, the results obtained are compared to what is expected by HAZUS.

Seismic performance evaluation of innovative balloon type CLT rocking shear walls

Abstract: Balloon type cross laminated timber (CLT) rocking shear walls are a novel seismic force resisting system. In this paper, the seismic performance of four 12-story balloon type CLT rocking shear walls, designed by a structural engineering firm located in Vancouver (Canada) using the performance-based design procedure outlined in the technical guideline published by the Canadian Construction Materials center (CCMC)/National Research Council Canada (NRC), is assessed. The seismic performance of the prototype CLT rocking shear walls was investigated using nonlinear time history analyses. Robust nonlinear finite element models were developed using OpenSees and the nonlinear behavior of the displacement-controlled components was calibrated using available experimental data. A detailed site-specific hazard analysis was conducted and sets of ground motions suitable for the prototype buildings were selected. The ground motions were used in a series of incremental dynamic analyses (IDAs) to quantify the adjustable collapse margin ratio (ACMR) of the prototype balloon type CLT rocking shear walls. The results show that the prototype balloon type CLT rocking shear walls designed using the performance-based design procedure outlined in the CCMC/NRC technical guideline have sufficient ACMR when compared to the acceptable limits recommended by FEMA P695.

Seismic damage state predictions of reinforced concrete structures using stacked long short-term memory neural networks

Abstract: Early and accurate damage evaluation after earthquakes is critical for planning an efficient and timely emergency response. State-of-the-art rapid evaluation techniques of structural damage include the use of fragility or vulnerability curves. However, fragility-based damage functions may vary significantly, depending on the ground motion characteristics, soil conditions, and structural geometric properties. A novel stacked long short-term memory (LSTM) network with overlapping data was developed in this study to overcome this issue. The ground motion time histories are divided into several stacks and feed to the LSTM network, and the data are overlapped with the preceding stack to link each stack. The stacked LSTM reduces the temporal dimension by stacking and generating new features, and shortens the time required for training. The proposed network significantly reduces the training time required (approximately 97%) and enhances the test accuracies (80%–95%) as the number of stacks increases. OpenSees is utilized for the creation of the numerical model of ductile frames (using concentrated plasticity modeling approach) and nonductile frames (using distributed plasticity modeling approach). Although these structures have different response mechanisms, the proposed LSTM network shows the diversity in predicting the earthquake-induced damage with a high degree of accuracy (80%–95%). The performance of the proposed model on different types of structures (nonductile and ductile building frames and a non-ductile bridge) with the same network shows the flexibility of the model.