Response Modification Factor of Steel Braced Frames Equipped with Smart Hybrid Re-Centering Device

Behrouz Asgarian,Alireza Jamalian,Ali Jalaeefar 한국강구조학회 2021 International Journal of Steel Structures Vol.21 No.6

Super-elastic shape memory alloy (SMA) is a unique material which has the ability to undergo large deformations and to return to the un-deformed shape upon unloading. Researches imply that using SMA in earthquake resisting component of structures leads to signifi cant positive eff ects such as reducing residual displacements (superelastic SMAs) and increasing energy absorbing capacity (martensitic SMAs). Among them, braced frames equipped with shape memory braces have been investigated by many recent researchers. This paper intends to study the behavior of such frames through nonlinear dynamic analysis and pushover analysis and to propose a response modifi cation factor (R) for them. For this purpose, detailed individual bracing members equipped with SMA have been designed and analyzed using OpenSees fi nite element software. In the following, response modifi cation factor of buildings with diff erent heights and various brace confi gurations have been estimated. Numerical results show low seismic response modifi cation factor for frames equipped with SMA simple device. Hence parallel Steel–SMA hybrid device has been proposed considering practical drawbacks and high price of SMA. Results imply that proposed hybrid system increases response modifi cation factor compared to SMA simple device while the recentering capability is assured and design problems are reduced to minimum.

Performance Evaluation of Different Types of Steel Moment Resisting Frames Subjected to Strong Ground Motion through Incremental Dynamic Analysis

Behrouz Asgarian,Hamideh Khazaee,Masoud Mirtaheri 한국강구조학회 2012 International Journal of Steel Structures Vol.12 No.3

Comparative studies on seismic performance for various types of steel moment resisting frames subjected to near field and far field earthquakes are performed through Incremental dynamic analysis (IDA) method in this study. Near field earthquake has a pulse like effects on the structures. It imports immediate force in very short duration to buildings. Therefore, destructive effects of surge energy are not negligible. Four intensity indices are used, namely, peak acceleration (PGA), spectral acceleration at the structure’s first-mode period (Sa(T1, 5%)), spectral acceleration at the structure’s nth effective-mode period (Sa(Tn, 5%)) and the Spectral velocity at the structure’s first-mode period (Sv(T1, 5%)). Numerical results illustrate that the intensity measure parameters related to ground velocity and the higher mode-related parameters present better correlation with the seismic responses of near source ground motion for given systems. The higher mode-related parameters are more suitable for tall systems subjected to near field earthquakes. Moreover, the chosen parameters Sa(Tn, 5%) and Sv(T1, 5%) of near-fault impulsive ground motions enhance the performance of intensity measure of corresponding conventional parameters, i.e. Sa(T1,5%). A comparison for the special and intermediate steel moment resisting frames is made as regard to performance using IDA method. A more efficient performance is observed for the special moment resisting frames compare to intermediate ones.

Effect of local joint flexibility on the fatigue lfe assessment of jacket-type offshore platform

Behrouz Asgarian,Parviz Kuzehgar,Pooya Rezadoost Techno-Press 2024 Ocean systems engineering Vol.14 No.1

This paper investigates the impact of local joint flexibility (LJF) on the fatigue life of jacket-type offshore platforms. Four sample platforms with varying geometric properties are modeled and analyzed using the Opensees software. The analysis considers the LJF of tubular joints through the equivalent element and flexible link approaches, and the results are compared to rigid modeling. Initially, modal analysis is conducted to examine the influence of LJF on the frequency content of the structure. Subsequently, fatigue analysis is performed to evaluate the fatigue life of the joints. The comparison of fatigue life reveals that incorporating LJF leads to reduced fatigue damage and a significant increase in the longevity of the joints in the studied platforms. Moreover, as the platform height increases, the effect of LJF on fatigue damage becomes more pronounced. In conclusion, considering LJF in fatigue analysis provides more accurate results compared to conventional methods. Therefore, it is essential to incorporate the effects of LJF in the analysis and design of offshore jacket platforms to ensure their structural integrity and longevity.

Effect of soil pile structure interaction on dynamic characteristics of jacket type offshore platforms

Asgarian, Behrouz,Shokrgozar, Hamed Rahman,Shahcheraghi, Davoud,Ghasemzadeh, Hasan Techno-Press 2012 Coupled systems mechanics Vol.1 No.4

Dynamic response of Pile Supported Structures is highly depended on Soil Pile Structure Interaction. In this paper, by comparison of experimental and numerical dynamic responses of a prototype jacket offshore platform for both hinge based and pile supported boundary conditions, effect of soil-pile-structure interaction on dynamic characteristics of this platform is studied. Jacket and deck of a prototype platform is installed on a hinge-based case first and then platform is installed on eight skirt piles embedded on continuum monolayer sand. Dynamic characteristics of platform in term of natural frequencies, mode shapes and modal damping are compared for both cases. Effects of adding and removing vertical bracing members in top bay of jacket on dynamic characteristics of platform for both boundary conditions are also studied. Numerical simulation of responses for the studied platform is also performed for both mentioned cases using capability of ABAQUS and SACS software. The 3D model using ABAQUS software is created using solid elements for soil and beam elements for jacket, deck and pile members. Mohr-Coulomb failure criterion and pile-soil interface element are used for considering nonlinear pile soil structure interaction. Simplified modeling of soil-pile-structure interaction effect is also studied using SACS software. It is observed that dynamic characteristics of the system changes significantly due to soil-pile-structure interaction. Meanwhile, both of complex and simplified (ABAQUS and SACS, respectively) models can predict this effect accurately for such platforms subjected to dynamic loading in small range of deformation.

Local joint flexibility equations for Y-T and K-type tubular joints

Asgarian, Behrouz,Mokarram, Vahid,Alanjari, Pejman Techno-Press 2014 Ocean systems engineering Vol.4 No.2

It is common that analyses of offshore platforms being carried out with the assumption of rigid tubular joints. However, many researches have concluded that it is necessary that local joint flexibility (LJF) of tubular joints should be taken into account. Meanwhile, advanced analysis of old offshore platforms considering local joint flexibility leads to more accurate results. This paper presents an extensive finite-element (FE) based study on the flexibility of uni-planner multi-brace tubular Y-T and K-joints commonly found in offshore platforms. A wide range of geometric parameters of Y-T and K-joints in offshore practice is covered to generate reliable parametric equations for flexibility matrices. The formulas are obtained by non-linear regression analyses on the database. The proposed equations are verified against existing analytical and experimental formulations. The equations can be used reliably in global analyses of offshore structures to account for the LJF effects on overall behavior of the structure.

Seismic response of steel braced frames equipped with shape memory alloy-based hybrid devices

Salari, Neda,Asgarian, Behrouz Techno-Press 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.5

This paper highlights the role of innovative vibration control system based on two promising properties in a parallel configuration. Hybrid device consists of two main components; recentering wires of shape memory alloy (SMA) and steel pipe section as an energy dissipater element. This approach concentrates damage in the steel pipe and prevents the main structural members from yielding. By regulation of the main adjustable design parameter, an optimum performance of the device is obtained. The effectiveness of the device in passive control of structures is evaluated through nonlinear time history analyses of a five-story steel frame with and without the hybrid device. Comparing the results proves that the hybrid device has a considerable potential to mitigate the residual drift ratio, peak absolute acceleration and peak interstory drift of the structure.

Seismic response of steel braced frames equipped with shape memory alloy-based hybrid devices

Neda Salari,Behrouz Asgarian 국제구조공학회 2015 Structural Engineering and Mechanics, An Int'l Jou Vol.53 No.5

This paper highlights the role of innovative vibration control system based on two promising properties in a parallel configuration. Hybrid device consists of two main components; recentering wires of shape memory alloy (SMA) and steel pipe section as an energy dissipater element. This approach concentrates damage in the steel pipe and prevents the main structural members from yielding. By regulationof the main adjustable design parameter, an optimum performance of the device is obtained. The effectiveness of the device in passive control of structures is evaluated through nonlinear time history analyses of a five-story steel frame with and without the hybrid device. Comparing the results proves that the hybrid device has a considerable potential to mitigate the residual drift ratio, peak absolute acceleration and peak interstory drift of the structure.

Element loss analysis of concentrically braced frames considering structural performance criteria

Farshad Hashemi Rezvani,Behrouz Asgarian 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.3

This research aims to investigate the structural behavior of concentrically braced frames after element loss by performing nonlinear static and dynamic analyses such as Time History Analysis (THA), Pushdown Analysis (PDA), Vertical Incremental Dynamic Analyses (VIDA) and Performance-Based Analysis (PBA). Such analyses are to assess the potential and capacity of this structural system for occurrence of progressive collapse. Besides, by determining the Failure Overload Factors (FOFs) and associated failure modes, it is possible to relate the results of various types of analysis in order to save the analysis time and effort. Analysis results showed that while VIDA and PBA according to FEMA 356 are mostly similar in detecting failure mode and FOFs, the Pushdown Overload Factors (PDOFs) differ from others at most to the rate of 23%. Furthermore, by sensitivity analysis it was observed that among the investigated structures, the eight-story frame had the most FOF. Finally, in this research the trend of FOF and the FOF to critical member capacity ratio for the plane split-X braced frames were introduced as a function of the number of frame stories.

Effect of seismic design level on safety against progressive collapse of concentrically braced frames

Farshad Hashemi Rezvani,Behrouz Asgarian 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.16 No.2

In this research the effect of seismic design level as a practical approach for progressive collapse mitigation and reaching desired structural safety against it in seismically designed concentric braced frame buildings was investigated. It was achieved by performing preliminary and advanced progressive collapse analysis of several split-X braced frame buildings, designed for each seismic zone according to UBC 97 and by applying various Seismic Load Factors (SLFs). The outer frames of such structures were studied for collapse progression while losing one column and connected brace in the first story. Preliminary analysis results showed the necessity of performing advanced element loss analysis, consisting of Vertical Incremental Dynamic Analysis (VIDA) and Performance-Based Analysis (PBA), in order to compute the progressive collapse safety of the structures while increasing SLF for each seismic zone. In addition, by sensitivity analysis it became possible to introduce the equation of structural safety against progressive collapse for concentrically braced frames as a function of SLF for each seismic zone. Finally, the equation of progressive collapse safety as a function of bracing member capacity was presented.

Reduced wavelet component energy-based approach for damage detection of jacket type offshore platform

Shahverdi, Sajad,Lotfollahi-Yaghin, Mohammad Ali,Asgarian, Behrouz Techno-Press 2013 Smart Structures and Systems, An International Jou Vol.11 No.6

Identification of damage has become an evolving area of research over the last few decades with increasing the need of online health monitoring of the large structures. The visual damage detection can be impractical, expensive and ineffective in case of large structures, e.g., offshore platforms, offshore pipelines, multi-storied buildings and bridges. Damage in a system causes a change in the dynamic properties of the system. The structural damage is typically a local phenomenon, which tends to be captured by higher frequency signals. Most of vibration-based damage detection methods require modal properties that are obtained from measured signals through the system identification techniques. However, the modal properties such as natural frequencies and mode shapes are not such good sensitive indication of structural damage. Identification of damaged jacket type offshore platform members, based on wavelet packet transform is presented in this paper. The jacket platform is excited by simple wave load. Response of actual jacket needs to be measured. Dynamic signals are measured by finite element analysis result. It is assumed that this is actual response of the platform measured in the field. The dynamic signals first decomposed into wavelet packet components. Then eliminating some of the component signals (eliminate approximation component of wavelet packet decomposition), component energies of remained signal (detail components) are calculated and used for damage assessment. This method is called Detail Signal Energy Rate Index (DSERI). The results show that reduced wavelet packet component energies are good candidate indices which are sensitive to structural damage. These component energies can be used for damage assessment including identifying damage occurrence and are applicable for finding damages' location.