Amir Shirkhani is an Assistant Professor of Structural and Earthquake Engineering and a Visiting Professor at UBC Smart Structures Group, The University of British Columbia, Vancouver. His current research works are on Structural Vibration Control, Seismic Resilience, Seismic Rehabilitation and Retrofit, Structural Optimization, Seismic Hazard Levels, Innovative Structural Systems, Performance-Based Earthquake Engineering, Seismic Loss Assessment, Cost-Benefit Analysis, Endurance Time (ET) Method, Machine Learning, etc. Email: shirkhani@tjamcaas.ac.ir; shirkhani.ac@gmail.com
Structural Vibration Control Seismic Resilience Seismic Rehabilitation and Retrofit Structural Optimization Seismic Hazard Levels Innovative Structural Systems Performance-Based Earthquake Engineering Seismic Loss Assessment Cost-Benefit Analysis Endurance Time (ET) Method Machine Learning
Triple Friction Pendulum Isolators (TFPIs) have been widely used to enhance the seismic capacity of structures in the recent decade. This study intends to measure the effect of different Ground Motion (GM) sets, including Far-Fault (FF) and Near-Fault (NF) records, on the seismic response of the Triple Friction Pendulum (TFP) isolated structures. For this aim, different Engineering Demand Parameters (EDP), including Inter-story Drift Ratio (IDR), absolute floor acceleration, base shear, residual displacement, and damage energy are measured using numerous Nonlinear Time History (NTH) analyses. A three-dimensional mid-rise special moment resisting frames (SMFs) steel building isolated with TFPIs has been designed as per ASCE 7-16. In addition, the separate and simultaneous effect of raising the damping ([Formula: see text]) and the period ([Formula: see text]) of the base isolation system on the seismic responses of the superstructure are measured to assess the structural performance and estimate the damage energy. The [Formula: see text] and the [Formula: see text] are amplified up to 30% and 4.5 times of the superstructure period in incremental steps, respectively. The results show that the damage energy of the superstructure in the Initial Design Parameters' Values (IDPVs) of the isolator under NF records with Forward-Directivity pulses (NF-FD-GMs) is more significant than damping energy, while an inverse trend has occurred for other GM sets. Increasing the IDPVs up to a certain level reduces most EDPs and consequently causes an improvement in the seismic performance of the superstructure. The novel developed empirical relationships can be utilized as useful tools to predict IDRs and the damage states of the superstructure. The variations of the EDPs with respect to simultaneous or separate increasing the IDPVs are also reported for different GM sets.
In this research, the superstructure behavior in isolated structures has been studied based on their ductility. For this purpose, three tall structures isolated by triple friction pendulum isolators (TFPI) have been designed. The ductility of superstructures is different due to their different seismic force-resisting systems. The performance of the structures has been evaluated by endurance time (ET) method. This method significantly reduces nonlinear dynamic analysis time by optimizing the number of desired earthquake records to one to three endurance time excitation functions (ETEFs). Additionally, the seismic response of structures under different earthquake hazard levels can be achieved by this method. Results show that the change in ratio of the isolator period to the superstructure period (TI/TS) can affect floor acceleration, TFPI displacement and interstory drift ratio (IDR). However, TFPI displacement and IDR are also sensitive to the type of superstructure system, whether it is a braced frame or a moment frame. Moreover, there is a possibility of entering the collapse phase of structural components in tall isolated structures with braced or moment frame which are designed by linear static and spectral methods, under an earthquake with a return period equal to the earthquake hazard level considered in the design step.
Steel structures with dual systems, including special moment-resisting frames (SMRFs) and special concentrically braced frames (SCBFs), have found extensive applications in seismically active regions due to their considerable lateral stiffness and ductility. However, the seismic performance of such system has not been investigated subjected to near-field ground motion records. To address this research gap, this paper evaluates collapse risk and earthquake-induced loss of multi-story steel structures with dual concentrically braced frames. A comprehensive seismic performance assessment is conducted on selected five-, 10-, and 15-story structures subjected to near-field ground motions (NF-GMs) with and without pulses based on the methodology provided in FEMA P-58. The results are also used to assess the effect of NF-GMs with pulses on the seismic performance measures , such as life-cycle cost and repair time of the studied structures at different seismic intensity levels. Finally, the contribution rate of collapse and demolition of structures, and contribution of structural and nonstructural members in the repair cost and time of the steel structures are estimated and compared subjected to NF-GMs. It is concluded that collapse and demolition loss play significant roles for NF-GMs with and without pulses, respectively, while the seismic collapse behavior is governed by the ratio of the pulse period of the GM to the period of the first mode of the structure.
Recently, an arch and ring yielding damper (ARD), composed of a metallic central ring surrounded by four arcs, has been proposed as an innovative energy dissipation device to enhance the seismic resilience of structures. Although the hysteretic behavior of the ARD was examined, the efficiency of this novel damper when implemented in building structures has not been investigated. This article focuses on the seismic performance of sub-standard steel moment resisting frames (MRFs) equipped with ARDs. First, a novel mathematical equation is developed to predict the hysteretic response of ARD based on an extensive nonlinear finite element analysis including various geometrical parameters of the device, using multivariate nonlinear fitting methods and artificial neural network. Then, to evaluate the effectiveness of ARDs, a comparative seismic response analysis of a four-story steel building without (MRF) and with ARDs (MRF-ARD) is performed under different seismic hazard levels within a multi-level framework. The parameters of the ARDs are determined using a displacement-based design method. The analysis is performed by Nonlinear Time History Analysis (NLTHA) and Endurance Time Analysis (ETA) methods. The numerical results show that upon adding ARDs to the structure, the inter-story drift and base shear ratios are reduced by about 20 % and 50 %, respectively, with the highest probability being for 10 %/50 years and 2 %/50 years hazard levels (BSE-1 and BSE-2, respectively). The obtained ET curves also show that the original MRF cannot meet the life safety performance level at the BSE-1 hazard level, while the MRF-ARD meets this requirement in an efficient manner. • Seismic performance assessment of steel MRF with novel arc-and-ring dampers (ARDs) • New expression for hysteretic response of ARD based on extensive parametric NLFEAs • A novel displacement-based design approach for the ARDs has been presented • Steel MRF with ARDs under different seismic hazard levels within a multi-level framework • ARDs dissipate a very high percentage of the input energy at all investigated hazard levels
Cement manufacture is a considerable industrial activity in terms of its volumes and contribution to greenhouse gas emissions. This study apprises the environmental impact of the clinker and Portland cement production in Iran, using life cycle impact assessment. Data used in the cement manufacture life cycle inventory are based on site surveys of energy consumption, raw material use, and transportation distances. Emissions were estimated based on U. S. EPA emission factors. Most of these pollutants were belong to kiln, preheater and diesel fuel, respectively. To a comprehensive impact assessment, some impact and damage categories based on CML baseline, Pfister et al 2009, IMPACT 2002+, cumulative exergy demand (CExD), and Eco‐indicator 99 methods were investigated. Environmental hotspots in all categories were detected. Production process was identified as a substantial contributor in most of the categories, such as global warming impact category and damage to human health. Electricity was the other main contributor. It had the highest share in the total of CExD indictor. Iron ore had the enormous contribution in the impact categories of mineral extraction. In this article, water scarcity footprint for cement manufacture was also investigated. It was concluded that diesel is the main impact categories related to water scarcity indicator. © 2018 American Institute of Chemical Engineers Environ Prog, 37: 1901–1907, 2018
Corrosion of the rebar embedded in concrete has a fundamental role in the determination of life and durability of the concrete structures. Researches have demonstrated that artificial neural networks (ANNs) can effectively predict issues such as expected damage in concrete structures in marine environment caused by chloride penetration, the potential of steel embedded in concrete under the influence of chloride, the corrosion of the steel embedded in concrete and corrosion current density in steel reinforced concrete. In this study, data from different kind of concrete under the influence of chloride ion, are analyzed using the neural network and it is concluded that this method is able to predict the bond strength between the concrete and the steel reinforcement in mentioned condition with high reliability.
The T-shaped friction damper (TFD) is a damping system that appropriately absorbs and dissipates input energy during seismic excitations. In this paper, a practical method for determining optimum slip load of TFDs in multi-storey steel frames is proposed. The seismic performance index (SPI) is used as a measure to quantify the effectiveness of TFDs in improving the seismic behaviour of prototype structures. The optimum slip load of TFDs is acquired based on this index. The endurance time (ET) method is a seismic analysis in which structures are subjected to gradually increasing dynamic excitation. It is shown that using the ET method, instead of the large number of time-history analyses, to obtain the SPI of the system, results in a considerable reduction in computational effort. An approximate relation to obtain the optimum slip load of the TFD is also proposed according to the design base shear of the frames. The performance of the TFDs in the steel frames is investigated by examining a prototype weak steel structure before and after rehabilitation using TFDs. The rehabilitated structure, by considering the optimum slip load of TFDs, satisfies the collapse prevention and life safety levels in BSE-2 and BSE-1 hazard levels, respectively.
Performance-based optimization of energy dissipation devices in structures necessitates massive and repetitive dynamic analyses. In the endurance time method known as a rather fast dynamic analysis procedure, structures are subjected to intensifying dynamic excitations and their response at multiple intensity levels is estimated by a minimal number of analyses. So, this method significantly reduces computational endeavors. In this paper, the endurance time method is employed to determine the optimal placement of viscous dampers in a weak structure to achieve the desired performance at various hazard levels, simultaneously. The viscous damper is one of the energy dissipation systems which can dissipate a large amount of seismic input energy to the structure. To this end, hysteretic energy compatible endurance time excitation functions are used and the validity of the results is investigated by comparing them with the results obtained from a suite of ground motions. To optimize the placement of the dampers, the genetic algorithm is used. The damping coefficients of the dampers are considered as design variables in the optimization procedure and determined in such a way that the sum of them has a minimum value. The behavior of the weak structure before and after rehabilitation is also investigated using endurance time and nonlinear time history analysis procedures in different hazard levels.
In this paper, the seismic performance of a five-story steel structure with a dual system used as a lateral load resisting system comprised of a moment-resisting frame and a concentrically braced frame is evaluated under near-field ground motion records with and without pulses. This research paper aims to evaluate the pulses’ effects on the probability of the collapse, global damage index, and the annual and 50-year collapse risks of the structure with such dual systems, which have been less considered in previous research works. To this end, incremental dynamic analyses are performed, and to determine the probability that the studied structure will exceed a specific damage state, fragility functions are developed. The global damage index of the structure is also computed, and a full assessment of the collapse risk of the structure is carried out under the near-field ground motion records with and without pulses. Finally, It is concluded that the probability of collapse, global damage index, and the annual and 50-year collapse risks of the structure subjected to the ground motions with pulses are higher than the ground motions without pulses. For the pulse periods larger than two times the period of the first mode of the structure, the intensification occurs due to the equalization of the increased period of the first mode of the structure and the period of the pulse.
This work presents a study on the seismic assessment of steel frames with Friction Damper Devices (FDDs). The devices were used to dissipate seismic input energy and protect buildings from structural and nonstructural damage during moderate and severe earthquakes. In the Endurance Time (ET) method, structures are subjected to a specially designed intensifying ground acceleration function and their performance is judged based on their response at various excitation levels. In this paper, steel moment frames equipped with FDDs is investigated under Nonlinear Time History (NTH) and ET analyses. According to the NTH and ET results, it is concluded that by adding FDDs, the reduction percentage of roof displacement of frames will be decreased by increasing the number of stories. ET results show that FDDs have a vital role in energy dissipation because their hysteresis loop is rectangular.
This research presents a study on the seismic assessment of steel frames with Rotational Friction Dampers (RFDs). The devices were used to protect structures from damage during earthquakes. In this study, steel moment frames equipped with RFDs is investigated under Nonlinear Time History (NTH) and Incremental Dynamic Analysis (IDA). Maximum interstory drift ratio is studied as Engineering Demand Parameter (EDP). According to the IDA curves, it is concluded that by adding RFDs, the behavior of steel frames changes from hardening phase to severe hardening phase.
This paper addresses the Direct Displacement-Based Design (DDBD) approach of multi-story RC frame structures consistent with changes to design criteria between Turkish earthquake codes of TSC-2007 and TBEC-2018. The corresponding response modification factor (R) of structures designed based on the DDBD approach is also estimated in this research. The design base shear forces of both codes are compared considering different R factors and also with that of the DDBD approach. The results showed that the DDBD approach, as per TBEC-2018, provides RC frame structures with higher R values compared to the similar approach in accordance with TSC-2007. The Endurance Time (ET) method is a time history-based procedure for seismic assessment of structures under intensifying dynamic excitations aided to judge their performance at various intensity levels. Since, up to now, the ET method has not been considered to evaluate the performance of the structures designed by the DDBD approach, this paper addresses this issue. The ET performance curves of RC frames show that structures designed by the DDBD approach in accordance with TBEC-2018 exhibit higher Interstory Drift Ratios (IDRs) values than TSC-2007 at various hazard levels.
