Seismic investigation of pushover methods for concrete piers of curved bridges in plan

Hamid Reza Ahmadi,Nariman Namdari,Maosen Cao,Mahmoud Bayat 사단법인 한국계산역학회 2019 Computers and Concrete, An International Journal Vol.23 No.1

The use of non-linear analysis of structures in a functional way for evaluating the structural seismic behavior has attracted the attention of the engineering community in recent years. The most commonly used functional method for analysis is a non-linear static method known as the “pushover method”. In this study, for the first time, a cyclic pushover analysis with different loading protocols was used for seismic investigation of curved bridges. The finite element model of 8-span curved bridges in plan created by the ZEUS-NL software was used for evaluating different pushover methods. In order to identify the optimal loading protocol for use in astatic non-linear cyclic analysis of curved bridges, four loading protocols (suggested by valid references) were used. Along with cyclic analysis, conventional analysis as well as adaptive pushover analysis, with proven capabilities in seismic evaluation of buildings and bridges, have been studied. The non-linear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. To conduct IDA, the time history of 20 far-field earthquake records was used and the 50% fractile values of the demand given the ground motion intensity were computed. After analysis, the base shear vs displacement at the top of the piers were drawn. Obtained graphs represented the ability of a cyclic pushover analysis to estimate seismic capacity of the concrete piers of curved bridges. Based on results, the cyclic pushover method with ISO loading protocol provided better results for evaluating the seismic investigation of concrete piers of curved bridges in plan.

Effects of geometrical parameters on the degree of bending in two-planar tubular DYT-joints of offshore jacket structures

Hamid Ahmadi,Mahdi Ghorbani Techno-Press 2023 Ocean systems engineering Vol.13 No.2

Through-the-thickness stress distribution in a tubular member has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures. This stress distribution can be characterized by the degree of bending (DoB). Although multi-planar joints are an intrinsic feature of offshore tubular structures and the multi-planarity usually has a considerable effect on the DoB values at the brace-to-chord intersection, few investigations have been reported on the DoB in multi-planar joints due to the complexity of the problem and high cost involved. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified based on available parametric equations, was used to study the effects of geometrical parameters on the DoB values in two-planar tubular DYT-joints. Parametric FE study was followed by a set of nonlinear regression analyses to develop six new DoB parametric equations for the fatigue analysis and design of axially loaded two-planar DYT-joints.

Flexible Prime-Field Genus 2 Hyperelliptic Curve Cryptography Processor with Low Power Consumption and Uniform Power Draw

Hamid-Reza Ahmadi,Ali Afzali-Kusha,Massoud Pedram,Mahdi Mosaffa 한국전자통신연구원 2015 ETRI Journal Vol.37 No.1

This paper presents an energy-efficient (low power) prime-field hyperelliptic curve cryptography (HECC) processor with uniform power draw. The HECC processor performs divisor scalar multiplication on the Jacobian of genus 2 hyperelliptic curves defined over prime fields for arbitrary field and curve parameters. It supports the most frequent case of divisor doubling and addition. The optimized implementation, which is synthesized in a 0.13 m standard CMOS technology, performs an 81-bit divisor multiplication in 503 ms consuming only 6.55 J of energy (average power consumption is 12.76 W). In addition, we present a technique to make the power consumption of the HECC processor more uniform and lower the peaks of its power consumption.

SCFs in offshore two-planar tubular TT-joints reinforced with internal ring stiffeners

Ahmadi, Hamid,Imani, Hossein Techno-Press 2022 Ocean systems engineering Vol.12 No.1

The majority of tubular joints commonly found in offshore jacket structures are multi-planar. Investigating the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works. However, due to the diversity of joint types and loading conditions, a number of quite important cases still exist that have not been studied thoroughly. Among them are internally ring-stiffened two-planar TT-joints subjected to axial loading. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified against available numerical and experimental data, was used to study the effects of geometrical parameters on the chord-side SCFs in two-planar tubular TT-joints reinforced with internal ring stiffeners subjected to two types of axial loading. Parametric FE study was followed by a set of nonlinear regression analyses to develop six new SCF parametric equations for the fatigue analysis and design of axially-loaded two-planar TT-joints reinforced with internal ring stiffeners.

Health monitoring of pedestrian truss bridges using cone-shaped kernel distribution

Hamid Reza Ahmadi,Diana Anvari 국제구조공학회 2018 Smart Structures and Systems, An International Jou Vol.22 No.6

With increasing traffic volumes and rising vehicle traffic, especially in cities, the number of pedestrian bridges has also increased significantly. Like all other structures, pedestrian bridges also suffer damage. In order to increase the safety of pedestrians, it is necessary to identify existing damage and to repair them to ensure the safety of the bridge structures. Owing to the shortcomings of local methods in identifying damage and in order to enhance the reliability of detection and identification of structural faults, signal methods have seen significant development in recent years. In this research, a new methodology, based on cone-shaped kernel distribution with a new damage index, has been used for damage detection in pedestrian truss bridges. To evaluate the proposed method, the numerical models of the Warren Type steel truss and the Arregar steel footbridge were used. Based on the results, the proposed method and damage index identified the damage and determined its location with a high degree of precision. Given the ease of use, the proposed method can be used to identify faults in pedestrian bridges.

Evaluation of prooxidant-antioxidant balance in in vitro fertilization-conceived mice

Ahmadi, Hamid,Fathi, Fardin,Moeini, Ashraf,Amidi, Fardin,Sobhani, Aligholi The Korean Society for Reproductive Medicine 2018 Clinical and Experimental Reproductive Medicine Vol.45 No.2

Objective: Concerns about the safety of assisted reproductive technology (ART) have been raised, as some studies have shown elevated incidence rates of childhood cancer, asthma, allergies, and other diseases in ART-conceived babies. Findings regarding the health of ART-conceived babies are controversial. The present study was conducted to evaluate the prooxidant-antioxidant balance (PAB) in in vitro fertilization (IVF)-conceived mice in comparison to naturally conceived offspring. Methods: Mice (6-8 weeks) were divided into two groups (IVF-conceived and naturally conceived) matched by sex, age, weight, and litter size. A 1-mL blood sample was taken and the sera were separated. The oxidant-antioxidant balance was evaluated using a fast and reliable PAB assay. The results were expressed as $mean{\pm}standard$ deviation. Results: The mean PAB values (HK units) in the IVF-conceived and naturally conceived groups were $59.70{\pm}22.30$ and $54.70{\pm}18.22$, respectively (p= 0.82). Conclusion: Since free radicals contribute to several pathological conditions and antioxidants play an important protective role against oxidative stress, evaluating the oxidant-antioxidant balance is very important. Although the results of this study showed that the quality of the defense mechanism against free radicals was not significantly different between the IVF-conceived and naturally conceived mice, other parameters of metabolic dysfunction need to be measured.

The Effects of Hearing Aid Digital Noise Reduction and Directionality on Acceptable Noise Level

Roghayeh Ahmadi,Hamid Jalilvand,Mohammad Ebrahim Mahdavi,Fatemeh Ahmadi,Ali Reza Akbarzade Baghban 대한이비인후과학회 2018 Clinical and Experimental Otorhinolaryngology Vol.11 No.4

Objectives. Two main digital signal processing technologies inside the modern hearing aid to provide the best conditions for hearing aid users are directionality (DIR) and digital noise reduction (DNR) algorithms. There are various possible settings for these algorithms. The present study evaluates the effects of various DIR and DNR conditions (both separately and in combination) on listening comfort among hearing aid users. Methods. In 18 participants who received hearing aid fitting services from the Rehabilitation School of Shahid Beheshti University of Medical Sciences regularly, we applied acceptable noise level (ANL) as our subjective measure of listening comfort. We evaluated both of these under six different hearing aid conditions: omnidirectional-baseline, omnidirectional-broadband DNR, omnidirectional-multichannel DNR, directional, directional-broadband DNR, and directional-multichannel DNR. Results. The ANL results ranged from −3 dB to 14 dB in all conditions. The results show, among all conditions, both the omnidirectional-baseline condition and the omnidirectional-broadband DNR condition are the worst conditions for listening in noise. The DIR always reduces the amount of noise that patients received during testing. The DNR algorithm does not improve listening in noise significantly when compared with the DIR algorithms. Although both DNR and DIR algorithms yielded a lower ANL, the DIR algorithm was more effective than the DNR. Conclusion. The DIR and DNR technologies provide listening comfort in the presence of noise. Thus, user benefit depends on how the digital signal processing settings inside the hearing aid are adjusted.

Cultural Semiotics Analysis of Carpet and Furniture in Iranian Lifestyle

Hamid Reza Shairi,Maryam Ahmadi 고려대학교 응용문화연구소 2020 에피스테메 Vol.0 No.23

The present study seeks to analyze cultural semiotics of carpet and furniture place, as significant objects rooted in Iranian culture for centuries, and in the process of paradigmatic and syntagmatic, they examine the functional, anthropological, semantic and value differences in Iranian cultural discourse. Thus, the main question is “what has been the influence of carpet and furniture as the main household objects in Iranian lifestyles during the contemporary era, and what elements and concepts of our identity and culture have transformed in this interaction?”. According to the findings of this research, it can be argued that carpet, together with many of its meanings in the contemporary era, has lost its central position, become smaller and found an auxiliary function alongside other furniture. Its practical value has diminished, and sometimes has an amusing aspect, while the furniture has enjoyed many signs meanings and has not only changed Iran's lifestyle in the contemporary era, but it also caused a greater distinction and formality of communications. It also acts as a sign of power and distinctive relations. As a result, it is understood how the objects are measured and valued based on social class and tastes in the contemporary lifestyle.

Synthesis and employment of PEGDA for fabrication of superhydrophilic PVDF/PEGDA electrospun nanofibrous membranes by in-situ visible photopolymerization

Hamid Reza Ashjari,Arsalan Ahmadi,Mir Saeed Seyed Dorraji 한국화학공학회 2018 Korean Journal of Chemical Engineering Vol.35 No.1

A methodology for the synthesis of light curable poly(ethylene glycol) diacrylate (PEGDA) is described. PEGDA synthesis was confirmed using 1H NMR, 13C NMR, and infrared spectroscopy. The resin was used for fabrication of the superhydrophilic PVDF/PEGDA nanofibrous membrane in a single processing step. For the in-situ photo cross-linking reaction during electrospinning process, the electrospinning apparatus was equipped with a visible light source. Degree of conversion of double bonds during electrospinning process and interaction between the two polymers were investigated by FT-IR spectrum. To determine the potential applications of the as-prepared the membranes in wastewater treatment, parameters such as morphology, hydrophilicity and water resistance were investigated by scanning electron microscopy (SEM), tensile strength, static water contact angle (WCA) and Fourier transform infrared spectroscopy (FT-IR). The results showed that PVDF/PEGDA (40/60) nanofibrous membrane is superhydrophilic and insoluble in water.

Superharmonic and subharmonic vibration resonances of rotating stiffened FGM truncated conical shells

Hamid Aris,Habib Ahmadi 국제구조공학회 2023 Structural Engineering and Mechanics, An Int'l Jou Vol.85 No.4

In this work, superharmonic and subharmonic resonance of rotating stiffened FGM truncated conical shells exposed to harmonic excitation in a thermal environment is investigated. Utilizing classical shell theory considering Coriolis acceleration and the centrifugal force, the governing equations are extracted. Non-linear model is formulated employing the von Kármán non-linear relations. In this study, to model the stiffener effects the smeared stiffened technique is utilized. The non-linear partial differential equations are discretized into non-linear ordinary differential equations by applying Galerkin’s method. The method of multiple scales is utilized to examine the non-linear superharmonic and subharmonic resonances behavior of the conical shells. In this regard, the effects of the rotating speed of the shell on the frequency response plot are investigated. Also, the effects of different semi-vertex angles, force amplitude, volume-fraction index, and temperature variations on the frequencyresponse graph are examined for different rotating speeds of the stiffened FGM truncated conical shells.