Implementation of Uniform Deformation Theory in semi-active control of structures using fuzzy controller

Reza Karami Mohammadi,Fariba Haghighipour 국제구조공학회 2017 Smart Structures and Systems, An International Jou Vol.19 No.4

Protection of structures against natural hazards such as earthquakes has always been a major concern. Semi-active control combines the reliability of passive control and versatility and adaptability of active control. So it has recently become a preferred control method. This paper proposes an algorithm based on Uniform Deformation Theory to mitigate vulnerable buildings using magneto-rheological (MR) damper. Due to the successful performance of fuzzy logic in control of systems and its simplicity and intrinsically robustness, it is used here to regulate MR dampers. The particle swarm optimization (PSO) algorithm is also used as an adaptive method to develop a fuzzy control algorithm that is able to create uniform inter-story drifts. Results show that the proposed algorithm exhibited a desirable performance in reducing both linear and nonlinear seismic responses of structures. Performance of the presented method is indicated in compare with passive-on and passive-off control algorithms.

TADAS Dampers in Very Large Deformations

Reza Karami Mohammadi,Arman Nasri,Azin Ghaffary 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.2

Triangular-plate Added Damping and Stiffness (TADAS) dampers are special kinds of passive control devices that can be used in seismic design and retrofitting of structural systems. However, when exposed to large deformations, primary members of a structure can be in danger of serious damage due to improper geometric characteristics of these dampers. In this study, response of a one bay frame equipped with a TADAS device, previously tested in the laboratory, was simulated using a detailed FE model in ABAQUS. A monotonic analysis was then conducted on the TADAS damper alone, which indicated that in large deformations, TADAS damper pins hit the top of the holes, resulting in an abrupt stiffness increase in the damper. Seismic analysis of a six story moment resisting frame with TADAS dampers, using a series of twelve scaled earthquake ground motions, was also conducted in OpenSees which indicated that with sudden stiffness increase in dampers, the value of moments in beams as well as axial forces in braces will increase, causing possible damages in these areas. At the end, a method for calculating the optimal height for the holes in the damper was proposed, which is shown to be in good agreement with detailed ABAQUS models.

Seismic mitigation of substation cable connected equipment using friction pendulum systems

Reza Karami Mohammadi,Masoud Mirtaheri,Mojtaba Salkhordeh,Erfan Mosaffa,Golsa Mahdavi,Mohammad Amin Hariri-Ardebili 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.72 No.6

Power transmission substations are susceptible to potential damage under seismic excitations. Two of the major seismic failure modes in substation supplies are: the breakage of brittle insulator, and conductor end fittings. This paper presents efficient isolation strategies for seismically strengthening of a two-item set of equipment including capacitive voltage transformer (CVT) adjacent to a Lightning Arrester (LA). Two different strategies are proposed, Case A: implementation of base isolation at the base of the CVT, while the LA is kept fixed-base, and Case B: implementation of base isolation at the base of the LA, while the CVT is kept fixed-base. Both CVT and LA are connected to each other using a cable during the dynamic excitation. The probabilistic seismic behavior is measured by Incremental Dynamic Analysis (IDA), and a series of appropriate damage states are proposed. Finally, the fragility curves are derived for both the systems. It is found that Friction Pendulum System (FPS) isolator has the potential of decreasing flexural stresses caused by intense ground motions. The research has shown that when the FPS is placed under LA, i.e. Case B (as oppose to Case A), the efficiency of the system is improved in terms of reducing the forces and stresses at the bottom of the porcelain. Several parametric studies are also performed to determine the optimum physical properties of the FPS.

An improvement to seismic design of substation support structures

Mohammadi, Reza Karami,Akrami, Vahid,Nikfar, Farzad Techno-Press 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.6

The acceleration that the electrical equipment experiences on a structure can be several times the ground acceleration. Currently, substation support structures are being designed according to ASCE (Substation Structure Design Guide 2008), without any consideration about effects of these structures on dynamic behavior of mounted equipment. In this paper, a parametric study is implemented in order to improve seismic design of candlestick substation structures based on this design guide. To do this, dynamic amplification factor (DAF) of different candlestick support-equipment combinations is evaluated and compared to the target DAF presented in IEEE STD 693 (2006). Based on this procedure, a new criterion is developed to restrict maximum acceleration at support-equipment intersection.

An improvement to seismic design of substation support structures

Reza Karami Mohammadi,Vahid Akrami,Farzad Nikfar 국제구조공학회 2013 Structural Engineering and Mechanics, An Int'l Jou Vol.45 No.6

The acceleration that the electrical equipment experiences on a structure can be several times the ground acceleration. Currently, substation support structures are being designed according to ASCE (Substation Structure Design Guide 2008), without any consideration about effects of these structures on dynamic behavior of mounted equipment. In this paper, a parametric study is implemented in order to improve seismic design of candlestick substation structures based on this design guide. To do this, dynamic amplification factor (DAF) of different candlestick support-equipment combinations is evaluated and compared to the target DAF presented in IEEE STD 693 (2006). Based on this procedure, a new criterion is developed to restrict maximum acceleration at support-equipment intersection.

On the optimum performance-based design of eccentrically braced frames

Reza Karami Mohammadi,Amir Hossein Sharghi 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.16 No.4

The design basis is being shifted from strength to deformation in modern performance-based design codes. This paper presents a practical method for optimization of eccentrically braced steel frames, based on the concept of uniform deformation theory (<i>UDT</i>). This is done by gradually shifting inefficient material from strong parts of the structure to the weak areas until a state of uniform deformation is achieved. In the first part of this paper, <i>UDT</i> is implemented on 3, 5 and 10 story eccentrically braced frames (EBF) subjected to 12 earthquake records representing the design spectrum of ASCE/SEI 7-10. Subsequently, the optimum strength-distribution patterns corresponding to these excitations are determined, and compared with four other loading patterns. Since the optimized frames have uniform distribution of deformation, they undergo less damage in comparison with code-based designed structures while having minimum structural weight. For further investigation, the 10 story EBF is redesigned using four different loading patterns and subjected to 12 earthquake excitations. Then a comparison is made between link rotations of each model and those belonging to the optimized one which revealed that the optimized EBF behaves generally better than those designed by other loading patterns. Finally, efficiency of each loading pattern is evaluated and the best one is determined.

Mode shape identification using response spectrum in experimental modal analysis

Babakhani, Behrouz,Rahami, Hossein,Mohammadi, Reza Karami Techno-Press 2018 Structural monitoring and maintenance Vol.5 No.3

The set of processes performed to determine the dynamic characteristics of the constructed structures is named experimental modal analysis. Using experimental modal analysis and interpreting its results, structural failure can be assessed and then it would be possible to plan for their repair and maintenance. The purpose of the experimental modal analysis is to determine the resonance frequencies, mode shapes and Mode damping for the structure. Diverse methods for determining the shape of the mode by various researchers have been presented. There are pros and cons for each of these methods. This paper presents a method for determining the mode shape of the structures using the response spectrum in the experimental modal analysis. In the first part, the principles of the proposed method are described. Then, to check the accuracy of the results obtained from the proposed method, single and multiple degrees of freedom models were numerically and experimentally investigated.