Incremental dynamic analyses of concrete buildings reinforced with shape memory alloy

Masoud Mirtaheri,Mehrshad Amini,Hossein Khorshidi 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.1

The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. Because of different mechanical properties of SMAs compared to the regular steel bars, the use of SMAs as reinforcement in the concrete may change the response of structures under seismic loads. In this study, the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3-, 6- and 8-story reinforced concrete (RC) buildings. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel) only, (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Incremental Dynamic Analyses (IDA) are performed using ten different ground motion records to determine the seismic performance of Steel, Steel-SMA and SMA RC buildings. Then fragility curves for each type of RC building by using IDA results for IO, LS and CP performance levels are calculated. Results obtained from the analyses indicate that 3-story frames have approximately the same spectral acceleration corresponding with failure of frames, but in the cases of 6 and 8-story frames, the spectral acceleration is higher in frames equipped with steel reinforcements. Furthermore, the probability of fragility in all frames increases by the building height for all performance levels. Finally, economic evaluation of the three systems are compared.

A Damage Mitigation Measure for Steel Structures under Blast Loading

Masoud Mirtaheri,Ehsan Sharei,Anahita Norouzi 한국강구조학회 2011 International Journal of Steel Structures Vol.11 No.3

The number of explosive attacks on civilian buildings has recently increased and the pattern of damage inflicted on structures when an explosion takes place remains quite difficult to predict. This paper performs a 3-dimensional dynamic response and damage analysis on steel frame structure, subjected to blast loads created by explosive devices. In this study, advantages of using polymer cables as a means of damage mitigation are investigated. Results from this study shows that synthetic fiber ropes as bracing for steel structures reduce the horizontal displacements of structure caused by air blast pressure. The contribution of fiber ropes in structural stability is also presented.

Mitigation of progressive collapse in steel structures using a new passive connection

Masoud Mirtaheri,Fereshteh Emami,Mohammad A. Zoghi,Mojtaba Salkhordeh 국제구조공학회 2019 Structural Engineering and Mechanics, An Int'l Jou Vol.70 No.4

If an alternative path would not be considered for redistribution of loads, local failure in structures will be followed by a progressive collapse. When a vertical load-bearing element of a steel structure fails, the beams connected to it will lose their support. Accordingly, an increase in span\'s length adds to the internal forces in beams. The mentioned increasing load in beams leads to amplifying the moments there, and likewise in their corresponding connections. Since it is not possible to reinforce all the elements of the structure against this phenomenon, it seems rational to use other technics like specified strengthened connections. In this study, a novel connection is suggested to handle the stated phenomenon which is introduced as a passive connection. This connection enables the structure to tolerate the added loads after failing of the vertical element. To that end, two experimental models were constructed and thereafter tested in half-scale, one-story, double-bay, and bolted connections in three-dimensional spaces. This experimental study has been conducted to compare the ductility and strength of a frame that has ordinary rigid connections with a frame containing a novel passive connection. At last, parametric studies have been implemented to optimize the dimensions of the passive connection. Results show that the load-bearing capacity of the frame increased up to 75 percent. Also, a significant decrease in the displacement of the node wherein the column is removed was observed compared to the ordinary moment resisting frame with the same loads.

Improving the behavior of buckling restrained braces through obtaining optimum steel core length

Masoud Mirtaheri,Saeed Sehat,Meissam Nazeryan 국제구조공학회 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.4

Concentric braced frames are commonly used in steel structures to withstand lateral forces. One of the drawbacks of these systems is the possibility that the braces are buckled under compressive loads, which leads to sudden reduction of the bearing capacity of the structure. To overcome this deficiency, the idea of the Buckling Restrained Brace (BRB) has been proposed in recent years. The length of a BRB steel core can have a significant effect on its overall behavior, since it directly influences the energy dissipation capability of the member. In this study, numerical methods have been utilized for investigation of the optimum length of BRB steel cores. For this purpose, BRBs with different lengths placed into several two-dimensional framing systems with various heights were considered. Then, the Response History Analysis (RHA) was performed, and finally, the optimum steel core length of BRBs and its effect on the responses of the overall system were investigated. The results show that the shortest length where failure does not occur is the best length that can be proposed as the optimum steel core length of BRBs. This length can be obtained through a formula which has been derived and verified in this study by both analytical and numerical methods.

Improving the behavior of buckling restrained braces through obtaining optimum steel core length

Mirtaheri, Masoud,Sehat, Saeed,Nazeryan, Meissam Techno-Press 2018 Structural Engineering and Mechanics, An Int'l Jou Vol.65 No.4

Concentric braced frames are commonly used in steel structures to withstand lateral forces. One of the drawbacks of these systems is the possibility that the braces are buckled under compressive loads, which leads to sudden reduction of the bearing capacity of the structure. To overcome this deficiency, the idea of the Buckling Restrained Brace (BRB) has been proposed in recent years. The length of a BRB steel core can have a significant effect on its overall behavior, since it directly influences the energy dissipation capability of the member. In this study, numerical methods have been utilized for investigation of the optimum length of BRB steel cores. For this purpose, BRBs with different lengths placed into several two-dimensional framing systems with various heights were considered. Then, the Response History Analysis (RHA) was performed, and finally, the optimum steel core length of BRBs and its effect on the responses of the overall system were investigated. The results show that the shortest length where failure does not occur is the best length that can be proposed as the optimum steel core length of BRBs. This length can be obtained through a formula which has been derived and verified in this study by both analytical and numerical methods.

Local and global buckling condition of all-steel buckling restrained braces

Seyed Masoud Mirtaheri,Meissam Nazeryan,Mohammad Kazem Bahrani,Amin Nooralizadeh,Leila Montazerian,Mohamadhosein Naserifard 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.2

Braces are one of the retrofitting systems of structure under earthquake loading. Buckling restrained braces (BRBs) are one of the very efficient braces for lateral loads. One of the key needs for a desirable and acceptable behavior of bucklingrestraining brace members under intensive loading is that it prevents total buckling until the bracing member tolerates enough plastic deformation and ductility. This paper presents the results of a set of analysis by finite element method on buckling restrained braces in which the filler materials within the restraining member have been removed. These braces contain core as the conventional BRBs, but they have a different buckling restrained system. The purpose of this analysis is conducting a parametric study on various empty spaces between core and restraining member, the effect of friction between core and restraining member and applying initial deformation to brace system to investigate the global buckling behavior of these braces. The results of analysis indicate that the flexural stiffness of restraining member, regardless of the amount of empty space, can influence the global buckling behavior of brace significantly.

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.

Investigation of shear lag effect on tension members fillet-welded connections consisting of single and double channel sections

Moien Barkhori,Shervin Maleki,Masoud Mirtaheri,Meissam Nazeryan,S.Mahdi S.Kolbadi 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.74 No.3

Shear lag phenomenon has long been taken into consideration in various structural codes; however, the AISC provisions have not proposed any specific equation to calculate the shear lag ratio in some cases such as fillet-welded connections of front-to-front double channel sections. Moreover, those equations and formulas proposed by structural codes are based on the studies that were conducted on riveted and bolted connections, and can be applied to single channel sections whilst using them for fillet-welded double channels would be extremely conservative due to the symmetrical shape and the fact that bending moments will not develop in the gusset plate, resulting in less stress concentration. Numerical models are used in the present study to focus on parametric investigation of the shear lag effect on fillet-welded tension connection of double channel section to a gusset plate. The connection length, the eccentricity of axial load, the free length and the thickness of gusset plate are considered as the key factors in this study. The results are then compared to the estimates driven from the AISC-LRFD provisions and alternative equations are proposed.

Progressive collapse analysis of steel building considering effects of infill panels

Mohammad Abbasi Zoghi,Masoud Mirtaheri 국제구조공학회 2016 Structural Engineering and Mechanics, An Int'l Jou Vol.59 No.1

Simplifier assumptions which are used in numerical studies of progressive collapse phenomenon in structures indicate inconsistency between the numerical and experimental full-scale results. Neglecting the effects of infill panels and two-dimensional simulation are some of these assumptions. In this study, an existing seismically code-designed steel building is analyzed with alternate path method (AP) to assess its resistance against progressive collapse. In the AP method, the critical columns be removed immediately and stability of the remaining structure is investigated. Analytical macro-model based on the equivalent strut approach is used to simulate the effective infill panels. The 3-dimentional nonlinear dynamic analysis results show that modeling the slabs and infill panels can increase catenary actions and stability of the structure to resist progressive collapse even if more than one column removed. Finally, a formula is proposed to determine potential of collapse of the structure based on the quantity and quality of the produced plastic hinges in the connections.

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.