In this paper, a new composite artificial magnetic conductor (AMC) surface with magneto-dielectric substrate is presented for wide band radar cross section (RCS) reduction. It is shown that magneto-dielectric substrate can increase the in-phase reflection bandwidth of AMC structure. In this structure, the composite surface consists of two AMC types that operate at two different resonance frequencies. The phase difference between these two AMC types is tuned to be close to ±180 over a wide bandwidth so that the reflections from them cancel each other. The results show with this technique, RCS reduction more than 13 dB was achieved with a 93% bandwidth.

Due to the growing popularity of Reinforced Concrete column with Steel beam (RCS) moment frame system in recent years, there are lots of publications about the performance of this structural system. In this paper, fifteen RCS joints with practical details are studied using a verified finite element method. Joint details of the models include Cover Plate, Additional Bearing Plate, Steel Doubler Plate, and joint stirrups. The results show that Cover Plate can be used instead of a combination of steel doubler plate and joint stirrups; it improves the joint performance by increasing the confinement of joint region and contributing to joint shear strength.

In this paper, the performance and sensitivity of the cylindrical electromagnetic cloak considering the effect of different simplified cloaks are investigated. The performance of simplified cloak is less than ideal cloak; however, it can be realized in practice with acceptable level of RCS reduction. The exact wave solution for different regions of cylindrical cloak is derived and validated with full-wave simulations results based on COMSOL Multiphysics. Numerical experiments of RCS are performed for frequency band from 10MHz to 3GHz. The results of simulation show more than 18dB RCS reduction for simplified cloak.

Advantages such as high ductility, reduction of dead load and higher energy dissipation of the structures made with steel beams and concrete columns compared to conventional reinforced concrete structures have resulted in the widespread use of these structures. On the other hand, the provisions of different codes of RCS connections lead to complex details and implementation. In this paper, the behavior of steel beam to circular concrete column connections was experimentally studied. Five real scale external RCS connections were made and tested. Variable parameters of the specimens were included the tie spacing around and inside the connections, confinement around the connection region with CFRP sheets and concrete type. The aim of the study was to propose a connection with simple details and desirable behavior. The results indicated that the proposed connection can appropriately transfer the moment from the steel beam to the concrete column in addition to having simple implementation. Also, the confinement of the connection region with CFRP sheets increased the ductility and energy dissipation of the RCS.

In this research the seismic demand of RCS structures under the near-fault earthquakes is investigated. For this purpose 5 RCS intermediate moment frames with 4, 7, 10, 15 and 20 stories and 5 spans (span length 5 and 7m) were designed. Then nonlinear dynamic analysis was performed on the structures using the OpenSees software. Results show that the stories displacement under the near-fault earthquakes is larger than the far-fault earthquakes so that with increase in the structure height the difference between them decreases. In high rise structure with 7m length span, the drift-angle due to the far-fault earthquake is greater than the near-fault earthquake.

Radar cross section (RCS) calculation is an important issue of objects stealth and identification. It is necessary to design the RCS software because of the high cost of RCS measurements in practice. In this paper, designing of efficient software using physical optics theorem for radar cross section calculation of the complex perfect electric conductors or complex dielectric objects for high frequencies is investigated. In this method, first the object will be meshed in Abaqus Software. Then the obtained data of every mesh is transferred to MATLAB Software and, after that, the physical optics theorem is applied for every mesh, with considering the summation of electric fields that is seen from each mesh. As the result, the radar cross section of total object will be obtained. Simulations results show the proposed method has good agreement with CST-MS results and determines the RCS of the objects with lower complexity in the lower time consuming.

Concealment and hiding of military equipment from the enemy is one of the most important issues in the design of this equipment. This hiding generally performed against microwave frequencies, and the quantity that minimized is the radar cross section (RCS). In order to measure the mentioned quantity, it is necessary to expose the target in an environment without reflection to electromagnetic waves and then to measure the reflected waves from it and thus determine the RCS. In most cases, RCS of an object is the desired in the absence of the ground effect. However, the object is exposed to the ground effect due to its position on the pylon, and in addition to measuring the real object, its image also be seen. One way to reduce the ground effect is to use metal fences. However, the edges diffraction and the large side lobe level of the reflected wave from these fences has made their use difficult. As shown, the use of resistive tapered fences solves both of the above problems. In this paper, for the first time, using 7 fences with tapered resistance and designing a desired arrangement for them, this effect has been removed in the form of five examples. Since the length of the fences is several meters and several tens of wavelengths, here the whole structure considered two-dimensional and therefore a two-dimensional moment code (2D-MoM), in addition to the asymptotic solution of CST software, used to analyze the structure.

The composite RCS moment resisting frame, including concrete columns and steel beams, has some advantages in comparison with the ordinary steel and concrete moment resisting frames. Previous studies have shown that these systems, in case of preserving sufficient strength and needed ductility in seismic condition, could be effective in design and construction. Notwithstanding the previous research, during the 1970s and 1980s, the use of this composite structural system was limited to areas with low seismic hazard in the US, and it was used as a replacement for steel moment resisting frames and high rise buildings. Besides, in Japan, it was used instead of concrete frames in low rise and short span buildings. In the previous research on these structures, studies were made on the frame and RCS connections, but there has not been any study on the seismic assessment of the RCS structure with time history and for the near-fault earthquakes. Investigating the structure behavior under near-fault earthquake, due to the special nature and characteristics of these earthquakes in comparison to the far-fault earthquakes, seems to be essential. In this research, the seismic demand of composite RCS and concrete structures under the near-fault earthquakes are investigated in comparison with the far-fault earthquakes.For this purpose, five composite RCS intermediate moment resisting frames with 4, 7, 10, 15 and 20 stories and five spans were designed, and then, nonlinear dynamic analysis was performed on the structures using the Open Sees software under 10 far-fault and 10 near-fault accelerographs. The obtained results in this research showed that the stories displacement demand due to the far and near-fault earthquakes in composite structures is lower with respect to the stories displacement of concrete structure due to the same record, and by increasing the number of stories, the values of this difference increase. The effectiveness of near-fault records on the composite structures is greater than the ordinary concrete structures. It seems that the assessment of high rise composite structures with respect to high rise concrete structures yields a better displacement response. Finally, the effect of steel beam in reducing displacement due to both of the records is observed.RESEARCH METHOD: In this research, the seismic demand of RCS and RC moment frames under the near-fault earthquakes are investigated with respect to the far-fault earthquakes. For this purpose, five RCS and RC intermediate moment resisting frames with 4, 7, 10, 15 and 20 stories and five spans were designed and then nonlinear dynamic analysis was performed on the structures using the Open Sees software. Then, 10 far-fault and 10 near-fault accelerographs were used respectively. All used accelerograms that have been received from the site of Peer, had a view to soil type of III on the basis of regulations of seismic design code of Iran (2800) or dirt Class of D based on the classification guidelines of FEMA. To draw the whole reactionary response, the software of SeismoSignal was used and all accelerograms before scaling had their equal maximum with acceleration (PGA). For nonlinear dynamic analysis on intended frames, Open Sees software was used and the results of story displacement, drift angle and story shear were provided in full paper. Selected records in this study were applied to the models and finally the decision has been made among the obtained responses. For scaling, accelerograms used method for scaling of the Fourth Edition of 2800 guideline. Finally, the effect of steel beam in reducing displacement due to both of the records is observed.CONCLUSION: Displacement and drift angle of RC structures under near-fault records was more than far-fault records. However, with increasing the number of stories, drift angle of RC structures under far-fault records was more than near-fault records By an increase in the number of stories, the RCS frames' drift angle due to near records is less than RC frames. The drift angle in RCS tall buildings under near-fault records and in RC tall buildings under far-fault records are more critical. Base shear of RCS structures under near-fault records was more than the base shear under far-fault records and by an increase in number of stories, the difference was reduced. In RCS frames, by an increase in the number of stories, steel beams cause a decrease in effectiveness of drift angle and displacement under near-fault records.