Linear antenna arrays are synthesized to have maximum Directivity for a specified beamwidth. The Directivity is maximized subject to a given beamwidth such as null to null or half power one. The excitation currents are obtained using a matrix equation obtained from the Lagrange multiplier method. The performance of the proposed method is studied by means of some examples. The synthesized arrays have the pre-specified beamwhidths and their Directivity is close to the number of elements.

In this study, we assessed the performance of a concrete bridge under the dynamic strain of an earthquake in the near and far domain of earth’s faults. With respect to available data and showing the effects of key factors and variables, we have examined the bridge’s performance. The modelling of a double span bridge has been done in CSI Bridge software and has been compared and examined to assess the capability of a bridge under the strain of a close-to-fault-line earthquake and a far-from-fault-line earthquake. Timeline interpretation was done on the resulting models and from 7 records from the past earthquakes and it was observed that the close to fault line earthquakes caused much bigger displacements when compared to far from fault line earthquakes. Bridges which are separated by a quake separator, have an acceptable response to far from fault line earthquakes. This means that by disassembling these bridges, the acceleration rate on the deck, the cut of the base, as well as the relative displacement of the deck relative to the undivided bridge, is reduced. This issue is not reflected in the response of the bridges to faults near earthquakes. By investigating the record of near-earthquakes, it was observed that these earthquakes produced large displacements to earthquakes that are far from faults, which could make the isolation system more critical, so, to avoid this event, it FDGM should be used to reform the response these bridges have to the earthquake.Based on these results, it can be stated that the displacements near the fault and with the effect of progressive movement will be greater than the distances from the fault, so that for the ratio of different distances from the fault, the lower this ratio is, the maximum displacement of the bridge and the maximum cutting force will also be greater.

Introduction: The nature of near-field earthquake records is very complicated and uncertain. Due to this complexity, the prediction of the real structural responses has become very difficult. Based on the analysis of the physical characteristics of near-field records, it is possible to use the simplified mathematical models. Near-field ground motions which are often associated with a progressive directional phenomenon due to their particular type of the causative fault, have much more destructive effects on the structures than the other quake tremors. The related research results show that under the influence of a strong near-field ground motion which contains forward Directivity effects, the structural responses would be entered to a great nonlinear domain. On the other hand, due to the limited number of available near-field records, it is needed to prepare artificial acclerograms which can simulate the characteristics of the strong ground motions. Thus, it is possible to achieve a vast data base corresponding to wide range of powerful ground motions using mathematical wavelets. As a result, it provides a general overview of these types of artificial quake tremors and prepares an extended knowledge on the performance of structures in confronting these destructive movements...

A special class of ground motions near the fault regions has distinct characteristics that are different from far-field ground motions. One of the critical features of these ground motions is the existence of a velocity pulse in the ground motion record in the direction perpendicular to the fault rupture. These pulse-like ground motions generally occur when the fault rupture propagates towards a site located near the fault. The accumulation of energy in the seismic wave front results in a velocity pulse with a relatively long period in the direction perpendicular to the fault line. This phenomenon could adversely affect the seismic performance of tall buildings with relatively long fundamental periods. In this paper the effect of velocity pulse on seismic response of a 42-story reinforced concrete building with a central core wall structural system is evaluated. The building has already been studied in the TBI project of the Pacific Earthquake Engineering Research Center (PEER). The structural model of the building is developed based on the information contained in the PEER report. The model is first verified by conducting a nonlinear response analysis using one of the ground motion records in the PEER report and comparing the results with that report. After verification, the model is subjected to three earthquake records each containing a velocity pulse (i. e., Northridge 1994, Cape Mendocino 1992, and Chuetsu-Oki, Japan 2007). Subsequently, the velocity pulse of each record is removed using a recently proposed wavelet-based signal processing approach and the building is analyzed again to determine the impact of the velocity pulse. The results of the analyses show that the velocity pulse significantly affects the seismic response of the building. By removing the velocity pulse, the lateral drift and rotation of the coupling beams decrease by about 50% and 60%, respectively. Also, the forces in the structure (shear and bending moment) are reduced by about 40%. The dominant effect of the velocity pulse on the seismic response of the building is due to the high energy content in the frequency range of the pulse velocity. However, due to the different frequency content of each record, the effect of the pulse period cannot be accurately assessed. Therefore, the study of buildings with the same lateral bearing system and different natural periods (i. e., different heights) can be considered as a way to evaluate the effect of the pulse period on seismic response of the building.

There are few actual records of near fault ruptures with features different from those of far fields. These features are mostly affected by forward Directivity in near field earthquakes. So, investigation into this field of study by using methods such to simulate records would be essential Until now, different methods have been used by researchers to simulate strong ground motion. Stochastic simulation is a method widely used for simulating high frequency ground motion in recent years. This method, which considers a point source, was presented by Boore (1983). The seismic source is considered to be a rectangular fault plane divided by some sub-faults in its longitudinal and traversal directions. Bersneve and Atkinson (1998) have introduced earthquake stochastic simulation based on finite fault modeling. In such simulations, each subfault is considered a point source, using the source model presented by Brune, with a corner frequency and a constant stress drop. The target accelerogram is obtained by summation of accelerograms generated by each subfault and by considering their corresponding delay times. This new modeling considers rupture geometry and the Directivity effect; therefore, its results will be more appropriate.The stress drop parameter is one of the most important parameters in stochastic simulation that has a high uncertainty. This parameter is studied here, based on both stochastic point source and finite fault modeling. For this purpose, the stress drop is calculated for 7 Iranian earthquakes with at least one near field record. Then, these earthquakes have been simulated by using the results of the stress drops. Finally, several parameters, such as nu, t0, gamma, and the impulse peak, which affect near field records and Directivity pulses, have been investigated.

Ground motions in the near field of a rupturing fault differ from ordinary ground motions, as they contain a large energy, or “Directivity” pulse. This pulse can cause considerable damage during an earthquake. Failures of modern engineered structures observed within the nearfault region in the recent earthquakes have revealed the vulnerability of existing RC buildings against pulse-type ground motions. This may be due to the fact that these modern structures had been designed primarily using the design spectra of available standards which was developed using stochastic processes with relatively long duration that characterizes more distant ground motions. Many recently designed and constructed buildings may therefore require strengthening in order to perform well when subjected to near-fault ground motions. This paper presents the results of a study of the response of typical existing RC buildings to near-fault ground motions and the potential improvements achievable after FRP retrofitting of the buildings. Results show that in case of near-fault records, they impose higher demands in comparison to far-fault records, though the maximum drift is generally concentrated at the middle story levels. It is demonstrated that strengthening with FRP is very effective in reducing drift demands for structures for a wide range of natural periods. The rehabilitated buildings possess an elastic stiffness 1.4 times that of the original buildings and have a total shear force capacity, 1.5 times that of the original buildings. The cumulative energy dissipation for rehabilitated specimens is 2.3 times that of the original building, on average.

The near-fault zone motions exhibit long-period pulses in the velocity and displacement time history diagrams. These large pulses can cause severe damage to structures; therefore, near-field records have a different nature compared to far-field records. The acceleration reflection spectrum of the earthquakes recorded in the stations located near the fault is out of the usual shape, and in the period of intervals greater than 7 seconds, the amplitudes of the reflection spectrum increase significantly. The orientation of the structure near the fault is crucial, and the directionality effect should be considered due to the high relative risk in the studied area.     Rupture starts from a point along the fault and propagates unilaterally to the beginning or end of the fault or propagates bilaterally to both directions. The propagation of rupture along the fault and the effect of rock fracturing velocity on shear wave velocity is called Directivity. When the direction of rupture propagation is towards the site, the Directivity effect can cause pulses with large amplitudes and medium to long periods. Directivity changes the energy distribution over time and can also occur in moderate and small earthquakes. Therefore, in addition to the distance to the fault, the direction of rupture propagation is also important.     A study on the probabilistic seismic hazard analysis in Kermanshah province (Iran) showed that increasing the structural period and return period increases the ground motion acceleration. The greatest acceleration increase occurs in the 4-second period and 2475-year return period. In return periods of 2475 and 475 years, the percentage increase in acceleration experiences a higher value, and the Directivity effect is more pronounced in a return period of 2475 year compared to 475 year.

In this study, considering the location of Dorud city in the area near the strike-slip and seismic fault of Doroud, the effects of the near site and the Directivity due to rupture have been investigated in seismic hazard analysis studies. Doroud fault is located near the cities of Doroud and Boroujerd, in the western part of Iran. Dorud and Boroujerd are among the important cities of Iran in the agricultural industry and also due to the pristine nature in these areas has always been of interest to tourists. The micro-earthquakes recorded in this area indicate the activity of the Doroud fault system. In order to prevent possible earthquake damage in this area, seismicity studies can be useful to study the acceleration of the ground by considering the effects of the site in order to strengthen the construction of civil structures. Abrahamson (2000) and Somerville et al., (1997) were among the first researchers to establish studies based on this, and the relationships and methods proposed by them are more acceptable today in applying the directional effect. These researchers considered two parameters of angle and ratio of fault length as a direct factor in the effect of orientation and examined the results for the acceleration spectrum created. The effect of orientation can lead to the formation of long-period pulses in the earth's motion, which some proposed models (eg Somerville et al., 1997) can measure the quantity of this effect in estimating earthquake risk analysis with a deterministic and probabilistic approaches. (Abrahamson, 2000). In this study, seismic hazard has been investigated, compared and evaluated by considering the effects of Doroud fault in different periods and different return periods by considering the effect of orientation and also without applying the effect of orientation. Near-field and directional effects can lead to long-period pulses in ground motion parameter, and for structures with long periods such as bridges and dams near faults with high activity rates. The inclusion of directional effects in attenuation relationships, to see whether for deterministic and probabilistic approach can have a great impact on the results of realistic seismic hazard analysis. Doroud fault is one of the most important faults in Iran with a history of large earthquakes in the early instrumental period and its mechanism of strike-slip mechanism, It can intensify the strong motion parameters during earthquakes for long periods in the city of Dorud, and consequently cause serious damage to structures with long periods in this area. In this study, the parameters of strong ground motion in the analysis of probabilistic earthquake hazard by applying direction for the range of Doroud fault have been estimated. In addition, by examining the disaggregation of earthquake hazard, the effect of direction for the contribution of distance and magnitude in estimating the strong motion parameter has been evaluated. In the short and long return periods, the effect of Directivity for different periods for the strong motion has been estimated and evaluated by the Somerville and Abrahamson method. The estimated acceleration is calculated and evaluated for three return periods, 50, 475 and 2475 years and in periods of 0. 75, 1, 2, 3 and 4 sec. The value of the strong motion parameter was directly related to the increase of the return period and the period, so that the highest amount of acceleration increase (17. 16 percentage) with the effect of Directivity was calculated in the return period of 2475 years and in the 4-second period.

Studies on behavior of structures under the effect of earthquakes in the near-field earthquakes, compared to far-field earthquakes, have shown more effects of this type of earthquake on the structure. Most of these effects depend on the characteristics of forward-Directivity and flip-step with permanent displacement effect. The characteristics of near-filed earthquakes should be considered in the design and analysis of structures. The present research, aimed to investigate the effect of Directivity characteristics of near-field earthquakes on the response of concrete structures. To this aim, first the different records of ChiChi earthquake in different stations have been determined as the basis for selecting accelerograms. Then, using analytical methods, the response spectrum of these records, considering the effect of forward-Directivity and without it (removing dominant pulses) in the east-west and north-south directions was determined. Next, using time history analysis on two concrete structures of 10 and 15 stories, the drift (relative displacement) and the inter-story base shear in the structures was investigated for seven records of ChiChi earthquake. The results showed that due to the unpredictable nature of the earthquake, the drift and base shear responses of stories in both structures have been increased or decreased in different directions in some cases. Therefore, it can be seen that Directivity does not always have a uniform effect on the behavior of the structure and does not follow a fixed pattern. Also, the results showed that by increase in the height of the structure and as a result of increasing its period, the effect of forward-Directivity on the response of the structure increases. This is despite the fact that in many cases of shorter structures, the Directivity does not have much effect on the response of the structure and even in some cases; it has caused a decrease in the response.

Design and simulation of high directive waveguide directional couplers based on supershapes are presented, in the present paper. In order to obtain high Directivity, circular holes in a conventional coupler are equivalently substituted with supershape holes. In the frequency range from 8 to 12 GHz, the coupling values of two proposed couplers are 19± 1 dB and 23± 2 dB and the directivities are better than 20 dB. The simulation results show that almost 20 dB improvement in the Directivity can be achieved as compared to a conventional coupler. The results are valuable for the design and development of broadband high directive waveguide couplers.