With the increase of knowledge in seism city and subsequent need to modify the earthquake engineering design specification for buildings, it would be essential to investigate the behavior of such buildings and structures and the probable need for seismic retrofitting. On the other hand there are construction problems in strengthening and retrofitting methods using bracing system that reduces the owners wish to do so. In this paper an attempt has been made to investigate the behavior of existing building designed by second version of standard 2800 for seismic design of buildings and retrofitting of such structures using ADAS (Added Damping and Stiffness).For this purpose steel buildings are retrofitted once using bracing members alone and then using both bracing and ADAS dampers. The behavior of the steel frames was compared using non linear time history analysis. The behavior factor 'R' was calculated for each case. The assumed buildings had pinned jointed braced frames having different number of bays and stories. The results showed significant improvement in behavior of retrofitted frames with ADAS damper associated with lower content of steel. Comparisions indicated that negligible damage occurred in members of these frames and acceptable behavior was observed under earthquake loading. The members showed higher potential of withstanding sever earthquakes. Investigations have indicated a lack of information and design specification for structures with ADAS dampers.

In this paper, steel ordinary moment resisting frame buildings designed according to the Iranian Earthquake Code (Standard No.2800, 2nd edition) are evaluated based on seismic retrofitting provision for existing buildings. Also, their seismic performance is investigated in the range of both linear and non-linear behaviors. At first, several common samples of these systems were designed through 2800 code. So, critical frame of these samples was controlled using the seismic retrofitting provision in base upgrading level through the several detailed numerical analyses (non-linear static, linear dynamic spectrum and time history). Based on the obtained results, bending performance of all members in all structures is controlled by deformation and with linear dynamic time history analysis using the record of happened earthquakes in Iran such as Bam, do not need to be strengthened. The shearing low-height structures showed a reasonable performance in the range of non-linear behavior. However the flexural structures (6 and 8-storeyed) with non-linear static procedure and all of structures with linear dynamic spectrum method should be improved.

Performance based seismic design usually requires nonlinear dynamic or static analyses to assess the performance level of the structure under seismic action. To trace the exact performance point of a structure, these analyses should sometimes be repeated several times over. Analysis iterations mainly depend on the initial design and performance of the structure. So, a method that can present an appropriate initial selection with minimum time and e_ort would be precious. Such a method would also be very e_ective for seismic structural assessment. In this paper, an intelligent system has been created for the estimation of plastic hinge distribution and lateral ductility distribution and, also, for the assessment of existing steel structures, based on a direct displacement based design procedure. The method has been applied to the steel braced frames with concentric bracing systems in low, medium and high rise buildings. The designer can use this knowledge based system to obtain the performance level of existing steel structures, according to proposed seismic code levels. Finally, the intelligent system has been veri_ed using nonlinear dynamic analysis.

Infrastructures such as bridges, buildings, pipelines, marine structures, etc., play an important role in human life. Since major disasters in these structures, such as the collapse of bridges or buildings, often result in many casualties, damages, and social and economic problems, most industrialized countries allocate significant funds to monitor their health. Failure detection strategies and continuous monitoring of the structure's condition, especially after natural and manufactured disasters, make necessary measures to be taken in the early stages of failure and can reduce the cost of maintenance and the possibility of collapse. Structural health monitoring methods often provide an opportunity to reduce maintenance, repair, and retrofit costs during the structure's life cycle. Most of the structural health monitoring methods proposed and implemented to identify possible damages depend on the structure's dynamic characteristics. One of the most practical methods, which uses the results of time domain system identification to detect failure, is the damage locating vector (DLV) method. The DLV method aims to identify load combinations that result in zero strain fields for damaged members in both healthy and damaged structures. To accomplish this, we find a vector in the null space of the difference between the plasticity matrices of the two structures. The singular value analysis method is used on the plasticity difference matrix to calculate this space. The method involves applying the space vectors to the healthy structure and recording the internal stresses of the members, which are then converted into weighted normal stress (WSI) using statistical tools. The member with a lower WSI is more likely to be damaged. Since truss structures are usually used in bridges, long-span structures, as well, as a wide range of steel buildings with simple and braced frames, this research uses the covariance-based random subspace optimal method in identifying the modal characteristics, which is very efficient in low excitations, has been taken into consideration to check and monitor health during operation. To investigate the capability of the DLV method in the damage detection of these structures, a 5-story residential building with a simple steel frame was subjected to the Centro earthquake. According to the desired damage scenario, the second and fifth floors were introduced as the damaged floors in this earthquake by applying a 30 and 50% reduction in the cross-section. To account for uncertainty in the data collection, we included the mean root square of the second sensor's data in the results for sensors 3 and 5. As a result of this uncertainty, the damping error between 5 and 10% has been shown in the damaged and healthy structure. Using the method (SSI_ORT), it was observed that two DLV vectors were extracted. Further, with the increasing uncertainty of the random vibration test results, it was observed that the extraction DLVs could extract the possible damaged elements with high accuracy. Next, the effect of input and output noises on the results obtained from the DLV method was investigated. This study found that by increasing the SNR of the outputs by 15% while increasing the error of the extracted modal characteristics, the extracted DlVs also lose sufficient accuracy in diagnosing structural damage.

One of the usual method for seismic retrofit of existing reinforced concrete buildings is steel bracing. The use of steel bracing and reinforced concrete shear wall for strengthening of existing reinforced concrete buildings usually leads to very complicated system and the study of this kind of structures is necessary. In this paper, the frame-shear wall and steel bracing interaction is investigated by the analysis of a then-story reinforced concrete building. The analytical results show that with an increase in the section area of steel bracing, the lateral displacement and earthquake shear absorption by the frame decreases. Increasing the section area of steel bracing improve the overall response of the structure, but it has a less significant effect on the results after a certain level. The behavior of steel bracing and frame and the amount of shear absorption by both of them is approximately the same in the lower part of structure. Application of steel bracing decreases the lateral displacement by about 50 percent.    

Protective steel doors are widely used in buildings due to their high resistance against the impact loads. However, its heavy weight has been always considered as a major drawback for these doors. In this paper, a new optimized stiffened impact-protective steel door incorporating sandwich panel with aluminum foam core (OSSA) is examined. This door consists of two face sheets, main and secondary stiffeners, and aluminum foam as the inner core. In order to optimize the door, at first the rigidity and weight functions of the stiffened steel door were extracted. Then an optimal door weighing 42% less than the primary door was obtained. Due to the high energy absorption capacity of the combined foam core and stiffened steel door structure, the use of aluminum foam core in the optimized steel door was proposed. By doing numerical analysis, and depending on the thickness of the face sheet of OSSA, 20 to 32% reduction in the maximum displacement was observed. The results also showed that, with 67% increase in the peak overpressure, OSSA has kept almost the same maximum displacement as that of the steel door without an aluminum foam. In other words, by using aluminum foam core in the optimized stiffened door, the door will resist 67% more impact load.

The reliability of structures under different loading conditions is the main objective of civil engineers. Progressive collapse is a catastrophic phenomenon which has been of greatest interest to many researchers and engineers during the last decade. The incidence of diverse accidents such as burst, fire, vehicle collision, miscalculation, mistake in construction can result in a partial failure in a structure, which sometimes extends to collapse the majority of or entire a building. This phenomenon is called the progressive collapse. This collapse is defined in some regulations in the same way. For example in NISTIR-7396 ``the progressive collapse is the expansion of a primary damage triggered by a primer incident from an organ to others consequently causing either major or entire damage to a construction''. The main aim of this project is to study the reaction of the steel moment frame with the rigid connection of SP, WUF-B and RBS under the progressive collapse. To pursue the study, we used six-, nine-and 12-floor buildings representing short, mid and tall structures equipped by the steel moment frame system. The alternative path method and UFC 4-023-03 regulation were used as standard methods to estimate the progressive collapse. The modelling of the buildings was run by software SAP 2000 which is in 3D, and then non-linear dynamic time history performed to analyze the data. Moreover, we predicted the different scenarios of column removals regarding the regulation criteria in order to study the progressive collapse. The results from the alternative path method showed that unlike the WUF-B and SP connections, the RBS has more potential resistance due to higher ductility. Furthermore, the tall buildings presented the better resistance against collapse as well, because of the higher indeterminate degree. The results from column removals in the given models showed the more destruction in the upper floors unlike the removals of columns in downward floors.

Pounding of adjacent building have been seen in the moderate and strong earthquakes. There are different methods to model the impact. One of these methods is contact elements. Contact elements include linear and nonlinear elastic and viscoelastic and Hertz-damp elements. Investigators have generally studied on contact elements in elastic structures. In this study, the ability of different contact modelings is added to Opensees software. Validation of modeling is achieved by comparing the numerical result of this study with other investigations' numerical studies. Simulations between analytical modeling and experimental studies show that to conquer displacement, results of different contact elements are the same, but velocity and contact force results of elements with and without damping have more accuracy. Finally these elements are used to model the contact of 5-story building under 6 records, in two left to right and right to left states. As regards, Hertz-damp has the least uncertainty of modeling; therefore results of other elements are compared with this element. Results generally show that accuracy of nonlinear elements is more than linear elements. This is more obvious in the maximum contact forces.