جستجوی مقالات مرتبط با کلیدواژه "x brace" در نشریات گروه "عمران"

Passive control devices dissipate a significant amount of earthquake input energy and thus reduce the seismic demand for structural members. They are widely used in civil engineering due to their relatively low cost of installation, maintenance and simplicity. A slotted bolt connection type friction damper has the ability to provide more flexible performance due to frictional sliding during dynamic and static cyclic loads compared to the yielding dampers. The purpose of this research is to investigate the probabilistic approach and the seismic fragility of structures with slotted bolt connection using vertical link and compare it with the case without slotted bolt connection. In this study, by performing an incremental dynamic analysis with the help of 22 pairs of far-field earthquake records based on FEMA P-695, three types of 4, 8 and 12-story steel structures modeled in the OpenSEES software are investigated. Seismic fragility in different damage states, collapse margin ratios of the structure and also the possibility of collapse of the eccentrically bracing structure with the slotted bolted connection and without it have been discussed. The conducted research shows that the story velocity and base shear responses of the structure decreases when using slotted bolt connection. The results also indicate that the used friction damper leads to the improvement of seismic fragility and the increase of the collapse margin ratios, which can be mentioned as a 20% increase in the 12-story structure. In addition, the probability of structural failure has decreased by 35% on average compared to the eccentrically bracing structure without damper.

A CBF frame is an earthquake-resistant system used in steel structures. The brace of this system can be used in various shapes, such as X-shaped, V-shaped, elbow, etc., each of which can change the behavior of the structure. However, low plasticity, high hardness, absorption, and low seismic energy consumption are among the disadvantages of this system. A seismic design should be such that the structure remains in a linear range without damage during small earthquakes. It will suffer non-structural damage in moderate earthquakes, and it will have structural and non-structural damage during severe earthquakes, but its stability will be maintained with a proper design. The brace can also be quickly and economically modified and strengthened after the earthquake damage. The literature has shown that the use of arc or ellipse braces can act properly in transferring lateral forces and improve the behavior of the structure. In this research, therefore, four models of CBF frames with arch braces in different shapes are proposed to investigate their seismic behavior in a two-story structure. The models designed by the finite element method were subjected to lateral and cyclic loading to compare their bearing capacity, seismic behavior, ductility, seismic energy consumption, behavior coefficient, stiffness reduction, failure mode, and economic index. A summary of the results shows that the use of ellipse braces in the two-story structure can be more compatible with the purpose of this research.

According to the experiences gained from past earthquakes, the need for a structure that has less damage and can be easily repaired after an earthquake is essential. One of the methods of depreciating seismic energy and having a repairable structure is to use the rocking brace system. In this study, the effect of using swing brace along with liquid viscous damper in improving the seismic fragility of structures has been investigated. The swing brace is formed by adding a liquid viscous damper. The set of this system has been installed at the base of the structure. For numerical studies, a three-story shear structural model with nonlinear behavior is considered. The examined structures in an uncontrolled state and equipped with a brace-swing-damper system have been subjected to the vibration of 60 earthquake records recommended in the seismic regulations with different specifications and frequency content. The results of dynamic analyzes are subjected to regression analysis to obtain the relationship between the intensity of earthquake excitation and the response of the structure and to estimate the seismic demand of the structure. Finally, the fragility curves for mild, mild, extensive, and complete performance levels for three performance criteria including drift ratio of structural members, drift ratio of non-structural members sensitive to drift and acceleration of non-structural members sensitive to acceleration have been determined and compared. The results indicate the effective performance of the brace-swing-damper system in improving the seismic fragility of the studied structures, so that the fragility has decreased by 35%.

Due to the mechanical behavior of brb braces and concrete frames differing, combining these shows complex behavior in a seismic. It can be used to dual system Brb-Rcf in a concrete moment frame to Improve structural responses. Considering that the behavior of the BRB brace in compression and tension is similar; It can solve the unbalanced force in the Double-K bracing system. The desirability of the Double-K arrangement and its combination with the RCF system as a dual system should be investigated in order to investigate the possibility of using Double-K braces in the RCF system and reducing residual deformations in the case of the dual system. For this purpose, a series of buildings have been analyzed and designed in three structural systems: Rcf, dual frame with brb brace, and bare frame with brb brace according to relevant valid regulations. The pushover and time history analysis have been done, and the capacity curves, base shear, and residual deformation have been investigated and studied. Adding brb braces to the concrete moment frame and dually using them increased the structure's capacity. In the studied structures, from 84% increase capacity in 4-story structure to 94% increase capacity in 12-story structure. This increase is due to the interaction of the concrete moment frame and the brb braces in a dual system. Also, the use of brb braces has made the structure repairable. Because in the concrete structure of the moment frame and the bare frame, the failures were concentrated in the beams and a little in the columns, respectively, but in the structure with Brb-Rcf, the losses were mainly transferred to the braces, which are easily replaceable. Also, the reduction of residual deformation of the structure reduces causes the cost of repair and reconstruction in the structure. Investigations on the formation of hinge showed Due to the Double-K brace that no hinge was formed in the middle of the columns. the losses were mainly transferred to the braces, which are easily replaceable. Also, the reduction of residual deformation of the structure reduces causes the cost of repair and reconstruction in the structure. It was also observed that the structure in combination with the brace in the Brb-Rcf system is designed more economically and with fewer consumables. It is shown in the structure of 8, 4 & 12 story; that the base shear has increased in the frames with brb braces and this increase has been greater in the dual system due to the bending frame and the brb braces. Also, in the hinge, it was observed that the failures of the double structure were less and the types of failures were better according to the replaceability. In general, due to less failure and more base shear that the dual system  structure has, it can be said that the stiffness and resistance due to the interaction of the bending frame and the non-buckling brace has increased, which is the result of the good performance of the dual structure. By comparing the base shear, the suitability of these values ​​with the bearing analysis is clear, so that there also the results showed the increase of the base shear due to the interaction of the frame and the non-buckling brace.

In this research, the progressive collapse of braced frames with knee braces in steel structures under fire load was investigated based on the software modeling method. In order to carry out the research 3, 6 and 9-story steel frames with coaxial and off-axis knee bracing systems were considered in the shape of inverted-V and were analyzed and analyzed using the software method and ABAQUS and SAP software. In this regard, at first, the frames were analyzed and designed by modeling the frames in SAP software, and the sections of the frames were determined. In the following, the frame was analyzed in ABAQUS software under the fire load. the frame without and with the removal of the critical elements was analyzed successively under the fire load in the SAP software to check and compare the energy of the frame samples in each case based on the results obtained from the analysis. Based on the study conducted on the frame with off-axis and coaxial knee bracing, it was determined that the bracing type of off-axis had a significant effect on reducing the energy of the frame compared to the coaxial bracing system. The 3,6 and 9-storyframes with off-axis knee bracing had 35%, 50% and 65% less energy than the frames with coaxial knee braces during the fire and in the entire time period.

A complex truss is a structure consisting of triangular units made up of long, narrow components that are joined at the end by a joint. Such structures are widely used in construction and industrial structures due to their ability to transmit force in long distances and spans between supports. The force of members of complex trusses, unlike simple and compound trusses, cannot be calculated using equilibrium equations alone. In recent years, Henneberg and virtual work methods that follow similar principles have been used to analyze and calculate the force of members of obscure trusses, in order to calculate the force of the members, the complex trusses have to be analyzed twice, their calculations are very long and time consuming. In this new method, there is no need to analyze the complex truss two or more times, and in a shorter time by writing less equilibrium equations and with one analysis structure, the force of the complex truss members is obtained. Another advantage of this new method is the control of calculations performed in each step independently. In addition to certain complex trusses, this method also has the ability to analyze indeterminate complex trusses and so simple hinged frame with concentrated brace, which other methods do not have this capability. This new method the force of all members is obtained with one analysis of complex truss.

Nowadays, with the advances in welding technology and increased use of steel structures in the construction of buildings, especially high-rises, the necessity of matching the construction procedure with the structure analysis procedure has become more evident. In steel structures with moment-resisting frame-concentrically braced frame (MRF-CBF) dual systems, as the moment-resisting frame can individually withstand gravity and seismic loads during construction, the braces can be installed on a story-by-story basis simultaneous with the installation of the moment frame or after its complete construction. This issue cannot be investigated and studied using ordinary analysis, where it is assumed that the entire structure is built at once, and then all the involved loads are applied to the completed structure. Accordingly, this research investigated the effects of staged construction on MRF-CBF dual systems with X brace. In this regard, 3D models with 5, 10, 15, 20, and 25 stories incorporating MRF-CBF dual system were first generated and subjected to pushover analysis under cyclic loading protocols. Subsequently, parameters such as column shortening and column axial forces under dead load, displacement and base shear corresponding to the first plastic hinge formation, effective lateral stiffness, ultimate lateral strength, and energy dissipation of the structure under cyclic loading protocols were investigated. From the obtained results, it was concluded that staged construction could lead to maximum increases of 17.9% in the axial forces in internal columns due to dead load, 3.8% in the displacement corresponding to the first plastic hinge formation, 8.3% in the base shear corresponding to the first plastic hinge formation, 18.4% in the ultimate lateral strength, and 4.3% in the effective lateral stiffness. Also, staged construction was not found to significantly affect the axial forces in corner and braced-bay columns due to dead load and the energy dissipation under cyclic loading protocols.

Regular structural systems have been designed based on supplying sufficient ductility in seismic events, which lead to considerable permanent deformation after major earthquakes. Buildings with Large permanent deformation usually are unusable or require extensive repairing. Therefore, low damage structural systems are recently focused. The present study aimed at introducing a new self-centering structural system having frictional sliding in their braces. It is compared with common dual steel moment frames. In the proposed system, post-tensioned cable is used in beam to column connections to provide self-centering. The frictional sliding connections in the braces are utilized as well, to provide energy dissipation capability for the system. Connections are modeled in OpenSees software and validated using previous experimental results. Then, Incremental dynamic analyses are carried out on some frame models under some real earthquake records. Then, their fragility curves are achieved for different performance levels and compared with those of regular dual systems. The results indicate that supplying post-tensioned cables and frictional sliding connections in dual moment frames, reduces the inter story drift, permanent relative displacement and vulnerability of the frames. Therefore, construction of such system for new buildings is recommended, regarding its high performance in earthquakes and repairability after intensive seismic events.

Today, extensively eccentrically braced structures are used to absorb seismic energy using link beam elements on beams. The function of this system is defined as yielding this beam elements during an earthquake and remaining safety and elastic of other structure elements. The length of the link beam is expressed as an effective parameter determining the type of behavior of it as shear or flexure, which determines the seismic performance and the amount of seismic energy absorbed by this element in this type of braced frames. In this research, using incremental dynamic analysis on steel frames under far field records and by performing modeling steps in Python version 3.8 and using of OpenSeesPy documentation, the variables of failure and frame reliability have been investigated. In this research, two samples of 6 and 12-story frames with changes the link beam length from 0.4, 0.6 and 0.8 m have been studied. The results show that the behavior of link beams is affected by the characteristics of the earthquake record and the capacity of the link beams with the same length is various for each record. The results of incremental dynamic analysis on the mentioned frames with different link lengths have shown that the length of short shear link beam in medium height frames has resulted in better seismic behavior and the optimal length of the link beam should be selected after seismic evaluation under different records. The maximum acceleration of the median collapse in this research has been obtained for 6-story frames and the link with 0.6 m length is 5.10, and for 12-story frame with the link of 0.6 m length, 4.20 times the acceleration of the earth's gravity.

One of the seismic retrofitting methods in concrete structures is the use of steel bracing. The present paper attempts to investigate the seismic response of 4 reinforced concrete structures with 10 and 15 stories and two different plans. The structural models are geometrically irregular in plan and they also have vertical structural irregularities due to the soft story. In this study, the seismic response predicted using different linear and nonlinear analysis methods are compared for the case of structures with combinations of irregularities in plan and height. The effect of combinations of irregularities has not been studied in the past and is not considered in current seismic design provisions.

The main direction of this research is the effect of using buckling buckle in steel buildings in order to achieve the IO level. The validation has been done by using Abaqus software. After validating the 3D simulation of the BRB braces, its parametric study is performed and the sensitivity of the buckling buckle brace is performed. The modeling phase in 2D bracing space and seismic analysis (history-time) of braced frames was performed under different acceleration mapping records. The parameters of this research are the opening member-radius dimensions, geometric shape of the member, type of brace, The effects of the number of floors and the length of the opening in the frame with BRB brace. The results are presented based on pushover diagrams and time-history and relative drift of stories. The results showed that the parameter that has the most impact on the hardness and ductility index is the cross-sectional area and the parameter that has the most impact on the strength index is the cross-sectional geometry. By changing the cross-sectional geometry from the circle to the square of the BRBF brace, relative percentage reduction in stiffness, strength and ductility were obtained 2%, 16% and 10%, respectively. By changing the type of brace from CBF to BRBF, the relative percentage of increase in stiffness was between 30 to 62%, the relative percentage of increase in strength was between 63 to 69% and the relative percentage of increase in ductility was between 12 to 30%. The amount of drift roof in the analysis of time history under different earthquakes, in BRB 4, 8 and 12 floors in the range of 1.19 to 1.51 times has been achieved. Hardness and ultimate strength and ductility indices decreased with increasing opening, decreased with increasing cross section and decreased with increasing height.

In this study the seismic performance of special concentrically mega braced frames with different spans ratio is investigated; For this purpose, eight configurations of four and eight-story structures with special concentrically braced frame were designed in three dimensions, with conventional X and mega brace configurations with different spans ratio, then a braced frame of them was modeled in OpenSees in two dimensions, taking into account the second-order effects of the removed gravitational section, through a leaning column. Finally, in order to investigate the seismic performance of structures and perform incremental dynamic analysis, 14 far field earthquakes were selected according to the characteristics of the construction site. Evaluation of analysis results according to NIST GCR 10-917-8 report and Hazus Technical Manual in maximum inter story drift ratio, comparison of fragility curves and comparison of period and weight of structures, indicates that in special concentrically mega braced frames, if the spans are equal, mega braces has a suitable and economical performance, and if the ratio of spans is different, the use of mega braces has a better performance than conventional X braces and is much more economical. For example, in eight-story structures with an span ratio of 1.5, the weight of the structure with mega brace is about 20% less than the similar structure with conventional X brace. Also, the main period of frames with conventional X braces is about 20 to 30% longer than structures with mega braces, which indicates the higher stiffness of mega braces.

In the present paper, the reliability of tubular members used in the horizontal braces of an offshore jacket structure against the failure induced by the presence of stresses higher than the allowable values is evaluated. In order to define the failure criteria, equations proposed by the 21th edition of API RP 2A-WSD (2007) for the design of tubular members under the combined axial pressure and bending are used. In this study, internal forces of the tubular members and the parameters involved in the member strength are considered as random variables and the probability distribution functions governing these forces including the axial compressive force and in-plane and out-of-plane bending moments are derived for a typical jacket-type platform installed in the Persian Gulf. For the modeling of environmental loads, information available on the sea states in the South Pars region has been used and the results of three different methods of reliability analysis including MVFOSM, HL-RF, and MCS are compared. Finally, based on the results of reliability analysis, a set of equations are proposed for the determination of suitable safety factors for designing the tubular members in horizontal braces of a jacket structure as a function of target reliability index and target failure probability.