جستجوی مقالات مرتبط با کلیدواژه "residual displacement" در نشریات گروه "عمران"

Modern damage-free systems are part of modern lateral seismic structures. These structures have minimal residual displacement and dissipate earthquake energy through replaceable fuses. self -centering rocking steel braced frame systems that have been investigated in this research are considered among these modern seismic systems. In self-centering rocking structures as well as other tall structures, the effect of higher modes can cause irreparable damages in the structure. In this research, an attempt has been made to reduce the effects of higher modes by using buckling restrained columns and braces (BRCs and BRBs) as energy dissipating fuses instead of standard columns and braces in self -centering rocking structures. Five 12-story structures were investigated, including;self -centering rocking steel braced frame system and four other structure with placement of BRBs and BRCs at the base, one-third, middle and three-quarter of the height. To investigate the seismic behavior of these structures, several analyses has been performed in OpenSees software under 22 far field records according to FEMA P695. Geometric and material nonlinearities is considered in the modeling. The results show the improvement of the seismic performance and the reduction of the effects of higher modes in the case of using BRBs and BRCs in the stories, compared to the case of the common self-centering rocking bracing system.

Permanent deformation after an earthquake increases the cost of the retrofit and even the implementation of the rehabilitation plan. A resisting system to control the lateral forces due to earthquakes is to use shear walls with good energy dissipation capability. Permanent deformation and cracking in the border and critical areas of the wall after relatively strong earthquakes leads to a decrease in the seismic performance of the wall. In this research, the responses and cyclic behavior of concrete shear walls under the cyclic loading protocol are investigated. For this purpose, using OPENSEES software platform, concrete shear wall modeling based on SFI-ΜVLEM method or wall modeling using multiple vertical elements based on the macro fiber method has been studied. The main models analyzed in this study include 2 concrete walls with steel rebars and memory alloy (SMA) with different dimensions and arrangement of reinforcements and innovative concrete wall with separate border elements in the form of concrete columns made of engineered concrete (ECC) and SMA rebars.  Validation of the models was based on previous studies. After validation of the initial models, the parametric study of the models was performed in order to investigate the effects of the dimensions of the boundary areas, the type and arrangement of the reinforcements and the amount of gravitational forces on the shear walls in the models. The results obtained from the outputs show that the use of SMA materials in the boundary areas of the wall has a significant effect on the self-centering behavior of the wall and the energy dissipation of the shear wall is reduced by using SMA materials.

In this research, the effect of P-Delta column (leaning column) on the response of gravitational frames with lateral-load resistance system of base-rocking wall has been investigated. The studied structures have 4-, 8-, 12-, 16-, and 20-stories. Nonlinear dynamic behavior is performed under 22 far-field seismic records and 28 near-field seismic records, half of which are pulse-like, via OpenSees software. The ground motions are scaled at both DBE and MCE levels and applied to the structure. The modeling is done in two dimensions. As a results, it has been shown that 1) the higher modes effect increases with increasing earthquake intensity, 2) the higher modes effect are more visible in the records of far-field and near-field-non pulse-like, 3) residual displacements in The both earthquake levels studied are insignificant and negligible, 4) P-Delta column has been more effective in structures under near-field-pulse-like records, 5) The maximum effect of P-Delta column in increasing the moment of wall under near-field-pulse-like earthquake that the value is 12%, and 6) In general, the effect of the P-Delta column on the base-rocking wall structures in especially the stepping-wall can be ignored.

Residual displacement after an earthquake disrupts the performance of the structure and leads to local stress. There has been special important in development and the using of self-centering lateral resisting systems that reduces residual drift after a large earthquake. Self-centering lateral resisting systems often include a restoring force component that dissipates seismic energy. Eccentrically braced frame with vertical link (V-EBF) is one of seismic system based on shear yielding of link beams. If link beam has short length and supplies seismic requirements, link will be able to tolerate significant rotation without strength degradation. Shear link beam has a fat hysteresis curve and height potential of energy dissipation; for this reason the use of short link beam in eccentrically braced frame was modeled by using experimental models which were provided by other researchers and compared with laboratory results. After validation, 8 and 12 story V-EBF and equipped with SMA rods were designed and their performance were compared with similar structures without SMA rods. In order to compare the structures, pushover, time history and Incremental Dynamic Analysis (IDA) were performed. The results of seismic analysis indicate that the using of SMA rods improves seismic performance and provides excellent reversibility capacity so reduces residual displacement of structure considerably.

Due to the suitability of the eccentric bracing system in terms of optimal performance and ductility on the other hand, as well as the effect of reversible materials such as shaped memory alloy in reducing the residual displacement at the end of the earthquake and seismic evaluation of structures with the different number of stories, structures with eccentric bracing dual steel bending frame system within 5, 10 and 15 stories equipped by shaped memory alloy rods, were subjected to the nonlinear dynamic analysis of time history. Maximum absolute displacement of the roof and relative displacement of stories, the maximum residual displacement of the roof, maximum base shear, and roof acceleration in the desired frames were evaluated and compared. Survey results showed that the absolute and relative inter-story drift in all three models due to the lower elastic modulus of shape memory alloy has been greater than models that have not been equipped with shape memory alloys. On the other hand, the residual displacement values of structural models due to the super-elastic property of the shape memory alloy materials and the shear stories and acceleration of the roof of structural frames due to the increase in period time and structural softness have shown a sudden sharp drop compared to models that have not been equipped with shape memory alloys. Comparison of structural responses in different models also showed a further reduction effect on the plastic displacement of the 5-stories model and base shear and roof acceleration of 10 and 15-stories structures.

In structural analysis, P-Delta effect refers to the changes in internal forces due to P-Delta moment which can be found by multiplying gravity load (P) by the lateral displacement of structure for earthquake lateral load (Delta). The influence of P-Delta in elastic response of structures is ignorable, but P-Delta effect should be given more attention when the structure responds in inelastic range. On the other hand, the influence of ground motion duration is magnified when P-Delta effect is considered in the structural analysis. In this paper, to consider the simultaneous effect of ground motion duration and P-Delta effect, an algorithm is implemented in MATLAB which employs OPENSEES for linear and nonlinear dynamic analysis of elasto-plastic systems subjected to long- and short-duration records. The analysis results indicate that the frequency of structural collapse for long-duration ground motions is about twice of short-duration ground motions. The frequency of collapse also increases when ductility and stability index increase, but decreases when the period of structure increases. Furthermore, the increase of ground motion duration has no influence on the residual displacement of structures, but nonlinear behavior of structures and gravity load effect increase the residual displacements.

Recently, in developed countries, a variety of self-centering structural systems have been developed using precast concrete bends and Accelerated Bridge Construction (ABC) method to reduce construction time, increase safety, reduce seismic damage, reduce repair and reconstruction costs, and increase seismic resiliency. In this system, bridge bents are constructed by precast elements tied together with post-tensioned tendons such that under the effect of lateral seismic forces, they are able to rock and self-center back to their original configuration. The use of this system greatly reduces the residual displacements and the seismic damage. Also, due to the use of prefabricated elements, the construction speed of the bridge is significantly increased. This paper compares the seismic performance of one type of the self-centering structural system with the conventional structural system for three typical highway bridges constructed in Iran. An analytical model for simulating nonlinear behavior due to the rocking motion in the self-centering system is first developed and verified by comparing the analytical response with the experimental results. Then, the concrete bends of the three typical bridges in Iran are modeled and analyzed once as a conventional system and once as a self-centering system, and the seismic performance of these two systems is compared with each other. The results of this study indicate that in spite of a modest increase in maximum lateral drifts, the residual drifts are substantially reduced when the conventional system is replaced by the self-centering system.

Nowadays, new and innovative methods have been proposed based on damage avoidance design (DAD) philosophy systems as the alternative conventional lateral load-resistant systems. These systems reduce damage to buildings and post-earthquake reconstruction costs. The self-centering rocking walls are one of them. In this research, multiple rocking wall systems have been investigated and designed. The effect of the number of self-centering blocks and the ratio of tendon prestressing in a 12-story structure examined. The structures have examined subjected to 22 far-field records and 28 near-field records, half of which have pulse. The modeling is done in two dimensions via OpenSees software. The design coefficients of rocking sections in different prestressings for each type of ground motions are specified. The results shown that rocking wall structures under near‐field pulse‐like ground motions need more design capacity than other records to control drift and capacity section. Furthermore, The design of base-rocking and multiple rocking structures has been done for specific drift that have similar drift profiles in height. Then, for this case design, it is not possible to expect the desired energy absorption and also the reduction of the effects of higher modes from the multiple rocking the system compared to the base-rocking system.

Conventional seismic resistant systems generally dissipate earthquake energy through the plastic deformation of structural elements. These systems withstand high residual displacements increasing the cost of repair or even necessitate reconstruction of the building. In recent years, researchers have focused on self-centering lateral load resisting systems due to earthquake energy absorption in replaceable elements and reduced residual displacement. One of the recent types of these systems is self-centering buckling restrained 2-story-X-brace system. In this study, the hysteretic performance of a 9-story structure with a dual steel moment resisting frame system equipped with a self-centering buckling restrained brace is investigated. At first, the parameters affecting the performance of the bracing were specified. These parameters included the yielding stress of the bracing core, the ratio of cable pre-stressing force to the cable yielding force, and the ratio of cable to core area. For the yielding stress of the core two values of 240 and 360 MPa, for the pre-stressing ratio five values from 0.1 to 0.5, and for the area ratio, seven values of 0, 0.25, 0.5, 1, 2.5, 5 and infinity were selected. So therefore, a total of 62 models of 9-story structures with dual steel moment resisting frame system equipped with self-centering buckling restrained brace were constructed. The models were analyzed using OpenSEES finite element software. Performing nonlinear analyses under cyclic loading, the hysteresis diagrams were obtained. The optimal design for these models was performed considering residual displacement and energy absorption as two main parameters. Finally, the performance of the optimized structure equipped with self-centering buckling restrained brace was compared with the structure equipped with ordinary buckling restrained brace. According to the results, the optimized self-centering structure may reduce 60% of the residual displacement while its energy absorption drops by only 37%. Generally, the results indicated the prominence of the optimized self-centering structure.

Today, there is an increasing interest in use of seismic isolation to protect the structures against earthquakes. The most common type of seismic isolation is called base isolation, in which the isolation layer is installed under foundations to separate the structures from the ground and reduce the earthquake forces. However, the use of this type of seismic isolation faces some difficulties such as construction in congested urban areas or construction of near sea structures. Furthermore, for seismic retrofitting of existing buildings, the installation of the isolation under foundations is difficult or even impossible; so, it needs to be located on the middle floors of the buildings. The method of isolation design is called floor or middle story isolation. Despite the advantages of seismic isolations, they have some limitations such as instability in large deformations, residual displacement, and the need for replacement after severe earthquakes. The use of Shape Memory Alloys (SMA) regarding their unique properties is considered as an appropriate solution to overcome the above problems. These smart materials show high strength and strain capacity, high recentering ability, and high resistance to corrosion and to fatigue. The purpose of this study is to investigate the effect of combination of middle story isolation utilized by Natural Rubber Bearing (NRB) and iron-based shape memory alloys in steel structures and to compare the performance of such structures with and without the presence of the shape memory alloy in the middle-story isolation system. Then, a three-story steel structure has been modeled and evaluated. For this purpose, a structure with floor isolation and iron-based shape memory alloy was modeled in OpenSees computer program. The structures were then subjected to seismic loading. The results were presented in the form of story drift, floor acceleration, floor shear forces, and base shear. The outcome of this research showed that the use of these alloys in the middle-story isolation reduced the overall base shear and floor shear forces. The overall story drift, floor acceleration and displacement are reduced; with the exception at the isolation level. Thus, utilizing the natural rubber bearing isolator along with the iron-based shape memory alloy can be considered as a desirable system for the seismic protective design of buildings.

Post-tensioned coupled shear wall system is a new type of seismic lateral force resisting systems with self-centering capability. In this system, the coupling beam is not embedded into the walls, and coupling of concrete walls is achieved by posttensioning beam to the walls using unbonded post-tensioning (PT) strands. In this research, the cyclic behavior of post-tensioned steel coupling beam with friction devices at the beam-to-wall connection region is experimentally evaluated. Three 2/3-scale specimens were tested subjected to quasi‐static lateral loading. The specimens consisted of one control specimen without energy dissipation system and two specimens equipped with friction devices with different levels of damper normal force. Friction devices are used at the beam-to-wall connections to slip and dissipate the seismic input energy. The test results revealed that the specimens equipped with friction devices have excellent lateral stiffness, strength, and ductility, and have significant energy dissipation capacity and negligible residual displacements under reversed cyclic loading. In addition, the specimens is able to tolerate large nonlinear rotations without significant damage in the beam and the wall region. Adding friction devices increased the load-carrying capacity by 47% to 62% and significantly increased the energy dissipation capacity of the specimens. With a 30% increase in the damper normal force, the load capacity increased by about 10%, the average relative energy dissipation ratio by about 15% and the mean cumulative energy dissipation capacity by about 33%.

Bucking restrained braced frame (BRBF) is a special type of concentrically braced frames that the braces do not buckle in compression and as a result shows a desirable energy dissipation behavior. However, low post-yield stiffness of these braces causes large residual deformations at high levels of earthquake itensities. The aim of this article is to evaluate the seismic behavior of a new steel structural system known as hybrid buckling-restrained braced frame (HBRBF). Nonlinear static analysis, nonlinear time history analysis and nonlinear incremental dynamic analysis (IDA) methods are used for standard and hybrid core BRBFs with different stories. The average values of seismic behavior factor (R) for HBRBFs are obtained as 10.2 and 14.7 for ultimate limit state and allowable stress design methods, respectively. In order to carry out response history analyses, past earthquakes records were used with different hazard levels. Hybrid buckling-restrained braced frames are shown to have a significant improvement over standard BRBFs in terms of behavior factor and damage measures including inter-story drift ratios and residual displacements.

Shape Memory Alloys (SMA) are a kind of smart materials that their unique mechanical and thermal performances such as the ability to return to its original shape (Shape Memory Effect) and the ability to recover large strain (Super Elasticity), caused their wide application in various industries such as civil engineering. Due to the superplastic behavior of theses alloys, undergoing cycles of loading and unloading, results very little residual strain, even after exceeding the yield strain. This property causes recover forces in the structure so that they can close the cracks in the tensile zone of RC members and therefore, it is significant for structural members located in earthquake zones. In this paper the F.E modeling of reinforced concrete (RC) beams utilizing of shape memory alloys is produced and results of different loads response of modeling is verified with the available experimental results. For this purpose, firstly the finite element model of three RC beams by adding Nitinol wires in the tensile zone was made by ANSYS software. Then the beams were subjected to cyclic loading and their hysteresis curves were compared with the similar available experimental beams. The numerical results revealed, utilization of Nitinol wires in tensile zone of the beams resulted, increase in both loading capacity and ductility and decrease in residual displacement.

There is a debate among earthquake engineers that the structural and non-structural damages initially occur due to lateral loads caused by earthquake excitation. American provisions, including FEMA356 estimates structural performance by means of maximum deformation demand. However, in addition to the maximum deformation, residual displacement plays an important role in structural performance. Amplitude of residual displacement is an important parameter in technically and economically determining rehabilitation of damaged structures for resisting aftershocks. In this study, residual displacements of a five-story steel frame is designed with vertical link beam as well as the effect of vertical link beam length have been investigated. For vertical link beam, the IPE sections with typical steel is considered, instead of using boxes and H-shaped cross-section.The IPE section has some advantages than box section such as lower cost, easier installation and replacement. The Vertical link beams with IPE cross-section has been studied in 5 separate models with length of 20, 25, 30, 35 and 40 centimeters. In this paper, experimental results of a frame model with vertical link beam tested in structural laboratory of Building and Housing Research Center (BHRC) has been used for verification of numerical model. As one of the fastest nonlinear softwares, OpenSees (Open System for earthquake engineering simulation) has been used for structural modeling. The steel material that has been used in this model is uniaxial material steel 02. In the following, seven near field and seven far field earthquake acceleration time histories that scaled by 2800 standard, are used analysis of five-story and five-bay structure with chevron bracing system. According to the seismic design of structures if ductile elements is used in a structure, then beams and columns should remain elastic during earthquake, while ductile elements dissipate input energy by nonlinear behavior of ductile members. By considering of the results, the vertical link beam with length of 20 and 25 centimeter for far field earthquakes and 20 centimeter for near field earthquakes have the best performance compare to the other cases. The Bam earthquake is selected to investigate of hysteresis diagram of the vertical link beam energy dissipation. The results for near field earthquake like the Bam earthquake show that link beam with length of 40 centimeter with moment behavior, has low energy dissipation capability. Furthermore, the vertical link beam with 40 centimeter length causes more residual displacement and yielding. By considering the station with equal 104.28 km distance from center of earthquake can use the Bam record as a far field earthquake. In this case link beams with more than 25 centimeter length have more fluxing. However, the link beams with length of 20 and 25 centimeter have better seismic performance. Considering the RMS (Root Mean Square) parameter as a controller criterion the vertical link beam with length of 20 centimeter is more suitable for near and far field earthquakes. Considering the seismic performance parameters of vertical link beam like appropriate stiffness, high stability, energy dissipation capability, appropriate control of maximum response of structure and less residual displacement, the vertical link beam with length of 20 centimeter has the best seismic performance for near and far field earthquakes compare to the other cases.

The force-based formulation is attractive because it can model the spread of plasticity along the length of column using only one element and a number of integration points; however¡ their sensitivity to modeling parameters and models of material behavior has resulted in the estimation of residual displacement seismic demand to be important in this modeling method. In this research¡ the effects of two theories of lumped plasticity and distributed plasticity on modeling the concrete bridge column for estimating the residual displacement in near field zones were investigated. For estimation of residual displacement¡ the effects of reinforcing slide¡ geometrical parameters¡ and material behavior parameters were studied. Due to the importance of residual displacement in the performance evaluation of damaged structures¡ estimation of residual displacement is very crucial. In this study¡ the effects of different modeling methods as well as material behavior parameters on estimation of residual displacement were investigated. For this purpose¡ five different models were studied and the sensitivity of optimum model to various parameters was evaluated. The results showed that the theory of distributed plasticity for bridge concrete column has a good accuracy for estimating the residual displacement. Reloading strain parameters of concrete behavior and forced-based beam-column fiber element modeling parameters have an important role in estimation of residual displacement.