BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2020 | Volume:7 | Issue:1|Papers Count:12

A fully Monte Carlo Simulation (MCS) that applies to the across region in each step, allows incorporation spatial correlations in each step conditional on the previous step and each simulation must repeat each several times; therefore, the size of computation is concern. The size of computation can be reduced at each step by developing scenarios. The relatively small set of probabilistic scenarios represents the full set obtained from a MCS. In order to consider spatial correlation of individual earthquake scenarios as well as when computational demands are of concern, the optimization-based probabilistic scenario (OPS) method are presented. This method is very appropriate approach that could be applied to a region with high seismicity and effect on the regional loss estimation and regional policy decisions. The OPS method can be important: 1-It is easy for users to understand, 2-The spatial correlation of the ground motion is recorded across the region, 3-It also eliminates concerns about the computation size. This method has a simple concept to record the temporal changes of vulnerability model. We use source– magnitude combination to obtain hazard-consistent annual occurrence probabilities. The OPS method produces a small set of probabilistic seismic scenarios instead of the millions number of scenarios to estimate the seismic hazard and loss estimation of lifelines. This method has a clear framework, includes a step-bystep method for producing earthquake scenarios and ground motion maps. After producing a relatively small set of seismic scenarios, the hazard-consistent annual occurrence probabilities of scenarios are estimated; so that their effect on the across the region approximates that described by given return period maps. For each ground motion map, a set of damage maps are then calculated. Finally, for each damage map, the lifeline system performance is estimated as a function of the system damage. The resulting database of performance levels and associated occurrence probabilities then describe the lifeline risk. Evaluation metrics for computation of the hazard curve errors and spatial correlations errors, introduced by Han and Davidson (2012). We apply the optimization-based probabilistic scenario method to identify the minimum number of scenarios. These scenarios can be used to loss estimation of Qom lifelines. The city of Qom is situated approximately in central Iran. Hazard curves for nine control points have been provided by PSHA, to generate probabilistic scenarios. These nine control points have been located on the study area boundary and equal distance of 12. 5 km from each other. Using OPS method, open source solvers and time-independent hazard analysis, has been presented a set of probabilistic seismic scenarios for Qom. First, the output of the conventional Monte Carlo simulation for 1 million years includes 1609087 simulated scenarios. Then scenarios have reduced to 55645 scenarios based on the ‘ true’ hazard curve. Finally, the reduced set of earthquake scenarios based on optimization includes three scenarios. The scenarios obtained by the PULP_CBC_CMD and Gurobi 8. 0 solvers are the same. Based on the evaluation metrics, the errors are in the appropriate range and there is no unintended bias in the results. The errors are small, 81% of errors in range of ± 10%, 91% in range of ± 30% and mean hazard curve error is 7. 34%. By comparison of the ‘ true’ and the reduced set hazard curves in all sites, site 9 has highest average HCEir. For the city of Qom, have been ensured that the difference between the ‘ true’ hazard and the reduced set is minimum. It is now possible to extend the probabilistic scenarios for Qom, thus overcoming limitations of the other hazardconsistent probabilistic scenario approaches. In this paper, the hazard is only measured by the PGA, but other terms (such as PGV, SA… ) can be considered for the city of Qom.

The Lut Zone, with about 900 km length, is in the eastern part of central Iran. The eastern boundary of this zone is specified by the Nehbandan fault and the eastern Flysch of Iran and its western border by the Nayband fault and the Tabas block. East of Iran consists of a series of strike-slip and step-down faults that are fractured-crustal deformable and its evolution is influenced by processes that dominated on the strike-slip shear zones. In other words, the potential energy accumulated in this region is used as a slip along the strike-slip faults of the region, folding and non-slip creep. Earthquake occurrence rates are an essential part of seismic-hazard analysis. Estimate of moment rate is comparatively reckoned as a new method for dealing with tectonic activities rate in different regions and it prepares the way for putting together different methods. There are now three major types of data available to estimate these occurrence rates: Geodetic moment rate, seismic moment rate (on the basis of historical and instrumental earthquake data) and geologic moment rate are estimated for Lut block in east of Iran. Lut block was affected by several large earthquakes in the past causing heavy damage in this region. Each approach has limitations, but in principle they should all yield similar estimates. Firstly, a catalog of historical and instrumental earthquakes was used. Then, while preparing the fault maps of the region, regarding the geometric information of the active faults, the latest information on the geometrical characteristics of the faults has been collected. Finally, geological, seismic and geodetic moment rates for the region were estimated and the results were compared. Depending on the type of deformation and geometry of fault, the study area divided to the five zones: northwestern (zone 1), southwestern (zone 2), north and northeastern (zone 3), southwestern (zone 4) and southern zone (zone 5). Then we compare the value of three types of moment rate in these zones to each other. The most moment rate in the Lut block belongs to geodetic approach (1. 2119x1018 Nm/yr) and then seismic moment rate (3. 9455x1018 Nm/yr), and finally the least quantity belongs to geologic moment rate (2. 4882x1016 Nm/yr). Each of these calculating methods of moment bring from a different perspective that can show different patterns in the style and extent of tectonic activity in the region. Geodetic moment rates include both seismic and non-seismic deformations and cover a highly short time range. Therefore, it is obvious that it shows higher values than the other two methods. The most of seismic moment rate was obtained respectively in Zone 3, 1, 4, 5 and 2. According to seismic map, maximum seismic moment is along Abiz, Dasht-e Bayaz and Tabas Faults. These faults are responsible for large earthquakes in the study area. Maximum geologic moment rate is related to West-Neh, East-Neh, Kahoorak, Abiz and Nosrat-abad Faults. According to values of geological and geodetic moment rates in the southeastern of Lut area and based on the value of the release seismic energy in the north and western part of Lut area, it seems that in the next time, the most of seismic potential and seismic hazard are in the southeastern part of the study area. According to the ratio of seismic to geodetic moment rate can be concluded that the northern part and northwestern part with ratio 2. 36 and 0. 69 are fast strain areas and south, southwestern and southeastern part with ratio: 0. 055, 0. 02 and 0. 03 are fast strain areas, respectively. Ratio of the geodetic moment rate to the seismic moment rate obtained more than 3. 07, which reflects the important role of the interseismic deformation in this area. Ratio of seismic moment rate to geological moment rate is 0. 63 %. This value indicates that 0. 63 % potential of the faults for seismic energy has been released ant not been released a significant part of the elastic energy in the area.

Accurate identification of seismic potential is the first step and one of the most important for seismic studies in each region. The study area, located in the middle part of the Urmia-Dokhtar magmatic arc belt, is one of the areas where identify and study of its seismic sources is necessary. In this study, for the first time, the Ezedin-Rahjerd fault system is introduced according to the interpretation of satellite images, field study and tectonic surveys of the area. The Cenozoic (Eocene) volcanic rocks of the Tafresh area, which are covered with Lower and Upper Red Formations have been cut by this N-150 transverse fault of 70 km. This fault system, like other transverse faults such as the Bidhend, Qom-Zefreh and Dehshir-baft faults, has cut volcanic rocks of the magmatic arc belt. Geometry pattern detection of the structures using satellite images and field observations in the area showed that the effect of this fault are observed as the change of the main structure trends such as the reverse faults and fold axes bending and the formation of minor structures with a different trend from the main structures trends of the Urmia-Dokhtar belt. The slicken lines of the fault plane and the right-lateral bending of the main fold axes along the fault zone and the formation of minor structures indicates the right lateral movement of the Ezedin-Rahjerd fault zone. One of the prominent features of the study area is the existence of several parallel dyke sets that are not very distant and sometimes outcropping at a distance of less than 200 m. These dykes with a thickness of about 2-5 m and a length of about 15-20 m with dip of more than 80 degrees are divided into two sets with dominant trends N40-45W and N20-30E. The first set of dykes with N40-45W trending are a semi-deep dolerite and porphyro gabbro diorite that exposed around the Gyan and Lalaein villages and cutting Eocene and older units. Whereas, the second N20-30E trending shallow dikes with combining of hornblende, andesite and basaltic andesite also cuts Miocene volcanic-sedimentary rocks, Qom Formation and Lower Red Formation. Alteration of the second dyke set is significant. The trend, including rocks and tectonic setting of the dykes, show their influence in several stages. These intrusive dikes also show tension fractures, so will assist in structural analysis of the area. In such a right lateral transverse fault zone, development of the tension fractures with N20-30E trend is not unexpected. Therefore, the second shallow N20-30E dyke set are formed in these tension fractures due to the Ezedin-Rahjerd transverse fault activity. While the first set with N40-45W trending that is older than the second one, has been created due to the main structures of the Urmia-Dokhtar magmatic belt. The most important geomorphological feature observed along the Ezedin-Rahjerd fault is the conformity of the Kamar (Tafresh) river as the main river of the area with the fault trend. The Kamar River flows north-south along the Ezedin-Rahjerd fault, passing through the Barezjan, Dadghan, and Ezedin villages, and then reaches the Ghareh-Chai River in Jalaier. Instrumental earthquakes of the area show 2

Shear wave velocity, Vs, is a useful soil mechanical property for determining the low shear strain (γ ≈ 0. 0001%) elastic shear modulus, which is required for both static and dynamic response analyses of earth structures. It is an important geotechnical soil property for the design and analysis of geotechnical structures. It can be employed to determine the maximum or small-strain (≤ 10-3%) dynamic shear modulus (Gmax or G0) of the soil mass. Vs can be easily obtained using laboratory or in situ testing techniques. Laboratory tests can be carried out on undisturbed soil samples by simulating the field stress conditions or reconstituted soil samples from a site. However, obtaining good quality undisturbed samples of granular soil deposits is very difficult and moderately expensive. In most geotechnical investigations, the seismic properties (P-or S-wave velocity and the dynamic elastic properties) of granular soil layers from in situ tests (such as the seismic cone penetration test) cannot be determined because of the high cost of undisturbed specimens and the need for highly specialized personnel and equipment. There is increasing interest in the use of Vs to study soil particle properties (e. g. shape, elastic properties, gradation) and the soil state and fabric (e. g. void ratio, boundary stress). In the current study, the bender element and resonant column tests were conducted on sand-gravel specimens. A bender element is an electro-mechanical transducer composed of two-layers of piezoceramic plates that are cross-sectionally polarized. This allows for straightforward wave velocity measurement of soil specimens. The BE converts electrical energy to mechanical energy (movement). The resonant column device is commonly used in the laboratory to measure the low-strain properties of soil. This includes the dynamic properties (shear modulus and damping ratio) of soil specimens at strain levels of 10-6 to 5×10-3 conducted according to ASTM standards. In the RC test, Vs can be calculated using the solution of the equation for the linear vibration of a columnmass system. The RC device is the most reliable laboratory method for measurement of Vs. The aim of this research was to explain the effects on Vs of the relative density, mean effective stress, grading characteristics, consolidation stress ratio and initial fabric anisotropy produced during specimen preparation. Five gradations of gravelly and sandy material were used to study the influence of grading characteristics, consolidation stress ratio, depositional method, relative density and mean effective stress on the dynamic properties of granular soil. The pure sand was clean, uniformly-graded fine sand with a mean grain size of 0. 6 and a silt content of less than 1% that was classified as SP according to the unified soil classification system (USCS). The pure gravel was uniformly-graded soil with a maximum particle size of less than 16 mm that was classified as GP according to the USCS. The measured values from the resonant column and bender element tests also were compared. Comparison of Vs-BE and Vs-RC shows that the results obtained by both techniques were in acceptable agreement for all specimens; however, there was a slight difference between the two techniques at low values of Vs in which Vs-BE was consistently lower than the corresponding values of Vs-RC. The results of these tests were employed to develop a generalized relationship for predicting the Vs of granular soil. The Vs model was validated using experimental data from the current study and from previous studies. The results indicate that the proposed model is capable of predicting the Vs of granular soil.

In seismic design codes, the maximum real relative displacement due to nonlinear behavior of the structure is estimated from variation coefficient of the relative linear displacement multiplied by the coefficient of deflection amplification factor (Cd). This coefficient is obtained by considering nonlinear displacement of the members of the structure and depends on the lateral load-resisting system. The previous studies indicate that the panel zone can have a significant effect on the behavior of a frame, and in particular, its lateral displacement. Therefore, to predict the precise behavior of the frame, the effect of the panel zone should be considered, but this factor has not been included in the estimation of the Cd value so far. Therefore, the storey drifts are under-estimated. The main purpose of this study is to consider the effect of the panel zone on Cd for Intermediate Moment Resisting Steel Frames (IMRSF). In this regard, two buildings have been designed based on the Iranian seismic design codes in ETABS software. A 4-story building is designed twice, once by I-section columns, and the other by box section columns. The structure with IPE sections has an IMRSF and, a Concentric Bracing Frame (CBF) with conventional ductility in two main directions. However, the structure of the box section has an IMRSF in both directions. After designing the structures, a flexural frame was selected from both structures and was modeled in the OpenSees Software for two conditions: with and without modeling panel zones. Incremental Dynamic Analyses (IDA) has been performed for 46 ground motion records. To determine a correction factor for Cd in order to consider the panel zone effects, the ratio of the nonlinear maximum drift that of the model without panel zone effects is calculated for each ground motion. The results of the analyses show that in general, considering the effect of the panel zone in the analytical model, leads to an increase in the maximum drift values and ignoring the effect of the panel zone in the structure with the I or Box sections, causes the displacement of the floors to be 28% and 16% less than actually estimated, respectively. This effect for the structure with IPE sections is greater than Box sections, for its smaller web thickness and thus lower thickness of the panel zone. Therefore, it can be concluded that the thickness of the panel zone plays a key role in the structural response. Finally, it is recommended to increase Cd coefficient of intermediate moment resisting frames as 1. 28 and 1. 16 for the structures with I-section and Box-sections in their columns, respectively.

Active control acts as an effective strategy to improve the seismic behavior of structures by calculating and applying the external forces and leads to the adaptive change in dynamic properties of the structure during the earthquake. In the LQR method as the most common control algorithm, the second-order performance index has been optimized to establish a balance between response and control force reduction. In defining the performance index, the relative importance of response reduction and control force reduction is regulated by the selection of Q and R weight matrices. Q and R are the weight matrices for the response and control forces, respectively, and their values indicate the relative importance of response or control force decrement. There is no systematic way to determine these matrices so far these weights are chosen based on trial and error and designer experience. This study has concentrated on metaheuristic algorithms in optimal active control of structures. In this paper, to facilitate the process of controller design, R and Q weighting matrices are considered as design variables and wavelet-based performance index as objective function of metaheuristic optimization. Imperialist competitive algorithm (ICA) as a socio-politically motivated algorithm, differential evolution (DE) as an evolutionary method, bat (BA) and firefly (FA) as natural-inspired algorithms, colliding bodies (CB) as physics-inspired algorithm and harmony search (HS) as music-inspired metaheuristic are used in this study to compare different aspects of metaheuristics in dealing with the optimal active control problem. Some of these metaheuristics have not been explored in control problem yet. In this study, in order to enhance the controller performance, DWT has been applied to decompose the excitation into different frequency bands. For decomposition process, signal is decomposed using Daubechies wavelet of order 10 (db10) mother wavelet in five levels. Defined wavelet-based performance index has been selected as objective function and weighting matrix elements considered as design variables of optimization process. Then, metaheuristic algorithm has been employed to search the optimum weights for each frequency band to calculate the control force in each domain. In addition to wavelet-based LQR performance index used as objective function of optimization, nine benchmark indices obtained from the results are calculated to evaluate the controller-performance by reduction of different design parameters such as interstory drift, story displacement, acceleration, base shear and needed control force compared to the uncontrolled cases. The best solution, convergence rate and computational effort of aforementioned optimization methods for a three-story structure under different artificial earthquakes have been compared. According to the results of simulations, the effectiveness of each algorithm in vibration reduction through various seismic excitations has been evaluated by numerical simulations. This formula is able to be easily performed with any metaheuristic algorithm providing the great flexibility in the active controller design. The results for active control of structures have shown the potential of wavelet and metaheuristic algorithms in vibration control for building structures depending on the user to select the appropriate algorithm or on the problem types and its requirements such as the quality of solution, convergence rate, computational effort, and consuming time. The results indicate the effective role of metaheuristic methods in reducing responses and control forces simultaneously over the LQR method. Considering total cost value, CB, ICA and DE have produced better results compared to all the mentioned algorithms. FA and BA have good convergence tendency compared to other algorithms. Each metaheuristic algorithm has advantages and disadvantages in solving active control problem, whiles the superiority of CB, ICA and DE over other methods in finding the optimal responses for active control problem has been shown as well.

This paper examines a newly developed seismic force-resisting system. To achieve improved seismic performance, the strongback system combines aspects of a traditional concentric braced frame with a mast to form a hybrid system. The mast acts like a strongback to help resist the tendency of concentric braced frames to concentrate damage in one or a few stories during severe seismic excitations. The purpose of the strongback system is to promote uniform story drifts over the height of a structure. For this purpose, in this paper, the design principles for achieving the desired goal, along with a new relationship for controlling the amount of story drift uniform index for this system is presented and the nonlinear dynamic behavior of structures 3, 6 and 12 stories with three seismic force-resisting system with different configuration at the intersection of the braces to the beam under seven acceleration of far and seven acceleration of near field for achieving the correctness of the design principles and comparing the effects of the near and far field earthquakes has been studied. The strongback bracing system is specifically designed to prevent the uniform story drift and alleviate the soft-story mechanism [2]. The design procedure is such to keep strong-back aspects elastic and stress ratio less than 0. 5. Although the seismic codes specify limits for story stiffness and resistance ratio, this limitation does not guarantee to avoid damage concentration. It should be noted that the concept of uniformity is a relative concept and all stories can never have equal and uniform drift in a structure under earthquake. However, a structure can be designed such that the drifts are distributed uniformly in all stories approximately. For uniform story drift and prevention of soft-story in this system, it is not just enough to keep the stress ratio less than 0. 5 so as to completely design this system, and the necessary examinations were carried out to reach a relation between conventional braces and aspects of strongback. In addition, studies by Lai and Mahin [2] show that the simple design strategy used does not result in adequate member sizes near the top of the strongback systems and limited yielding of the strongback spine occurs at these levels. According to the ratio of the braces length and Dimensions of their sections, when the stress ratio in strongback should be less than 0. 5, this result was obtained some limitation must be considered about conventional braces stiffness ratio and the aspects of strongback. Therefore, by considering the issue of elastic state of the components of strongback in earthquakes, conventional braces were designed for code earthquakes force and stiffness ratio of strongback braces to conventional braces is in each story equal to or more than 2. 5 and section of strongback zipper member was considered equal to section of strongback brace member in the story. During these tests, which were performed using the trial and error method, various earthquakes were used to perform the nonlinear time history analysis and various values were considered for the stiffness ratio of strongback braces to conventional braces and were evaluated, which revealed that the stiffness ratio of 2. 5 would cause a more uniform distribution of drift along the height of the structure and was the basis for the design of the braces of this system. Results show that the proposed design principles, which are proportional to the stiffness ratio of bracing, are presented by providing an index of uniformity distribution error in structures 3, 6 and 12 stories, which occurred less than 6, 4. 8 and 8. 6 respectively. Also by creating a difference of 0. 5% between the maximum and minimum of the story drift ratio in most of the structures studied, it has been able to hold the strongback truss in elastic to nonlinear analysis, reduce the concentration of deformations and prevent the creation of a soft story structure.

One of the most up-to-date seismic control devices are friction tuned mass damper (FTMD). This type of damper is a combination of a tuned mass damper (TMD) and a nonlinear frictional damper. In this paper, the governing equations for a single-degree-of-freedom (SDOF) structure equipped with a FTMD and effective parameters on these systems performance are expressed first. Then, SDOF structures with linear behavior equipped with a FTMD are modeled and validated in OpenSEES software. Finally, the sensitivity analysis of these models to their effective parameters is performed. The structures mass is assumed to be 10 tons, their period is 0. 5 second and their damping ratio is assumed to be 2%. Nonlinear time history analyses are done for these structures using 40 strong ground motions from the SAC project. These ground motions consist of 20 records (La01-La20) at design basis earthquake (DBE) level and 20 records (La21-La40) at maximum considered earthquake (MCE) level for the Los Angeles area. Effective parameters on the performance of FTMD assumed in this study are the friction coefficient of the damper, the mass ratio of the damper to the structure and the frequency ratio of the damper to the structure. Average of the structures' maximum displacement is determined for two ground motion records sets and effects of the mentioned parameters on the structural performance are discussed. Results show that the responses are more sensitive to frequency ratio rather than friction coefficient and mass ratio. The best value for the friction coefficient varies between 0. 1 and 0. 3 at DBE level, and varies between 0. 2 and 0. 4 for MCE level. Based on the results obtained for SDOF structures, application of FTMD on multi-degree-of-freedom (MDOF) is discussed in the next step. This is done for short period structures because this type of damper is more effective on these structures. Three MDOF structures with linear behavior and period of 0. 3, 0. 5 and 1 second are selected and the seismic performance of these structures equipped with FTMD is investigated and compared with the same structures equipped with tuned mass damper (TMD). The mass of stories is uniformly distributed among structure and the mass of each story is 10 ton. In addition, the damping ratio for the main structure in all models is assumed to be 2% and the stiffness of the stories is decreased linearly with the triangular pattern. Same ground motion records are used for the nonlinear time history analysis of MDOF structures and the results for the mean maximum relative displacement of the stories under DBE and MCE levels are compared for structures with FTMD and TMD. Results show that the structures equipped with FTMD have better performance than the structures equipped with TMD, but with increasing structures period, performance of two systems approach each other. In addition, 3 and 5 story structures equipped with FTMD have better performance at DBE level while a 10-story structure equipped with this damper has better performance at DBE level

Depending upon whether or not they are connected to the frame, infill walls display different performances and have varying effects on the structure and the force distribution between building frames. In most of buildings with steel or reinforced concrete frames, to partition the internal space and also to separate the inside of the building from outside, walls with masonry materials are used as infills. Masonry infill walls are composed of small, distinct elements which collectively act as a single unit. Videlicet, the masonry infill wall consists of discrete materials and since discrete materials generally exhibit a brittle behavior, they crack or fail during earthquakes which in most cases results in the loss of lives and capital. Thereupon, predicting solutions for bracing infill walls and preventing them from being destroyed in such a way that the structure can maintain its desirable performance seems necessary. The specifications of infills and the way they are connected to frames can exert considerable influences on the seismic behavior of the structure. In this study, to investigate the conventional methods of anchoring masonry infills to steel frames in Iran, the experimental results of four single-story, single-bay steel frames with the scale of 1: 3 are presented, with a special focus on the different details of the connection between the infill wall and the surrounding frame. Three frames with masonry infills and one frame without an infill were constructed using conventional materials in Iran. All of the samples were tested by applying a lateral load on the upper beam. Different details regarding the connection of the infill to the frame including how the infill is connected to an un-anchored frame, connecting the infill to the frame using vertical separating angles, and the use of embedded rebars in the infill. The results showed that using the mentioned details to anchor the infill to the frame is not only quick and convenient, it also suitably delays the cracking of the infill panel, changes the failure modes of the wall, decreases the level of damage and maintains stability in the wall. The employment of these details also exerts a significant influence on the cracking patterns, failure modes, stiffness, strength, ductility, out-of-plane deformations, and energy dissipation.

Experience of the past earthquakes reveals that conventional force based design (FBD) approach, only provide minimum requirement for life safety performance level of structures. While these methods do not capable to control structural seismic damages. In recent years, displacement based design approaches have been proposed as the main tools of performance based design. Direct displacement based design (DDBD) is recognized as one of the most efficient methods. In this method, an inelastic multi degree of freedom structure is substituted with an equivalent elastic single degree of freedom. The substitute structure is designed for a target displacement and an equivalent viscous damping using elastic displacement response spectrum. The effectiveness of this method has been examined in controlling the overall seismic demands of many structural systems, while the least attention has been paid to the effects of local damages. In this study, seismic performance of a set of RC frames designed with DDBD and FBD approach (based on Iranian seismic code) has been investigated and compared with a focus on local damages. DDBD and FBD method was applied to four reinforced concrete regular frames of 3, 5, 7 and 11 story and performance of the methods was compared using inelastic time history analysis (ITHA). In the seismic assessment process, in addition to general structural responses, the distribution of local damages has also been investigated. The Park– Ang damage index was selected as the seismic damage index and probability of exceedance of the damage limit state was compared using fragility curves developed for five damage levels. Results show that very good control of displacement and inter-story drift of RC frames designed with DDBD approach. Evaluation of the plastic hinge rotation shows, DDBD unlike FBD approach has been satisfied expected performance level. Furthermore DDBD approach provided more control on selected seismic damage index and distribution of damage index at height of structures is more uniform than FBD approach. The cost analysis shows that consumable rebar is increased 6. 6%-52. 11% and consumable concrete is up to 3. 4% in DDBD approach compared with FBD approach, which is more exponential in frames with higher elevations.

Purpose Different structural solutions are employed to enhance the capacity of weak structures under the earthquake excitations to satisfy the target of the rehabilitation regulations. These retrofitting methods include adding new seismicresistant components or increasing the strength and ductility of existing components. Given the probability of the earthquake occurrence, it is necessary to evaluate the effect of different retrofitting scenarios on the probabilistic performance of the structure. In this paper, a framework using fragility curves is presented to select the most efficient retrofit scenario in terms of the cost-benefit analysis. For this purpose, two methods of adding reinforced concrete (RC) shear walls and use of polymeric reinforced carbon fiber (CFRP) sheets are employed to retrofit weak RC frames of 5, 8 and 12-stories. Different retrofitting scenarios for RC frames were compared using the proposed framework. Methodology Following the presented framework, the damage indices of structures of each scenario are extracted from the incremental nonlinear dynamic analysis. Then, the fragility curve, the damage probability matrix, and the expected annual damage costs are obtained. In the last step, different scenarios were compared using cost-benefit analysis. The benefits and costs included in the cost-benefit analysis were the reductions of the annual damage cost and cost of each structural retrofitting scenario, respectively. The higher the benefit-cost ratio, the more economical the scenario is. IDARC [1] software was employed for dynamic nonlinear structural analysis. For modeling the hysteresis deteriorations in dynamic analyses, stiffness, resistance, and pinching deterioration parameters were employed. These parameters are obtained based on the relationships proposed in [2] to accommodate the hysteresis of the numerical modeling with the experimental one. The weak RC frames were retrofitted with the basis rehabilitation target by the Iranian rehabilitation Guidelines [3], signifying that the performance level of the structure is life safety (LS) under the design seismic risk (0. 25 g). Also, for better evaluation of the retrofitting methods, retrofitting was conducted at two higher levels. Conclusions The results of the nonlinear dynamical analysis showed that shear walls can reduce the inter-story drift ratios significantly more than CFRP sheets do. The results of the cost-benefit analysis revealed that retrofitting with the CFRP sheets is a more preferable method than retrofitting with the shear walls in terms of the economic approach, especially for the shorter height structure (5-story frames). It is because the cost of executing shear walls and shear wall foundations is very expensive. By increasing the structural height (from 5 to 8 and 15 stories), CFRP sheets outperformed shear walls, while for the 15-story frame, adding the CFRP sheets was a better solution than adding the shear walls. For high-and middle-height structures (8-and 15-story frames), the differences in the cost-benefit ratio of the two methods were ignorable. The CFRP sheets further reduced the exceedance probability of damages at low earthquake hazard levels, while shear walls further reduced the probability of damage occurrence and damage exceedance (especially highperformance levels such as collapse prevention). This is especially the case for higher-rise structures where the collapse probabilities are higher than for the shorter structures, leading to a close cost-benefit ratio of the two retrofitting methods.

One of the main concerns for structures and infrastructures is to evaluate their reliability and functionality as they can suffer long-term damage due to gradual deterioration over time, or they can be imposed to natural or manmade hazards and overloading during their lifetime. Thus, Structural Health Monitoring (SHM) has been a hot research topic in order to introduce efficient methods and feasible techniques for evaluating, monitoring and improving structural reliability and life cycle management. The SHM process typically includes three stages: a) data acquisition: measurement of the structural responses using an array of sensors; b) extraction of damage-sensitive features; and c) analysis of extracted features to develop statistical models and estimate structure health condition. During the last decades, vibration-based damage detection methods have been greatly developed. The purpose of these methods is to determine the resulting changes in structural properties including stiffness, natural frequency, mode shape and damping ratio of the structure. For example, the basis of the Fourier Transform (FT) method is to determine the structural modal parameters from the random vibration data in the frequency range. Since local damages mostly impact higher frequency modes which are hard to excite and detect, most of FT based methods are unable to detect local or light damages accurately. Therefore, time-frequency analysis is introduced to overcome the limitations of the Fourier method, the most important of which is not providing a frequency-time range of a signal. The first case of frequency-time analysis was the short-time Fourier transform method based on the Fourier transform of the data divided by the time window function. According to this method, the interaction between time and frequency is difficult due to the existence of the time window function. If the windows are smaller in the time segment, its accuracy increases and in the frequency domain it becomes less accurate. The signal processing techniques such as wavelet transform and the Hilbert-Huang transform are playing an increasingly important role in structural health monitoring. Hilbert-Huang transform (HHT) is a novel signal-processing technique for analysing nonstationary and nonlinear signals. HHT method consists of empirical mode decomposition (EMD) and Hilbert transform (HT). According to this theory, the primary signals can be decomposed into different basic time-dependent intrinsic mode functions (IMFs) through the empirical mode decomposition (EMD). Afterward, instantaneous frequency and amplitude of each IMF can be obtained as Hilbert– Huang spectrum. The application of HHT based approaches in structural health monitoring has been widely studied through the numerical and experimental researches. This paper proposes a damage detection method based on the amplitude coefficient correlation of responses of damaged and undamaged structures using Hilbert– Huang transform (HHT). Structural responses have been decomposed to intrinsic mode functions (IMFs) through the empirical mode decomposition (EMD) method and the changes appear in the first IMF. Therefore, every change on the original signal can be revealed on IMFs, since the original signal depends on IMFs. Also, these changes have an effect on the analytical signal and the Hilbert transform. The instantaneous amplitude in measured joints on the structure is calculated using the Hilbert transform of the first IMF of response. The coefficient correlation matrix of the damaged and undamaged elements is demonstrated by graphical diagram in order to estimate the location of the damage. In this research, the accuracy of proposed damage detection method has been verified by applying the method on a finite element model of two-span continuous concrete beam structure. The concrete beam is 80 m long with two equal 40 m span bays covered by a concrete deck with 0. 5 m thickness. The dynamic responses of the beam at all sensors have been obtained by numerical analysis of finite element model under triangular pulse loading. The responses were also contaminated with 2% random noise to consider measurement uncertainties. The damage has been modelled as stiffness reduction in a 1. 25 m long segment of finite element model of beam. To evaluate the efficiency of the proposed method, different damage scenarios are studied. IMFs of all responses at sensor locations were obtained by combination of EMD and HT, and the instantaneous frequency and amplitude of Hilbert were derived. Auto correlation of instantaneous amplitude of undamaged and damaged structures were calculated and introduced as Damage Index Correlation. According to the results, this method is able to trace the location of the damage by the comparison of the correlation coefficients. Therefore, the locations of damages in different scenarios were located with a variety of coefficients correlation in sensors. The results show that the proposed method can determine the location of the damage with an acceptable accuracy for low and moderate damage intensities in all damage scenarios.