نشریه مهندسی سازه و ساخت
سال هشتم شماره 8 (پیاپی 47، آبان 1400)

Steel braced frames are among the most effective lateral load resisting systems. The eccentrically braced frame has a higher ductility, less stiffness, and a better serviceability (limited retrofitting needed after the seismic excitations) compared to concentrically braced ones. Static indeterminacy is generally considered as the number of extra constraints or members in a structural system. In other words, redundancy is the ability of a structure to keep its stability after the onset of the failure or removal of its lateral load resisting elements, preventing it from collapse in the initial stages of loading. The redundancy of a system depends on the “dynamic” characteristics of its structure and properties of the applied earthquake excitations as well as its structural geometric features and details. This indeterminacy is called dynamic redundancy.In this study, the effects of the number and location of braced bays on redundancy were investigated to obtain the best pattern for regular 5 and 8-story buildings using nonlinear analysis. It also develops a relationship for the redundancy factor of the dual structural systems. Results show that position of braced bays is more effective on redundancy than the number of bays. It is also concluded that the building’s height affects the required number of bracing bays. The study also showed that the dynamic redundancy is different from the over-strength. According to the results of this research, for dual structural systems, it is recommended not to arrange the braces only in the perimeter of the plan

Tuned mass dampers (TMDs) are being increasingly used for protection of structures against seismic and environmental loads. An important step in design and application of TMDs is the evaluation of TMD parameter which can cause be associated with serious difficulties. In this paper, we attempt to provide a framework to evaluate the modal parameters of TMDs using a combination of experimental test on shake table and a relatively recent modal analysis technique, namely Frequency Domain Decomposition (FDD). In order to achieve this, a series of test were conducted on a 5-storey steel frame was subjected to excitations from two scaled earthquakes (Imperial Valley and Kobe) ) while damped using two TMDs with mass ratios of 0.01 and 0.1.Mounted instrumentations recorded the structural response during the earthquakes and the recorded response was then used for an operational modal analysis (OMA) in order to estimate the dynamic characteristics of the TMDs. The FDD technique was used in this paper which was employed to estimate the parameters of TMDs. The damping ratios obtained from FDD method was compared with classical methods to verify its accuracy and capabilities in extraction of the modal parameters of TMDs. This paper shows that the use of shake table experiments coupled with the post-experiment modal analysis can be successfully used in TMD design and enables the researchers and practitioners to accurately estimate and test the response of the structures under relatively realistic conditions, which consequently allows low-cost testing of TMDs for optimum TMD selection.

Deep foundation are used to transfer loads of large and high rise building to subsurface layers that have sufficient strength. Piles are one of the most common deep foundations which are installed in the form of driven an bored for many years, the high noise and variation by the driving and the hardness and the limitations of the performance of the bored piles caused to use a new type of pile which installed to the soil using torque and a small amount of axial compressive load, Helical pile can be considered as such piles. Drilled displacement piles are another type of this piles. Due to the increasing use of these piles, there are still limit studies on them and there is a need to study their behaviour in different soils and conditions. Three models of piles in the laboratory section were implemented and loaded in FCV-AUT and compared with studies in the field. Compressive and tensile static load were performed according to ASTM D1143 and ASTM D3689 standard and rapid loading test.Drilled displacement pile in tensile and compressive performance was better than other torque driven pile. Because of concrete is cheaper than steel, these piles can be a good alternative for driven and bored pile in urban areas.

In this study, a simplified approach is proposed for design optimization of the reinforced concrete frame considering the effects of chloride-induced corrosion. The objective function is to minimize the frame weight, and optimization will be conducted utilizing the genetic algorithm. The constraints of the optimization problem are set in a manner that bending moment of beams and axial force of columns are not exceeding the respective resistant values, and the maximum drift of the frame is not exceeding the code-defined allowable drift. In order to examine the corrosion effects, a 5-story reinforced concrete frame is optimized in two different time points 0 and 50 years in its service life. The zero time point indicates the sound uncorroded frame. Monte Carlo sampling method in Rt software is utilized to estimate the corrosion initiation time incorporating the involved uncertainties. At time point of 50 years, a cross-sectional area of steel bars in beam and column sections is reduced due to the corrosion effects. The proposed framework for the frame optimization is implemented in MATLAB software; and for computing the structural response during the optimization process, the linear static analysis of the structure in OpenSees software is conducted. Results indicate an ability of the proposed framework for design optimization of reinforced concrete frames considering the corrosion effects in their service life.

Up to date, most of the bending moment connections are designed to follow a weak beam-strong column rule, which imposes extensive fabricated and material costs and welding applications at the project site. Therefore, in order to eliminate these shortcomings, a relatively new bending moment connection that connects steel beam and column to each other only by connecting a plate in the direction of the beam and column web are studied as the parametric studies. The design criterion for the connection sheet was such that its flexural bending capacity was less than the bending capacity of the beam so that the connection plate would act as a metallic yielding damper and other elements would remain in the elastic state. Parameters such as thickness, height, slope, and plate material were considered in nonlinear static analyzes and the simulation of 12 numerical models of finite element in the Abaqus program under cyclic loading. Initially, the numerical model was compared with the test sample, and the behavior of the two samples in terms of failure mode and the hysteresis curves of the bending moment-rotation were well matched. Numerous numerical models were then simulated to consider the effect of parameters on the overall behavior of the connection. The results of the analysis showed that the appropriate range for the thickness of the connection plate to act as a fuse and energy absorber must be between one and twice the thickness of the beam web. Also, the free distance should be between 4 and 6 times the thickness of the plate.

Nowadays, with the spread of terrorist attacks in many parts of the world, the design approach to abnormal loadings, such as a blast load, has also become noted of design regulations. In recent years, the dual moment-resisting frame system with steel plate shear wall has been used in the design of structures as a load-bearing system and has several advantages such as low construction cost, rapid installation, high energy absorption potential, suitable ductility, Increasing stiffness and decreasing displacement have made the steel plate shear wall as a proper system for retrofing existing structures, so it is necessary to investigate the behavior of this system against blast loads. In this study, moment-resisting frame structures with and without steel plate shear wall (3, 6 and 9-story) were designed in 3D by ETABS software based on code guidelines and then two-dimensional side frame was extracted in order to be analyzed under the effect of blast loading in 2 scenario such as in-plane and out-plane frame with finite element ABAQUS software and finally the possibility of occurrence progressive collapse were investigated and compared. The results of the present study showed that steel plate shear wall dual system has a suitable performance in comparison to moment-resisting frame in the scenario "in-plane blast loading". It restricted the progressive collapse potential while in the scenario "out-of-plane blast loading" because of the blast load wave propagation in steel plate shear wall, then the moment frame has a better performance. Also, according to the Robustness Index (RI) comparison, with regarding to the in-plane and out-of-plane blast loadings, the steel plate shear wall and moment-resisting frame structures had the best performance, respectively.

This paper presents the dynamic analysis of flat slab buildings using macro modeling method to evaluate their progressive collapse resistance. In these analyzes, the post-punching behavior of slab-column connections is considered. The presence of lateral restraints, by development compressive membrane force in the slab, increases the stiffness and flexural strength of the slab and ultimately increases the punching shear strength. In continuous slabs, the lateral restraint is provided by the slab itself. In experimental testing, part of the flat slab structure is typically extracted in the tests due to cost reduction and limited test space, and an additional load is applied to the slab edges to simulate the influence of the surrounding slabs. The effect of compressive membrane action and surrounding slabs on the response of flat slab structures was investigated using a validated macro-model. The findings of the study indicate that the slab 's compressive membrane force enhances the ultimate load bearing capacity in the column removal scenario. This increase in bearing capacity of the structure is, of course, not proportional to the increase in punching resistance in slab-column connections. The results also indicate that ignoring the lateral restraint effect of the surrounding slabs underestimates the capacity of the substructure for load redistribution. It is suggested that rotational restraints be placed on the slab edges in order to simulate the effect of surrounding slabs on the behavior of the substructure.

Dissolution of soluble minerals in the construction site of dams will lead to the development of cracks and increase the permeability of foundations and abutments, destruction of injection molding and problems in the stability of dams. Increasing the dissolution rate with the development of cracks and fissures leads to increasing the permeability of the foundation and then the currents passing through the joints will not be similar to groundwater flows and the flow behavior will be similar to surface currents. The passage of current through the surface of gypsum and anhydrite-containing materials, the mechanism of behavior of gypsum and anhydrite materials against surface currents have been investigated, and then, using the experiences gained from past research, finally relations to estimate the constant rate of dissolution K It has been extracted in these two materials. the highest correlation with flow and temperature flow is linear and time parameter is exponential. Also, the solubility coefficient of gypsum materials is higher than anhydrite in the presence of surface currents. For a constant temperature, the gypsum K coefficient is about 10,000 times that of anhydrite, and at a constant temperature, K for gypsum is equivalent to 1000 times that of anhydrite. In general, the effect of discharge on the dissolution of gypsum is greater than anhydrite.

Model predictive control is one of the optimal control methods for systems based on their behavior on future horizons. One of the salient features of this control method is the optimal consideration of control constraints in the system control process. Accurate states are required to perform an optimal control performance with this technique. On the other hand, state sensors are unable to provide accurate states due to the uncertainty in their structures. This shortcoming causes problems in the optimal control process. In this study, a discrete-time Kalman filter-based model predictive control scheme with actuator saturation consideration is presented. As a state estimator, the Kalman filter is able to provide more accurate states. On the other hand, the application of performance constraints in the control process causes the saturation of the actuators to be optimally regarded. In the present study, to investigate the effectiveness of the proposed control method in reducing seismic responses, a nine-story benchmark steel structure (SAC) under seismic excitation is utilized. Then, the results obtained from the proposed method considering three different control force constraint scenarios are compared with the results of the uncontrolled case. The results of numerical studies demonstrate the appropriate performance of the proposed control process in reducing seismic responses. Also, the replacement of low-capacity actuators with high-capacity ones, while making the control process more economical, do not significantly change the other responses quantity. For example, the highest change in the Drift Ratio Index (J1) for the controlled case with control force constraints to the controlled case without control force constraints for the Elcentro earthquake is by up to 4%, while the same conditions for the maximum control force index (J12) is 78%.

In One of the most important issues of project-oriented employers and senior managers is evaluating the performance of the organization's projects as well as ranking the projects based on applied indicators during project implementation. The lack of a system of method in a system means not knowing the contractors' work defects during execution, which in itself causes time, quality and economic losses. The purpose of this study is to identify and compare current operational strategies to standardize contractors' decisions in construction projects. In this research a questionnaire is designed by studying and reviewing scientific articles from databases and interviewing executives of companies that formulate and execute contractors' operational strategies. Then, the questionnaire is distributed among the executives of the contractor firms and they score the factors according to the two hypotheses. The answer will be weighted and analyzed using statistical software. The published factors are then prioritized around operational strategies. The results show that the strategy of managing the additional work done in the project is in the first place and in the next rankings respectively of the other strategies including contractor performance, resource management and stakeholder management.Also, all the factors that were designed in the questionnaire are the published characteristics regarding the common operational strategies in terms of decision categorization. In the analysis, the factors have an acceptable value and none of them can be ruled out.

Nowadays, all managers in all organizations want to make optimal use of facilities and capacities in various departments. Therefore, the existence of a model to provide feedback on destructive factors in bridges with the aim of improving the management of concrete bridges and obtaining a tool to satisfy the needs of managers, seems very necessary and logical. In line with the above necessity, concrete road bridges under the supervision of the Highway and Road Transportation Organization of the country will be selected as a statistical sample and the performance of concrete bridges will be compared with each other using data envelopment analysis (DEA) method. In order to evaluate the performance of bridges, efficient and inefficient bridges are determined and the effective factors in their inefficiency are determined. In order to evaluate the efficiency of inputs such as weather and traffic conditions, and the outputs including structural failure factor and serviceability were examined using the input-axis CCR model through DEA-Master software. The results showed that 35 bridges out of 384 concrete road bridges measured in the main axes of Zanjan province have strong performance and the average efficiency of these 384 bridges is 0.98 out of 1.Also, the 8 km bridge of Zanjan-Qazvin freeway is the most efficient bridge in terms of threat of reference times.

The dry shrinkage of mortars is one of the primary causes for the reduction of bond strength between repair mortars and concrete substrates. Utilizing fibers in the mortars is one of the methods used to reduce shrinkage. The current study used polypropylene fibers in mortars to improve the bond between repair mortar and concrete substrate, and also to control the dry shrinkage of mortars. The “friction-transfer” and "pull-off” methods were used to determine the bond strength between the repair mortar and concrete substrate. In addition to determining the amount of shrinkage and bond strength, the amount of compressive strength of fiber reinforced mortar by using the above methods and by modeling finite element with ABAQUS software has been investigated. In addition, the methods of initiation and distribution of cracks and stresses were shown. In order to assess the in-situ compressive strength of polypropylene fiber-reinforced mortars, the correlation of records obtained from semi-destructive methods of “friction-transfer” and “pull-off” with those of laboratory tests was determined, using the linear and exponential regression analyses. Then, using calibration curves, the equations required to convert the results of in situ methods to the compressive strength of polypropylene fiber-reinforced mortars were presented. The results demonstrate the positive effect of fibers on shrinkage, shear and tensile bond strength and compressive strength of mortars. The correlation coefficients of the “friction-transfer” and “pull-off” methods are indicative of a strong linear relationship between the two methods that instead of using an expensive “pull-off” device, a simple and inexpensive "friction-transfer" device can be used.

In this study, the nonlinear behavior of a studied 20story steel bundled tube frame structure is evaluated under applying the assumed incidence angles to the imposed directions of near-field records. Additionally, the related effects on the stability of the studied structure subjected to the probable forming of progressive collapse, have been studied too. The results of this research were obtained based on conducting nonlinear dynamic time history analyses. Four assumed incidence angle case studies were considered to an ensemble of three-component earthquake records. Moreover, three-member removal situations were also assumed for the selective column elements of the studied structure subjected to all chosen ground motions.The results of this study show that the structural response parameters have a relatively larger amplitude under removing of the corner column at the first story, than the other two cases of column removal which to be assumed at 10th story and also for the middle column of the outer frame. Furthermore, the structural responses did not change significantly with the increase of the incidence angle from 0° to 45°. The obtained results show that the formation of plastic hinges and inelastic zones in the structure would indicate high deformation demands at the middle stories and also the induced demand variation decreases along upward of the height. Additionally, removing of the corner column would result in the formation of more plastic hinges, which cause relatively greater structural damages and gradually reduces the stability of the studied structure. It is worth noting that the structural response parameters under each element removal and subjected to strong near-field records, remains in a relatively stable domain. Furthermore, the variation of response parameters did not exceed the life safety limit.

The earthquake is a phenomenon that is likely to occur all over the world and so far it has caused a lot of human and financial losses. During earthquake events, it is not uncommon to observe after-shocks following a mainshock, aftershocks have the potential to cause severe damage to buildings and threaten life safety even when only minor damage is present from the mainshock, but in the current regulations, the effect of aftershocks is not considered.Another factor affecting the behavior of the building during the earthquake is a torsional irregularity that may be due to architectural constraints in the building and, if accompanied by aftershock, results in further damage to the structure.In this article, for assessing the effects of torsional irregularity and also the aftershocks, 3,5 and 8 story models with steel moment frame seismic system, first regular in plan and then with torsional irregularity are carried out according to the Iranian seismic code and then 3-dimensional analytical models analyzed based on Incremental Dynamic Analysis (IDA) in OpenSees. The maximum inter-story drift ratio is obtained for 20 sets of ground motion records with aftershocks compatible with the conditions of the region and the capacity is determined according to HAZUS-MH limit states and finally, the corresponding fragility curves for seismic performance levels of slight, moderate, extensive and complete are developed.The resulting seismic fragility curves revealed the destructive effect of torsional irregularity in 5 and 8 story is more than 3 story and the aftershock outputs illustrated that the effect of aftershock on the damage level increase when building have torsional irregularity.

In this research, the cyclic behaviour of a perforated yielding shear panel device in an inverted v- braced steel frame has been studied. In 40 samples the effects of web thickness, amount of cut-out and amount of cut sector, in two samples the web length, in seven samples the variation of frames components and boundary conditions, and in two samples the centre to centre distance of the cut-outs have been studied. Non-linear analysis has been performed using the finite element ABAQUS code. Cyclic displacement control loading based on FEMA 461 protocol has been applied to the two sides of the beam. The von Mises yield criterion has been used. Obtained results show that if the web thickness of the yielding shear panel exceeds a certain value, the panel will not yield. Making cut-outs in the web and cutting sectors at the two sides of the web up to a certain amount increases the dissipation of energy, and thereafter it has an opposite effect. The amount of cut-outs for which the maximum damping occurs increases with the increase of the web thickness. Therefore, the favourable amount of cut-outs increases approximately proportional to increase of the web thickness. For instance, the favourable percentage of cut-outs without cut sectors with a web thicknesses of 10 mm, 15 mm and 30 mm are approximately 10%, 20% and 30%, respectively. These values for samples with cut sectors of 20% are respectively 10%, 10% and 30%. A yielding shear panel with a shorter web length absorbs more energy. Increasing the beam moment of inertia and the bracing cross-sectional area does not have a significant impact on increasing the damping.

A large number of structures experience minor damage in some elements during operation, therefore, the development of this type of damage reduces the service life of the structures and in some cases leads to total destruction. That's why, today, being assured of the health status of structures and their performance is proposed as one of the most important engineering issues. Considering the limitations of traditional damage detection methods, the methods based on changes in the vibrational characteristics of the structure have been formed. In this paper, given the modes shape of the panel prefabricated wall before and after destruction as a 2-D signal processing, the damaged zone was detected using discrete 2-D wavelet transform. At first, the panel prefabricated wall was modeled in the ABAQUS finite element software, and the frequency analysis was done to extract modal responses and was validated using modal responses of the corresponding laboratory sample. Changes in the values of natural frequencies, as well as the incompatibility of the modes shape based on the Modal Assurance Criterion (MAC) and the angle between the modes shape confirm the damage in the structure. Additionally, diagonal details from differential or summation wavelet transform analysis of the interpolated healthy and damaged modes shape (depending on the angle between the modes shape, if it approximately equals zero degree, the differential of modes shape is analyzed, and if it approximately equals 180 degree, the summation of modes shape is analyzed) indicate more irregularity of the wavelet coefficients in the damaged zone compared to other zones such that the jump relative maxima and minima in the wavelet coefficients have occurred in the damage occurrence zone.

Concrete-filled tubular (CFT) steel columns are a group of composite sections that are considered due to their higher load-bearing capacity, good ductility and good strength. These sections are widely used in a variety of high-rise buildings, offshore structures, subway stations and bridge piers. Therefore, these structures may be exposed to dynamic loads such as axial impact loads (due to accidents or intentional impacts such as falling and releasing various devices, military or terrorist activities). One of the most important techniques in the application of CFT columns is the use of partially concrete-filled steel columns, which are now available due to their cost-effectiveness and weight reduction of the structure, especially in bridge piers and docks. Due to the increasing use of partially concrete-filled steel columns in various structures, it is necessary to know their behavior against axial impact loading, which has not been considered to date. In this paper, the dynamic response of partially concrete-filled cold-formed steel columns against simultaneous loading of static axial compressive load and axial impact load using finite element modeling in ABAQUS software by performing nonlinear dynamic analysis are discussed. Parametric studies to investigate the effects of impact speed, the ratio of the height of the filled concrete to the total height of the column, the height of the impact hammer falling, the ratio of the impact mass to the total mass of the column, the ratio of static axial compressive load and eccentricity of axial impact load are performed. The desired columns have rectangular cross section. The results of this study show that with increasing the parameters of static axial compressive load, filling ratio, eccentricity of axial impact load and the height of the impact hammer falling, the impact load decreases. Also, with increasing the mass ratio and impact speed, the impact load increases.