نشریه مهندسی سازه و ساخت
سال هشتم شماره 6 (پیاپی 44، شهریور 1400)

One of the challenges in the health monitoring of bridge structures is the "data" extraction from the structure. This is done by sensors in the structure. The layout and use of the fewest possible number of sensors, so as to provide the most needed data on structural status, has always been of interest. There are shortcomings in the methods used to determine the location of sensors in bridges, such as the use of one optimization indicator, determination of the number of sensors experimentally, high environmental noise, and a long calculation time. In order to overcome these shortcomings, a new MSE-MGA (Modal Strain Energy-Modified Genetic Algorithm) method is proposed in this study. In this method, two modal strain energy indices and modal contribution coefficient are used to reduce the noise effect of vehicles passing through. All the appropriate locations of the sensors are selected by these indices, and then the optimal number of sensors and their location are determined by using the genetic algorithm. The results show that increasing the number of sensors from a given optimal value has no effect on increasing the required data. Also, the simultaneous use of two optimization indices has resulted in the elimination of a large number of inappropriate points for sensor placement, resulting in a significantly reduced computational time. To investigate the performance and practical application of this method, a model of a steel bridge is modeled and the optimal number of sensors and their layout are determined.

In recent years, the use of composite rebars in reinforced concrete structures has received much attention due to its high corrosion resistance, significant tensile strength, and appropriate non-magnetization characteristics.  Due to the lower modulus of elasticity of composite rebars than steel rebars, concrete beams reinforced with composite rebars have relatively lower shear strength compared to beams reinforced with steel rebars. On the other hand, shear failure in concrete beams reinforced with composite rebars is generally brittle and requires accurate prediction of the behavior of these members. Therefore, in this study, the shear strength of concrete beams reinforced with composite rebars is predicted using a combination of GMDH type neural networks and genetic algorithms based on a wide range of experimental results. The key effective parameters that consider in this study are the width of the web, effective depth of the beam, shear span to depth ratio, concrete compressive strength, modulus of elasticity of FRP longitudinal bars, and longitudinal reinforcement ratio. The accuracy of the proposed method has been verified by comparing the model predictions with the collected experimental results and existing shear design equations. The results show that the proposed model has more accurate results in calculating the shear strength of concrete beams than other existing relationships. A sensitivity analysis is also performed to assess the effect of the input parameters on the shear strength of FRP-reinforced concrete beams.

This paper presents an approach for evaluating structural resistance degenerate due to reinforcement corrosion and for predicting future structural performance during the service life of the deteriorating reinforced concrete beams due to corrosive environments. a finite element method is adopted for envisioning the nonlinear flexural behavior of intact and corroded RC beams based on Ultimate strength design method and Load and resistance factor design method approaching this aim, the impact of corrosion of embedded reinforcing element on the flexural capacity of corroded reinforced concrete structures is estimated. A stochastic degeneration model based on gamma process is utilized to assess the probability of failure of structural flexural capacity over the lifetime. Optimal repair planning and maintenance strategies throughout the service life are circumscribed by evaluating the cost for maintenance and the risk of structural failure. Based on the conclusions from the numerical model including two RC beams subjected to reinforcement corrosion the following results are drawn: The permissible deterioration limits that describe the thresholds of the deterioration for the safety and repair requirement, held major effects on the probability of failure. The results from the worked example show that the proposed method can afford reliable predictions for structural strength deterioration and efficiently implement a risk-cost-benefit optimized repair procedure through the service life of the structure affected by bar corrosion. The lifetime distribution increases 5years for LRFD method and 3.5 years for USTD method while allowable limits enlargement 10%. The lifetime distribution extends 5years for LRFD method and 3.5 years for USTD method while allowable limits increase 10%.

Collapse performance evaluation of structures has been a concern for researchers due to its complexity and uncertainty in modeling and simulation. Concentrate plastic hinges are best candidates for modeling collapse behavior of structures. Collapse fragility curves are affected by various sources of uncertainty. Existing uncertainties in modified Ibarra and Krawinkler moment-rotation model for concrete moment frame buildings were investigated in this paper. LHS simulation method was used to generate random variables considering the correlation among modeling uncertainties in one component and two structural components. Collapse responses including mean collapse capacity and standard deviation were obtained for each simulation by generating random samples for uncertainties using incremental dynamic analysis (IDA). As much effort is needed for implementation of IDA, MLP artificial neural networks, GMDH artificial neural network and response surface method were used to estimate and anticipate the collapse behavior of the structure. Results show that using above methods will lead to high accuracy anticipations with an error of less than 10% for GMDH neural network and an error of less than 7% for MLP and response surface methods.

Pipe racks or pipe bridges are one of the most important refinery structures which are used to maintain pipes and other equipment at the required levels and are usually made of concrete, steel or a combination of these two. Measures should be taken to reduce the damage of piping system due to separation of pipe-racks, the separate behavior of each of these parts during the earthquake, and also the large force involved in the separation of the pipe supports. Dampers are one of the most powerful earthquake engineering tools as a passive control system. Although the use of dampers in pipe-rack structures is unusual, it can be very useful in some cases. In this study, the function of dampers in a four-part pipe-rack under the influence of faults near faults and earthquakes was investigated. Our Findings revealed that when dampers placed in a longitudinal braces, the use of dampers in the pipe-rack has a very good performance and reduces the damage to the structures and piping system after the earthquake. Adding dampers to these structures can dramatically reduce the inter-levels drainage and acceleration of floors, and thus protect the pipes. In this way, these structures can fully maintain their usability during the earthquake and can be exploited immediately after the earthquake, which is very important in refineries.

The amplification pattern of earthquake waves and extensive damages due to that in alluvial valleys are influenced by two phenomena such as alluvial characteristics and topographic features of the site. Therefore, local effects assessment of the site is considered as one of the effective parameters in designing reinforced structures to withstand seismically excitations. For the first time after the destructive and historic earthquake on November 12, 2017, in Sarpol-e-zahab, using geotechnical reports of drilled boreholes by housing foundation, this article has studied two dimensional modelings of the subsurface structure of Fooladi zone. Sarpol-e-zahab's bedrock accelerogram was also used to perform nonlinear dynamic analysis using ABAQUS software. The response spectrum of different parts of soil surface was used in one and two-dimensional forms to investigate the impacts of topographic and stratigraphy factors. Determining the dominant dynamic period of the site and the maximum amplification values are the other findings of this study. The amplification graph over different times shows buildings with the periods from 0.7 to 1.1 seconds have been affected amplification and site factors more than any other period. In the end, considering the calculation of the average shear wave velocity up to 30m borehole, the investigated land showed the highest compatibility with level 3 of land type classification table of Standard Code No.2800 and response spectra obtained from this study were compared with design spectrum of Standard Code No.2800. Contrary to the fifth edition published report of the International Institute of Earthquake Engineering and Seismology (IIEES), the findings generally show the right and appropriate performance of the Standard as well as using tall structures with sufficient safety.

Due to the increasing need to use rebar in construction, many efforts have been made to optimize its use. One way to reduce rebar usage is to use welded splice instead of overlap splice. However, the Iranian Concrete Code only refers to the welded splice generalities and there are no rules on how to splice. Therefore, the purpose of this study is to investigate the tensile strength of welded splice bars with different configurations. For this purpose, rebars with diameters of 10, 14, 18, 22 and 25 were connected to each other by a variety of discontinuous and continuous overlap patterns by welding with the E6013 electrode. Then the tensile strength of the connected rebars was obtained by tensile test. Then, with Abaqus software and the birth and death method, a variety of splice patterns were modeled and the results were compared with laboratory results. The results show that the optimum welded splice is the model with discontinuous weld with a weld length of 5d.

While the fibers in concrete cause soft rupture, the compressive and tensile samples are not ruptured after failure. This is one of the benefits of metallic fibers, especially the sinusoidal and hooked fibers: using these gives residents the opportunity to escape during an earthquake. In addition to positively impacting mechanical properties, metal fibers improve the matrix of concrete, provide ductility and response to impact load, and control crack width and propagation. Fly ash and micro-silica improve the durability and performance of concrete and are effective in protecting the environment: they can, thus, be used to replace cement. In this study, the samples’ compressive and tensile strength was prepared: they were of non-fibrous concrete and concrete containing steel fibers with 6 different percentages (0.4, 0.6, 0.8, 1, 1.2, 1.5). They were also composed of metallic fiber and polypropylene in three different compositions (0.3PP + 0.8SF, 0.4PP + 0.4SF, and 0.15PP + 1.5SF). These were investigated: seismic parameters were extracted after achieving the optimal percentage (the percentage with the highest compressive and tensile strength given economic considerations) under the loading protocol SAC/BD 97.02. This allowed investigation of the curves of hysteresis, energy absorption, lateral displacement, and effects of the use of these fibers. The major properties of pozzolanic materials were considered in the last step of this research: fly ash and microsilica were added to concrete containing metal fibers with the optimum percentage of metallic fibers. These were compared with concrete containing metallic fibers and non-fiber concrete. Thereafter, the appropriate percentage of cement replacement was determined so as to better understand the effect of the use of fly ash and microsilica in preventing the buckling of buckling restrained braces.

In PPP toll road projects, public sector supports project companies that face the risk of revenue, by different mechanisms. It is necessary for the public sector to evaluate these mechanisms before granting them to the private sector. This study evaluates the support mechanisms defined in the Iranian PPP toll road projects legislations by real options and compares them with a proposed mechanism. Additionally, the uncertainty of the project revenue during the concession is modeled by the options theory. The impacts of the revenue risk on public and private sectors is evaluated by Monte Carlo simulation in a Flexible-term mechanism, a Flexible-term mechanism alongside a Revenue Guarantee mechanism defined in the legislations, and a Flexible-term mechanism alongside a proposed Guarantee based on Barrier Option. Subsequently, the sensitivity of these impacts to the revenue projection errors is analysed. This process is implemented in a real PPP freeway project. The results show that the combining Flexible-term and Revenue Guarantee mechanisms improve the financial viability of the project, indicating the continuance of adequate yearly cash flows through the whole concession period. Adjusting the Revenue Guarantee defined in legislations by Barrier options reduces the public sector’s payment commitments. The analysis of the uncertainties of the project revenues reveals that the revenue projection errors have a great impact on the consequences of the revenue risk on both parties. Since the public sector often faces budgeting challenges to support projects, the proposed mechanism can help public sector decision-makers to better allocate financial resources by supporting the projects that struggle with financial viability. The sensitivity analysis of revenue projection errors on risk impacts in each mechanism provides public sector decision-makers with a broader and more realistic spectrum of the revenue risk impacts on pubic and private parties.

Awareness of the probability of failure and the safety index of a structure designed and implemented on the basis of regulations and codes can enhance the designer's attitude towards the failure or safety of the structure. This paper examines the probability of failure and safety index of 3D steel moment frames. A three-story steel moment frame and a six-story steel moment frame loaded and designed on the basis of the previous drafts of National Building Regulations of Iran have been selected. In order to perform the finite element analysis of the 3D moment frame and system reliability analysis, a program with CSHARP programming language is written incorporating the Monte Carlo method. In reliability analysis, the uncertainties in the yield strength and the Young's modulus of steel, gravity loads and lateral forces, cross-sectional and plastic section modulus of the frame members were considered. The calculation of the probability of failure and the safety index of the framing system in two cases, according to the old, 2008 edition and new, 2013 edition of Iranian National Building code, Part 10: Steel Structures, have been done and compared. It was noted that assessment of buildings constructed on the basis of the old regulations with new drafts of National Building Regulations of Iran resulted in decreased safety levels. Also, the effect of statistical correlation between gravity loads and lateral forces in determining the frame safety index has been investigated. The sensitivity analysis performed for the steel coefficient of variation showed that its variation after the value of 0.07 can have a significant effect on the reliability of the steel moment frame.

Shear walls can be designed to have sufficient bearing capacity and deformation and absorb energy due to nonlinear shear-bending and axial load - bending, interactions. However, in the event that reinforced concrete walls do not have sufficient seismic resistance, the effective solution is to use new composite wall options. The use of steel trusses, consisting of steel columns and embedded steel brace in the reinforced concrete shear wall is one of the types of composite shear walls. In this study, seismic behavior of composite shear wall with embedded steel truss is investigated. For this purpose, various models of these walls have been modeled using finite element method at 5, 10 and 15 storys. The influence of various factors such as bracket area, column area, and axial load ratio on the performance of this system against lateral loads is evaluated. The influence of various factors such as brace area, column area, and axial load ratio on the performance of this system against lateral loads is evaluated. The results show the steel braces to increase lateral bearing capacity and column steel has been more effective in absorbing energy. Axial load had a greater effect on increasing the initial hardness. But , to avoid the adverse effects on ductility behavior, the axial load ratio must be limited to the medium level

Design, construction and maintenance of liquid storage tanks, which have been extensively used to store liquid in industrial factories, oil refineries and petrochemical sites, are crucial. Vulnerability of liquid storage tanks have been recognized regarding to the experiences of major earthquakes occurred specifically in Japan, United states and Turkey. Therefore, evaluation of seismic responses of steel storage tanks is important. In this research, due to the complexity of ground motion behavior and the effects of different parameters such as frequency content of excitations on damage assessment of liquid storage tanks, more precise seismic analyses under near-fault and far-fault ground motions considering bi-directional horizontal components is carried out. For this purpose, the fixed base steel liquid storage tanks with height to diameter ratio equal to 0.4 is considered. The finite element analysis of the tank-liquid is carried out using ABAQUS software considering fluid-structure interaction based on added-mass method and nonlinear time history analysis. Significant difference between the seismic responses of the tank to uni-directional and bi-directional earthquake is obtained. More interestingly, the effect of frequency content of excitations on the dynamic response of steel liquid storage tanks are discussed.

In this study, the use of precast laminates, made of high-performance fiber-reinforced cementitious composite (HPFRCC), was investigated for strengthening of continuous reinforced concrete (RC) beams. HPFRCCs are characterized by their high tensile strength and remarkable durability properties. To find the effect of strengthening, eight continuous (two-bay) RC beams were tested under monotonic load in the middle of spans; two of which were the control specimens and six of which were strengthened specimens. The HPFRCC laminates were prefabricated with 25 mm thickness and bonded to the tensile surface of beams using epoxy and mechanical anchorage. The longitudinal bars were added to laminates in four specimens to survey their effect on strengthened beams. Comparison of results declared that the load carrying capacity was increased up to 59 % in strengthened beams.  Ductility index of the strengthened beams was acceptable, and also up to 35 % growth in energy-absorption capacity was observed. Applying laminates to the tensile surface delayed crack propagation and decreased the midspan deflection. Also, stiffness of specimens in the cracked concrete stage was increased up to 78 % that led to decrease the service deflection. It is concluded that the use of HPFRCC laminates, especially in case of applying longitudinal bars, is an efficient method to enhance the flexural capacity of continuous RC beams.

Considering that a significant portion of the share of energy consumption among consumer sectors is in the home and commercial sectors and this share is still increasing, there is a need for research in energy consumption management and evaluation of effective indicators in the building industry. Building the country is vital to optimizing energy consumption. One of the most appropriate ways to optimize fuel consumption in the building and housing sector is the implementation of zero energy buildings which is considered as the main solution in the world. In this research, after analyzing the population and statistical sample, data were collected to evaluate effective criteria and options related to energy consumption management. First, fuzzy Delphi method was used to evaluate the sub-criteria and select the main options of each. At first level the criterion is discussed and at the second level the data analysis and research model is analyzed through paired comparisons using fuzzy hierarchical analysis technique. Finally, the most important indicators and criteria are obtained using fuzzy hierarchical analysis. According to the research findings, among the energy consumption optimization management indices investigated by the FAHP method, the economic, construction and utilities indices with 0.333, 0. 201 and 0.176 have the highest management priority, respectively. Energy-efficient optimization has a zero-energy building approach.

Nowadays, the glass fiber-reinforced polymer (GFRP) sheets have been known to be one of the most effective composite materials that are used to increase the strength and durability of concrete structures. Owing to the light weight, corrosion resistance, high tensile strength and the ease of application without any interruption of the services, the use of these sheets has become very wide spread. In recent years, some organizations in Iran have opted for the use of GFRP sheets for the strengthening and protection of their concrete structures that are located in the areas exposed to the Persian Gulf water. Therefore, in the present paper, the results of the permeability tests conducted on GFRP strengthened concrete samples, using the newly developed “Cylindrical chamber” method are discussed. Since the deterioration of concrete structures exposed to extreme environmental conditions due to the water penetration, appears to be a critical issue, the above mentioned samples have been exposed to different cycles of wet-dry, high and low temperatures and freeze- thaw tests, before measuring their permeability’s.  The results showed that the temperature change cycles have a small effect on the permeability of GFRP in comparison to the freeze-thaw and wet-dry cycles. The penetrated volume of water after 30, 90, 150 wet-dry cycles, was 61%, 100%, 18% lower than the respective values obtained after the same cycles of temperature changes. Considering the freeze-thaw conditions it was found that similar cycles of freeze-thaw tend to increase the permeability of the samples by about 12%, 36%, 29%, compared with the respective values of the temperature change conditions.

The present article involves evaluating the efficiency of an active viscous damper in controlling vibrations caused by near and far field earthquakes. Being installed on chevron bracing systems, the damper is able to provide necessary controlling forces to diminish vibration amplitude up to its' saturation limit. Many researchers have worked on the concept of seismic active control under far field waves. But the efficiency of this system is not guaranteed in near field ones due to time delay phenomenon. Pulse and shock entity of near field seismic waves leads to decreasing active control effects and the present research also proves the fact. A computer based algorithm is developed using Newmark instantaneous optimal control method in MATLAB software.The performance of this code is validated and evaluated based on three different reference problems. Then the analysis results of a 7-storey structure are calculated based on the code. The analyses are developed using both controlled and uncontrolled states. Also near field and far field earthquake records are used in this process and the results are compared in different tables and graphs. Based on the results, it seems that active control systems in spite of their effectiveness in near field earthquakes, needs necessary scheming and changes in the process.

Health-care applications are those types of uses that, in the event of inaccurate location, may lead to irreparable loss of life in addition to the economic and financial constraints. The geographical location is the main component of access to medical services. Therefore, the importance of optimal and suitable location for this type of user should be considered. In this paper, a compilation of GIS capabilities and an ANP model in a fuzzy environment was conducted to determine the optimal locations for the establishment of a hospital in Markazi province, Arak city. For this purpose, firstly, effective and suitable criteria for locating the hospital in view of the location is the geographic and geographical conditions of Arak, hospitals, experts, books and articles were selected and then weighed in fuzzy environment. Finally, the results obtained by fuzzy GIS in fuzzy mode were used by five fuzzy operators (AND, OR, SUM, PRODUCT, GAMMA) combined in ArcGIS. According to the results obtained from five fuzzy operators, the accessibility criterion, which had the highest weight, was prioritized in order to find the optimal location for the establishment of hospital, and the locations were identified with the least distance from main road/paths for quick and easy access in the shortest time to the hospitals.

Buckling-restrained braced frames can considerably reduce the seismic responses, because of their high energy dissipation capacity. However, they have big residual drifts subjected to great earthquakes. In this paper, buckling - restrained braced frames with eccentric configurations connected to frames with post-tension connections is studied. The results show that this system is able to decrease the residual drift. For evaluation the proposed method, 3 and 6 story frames, for different combinations of self - centering parameters are designed. Self-centering parameters are gradient of disengage connection and ratio of self - centering. Base shear used for the models are calculated using performance-based seismic design. Performance-based seismic design is obtained based on energy-work balance using pre-selected target drift and yield mechanism. Then in Abaqus software, pushover and cyclic analysis method for different combinations of self-centering parameters on the frames is done. Pushover analysis verifies the design method. Cyclic analysis show that the residual drift is decreased by adding frames with post-tension connections to a buckling – restrained braced frame with eccentric configuration. The results show that in order to reach self - centering, the ratio of base shear of the frames with post-tension connections to the total base shear is required to be more than 50%.