نشریه مهندسی عمران مدرس
سال بیست و یکم شماره 5 (آذر و دی 1400)

Improvement of the river route is one of the goals that considered in using a spur dike to control the flood, prevent bed erosion, stabilize and protect the walls, and set river width. Spur dikes are structures that with adjustment hydraulic conditions and make smooth flow cause to reduce flow erosion power and the ability to carry sediments. And also makes good situations for sedimentation and sides consolidation. Spur dikes are permeable and impermeable. Impermeable spur dikes have different shapes which according to erosion amount and condition can be used. Common spur dikes have simple, L and T-shaped geometric shapes. This research has been conducted to optimize the various combinations of spur dikes to reduce scouring. All of the scour and flow measurements were collected in a flume with 14 m long, 1.5 m wide, and 0.6 m deep located at the Soil Conservation and Watershed Management Research Institute. Impermeable spur dike with different geometric shapes were tested in a series with 3 spur dikes for different compositions in U/Ucr≈1 conditions. Due to threshold flow condition by using Shields parameters in all tests, the calculated discharge at the mentioned conditions is 28.5 Lit/s. So according to discharge and flume dimensions in all the experiments, thereby concentrating on clear-water scour condition, flow depth (y) was taken as 0.06 m. For determine the equilibrium scour depth for each geometric, control test with 30 hours have been done. The first spur dike in all combinations was T-shaped. The results show that for first spur dike in combinations, in 10% of scouring equilibrium time, about 90% of scouring occurred. So with these results, 300 min (5 hours) test time was selected for do all main tests to achieve more than 85% of scouring. Also, in the results of different tests it was observed that maximum scour depth happens around first spur dike. So geometry of first spur dike is very important in reduce average scour depth in combinations. Mean scour depth in these combinations for first, second and third position respectively are about 2.44y, 1.21y and 0.75y which in that for second and third positions with 50% and 69% have fewer scour depth in comparison with first position. Combination (T L T) is the best composition for the lowest average scour depth in all three positions, which 2 times the flow depth have erosion. The best performance in the whole range of spur dikes due to the amount of erosion volume is for the composition (T I I), that’s about 70% of the massive erosion in other compositions. Mean scour depth in all positions for these 2 series are 1.39y and 1.63y. Average scour depth in (T T T) series is 1.41y which more than (T L T) combination. The reason for this results can be effect of middle L-shaped spur dike on T-shaped spur dike scour depth in third position. This effect cause to reduce scouring in about 28%. (T I I), (T L T) and (T T T) series spur dikes are the best combinations which each one has special performance, therefore, for design, the best composition should be choice for target of exploitation and optimal economic conditions.

Considering the goals of sustainable development and increasing environmental pollution, attention to the environmental effects of each product has increased more than ever. In the meantime, the building industry plays a major role in environmental pollution, as a major part of the urban waste comes from the industry. The most important factor affecting the amount and nature of environmental impacts is the type of building system. Life cycle analysis is a method used to assess environmental impacts along with all stages of the life of a product from cradle to grave. It is a method for designing sustainable structures, identifying environmental impacts of materials throughout the life cycle, providing financial and environmental details for choosing between different options by the relevant user, and the ability to select different indicators for assessing the life cycle of the application. In this research, a framework for evaluating the environmental life cycle of buildings is described. Due to the fact that in most buildings in Iran there are steel or concrete frames, the environmental impacts of two types of steel and concrete buildings in Isfahan have been estimated and compared. The analysis of the life-cycle analysis is carried out in four stages of the production and processing of materials, materials, construction, operation and end-of-life. Environmental impacts are categorized in the form of potential warming groups, acidification potential, water nutrition, reduction of fossil fuel resources, air pollutants, human health, photochemical smoke formation potential, ozone depletion and toxic emissions. . The analysis of effects is performed during the steps of classification, determination of the coefficient of influence and normalization and weighing. This analysis is performed in steps of classification, determination of the coefficient of influence and normalization and weighting. In the stage of classification of resources or contaminants that are similar in terms of environmental effects, Commitment and the determination of a single index for the effects defined in the groups through the process of determining the coefficient of influence of each work belonging to a group, normalization (converted to a comparable and comparable scale), and ultimately weighing the effect based on the importance of the type of effect is obtained. Weighing in these methods is performed as a triangle of weighting Showed that the highest pollution was related to the production of materials and in particular the manufacture of steel. The percentage of the raw materials used was generally more than 95%. Steel structures have been contaminated with most of the environmental impacts, including global warming, suspended particles, acidification, nutrition, and smog emissions. The impact of concrete building on greenhouse gas and particulate emissions is much higher and contributes significantly to the production of steel in the production of cancerous and toxic substances. It also showed that due to the increased importance of the release of carcinogens and toxic substances in The whole effect is more and more severe on human health and environmental degradation, and the greater role of steel in the release of these contaminations, the environmental contamination of the steel structure for the release of toxic carcinogens and toxic chemicals such as chromium multiplicity, is much greater than the concrete structure.

Time-dependent behavior in soils causes mechanical, chemical, and geo-mechanical changes. This behavior in soils considers as a major challenge in geotechnical engineering, and yet need more attentions. The impact of time on geo-materials and their behavior such as rock and soils are undeniable. Based on researches previously performed on this issue, the importance of time-dependent behavior emerged. Creep (strain deformation under constant stress level), stress relaxation (stress deformation under constant strain level), and loading pace are among time-dependent special features, which are seen in experimental models. Creep divided in three categories: primary creep, in which rate of deformation reduced with time. This creep starts immediately after loading procedure. Secondary creep in which rate of deformation is constant. Finally, tertiary creep in which rate of deformation increased and at last material failed. In this research, the effect of time on the stability of the saturated sand has been investigated by building a small-scale experimental model and using finite element numerical method. Preparation of the sand slope was using sand downfall and the saturation process of the experimental models are carried out artificially with a flow rate of 1 liter per minute. Due to the friction angle of the sand, two physical models were created with slope angle of 35 degrees and 37 degrees. The results of physical modeling showed that drainage in sandy slopes, despite stability in non-drainage conditions, gradually increases the deformation in the slope so that over time it will cause failure in the slope. The results of physical modeling showed that in the first model, the maximum horizontal and vertical displacements are 10.5 and 9 cm, respectively. For the second model, these values ​​are 10.5 and 7 cm, in order. At the end of this research, statistical analyzes have been used to provide relationships for predicting vertical settlement in saturated sand slopes. Using numerical models with dimension analysis rules (make the dimensions 100 times in numerical models), in first model in order to reach 8.81 meter displacements, 3780 minutes of raining needed. While in second model, for reaching 7.20 meter displacement, 2280 minutes needed. Results indicate that by increasing cohesion, vertical displacement decrease. As friction angle increase, vertical displacement also decreases. While by increasing slope angle, vertical displacement increase. At the end of this study, statistical analysis has been used to provide relationships to predict the amount of vertical displacement in the slope crown, which is the maximum amount of displacement in the slope.

Owing to their excellent stiffness, reinforced concrete shear walls, as lateral load-bearing elements, considerably reduce the structurechr(chr('39')39chr('39'))s seismic demand. Structural walls are designer-favorite components for their excellent stiffness and rigidity under lateral loading. Unlike steel chevron braces that buckle after a few loading cycles, shear walls retain stiffness and promote damping within the system by allowing cracks in the web plate. Meanwhile, openings placed in the wall for architectural reasons or to give access between different parts or to run facilities can considerably affect the behavior of these structural elements by forming new elements in the wall, besides reducing the wall stiffness. The seismic behavior of each of these elements can affect the wall system and its behavior. These less investigated structural elements include base walls, the seismic regulations of which were first outlined in ACI318-14. Unique seismic regulations apply to these structural elements based on their aspect ratio. Accordingly, certain seismic design considerations are required for these elements. The present study investigates the cyclic behavior of squat walls with eccentric non-predesigned openings at the top, under cyclic loading. Given the complex behavior of squat walls in stress transfer, a 155-cm-tall, 160-cm-wide, and 13-cm-thick experimental model integrating a 50 cm by 100 cm opening was used. The non-predesigned opening in the shear wall results in inconsistencies with the development length and rebar bending and cutting regulations aro9und openings, all of which are important in designing reinforced concrete elements. The opening introduces new elements, including the base wall and the coupling beam, which exhibit different behavior and failure mechanism under cyclic lateral loading. The present study discusses experimental parameters, such as the hysteresis loop, equivalent damping, and the dissipated energy curve of the wall. Further, cracking patterns in different parts of the wall are studied. Experimental results showed that a concrete-wall opening that stretches across 21.85% of the wall area changes the wall cracking pattern by introducing new elements and the shear wall does not exhibit a specific failure mode upon collapse. Asymmetry of the opening location also affects the maximum load-bearing capacity in compression and tension, as the peak load-bearing capacity was estimated at 189.645 kN under tension and 195.5 kN under compression. Violating bending and development length requirements around opening edges resulted in rebar slip and concrete separation after cracking.

Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level. Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level. Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in PERFORM-3D software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level.

Awareness of the sensitivity of the input data of simulation models is important for their development and application, and leads to better understanding and better estimation of values and reduces uncertainties. In this study SWMM software has been calibrated with real meteorological and hydrometric data for the part of the northern catchments of Tehran, simulation parameters have been obtained. For this purpose, five rainfall events and runoff data related to these rainfalls, recorded at the outlet of Zargandeh catchment were used. This model is calibrated with three events and verified with two other events. By comparing the results of observational and computational, the output flows of Zargandeh basin, the root mean square error (RMSE) are obtained for the first to fifth events were 0.05, 0.22, 0.39, 0.37 and 0.16, and the Nash-Sutcliffe coefficient (NS) are obtained 0.91, 0.94, 0.93, 0.9 and 0.94, respectively, that shows the appropriate adaptation of the model output results with the real observational values. The aim of this study was to investigate the effect of sensitivity of seven input parameters of SWMM model for the north catchments of Tehran city. Based on comparing the Sensitivity Index (I), Impervious area percentage (Imp%), N-Manning of impermeable areas (Nimp), Width equivalent (W) and slope (S0) of sub-basins had the greatest impact on the output results and  the depth of depression storage (Dp) and N-manning of permeable areas (Np) were diagnosed as the least effective input parameters. The effect of increasing three parameters, percentage of impermeable lands (Imp%), equivalent width (W) and slope (S0) of subbasins on the output results of the model is incremental and the reaction of the output results to increasing other parameters such as Manning roughness coefficient (Nimp) and storage depth of impermeable (Dp) areas is decreasing. Also, the sensitivity index (I) of peak flood flow, runoff volume and runoff depth for the percentage of impermeable lands (Imp%) and the width equivalent (W) of sub-basins are higher in mountainous areas than urban areas of this study area. The reason can be considered as a higher percentage of mountainous areas (84%) than urban areas (16%) in this study. On the other hand , the results showed that 10% increasing of the impermeable areas (Imp%), 5% peak runoff flow rate, 7.79% runoff volume and 5% runoff depth increase Also, 10% decreasing of the roughness coefficient of impermeable areas (Nimp), 4% of maximum runoff flow, 1.7% of runoff volume and 3% of runoff depth at the outlet point of the catchment area increased. However, land use changing and urbanization, which results of increasing the impermeability of the urban surfaces and reducing the roughness coefficient of these areas, can increase the peak flow of floods, the volume of runoff and the overflow of runoff from urban canals and it causes of the property and human losses risk. The results of this study can be useful for future modeling in the northern part of Tehran city and other areas that are similar to the catchment in terms of the hydraulic and physiological characteristics..

Offshore wind turbines (OWTs) are one of the approaches that make it easy to use renewable energy sources such as wind to generate energy. In recent years, the use of offshore wind farms has become attractive due to the high quality of offshore wind energy, no need of land extraction, less destructive effects on the environment. Foundation is one of the most important parts of these systems due to the presence of this structure in specific climatic conditions and location, so that include about 34 percent of constructing and execution cost of a wind turbine. These structures foundation is selected based on water depth, distance from the coast and etc. that the gravity based foundation is one of it. This foundation with its high weight in general stability of the structure against slipping and overturning is a good one for these turbines in shallow water and easily transfers the load from the structure to the soil below and around it. Investigation of foundations in marine and seismic zones under earthquake loading is one of the important design criteria. In the marine environment, soils can soften by increasing the pore water pressure under seismic loading. In the worst case, the earthquake causes liquefaction in the soil and leads to a sudden decrease in bearing capacity and lateral stability of the foundation, which can cause settlement or rotation in the foundation and structure. So the occurrence of liquefaction in relatively loose sand caused by rapid earthquake loading should be evaluated. In the present research, a 3D numerical study of gravity based foundation of OWTs with its structure are performed using Opensees software to investigate the behavior of saturated sandy soils at near and far from Foundation under seismic loading. In order to consider the soil saturation conditions, the mentioned software has been used, which has a good ability in simulating the process of changes in excess pore water pressure due to the existence of numerous and suitable soil behavioral models, including PDMY behavioral models and solid-fluid correlated elements. For this purpose, modeling was performed based on laboratory research of Yu et al. (2015) and Validation be done in good agreement and adaption with the laboratory model on soil response in acceleration and ru (ratio of additional pore water pressure Δu to the effective stress σ’), on the response of gravity foundation in settlement and rotation, and horizontal displacement of the structure. Parametric studies are conducted to investigate dimensions and embedded depth of foundation on soil response at near and far from the foundation, foundation and structures performance (settlement and tilt of foundation and structure horizontal displacement). The results show that increasing the foundation dimensions decreases the settlement and tilt of foundation, but the maximum amount of ru in the soil increases and the acceleration does not change. By increasing the embedded depth of foundation, in the maximum value of ru in the center position of the model and near to the foundation is increased. Also caused a decrease in settlement and tilt.

History of past earthquakes and the destruction caused by them show that irregular structures have the vulnerability potential more than other structures. Reinforced concrete (RC) walls are commonly used as the primary lateral-force-resisting system for tall buildings, although for buildings over 49 m (160 ft), IBC 2006 requires use of a dual system. Use of nonlinear response history analysis (NRHA) coupled with peer-review has become a common way to assess the expected performance of tall buildings at various hazard levels to avoid the use of a backup Special Moment Frame for tall buildings employing structural walls. Modeling of the load versus deformation behavior of reinforced concrete walls and coupling beams is essential to accurately predict important response quantities for NRHA. The design of tall buildings essentially involves a conceptual design, approximate analysis, preliminary design and optimization, to safely carry gravity and lateral loads. New developments of tall buildings of ever-growing heights have been continuously taking place worldwide. Consequently, many innovations in structural systems have merged. The design criteria are strength, serviceability, stability and human comfort. The strength is satisfied by limit stresses, while serviceability is satisfied by drift limits in the range of H/500 to H/1000. Stability is satisfied by sufficient factor of safety against buckling and P-Delta effects. The factor of safety is around 1.67 to 1.92. The human comfort aspects are satisfied by accelerations in the range of 10 to 25 milli-g, where g=acceleration due to gravity. The aim of the structural engineer is to arrive at suitable structural schemes, to satisfy these criteria, and assess their structural weights in weight/unit area in square feet or square meters. This initiates structural drawings and specifications to enable construction engineers to proceed with fabrication and erection operations. The weight of steel is often a parameter the architects and construction managers are looking for from the structural engineer. This includes the weights of floor system, girders, braces and columns. The premium for wind is optimized to yield drifts in the range of H/500, where H is the height of the tall building. In this paper, the seismic behavior of steel frames with reinforced concrete core in the duplex and common high rise building are investigated. In this research, linear analysis under 3 kind of earthquake loading (equivalent static, spectral dynamic and dynamic time history) and wind load on structures with 20, 40 and 60 stories have been accomplished and different parameters, such as structure’s base shear and effect of increasing height on seismic behavior have been discussed. Based on results, making structures duplex, causes changes in modal shapes and mass participation percentage of modes. For this reason, there is no change in linear static methods and wind load of common structures and duplex structures response but it has seen changes in structure’s response for 12 far and near earthquake records. In some earthquakes, base shear has been increased maximum 32 percent of common structure’s base shear and also there is no change in base shear in some of them. In some structures, base shear has been decreased maximum 16 percent of common structure’s base shear.

Nowadays, extraction of materials from river bed is one of the effective factors in the occurrence of scouring phenomena around bridge piers. The extent of scouring around the bridges depends on a number of factors, including the type of foundation, the Froude number, flow rates and bed granulation. In , in vitro evaluation of scouring around piers groups in two different grains was investigated. The effect of scouring and armoring of scours in scouring control was investigated in both natural and river conditions. In the present study, 44 experiments with identical laboratory conditions were tested in a rectangular channel with of 13 m, width of 1.2 m and depth of 0.8 m. In this study, 44 experiments were conducted in two models 1 (control or simple groups) and model 2 (modified groups), both scaling behavior. B = 0.7) and Bꞌꞌ (= 1.7 mm) were analyzed. In addition, to investigate the effect of material extraction on the scour rate of bridge pedestals, experiments were conducted for both pit-bed (pit-extraction mode) and pit-free bed (river natural state). A removable sand bed with a height of 22 cm was placed between the floorboards. Two series of pedestals were located upstream and downstream of the bed with a clear distance from the flooring. The pedestals were arranged in the same arrangement (consecutive tripods in the direction of flow and in the center of the channel width) with center to center 21 cm apart.   The results showed that the armed (rough) pier group was less than the simple pier group (flat surface), due to the excavation of river materials, it increased the scour equilibrium time. The armed pier group also controlled the impact of extraction of materials on the scour rate. By examining the upstream and downstream materials mining, it was observed that extraction of materials of upstream of pier group decreased and extraction of materials of downstream pier group increased the scour. Therefore, it can be concluded that the scouring of pier is more sensitive to the downstream pit hole and even the mining of materials from upstream of the pier should be possible. In other words, the percentage of scour depth reduction in downstream bed due to extraction of materials and percentage of scour depth in upstream bed of extraction of materials in model with armed pier group were higher and lower than model with simple pier group, respectively. The percentage of scour reduction due to armed of the pier was also studied and it was observed that at best, the maximum scour depth in the aggregate with mean diameters of 0.78 mm and 1.7 mm by armed pier group were 55 and 66 percent, respectively. It is also observed that the extraction of materials from the bed increases the equilibrium time. It should be noted that scour is balanced when the driving force is approximately equal to the resistive force (particle saturation weight). The results show that the presence of the pit leads to an increase in the scour equilibrium time. In other words, when the sediments reach the pit site, due to the decrease in water velocity and increasing depth, the flow cannot carry the larger sediments and the sediments settle in the upper wall of the pit.

It is vital to consider the spatial variations of ground motions in the design of extended structures and long bridges. In this paper, the effect of spatial variations of ground motions and local site conditions on the response of non-uniform column heights bridge is studied. To generate non-uniform accelerometers of ground motion, a simulated algorithm based on the spectrum design with unstable multivariate random process functions and a spectral density matrix is used. Accelerometers were generated with a coherence function including the effect of wave propagation and the duration of the earthquake that is consistent with the selected response spectrum. In addition, the simulation is performed in 800 time intervals with a time step of 0.025 seconds. The maximum ground acceleration is assumed 0.35 g. The response of the bridge with a length of about 242 m with 5 spans under the effect of uniform and non-uniform accelerometers was investigated by nonlinear time history analysis in OpenSees program. The local site effect was assumed by changing soil type (soil under the two piers is softer than the other piers) and apparent wave velocity under different bridge piers. The apparent velocity of the wave propagation of the soft soil assumed 1000 m/s and for the hard soil 2000 m/s. To verify the acceleration of the generated accelerograms, the generated spectrum is compared with the Eurocode design spectrum, and to validate the analysis performed on the bridge, the ratio of M/  calculated and compared with ratio that calculated by Shinozaka and Deodatis. In this paper variations of axial force, shear force and bending moments in bridge piers in different positions were studied as comparison criteria. The results showed that the simultaneity of spatial variations of ground motions and changes in the soil conditions causes a significant increase in the bridge response. Comparison of the results in the two input cases of uniform and non-uniform spatial variations of ground motions shows that the properties of spatial variations of earthquake motions can affect the response of the bridge. The results are compared based on the ratio of the maximum stress created at the base in the non-uniform excitation state to the maximum created in the uniform excitation state or the ratio of the maximum stress created at the base in the variable soil to the same soil. Based on the presented results, it was observed that the maximum bending moments in variable soil conditions can be increased to about 2.5 times to the maximum created in the same soil condition in the piers and also the maximum axial force created in the two shorter piers in the non-uniform excitation state is up to 2 times larger than in the uniform excitation state, and if the effect of different soils is applied to the two middle piers, the axial force in the middle two piers can be increased up to 3 times. Based on the obtained results, it is observed that the maximum shear force created in the direction of the transverse axis in the two middle piers occurred in a situation where non-uniform excitation coincides with the change of soil conditions under the piers and the bending moment in the direction of the transverse axis in the piers in this case has increased up to 120%.

In the present paper, the behavior of eccentric braced steel frames with thin infill plates is investigated. The main purpose is to provide a new form of eccentric bracing, which improves the seismic behavior by adding a thin steel plate under the link beam. In the proposed model, due to the increase in frame stiffness, flexural stiffness and shear of the beam in the bracing frame will not respond to the forces. Therefore, in order to provide the required stiffness and ductility of the frame, it is suggested to use a steel plate under the link beam connected to the bracing connection plates. In the proposed models, two groups of models with steel plate under the link beam (middle steel plate) have been studied. In the first and second groups, all analysis are of static type, taking into account the geometric nonlinear effects in an eccentric frame with infill plates, the height of the plate under the link beam (middle steel plate) is 460 and 742 mm, respectively. The studied parameters include the height of the middle plate, the thickness of the middle plate and the effect of the arrangement of stiffeners on the performance of the frame. For numerical analysis of the models, the finite element method using Abaqus finite element software with increasing load has been used. Extraction results in the models include force-displacement curve, stiffness decay, amount of wall out of plane displacement due to buckling, inelastic dissipation energy and stress distribution in the structure (stress contour). According to the results of numerical models, the middle steel plate is very important in providing ductility and increasing the strength of the structure. Also, with increasing the height of the middle plate, the development of the diagonal tensile field into the infill plate increases, so local buckling can be converted into general buckling in the infill plates. Among the arrangements of stiffeners, it was observed that the stiffener under the middle plate has the least effect on increasing the force-displacement response of the structure. By evaluation of models with a middle plate with a height of 460 mm and two vertical stiffeners, compared to the model with four stiffeners, the structural capacity (force-displacement) has increased by about 31%. By evaluating the models with a middle plate height of 760 mm, it can be found that the use of stiffeners with different geometric arrangements do not have a major effect on increasing the stiffness in the elastic and inelastic stages, prevent the sudden decrease in stiffness in models without stiffeners due to buckling observed at the junction of the brace to the middle plate. Also, the free edge stiffener of the middle plate has practically no effect on the sudden decrease in stiffness, but on the other hand, vertical stiffeners or a combination of horizontal and vertical stiffeners have performed well in terms of preventing a sudden decrease in structural stiffness. The thickness of the steel plate has a significant effect on increasing the strength and reducing the local buckling in the middle plate. Local buckling was observed at the junction of the middle plate to the brace, which is recommended to use stiffeners for the middle steel to reduce the effects of local buckling of the plate and to prevent a sudden decrease in strength and stiffness. In steel plates with shear behavior that do not allow the complete formation of diagonal tensile fields, stiffeners prevent a sudden decrease in strength but do not have a significant effect on increasing the overall stiffness of the structure.

Fire is one of the risks that the study of its effects on different structures is essential. Fire can lead to extensive social and economic damage. Furthermore, knowing the extent of damage to concrete under heat can also help designers in the strengthening of structures. Connections are one of the most sensitive areas in all structural frames, steel and concrete, affected by large forces during earthquakes and their performance has a very important effect on the structurechr(chr('39')39chr('39'))s response. For this purpose, it is important to study the behavior of different types of beam-column joints in different environmental conditions. However, experimental and numerical data on the behavior of RC beam-column joints under high temperature are not available. In addition, due to the special feature of beam-column joints, ie passing part of the longitudinal reinforcements of the beam outside the connection spring, in this study, the behavior of beam-column reinforced concrete joints under the influence of thermal stresses has been investigated. In this research, 9 numerical models of wide beam-column joints under post-earthquake fire were investigated. After validation of modeled specimens, parametric study was conducted. Parameters such as wide beam height, beam reinforcement area, concrete grade and percentage of passing bars through the column core were studied. Results showed that with increasing the height of the beam, the fire resistance of the structure increases. Also, with increasing rebar area and concrete strength, the structurechr(chr('39')39chr('39'))s fire resistance increases. In addition, by reducing the rebar passing through the column core, the fire resistance of the structure is reduced. There is one thing in common in all these matters; all joints begin to form plastic joints at a temperature of about 450°C, and this temperature in the joints is formed about 200 minutes after the start of the fire.

The structure must be able to maintain its stability and resistance in the event of a fire to protect human life. From time immemorial, concrete has been known to have fire-retardant properties. Thatchr(chr('39')39chr('39'))s why the biggest concern with concrete structures at the time of the fire was the reinforcement and their non-flow. But with the development of concrete technology, the focus has also shifted to improving the mechanical properties of concrete to increase its fire resistance. The use of pozzolans and additives in concrete to achieve high-strength and durable concrete has been in the concrete industry for several years. In this study, the role of seashell and lumashell powder and their effects on the mechanical properties of concrete and achieving the optimal percentage of using shellfish powder to achieve high fire resistance and durability have been studied. For this purpose, laboratory tests involving slump evaluation, water absorption percent, and compressive strength under high temperature were conducted on samples in which the replacement ratios of Portland cement with the same weight of shell powder were 2.5, 5, 10, 15 and 20% weight percent. Experimental results showed that seashell and lumashell powder increase the hydration rate and consequently caused an increase in the heat of hydration which resulted in a faster loss of water in the concrete. Furthermore, Seashell and Lumashell powder absorbed more water than cement due to their finer particles. All these ultimately resulted in a reduction in concrete slump such that regardless to the shell powder type, adding 2.5, 5 and 15% of shell powder, in average led to 13.5, 27.5 and 52% reduction in concrete slump respectively and it became approximately constant when the used shell powder was in excess of 15%. In addition, results showed that the presence of seashell and lumashell powder decrease water absorption in samples and made them more impenetrable. It happened because by filling the void in the cement paste with fine powder particles, the permeable cavities have been reduced and the connection paths of the cavities have been somewhat blocked. Replacement of cement with 2.5%, 5% and 10% of Seashell and Lumashell powder led to (27%, 44%, 73%) and (7%, 59%, 73%) reduction in concrete water absorption values respectively and it became approximately constant when the used shell powder was in excess of 10%. The results of this study also showed that the replacement of cement with Seashell and Lumashell powder slightly increases the thermal resistance of concrete and the amount of replacement of 5% by weight of cement with shell powder is reported as the optimal percentage. Adding more than 5% shell powder as a substitute for cement, regardless of its type, is harmful and significantly reduces the thermal resistance of concrete. Also, the results of laboratory tests showed that when concrete is exposed to high temperatures, properties such as load-bearing capacity and durability are reduced, leading to cracking, loss of compressive strength and concrete divot. Finally, it can be concluded that the optimal percentage of using seashell and lumashell powder instead of Portland cement can lead to a suitable concrete in terms of respect for the environment.

The safety of bridges as the vital arteries of cities is of great importance. There are several factors that raise concerns about the safe performance of bridges, and resolving these concerns are dependent on the appropriate decision-making of urban managers throughout the service life of bridge. These factors can be divided into two major types. The first type are factors affecting the safety of a part or whole structure of bridge and producing concerns about the bridge collapse. For easing the danger of collapse, totally or partially, a proper decision should be made to improve the behavior of a specific part of bridge at a certain time during its service life. The second type are factors influencing the safety of one or more bridge elements and increasing the life cycle costs of bridge. To prevent the growth of bridge costs due to deterioration, an appropriate plan for repair and maintenance should be implemented in order to enhance the condition of one or several elements.  In order to make the right decision, it is necessary to obtain accurate information on the condition of bridges. One of the best ways to get this information is to use bridge health monitoring. Health monitoring is the process of information acquisition from structure by installing sensors on its components and analyzing the data obtained from implemented sensors. By bridge structural health monitoring and interpreting the gathered data, the access to accurate and timely information, which is consistent with the reality of the bridge structure, is provided. Having the correct information about the bridge, the managers can decide at a lower level of risk. However, choosing specific monitoring strategy among different health monitoring systems for a bridge is a challenge that should be solved. A Quantitative index is needed to find the best technically and economically monitoring system.  The value of information (VoI) analysis is used for determining the effectiveness of monitoring information in decision-making. VoI is a method which quantifies the price of information and specifies the cost-effectiveness of decisions made on the basis of monitoring. This analysis also makes it possible to choose the most economical monitoring strategy among several alternatives. In the VoI calculation, all the uncertainties involved in the performance of a Health monitoring and probabilities of any anticipated event are considered. Thus, the decision making based on VoI is risk-based and reliable especially for important structures like bridges. In this paper, after investigating the worries and solutions for eliminating worries about the bridges in detail and introducing the applications of structural health monitoring (SHM) systems for bridges, the equations governing the VoI analysis is presented and the procedures for determining the VoI is discussed, and as an example, the VoI analysis of a bridge is discussed. According to the results of this analysis, implementing a specific amount of strain gauges with specific accuracy can provide worthy information about the bridge safety for the manager. Moreover, by the VoI analysis, the best approach for sensing system of SHM in the bridge is determined.