JOURNAL OF STRUCTURAL AND CONSTRUCTION ENGINEERING
Year:2020 | Volume:6 | Issue:4 (29)|Papers Count:15

The past severe earthquakes around the world have shown that the beam to column connection is prone to failure. Therefore, significant provisions should be considered in the design of the connection. RCS momentresisting frame systems, consisting of Reinforced Concrete (RC) columns and Steel (S) beams, take advantage of the inherent stiffness and damping, as well as low-cost of concrete, the lightweight and construction efficiency of structural steel. Since two types of materials including steel and concrete are used in a RCS system, the detail of the connection plays a significant role on the overall performance of the system. In general, there are two types of RCS connections, column through type & beam through type. The main objective of this study is to investigate the effect of parallel and diagonal stiffeners on stress-strain propagation and concrete damage in column through type RCS connections. For this purpose, RCS connections with different joint details were modeled and analyzed in ABAQUS. Finite element analyses results showed that parallel stiffeners are more capable to provide confinement in comparison to the diagonal types. However, the performance of diagonal stiffeners in terms of strength and plastic hinge formation in the joint is better than parallel stiffeners. Increase of stiffener thickness causes to improve the performance of joint core and decreases its damage level. Furthermore, increasing in cover-plate thickness improves the performance of connections in terms of of strength and plastic hinge formation.

The purpose of this study is to investigate the behavior of continuous pipeline passing through two different layers of soil with different levels of resistance under displacement time-histories of the same earthquake. The values of stress and displacement are studied for different angles between pipe and interface of soil layers. To this end, pipe and the surrounding soil are modeled using shell and solid elements, respectively, in ABAQUS Software. Stress and displacement values are calculated along the intersection and for different values of intersection angle between soil layer and pipeline and different values of Young's modulus of the soils. These evaluations indicate that, the maximum stress along the pipeline occurs at the node in certain distance before the interface in the harder soil. Moreover, with increasing the angle, the resulting displacement increases, and the value of stress increases with angles up to 30˚ , beyond which angle it decreases. Also, a decrease in the ratio of Young's modulus increases the stress both before and after the interface. Significant changes are observed in displacement and stress along the pipeline with changing the pipe thickness, so that a decrease in the pipe thickness in the studied model from 20 to 15 mm (33% reduction) results in some 15% increase in the stress. Soft soil (two-layered soft soil) increases pipe displacement and response capacity in every condition.

Restoration of the steel structures by heat straightening process has a long history, but national studies in this field have not been reported yet. The physical nature of this process is thermo mechanical, and the most of conducted studies have included the empirical investigation of angular distortions and mechanical deformations of structures and the restoration with the help of accelerators such as hydraulic jacks. In the present study, the numerical heat transfer and structural analysis of the process were carried out on an I-shaped cross section steel beam without application of external load. Oxy acetylene torch was considered as the heat source, and the Gaussian normal distribution model was used to model the input heat flux from flame to the beam surface. Three dimensional transient heat transfer and thermo elastic plastic deformations were analysed by finite element method in ANSYSTM software, and the results of thermo elastic plastic deformations were evaluated based on the amount of plastic rotation in the beam. Also role of the effective parameters such as supporting conditions, torch speed in different heating zones, heating dimensions and the path of torch movement on upper wing of the beam were studied. The results of numerical simulations carried out were in reasonable agreement with existing empirical data and showed the contribution of thermal deformation in the final deformations of the beam due to the non-application of external force.

Considering the importance of the deflection amplification factor, Cd, in the structural design and the lack of consideration of the structure-soilstructure interaction effects on structural response, this paper has investigated the effects of the most important parameters affecting this factor in the structure-soil-structure systems. Key parameters are period of main (T1) and adjacent (T2) structures, distance between the structures (d) and type of soil. The purpose of this study is to correct the Cd coefficient in steel moment frames under the influence of structural-soil-structure interaction effect. For this aim, 6 structures of 2 to 15 story based on two types of clay soil in a three distances of zero, 10 and 25 meters using direct method is modelled and analyzed with nonlinear time history method. According to the results, most of the story drifts is concentrated at the first story due to soft base. The minimum ratio of first story drift with respect to the fix-base, is 1. 1 and the maximum is 3. 61. Increasing T1 and T2, the value of this ratio is increased. For the main structures with T1 in the range of 0. 7 to 1. 5 times the soil period, the structural drift is intensified. Finally, using the results of this study and regression analysis, a correlation coefficient for the Cd is presented based on the spectral response of the structural drift. Based on the obtained relationship, story drifts, especially at first story, should be increased for the design of the structures.

The presence of concrete slab in steel framing frame structures always makes retrofitting problems difficult. On the other hand, most of damages reported from Northridge earthquake (1994) has focused on the bottom flange of the beam. Therefore, in order to reduce the cost of retrofit, this operation can be done only at the bottom flange of the beam. In other words, by defining and applying a ductile fuse in the beam, by weakening the bottom flange of the bottom, it is possible to reduce the concentration of tension in the near-weld regions in connection and fracture failure in these areas. In this paper, a steel frame connection was analyzed numerically and after ensuring the modeling accuracy, it was under rehabilitation. Retrofit techniques have been made on the bottom flange of the beam. Two general "cut-off" and "heat" methods were considered to weaken the beam. In this research, incomplete penetration of the weld was placed in the bottom flange connection to the column as a deficiency in the joint. The modeling results showed that the connection with incomplete weld, underwent 4/4%, suffering a deflection in the weld area in the flange. In the specimens which were retrofitted asymmetrically, the possibility of brittle fracture in the weld region was decreased due to relocation of the plastic hinge in the weakened area of the beam. In the method of reducing the bottom flange, lateral buckling led to sudden decrease in flexural strength at 2. 5 % inter story drift. In the heat-induction method accompanied with steel annealing, the out of buckling occurred at 5% drift. The retrofitted connection with this method showed a post elastic displacements of 3% and could be expected to be suitable for special moment frames.

In this research, we investigate the possibility and possibility of replacing Ardabil type 2 Pozzuoli cement instead of Sufian type 2 cements from the standpoint of compressive strength in dam construction projects. Experiment on samples shows the possibility of just using Ardebil's pozzolan cement is not possible in concrete projects. In order to achieve this, we need to think about the measures. In order to achieve this, we need to think about the measures. Among the mechanical properties of the compressive strength of the concrete made with cement type 2 pesulani of Ardebil, there is a severe drop. The most important priorities for using additives are the availability of materials along with economic discussions. For this purpose, four cement substitute additives were used in this study: stone powder, sand, microsilica, and fly ash. The results of the experiments show that the fly ash in the long run increases the compressive strength of the concrete and in the first days reduces the compressive strength. Microsilica for 8% and 11% increases resistance initially, but for replacement percentage 5, it reduces the compressive strength of the concrete. The fine sand also causes a slight reduction in compressive strength; ultimately, the replacement of stones in the long run will increase the compressive strength of the concrete

The private sector has an important role on the development of cities, and governments are encouraging this sector to implement civilian projects. The BOT approach is one of the ways that increases private sector participation in government infrastructure development. Today, paying attention to the financing of urban projects and new financing approaches, including the BOT approach, is necessity in most of the major cities, especially in Tehran. But it is necessary to use the BOT method to address and understand all the dimensions and issues behind the implementation of this method. In many cases, failure to complete the projects in due time is due to the lack of proper management of the project, which results from a lack of understanding of the risks involved in these projects. Therefore, assessment and prioritization of risks in BOT projects, especially when the number of risk factors increases, is considered as an important part of the complex risk management process. In this paper, the method of structural equations and integrated model of fuzzy AHP and fuzzy TOPSIS are used to evaluate and prioritize the risks in Tehran Municipality's development projects that are implemented in the form of BOT contract method. Structural equations are used to measure the validity of identified risks. The fuzzy AHP method is used to determine the weight of the risk assessment criteria and the fuzzy TOPSIS method is utilized to evaluate and prioritize the risks of BOT projects. The results indicate that the risk of commodity price fluctuations, the risk of rising inflation, the risk of exchange rate fluctuations, and the risk of nonapplication of techniques and project management knowledge are the most important risks in BOT projects.

Different types of the lateral-load resisting systems to deal with lateral forces entering the building are used in buildings such as the concentrically braced frames (CBFs). The application of the concentrically braced frames is welcomed due to its lateral stiffness and other benefits. In accordance with the regulations, the brace axis should meet at the intersection point of the column centroid and the beam centroid axes. In many cases, the eccentric gusset plates at the connection of the brace and the beam are observed in the concentrically braced frames. Therefore, in this paper, the effect of the eccentricities at the connection of braces on the behavior of the CBFs including the in-plane and out-plane eccentricities of the gusset plate by finite element method is investigated in order to determine the optimal performance of the structure when the if the failure of the regulations observes. Hence, 11 models are used to determine the margin of confidence for nonobservance of the rules of the regulations in the frames with Eccentric Gusset Plates using the Abacus software. The results show that the effect of the in-plane eccentricities is far more unfavorable than the out-plane eccentricities and there is little margin of confidence for non-observance of the rules of the regulations.

Todays due to expansion of population and industry, the collection and storage of liquids has been paid attention more and more. Saving oil and chemical liquids require great care to maintain it. One of the most important and commonly structures for storing liquids is steel cylindrical above ground tanks. On the other hand, due to damage of tanks in past earthquakes, they persuade scientists to better understand the seismic behavior. As a consequence, this research has been studied examines the phenomenon of buckling under Bam, Golbaf, Firuzabad, Bojnurd, Manjil, Tabas and Sarein eartquakes with regard to the fluid and structure interaction. Tanks were selected with ratio of 0. 5, 1. 0, 1. 5 and 2. 0 with fixed and variable thickness in full mode. These Cases were analyzed with non-linear time history analysis by ABAQUS Software. Finally, Compare the results with American petroleum institute regulation (API), Iranian seismic design code for oil industries and forces show, both height and diameter increase to growth the risk of Elastoplastic buckling and also by increasing the height to diameter ratio reduces the risk of Elastoplastic Buckling. The amount of this damage has declined by increasing shell thickness and in the same vein designing these structure by define standards is not safe method.

Use piles with variable section can improve the bearing capacity of the piles, due to the larger cross-section upper part of piles. The function and easy implementation of semi-tapered piles that only the top half is in the form of a cone are better than the previous one. The purpose of this paper is determine the bearing capacity increase tapered and semi-tapered tapered piles and comparing with the cylindrical piles in the same volume condition. The modeling of this research paper is based on finite element method (Plaxis 2D software) of numerical analysis for changing the angle and tapered height of mentioned piles, axial bearing capacity of these piles in sand is estimated. Linear elastic behavior is assumed for pile and the hardening soil criterion is considered for soil. The analysis was performed for piles with different lengths. Load carrying capacity and settlement at the given particular loading were examined. Influences of stresses are also discussed with respect to change in taper angle. The results show that settlement decreases with increase in taper angle. Loaddisplacement curve shows that the tapered pile can take more loads compared to cylindrical pile when the taper angle load-settlement curve of piles compare showed that tapered piles bearing capacity and especially semi-tapered piles greater than cylindrical piles. It was also observed that the increase in capacity, more piles occur with short length.

Choosing construction methods and how resources are allocated are important in the project control. The multi-mode resource constrained project scheduling problem (MRCPSP) is a significant subject in project management. The development of the above model for construction projects is an important issue because of uncertainty. Fuzzy logic has been used to display the uncertainty in the duration of activities and the delay between them. This paper examines this problem and schedules project with providing an intelligent algorithm combining fuzzy sets and genetic algorithms (GAs). The Fuzzy MRCPSP problem can be considered as the scheduling of a set of activities with the aim of finding an activity operation mode and the activity operation priority; so that the resource constraints (renewable resources and non-renewable resources) as well as the precedence constraints are met simultaneously and the time for completion of the project is minimal. In the first step, the above problem is modeled mathematically, and then the model is coded using GA-based algorithm in Matlab software and finally the model is solved. The results of the implementation of this algorithm on the standard instances of the PSPLIB site, in comparison with the GAMS software, indicate the successful performance of the combined GA algorithm with fuzzy sets. The approach used in this research can be easily used by project managers. This prevents human errors caused by people who are responsible for controlling the project at resource leveling phase and is a way to the optimized project scheduling.

Considering using self-compacting concrete – because of no need to vibration and flow ability of this kind of concrete under its weight – under challenging situation for consolidation, it would be a very suitable option for using as repair layer in repairing and retrofitting of concrete structures. In this issue, quality of bonding between the repair layer and concrete substrate is one of the most important factors in durability and suitable performance of repairing works. On this base, in this research, some effective factors on bonding between two layers i. e. volume paste, water to cementitious materials and fiber dosages and their effects on rheological properties of repair self-compacting concrete firstly, on mechanical properties of it including compressive strength, tensile strength, modulus of elasticity and shrinkage secondly and on bonding quality between the self-compacting repair layer and concrete substrate finally have been assessed. For assessment of bonding between two concrete layers, three methods including pull-off, push-out and splitting prism have been used. The results show that because of highly effects of shrinkage on bonding, the factors that reduce shrinkage, i. e. volume paste, water to cementitious materials and fiber dosages will increase the bonding of the two concrete layers. In this issue, the exact effect of each of these parameters on bonding between the two concrete layers and the optimum value of them have been assessed. Also, the correlation between all three methods of assessment of bonding between self-compacting concrete as a repair layer and concrete substrate and preciseness of the methods have been found.

Isolation of buildings from earth vibrations is a new method that has been considered in the last few decades and is the only way to reduce simultaneously the inter-story displacement and acceleration of stories. In this method, increasing the period of rotation and damping of the structure at the separated level, the energy from the earthquake force to the structure decreases. Furthermore, recent earthquakes, including the Bam earthquake, have horizontal and vertical components, which resulted in the destruction of more structures, depending on the time of the start of the vertical or horizontal components or their combination. This issue highlights the importance of examining the vertical component of the earthquake in addition to the horizontal component. According to the mentioned cases, the main objective of this research is to investigate the behavior of asymmetric sliding structures with different separators under the horizontal component and the combination of horizontal and vertical components of the earthquake, taking into account the effects of soil and structure interaction. For this purpose, structures of 1, 5, and 10 stories irregular building(irregular amount of 40%) with seismic separators RFBI, LRB and P-F on soil type IV are considered. In order to obtain the results of the research, the numerical method of finite element method has been used with modelling of materials in nonlinear area and performing explicit dynamic analysis. The results of the study showed that with increasing number of stories, the seismic separation function of R-FBI is better than other LRB and P-F separators. Also, the results of this study show that the simultaneous effect of horizontal and vertical components on structures 1 and 10 is remarkable.

The use of fibers or recycled materials in concrete will results in improving the strength, plasticity and durability of concrete. Therefore, one of the suggestions to improve the mechanical properties of concrete is the use of fibers as well as alternative materials such as recycled steel springs. In this paper, we investigate the performance of concretes containing steel and polypropylene fibers and recycled metal springs using 0. 2, 0. 4, 0. 6 and 0. 8 percent volumetric percentages. For this purpose, a number of cylindrical and prismatic samples at the age of 28 days were tested for compressive, tensile and flexural strength tests. It should be noted that the steel fibers used have a length and diameter of 50 and 0. 8 mm, polypropylene fiber has 12 mm length, as well as a metal spring with a wire diameter of 0. 8 mm, a length of 25 mm and a hole diameter of 8 mm. The results indicate that the use of recycled metal springs in concrete has a better performance than other fibers in the control of cracks caused by tension. Also, in low percentages, the use of springs has improved the mechanical properties of concrete. Also, polypropylene fibers and metal springs increase the flexural strength of concrete up to 2 times, which for the use of steel fibers this amounts to 13 times. So, with better recognition and changes in the type and characteristics of the spring, better resistance can be achieved.