نشریه مهندسی سازه و ساخت
سال هفتم شماره 4 (پیاپی 36، زمستان 1399)

In order to solve the problem of access to inside of hollow columns for tightening bolts and achieving a suitable connection both in terms of rigidity and stiffness and in terms of the proper behavior, various solutions have been suggested by researchers. One of these solutions is steel beam to hollow column connection by an angle and blind bolts. This connection can be made in different types with different number of blind bolts. Connection with flange angle and blind bolts have showed proper and semi-rigid behaviour.In this research, the effect of changing various parameters on the behavior of steel beam-hollow column connection with angle and blind bolts was investigated under monotonic loading. The nonlinear finite elements method and Abaqus software was considered and solid three-dimensional elements as continuum elements was supplied in connection models. The behavior of connection was studied by changing various parameters such as beam height, column thickness, length of angle leg and number of blind bolts. The results show that increasing height of the beam, thickness of the column and length of angle leg raises the connection’s rigidity. Also, increasing the above mentioned parameters leads a simple connection toward semi-rigid connection. Also, by studying the models, the rigidity degree of most models except a few of them, which is less than 20%, is between 20% and 90%. Considering the rigidity degree, studied models behaved as semi-rigid connections.

The main objective of this study was to assess engineering properties of self-compacting concrete (SCC) incorporating magnetic water and various percentages of natural zeolite. The fresh properties of SCC were investigated by means of slump flow, T50, V-funnel, L-box and visual stability index (VSI). At hardened state, mechanical properties and durability characteristics of concrete were evaluated by means of compressive and tensile strength tests, modulus of elasticity test and water absorption test at different ages under both wet and dry curing conditions. The results of fresh concrete indicated that magnetic water and natural zeolite in SCC can improve the rheological properties and stability of SCC where the magnetic water is able to increase the slump flow up to 3% and decrease plastic viscosity of concrete mixture up to 6% without aggregates segregation. In addition, the presence of magnetic water and natural zeolite improves mechanical properties and durability of SCC. According to this, compressive and tensile strengths and modulus of elasticity of SCC containing magnetic water and 20% natural zeolite were increased up to 42, 12 and 33 %, respectively, at the age of 90 days. In the same concrete mixture, the value of water absorption was decreased up to 48%.

One of the useful and efficient ideas in pavement and flooring is use of permeable concrete which is called pervious concrete. Pervious concrete that has many economic and especially environmental impacts can be used for reducing surface runoff during rainfall, delaying the entry of rainwater into the sewage system due to its absorption by the ground, improving the quality of groundwater due to lack of water flow from the ground and contact with possible contamination. In this study, four different mix design were used for three types of aggregating aggregates, which contains 12 general mixing states, including samples of simple concrete and examples of microsilica fume additives. At the end, compressive strength and permeability tests have been carried out on them. The results obtained from the research show that the individual with a higher density or, in other words, a finer grain size, exhibited a compressive strength of 9 Mpa, but had a 15% lower permeability. In general, according to the results of these experiments, the factors affecting the density of pervious concrete can be expressed by the size of the aggregates, the efficiency and the amount of microsilica fume. Because of its superplasticizering, the microsilica fume increases the strength and durability of concrete but reduces porosity of concrete, but its permeability is still acceptable to simple concrete. Finally, the optimum aggregate for compressive strength and optimal permeability, is obtained in third type of aggregating in this study, In which half of the aggregates have been formed of residues on the sieve of 3.8 and the remaining half of the residues on the sieve of 4 and depending on the need for greater resistance or permeability, parameters such as water to cement ratio, sand/cement ratio and microsilica fume addition can be obtained, which has been investigated in this study.

Natural disasters have always existed as natural phenomena during the life of the planet. The occurrence of natural disasters such as earthquakes, floods, storms, etc. has often left destructive impacts on human settlements and has caused heavy casualties on its inhabitants and has imposed heavy economic and social burdens on human societies and countries of the world. . In view of the increasing population, especially in the Third World and developing countries, on the other hand, population density and settlement in old-fashioned and old-fashioned urban contexts and the emergence of problems caused by these issues, cities and cities in particular Babylon has been exposed to adverse effects and management abnormalities. Because the vacant areas have quickly become residential uses, the magnitude of the earthquake hazards has increased as a result. Therefore, the need to reduce the city's vulnerability to earthquakes has become one of the main goals of physical planning and urban planning. In this research, data and information were collected in both documents and field and analyzed in the ArcGIS software environment and after analyzing the risk and vulnerability of the region, it was examined whether the city of Babylon after the emergence of a The earthquake can have the least financial and fatal losses, and there are facilities and facilities available in the city that respond to the conditions of the crisis. Finally, some areas of Babylon were identified as having a high risk of earthquake, and solutions were presented for crisis management in these areas.

In recent years, several systems have been considered as lateral load systems in buildings. Corrugated steel shear walls are one of these systems which are widely used in buildings for seismic areas. The main advantage of steel shear walls is their ductility and high strength. By making changes in the geometry of the steel shear walls, such as corrugating them, their strength and ductility can be increased. However, sometimes due to reasons such as architectural conditions, executive issues, or wall hardness reduction, they have openings. Due to physical and geometrical nonlinear behavior, the structural behavior of the corrugated steel shear walls with opening is complex. In this paper, by using finite element method on the ABAQUS software, which its results are validated by comparing with experimental results extracted from literature, a wide study on the effect of the shape and location of the opening on the performance of the corrugated shear walls is carried on. The behavior coefficient (R) obtained by applying a non-linear Push-Over is a criterion for comparing the structural behavior of the study samples. The results showed that the presence of openings in the corners of the corrugated steel shear wall would increase the behavior coefficient up to 7.2, and In this situation, the shape of the opening does not affect the amount of the behavior coefficient. If the opening position is in the vicinity of the boundary element of the frame, a more elasticity factor will be created in the case of circular openings in the vicinity of the beams, and square openings in the vicinity of the columns.

Nonlinear time history analysis is recognized as the most appropriate tool for assessing the real behaviour of structures during seismic excitations. Validity rate of obtained results from this analysis significantly depends to the modeling, details and defined parameters. One of the main aspects of dynamic modeling is the consideration of natural viscous damping as well as value of damping ratio (ξ), which during last years evaluating the effects of these factors on nonlinear responses of moment-resisting steel frames has been limited, and Rayleigh damping model with ξ of 5% was used by researchers. Therefore, in this study attempt has been made to examine the impacts of value and modeling approach of natural damping on nonlinear responses of moment-resisting steel frames. For this purpose, a full scale 4 story steel structure which tested on shake table in 2007 has been considered as reference and modeled by OpenSees software. Natural damping has been defined with three methods; Rayleigh damping, mass-proportional damping and stiffness-proportional damping, for five different values of damping ratio (ξ=0.01, 0.02, 0.03, 0.04, 0.05). After conducting the nonlinear time history analyses, difference of obtained structural responses compared to the experimental responses has been investigated, and then errors of them have been extracted. Results indicate that reduce of damping ratio leads to the notable decrease of responses, specially, for story shear and overturning moment. The use of 5% damping ratio for nonlinear dynamic analysis of low rise moment-resisting frames is not appropriate and in most of cases leads to the underestimate and unreal results. Besides, it should be noted that the mass-proportional and Rayleigh damping models have higher accuracy in comparison with stiffness-proportional damping model, and these models show lower error.

The shortcoming of loose sandy soils in terms of shear strength besides placement of a huge number of structures on them drive the critical requirement for exploring the shallow foundations treatment, their positioning and shapes. In this regard, stabilization of loose sandy soils through fabricating cement and an appropriate additive is one of a promising solution. Hence, in this study, a series of unconfined compressive strength tests have been conducted to find out the mechanical properties of zeolite cemented sand composites. Afterwards, 1g small scale tests have been performed to measure the behavior of shallow foundations placed on the stabilized ground. The main aims of this study are enhancing the bearing capacity and conversely decreasing the settlement of foundations attributed to the chemical reactions between sand, cement and zeolite particles. The results demonstrate that placing a zeolite pad with B/3 thickness underneath the shallow foundation, which contain 3% and 7% cement content, increases their bearing capacity in a range between 11% and 23% respectively compared to those of without a zeolite pad. This is followed by respectively 44% and 67% enhancement in the bearing capacity through doubling the thickness of the zeolite pad. Considering the cement content as a comparing factor between the samples, increasing in the resistant coefficient is in a range between 9% to 23%, while it is constantly 6% for the decreasing coefficient. In summary, this stabilization approach improves the behavior of shallow footing on loose soils.

Nowadays, the use of control systems in buildings has been increased and the importance of vibration reduction of structures is considered more than ever. In addition to improve the dynamic behavior of buildings, control systems can be installed between adjacent buildings as activated, semi-active and inactivated systems. Fluid viscous dampers are one of the most important approaches for inactivated control systems in which the dynamic response of two adjacent buildings reduces according to the high resistance of the viscous fluid. The main purpose of this study is the use of control systems in two similar adjacent buildings to reduce the entire system response which will be the analytical study of the impact of viscous dampers to control system performance. In order to provide the analysis and to study the dynamic behavior improvement of different adjacent buildings connected with dampers, two models of the original sample was investigated. All examples are different from each other and response analysis and time history was provided using SAP 2000 software. According to the acquired results, the effect of fluid viscous dampers for tall buildings is less than the shorter ones. Moreover, these dampers are more efficiently working for adjacent buildings with different heights rather than buildings with the same height.

Dynamic interaction analysis of deep excavation-piled foundation in soft soils is studied. In this contribution, deep excavation is considered to be adjacent to the piled foundation. In fact, the interactive influences of a deep cavern and a piled foundation is studied. Loose sands and soft clayey layers are considered. Also, due to the significant effects of the pore water pressure on the soil strength, all sequences of excavations are accompanied with the seep analysis. In order to investigate the seismic effects of the excavation, time history analysis is performed. Therefore, the susceptibility of the loose sand layers to the soil liquefaction is studied. Due to the fact that frequency domain analysis is more acceptable that time domain analysis for transient phenomena, soil liquefaction is controlled in frequency domain analysis. Frequency domain analysis is considered using Fast Fourier Transform. In fact, the frequency domain informations of a saturated loose layers are compared in two different of stages. So, the frequency domain data for seismic ground response, before and after the excavation is shown to predict the soil liquefaction. All results demonstrate the meaningful influences of the excavation on the soil behavior and the structural piles. The results show that the structural beams, might fail due to the additional internal forces which are exerted on the piles during excavation stages.

Buried structures such as tunnels, depending on geometric shape, burial depth and various geotechnical and seismic parameters, exhibit different behavior in the event of an earthquake. Tunnels with circular cross-sections are now widely used in the field of transport. One of its most prominent uses is the urban metro that is created using tunnel drilling machines. The behavior of these structures against earthquakes at the time of operation is something that must be considered when designing. The tunnel structure is more sensitive to the ground's displacement than other seismic parameters, on the other hand, the effect of the vertical component of the earthquake on the tunnel structure is less in the far field. Therefore, vertical displacement of the tunnel is less important than horizontal displacement. In this study, variations in depth of placement, diameter and thickness of the tunnel lining and soil properties were performed and in this regard, the vibrating frequency of the soil and tunnel mass has been calculated. In the following, the maximum horizontal displacement component of the tunnel crown was calculated under eleven important and well-known earthquake record. Also, the relationship between the maximum horizontal component of the tunnel crown displacement and the frequency of soil and tunnel mass has led to the production of spectrum of the displacement. Using Plaxis and Ansys finite element softwares, a study was conducted on an urban metro tunnel with horizontal components of earthquake records similar to alluvial soils of the site. The results indicate that the envelope diagram on the horizontal displacement of the tunnel crown is changed in a nonlinear function during the investigating period. Also, the effect of changing the depth of placement and the thickness of the lining and the diameter of the tunnel on reducing the horizontal displacement of the tunnel's crown have been studied.

With the growing progress in the use of concrete, novel technologies have been introduced into the production of this building material. Self-consolidating concrete (SCC) is one of the concrete types, which has been extensively applied in building industry nowadays. SCC could be empowered in terms of durability and mechanical properties and, as a result, the service-life of SCC and efficiency of concrete structures could be increased using complementary materials such as Pozzolans and nano-materials. Considering their structures, nano-materials such as nano-silica, nano-calcium carbonate and other similar materials could be helpful in making SCC. This paper aims to investigate the effect of nano-calcium carbonate and nano-silica on the durability and mechanical characteristics of SCC. Thus, different concrete forms with the mixture designs containing 0%, 1%, 2% and 3% nano-calcium carbonate and nano-silica were developed. The samples were made in 15*15*15 cubic and cylindrical forms, depending on the experiment type, and tested at the ages of 7 and 28 days. In all the mixture designs, the rheological tests relating to fresh concrete including concrete flow, slump test, V-funnel, L-box, J-ring and U-box tests were performed. Finally, in order to examine the durability, permeability, freeze and thaw cycle, electrical resistance and pulse rate determination in concrete were employed. At the end, micro-structural properties of concrete containing nano-carbonate were tested using XRD and SEM tests. In all the samples, use of nano-calcium carbonate increased durability and resistance properties of SCC.

This paper presents the results of an axial pressure test on reinforced concrete columns made of high-strength concrete, which are encapsulated using a glass-fiber reinforced plastic pipes (GRP) and also with fiber reinforced polymer (FRP). The purpose of this study was to investigate the load bearing behavior of concrete columns enclosed with GRP casings and CFRP composites under compressive loads. In this research, the effect of using the GRP casings, CFRP sheets, and also the number of CFRP layers has been investigated. In this research, six circular reinforced concrete columns were manufactured from high-strength concrete, half of columns (group 1) had a GRP casing and the other half (group 2) without casing. From each group, a column had no CFRP reinforcement layer, a column with one layer and another column with two layers of CFRP reinforcement. All columns were tested under concentrated compressive force. The results showed that the use of CFRP sheets and GRP casings improved the compressive strength and durability of the reinforced columns. The addition of a layer and two layers of CFRP increased an average of 10.2% and 24.8% in compressive strength, while the use of a GRP casing increased averagely 3.83 times in compressive strength of the columns. The results indicate that although the CFRP sheets and the GRP casings are both enclosed, the GRP casings, due to their greater enclosure, have a much greater effect on the compressive strength and the ductility of the reinforced concrete columns.

Parking floors in buildings are of the most likely places for terrorist bombings. While terrorist attacks across the globe have increased remarkably in the last decades, it is important to recognize the behavior of existing structures against explosions and to find appropriate solutions to reduce the resulting damages. In this study, the failure probability of a 10-story reinforced concrete building subject to a vehicle bombing in random locations in the ground floor is evaluated. For this evaluation, reliability analysis of the building structure is conducted using a Monte Carlo simulation method and the results are obtained using a dynamic analysis of a finite element model and LS-DYNA software. The random variables considered herein are the location of the explosion, the time history of the blast loading, the gravity loads and the slab depth. In order to investigate the effect of the explosion location on the probability of failure, the building plan was first divided into three categories including the center, side and corner areas, then by randomly generating the explosion in each area, the probability of different level of damages to the building was calculated. Based on the results obtained in this study, the probability of failure in the central area of the plan is more significantly compared with those of the other areas. Finally, it is shown that by strengthening the central columns, the probability of heavy damages (damages greater than 55%) for blast loadings containing 600, 750 and 900 Kg TNT charge weights is reduced to 52%, 56% and 77%, respectively.

The earthquake is one of the natural disasters that caused the many death. 10,000 people die annually due to earthquake around the world, and this incident has so far caused a lot of economic damages. In the structures review, earthquake damages can be classified into three categories: physical, social, and economical. In order to quantify physical damages, it is possible to introduce damage indexes. By knowing the damages of a structure, in addition to determining a proper understanding, redlines are possible to be designed. In other words, knowing the damage index in a structure makes it possible to determine the structure stablity against forces such as earthquakes. This issue becomes more important in retrofitting programmes. In this research, which the purpose is to determine the earthquake damages and structure performance, the Drift and Ghobarah Index are selected as damage Indexes, and the effects on the performance of two-dimensional special concrete moment resisting frames designed with the regulation (ACI 318-14) and the American loading standard (ASCE 7-10) has been investigated. In this regard, performance levels with the Drift index and the Ghobarah index along with the estimated damages have been investigated in different analysis and the correlation between these two Indexes is established. Analyses results show that Ghobara index is more conservative than maximum drift index. Another obtained result is that intensity measure which cause to low rise and medium rise buildings to reach life safety level has about 50% and 40 % differences, respectively, for two assumed indices.