JOURNAL OF STRUCTURAL AND CONSTRUCTION ENGINEERING
Year:2021 | Volume:8 | Issue:3|Papers Count:18

The use of self-compacting high performance composites due to its unique properties has attracted the attention of researchers. The high compressive strength and tensile strength, high flexural strength, have attracted the attention of researchers to this type of cement composites. In this research, in the form of a comprehensive experimental work, using six basic mixing designs, 24 rectangular composite slabs 300 to 400 mm, with two thicknesses of 30 and 50 mm, were built and tested under impact load. Compressive, tensile and flexural strength tests were made on each of the six mixing designs. Also, to determine the efficacy of high performance composite, slump flow, L-box, U-box and V-funnel on mix designs have been done. Steel fibers with percentages of 0, 0. 5 and 1% by volume fraction, with lengths of 25 and 50 mm, were used for the construction of cementitious composites. The impact test apparatus was made from a 5. 6 kilogram steel ball and a retaining system. The steel ball was raised to a height of 1. 5 meters and was freed repeatedly until failure cracking in the samples have been Developed. According to the results of the experiment, It was noted that the maximum energy absorption in a slab with a thickness of 30 mm was 34. 22 kJ, and in a slab with a thickness of 50 mm was 47. 49 kJ. The results of this experiment shows the high effect of steel fibers on increasing the impact resistance and absorbed energy of the composite slabs.

Since the batching, transportation, pouring, compaction and curing of the specimens used in laboratory testing of concrete, either from these employed in real structures, the in-situ methods are needed for assessing the quality of existing concrete in structures. Among the tests with partial failure, the "twist-off" method is used for determining the strength of concrete both in the laboratory and in-situ. In this paper the use of “ twistoff” method for determining the strength of three types of fibre concrete is presented. In total 234 concrete samples were prepared, using three types of fibre (steel, glass and polypropylene) and their strength were measured using both “ twist-off” and “ compression” testing. The results show that a strong linear correlation exists between the compressive strength and the failure modulus with the results of the "twist-off" test. Also, to study the pattern of stresses in concrete, glue and cylinder of the "twist-off" test and the pattern of the formation and expansion of the cracks in concrete samples during the test, nonlinear modeling and finite elements were carried out using Abaqus/CAE. The finite element analysis with consideration of the nonlinear shape functions for the elements in tension and pressure on concrete specimens with a strength of 40 MPa shows that, with the distance of at least 20 mm, the results of the "twist-off" test and dispersion are not affected.

Composite steel plate shear wall is usually made up of a steel plate and also a reinforced concrete cover, which is attached to one side or both sides of the plate by means of a shearing device. In innovative composite steel plate shear wall system, a gap is created between concrete cover and boundary beams and columns. The presence of this gap in small earthquakes does not cause the concrete to interfere with the frame and thus prevent its failure. In relatively large quakes, this distance between the concrete wall and the boundary members is closed and added to the resistance of the system. In this paper, steel plate, concrete cover and frame were separated to calculate the strength of composite steel plate shear wall by their interaction. To evaluate the effect of concrete strength on composite steel plate shear wall strength, the gap between concrete cover and boundary members has been discussed, and then two relationships have been proposed to calculate the strength of composite steel plate shear wall. For this purpose, this paper has been used for analyzing pushover. In order to verify the numerical modeling, the characteristics of a steel plate shear wall model, composed of a laboratory study by Arabzadeh and colleagues at Tarbiat Modares University in 2011On the behavior of composite steel plate shear walls, it has been selected.

Vertically-mixed structures are buildings constructed with different materials progressing in the vertical direction. These buildings feature a concrete frame on the lower stories but a steel one on top. Reinforced Concrete (RC) column connected to steel column in story that called transition story. The sudden change of stiffness in the transition story in these structures and the mass irregularity prompted research attempts concerning the response modification factor and the analytical period of the structures. There isn’ t much research on this issue. Due to below concrete column dimensions upper steel column dimension is limited. To accurately study the transfer of loads, the stiffness of the transition story column, and its failure and seismic behavior, this study investigates fullscale experimental a test specimen under axial and lateral cyclic load. Proposed connection in this study that called trough bolt lap connection had good behavior in seismic load up to 4% drift ratio. No sign of failure and stiffness reduction observed in test results. Analytical finite element study is done for verification and parametric study in transition story column in variable axial load and longitudinal bars ratio to grass section of concrete. Studies have shown no failure in the column connection. Column had force-control behavior in lateral loads.

In this paper, a new kind of ring damper composed of three rings is introduced and investigated numerically and experimentally. The proposed damper combined three steel ring damper in order to dissipate energy of two different level of predefined excitation such as moderate and severe one. first fuse (outer pipe) and second fuse (inner pipes) can absorb energy in moderate and severe earthquakes respectively. To evaluate the introduced damper, numerical finite element models are developed to clarify the effect of thickness and diameter variation of main fuse. Results of force-displacement curves obtained from cyclic loading confirmed the two level performance of models. Stiffness and fore increase improved the energy dissipation capacity after the predefined displacement gap. Also, damping ratio are calculated for all samples and results showed that equivalent damping ratio have been improved when main fuse was engaged. Two experimental samples have been constructed based on numerical models and examined under cyclic loading. Defined results of experiments showed that samples could tolerate 20 cycles of 10 times of yield displacement amplitude. Good agreement between numerical model and experimental samples results have been achieved.

Masonry infilled reinforced concrete frame buildings built prior to the introduction of modern seismic provisions have been observed to undergo damage in and around the masonry infill walls during most recent moderate to severe earthquakes. Considering interaction between masonary infill and frame is one of the challenges in the field of engineering research. Observation of past earthquake indicates that in the pre-damaged infill wall in the in-plane mode, the probability of out-ofplane failure of infill walls will increase. However various studies have shown that if the infill wall correctly restrained by the frame, there is a significant capacity, in terms of force and displacement against the out-ofplane demands. The prediction of interaction and effect of in-plane behavior on the out-of-plane beahaviour of infill, is one of the new issues in the field of seismic evaluation of masonary infills. This paper present comparative parametric review of the strength and displacement capacity models that predict the infills out-of-plane responses. Also, models that consider influence of in-plane damage on the out-of-plane capacity, it has also been investigated. The parametric comparison of different models in the capacity estimation of masonary infills in out-of-plane mode is shown that interaction of in-plane and out-of-plane beahviour of infills has a significant effect on capacity reduction of infills in out-of-plane mode and the model presented in FEMA360 for out-of-plane capacity of infills has a conservative results.

The public sector has always sought to attract the private sector to partnership in the construction of infrastructure projects. The process of partnering in developed countries have less problems, while in developing countries, it faces with more serious barriers and problems. In these countries, including Iran, in spite of the proper initial reception, numerous complexities and challenges have affected project performance and also continuity partnership. This research was performed to identify the factors of environmental complexity of the projects involved public and private sectors in build, operate and transfer contracts (BOT). Multiple case study strategy was used for deep study of freeway projects. Each case was studied in detail and then the research data were analyzed by grounded theory strategy. The main product of this research is the paradigmatic model of the pathology of freeway partnership projects. In this model, the axial phenomenon was identified the private sector's dissatisfaction duo to uncertainties in cost, time and revenue of the freeway. The causal conditions were found the economical, political, and legal instabilities along with the cultural and social challenges in project environment. Context conditions were identified such as mismatches in the rules, contractual weaknesses, banking system, and finally, immaturity. Intervening conditions were obtained such as the lack of suitable market for investment projects, the influence of powerful institutions, lack of commitment and lack of a national transportation plan. According to this research, the most important outcomes of complexity were obtained increased distrust and increased ambiguity of return on investment.

In this research the simultaneous effects of foundation uplift and nonlinear behavior of soil are investigated. Previous studies have showed that the effects of soil-structure interaction on seismic performance can be described through introducing a limited number of non-dimensional parameters. In most studies it was assumed that the foundation is bonded to the soil and the behavior of the soil was considered to be linear or equivalent linear. In this study it is showed that this concept can be extended to the nonlinear soil-structure systems by introducing number of new non-dimensional parameters. The main goal of this investigation is to study the variations of nonlinear displacement and ductility of nonlinear soil-structure systems. To achieve this goal, the structure is considered as a nonlinear single degree of freedom with concentrated mass which mounted on rigid foundation rested on distributed dampers and springs. Then the variations of the response of nonlinear soil-structure systems are assessed by conducting nonlinear time history analyses for a wide range of non-dimensional parameters. It is shown that the total displacement of soil-structure systems increases because of nonlinear soil behavior but the ductility of the structure as a part of soil-structure system decreases in comparison to the systems with linear soil behavior. So in this study, it is proposed to decrease the safety factor for the design of foundation. Since the permanent settlement of foundation is an important index in performance of soil-structure systems, therefore it was calculated for some applicable systems and it is shown that although the permanent settlement of the foundation increases by decreasing safety factor of foundation but the value of permanent settlement is acceptable for ordinary systems.

Since, generally, in high population areas and large cities for maximum use of land, buildings are constructed without distances or with insufficient distance, thus, during severe earthquakes, due to unbalanced vibration of the structure Adjacent bodies (which do not have enough distance from one another) and without considering the effects of the soil, the impact phenomenon occurs. The most natural way to avoid impact is to provide sufficient distance between adjacent structures. In the present article, the proposed distance between the standard 2800 Iran between two adjacent structures is also evaluated for the impact of impact phenomena using time histories analysis of structural-soil-structural models. To this end, evaluation of seismic behavior of structures 3, 6, and 12 of 3rd and 5th craters on type I and III soils was performed and for analysis of 6 earthquake records with different earthquake hazard levels Has been used. These structures were modeled in the OpenSees software. Then, to obtain an optimum distance between the structures, the PSO algorithm was used, the code of this algorithm was written in MATLAB software and connected with the OpenSees software. After reaching the convergence condition, the optimum interval was presented and compared with the proposed interval in the standard 2800. The results indicate that the proposed distance in standard 2800 for high-risk earthquakes is not adequate and is not suitable and, given the soil conditions, structures and earthquakes, there is a possibility of collision.

The use of fibers in concrete in order to improve concrete properties and mechanical behavior has started four decades ago and is growing. Fibers in concrete reduce the brittleness and provids ductile behavior of concrete. Fiber may be of plant species, artificial and metral which can improve mechanical properties of concrete under compressive load, tensile, flexural, shear, dynamic and hit, as well shrinkage and creep, resistance to freezing and thaw, abrasion and erosion and can create a uniformmaterial. In this research we have studied the impact of palm fiber so – called Cis which is abundant in Balouchistan on mechanical properties of concrete. For this purpose, we used ac laboratory method in which samples with varoous shapes and different percentages of palm fiber (CIS) have been made and different properties of concrete have been tested. The result showed that concrete made with broken fibers 2%, shear fiber 2%, waste fiber 1% has a comperssive strength greater than control sample and concrete with broken fiber 2% has higher tensile stergth than the control sample.

Understanding the behavior of steel structures under fire loading is very important because many recent events indicate the vulnerability of steel structures to such a hazard. Extensive numerical and experimental studies have been conducted to investigate the behavior of different types of structural steel elements individually, steel structure connection, and steel moment frames in fire conditions. However, the response of concentrically braced frames in fire conditions has not yet been investigated. This paper examines the global response and the local behavior of special steel concentrically braced frames under a series of uniform fire scenarios considering the heating and cooling phases at different levels of floors by numerical analysis of finite element method. The analyzes results show that the buckling of the beams and braces is exposed to high temperatures due to the large compressive axial force due to lateral constraints to expansion. Also, the fire resistance of the braced frames is affected by the position of the fire. As with increasing gravity load at lower levels, the effect of P-Δ , which is an effective factor in the destruction of the structure, has increased and potentially risk the early destruction of the structure Increase. The results of analyzes can help engineers understand the local and global responses of steel bracing frames under fire loading.

One of the most important deficiency of buckling restrained braced frames is the concentration of lateral drifts in some specific stories and the soft story mechanism, under moderate to severe earthquakes. In this paper, in order to prevent the development of soft story mechanism in buckling restrained braced frames, asymmetric configuration along with a zipper strut is proposed for chevron type ordinary buckling restrained braced frame. The zipper strut connects the midpoints of beams at the brace intersections in all stories and carry the unbalanced axial force developed at the intersection. In addition, it causes the BRBs to uniformly yield over the height of structure. For this purpose, 4, 10, and 14 story buckling restrained braced frames were designed according to Iranian seismic code, and the nonlinear time history analyses were performed in Opensees, subsequently. The analysis results showed that the asymmetric buckling restrained braced frames possess more uniform lateral drift demands in comparison to ordinary symmetric buckling restrained braced frames, is less prone to the formation of soft story mechanism. The zipper elements were found to carry a significant axial forces during analyses, and were responsible for distribution of unbalanced forces among BRBs over the height of braced frames.

One of the latest innovations in nano-technology is the use of Micro-Nano Air Bubbles (MINAB) as a substitute for water in concrete. Using MINAB as a substitute for water used in concrete can be used to improve the properties of concrete. The use of super-Plasticizer can have an effective role in reducing negative effects MINAB on concrete properties. In this study, to investigate the effects of MINAB with water in concrete in the presence of different super-Plasticizer percentages, the effect of MINAB on the setting time, cement mortar flow and compressive strength of cement mortar is investigated. For this purpose, 16 samples of VICT needles, 48 samples of cement mortar and 16 samples of cement mortar flow were used to check the curing time, compressive strength and cement flow with different percentages of super-Plasticizer (0. 5, 0. 9 and 1. 4) were tested in the presence and absence of MINAB. The results showed that the compressive strength of cement mortar with MINAB increased by 16 and 7%, relative to water at 7 and 28 days respectively. The compressive strength of cement mortar with MINAB has increased in presence of super-Plasticizer in comparison to cement mortar with water in presence of super-Plasticizer at the age of 7 and 28 days, with the highest resistance in 0. 5% super-Plasticizer, which increased by 21% at 7 days and increased by 10% at the age of 28.

High-performance reinforcement concrete due to its ductility and higher energy absorption has many applications in the field of passive defence than the normal concrete. These high-performance materials can be used in many cases, such as seismic improvement of building members. In some cases the structural capacity is increased, which is called strengthening. Strengthening can be carried out by increasing the toughness and increase of resistance. In this study, the use of Explosion Proof concrete in order to protect the structural components (in this study: Weak-one Slabs). In this paper, four weak-one way slab that were strangled in various zones have been studied. The numerical modelling is proceeding in Abaqus / explicit. For modelling the behaviour of concrete, CDMP method has been used. The results of this study show that the energy absorption in the strengthened slab in the tense region has increased to seven times compare to other zone of strengthening. The use of fiber reinforced concrete has a significant effect on the increase of bearing capacity and the ductility of a one-way slab. In other words, the use of high-performance fiber reinforced concrete as a method for the strengthening of structural elements such as slabs will be effective in improving the behaviour of them, especially in the field of passive defence. Also, the maximum tolerable explosive load in compression, tensile and compression-tensile strengthed zone specimens was 1. 3, 0. 85 and 1. 21 times compare with the reference specimen. The results of this study show that the use of high-performance fiber concrete laminates in all zones of the slab simultaneously, increase stiffness and reduce the deflection of the specimen.

The goal of this research is to identify and evaluate the factors of design excellence based on building information modeling (BIM) compared to the traditional method in relief structures including fire station centers and hospitals with an emphasis on crisis reduction. For this purpose, by studying the previous studies, simulation and modeling of the case study of firefighting buildings and Ayatollah Borujerdi Hospital in city of Boroujerd, the most important criteria and effective factors were identified using the Autodesk Revit software as well as experts’ comments. Then, they were prioritized using analytical hierarchy process (AHP). The results obtained indicated that the selected criteria in the order of preference included life, exploitation, time and finance. Also, the factors of excellence were as follows: 1) Access to information of building spaces for quick detection of more incidental and damaged sites; 2) Investigating and troubleshooting the most detailed information of the structural damages; 3) Accurate and smart travel in the building to locate the injured; and 4) Designing the smart movable ceilings (convertible), 5)Build fast buildings (from design to operation) during crises like warfare 6) The ability to use sun and wind energy in the event of power and gas interruptions, . . . Considering the above factors in the design of fire fighting buildings and hospitals, building information modeling can save lives in times of earthquake crises.

Currently, to obtain the dynamic properties of structures in structural engineering, experimental relationships, mathematical models and computer software aids are mainly used. These dynamic properties depend on many details about material behavior and the compound of the structures, which could not all be taken into account in analytical models. Therefore, there are always differences between the analytical models and the actual structures. So, seismic tests on structures is the most reliable method for obtaining these properties, so far, various methods have been developed in the world to preform these seismic experiments on the experimental structures such as image processing method. In this paper, the image processing method utilized through the dynamic properties of structures for mass change detection in the structure. For this purpose, a cantilever beam oscillated and the recorded displacements are considered as the inputs of the system identification. By deriving these displacements twice, the acceleration of the structure obtained and by processing these accelerations, natural frequency and shape mode of structure have been extracted and compared with the results of the accelerometer sensors embedded on the structure. Finally, mode shape curvature method utilized and the location of the sensors on the structure has been detected with good accuracy.

Despite conservative requirements of existing building code regarding clear seismic gap distance of base-isolated (BI) structures to surrounding moat walls, seismic performance of these structures is still ambiguous under severe earthquake ground motions that may push the base slab of the isolation system to collide to the surrounding moat walls. Moreover, the temptation of reducing seismic gaps in congested urban areas exacerbates the risk of pounding. Excessive horizontal displacement response of these long-period structures subjected to a rare near-field ground motion may lead to pounding to adjacent structures and subsequently, severe and uncontrolled damage or even total collapse of the superstructure. Pounding of BI structures to moat walls is usually considered as an unwanted response that may inflict critical damage to a high importance structure designed for high performance levels. Pounding effects to the moat walls depend on several parameters including superstructure and isolated periods, damping, seismic gap as well as characteristics of the earthquake ground motion. This study aims to evaluate seismic response of base-isolated moment resisting steel frames subjected to pounding effects under near-field earthquake ground motions with different clear gap distances to surrounding moat walls. A seven story and a three story buildings isolated with elastomeric bearings have been modeled. Base slab displacement, global displacement ductility demands, yield strength reduction factors, and maximum inter-story drifts have been computed under recorded severe near-field earthquake ground motions. Results showed that for most of the seismic gaps lower than those of prescribed by codes, seismic demands remain in acceptable ranges corresponding to low performance levels, i. e., life safety or collapse prevention of fixed-base structures. This implies that performance of BI buildings with codified seismic gaps or insufficient seismic gaps is not much different than that of fixed-base buildings when they are pushed to their displacement limits under maximum considered earthquakes.

Magnetic water changes the electron configuration of the ions, followed by significant changes in hardness, electrical conductivity of surface tension and other physical and chemical properties of water. These changes in the cement reaction create a situation that has a significant impact on the improvement of the properties of concrete in fresh and hardened states and is therefore of concern to the researchers. One of the basic characteristics of magnetic water, which is very important in the production of concrete, is the dependence of water on particles and colloidal solutions. When water is mixed with cement, a colloidal solution of cement is obtained, which if the water magnetic is used, the particles of the cement are surrounded by a single molecular layer of water with a lower density. This phenomenon makes it possible to reduce the amount of water used in the mixing of concrete, which will have a lot of benefits in concrete. Magnetization of water increases the hydration of negative ions, which damages the crystalline structure of the water. This paper studies the researches on magnetic water and its effect on the mechanical properties of lightweight concrete has been analyzed. The most influence of magnetic water on the mechanical properties of lightweight concrete has been obtained at the intensity of the magnetic field of 1 Tesla. The highest workability of cement paste made with magnetic water was obtained by rotation of 65 minutes of water in a magnetic field with intensity of 1 Tesla. The most effective magnetic field intensity is achieved in 1 Tesla for magnetic field.