نشریه مهندسی سازه و ساخت
سال هفتم شماره 2 (پیاپی 33، تابستان 1399)

Lowering the weight of concrete used in buildings and other structures has been one of the main priorities of the specialists. This will reduce the dead load and the forces involved in the structure during the earthquake. A wide range of research has been done around the world.In this work, a research on the construction of lightweight aggregates of Scoria has been used to increase the flexural strength of the beams tested in the glass fiber, as well as to reduce the use of cement, reduce the amount of pollutants in Iran, as well as increase the efficiency of concrete from zeolite and ash powder The wind has been used and the mechanical characteristics of these lightweight concrete structures, in particular the flexural behavior of lightweight structural beams, have been investigated in the laboratory environment, and the results indicate that light concrete was constructed and pressurized in Due to the presence of a network of fibers up to 3% by weight of cement and the resulting flexibility, the strain is very crisp And preventing it from breaking down and increasing the compressive strength by up to 20% and 10% of the flexural strength compared to the control sample. Addition of powdered zeolite along with ash to 15% by weight of cement has the same adhesion properties as cement to light concrete Data has increased the flexural strength by up to 15%.

Today, geotechnical studies are an integral part of any development project, and having sufficient information about the depths of soil without conducting soil mechanics studies is not possible. The proper design of the structures requires the application of appropriate amounts of soil capacity, this is not possible with the geotechnical information obtained from the drilled boreholes. Therefore, in this research, geotechnical parameters have been collected in Bandar Abbas by collecting geotechnical data from 241 drilled boreholes to a depth of 15 meters. Using geological information system software (ArcGis), geotechnical parameters are zoned. This zoning provides a very good approximation of the geotechnical parameters of the soil to the engineers, which can be used in the design of the pion. The results obtained in this study show that more than 85% of the study area has coarse-grained soil layers with a moderate and dense density of sandy sand, which, by increasing the depth, especially from 10 meters below, to the density of soils They are added in the group of dense soil soils. On the other hand, the general soil layers are 6 m below and saturated with a maximum natural moisture content of 30%. Regarding the dominant soil of the region and the need to consider the geotechnical hazards in the design of the plies, zoning maps of the coefficient of reliability versus liquefaction are also provided.

The particular weaknesses of concrete are brittle fracture and lack of material ductility, so using steel reinforcements and discrete fibres are an attempt to overcome this weakness. Strain hardening behaviour under tensile force has made new material HPFRCC as a high performance material with high energy absorption capability and high cracking ability before failure, Therefore the structural application of this composite material in the structural members such as continuous beams to control cracks and improve ductility has come to the believed border. In this paper, the effect of using HPFRCC containing 2% steel fibres on the flexural performance of four large two-span reinforced concrete beams has experimentally been investigated. Two beams were conventional concrete with two different arrangements of stirrups in the central support area and two other beams were companion but made with full HPFRCC composites, all beams with two equal spans of 1800 mm were loaded under concentrated force applied in the middle of the span symmetrical and incrementally. The results indicated that the use of HPFRCC with 2% steel fibre in the specimens increased the ductility, energy absorption, and bearing capacity, as well as an appropriate re-distributing moment in the plastic area of reinforced concrete continuous beam with two spans.

At present, certain types of concrete such as ultra high performance concrete (UHPC) provide some concrete properties such as high resistance. Reactive powder concrete (RPC) is one of the UHPC concrete with superior physical and mechanical properties. Reactive powder concrete is produced using cement and very fine powdered materials including crushed quartz, silica fume and low water-to-cement ratio using super plasticizer. In this study, a mixing scheme of RPC, in which water/binder ratio (W/B) is equal to 0.15 and the ratio of super plasticizer to cement (SP/C), is equal to 3%, with interest of the selection of native materials was determined. Subsequently, by performing several experiments, the compressive strength, rupture modulus and tensile strength of RPC have been investigated at different ages. In order to determine the resistance of RPC at different ages, samples with W/B and SP/C were made up to the mixing scheme and tested after 3, 7, 14, 28 and 56 days of normal operation. Each group consisted of six samples, and the mean values, standard deviation and coefficients of variations of the samples were determined. The relationships have been proposed to predict the compressive and tensile strength of reactive powder concrete in different ages, which are accurate and can be used in practice.

Historical buildings are valuable structures. Therefore, performance evaluation of these structures under different loadings such as seismic effects has been considered in several research projects in recent years. Masonry towers are known as one of the common types of historical structures that exist in different countries. To evaluate the seismic performance of masonry towers, their dynamic properties are needed. Among the dynamic characteristics of the towers, fundamental vibration frequency is known as the most important one. In this regard, formulations for estimation of the vibration frequency of these structures in useful. For this purpose, a database consisting properties of 38 towers which were identified through in-situ dynamic tests or numerical analysis before, are collected. Then, based on a nonlinear regression on the collected database, empirical equations are proposed for estimation of the vibration frequency of historical masonry towers. Evaluation of the database indicates that height of the towers is the most effective parameter on their vibration frequency. In addition, thickness of the perimeter walls, cross-section dimensions of the towers and elastic modulus of masonry can affect the dynamic response of the towers. The average errors of the estimated frequencies by means of the proposed equations indicate that the proposed equations have acceptable accuracy.

One of the most important issues in many project-oriented organizations is the risk management of the ongoing projects of that organization. In this regard, in the first step, the potential risks of projects should be identified under a systematic and comprehensive scheme, and then, using appropriate and desirable methods, they should be evaluated in terms of their probability and their impact on project goals. In this study, considering Bakhtar Petrochemical Company, a holding company, as one of the largest companies that construct and operate petrochemical projects in Iran as a case study, the current and potential uncertainties and risks of petrochemical projects in Iran have been identified and evaluated. Two methods, namely documentation review and interview, have been used to identify risks. This procedure has led to the identification and classification of 104 potential risks in petrochemical projects in two categories and eight sub-categories. Also, since the risk assessment is an evidential, intuitive, and empirical decision-making process, the Evidential Reasoning approach has been used for this stage. Evidential Reasoning, based on the Multi-Attribute Decision-Making approach and Dempster-Shafer's Theory of Evidence, is a useful and effective method to deal with overly intuitive and inaccurate judgments made in this uncertain environment. Using this method, in addition to assessing and ranking the identified risks, has also produced a measurement of the level of recognition of the identified risks.

The widespread use of energy dissipation systems has led researchers to investigate the optimal mechanical properties of these systems for improving the seismic performance of a structure with the installation of such devices. So far, considerable researches have been conducted on optimum seismic design of fixed-base systems with passive dampers. On the other hand, recent studies have shown that effect of soil-structure interaction (SSI) can have remarkable effects on optimum seismic loading patterns of structures in both elastic and inelastic states. In these investigations, several new optimization algorithms were proposed for optimum seismic design of buildings considering soil-structure interaction effects. However, very rarer optimization studies have performed on soil-structures systems with dampers. In this paper, a new optimization algorithm based on uniform damage distribution of equivalent shear building model considering soil-structure interaction effect is developed. To this end, shear buildings models with hysteretic dampers located on flexible base soil are optimized under 16 far-fault earthquake ground motions without pulse, and the effect of key soil-structure interaction parameters on optimum response is investigated. Results of this study indicate that using proposed optimization algorithm for soil-structure systems with hysteretic dampers to achieve optimum distribution of dampers will lead to significant improvement of the seismic performance of the primary structure. In addition, it was concluded that the soil-structure key parameters such as dimensionless frequency and structural slenderness ratio can significantly affect the optimum load patterns such that increasing SSI effect will lead to increasing seismic load on base and top of the structure compared to the fixed-base systems. This can be attributed to the flexibility and higher modes effect of soil-structure systems when compared to the corresponding fixed-base system.

Using central core system with peripheral columns and outrigger and employing the energy dissipation devices, such as viscous damper, is one of the structure lateral displacement mitigation’s methods. The central core system with the damped outrigger under seismic loads can be assessed by transverse vibration of a cantilever beam subjected to a concentrated moment due to spring-damper system. In this paper, two models are proposed for damped outrigger. After obtaining differential equation of vibration of a beam interacted with damped outrigger modeled as viscous and viscoelastic, and eigen value analysis, characteristic equations are derived. Complex frequencies and mode shapes are obtained with respect to non-dimensional parameters such as damping ratio and outrigger location and results are presented as modal damping ratio surfaces versus damping ratio and outrigger location and so optimal of these parameters for each mode are attained. The optimal locations of outrigger at first mode are 0.47 and 0.5 of the building height for viscous and viscoelastic models, respectively. In second mode, this value is 0.8 for both models. Analyzing a finite element model of a 40-story building and comparing frequency responses of the optimal and non-optimized models and the undamped models including the traditional outrigger and traditional core system without outrigger, validity of the proposed method is verified. The maximum of roof displacement in viscous and viscoelastic models are respectively about 16.4 cm and 1.1 cm, while it exceeds than the criteria of 1/400 of building’s height in the undamped models. In spite of greater modal damping ratio of viscous model, performance of the viscoelastic model is better. This is an indication of unrealistic viscosity model.

The major damage observed in recent earthquakes is the separation of non-structural walls from structural components and large longitudinal and diagonal cracks in them; so, selecting the appropriate wall is very important. Considering the diversity of the existing walls and the multiplicity of the criteria, making an inclusive decision for choosing the most practical wall which considers all the relevant criteria seems necessary. Therefore, Analytical Hierarchy Process method was used for analysis in this paper. This method is compatible with multiple criteria and decision making purposes. In order to identify and determine the importance of effective criteria in choosing the appropriate wall, the Empirical comparisons have been used and for a more accurate comparison between the types of walls based on quantitative criteria, in addition to the questionnaire, numerical modeling has also been used. criteria include design criterion, performance criterion, economic criterion, and time criterion. Finally, using the hierarchical analysis method, the suitable types of walls in seismic areas have been prioritized. The materials used to evaluate the non-loaded walls are: 3D-panels, drywalls, cement blocks containing lightweight expanded clay aggregate (lECA), Autoclaved aerated concrete. The gained results of the study indicate that in order to achieve a safe and earthquake-resistant hospital structure, the drywalls is considered to be the best option and autoclaved aerated concrete as well as blocks options the light expanded clay aggregate and 3D-panel were selected respectively.

The main sources of the uncertainty in estimation of structural seismic responses is the uncertainty of the earthquake records as the input excitations. In recent years, along with the development of performance-based seismic design approaches, importance of the record selection strategies in nonlinear response history analysis of structures has been highlighted and has attracted the attention of many researchers. Record selection in performance-based seismic design approaches is often done based on the intensity measure of the records. The spectral shape has been introduced as a powerful intensity measure in record selection techniques for estimation of some structural responses such as the maximum inter-story drift ratio. In the present study, the sufficiency of the spectral shape in assessment of hysteresis energy of the structure and the maximum Park Ang damage index in plastic hinges has been investigated in special moment-resisting RC frames. In this way, four 2D structural models of special moment-resisting RC frames with inelastic characteristics have been analyzed under a set of strong ground motion records selected based on the spectral shape by the conditional spectrum method. After determination of numerical values of hysteresis energy of the structure and maximum Park-Ang damage index in the plastic hinges, the correlation of such responses have been investigated with the various secondary intensity measure. These intensity measures are selected such that they cover various properties of strong ground motion records such as frequency content and duration. The results indicate that spectral shape is not sufficient for prediction of hysteresis energy and Park-Ang damage index of special moment-resisting RC frames. To obtain an unbiased and reliable estimate of such responses, more studies on record selection strategies is needed. Among the secondary intensity measure, those associated with the energy content and duration of the records are more correlated with the aforementioned structural responses.

This paper deals with numerical study of a newly developed seismic load resisting system called “linked column frame (LCF) system” which can be used to dissipate the earthquake energy and aids the structure to quickly revert to the serviceability level Dominant behavior of this system resembles that of the ductile link beam and as the shear fuse, it mitigate structural damages in various seismic events. In order to investigate the structural behavior of this in the event of near and far-filed earthquakes, after validationg the models by means of laboratory models, 3, 6 and 9-storey buildings were deigned making use of performance based design approach and then, the earthquake-induced responses were investigated by applying near and far-field earthquake records. Based on the results derived from the nonlinear dynamic analysis, the maximum inter - storey drift developed by the near and far-field earthquakes are equal to 3.91, 1.08, 1.65% and 1.74, 3.91 and 4.06, respectively. These values are related to the lower half of the building’s height and in compliance with the comparison between maximum displacement and inter-storey drifts obtained by the method proposed by Shoeibi and Malakoutian et al; the structure takes advantage of the controlled maximum and inter-storey drifts.

In this paper to increase the efficiency of direct displacement based design (DDBD) in designing structures equipped with viscous dampers (VDs), a method has been proposed to determine optimal distribution of VDs. The proposed method has been based on defining an optimization problem which minimizes the sum of damper coefficients to achieve the required equivalent viscous damper. To solve the optimization problem the distributed genetic algorithm (DGA) has been applied. To illustrate the method, three 2, 5 and 20 story steel frames equipped with linear VDs and designed using DDBD, have been considered and optimal placement of VDs has been determined. The controlled structures using uniform distribution (UD) and optimal distribution (OD) of VDs subjected to ten artificial earthquakes compatible with design spectrum and nonlinear time history analysis has been conducted. Results show that to achieve the same equivalent viscous damping for both uniform and optimal distributed VDs distribution, using OD has reduced significantly the sum of dampers coefficient (up to 30%) as well as the maximum damping force(up to 24%). Also evaluating the performance of controlled structures under different artificial records has shown that using OD has led to less control system cost while both distributions has similar performance.

Seismic behavior in concrete weights due to the need to increase the safety of dams during earthquakes has been very much considered in recent years. Most concrete dams are exposed to cracking damage. These cracks are created by various factors such as operation, concrete treatment, volumetric changes in concrete mass, loads, etc., and the possible expansion of these cracks may reduce the efficiency, failure and instability of such dams. The use of fracture mechanics as a new method for estimating the instability and durability of concrete dams has been recommended in world-renowned journals and papers. Due to the sensitivity of the subject of crack-erosion in concrete dams, as well as considering that in the past the behavior of the Gotvand dam was not investigated due to trapping, this study examined the behavior of the Gotvand Regulatory Dam due to trapping Has been. Abkhus software is used to model this research. Parameters that are considered as variables include the length of the variable for the cracks and the crack angle. In the case of the effect of the crack angle, the results indicate that the worst case for the dam section is to leave a negative angle. The horizontal displacement value for the -30 degree angle is 0.031 m and is 0.025 m for cracking at an angle of +30 degrees. Also, the increase in the length of the crack increased the amount of displacement, tension and rebound response in the dam. Maximum reciprocating photo in a model with a length of 200 cm, with a crack angle of +45, is 4% higher than the model with a gap of 30 cm and equal to 1.78E+8 of Newton.

In the present paper, the behavior of steel shear walls connected to frame beams only was investigated under various loading conditions (nonlinear static, cyclic and blast) using the finite element method and compared with that of the corresponding system with fully-connected infill walls (typical SPSW). The obtained results were discussed in terms of strength, initial stiffness, ductility, max of Von-Mises stress and max of in-plane and out-of-plane deformations. In the study, the effects of different system aspect ratios and various infill plate thicknesses were also considered. The adequacy of the finite element modeling approach for representing the responses of SPSWs under loading conditions was verified through comparison with experimental results. Results of pushover analyses showed that releasing of the infill wall connection to the columns limits the widespread yielding of the infill plate. This, in turn, affects the strength, initial stiffness and ductility of the system. Notably, the behavior of SPSW frames is not affected much by such configuration. Increasing the infill plate thickness in proportion to the decrease of its strength, not only offsets the effect of this configuration on the system strength, but also improves the system behavior in terms of initial stiffness and ductility (compared to the corresponding system with infill plate connected to boundary columns and beams). Results of cyclic analyses showed that the dissipated energy by the semi-connected SPSW is relatively decreased mainly due to the decrease of plate strength and energy absorption. Results of analyses under blast loading condition showed that both fully-connected and semi-connected SPSWs designed for seismic loading can partially resist against out-of-plane blast loading effects without failure.