نشریه مهندسی سازه و ساخت
سال هشتم شماره 9 (پیاپی 48، آذر 1400)

Reliable long-term bond durability is required in order to have successful performance of concrete structures reinforced with CFRP sheets. In this paper, the results of investigating the effect of using protective coating applied on CFRP sheets in increasing the strength and bond durability of these sheets under acute environmental conditions are presented. The environmental conditions considered are: wet-drying cycles, freeze- thaw and temperature changes. The results show that the bond durability of CFRP-reinforced specimens without protective layer is reduced by 24, 40 and 75% under cyclic conditions of temperature change, wet-dry and freeze-thaw. In order to protect CFRP sheets, four types of mortar were used, consisting of cement-based fiber mortar, fiber mortar with air Entrainment, cement-sand mortar containing epoxy adhesive and epoxy-based waterproof mortar were applied on their surface. Tests performed include measuring the bond strength using the "pull-off" and "twist-off" methods, as well as determining the compressive strength of the protective coating mortars, before and after exposing specimens to acute conditions. The results obtained tend to indicate that the proper selection of protective coating had a significant impact on the performance and bond durability of the CFRP coated concrete cubes that were under harsh environmental condition. By applying these coatings on concrete specimens reinforced with CFRP sheets, under conditions of temperature change, wet-drying and freeze-thaw, the bond strength increased by 12%, 22% and 84% compared to the specimens without protective coating.

Due to good ductility and stiffness, the eccentrically braced frame (EBF) has attracted the interest of seismic design regulations. Recently, the replaceable link beams (RLBs) were proposed as a new approach to solve the problems in designing the EBF system. This approach allows to easily repair or replace the damaged link beam by uncoupling the yielding element (link beam) from the main floor beam. One of the most common types of RLB is the double-channel link beam with the web-bolted connection. The identification of factors involved in the behavior of this type of link beam is less commonly found in the studies. In this paper, therefore, using the ABAQUS software, the numerical modeling was first validated to a laboratory model. Then, by changing the validated link components (including the number and thickness of plates, number and spacing of bolts, number and steel grade of link beam section), a total of 16 new numerical models were generated and evaluated under cyclic loading. The results limited to the assumptions of this paper show that in the web-connected horizontal replaceable shear link, the full shear yielding occurred, achieving the full functionality of ductile seismic fuse. In addition, the bolted, web-connected RLB demonstrates excellent seismic performance and plastic rotation capacity. Also, the smart selection of link components increases the shear strength capacity, stiffness, ductility and energy dissipation. However, the effect of increasing the size of beam cross-section is more noticeable. In addition, in order to ensure the full shear yielding behavior for RLB, it is necessary to add the upper and lower flange stiffeners near the connection.

In urban areas with high population density, lack of surface space has led to the development of the transport network, especially the construction of underground tunnels, which is usually inevitable in the construction of buildings near deep foundations. When a tunnel is excavated, the surface settlements will result in damage to the surface and deep structures. Therefore, control of surface settlements and other environmental impacts is key to the design of tunnelling projects. Thus, in the present study, using the three-dimensional analysis by Abaqus finite element software, the effect of New Austrian tunnelling method (NATM) including Top heading (TH) and Central diaphragm wall (CDW) on the surface settlements and the forces applied to the single pile and the 2 × 2 pile group was investigated when the tunnel is adjacent to the piles in weathered residual soil. The results showed that the amount of net forces applied to the pile due to tunnelling patterns when running as a pile group was significantly lower than those for the single pile. It was also proved that, in the pile group, the CDW method created a lower amount of net surface settlements and net axial forces compared to the TH method. Also, unlike surface settlements, the influence zone on the pile head settlement in the longitudinal direction can be identified as ±2D in TH, and in the CDW method from -2D to +1D from the pile center (behind and ahead of the pile axis), where D is the tunnel diameter.

Successful projects are the result of good contracts. Contracts in development projects meet their defined objectives, with opportunities and threats to key elements of the project including time, cost and quality that can be traced back to a set of uncertainty conditions called risk. The purpose of this study was to identify the risk factors for contracting construction participation in mass housing projects. For this purpose, the SWOT Matrix Model (SWOT) has been used to identify internal factors (including strengths and weaknesses) and environmental factors (including opportunities and threats) related to the subject of contract risk. Based on the above model and based on the data of a case study as well as the analysis of the new type contract, it has been attempted to identify the strengths, weaknesses, opportunities and threats of these contracts.

The frames with Buckling Restrained Braces (BRB’s) are used as a lateral system. The braces often have a limit amount of ductility and dissipated energy in cyclic loading. Therefore, the use of Shape Memory Alloys (SMA’s) in braced frames with regard to the specific properties of these can be an effective improvement in the seismic behaviour of frames. These alloys become known without the need for replacement after an earthquake and the possibility of many deformations and reversal to initial state. Seismic fragility analysis is one of the most important methods in seismic performance-based design that which lead to seismic fragility curves. Fragility curve is a powerful tool for probabilistic vulnerability assessment of structures. In this paper, seismic behavior of frames with BRB’s and the effect of utilizing SMA’s were studied. Then, three 2D-frames with 3, 6 and 9 story were utilized. The OpenSees software used for the nonlinear time history analysis of frames. The BRB’s considered in two cases, with and without SMA’s. For development of fragility curves, 7 strong ground motion accelerograms including main shock-aftershock earthquake records utilized. By defining the three performance levels for Immediate Occupancy (IO), Life Safety (LS) and Collapse Prevention (CP) based on maximum drift and base shear, the values of the probability of exceedance from these thresholds has been calculated. By comparison the achieved curves, it was found that the frames with the SMA often has the range of IO and LS performance, and the probability of occurrence of the CP level is 38% and in the case of the without SMA the CP performance level will have the of 65%. Using a SMA’s in these frames can reduce the cost of restoring and recovering of damaged systems and make the more resilience building system.

The steel bracing system is one of the appropriate methods for the strengthening of concrete moment frames against lateral forces. The article purpose is the evaluation of the new strengthening method of reinforced concrete moment frame with convergent bracing and interchangeable link beams that is embedded in the steel frame and installed in the concrete frame spans. This new method is easy to execute, economical and ductile with appropriate performance because of the existence of ductile fuse in its accession section. Therefore, this method is introduced and compared to other strengthening methods by steel bracing. In this article six concrete frame strengthening methods investigated include x-convergent bracing, reverse chevron bracing, divergent bracing with concrete link beam, divergent bracing with steel link beam connected to steel columns in the steel frame, divergent bracing with steel link beam connected to the steel frame with steel columns between those two, divergent bracing with steel link beam connected to the steel frame. All strengthening models attached to concrete frames by a steel frame surrounding them. The linear dynamic analysis results showed a decrease in relative lateral displacement and stress ratio of concrete frame members in all strengthed frames compared to the nonstrengthed frame. Also in the strengthed frame by divergent bracing and steel link beam, the results revealed a 38% steel consumption decrease and an 18% base shear decrease compared to strengthed frame by x-convergent bracing. Nonlinear static and dynamic analysis of models were done by PERFORM-3D software. The nonlinear behavior results of the strengthed concrete frame by divergent bracing with steel link beam connected to the steel frame showed more stiffness, ductility, behavior coefficient and energy dissipation than other models. Also, in this model, an appropriate performance of the structural fuse was shown by the plastic hinge formation of the link beam.

Due to the increasing demand for housing, various communities are using the technology and advanced equipment to build housing. Precast RC frame system is one of the methods used for this purpose. The most important features of this structural system are the high quality of construction due to the manufacturing of parts in the factory, the ease and speed of implementation, thus reducing the time gap between investment and utilization, also the possibility of working in poor atmospheric conditions. One of the important points in the implementation of precast concrete structures is how to connect the precast elements of the beam to the column, which will have a significant effect on the seismic behavior of these structures. In this paper, we have tried to estimate the seismic behavior of these structures using the behavior of some experiment specimens of precast joints, which are close to the executable details in Iran. To do this, a numerical model has been presented to consider the nonlinear behavior of this type of connection in the Opensees software and has been used to calibrate the numerical model results from the experiment behavior of the above specimen. The advantages of this nonlinear model include a very good match between the experimental and numerical results of Hysteresis Load- Displacement curve, also hysteresis parameters such as maximum bearing capacity, joint strength, dissipation energy and ductility capacity, that the difference between these results is less than 5%.

These types of structures are very disposed to instability, which can limit the amount of load that can be tolerated and deformed structures, and play a fundamental role in designing structures whose loads borne by their members are mainly axial-compressive or axial-tensile. So it is important to study the stability of these structures to determine the maximum load-bearing capacity of the structure, to find the optimal geometric shape, the stiffness of the structure and collapse behavior under different loading conditions. Under different loading conditions, dome-shaped space structures exhibit various modes of instability, including member instability, nodal instability, member length instability, and general instability. Considering this type of instability, in this study, the dome-shaped space structure of the tomb of Sheikh Safi al-Din Ardabili with the special form of the dome, which has been obtained by parametric study, have been investigated. These are done by collapse analysis and the use of finite element methods. Factors such as early geometric imperfections, balanced snow load pattern in nodes, unbalanced snow load pattern in two orthogonal directions, taking into account three different height to span ratios, two lengths to width ratios of the dome and yield stress are considered In the stability behavior of the single-layer space structure of Canopy the tomb of Sheikh Safi al-Din Ardabili. The results show that the height to span ratio is an influential factor in this type of structure and with increasing this ratio, weight, the initial hardness and load capacity (for design with the same sections for all structures) increases; also the structural form of the single-layer dome-shaped space structure of the tomb of Sheikh Safi al-Din Ardabili, with its special form, is very uneconomical and inefficient, and is not recommended for structural designs and has only a beautiful aspect.

Engineering structures experience different conditions during their life time that may result in damages in some structural elements under these conditions. Beams are considered as the main components of building structures, bridges, and the most important parts of the industrial machinery therefore, it is important to identify the various situations of occurred local damages. In this paper the steel beam was modeled by the plain-ends of support conditions in the healthy and damaged states in the finite element software of ABAQUS and the static analysis was performed by the influence of constant static load. The frequency analysis of the steel beam was conducted without the influence of loading. Changes of fitting curve coefficients of static displacements resulting from the polynomial regression and also changes in the frequency values of the different modes of healthy and damaged states confirm the damage of the beam. In order to detect the various failure situations, the difference of static displacements and also the difference of the interpolated modes of healthy and damaged states analyzed using the continuous and discrete wavelet transformations. The interpolated details resulted from analyzing the continuous and discrete wavelet transformations at the site of damages show the irregularities and perturbations in the wavelet coefficients, such that the relative minimums and maximums of jump in wavelet coefficients happened in all investigated states in the site of damages. Also, results show the wavelet coefficients sensitivity at the site of each damage independent of the wavelet coefficients sensitivity in other damaged sites with different intensities. Also, the occurrence place of minimums and maximums of wavelet coefficients coincide in a damaged situation with different intensities (with approximately zero error).

The seismicbehavior of the on ground quadroplete elliptical tanks has been investigated in the current study. Basically, the tank is a structure used to store different types of fluid, and it is also widely used in refineries, sewage treatment plants and factories in the form of on ground and elevated tanks made from concrete and steel. Regarding the application of the huge dynamic and hydrodynamic loads on a tank at the time of earthquake and the great importance of the structure’s complete function continuity in the critical situations, it is highly important to study its seismic behavior. Among the different analyses, the seismic analysis of the tank is highly important because by investigating the results obtained from this analysis, a useful recognition of the quality of the tank’s behavior at the time of a real earthquake can be obtained. The monoplete and quadroplete on ground elliptical tanks have been dinamicallyanalyzedunder Cape and Tabas and Manjil earthquakes simoultaneously in the longitudinal and transverse directions in various conditions of prolateness and slenderness of the tankand the maximum impulsive pressure and the maximum wave height parameters of corresponding cases have been compared with eachother in the current research. By study of the concluded diagrams, it was revealed that the reductionpercent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is higher in the more slender tanks. It also was revealed that the reductionpercent of the maximum impulsive pressure and the maximum wave height parameters due to partitioning of the tank is lower in the more prolate tanks.

Due to their lightweight, high tensile strength, and ease to install on irregular surfaces, the use of FRP systems for the repair and strengthening of reinforced concrete structures has become an accepted practice within civil engineering community and codes. Extensive research has been conducted on structural members to identify the improvement in their flexural and axial capacity due to FRP strengthening. However, the analytical and experimental studies on shear strengthening with FRP systems, especially exact determining FRP contribution, are limited. This study provides a multi-layer artificial neural network and group method of data handling approach for predicting the shear contribution of FRP in RC beams strengthened by externally bonded FRP sheets. To achieve the main purpose; ultimate strain of FRP, thickness of FRP, elastic modulus of FRP, width, spacing and angle of FRP sheet, effective depth of FRP, width and of effective depth of beam, compressive strength of concrete, and shear span to depth ratio were considered as input parameters while the shear contribution of the FRP is calculated as the target one. In order to verify the validity of the proposed models, a comparative assessment was conducted between experimental results and predicted values obtained directly from the models and existing guideline equations such as ACI 440, fib-TG9.3, and JSCE. The results indicate that the proposed models could predict the shear contribution of FRP in RC beams strengthened by FRP sheets with a good degree of precision and can be used as a confident approach for pre-design concrete beams strengthened with externally bonded U-shape FRP plates.

The use of self-sensing concrete sensors to estimate the amount of force applied or to estimate damage levels to structures as a new approach has been considered in structural health monitoring studies. In this study, the possibility of using piezoelectric concrete sensors as load or stress sensors to the concrete column has been investigated. The importance of this research in the development of smart infrastructure is based on the response of concrete sensors to conventional sensors. For this purpose, different piezoelectric concrete sensors were made with different percentages of carbon nanotubes and were subjected to dynamic loading and the appropriate sensor with appropriate sensitivity and less turbulence was obtained by adding at least 0.15% carbon nanotubes by weight of cement. In order to simulate the performance of the concrete column under external load until the failure and analysis of its behavior, based on the response of the concrete sensor, a small cubic concrete sensor with dimensions of 5 cm was made and placed in a concrete column. By loading the concrete column until the failure, the output of the sensor was monitored and the behavior of the concrete column was analyzed based on the concrete sensor response. The results showed that the concrete sensor could accurately estimate the final force that can be applied to the column up to failure. The sensor demonstrated that it could differentiate the different phases of the concrete column under the loading up to failure.

Accuracy in the design and implementation of the connections as joint elements, similar to main building elements, is of importance and each type of defects in these elements could leads to irrecoverable consequences. In this regard, gusset plate connections are a common type of connections which are of significant importance especially in structures with bracing system. Block shear is failure mechanism in these connections by which a piece of part or a block of materials in the connection fails due to the combination of tensile and shear forces. In the current study, block shear mechanism of gusset plate in welded connections is investigated using finite element simulation by ABAQUS software considering the effects of both material and geometrical nonlinearity. Also, the Effects of connection’s parameters such as welds arrangement, plate thickness, weld region length, existence and absence of transverse weld and single or double type of tension part in the behaviour of connection are studied. Results are indicating that in both single and double connections, magnitude of longitudinal weld is mainly important in the way that it could improve the connection’s strength before the formation of plastic areas. The general behavior of the joint in the two states of presence and absence of transverse weld in the tensile region is very close to each other and the level of force corresponding to the start of yield in the joint plate is almost the same in both joints. Increasing the thickness of the sheet in double joints has a greater effect on the force corresponding to the yield of the sheet, while the effect of thickness on the maximum bearing force of the joint has been almost the same in both cases.

 Bridges, as one of the most important structures, play a prominent role in the development of each country as vital vessels. In recent decades, several studies have been conducted on the seismic behavior of bridges under different earthquakes, in which the shear keys were considered as fuse-like elements to prevent collapsing of the deck on the substructure. However, an important issue that has not been addressed in these studies is the effect of site behavior on the stress response in the shear keys that is, the analysis at the earthquakes of varying frequency content is realistic and in three-dimensional terms and with the effect of soil, due to the impacts of the shear keys on the girder. In the present study, after validating a three-dimensional bridge with a valid research, and considering conditions close to reality with three-dimensional numerical modeling in ABAQUS finite element software, the response behavior in bridges and shear keys is evaluated by considering different frequency content earthquakes under conditions with and without considering soil-structure interaction.The results of this study show that the acceleration decrease in bridge structure with respect to soil-structure interaction in cohesionless soils. This rate is different for with different frequency content. Also taking into account the effects of soil-structure interaction in far field earthquakes, we see a greater reduction in stress values in shear keys than some earthquakes and structures located on bed rock. In other words, not assuming soil-structure interaction in the seismic analysis of bridges will lead to unrealistic results.

Wastes and by-products of industrial plants can be useful in road construction. One of these wastes is the slag of Ahvaz steel plant, which produces about one million tons per year. The lack of riverbeds and aggregates in country, especially in Ahvaz, is hampering construction projects and increasing construction costs in these areas. All construction projects in Ahvaz are made of non-renewable river or mountain materials. Slag is one of these materials that can be a useful replacement for river or mountain materials. The high utilization of lime-based materials for bed consolidation in road infrastructure has led this study to investigate the use of slag as a substitute for Kopal-Lime mixture in road construction. In this study, a thorough review of the use of slag as a substitute for natural materials from viewpoint of quality, time, cost and environmental protection is undertaken. It was found that the bearing strength in the saturated mixture containing 70% slag and 30% soil was increased by 62% compared to of kopal-lime mixture application with a concentration of 150 kg/m3, and 30% in the dry mix condition. The Rial estimate for project implementation as per Cost List 1398 with a mixture containing 70% slag and 30% soil was reduced by 65% compared to the Kopal-Lime mixture. The optimal mix design time is 80% less than the kopal-lime mixture. Overall, the results are remarkable from a qualitative and economic viewpoint, so the use of slag as a substitute for river materials is strongly recommended.

In this study, the mechanical properties of self-compacting lightweight green concrete were investigated by replacing copper slag as part of cement. Due to the positive effect of microsilica in this concrete, in order to reduce the grade of cement in self-compacting lightweight green concrete, a basic design without copper and microsilica slag and 7 mixed designs with 0, 5, 10, 15, 20, 25 and 30% copper slag It was provided with 10% microsilica. In order to study the properties of fresh concrete, experiments were performed on slump flow, T50, V funnel and J-ring. Also, compressive, tensile and bending strength tests were performed on hardened concrete at different ages of 7, 28 and 90 days. . Finally, microsilica has been shown to reduce concrete performance and improve compressive, tensile and flexural strengths. Copper slag also increases the performance of concrete and improves its self-compacting properties, but with increasing copper slag, the specific gravity of concrete increases. Also, the optimal percentage of copper slag replacement was 15%. The optimal mix design, with its self-compacting and lightweight properties, weighed 1871 kg / m3. Also, the 28-day compressive, tensile and flexural strengths of this mix increased by about 17%, 18% and 11% compared to the control mix.

Reinforced concrete connections are one of critical points in concrete frames due to changing in concrete characteristics in high temperatures and cyclic loads. In present study the residual capacity of concrete connections was evaluated under seismic and fire loads with push-over analysis. The ABAQUS software was used for parametric study and the experimental results were used for verification of numerical study. In present study the compressive strength of concrete and the area of longitudinal reinforcement of column are considered as variable parameters. The modeled connections were loaded under seismic loads at ambient temperature, so, the temperature analysis was done to evaluate the loading capacity, ductility, stiffness and wasted energy of model under fire situation. The results show that by increasing the compressive strength of concrete from 25 to 45 MPa, the wasted energy and stiffness of connection were increase 10% and 35%, respectively, and the ductility was decreases 8%. Also, with increasing the area of longitudinal reinforcement of column from 1% to 8%, the wasted energy and stiffness of connection were increase 190% and 50%, respectively, and the ductility was decreases 290%. The connections were stable up to 200℃, but, the lateral resistance, ductility and stiffness of connections decrease 55%,60% and 60%, respectively, at 600℃ and 80%, 80% and 340%, respectively, at 1000℃.

In historical structures, vulnerability and probable behavior of structures against stresses are very effective in Restoration action. For this reason, a correct diagnosis will be necessary for the correct conservation process for action. Attention to valuable aspects as well as accuracy in using non-destructive tests for detection in historic buildings is considered an essential issue. With this need, this paper introduces the experience of using software analysis along with field surveys in the Samiran Small Tower (Borj-e Koochak Semiran) as a Method approach for vulnerability and structural behavior analysis. The study tries to answer the question, "Given the field study and software analysis, what are the proposed preventive conservation actions for the small Samiran Tower to reduce damage?"General approach in this study is descriptive-analytical and the data collection method is shaped by library, field, and experimental studies. The analysis process has also been carried out by software with field surveys. After field investigations and determination of required parameters, and Material properties, the analysis was performed with Ansys 2018 software. Finally, according to the results of the analysis, proposed conservation action by creating a protective belt for the upper part and general actions for the other cases are presented.