نشریه مهندسی سازه و ساخت
سال یازدهم شماره 9 (پیاپی 86، آذر 1403)

In recent years, the use of offshore pipelines in the Persian Gulf has increased greatly. With the increase in the use of offshore pipes, the need to check the safety and the possibility of damage of these pipes during an earthquake has increased. In this research, numerical modeling of non-buried offshore gas pipelines using SAP2000 V.14 software is considered and the effect of seismic wave propagation and responses of offshore pipelines with free and fixed end conditions on different soil textures. It has been discussed and investigated in two ways lying on the sea bed and open mouth. Seismic reliability analysis of the pipeline using OpenSees software to find the reliability index (β) and the annual failure probability of the marine pipeline based on the FORM, SORM and FOSM reliability analysis methods for different seismic limit states respectively. Design level earthquake (DEQ), operational level earthquake (SEQ), maximum level earthquake (MEQ) and maximum probable earthquake (MPE) have been conducted and investigated. The results showed that in the case of free opening due to the free opening of the pipe with a length of 80 meters, the displacement caused by the seismic movements of the earth is maximum. The maximum seismic displacements of the pipeline in the state of open mouth are about 4 times compared to the state of the pipeline lying on the sea bed. In terms of the design of a marine pipeline with a free opening with a fixed end state, it is reliable in terms of operation when the annual probability of marine pipeline failure related to service conditions is less than or equal to 0.01 and the seismic reliability index β is greater or be equal to 2.The findings can be instrumental in improving the safety and reliability of offshore pipelines.

Passive control devices dissipate a significant amount of earthquake input energy and thus reduce the seismic demand for structural members. They are widely used in civil engineering due to their relatively low cost of installation, maintenance and simplicity. A slotted bolt connection type friction damper has the ability to provide more flexible performance due to frictional sliding during dynamic and static cyclic loads compared to the yielding dampers. The purpose of this research is to investigate the probabilistic approach and the seismic fragility of structures with slotted bolt connection using vertical link and compare it with the case without slotted bolt connection. In this study, by performing an incremental dynamic analysis with the help of 22 pairs of far-field earthquake records based on FEMA P-695, three types of 4, 8 and 12-story steel structures modeled in the OpenSEES software are investigated. Seismic fragility in different damage states, collapse margin ratios of the structure and also the possibility of collapse of the eccentrically bracing structure with the slotted bolted connection and without it have been discussed. The conducted research shows that the story velocity and base shear responses of the structure decreases when using slotted bolt connection. The results also indicate that the used friction damper leads to the improvement of seismic fragility and the increase of the collapse margin ratios, which can be mentioned as a 20% increase in the 12-story structure. In addition, the probability of structural failure has decreased by 35% on average compared to the eccentrically bracing structure without damper.

Predicting project time and cost prior to any operational activities and financial issues is crucial for project managers and planners. It plays a vital role in decision-making throughout the project. Therefore, a high level of risk and uncertainty in initial estimates can undermine the value of estimates during the project's stages, leading to a mismatch between the cost and time of project activities. Previous studies have investigated various methods to mitigate potential events (risks) and minimize their impact on project objectives. Various tools and techniques have also been employed to manage risks in projects. This proposed research aims to enhance the predictability of initial cost and time estimates for projects by considering the influence of potential events over time through the integration of probable events using the concept and idea of classification. The study focuses on examining the initial cost and time estimate for the construction project of the SE4 reservoir with a volume of 10,000 cubic meters in Tabriz. The initial estimate was conducted based on a three-factor civil project contract, taking into account the base price list and circular No. 4311 (General Contractual Conditions). The projected amount for the project was estimated to be 37,152,190,395 Iranian rials, with a duration of 730 days. Using the research method, the estimated project completion time was adjusted to 978 days, and the final project cost was predicted to be 54,001,959,748 Iranian rials. This difference indicates that probable events that may occur during the project execution have an impact on the cost and time estimates of the project. Therefore, by identifying probable events and assessing their impact on the project's time and cost using a classification approach, a significant improvement in the accuracy of cost and time estimates can be achieved.

One of the common techniques for enhancing the strength of existing reinforced concrete bridge beams involves adding reinforcing elements to the lower section of the beam. In the recent years, the reinforcement of concrete bridge beams is developing with the installation of precast high performance fiber reinforced cement composites, in addition to Fiber-Reinforced Polymer (FRP) sheets or strips and placed rebars near the surface. This study explores both the mechanical properties of composite cement laminates and how the presence of polymer rebars impacts these laminates. To create specimens, a total of 45 mixing designs were utilized, incorporating fibers and consumable materials. For comparison purposes, the specimens underwent various tests including four-point bending test with dimensions measuring 25×125×500 and 25×125×1700 mm, three-point bending test with dimensions measuring 40×40×160 mm, direct tension test on 8 shaped briquettes and compressive strength tests on cubic shapes measuring 40 mm. The results indicated good compliance with both direct tension and bending tests. After evaluation, the most suitable design was determined to consist of 1.8% micro steel fibers, 0.5% polyvinyl alcohol fibers, 42 kilograms of quartz powder, 28.6 kilograms calcium carbonate particles and 482 kilograms of silica fume slurry, per cubic meter of mortar. To analyze the chosen specimen, we conducted direct tension test on dogbone-shaped specimen and compressive strength test on cubic specimen measuring 100 millimeters. Adding quartz powder has a positive impact on enhancing the energy absorption capability of the laminate specimens. The use of two polymer rebars with a diameter of 8 millimeters lead to 2.3 times increase in the flexural stress tolerance. No significant difference was observed between the flexural behavior of the precast laminate under cyclic loading and the monotonic loading.

Investigating of the lateral force on structures under wind loading is very important, especially in the analysis and design of wind-sensitive structures and structures located in windy areas. In the building design regulations, the basic wind speed in each area is presented as a basic parameter for the initial estimation of the amount of load on the structures. Due to the lack of provision of the basic wind speed in the latest edition of the sixth topic of the National Building Regulations for the region of Namin city and considering the establishment of meteorological stations in the aforesaid region. In the present work, the wind speed data was investigated in terms of probabilistic distribution and the determination of the return period. The results show that the prevailing wind direction in Namin region is from the east. The maximum annual wind speed is 17.7 m/s and the average annual wind speed is 30 m/s. Also, Weibull, Log-Normal, and Gamble distribution functions have the highest compatibility with the investigated data, respectively. The basic wind speed of Ardabil station is 38.9 m/s according to the latest edition of the sixth topic of the National Building Regulations (which is the closest station to Namin city area used in the analysis and design calculations of structures under wind loading). Based on the data available in Namin city, the basic wind speed is 31.28 m/s with a return period of 50 years, and it is less than the value mentioned in the sixth topic of the National Building Regulations.

Structural engineers have always sought to design structures that can predict their performance during earthquakes. By using the performance-based design method, the structures can be examined to observe the behavior they show when dealing with the expected earthquake. Nowadays, optimization is very important in the design of structures. Because the amount of cost to implement a structure that is economical from the point of view affects the importance of this issue. In this study, the weight optimization of convergent bracing frames has been measured based on the performance-based design method. Because one of the most common methods of analysis to evaluate the seismic performance is the non-linear static analysis method, this method has been used as the basis of analysis. In this study, the objective function is considered based on the weight of the structure. The optimization problem considers the acceptance criteria for force-controlled and deformation-controlled members at desired performance levels, as well as geometric constraints. To make the optimal design possible based on the defined problem, optimizing the weight of three- and six-story concentrically braced 2D steel frames have been investigated using EVPS and EWOA algorithms. The results of the optimization show that it is possible to optimize the weight of the concentrically braced frame based on the performance-based method and using the algorithm.

The triple friction pendulum isolator is adaptable and can exhibit variable stiffness and damping in response to different earthquakes. Therefore, the need to optimize the effective parameters of this isolator to achieve the desired performance is significant. In this research, the Covariance Matrix Adaptation Evolution Strategy (CMA-ES) algorithm is used to optimize the effective parameters of the triple friction pendulum isolator to minimize the maximum relative displacement between floors and the roof acceleration in two separate optimization processes. As optimizing complex models is computationally intensive and time-consuming, substituting the actual responses of the finite element model with cost-effective surrogate models results in significant time savings. In this article, structural analysis is performed using a nonlinear model implemented in OpenSees software, making the structural optimization process time-consuming and computationally expensive. To address this challenge, the Kriging model is employed as a surrogate to replace the finite element analysis computations necessary to calculate the responses, i.e., minimizing the maximum relative displacement between floors and the roof acceleration. The optimization results using the combination of the CMA-ES algorithm and the surrogate model are compared with optimization using the genetic algorithm. The findings reveal that utilizing the surrogate model for optimization reduces relative displacement between floors by 66.39% and roof acceleration by 12.28%. Additionally, computational costs are reduced by over 84%.

Clay soils with a water content of more than 35% or close to the liquid limit are known as soft clay. These soils have an unconfined compressive strength (UCS) of less than 25 kilopascals. In order to improve the strength of these soils, additives such as cement and nanoparticles are added to them. These additives are combined with soil, which is called cemented mixed soil. Therefore, this research investigated the effect of the simultaneous addition of Nano-silica with cement on changes in UCS of soft clays with low plasticity (cl). The research considers soil with a constant water content of 40%, exceeding its liquid limit, for all samples. The changes in three factors, the cement and Nano-silica content consumed and the curing time of the specimens, were investigated as effective factors. For cement, 8%, 10%, and 12% relative to the weight of dry soil were considered. Nano-silica at eight levels from zero to 1.4% relative to the weight of dry soil and three curing times 7, 14, and 28 days were considered. A total of 72 series of specimens were made, and the unconfined compressive strength was measured. The results indicate that using nano-silica up to 1.2% in combination with cement increases the UCS by an average of about 170% after seven days, 120% after 14 days, and 48% after 28 days compared to using cement alone. Additionally, adding nano-silica led to a reduction of up to 4% in cement usage. Equations were derived based on the consumption rates of cement and nano-silica, along with the curing period, to estimate the uniaxial strength of the samples. The average difference between the estimated and measured values for all samples ranged from 1% to 3%.

One of the essential difficulties in the field of foundation construction in construction projects is the low resistance of the subsoil, the presence of voids, and the presence of water in these holes in an undesirable amount, and this is the problem in the soil of the coastal area, which is more of the type of windy sand or loose sand. and is saturated; It causes many problems for engineers. Various methods are used in soil improvement according to the project's economic, operational, and environmental conditions. Considering the high adaptability of the chemical stabilization method to the different conditions governing the projects, it is considered one of the most common ways of soil improvement. Using chemical additives such as cement is one of the most common methods of improving soil engineering properties, which geotechnical engineers often use. On the other hand, the production of this highly consumed substance causes the release of 8% of the carbon dioxide entering the atmosphere in human activities. Therefore, considering an approach to reduce cement consumption is considered essential. One of the ways to reduce cement consumption in the stabilization method is to use natural pozzolanic materials such as zeolite So that part of the cement can be replaced with these materials. Therefore, adding natural fibers such as hemp can be a suitable choice to solve this problem of chemical stabilization of soils. This research investigated the direct shear behavior of improved samples after conducting unconfined compressive strength tests to achieve the optimal percentage of sand, cement, zeolite, and hemp fiber compounds and, according to the results, adding 1% of hemp fibers with a length of 1 cm results in the best resistance properties in the stabilized samples. The highest resistance was achieved in the sample with 8% cement and replacing 30% cement with zeolite.

A CBF frame is an earthquake-resistant system used in steel structures. The brace of this system can be used in various shapes, such as X-shaped, V-shaped, elbow, etc., each of which can change the behavior of the structure. However, low plasticity, high hardness, absorption, and low seismic energy consumption are among the disadvantages of this system. A seismic design should be such that the structure remains in a linear range without damage during small earthquakes. It will suffer non-structural damage in moderate earthquakes, and it will have structural and non-structural damage during severe earthquakes, but its stability will be maintained with a proper design. The brace can also be quickly and economically modified and strengthened after the earthquake damage. The literature has shown that the use of arc or ellipse braces can act properly in transferring lateral forces and improve the behavior of the structure. In this research, therefore, four models of CBF frames with arch braces in different shapes are proposed to investigate their seismic behavior in a two-story structure. The models designed by the finite element method were subjected to lateral and cyclic loading to compare their bearing capacity, seismic behavior, ductility, seismic energy consumption, behavior coefficient, stiffness reduction, failure mode, and economic index. A summary of the results shows that the use of ellipse braces in the two-story structure can be more compatible with the purpose of this research.

Corrosion is a major challenge for the performance and health of structures. Structures in offshore, industrial, and urban settings corrode due to humidity, pollutants and various chemical agents, leading to performance reduction. plate girders have been increasingly used, and the web corrosion of such girders reduces their shear strength. This study evaluated the shear strengthening of corroded plate girders using different stiffener patterns. Corroded and non-corroded plate girders were nonlinearly analysed in ABAQUS. corrosion was modeled through thickness reduction in the numerical models. Uniform, pitting, and groove corrosion patterns as large as 25-75% of the web thickness were considered. Stiffeners were employed to strengthen the corroded plate girders. The effects of different stiffener parameters, including shape, size, and spacing, were investigated. It was found that a 50% web thickness reduction due to corrosion could decrease the shear strength of the plate girder by 47%. Pitting corrosion in the top and bottom of the web led to a 36% shear strength decline, and the top corrosion was more critical than the bottom corrosion. Flange-web disjoining due to groove corrosion diminished shear strength by 55%. Vertical stiffeners enhanced the strength of the plate girder by 54%. The results showed that T- and L-shaped stiffeners outperformed rectangular stiffeners under the same conditions.

Generally, the design of buildings must satisfy two criteria. First, under frequently occurring low to moderate earthquakes, the structure should have sufficient strength and stiffness to control deflection and prevent any structural damage. Second, under rare and severe earthquakes, the structure must have sufficient ductility to prevent collapse. In this research, the performance of a new innovative eccentrically and zipper element called Zipper Eccentrically Bracing Frame (ZEBF) is discussed and the behavior is investigated. A combination of eccentrically braced steel frames and Zipper element has been assessed and concepts of the design of defined schemes are reviewed. The ZEBF is made up of four structural elements, the zipper element, the diagonal brace element, the link element and the columns elements. The zipper and link elements are a fuse-like element that dissipates energy by the formation of plastic shear hinges or flexural hinges at its ends and midspan when the building is subjected to moderate and severe lateral loads, respectively. The knee element is a disposable beam element that can be replaced once its energy dissipation capacity is utilized. In large earthquakes, both of them contribute in dissipating energy. Three half-scale ZEBF were tested using the ATC protocol. The experimental results indicated that in this system, shear strength and cumulative dissipated energy can be significantly increased. The ultimate displacement to yield displacement ratio for the samples was 7. Also Incremental dynamic analysis has been used to evaluate the seismic capacity of the ZEBF using OpenSEES software. The structural models that represented 4, 8, and 12 story residential buildings (CBF, EBF and ZEBF) were subjected to the IDA process and their seismic performance was probabilistically quantified following the PBEE methodology. Numerical results show an improvement in the probability of collapse between 15 and 20 percent compared to other similar structural systems.