In recent years, the application of tapered frames has increased in industry. In this regard, many researchers investigate different approaches to optimizing the design procedure of the industrial tapered frame. In this paper, optimization of tapered frames by applying prestressing force has been demonstrated to minimize the weight of the whole structure. Multi-Search Method (M. S. M) based on GA has been selected as the approach to optimization. Therefore, steel tapered frame has been optimized using M. S. M on the base of AISC code. The results of the process in each step, including analysis, design, and optimization, have been verified by comparing it with analytical solution. In the aforementioned process, each member of frame has 5 optimized design variables including height of web at the end of member, thickness of web, thickness of flange, and width of flange. In addition, the optimal prestressing force is provided by the code. The place of the applied prestressing force has been determined at the bottom and the top of column. The prestressed cable is one of the practical methods for applying force. The location and amount of prestressing force are the variables of optimization. Regarding the practical approach to applying prestressing in the steel structure, the prestressing force has been applied in three locations. In the first, second, and third cases, the force has been applied to the bottom of the column, the top of the column, and the top and bottom of the column, respectively. In each case, the prestressing force as a variable will be optimized. The efficiency of applying prestressing force has been evaluated by means of examples with different geometries and spans. The obtained results indicate the effect of applying presressing force to the tapered frames. The effectiveness of this method is dependent on the location of the force applied to the span or the frame. The results show the effectiveness of this approach, particularly in the third case.

Researchers' attention has recently been focused to the measurement and tracking of prestressing force in the tendons of prestressed concrete (PC) constructions. Older structures need non-destructive testing techniques to evaluate these forces, even if modern structures are fitted with sensors to monitor prestress losses. This work presents a new approach that uses static displacement data under experimental loads to determine the real prestress force in the tendons of a prestressed concrete beam. This approach offers a more economical alternative by doing away with the requirement for destructive tests or pre-installed sensors. A genetic algorithm (GA) is created to precisely calculate the prestress force of tendons. Laboratory testing shows that the proposed method can detect prestress losses with excellent accuracy, even in the presence of intentional measurement mistakes of up to 10%.Researchers' attention has recently been focused to the measurement and tracking of prestressing force in the tendons of prestressed concrete (PC) constructions. Older structures need non-destructive testing techniques to evaluate these forces, even if modern structures are fitted with sensors to monitor prestress losses. This work presents a new approach that uses static displacement data under experimental loads to determine the real prestress force in the tendons of a prestressed concrete beam. This approach offers a more economical alternative by doing away with the requirement for destructive tests or pre-installed sensors. A genetic algorithm (GA) is created to precisely calculate the prestress force of tendons. Laboratory testing shows that the proposed method can detect prestress losses with excellent accuracy, even in the presence of intentional measurement mistakes of up to 10%.

The problem of determining the prestressing force in the tendons of prestressed concrete structures and monitoring the non-exceedance of prestressing drops is an issue that has been addressed by many researchers over the past decades and has provided methods in this field. Today, pre-installation sensors are installed in important prestressed concrete structures to monitor prestressing loss. However, due to the unpredictability of such equipment in older structures, monitoring of these forces requires destructive or non-destructive testing but is inaccurate. Therefore, in this paper, a method is presented that without the need for these sensors and destructive tests, only by measuring static displacement, is able to detect the amount of prestressing loss in the cross-sectional tendons of a prestressed concrete beam. In this regard, an algorithm in the Python program environment based on genetic algorithm as well as modeling in the finite element analysis program is provided. The numerical example presented in this research shows that the proposed algorithm detects the values ​​of prestressing loss with good accuracy even in spite of 10% of the intentional error due to measurement. In recent years, the use of prestressing methods has become much simpler and more effective, and its materials have been optimized. Today, a high percentage of structures under construction worldwide are built using this technology, and the advance has found wide applications in the construction of office buildings, residential, commercial, parking lots, sports stadiums, concrete tanks and special structures such as piers. Therefore, in recent years, for long-term monitoring of prefabricated structures, equipment and sensors sensitive to force drop, such as fiber optic sensors and FBG sensors in the construction phase are predicted and installed in the desired locations. [13] However, since the above equipment requires a lot of money and it is not possible to use them in old structures, the need for a technique that shows the amount and location of force reduction in all tendons without using them remains. Therefore, in this paper, a method is presented that, while using the simplest tools, provides the most accurate results only by measuring static displacements under the effect of various loading scenarios and using an artificial intelligence algorithm based on genetic algorithm. The proposed method is based on computer analysis and comparison of the results of two prestressed concrete beams with the same geometry, loading and arrangement of tendons. First, a specific prestressing beam is modeled in the SAP2000 analysis program and the desired prestressing forces are applied to it, and then these forces are reduced in some of the studied tendons. This deliberate change in prestressing values ​​is considered as failure and the technique presented in this mapping tries to discover the extent and location of failure of this beam. In other words, this paper is the determination of the amount of prestressing force in prestressed concrete beams in which force measuring sensors are not predicted without the need for destructive testing and only by measuring the static displacement under load. In the form of a numerical example on a prestressed concrete beam consisting of 6 steel tendons and using a genetic algorithm, it was shown that the displacement is a function of the amount of prestressing and its location and amount of reduction by the technique used. It was correctly detected with 93% accuracy when 10% of the deliberate error due to displacement field measurement was applied. As a suggestion for future work, this research will be able to be developed in the simultaneous diagnosis of prestressing reduction and beam concrete failure.

In statically indeterminate prestressed concrete structures, prestressing force produces secondary moment in addition to primary moment due to eccentricity. This condition is different from statically determinate structures where there is no secondary moment effect and the moment due to prestressing is due to primary moment only, i.e., prestressing force times eccentricity. With the presence of secondary moment, prestressing force design becomes more complex, because the secondary moment is a function of prestressing force and the geometry of the structures. In addition, considering that in general the cable profile is parabolic or another type of curves, which also occurs at continuous supports, the load balancing method may not be used. To cope with this problem moment due to prestressing force is assumed to be the prestressing force times a b coefficient. In statically determinate structures the b coefficient equals the cable eccentricity to the center of gravity of the section. Therefore, the b coefficient can be considered as a statically indeterminate eccentricity. By assigning that the moment due to prestressing force as a function of prestressing force and by considering the allowable stress requirements at top and bottom fibers, equations can be derived to compute the prestressing force in statically indeterminate structures. From the derived equations, the upper and lower bounds of prestressing force can be determined if the section satisfy the requirements. If the optimum prestressing force is needed, the difference of lower and upper bounds should be minimum. Nevertheless, the difference of lower and upper bounds can be considered as a safety level. At the end of the paper examples are presented to show the application of the proposed method.

Experimental investigations have been carried out on five specimens, out of which three were of single-draped tendon profile and two were of straight tendon profile.Rectangular RC beams of section size 150 mm X 275 mm with 4 m length were used for investigation. Crack was induced in RC beams to a limit in which strain in reinforcing steel was around 85 % of the yield strain by monotonically increased static two-point load at flexural zone. Strengthening by external prestressing was done while the member was subjected to superimposed dead load of a bridge girder, equivalent to 25 % of the calculated ultimate load of the specimen. Strengthened members were tested by monotonically increased two-point load. Role of the reinforcing steel were observed from electrical strain gauges, which were fixed throughout the length of the beams. It was observed that the ultimate load carrying capacity of strengthened members have increased 48 % and 17 % for single-draped tendon profile and straight tendon profile respectively.

Structural control mechanisms are used as a reliable and efficient methods to enhance seismic performance and stability of structures. Ensuring the integrity and stability of civil infrastructures such as marine structures, especially oil platforms exposed to difficult environmental conditions, poses challenges that engineers strive to overcome. Introducing innovative methods and improving existing system performance can significantly aid in addressing these challenges. The objective of the present research is to investigate the effect of different levels of pre-stressing on shape memory alloy wires in a passive damper based on shape memory alloy and its impact on reducing the seismic re-sponse of marine structures. For this purpose, a simplified marine structure is modeled, and a struc-tural control system with a passive damper using shape memory alloy is incorporated. The results of different scenarios after applying seven sets of scaled ground motions from far field earthquakes and time history analyses have been evaluated. The obtained results indicate that increasing the cross-sectional area of the wires and increasing their pre-stress level reduces the maximum displacement of the structure and improves the overall performance of the structural control system. Furthermore, considering three different scenarios for the frame, the influence of frame stiffness on the results has been assessed.

Concrete-encased concrete-filled steel tube (CFST) has been presented to integrate reinforced concrete (RC) and CFSTs that have been used increasingly in high-rise buildings and bridges in the world. Concrete-encased CFST exhibits higher confinement of the concrete core, high stiffness and strength, better durability and ductility, small sectional size, higher fire resistance due to the protection of the outer RC encasement compared to CFST, avoidance of local buckling and corrosion of steel tube, and easier connection with steel RC beams. On account of the insufficient research and the unknown behavior of these beam types, in this research, prestressed concrete-encased CFST (PCE-CFST) beams that incorporate CFST in the compression zone to improve the strength of concrete, and prestressed strands in the tension zone to control cracks in reinforced concrete (RC) beams are numerically investigated. The objective of this study is the finite element analysis of parameters that are not feasible to be examined through experimental specimens. Hence, the experimental study has been done to validate the nonlinear finite element modeling and a full-scale model is constructed to explore the flexural behavior of the cross-section. The model is then developed to include parameters such as the longitudinal rebar ratio, prestressed strand ratio, core concrete ratio, and the steel tube ratio indices. Based on findings, a good agreement was observed in the moment-deflection diagrams and the failure modes between the experimental and numerical results. Then the model was developed and 9 PCE-CFST beams is modeled by finite element software of ABAQUS to investigation of longitudinal rebar ratio (0. 0257, 0. 00856, 0. 00286), prestressed strand ratio (0. 00228, 0. 00912, 0. 000569), core concrete ratio (0. 0206, 0. 07799, 0. 0281), and the steel tube ratio (0. 01385, 0. 00615, 0. 000385) indices. The beam specimens were subjected to four-point loading and the parameters of bearing capacity, moment-deflection curve, energy absorption, ductility, failure mode, bending stiffness were investigated. Examination of indices revealed that as the prestressed strand ratio increases, displacement ductility, flexural stiffness and ultimate moment increase by 1. 47, 1. 06 and 3. 22 times, respectively. Further, the elastic and entire absorbed energy of cross-section escalate by 1. 04 and 3. 22 times respectively, with increasing prestressed strand ratio. Likewise, by increasing the index of longitudinal rebar ratio, flexural stiffness and ultimate moment are 1. 18 and 1. 22 folded, respectively. In addition, the elastic absorbed energy is increased by 2. 85 times as the longitudinal rebar ratio increased. As the ratios of core concrete and steel tube increase, the flexural stiffness is reduced by 5% and 6%, respectively. While, by increasing the core concrete and steel tube ratios, the ultimate moment grow by 1. 05 and 1. 29 times, respectively. The only effective index on the cross-section ductility and the entire absorbed energy is the prestressed strand ratio. The longitudinal rebar ratio has also the greatest increasing impact on the flexural stiffness and the elastic absorbed energy. Moreover, the core concrete ratio has the least effect (less than 10%) on the flexural stiffness. The prestressed strand and core concrete indices have respectively the highest and lowest escalating effects on the ultimate moment. As a consequence, an increase in the prestressed strand and longitudinal rebar ratios lead to a rise in the flexural stiffness and ultimate moment. On the contrary, an increase in the steel tube and core concrete ratios, decrease the flexural stiffness and gives a marginal increase to the ultimate moment. It was also unveiled that the failure mode of full-scale beams is flexural, and shear crack and shear capacity govern the behavior of PCE-CFST beams with shear span-to-depth ratios of less than 2. As shear span-to-depth ratio increases, that is, the shear failure mode shifts to flexural, flexural stiffness decreases, yet the ultimate bending moment increases. Additionally, a strut-and-tie model was proposed to describe the load transfer mechanism of PCE-CFST beams.

This study has been conducted to investigate the ability of prestressed concrete slabs against explosion with passive defense objectives by the structural method. In this research, one-way and two-way concrete slabs have been modeled with Abaqus finite element software. The dynamic analysis has been performed by the explicit step-by-step time history method. The non-linear plastic failure model has been used for the concrete behavior, whilst a linear model has been used for the steel and prestressed tendons. Explosive loading has been applied to the slab samples experimentally using the CONWEP model and free boundary conditions have been defined for the edges of the studied slabs. The results of the finite element model shows that the maximum stress in prestressed concrete reaches three times the stress experienced in the reinforced concrete. Also, prestressing the slab reduces the maximum deformation by about 3 cm compared to the reinforced concrete slab. The results show that the behavior of concrete against explosion is remarkably improved by prestressing. However, the optimal amount of prestressing and the distance of the tendons required to improve the slab behavior against explosion, can be calculated through more modeling. It can be said with certainty that prestressing is a good way to improve the behavior of slabs against explosion in explosion-proof defensive fortifications. The results show that the effect of slab geometry, whether it is one-way or two-way and the location of the explosion, affect the values of stress and deflection due to the explosive load.