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.

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.

Accelerated construction methods are extensively used worldwide to reduce the negative impacts of bridge construction on urban traffic. These methods usually require prefabricating parts of the bridge off-site, which reduces on-site construction time and improves the quality and safety of construction. While the use of precast elements for bridge decks is relatively common, using precast elements for bridge piers is a recent development, especially in high-seismicity regions. Prefabrication of bridge piers can further expedite the construction of bridges. Moreover, the use of precast elements can be combined with a self-centering capability, through which the earthquake-induced damage and cost of post-earthquake repairs are greatly reduced. Despite a number of previous numerical and experimental studies on the behavior of precast, self-centering bridge piers, limited information is available on the selection of design parameters for such piers, and important decisions such as the prestressing force needed to achieve suitable seismic behavior remains to a large extent uncertain. This study aims to investigate the seismic behavior of concrete bridges consisting of precast self-centering piers, in which unbonded, post-tensioned tendons are used for self-centering and reinforcing steel is used to dissipate earthquake energy. A two-dimensional numerical model was developed in OpenSees to simulate the behavior of concrete bridges consisting of precast self-centering piers. The model consisted of fiber elements to model concrete and mild steel, as well as truss elements to model unbonded post-tensioning steel. The model also involved the use of zero-length sections to model the bond-slip behavior of mild steel bars. The modeling approach was validated based on experimental results available in the literature on cyclic loading of four bridge piers. To evaluate the effects of various design parameters on the behavior of precast segmental bridge piers, 9 segmental piers with different percentages of prestressing force and reinforcing steel were designed according to 2017 AASHTO LRFD Bridge Design Specifications. All piers were designed to possess similar nominal flexural capacities. The piers were then subjected to monotonic, cyclic, and dynamic time history analyses. The results showed the positive effects of prestressing in delaying cracking and reducing the residual drifts of precast bridge piers. Increasing the prestressing force ratio up to 10 percent of compressive strength of the pier cross section was observed to improve the overall seismic behavior of the structure, above which a further increase in the prestressing level may result in a diminished performance. The optimal value for the prestressing force ratio, which resulted in the most desirable behavior for cyclic and dynamic loadings was therefore found between 0.1 and 0.15. In piers with a prestressing ratio above 0.15, a decrease was observed in the area of hysteresis loops, which was accompanied by negative stiffness of the base shear versus drift curve. Moreover, the residual drift of the pier increased when prestressing ratios greater than 0.15 were used. The maximum drift of the structure was found to be insensitive to the prestressing force ratio. The results of this study are of great value for optimal design of precast, self-centering bridge piers in high-seismicity regions.

Prestressing steel has been popular in the recent past, due to the developments in the field of anti-corrosive coatings. The literature substantiates the application of technique of prestressing to steel structures both in safety and economy point of view. However, for all design calculations, the maximum allowable span for a given load carrying capacity is based on maximum deflection which is calculated by principle of superposition (considering the effect of prestress and total load individually). This paper proposes a method of arriving at expression for deflection of simply supported, prestressed homogenous steel I-beams calculated by considering the combined effect of prestressing and total load. A straight tendon configuration with an eccentric prestressing force is considered for study.

Prestressing steel has been popular in the recent past, due to the developments in the field of anti-corrosive coatings. The literature substantiates the application of technique of prestressing to steel structures both in safety and economy point of view. However, for all design calculations, the maximum allowable span for a given load carrying capacity is based on maximum deflection which is calculated by principle of superposition (considering the effect of prestress and total load individually). This paper proposes a method of arriving at expression for deflection of simply supported, prestressed homogenous steel I-beams calculated by considering the combined effect of prestressing and total load. A straight tendon configuration with an eccentric prestressing force is considered for study.