A new method for seismic retrofitting concrete structures is proposed using an X-shaped precast prestressed concrete brace. This PPC brace is made of four precast concrete parts and middle section that are assembled and added to the existing frame. This method has the following benefits: there is no need to work with wet concrete in site or anchor and bolt to the existing frame, which may lead to a fast and economic retrofitting method. The X-shaped concrete brace was made in half size and its efficiency is confirmed. That X-shaped precast prestressed concrete brace was simulated and evaluated by computerized analysis using ABAQUS FEA modeling by authors of this paper earlier, and the proposed brace showed proper results in reducing lateral drifts and that method is considered as a proper method for seismic retrofitting. Here we are suggesting a different setup for the brace, which may lead to faster and more economic strengthening of RC structures. The new setup is omitting the middle section and suggests the brace to be used as a single diagonal. A model of this proposed method is simulated in ABAQUS FEA and the results show it is proper in reducing lateral displacements.

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.

The focus of this research is on presenting an optimized structural design for priestesses concrete sleeper type B70. In approaching this optimized design, current practices in the design of concrete sleepers, assumptions and design criteria are surveyed and then the sensitivity analysis with SAFE software is made based on 5 criteria. 40 sleepers with different dimensions are put in this analysis. Having chosen the one with the best geometrical condition among those 40 sleepers, the priestesses concrete design method is used for determining the number and the place of rebars. Finally, the designed sleeper is analyzed and a comparison between the proposed sleeper and the current B70 with regard to the structural strength and the construction costs is presented.

The sections composed of concrete and steel, which include concrete-encased concrete-filled tubes, generally have defects due to the low tensile strength of concrete. Therefore, an appropriate method was used for the combination of concrete-filled tubes (CFT) and prestressing strands which is encased in concrete. The conventional design guidelines are commonly developed for materials with normal strength thus further investigation is required to be conducted for sections with high-strength materials. In order to develop the design process, high-strength concrete and steel have been utilized in this study to examine the effects of steel and concrete strengths on the core concrete confinement, sectional size and flexural behavior of high-strength prestressed concrete-encased CFST (HS-PCE-CFST) beams. Hence, a total of thirteen HS-PCE-CFST beams were modeled via ABAQUS finite element software. The main variables include the steel tube yield strength, compressive cylinder strength of the core and outer concrete and the steel tube diameter to section width ratio. Furthermore, experimental results were employed to verify the finite element model. The bending moment, ductility, flexural stiffness and failure mode of beams are also examined. The results confirm that among the compressive strength of the outer and core concrete and the steel tube yield strength, change in the outer concrete compressive strength has a greater effect on the change of flexural parameters, also increasing the ratio of steel tube diameter to section width causes a minor increase in the ultimate bending moment and serviceability level flexural stiffness, but a major escalation in the initial flexural stiffness.

The addition of steel fibers to concrete helps improving post -cracking tensile strength and hence leads to a significant increase in shear strength of reinforced concrete beams. Using steel fiber in structural elements such as pre-cast concrete beams or prestressed beams in road and railway bridges ductility, increase the energy absorption, gives better performance in fatigue, increase shear capacity and incorporates less stirrups spacing. In this paper, the shear performance of steel fiber in monoblock priestess’s concrete sleepers is investigated. From the analyses result, equations for determination of shear capacity of steel fiber used in concrete are determined. Monoblock priestess’s concrete sleepers are in fact priestess’s concrete beams with critical loading compared to conventional concrete beams (bridge beams in road and railway), where the beams have no stirrups even in area where the prestressing is applied. According to the results when steel fibers are adde d to the Prestressed concrete beams, of shear capacity, a decrease in stirrups amount, a better crack control, and some increase in stiffness and an increase ultimate strength of such beams can be gained. Hence, it can be said that in Prestressed concrete sleepers instead of increasing the prestressing parameter (which reduces the ultimate stiffness of the sleepers), addition of fibers is useful increase the beam stiffness after cracking and to increase the ultimate shear capacity of the beams. The results of experimental study also showed that the presented formulae for calculation of shear capacity of steel fiber in concrete have been are overestimated.

Pre-stressing is becoming a most common and indispensable technique in the recent past for beams and girders in buildings and bridges. This paper presents the application of Finite Difference Method (FDM) for finding deflections in Pre-Stressed Concrete (PSC) beams with non-prismatic sections. Equations are derived for dead and live load bending moment, eccentricity, and depth at any required section. Based on these equations, it is initially established that conventional techniques cannot be adopted for finding deflections in pre-stressed concrete beams with non-prismatic cross-sections and hence FDM was adopted as an alternative. The calculated deflections using FDM are compared with those obtained from equivalent STAAD. Pro. Model and they found to be in close agreement.

Due to the large number of fire and the resulting financial and human costs, it is necessary to prevent the roof from collapsing as one of the key members of the building during a fire. Because concrete has an inherent weakness in tensile stress, cracking in the tensile area of slabs is inevitable. On the other hand, in a system of prestressed concrete joist slab system, the tensile area of the concrete is usually completely eliminated or effectively reduced, and the performance of the floor can be expected to improve under fire conditions. The critical temperature was obtained and compared in 9 samples that differed in the amount of prestressing force, strength and concrete cover as well as the span length. The thermal load was applied to the studied samples according to the ISO 834-1 standard protocol. The temperature distribution across the slab was applied uniformly and incrementally and the failure states in the model were predicted and verified with laboratory results. The results showed that the prestressing force has the greatest effect and the span length has the least effect on decreasing or increasing the critical temperature index. Changing the prestressing parameter from zero to 600 and 1120 MPa, increases the critical temperature index by 20 and 43% and changing the beam length parameter from the initial value of 4.5 m to 6 and 7.5 m, decreasing the critical temperature index by 1 and 2%, respectively. Changing the parameter of concrete cover from 20 mm to 10 and 30 mm has caused a decrease and increase of critical temperature index by 11 and 9%, respectively. Also, in all samples, the same failure mode occurred in the middle of the joist in a bending manner.