مجله مهندسی زیر ساخت های حمل و نقل
سال دوم شماره 1 (پیاپی 5، بهار 1395)

The significant problem with reinforced concrete rigid-framed railway bridges can be insufficient ductility due to shortage of transverse reinforcement in the joint region and also lack of embedded length of the beam reinforcements within this region. The investigations of such structures, based on current standard codes, approve the improper efficiency under severe earthquakes. The objective of this study was to investigate the seismic behavior of deficient reinforced concrete exterior beam-column joints in bridges before and after retrofitting with precast HPFRCC (High performance fiber reinforced Cementitious Composite) panels. In the first part of the study, mechanical properties of HPFRCC panels having different ratios of Polypropylene and hooked end steel fibers have been determined by compression and four-point flexural tests. In the second part of the study, behavior of the HPFRCC panels in retrofitting of beam-column joints of the bridges has been modeled using the results of the first part of the study. After validation, by using a finite element software, the nonlinear behavior of reinforced concrete beam-column joints, which have been designed based on criteria for railway bridges, has been evaluated. In the present resaerch, three types of beam–column joints are modeled and investigated. Results of the first part of the study reveald that adding fibers can significantly increase the tensile strength of the specimens and also the toughness mechanisms, such as bridging of the fibers, can dissipate energy, decrease brittle failure and also cause ductile behavior of the load-deflection curve after the peak load in fiber reinforced composites. Moreover, the analytical results of the second part of the study showed that such high performance materials can enhance bearing capacity and ductility of the joints. Behavior of the exterior beam-column joints, retrofitted with HPFRCC panels, have caused an increase in ductility, lateral strength and drift rather than reference joint specimen which is fully casted with normal concrete nearly 93% , 45% and 102% , respectively.

Strengthening of poor and improper soils, in order to be utilized in civil engineering projects, for fabricating a soil with ideal engineering properties, is called stabilization and reinforcement. Soil stabilization is used for various purposes such as prevention of surface erosion, improvement of poor subgrades, controlling of shifting soils, rehabilitation of base layers and retrieving of old paths. Today, because of weaknesses such as poor strength and long duration for curing with common stabilizers (lime and cement), the attitude for finding new materials which can improve these deficiencies has increased. In this research, a sandy soil, a petrochemical material called epoxy resin (as stabilizer), and also a fiber (as soil reinforcing agent) were used to evaluate their effects on soil resistance-parameters. The behavior of stabilized soil in compression and shear was determined in this project. Results of the tests revealed that compression and tensile strengths of stabilized soil with epoxy resin were increased significantly; while the strengths of the sandy soil without epoxy were too weak. By addition of fiber to the soil samples, the soil compression strength was not increased; whereas, it has profound effect to promote tensile strength. Also, soil samples containing fiber showed more deformation. This means that they absorb more energy under loading to reach the rupture stage.