• Steel and Composite Structures
• /
• v.36 no.2
• /
• pp.163-177
• /
• 2020

Concentrically Braced Frames (CBFs) are commonly used in the construction of steel structures because of their ease of implementation, rigidity, low lateral displacement, and cost-effectiveness. However, the principal disadvantage of this kind of braced frame is the inability to provide deformation capacity (ductility) and buckling of bracing elements before yielding. This paper aims to present a novel Composite Buckling Restrained Fuse (CBRF) to be utilized as a bracing segment in concentrically braced frames that allows higher ductility and removes premature buckling. The proposed CBRF with relatively small dimensions is an enhancement on the Reduced Length Buckling Restrained Braces (RL-BRBs), consists of steel core and additional tensile elements embedded in a concrete encasement. Employing tensile elements in this composite fuse with a new configuration enhances the energy dissipation efficiency and removes the tensile strength limitations that exist in bracing elements that contain RL-BRBs. Here, the optimal length of the CBRF is computed by considering the anticipated strain demand and the low-cyclic fatigue life of the core under standard loading protocol. An experimental program is conducted to explore the seismic behavior of the suggested CBRF compare with an RL-BRB specimen under gradually increased cyclic loading. Moreover, Hysteretic responses of the specimens are evaluated to calculate the design parameters such as energy dissipation potential, strength adjustment factors, and equivalent viscous damping. The findings show that the suggested fuse possess a ductile behavior with high energy absorption and sufficient resistance and a reasonably stable hysteresis response under compression and tension.

• Nuclear Engineering and Technology
• /
• v.47 no.6
• /
• pp.756-765
• /
• 2015

Background: Fibers have been used in cement mixture to improve its toughness, ductility, and tensile strength, and to enhance the cracking and deformation characteristics of concrete structural members. The addition of fibers into conventional reinforced concrete can enhance the structural and functional performances of safety-related concrete structures in nuclear power plants. Methods: The effects of steel and polyamide fibers on the shear resisting capacity of a prestressed concrete containment vessel (PCCV) were investigated in this study. For a comparative evaluation between the shear performances of structural walls constructed with conventional concrete, steel fiber reinforced concrete, and polyamide fiber reinforced concrete, cyclic tests for wall specimens were conducted and hysteretic models were derived. Results: The shear resisting capacity of a PCCV constructed with fiber reinforced concrete can be improved considerably. When steel fiber reinforced concrete contains hooked steel fibers in a volume fraction of 1.0%, the maximum lateral displacement of a PCCV can be improved by > 50%, in comparison with that of a conventional PCCV. When polyamide fiber reinforced concrete contains polyamide fibers in a volume fraction of 1.5%, the maximum lateral displacement of a PCCV can be enhanced by ~40%. In particular, the energy dissipation capacity in a fiber reinforced PCCV can be enhanced by > 200%. Conclusion: The addition of fibers into conventional concrete increases the ductility and energy dissipation of wall structures significantly. Fibers can be effectively used to improve the structural performance of a PCCV subjected to strong ground motions. Steel fibers are more effective in enhancing the shear performance of a PCCV than polyamide fibers.

• Advances in concrete construction
• /
• v.15 no.3
• /
• pp.161-170
• /
• 2023

Ultra-high-performance concrete (UHPC) is produced using high amount of cementitious materials, very low water/cementitious materials ratio, fine-sized fillers, and steel fibers. Due to the dense microstructure of UHPC, it possesses very high strength, elasticity, and durability. Besides that, the UHPC exhibits high ductility and fracture toughness due to presence of fibers in its matrix. While the high ductility of UHPC allows it to undergo high strain/deflection before failure, the high fracture toughness of UHPC greatly enhances its capacity to absorb impact energy without allowing the formation of severe cracking or penetration by the impactor. These advantages with UHPC make it a suitable material for construction of the structural members subjected to special loading conditions. In this research work, the UHPC mixtures having three different dosages of steel fibers (2%, 4% and 6% by weight corresponding to 0.67%, 1.33% and 2% by volume) were characterized in terms of their mechanical properties including facture toughness, before using these concrete mixtures for casting the slab specimens, which were tested under high-energy impact loading with the help of a drop-weight impact test setup. The effect of fiber content on the impact energy absorption capacity and central deflection of the slab specimens were investigated and the equations correlating fiber content with the energy absorption capacity and central deflection were obtained with high degrees of fit. Finite element modeling (FEM) was performed to simulate the behavior of the slabs under impact loading. The FEM results were found to be in good agreement with their corresponding experimentally generated results.

• Steel and Composite Structures
• /
• v.16 no.5
• /
• pp.481-489
• /
• 2014

The function of carbon fibre reinforced polymer (CFRP) reinforcement in increasing the ductility of reinforced concrete (RC) deep beam is important in such shear-sensitive RC member. This paper aims to investigate the effect of CFRP-strengthening on the energy absorption of RC deep beams. Six ordinary RC deep beams and six CFRP-strengthened RC deep beams with shear span to the effective depth ratio of 0.75, 1.00, 1.25, 1.50, 1.75, and 2.00 were tested till failure in this research. An empirical relationship was established to obtain the energy absorption of CFRP-strengthened RC deep beams. The shear span to the effective depth ratio and growth of energy absorption of CFRP-strengthened deep beam were the significant factors to establish this relationship.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.11
• /
• pp.259-272
• /
• 2019

Steel-concrete single-leaf blast-resistant doors are protective structures consisting of a steel box and reinforced concrete slab. By the domestic blast-resistant doors, the structure is not designed efficiently because few studies have examined the effects of variables, such as the blast pressure, rebar ratio, and steel plate thickness on the structural behavior. In this study, the structural behavior of the doors was analyzed using the FE method, and the support rotation and ductility ratio used to classify the structural performance were reviewed. The results showed that the deflection changes more significantly when the plate thickness increases than when the rebar spacing is a variable. This is because the strain energy absorbed by the door is reduced considerably when the plate thickness increases, and as a result, the maximum deflection becomes smaller. According to a comparison of the calculated values of the support rotation and the ductility ratio, the structural performance of the doors could be classified based on the support rotation of one degree and ductility ratio of three. On the other hand, more explosion tests and analytical studies will be needed to classify the damage level.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.17 no.1
• /
• pp.114-123
• /
• 2013

This study was performed to verify the structural reinforcing effect of recycled polyethylene terephthalate (PET) fiber. In order to verify the structural reinforcing capacity of RPET fiber, recycled PET fiber added RC slab specimens were prepared to examine the flexural capacity while those of plain concrete and those of added with PP fiber, and the behavior of the specimens were also evaluated. The result shows that the compressive strength reduces as the fiber volume fraction increases, and the rate of reduction varies from 2% to 7%. The result of the flexural capacity shows that the ultimate capacity of plain specimens is the highest compare to those fiber reinforced specimens, but it has shown that specimens reinforced by 5% PET fiber has the highest energy absorption and the ductility index. In the application of PET fiber in slab specimens has shown that ductility capacity have increased where the ultimate capacity decreasing. That is the different tendency of beam specimens, which the ultimate capacity and the ductility of those have both shown the improvement compare to plain concrete specimens, which means the reinforcing effect of PET fiber in slab is less strong than in beam. Therefore, the application of PET fiber in slab structures as reinforcement needs the proper mix proportion of concrete and volume fraction of PET fiber with deep consideration of the structures.

• Structural Engineering and Mechanics
• /
• v.70 no.1
• /
• pp.67-80
• /
• 2019

Strengthening with near surface mounted carbon fibre reinforced polymers (NSM-CFRP) is a strengthening technique that have been used for several decades to increase the load carrying capacity of reinforced concrete members. In Iraq, many concrete buildings and bridges were subjected to a wide range of damage as a result of the last war and many other events. Accordingly, there is a progressive increase in the strengthening of concrete structures, bridges in particular, by using CFRP strengthening techniques. Near-surface mounted carbon fibre polymer has been recently proved as a powerful strengthening technique in which the CFRP strips are sufficiently protected against external environmental conditions especially the high-temperature rates in Iraq. However, this technique has not been examined yet under repeated loading conditions such as traffic loads on bridge girders. The main objective of this research was to investigate the effectiveness of NSM-CFRP strips in reinforced concrete beams under repeated loads. Different parameters such as the number of strips, groove size, and two types of bonding materials (epoxy resin and cement-based adhesive) were considered. Fifteen NSM-CFRP strengthened beams were tested under concentrated monotonic and repeated loadings. Three beams were non-strengthened as reference specimens while the remaining were strengthened with NSM-CFRP strips and divided into three groups. Each group comprises two beams tested under monotonic loads and used as control for those tested under repeated loads in the same group. The experimental results are discussed in terms of load-deflection behavior up to failure, ductility factor, cumulative energy absorption, number of cycles to failure, and the mode of failure. The test results proved that strengthening with NSM-CFRP strips increased both the flexural strength and stiffness of the tested beams. An increase in load carrying capacity was obtained in a range of (1.47 to 4.49) times that for the non-strengthened specimens. Also, the increase in total area of CFRPs showed a slight increase in flexural capacity of (1.02) times the value of the control strengthened one tested under repeated loading. Increasing the total area of CFRP strips resulted in a reduction in ductility factor reached to (0.71) while the cumulative energy absorption increased by (1.22) times the values of the strengthened reference specimens tested under repeated loading. Moreover, the replacement of epoxy resin with cement-based adhesive as a bonding material exhibited higher ductility than specimen with epoxy resin tested under monotonic and repeated loading.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.29 no.5A
• /
• pp.543-550
• /
• 2009

This study was performed to prove the possibility of utilizing short plastic fibers made for recycled polyethylene terephthalate (RPET) as a structural material. In order to verify the capacity of RPET fiber, it was compared with polypropylene (PP) fiber, most widely used short synthetic fiber, for fiber volume fraction of 0%, 0.5%, 0.75%, and 1.0%. To measure material properties such as compressive strength, split tensile strength, appropriate tests were performed. Also, to measure the strength and ductility capacities of reinforced concrete (RC) member casted with RPET fiber added concrete, flexural test was performed on RC beams. The results showed that compressive strength decreased, as fiber volume fraction increased. These trends are similarly observed in the tests of PP fiber added concrete specimens. Split cylinder tensile strength of RPET fiber reinforced concrete increased slightly as fiber volume fraction increased. For structural member performance, ultimate strength, relative ductility and energy absorption of RPET added RC beam are significantly larger than OPC specimen. Also, the results showed that ultimate flexural strength and ductility both increased, as fiber volume fraction increased. These trends are similarly observed in the tests of PP fiber added concrete specimens. The study results indicate that RPET fiber can be used as an effective additional reinforcing material in concrete members.

• Structural Engineering and Mechanics
• /
• v.52 no.6
• /
• pp.1177-1191
• /
• 2014

Reinforced concrete (RC) shear walls are one of the most commonly used lateral-load resisting systems in high-rise buildings. RC Parallel redundancy walls studied herein consist of two parts nested to each other. These two parts have different mechanical behaviors and energy dissipation mechanisms. In this paper, experimental studies of four 1/2-scale specimens representing this concept, which are subjected to in-plane cyclic loading, are presented and test results are discussed. Two specimens consist of a wall frame with barbell-shaped walls embedded in it, and the other two consist of a wall frame and braced walls nested each other. The research mainly focuses on the failure mechanism, strength, hysteresis loop, energy dissipation capacity and stiffness of these walls. Results show that the RC parallel redundancy wall is an efficient lateral load resisting component that acts as a "dual" system with good ductility and energy dissipation capacity. One main part absorbs a greater degree of the energy exerted by an earthquake and fails first, whereas the other part can still behave as an independent role in bearing loads after earthquakes.

• Earthquakes and Structures
• /
• v.15 no.4
• /
• pp.351-360
• /
• 2018

Energy-based methodology is utilized to design novel timber-steel hybrid core wall system. The timber-steel core wall system consists of cross laminated timber (CLT), steel columns, angled brackets and t-stub connections. The CLT wall panels are stiff and strong, and ductility is provided through the steel t-stub connections. The structural system was modelled in SAP2000 finite element program. The hybrid system is explained in detail and validated using first principles. To evaluate performance of the hybrid core system, a 7-story building was designed using both forced-based design and energy based design (EBD) approaches. Performance of the structure was evaluated using 10 earthquakes records selected for 2500 return period and seismicity of Vancouver. The results clearly served as a good example of the benefits of EBD compared to conventional forced based design approaches.