Finite element development of a Beam-column connection with CFRP sheets subjected to monotonic and cyclic loading

Arash Rahimipour,Farzad Hejazi,Ramin Vaghei,Mohd Saleh Jaafar 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.6

Beam–column joints are recognized as the weak points of reinforcement concrete frames. The ductility of reinforced concrete (RC) frames during severe earthquakes can be measured through the dissipation of large energy in beam–column joint. Retrofitting and rehabilitating structures through proper methods, such as carbon fiber reinforced polymer (CFRP), are required to prevent casualties that result from the collapse of earthquake-damaged structures. The main challenge of this issue is identifying the effect of CFRP on the occurrence of failure in the joint of a cross section with normal ductility. The present study evaluates the retrofitting method for a normal ductile beam–column joint using CFRP under monotonic and cyclic loads. Thus, the finite element model of a cross section with normal ductility and made of RC is developed, and CFRP is used to retrofit the joints. This study considers three beam–column joints: one with partial CFRP wrapping, one with full CFRP wrapping, and one with normal ductility. The two cases with partial and full CFRP wrapping in the beam–column joints are used to determine the effect of retrofitting with CFRP wrapping sheets on the behavior of the beam–column joint confined by such sheets. All the models are subjected to monotonic and cyclic loading. The final capacity and hysteretic results of the dynamic analysis are investigated. A comparison of the dissipation energy graphs of the three connections shows significant enhancement in the models with partial and full CFRP wrapping. An analysis of the load-displacement curves indicates that the stiffness of the specimens is enhanced by CFRP sheets. However, the models with both partial and full CFRP wrapping exhibited no considerable improvement in terms of energy dissipation and stiffness.

Development of a Nonlinear Conical Spring Bracing System for Framed Structures Subjected to Dynamic Load

Amir Fateh,Farzad Hejazi,Mohd Saleh Jaafar,Izian Abd. Karim 한국강구조학회 2016 International Journal of Steel Structures Vol.16 No.1

In this study, a nonlinear conical spring bracing (NCSB) system that can be applied as a lateral resistance component in framed structures was developed to mitigate the vibration effects of earthquake and wind. The NCSB device consists of two solid telescopic conical springs attached to steel wire ropes. The application of NCSB in framed structures, particularly moment-resisting steel frame (MRSF), improves the seismic behavior of the frame because of the variable action of the NCSB device. NCSB stiffness is not considerable in the low to medium vibration range compared with structural stiffness. Therefore, the inherent ductility of MRSF is unaffected because of the addition of the NCSB device to the frame. However, with its large displacement value, NCSB stiffness increases and prevents excessive displacement in structures. A mathematical model of the NCSB device that considers the effect of cable stiffness is developed and implemented in program code. Furthermore, the seismic behavior of eight types of NCSB applications in frames subjected to different earthquake accelerations is evaluated in terms of displacement, velocity, and acceleration, as well as compared with bare and brace frames. Results reveal the reduction influences of the NCSB device on framed structures. The best geometric configuration for the NCSB system is also determined by using the proposed numerical analysis.

Flexible Foundation Effect on Seismic Analysis of Roller Compacted Concrete (RCC) Dams Using Finite Element Method

Khaled Ghaedi,Farzad Hejazi,Zainah Ibrahim,Parveen Khanzaei 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.4

Recently, Roller Compacted Concrete (RCC) dams have become one of the most applicable types of dams across the globe. However,the basic challenge in analysis of RCC dams is evaluation of the actual response under earthquake excitations with considering flexiblefoundation and impounded water. For this purpose, a finite element model of RCC Dam-Reservoir-Foundation is accurately developedand dynamic time history analysis is utilized to assess the seismic responses in terms of acceleration, displacements, stresses, crackingpatterns and crack propagation by implementation of concrete damaged plasticity model. A verification model is carried out to show thework accuracy. Based on these explanations, the obtained results showed that, however, the hydrodynamic pressure due to the reservoirwater had great influence on seismic responses of the RCC dam with rigid foundation especially in terms of displacement response butoverall responses of the dam are greatly fluctuated while flexible foundation is taken into consideration

A new precast wall connection subjected to monotonic loading

Ramin Vaghei,Farzad Hejazi,Hafez Taheri,Mohd Saleh Jaafar,Abang Abdullah Abang Ali 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.17 No.1

Final construction project cost is significantly determined by construction rate. The Industrialized Building System (IBS) was promoted to enhance the importance of prefabrication technology rather than conventional methods in construction. Ensuring the stability of a building constructed by using IBS is a challenging issue. Accordingly, the connections in a prefabricated building have a basic, natural, and essential role in providing the best continuity among the members of the building. Deficiencies of conventional precast connections were observed when precast buildings experience a large induced load, such as earthquakes and other disasters. Thus, researchers aim to determine the behavior of precast concrete structure with a specific type of connection. To clarify this problem, this study investigates the capacity behavior of precast concrete panel connections for industrial buildings with a new type of precast wall-to-wall connection (i.e., U-shaped steel channel connection). This capacity behavior is compared with the capacity behavior of precast concrete panel connections for industrial buildings that used a common approach (i.e., loop connection), which is subjected to monotonic loading as in-plane and out-of-plane loading by developing a finite element model. The principal stress distribution, deformation of concrete panels and welded wire mesh (BRC) reinforcements, plastic strain trend in the concrete panels and connections, and crack propagations are investigated for the aforementioned connection. Pushover analysis revealed that loop connections have significant defects in terms of strength for in-plane and out-of-plane loads at three translational degrees of freedom compared with the U-shaped steel channel connection.

Simplified Constitutive and Damage Plasticity Models for UHPFRC with Different Types of Fiber

Doaa Talib Hashim,Farzad Hejazi,Voo Yen Lei 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.5

In this study, several simplified constitutive models and a damage plasticity model for ultra-high performance fiber reinforced concrete(UHPFRC)material with micro and hooked ends steel fibers, Bekaert Dramix 5D steel fiber, and Forta-Ferro synthetic fiber had been developed. Later, these constitutive and damage plasticity models were applied as analytical model to numerically simulate the concrete members with different fibers, and to evaluate the behavior of the concrete sections. The constitutive models for UHPFRC of three mix designs were obtained experimentally by conducting uniaxial compression and tensile tests on both cylinder and dog-bone specimens. Next, a comparison was made among the three mix designs based on the outcomes retrieved from uniaxial compression and tensile stress–strain. These results were validated by numerically analyzing three hollow circular columns via finite element method. The numerical results revealed that the proposed material model possessed appropriate tensile strainhardening behavior and uniaxial compression strengths of UHPFRC with different types of fiber. The lateral resistance responses of the tested hollow sections, which were obtained by using developed constitutive and damage plasticity models, displayed exceptional agreement with the experimental outcomes.

Optimization of the Multi-Level Spring Restrainer for Bridges by Hybrid Particle Swarm and Gravitational Search Algorithm

Mustafa Kareem Hamzah,Farzad Hejazi,Najad Ayyash 한국강구조학회 2023 International Journal of Steel Structures Vol.23 No.4

This paper proposes a new multi-level spring restrainer (MLSR) that exhibits multi stiffness performance in different levels of movement of bridge superstructure to prevent unseating during applied dynamic loads. The analytical model of the proposed MLSR was formulated and the fabricated prototype was tested using dynamic actuator. Based on the developed analytical mode, the function of MLSR device relied on 12 parameters that further complicated the design process to achieve the best performance. However, the conventional optimization techniques utilized only one or a few factors for simple systems. Therefore, a multi-objective optimization method is proposed in this study by introducing the hybridization of Particle Swarm Optimization and Gravitational Search algorithm (PSOGSA) to optimize the restrainer parameters, as well as to improve the seismic performance of bridges using the optimum design. The optimized MLSR was implemented in the bridge subjected to multi-directional ground motion and its multi-level action to prevent unseating of bridge deck when the applied excitation was evaluated. The optimization process revealed girder displacement in three directions and the number of plastic hinges decreased from 44 to 99% for the optimized design. The time history analysis disclosed that the use of optimized MLSR device decreased the structural seismic response, such as the 3D deck movements, from 79 to 90%. Next, the base shear and drift ratio of bridge bent reduced to 75 and 85% in longitudinal direction and to 72 and 90% in transverse direction, correspondingly. The outcomes signify that the proposed MLSR device and the optimization algorithm have successfully improved the bridge structure resistance against severe ground motions.

Vertical Cyclic Performance of Precast Frame with Hook-end U-shaped High-damping Rubber Joint

Kai-Siong Woon,Farzad Hejazi 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.5

High-damping rubber (HDR) has been commonly used to dissipate cyclic energy and reduce the bumping effect of a building structure. Studies on the application of HDR in precast reinforced concrete structures have mainly focused on the effects caused by lateral cyclic loads, but joints in precast structures are also highly susceptible to damage when frames are subjected to vertical cyclic loads. Therefore, this research aimed to develop a new hook-end U-shaped joint by using HDR so that the formation of cracks on precast frames could be minimized and the accumulated energy dissipation capacities could be enhanced under the actions of a vertical cyclic load. The developed joint was experimentally tested and compared with a single dowel beam-column-connected precast frame. Results revealed that the performance of the joint was similar to that of hysteresis loops and yield force. But, its maximum force and strength ratio were slightly lower than that of the control precast frame. A nonlinear 3D numerical model was also created and subjected to a vertical cyclic load to predict the behavior of the precast frame with the proposed and single dowel beam-column connections. Differences between numerical and experimental results were identified by comparing numerical data with experimental data.

Enhancing the Performance of Knee Beam-Column Joint Using Hybrid Fibers Reinforced Concrete

S. M. Iqbal S. Zainal,Farzad Hejazi,Raizal S. M. Rashid 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.3

The knee beam–column joint is a critical location in a Reinforced Concrete (RC) structure particularly when subjected to earthquake vibrations. The current structural design codes dictate the use of high amounts of steel reinforcements in the frame joint to manage large strain demands in seismic-prone regions. However, these codes could result in the congestion of steel reinforcements in the limited joint area which can consequently produce numerous construction complications. This study aims to improve the structural performance of Knee Joint (KJ) by reducing the load induced to the embedded steel reinforcements during seismic vibrations. Hence, this study attempted to develop a Hybrid Fiber Reinforced Concrete (HyFRC) by combining multiple synthetic fibers to be introduced onto KJ. Six KJ specimens were cast using five developed HyFRC materials and one Control specimen to be experimentally tested under lateral cyclic loading. The results indicated significant improvements for the HyFRC KJ specimens particularly in energy dissipation capacity, stiffness degradation rate, displacement ductility toughness, steel reinforcement strain and hysteretic behavior. A total of six Finite Element (FE) KJ models were developed using the HyFRC materials to verify the results from the experimental testing. The accuracy of the proposed FE models resulted in average percentage differences of 25.89% for peak load, 3.45% for peak load displacement and 0.18% for maximum displacements from the experimental data. In conclusion, this study developed HyFRC materials that are beneficial in providing cost-efficient alternatives to Reinforced Concrete (RC) KJ structures in areas with low to moderate level of seismic risks.

The Synergistic Effects of Different Types of Hybridized Synthetic Fibers on Concrete Post-Crack Residual Strength

S. M. Iqbal S. Zainal,Farzad Hejazi,Farah Nora Aznieta Abd. Aziz,Mohd Saleh Jaafar 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.1

The use of fibers in cement composites has been shown to improve the mechanical properties of concrete through the fiber-bridging effect, which implies the fiber’s crack-resisting property. Additionally, the combination of two or more different fibers in the concrete mixture yielded better strength than the individual fibers due to its more versatile applications. Therefore, this study was conducted to investigate the combination of multiple synthetic fibers to improve the concrete residual strength and evaluate the hybridization synergistic effect. Ferro macro-sized fiber (FF) as the primary load-bearing fiber and four different secondary synthetic microfibers comprising Ultra-Net (UN), Super-Net (SN), Econo-Net (EN), and Nylo-Mono (NM) were utilized to develop a total of 16 hybrid fiber reinforced concrete (HyFRC) combinations and the performance were compared against their single-fiber counterpart. The tensile strength, bonding power, physical form, length, and volume fraction of the fibers were measured under the ASTM C1399 test standard in order to calculate the average residual strength (ARS) of concrete in the post-cracking region as well as to assess the synergistic effect of the fiber combination. The results recorded positive fiber synergy for all specimens tested. In addition, the Ferro-Nylo, Ferro-Super, Ferro-Econo, and Ferro-Ultra hybrids improved the ARS compared to the controlled specimens by 20.41, 10.2, 7.48, and 6.12%, respectively.

Thermal Resistance of Insulated Precast Concrete Sandwich Panels

Sani Mohammed Bida,Farah Nora Aznieta Abdul Aziz,Mohd Saleh Jaafar,Farzad Hejazi,Nabilah Abu Bakar 한국콘크리트학회 2021 International Journal of Concrete Structures and M Vol.15 No.6

Many nations are already working toward full implementation of energy efficiency in buildings known as Green Building. In line with this perspective, this paper aims to develop a thermally efficient precast concrete sandwich panels (PCSP) for structural applications. Therefore, an experimental investigation was carried out to determine the thermal resistance of the proposed PCSP using Hotbox method and the results were validated using finite element method (FEM) in COMSOL Multiphysics Software. The PCSP were designed with staggered shear connectors to avoid thermal bridges between the successive layers. The staggered connectors are spaced at 200 mm, 300 mm and 400 mm on each concrete layer, while the control panel is designed with 200 mm direct shear connection. In the experimental test, four (4) panels of 500 mm × 500 mm and 150 mm thick were subjected to Hotbox Test to determine the thermal resistance. The result shows that thermal resistance of the PCSP with staggered shear connection increases with increase in spacing. The PCSP with 400 mm staggered shear connectors indicates the best thermal efficiency with a thermal resistance (R value) of 2.48 m²K/W. The thermal performance was verified by FEA which shows less than 5% error coupled with a precise prediction of surface temperature gradient. This indicates that, with conventional materials, thermal path approach can be used to develop a precast concrete building with better thermal resistant properties. Hopefully, stakeholders in the green building industry would find this proposed PCSP as an alternative energy efficient load bearing panel towards sustainable and greener buildings.