Three Dimensional Finite Element Simulation of Reinforced Concrete Beams Post-tensioned in Shear Region

Omid Kohnehpooshi,Mohd Saleh Jaafar,Jamaloddin Noorzaei,Raizal Saifulnaz Muhammad Rashid 대한토목학회 2011 KSCE JOURNAL OF CIVIL ENGINEERING Vol.15 No.6

Reinforced concrete beams are generally designed to have enough shear strength to achieve flexural capacity; however, some structural component designed may not have sufficient shear capacity to resist big forces. Therefore, shear strengthening is required to strengthen these components. Aim of this work is to propose 3D finite element formulations of reinforced concrete beams in order to investigate the structural behavior of Reinforced Concrete (RC) beams post-tensioned in the shear region. Twenty seven node lagrangian elements have been used for modeling the concrete. Bar and bond-slip between bar and concrete were modeled together by three dimensional truss-linkage elements. The steel plates which was used for strengthening and to transfer the post-tensioning stresses in shear region to the RC beam, is modeled using 8 node isoparametric plate bending element with five Degrees of Freedom (DOF) in each node. These elements have been added to the existing three dimentional finite element program. Several reinforced concrete beams strengthened or unstrengthened, have been modeled and analyzed to determine the variation of deflection, stresses,and slip between concrete and tendons. The study leads to results that show the significant effectiveness of post-tensioning in the shear region on structural behavior of reinforced concrete beams.

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.

Effect of Autoclave Curing on the Microstructure of Blended Cement Mixture Incorporating Ground Dune Sand and Ground Granulated Blast Furnace Slag

Omer Abdalla Alawad,Abdulrahman Alhozaimy,Mohd Saleh Jaafar,Farah Nora Abdul Aziz,Abdulaziz Al-Negheimish 한국콘크리트학회 2015 International Journal of Concrete Structures and M Vol.9 No.3

Investigating the microstructure of hardened cement mixtures with the aid of advanced technology will help the concrete industry to develop appropriate binders for durable building materials. In this paper, morphological, mineralogical and thermogravimetric analyses of autoclave cured mixtures incorporating ground dune sand and ground granulated blast furnace slag as partial cementing materials were investigated. The microstructure analyses of hydrated products were conducted using scanning electron microscopy (SEM), energy dispersive X ray spectroscopy (EDX), differential thermal analysis (DTA), thermo graphic analysis (TGA) and X ray diffraction (XRD). The SEM and EDX results demonstrated the formation of thin plate like calcium silicate hydrate plates and a compacted microstructure. The DTA and TGA analyses revealed that the calcium hydroxide generated from the hydration binder materials was consumed during the secondary pozzolanic reaction. Residual crystalline silica was observed from the XRD analysis of all of the blended mixtures, indicating the presence of excess silica. A good correlation was observed between the compressive strength of the blended mixtures and the CaO/SiO₂ ratio of the binder materials.

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.

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.

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.

Coupled thermal and structural analysis of roller compacted concrete arch dam by three-dimensional finite element method

Bayagoob, Khaled H.,Noorzaei, Jamaloddin,Abdulrazeg, Aeid A.,Al-Karni, Awad A.,Jaafar, Mohd Saleh Techno-Press 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.4

This paper focuses on the development, verification and application of a three-dimensional nite element code for coupled thermal and structural analysis of roller compacted concrete arch dams. The Ostour Arch dam located on Ghezel-Ozan River, Iran, which was originally designed as conventional concrete arch dam, has been taken for the purpose of verication of the nite element code. In this project, RCC technology has been ascertained as an alternative method to reduce the cost of the project and make it competitive. The thermal analysis has been carried out taking into account the simulation of the sequence of construction, environmental temperature changes, and the wind speed. In addition, the variation of elastic modulus with time has been considered in this investigation using Concard's model. An attempt was made to compare the stresses developed in the dam body five years after the completion of the dam with those of end of the construction. It was seen that there is an increase in the tensile stresses after five years over stresses obtained immediately at the end of construction by 61.3%.

Coupled thermal and structural analysis of roller compacted concrete arch dam by three-dimensional finite element method

Khaled H. Bayagoob,Jamaloddin Noorzaei,A. Abdulrazeg,Awad A. Al-Karni,Mohd Saleh Jaafar 국제구조공학회 2010 Structural Engineering and Mechanics, An Int'l Jou Vol.36 No.4

This paper focuses on the development, verification and application of a three-dimensional nite element code for coupled thermal and structural analysis of roller compacted concrete arch dams. The Ostour Arch dam located on Ghezel-Ozan River, Iran, which was originally designed as conventional concrete arch dam, has been taken for the purpose of verication of the nite element code. In this project, RCC technology has been ascertained as an alternative method to reduce the cost of the project and make it competitive. The thermal analysis has been carried out taking into account the simulation of the sequence of construction, environmental temperature changes, and the wind speed. In addition, the variation of elastic modulus with time has been considered in this investigation using Concard’s model. An attempt was made to compare the stresses developed in the dam body five years after the completion of the dam with those of end of the construction. It was seen that there is an increase in the tensile stresses after five years over stresses obtained immediately at the end of construction by 61.3%.

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.