• Computers and Concrete
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• v.26 no.3
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• pp.275-283
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• 2020

Reinforced concrete (RC) does not provide sufficient resistance against impacts and blast loads, and the brittle structure of RC fails to protect against fractures due to the lack of shock absorption. Investigations on improving its resistance against explosion and impact have been actively conducted on high-performance fiber-reinforced cementitious composites (HPFRCCs), such as fiber-reinforced concrete and ultra-high-performance concrete. For these HPFRCCs, however, tensile strength and toughness are still significantly lower compared to compressive strength due to their limited fiber volume fraction. Therefore, in this study, the tensile behavior of slurry-infiltrated fiber-reinforced cementitious composites (SIFRCCs), which can accommodate a large number of steel fibers, was analyzed under static and dynamic loading to improve the shortcomings of RC and to enhance its explosion and impact resistance. The fiber volume fractions of SIFRCCs were set to 4%, 5%, and 6%, and three strain rate levels (maximum strain rate: 250 s^-1) were applied. As a result, the tensile strength exceeded 15 MPa under static load, and the dynamic tensile strength reached a maximum of 40 MPa. In addition, tensile characteristics, such as tensile strength, deformation capacity, and energy absorption capacity, were improved as the fiber volume fraction and strain rate increased.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.149-152
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• 2005

In recent years, the repair of damaged reinforced concrete members strengthened by the external bonding of fiber-reinforced polymer laminates has received considerable attention. This paper investigates shear capacity of RC beams strengthened in the shear span with the Glass-Fiber and Steel-Composite Plate(GSP) experimentally. There are 2 types of strengthening method by GSP in RC beams. Test results are compared with that of each reference specimen which is not strengthened with GSP.

• Steel and Composite Structures
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• v.33 no.3
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• pp.333-346
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• 2019

Foam ceramic materials contribute to the explosion effect weakening on concrete structures, due to the corresponding excellent energy absorption ability. The blast resistance of concrete members could be improved through steel-foam ceramics as protective cladding layers. An approach for the modeling of dynamic response of steel-foam ceramic protected reinforced concrete (Steel-FC-RC) slabs under blast loading was presented with the LS-DYNA software. The orthogonal analysis (five factors with five levels) under three degrees of blast loads was conducted. The influence rankings and trend laws were further analyzed. The dynamic displacement of the slab bottom was significantly reduced by increasing the thickness of steel plate, foam ceramic and RC slab, while the displacement decreased slightly as the steel yield strength and the compressive strength of concrete increased. However, the optimized efficiency of blast resistance decreases with factors increase to higher level. Moreover, an efficient design method was reported based on the orthogonal analysis.

• International Journal of High-Rise Buildings
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• v.9 no.2
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• pp.155-166
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• 2020

To connect exterior reinforced concrete (RC) columns with the steel belt truss, the gusset plates are welded to the steel plates embedded in the RC column. Then, the concrete around an embedded plate is very likely to be damaged by the heat input from a long-time (6 to 48 hours) welding of the embedded and gusset plates at a joint between RC columns and steel belt truss. However, very few studies have assessed the concrete damage caused by the welding heat between embedded and gusset plates, and no clear onsite solution has been found. In this paper, experimental tests have been carried out on 4 full-scale specimen to analyze the effect of long-time (about 6 hours) onsite welding (1-side welding and 3-side welding) between a gusset plate and an embedded plate in high strength concrete with compressive strength of 55 MPa and 80 MPa on RC columns. The effect of the long-time welding heat of embedded and gusset plates, which are used in real high-rise building construction sites, on concrete is analyzed in terms of the following three items: 1) temperature distribution, 2) pattern and characteristics of cracks, and 3) effect of the cracks on the compressive strength of RC column. Based on the experimental results, even though the heat input up to about 150? from the long-time onsite welding on the high-strength concrete column for the joint could result in concrete cracks in a radial form, it is found that the welding cracks have no effect on the axial stiffness and strength of the concrete column.

• Steel and Composite Structures
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• v.11 no.5
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• pp.391-402
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• 2011

It is clear from the former researches on reinforced concrete filled steel tubular (RCFT) structures that RCFT structures have higher strength and deformation capacity than concrete filled steel tubular (CFT) structures. However, in the case of actual applications to large-scaled structures, the thin-walled steel tube must be used from the view point of economic condition. Therefore, in this study, compression tests of RCFT columns which were made by thin-walled steel tube or small load-sharing ratio in cooperation with high strength concrete were carried out, meanwhile corresponding tests of CFT, reinforced concrete (RC), pure concrete and steel tube columns were done to compare with RCFT. By the a series of comparison and analysis, characteristics of RCFT columns were clarified, and following conclusions were drawn: RCFT structures can effectively avoided from brittle failure by the using of reinforcement while CFT structures are damaged due to the brittle failure; with RCFT structures, excellent bearing capacity can be achieved in plastic zone by combining the thin-walled steel tube with high strength concrete and reinforcement. The smaller load-sharing ratio can made the reinforcement play full role; Combination of thin-walled steel tube with high strength concrete and reinforcement is effective way to construct large-scaled structures.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.61-64
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• 2008

Reinforced Concrete structures are constructed under the basic assumption of perfect bonding between steel and concrete. The corrosion of steel in the reinforced concrete columns results in the excessive cracks and gradual deterioration of concrete between steel and concrete. The cyclic loading test was conducted with the three corrosion rates in the laboratory. Throughout this test, it is investigated a bond behavior of reinforced concrete columns under a steel corrosion. Main variables of the test are a corrosion of steel reinforcement and a level of stress.

• Steel and Composite Structures
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• v.29 no.2
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• pp.243-256
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• 2018

This study conducts an optimization and sensitivity analysis on rectangular reinforced concrete (RC) beam using Lagrangian Multiplier Method (LMM) as programming optimization computer soft ware. The analysis is conducted to obtain the minimum design cost for both singly and doubly RC beams according to the specifications of three regulations of American concrete institute (ACI), British regulation (BS), and Iranian concrete regulation (ICS). Moreover, a sensitivity analysis on cost is performed with respect to the effective parameters such as length, width, and depth of beam, and area of reinforcement. Accordingly, various curves are developed to be feasibly utilized in design of RC beams. Numerical examples are also represented to better illustrate the design steps. The results indicate that instead of complex optimization relationships, the LMM can be used to minimize the cost of singly and doubly reinforced beams with different boundary conditions. The results of the sensitivity analysis on LMM indicate that each regulation can provide the most optimal values at specific situations. Therefore, using the graphs proposed for different design conditions can effectively help the designer (without necessity of primary optimization knowledge) choose the best regulation and values of design parameters.

• Structural Engineering and Mechanics
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• v.61 no.1
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• pp.125-142
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• 2017

Extensive research work has been performed on shear strengthening of reinforced concrete (RC) beams retrofitted with externally bonded carbon fiber reinforced polymer (CFRP) in form of strips. However, most of this research work is experimental and very scarce studies are available on numerical modelling of such beams due to truly challenging nature of modelling concrete shear cracking and interfacial interaction between components of such beams. This paper presents an appropriate model for RC beam and to simulate its cracking without numerical computational difficulties, convergence and solution degradation problems. Modelling of steel and CFRP and their interfacial interaction with concrete are discussed. Finally, commercially available non-linear finite element software ABAQUS is used to validate the developed finite element model with key tests performed on full scale T-beams with and without CFRP retrofitting, taken from previous extensive research work. The modelling parameters for bonding behavior of CFRP with special anchors are also proposed. The results presented in this research work illustrate that appropriate modelling of bond behavior of all the three types of interfaces is important in order to correctly simulate the shear behavior of RC beams strengthened with CFRP.

• Steel and Composite Structures
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• v.21 no.2
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• pp.411-427
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• 2016

While the cyclic behaviour of fiber-reinforced polymer (FRP)-confined columns is studied rather extensively, the cyclic response especially the energy dissipation of FRP-confined damaged and undamaged square RC columns is not yet fully understood. In this paper, an experimental and numerical investigation was conducted to study the cyclic behavior of two different types of Carbon FRP (CFRP)-confined square RC columns: strengthened and repaired. The main variables investigated are initial damage, confinement of CFRP, longitudinal steel reinforcement ratio. The experimental results show that lower initial damage, added confinement with CFRP and longitudinal reinforcement enhance the ductility, energy dissipation capacity and strength of the columns, decrease the stiffness and strength degradation rates of all CFRP-confined square RC columns. Two hysteretic constitutive models were developed for confined damaged and undamaged concrete and cast into the non-linear beam-column fiber-based models in the software Open System for Earthquake Engineering Simulation (OpenSees) to analyze the cyclic behavior of CFRP-confined damaged and undamaged columns. The results of the numerical models are in good agreement with the experiments.

• Computers and Concrete
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• v.22 no.2
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• pp.143-152
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• 2018

This paper deepens the finite element modeling (FEM) method to reproduce the compressive behavior of partially steel-jacketed (PSJ) RC columns by means of the Concrete Damaged Plasticity (CDP) Model available in ABAQUS software. Although the efficiency of the CDP model is widely proven for reinforced concrete columns at low confining pressure, when the confinement level becomes high the standard plasticity parameters may not be suitable to obtain reliable results. This paper deals with these limitations and presents an analytically based strategy to fix the parameters of the Concrete Damaged Plasticity (CDP) model. Focusing on a realistic prediction of load-bearing capacity of PSJ RC columns subjected to monotonic compressive loads, a new strain hardening/softening function is developed for confined concrete coupled with the evaluation of the dilation angle including effects of confinement. Moreover, a simplified efficient modeling approach is proposed to take into account also the response of the steel angle in compression. The prediction accuracy from the current model is compared with that of existing experimental data obtained from a wide range of mechanical confinement ratio.