• Journal of Mechanical Science and Technology
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• v.15 no.6
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• pp.709-719
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• 2001

In particle or short-fiber reinforced composites, cracking of reinforcements is a significant damage mode because the cracked reinforcements lose carrying capacity. This paper deals with elastic stress distributions and load carrying capacity of intact and cracked ellipsoidal inhomogeneities. Three dimensional finite element analysis has been carried out on intact and cracked ellipsoidal inhomogeneities in an infinite body under uniaxial tension and pure shear. For the intact inhomogeneity, as well known as Eshelbys solution, the stress distribution is uniform in the inhomogeneity and nonuniform in the surrounding matrix. On the other hand, for the cracked inhomogeneity, the stress in the region near the crack surface is considerably released and the stress distribution becomes more complex. The average stress in the inhomogeneity represents its load carrying capacity, and the difference between the average stresses of the intact and cracked inhomogeneities indicates the loss of load carrying capacity due to cracking damage. The load carrying capacity of the cracked inhomogeneity is expressed in to cracking damage. The load carrying capacity of the cracked inhomogeneity is expressed in terms of the average stress of the intact inhomogeneity and some coefficients. It is found that a cracked inhomogeneity with high aspect ratio still maintains higher load carrying capacity.

• Structural Engineering and Mechanics
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• v.70 no.6
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• pp.751-763
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• 2019

Steel-concrete composition is widely used in the construction due to efficient utilization of materials. The service load behavior of composite structures is significantly affected by cracking, creep and shrinkage effects in concrete. In order to control these effects in concrete slab, an efficient and novel strategy has been proposed by use of fiber reinforced concrete near interior supports of a continuous beam. Numerical study is carried out for the control of cracking, creep and shrinkage effects in composite beams subjected to service load. A five span continuous composite beam has been analyzed for different lengths of fiber reinforced concrete near the interior supports. For this purpose, the hybrid analytical-numerical procedure, developed by the authors, for service load analysis of composite structures has been further improved and generalized to make it applicable for composite beams having spans with different material properties along the length. It is shown that by providing fiber reinforced concrete even in small length near the supports; there can be a significant reduction in cracking as well as in deflections. It is also observed that the benefits achieved by providing fiber reinforced concrete over entire span are not significantly more as compared to the use of fiber reinforced concrete in certain length of beam near the interior supports in continuous composite beams.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.307-310
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• 1999

In this panel test, the toughness and post-cracking tensile strength of SFRC(Steel Fiber Reinforced Concrete) measured on 24 panels(size; 60cm $\times$ 60cm $\times$ 10cm) which are the basic characteristics than can determine the load bearing capacity of SFRC are investigated. Those values are calculated using load-deflection curves and load-absorbed energy curves. Post-cracking tensile strength of SFRC in this study are determined by yield line theory. From the test results, it is seen that the higher the volume of steel fiber is, the higher the absorbed energy is.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.900-909
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• 2002

Fibers play a role to increase the tensile strength and cracking resistance of concrete structures. The post cracking behavior must be clarified to predict cracking resistance of fiber reinforced concrete. The purpose of this study is to develop a realistic analysis method for the post cracking behavior of synthetic fiber reinforced concrete members. For this purpose, the cracked section is assumed to behave as a rigid body and the pullout behavior of single fiber is employed. A probabilistic approach is used to calculate effective number of fibers across crack faces. The existing theory is compared with test data and shows good agreement. The proposed theory can be efficiently used to describe the load-deflection behavior, moment-curvature relation, load-crack width relation of synthetic fiber reinforced concrete beams.

• Computers and Concrete
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• v.21 no.2
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• pp.117-126
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• 2018

This research investigate the behavior of reinforced normal and lightweight aggregate concrete hollow core slabs with different core shapes, shear span to effective depth (a/d). The experimental work includes testing seven reinforced concrete slabs under two vertical line loads. The dimensions of slab specimens were (1.1 m) length, (0.6 m) width and (0.12 m) thickness. The maximum reduction in weight due to aggregate type was (19.28%) and due to cross section (square and circular) cores was (17.37 and 13.64%) respectively. The test results showed that the decrease of shear span to effective depth ratio from 2.9 to 1.9 for lightweight aggregate solid slab cause an increase in ultimate load by (29.06%) and increase in the deflection value at ultimate load or the ultimate deflection by (17.79%). The use of lightweight aggregate concrete in casting solid slabs give a reduction in weight by (19.28%) and in the first cracking and ultimate loads by (16.37%) and (5%) respectively for constant (a/d=2.9).The use of lightweight aggregate concrete in casting hollow circular core slabs with constant (a/d=2.9) (reduction in weight 32.92%) decrease the cracking and ultimate loads by (12%) and (5.18%) respectively with respect to the solid slab. These slab specimens were analyzed numerically by using the finite element computer program ANSYS. Good agreements in terms of behavior, cracking load (load at first visible crack) and ultimate load (maximum value of testing load) was obtained between finite element analysis and experimental test results.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.625-633
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• 2003

For the construction of open-topped steel box girder bridges, prefabricated concrete slab could offer several advantages over cast-in-situ deck including good quality control, fast construction, and elimination of the formwork for concrete slab casting. However, precast decks without reinforcements at transverse joints between precast slabs should be designed to prevent the initiation of cracking at the joints, because the performance of the joint is especially crucial for the integrity of a structural system. Several prestressing methods are available to introduce proper compression at the joints, such as internal tendons, external tendons and support lowering after shear connection. In this paper, experimental results from a continuous composite bridge model with precast decks are presented. Internal tendons and external tendons were used to prevent cracking at the joints. Judging from the tests, precast decks in negative moment regions have the whole contribution to the flexural stiffness of composite section under service loads if appropriate prestressing is introduced. The validity of the calculation of a cracking load fur serviceability was presented by comparing an observed cracking load and the calculated value. Flexural behavior of the continuous composite beam with external prestressing before and after cracking was discussed by using the deflection and strain data.

• Korean Journal of Materials Research
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• v.12 no.2
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• pp.103-111
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• 2002

The thermally insulated underground pipelines have been used for district heating system. The sensor wire embedded in the insulation was used for monitoring the insulating resistance between the sensor wire and the pipe. The resistance measurement system detects corrosion of steel pipe under insulation. The corrosion and stress corrosion cracking(SCC) characteristics of sensor wire in synthetic ground water were investigated using the electrochemical methods and constant load SCC tests. The polarization tests were used to study the electrochemical behavior of sensor wire. The sensor wire was passivated at temperatures ranging from 25 to $95^{\circ}C$. However, the applied sensing current larger than passive current resulted in breakdown of passive film. The constant load SCC tests were performed to investigate the effects of applied current and load on the fracture behavior. Stress-corrosion cracks initiated at pits that were produced by sensing current. The growth of the pit involves a tunnelling mechanism, which leads to ductile fracture.

• Structural Engineering and Mechanics
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• v.61 no.3
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• pp.427-436
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• 2017

This paper presents an experimental and analytical investigation on the behavior of a U-shaped girder subjected to operation, cracking and ultimate loads. A full-scale destructive test was conducted on a U-shaped girder to study the cracking process, load-carrying capacity, failure mechanism and load-deformation relationships. Accordingly, the tested U-shaped girder was modeled using ANSYS and a non-linear element analysis was conducted. The investigation shows that the U-shaped girder meets the specified requirements of vertical stiffness, cracking and ultimate load capacity. Unfavorable torsional effect is tolerable during operation. However, compared with box girders, the U-shaped girder has a more transverse mechanical effect and longitudinal cracks are apt to occur in the bottom slab.

• Structural Engineering and Mechanics
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• v.12 no.4
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• pp.377-396
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• 2001

The excessive cracking of RC cantilever decks, which often requires special attention for structural engineers, is studied using a three-dimensional crack analysis model. The model is based on a fracture energy approach for analyzing cracks in concrete, and the numerical analysis is carried out using a modified load control method. The problem of excessive cracking is then studied with four different span-ratios. Based on the numerical results, the crack behavior with respect to the patterns of crack propagation, dissipation of the fracture energy, and effects on the structural integrity are discussed. The mechanisms which cause the excessive cracking are also explained.

• Steel and Composite Structures
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• v.7 no.3
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• pp.219-240
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• 2007

An analytical-numerical procedure has been presented in this paper to take into account the nonlinear effects of concrete cracking and time-dependent effects of creep and shrinkage in the concrete portion of the continuous composite beams under service load. The procedure is analytical at the element level and numerical at the structural level. The cracked span length beam element consisting of uncracked zone in middle and cracked zones near the ends has been proposed to reduce the computational effort. The progressive nature of cracking of concrete has been taken into account by division of the time into a number of time intervals. Closed form expressions for stiffness matrix, load vector, crack lengths and mid-span deflection of the beam element have been presented in order to reduce the computational effort and bookkeeping. The procedure has been validated by comparison with the experimental and analytical results reported elsewhere and with FEM. The procedure can be readily extended for the analysis of composite building frames where saving in computational effort would be very considerable.