• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.365-373
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• 2016

Ultra-High-Performance Steel Fiber-Reinforced Concrete (SUPER Concrete) exhibits improved compressive and tensile strengths far superior to those of conventional concrete. These characteristics can significantly reduce the cross sectional area of the member and the anchorage strength of a headed bar is expected to be improved. In this study, the anchorage strengths of headed bars with $4d_b$ or $6d_b$ embedment length were evaluated by simulated exterior beam-column joint tests where the headed bars were used as beam bars and the joints were cast of 120 or 180 MPa SUPER Concrete. In all specimens, the actual yield strengths of the headed bars over 600 MPa were developed. Some headed bars were fractured due to the high anchorage capacity in SUPER Concrete. Therefore, the headed bar with only $4d_b$ embedment length in 120 MPa SUPER Concrete can develop a yield strength of 600 MPa which is the highest design yield strength permitted by the KCI design code. The previous model derived from tests with normal concrete and the current design code underestimate the anchorage capacity of the headed bar anchored in SUPER Concrete. Because the previous model and the current design code do not consider the effects of the high tensile strength of SUPER Concrete. From a regression analysis assuming that the anchorage strength is proportional to $(f_{ck})^{\alpha}$, the model for predicting anchorage strength of headed bars in SUPER Concrete is developed. The average and coefficient of variation of the test-to-prediction values are 1.01 and 5%, respectively.

• International Journal of Highway Engineering
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• v.8 no.1 s.27
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• pp.33-43
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• 2006

Pull-out strength of tie-bin used in pavement construction is not an issue because those are embedded in newly placed concrete slabs. However, sufficient pull-out strength should be secured in widening constructions because, in case, the tie-bars are inserted into drilled holes of the existing slabs with liquid filler. Insufficient pull-out strength will result in lowered load transfer efficiency between adjacent slabs in addition to poor serviceability and durability due to joint widening. The pull-out strength of the tie-bars installed by current method is evaluated and improved methods are proposed. The field pull-out strength obtained by the current method was only 42.7% of required strength. Its first counterproposal is using to insert the liquid filler into drilled holes and stoppers to prevent it from flowing out of the holes. However, this method was not judged to secure desired level of quality control. The second counterproposal which substitutes the existing type of the tie-bars by SL anchor bolts was judged to secure sufficient pull out-strength in addition to the quality control and constructibility.

• Land and Housing Review
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• v.2 no.1
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• pp.53-60
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• 2011

In this study, development tests varying with concrete strength, development length, and the rate of fiber mix ratio are carried out to evaluate the development characteristics of high-strength concrete member with 80MPa, and the applicability of estimated standards of development length in KCI 2007. As a result, it can be expected that minimum development length of KCI 2007 is applicable to high-strength concrete member with 80MPa. Although the mixed fiber(NY+PP) to secure fire resistance performance of high-strength concrete is included up to 0.1%, it does not affect the development characteristics.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.217-224
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• 2013

Design provisions for the development length of headed bars in ACI 318-08 include concrete compressive strength and yield strength of headed bars as design parameters but do not consider the effects of transvers reinforcement. In addition, they have very strict limitation for clear spacing and material strengths because these provisions were developed based on limited tests. In this study, splice tests using SD600 headed bars with $2d_b$ clear spacing and transverse reinforcement were conducted. Test results show that unconfined specimens failed due to prying action and bottom cover concrete prematurely spalled. The contribution of head bearing on the anchorage strength is only 15% on average implying that unconfined specimens failed before the head bearing was not sufficiently developed. Confined specimens with stirrups placed along whole splice length have enhanced strengths in bearing as well as bond because the stirrups prevented prying action and improved bond capacity. Bond failure occurred in locally confined specimens where stirrups were placed only at the ends of splice length. The stirrups at ends of splice lengths can prevent prying action but the bond capacity did not increase. From regression analysis of test results, an equation to predict anchorage strength of headed bars was developed. The proposed equation consists of bond and bearing contributions and includes transverse reinforcement index. The average ratio of tests to predictions is 1.0 with coefficient of variation of 6%.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.148-156
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• 2020

The paper is a summary of the results of the basic pullout test which is conducted to evaluate the anchorage capacity of high strength headed bars that is mechanical anchored vertically on steel fiber reinforced concrete members. The main experimental parameters are volume fraction of steel fiber, concrete strength, anchorage length, yield strength of headed bars, and shear reinforcement bar. Both sides of covering depth of the specimen are planned to double the diameter of the headed bars. The hinged point is placed at the position of each 1.5𝑙_dt and 0.7𝑙_dt around the headed bars, and the headed bars are drawn directly. As a result of pullout test experiment, concrete fracture and steel tensile rupture appear by experimental parameters. The compressive strength of concrete is 2.7~5.4% higher than that of steel fiber with the same parameters, while the pullout strength is 20.9~63.1% higher than that of steel fiber without the same parameters, which is evaluated to contribute greatly to the improvement of the anchorage capacity. The reinforcements of shear reinforcements parallel to the headed bars increased 1.7~7.7% pullout strength for steel fiber reinforced concrete, but the effect on the improvement of the anchorage capacity was not significant considering the increase in concrete strength. As with the details of this experiment, it is believed that the design formula for the anchorage length of KCI2017and KCI2012 are suitable for the mechanical development design of SD600 head bar that is perpendicular to the steel fiber reinforced concrete members.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.185-188
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• 2008

Flat plate system has structural weakness such as punching shear. Punching shear resistance can be increase by using a lager column section and effective depth, higer concrete compressive strength, and more flexural reinforcement ratio. But using a shear reinforcement is most economical, enable, workable solution in flat plate. The slab with thickness smaller than 250mm can not perform effectively due to insufficient development length of shear reinforcement in the slab. In case of proposed reinforcements, since the shear reinforcements were installed between the top bar and the bottom bar, shear elements generated slip failure before they reached yield. strength. effect of anchorage strength were effective anchorage length, concrete strength, diameter of shear element and anchorage detail. considering effect of slab thickness and concrete strength, formula of K factor propose in thin flat plate slab. by considering effect of anchorage length and concrete strength, strength of shear reinforcement will be computed correctly in thin flat plate slab.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.72-80
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• 2018

Whilst it is common to construct high-rise buildings and long-span structures in the construction and building industry, there might be a number of problems such as excessive re-bars arrangement, deterioration of concrete quality, unnecessary quantity take-off and so forth. As these types of buildings and structures are getting more popular, it is widespread to apply high-strength materials such as high-strength concrete and re-bars to sustain durability and stability. This research aims to investigate the effectiveness of the high-strength reinforcing bars on the underground parking in a rigid-frame structure. In this study, the reinforcing bars with different yield strength were applied to corroborate the usefulness and practicability of the high-strength re-bars on the underground parking in a rigid-frame structure. The test results show that the quantity of reinforcement bars is lowered, as the yield strength of the re-bars are grown in general. However, the quantity of reinforcement bars on the development and splice has a tendency to increase slightly. Despite of the increase of the development and splice, the total quantity of reinforcing bars was reduced since the increasing ration of the pure quantity is higher than the development and splice. Base on the test results, it would be possible to achieve the reduction of reinforcing bars arrangement and lowering the amount of work to be done during a construction phase. Moreover, the reduced amount of bar arrangement will make it possible to improve workability and constructability of reinforced concrete structures. Ultimately, we will be able to attain improved quality and efficiency of construction using reinforced concrete.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.111-117
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• 2019

Shear experiments were carried out to evaluate shear performance of SFRC deep beams with end-anchorage of SD600 high strength headed reinforcing tensile bars. The experimental variables include the end-anchorage methods of tensile bars (headed bar, straight bar), the end-anchorage lengths, and the presence of shear reinforcement. Specimens with a shear span ratio of 1 showed a pattern of the shear compression failure with the slope cracks progressed after the initial bending crack occurred. Specimens with end-anchorage of headed bars (H-specimens) showed a larger shear strengths of 5.6% to 22.4% compared to straight bars (NH-specimens). For H-specimens, bearing stress reached 0.9 to 17.2% of the total stress of tensile bars up to 75% of the maximum load, and reached 22.4% to 46%. This shows that the anchorage strength due to the bearing stress of headed bars has a significant effect on shear strength. The experimental shear strength was 2.68 to 4.65 times the theoretical shear strength by the practical method, and the practical method was evaluated as the safety side.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.615-622
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• 2003

The purpose of this study is to propose the more reasonable equation of bond strength of grout-filled splice sleeve. To accomplish this objective, total 60 full-sized specimens were tested under monotonic loading. The experimental variables are compressive strength of mortar, embedment length and size of reinforcing bars. Following conclusions are obtained; 1) If the adequacy of existing equations which estimate the bond strength of grout-filled splice sleeve are investigated, they underestimate the bond strength of grout-filled splice sleeve by 8-18%. Also the existing equations have a tendency to underestimate with decrease in the embedment length of reinforcing bars. 2) From the test result of bond failure, the equation which estimates the confining pressure of grout-filled splice sleeve was proposed by making multiple regression analyses of which independent variables are embedment length of reinforcing bars and compressive strength of mortar. This equation predicted the measured bond capacity of this test more accurately than existing equations and eliminated the deviation according to the embedment length of reinforcing bars.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.75-82
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• 2015

An experimental study has been carried out to examine development length effects for high strength headed deformed bars. Current design codes limit the specified yield strength of headed bars to 400 MPa. Such the limit is due to the lack of experimental studies on headed bars made of high strength materials. Thus a test program was planed with headed bars with the yield strength of 600 MPa. The threaded head type with head shapes of round plate and circular cone was selected in this study. The experimental variables were development length, number of bars, and head shape. Specimens were classified into L-type and S-type depending on the development length. The development length of L-type was computed according to the design code without considering the limit. S-type specimens had shorter development lengths than the L-type. Further classification was made depending on the shape of heads. A-types have the head shape of round plate and B-types have the shape of circular cone. Three L-type specimens were fabricated with the variable of number of bars (1, 2, and 3). Four specimens for each of SA and SB types were made with development lengths of 50%, 45%, 40%, and 35% compared with L-type. Pullout tests was carried out with 11 specimens. The test results were compared with computed strengths with the design code equations (Appendix II). Based the current studies, it can be said that high strength headed deformed bars used in this study be able to provide such strengths computed with the current design code without considering the yield strength limit.