• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.71-74
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• 2005

The increasement in the floor hight may be one of the most significant problem in the use of precast concrete double slab in the multi-story buildings. The modified double-tees including duct space at the ends of slab were considered in this study. The length and thickness of nib of modified double tee was increased to receive the uniform reaction from rectangular beam, while the original PCI dapped one to receive the point load from inverted tee beam to the leg of double tee. Shear tests were performed on the ends of the modified double tees which were designed by strut-tie model. The modified double tees generally show more ductile flexural failure in the long thickened nib. It is concluded that they show superior failure patterns than that of original dapped one with shear failure.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.511-520
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• 2012

The double split Tee connection, a type of full strength-partially restrained connection, has adequate flexural strength according to the changes in the thickness of the T-stub flange and the gauge distance of the high-strength bolts. Moreover, the double split Tee connection is designed and constructed with seismic connections that have enough ductility capacity applicable to ordinary moment frame and special moment frame by grade of steel, size of beam and column and geometric connection shape. However, such a domestic research and a proposal of a suitable design formula about the double split Tee connection are insufficient. Thus, many experimental and analytical studies are in need for the domestic application of the double split Tee connection. Therefore, this study aimed to examine and suggest feasibility of a design formula of the double split Tee connection of FEMA.

• Journal of Korean Society of Steel Construction
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• v.28 no.1
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• pp.53-64
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• 2016

The double split tee connection, a type of beam-to-column moment connection, exhibits different behavioral characteristics according to changes in the thickness of the T-stub flange, the gauge distance of the high-strength bolt, and the number and diameter of high-strength bolts. In general, the double split tee connection is idealized and designed so that a T-stub fastened to the top and bottom supports a flexural moment, and a shear tab supports a shear force. However, if the double split tee connection is applied to low-and medium-rise steel structures, the size of the beam member becomes small, and thus the shear tab cannot be bolted to the web of a beam. In this regard, this study was conducted to propose connection details to ensure that the double split tee connection with a geometric shape can display sufficient shear resisting capacity. To this end, experiments were conducted using full-scale specimens for the double split tee connection.

• Journal of Korean Society of Steel Construction
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• v.26 no.2
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• pp.133-142
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• 2014

Double split tee connection is a full strength-partial restrained connection that suitable for ordinary moment frame and special moment frame which demonstrates behavior characteristics depending on the stiffness ratio of columns and beams, changes in the geometric shape of the T-stub, number of fasteners and effect of panel zone. For the double split tee connection to ensure structurally safe behavior, it needs to exhibit sufficient strength, stiffness and ductile capacity. This study sought to investigate the effects of the moment-rotation angle relationship of the double split tee connection and to evaluate the initial rotational stiffness of the double split tee connection depending on changes in the geometric shape of the T-stub. To this end, two different double split tee connection specimens are experimented which designed to change geometric parameter values (${\alpha}^{\prime}$) of the T-stub, and a three-dimensional finite element analysis was performed.

• Journal of Korean Society of Steel Construction
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• v.28 no.2
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• pp.85-96
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• 2016

Double split tee connection has various strength, stiffness, and energy dissipation capacity according to changes of thickness of T-stub flange and gauge distance, number, and diameter of high-strength bolt. If the double split tee connection is applied to a low- or medium-rise steel structure, a shear tab can't be applied for supporting shear force because of geometrical limitation. So it is required to propose details of improved double split tee connection to support shear force as well as flexural force. This research was performed to see if enough rotational stiffness is found when the double split tee connection without shear tab which was obtained through analytic and experimental researches by Yang et al. is applied to a low- or medium-rise steel structure. Also, it was seen if the low- or medium-rise steel structure having double split tee connection without shear tab has safe structural behavior, as well as material saving effect.

• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.809-820
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• 2008

A new modified full scale double tee slabs with the length of nib plate - 1,500 mm were suggested, designed, and experimentally evaluated up to the loading of flexural failure. This slabs were composed of the tee section which was same to original PCI double tee and the plate section which was modified in a new shape, and the prestressing force was applied at the bottom of tee section only. This specimens were made from the domestic precast factory. The safety and serviceability of the modified nib plate with the dapped ends were evaluated up to the ultimate flexural strength of tee section. As the experimental loading increased, the flexural crackings developed first in the bottom of the slab and they changed to the increased flexural shear and inclined shear crackings in the nib and dapped portion of the double tees. The suggested modified double tee slabs failed in ductile above the design loading with many evenly distributed flexural crackings. The thickness of nib plate - 250 mm does not show any cracking under the service loading and show several minor flexural cracking up to the ultimate state of tee portion. The proposed specimens were satisfied with the strength and ductility requirements in the design code provisions in the tests. Additional experimental tests are required to reduce the depth and tensile reinforcement of nib plate concrete for the practical use of this system effectively.

• Journal of the Korea Concrete Institute
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• v.11 no.3
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• pp.141-152
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• 1999

Precast prestressed double-tee slab may be designed by the PCI Design Handbook. It is based on the bridge construction and is required for reorganization for the use of buildings in the domestic construction environments. Much enhanced sections are developed from the reforming process on the determined design factors in the previous experimental works on double tees. Pre-determined shape, reinforcement detail, and 5000 psi concrete strength can not be expected as the best solution for the domestic construction requirements because large amount of use on that systems are anticipated. Flexural tests are performed on four full-scale 12.5m proto-type models, "least depth double tee", which are resulted from the optimization process. Domestic superimposed live load regulation, domestic material properties which is available to product, building design requirements and economy in construction are considered as the main factors to establish. the first two sections are double tee section for 1.2 ton/$\m^2$ market live load with straight and one-point depressed strands and the second two are for 0.6 ton/$\m^2$ parking live load with those strand types. All of the specimens tested fully comply with the flexural strength requirements as specified by ACI 318-95. However, the research has shown that following improved considerations are needed for better result in practice. The locations and method of connection for the lowest bottom mild bar, connection method between precast and cast-in-place concrete, and dap-end reinforcement are need to be improved.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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• pp.57-67
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• 1999

Optimization scheme is presented for the design of precast prestressed double-tee beams used as slabs in the parking or market structures. The objective considered is defined by a function that minimizes the hight of the double-tee beam, including the prefabricated element and the concrete topping poured in a second phase. The Sequential Quadratic Programming method is adopted to solve the problem. As an example 12 double-tee beams are designed with the design loads of the current design code of our country. The results from optimization process show that at least 29cm less in overall height than that designed by PCI design handbook. The section determined from the optimization process was refined for practical considerations. A MathCad 7.0 Pro Spreadsheet was prepared to verify all ACI requirements for flexure, shear and deflections. Flexural tests are performed on four full-scale 12.5m prototype models and show that all the specimens are fully comply the flexural strength requirements as specified by ACI 318-95. The present optimization scheme can be used for wider application of the design of precast prestressed double-tee beams with different materials and configurations particularly for in a large scale or for important designs.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.99-106
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• 2001

The main objective of this study is to develop a continuity of double tee slab with two modified dap-ends to solve the problems of excessive moment, slab depth, deflection, and joint cracking in the original simply supported double tee slab systems. The modified joint is produced in a combination with two slabs with modified dap and one rectangular beam. The modified joint can be justified as following different merits. The span capacity for a design load is increased, while the deflection of the slab is decreased due to the decrease of positive moment at the center span of the slab. The joint cracking between slab and beam, which occur frequently in the original slab systems of double tee will be reduced. No more additional form work is needed to cast topping concrete for continuity. Three point loading tests are performed on the specimens with a variable of an amount of main longitudinal reinforcement to evaluate flexural and shear behavior. Following conclusions are obtained from the experimental investigation. The continuity of double tee slab effectively is provided by placing longitudinal steel reinforcement in the topping concrete over the connection, and generally leads to an increase in span capacity of double tee slabs with reduced deflection. It is more effective to control the initial cracking at the connection than that of some simply supported double tee slab systems.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.267-270
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• 2005

The section of double-tee is considered as one of the most efficient type for flexure. However, the depth of it is bigger then that of other slab systems. The story height of it is also increased because the duct space is required under the double tee in addition to their net depth. Thus, a new modified double-tees with the nib length of 1.58m was suggested in this study. The story height of this one is reduced up to 450mm by including duct space under the nib at the ends of slab. The four ends of the modified two single tees were designed by strut-tie models. Shear tests were performed on them to verify the safety. The ultimate shear strengths of non-prestressed two specimens were larger than the design shear strength by strut-tie models. They were failed in ductile with many distributed flexural crackings. However, the other prestressed two specimens showed much stiffer behaviors, less deflection. and strength than those of prestressed.