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A torque shear type high strength bolt is clamped as the pin-tail is broken by a specially designed electric wrench. However, it is uncertain that the tension is properly induced to the shank of a bolt when the pin-tail is removed from the bolt. In order to solve a problem involved in the uncertainty, this study was conducted to develop a method to identify the clamping force of high strength bolts quantitatively. The new method to identify the induced tension suggested in this study is to analyze electric energy applied to high strength bolts until the pin-tails are broken by diverse type of electric torque wrenches. Clamping force was measured and accumulated current data was obtained through various tests. Regression analysis of tension as a function of accumulated currents was conducted with various values of bolt diameter and wrench rpm. The error between the values measured by a tension meter and those estimated by a trial product of a measuring device developed in this study was 4% regardless of different parameter values. The device including algorithms to compute load based on electricity was found reliable enough to be applied to construction sites. The trial product embedded with the algorithms for different bolt diameters and electric wrench types was upgraded through three stages. The method to determine the clamping force of a high strength bolt is deemed reasonable because total energy applied to the clamping force of the bolt is the same as the electric energy accumulated by an electric torque wrench.

Concrete filled tube (CFT) system provides excellent structural performance thanks to the composite effect between the tube and the concrete. However, its closed sections impose complication on the fabrication of the column-to-beam connection and only a small number of connection methods have been developed. In square CFT column-to-beam connections, internal diaphragms reinforce the inside of the column for the loads and moments delivered from the beam. It is required to develop various connection types to secure structural capacity and concrete filling. In the process of making the square Hollow steel section (HSS), diaphragms are placed in channel members in advance and then the two channel members are welded longitudinally to produce a square HSS. It is superior to other connection types in terms of the degree of Complication in placing the internal diaphragms, economical efficiency and workability. In this study, strength formulas were suggested based on the yield line theory to evaluate the load capacity of the column-to-beam connections. For the connection of horizontal diaphragms, the strength of steel tube faces, internal diaphragms, and concrete cone failure were accumulated. For the connection of vertical perforated plates, the strength of steel tube faces, concrete cone failure, and perfobond were accumulated. Although there was a slight difference between the formula and test result, it can be used to estimate the strength of columnto- beam connections.

Top-down construction is a construction technique in which pit excavation and structure construction are conducted simultaneously. Reducing construction time and minimizing noise and vibration which affect neighboring structures, the technique is widely employed in constructing downtown structures. While H-steel columns have been commonly used as core columns, concrete filled steel tube (CFT) columns are at the center of attention because the latter have less axial directionality and greater cross-sectional efficiency than the former. When compared with circular CFT columns, square CFT columns are more easily connected to the floor structure and the area of percussion rotary drilling (PRD) is smaller. For this reason, square CFT columns are used as core columns of concrete encased and filled square (CET) columns in underground floors. However, studies on the structural behavior and concrete stress transfer of CET columns have not been conducted. Since concrete is cast according to construction sequence, checking the stress of concrete inside the core columns and the stress of covering concrete is essential. This paper presents the results of structural tests and analyses conducted to evaluate the usability and safety of CET columns in top-down construction where CFT columns are used as core columns. Parameters in the tests are loading condition, concrete strength and covering depth. The compressive load capacity and failure behavior of specimens are evaluated. In addition, 2 cases of field application of CET columns in underground floors are analyzed.

Professor, Department of Architectural Engineering, University of Seoul, Seoul, 02504, KoreaAbstract - Concrete filled steel tube system has two major advantages. First, the confinement effect of steel tube improves the compressive strength of concrete. Second, the load capacity and deformation capacity of members are improved because concrete restrains local buckling of steel tube. It does, however, involve workability problem of using stud bolts or anchor bolts to provide composite effect for larger cross-sections. While the ribs inside the columns are desirable in terms of compressive behavior, they cause the deterioration in load capacity upon in-plane deformation resulting from thermal deformation. Since the ribs are directly connected with the concrete, the deformation of the ribs accelerates concrete cracking. Thus, it is required to improve the toughness of the concrete to resist the deformation of the ribs. Welding built-up tubular square columns can secure safety in terms of fire resistance if the problem are solved. This study focuses on mixing steel fiber in the concrete to impro ve the ductility and toughness of the columns. In order to evaluate fire resistance performance, loaded heating test was conducted wit h 8 specimens. The behavior and thermal deformation capacity of the specimens were analyzed for major variables including load ratio. The reliability of heat transfer and thermal stress analysis model was verified through the comparison of the results between the test and previous study.Keywords - Fire resistance, Composite column, Steel-fiber, Heat transfer, Thermal stressNote.-Discussion open until August 31, 2016. This manuscript for this paper was submitted for review and possible publication on June 22, 2015; revised December 22, 2015; approved on January 13, 2016.Copyright ⓒ 2016 by Korean Society of Steel Construction

To accommodate growing demands on either heavy steel structures or unique buildings with irregular configurations, built-up wide-flange steel (BWS) beams are being popularly used in modern steel construction. In current fabrication practices of BWS members, high-performance steels produced in steelmaking factories under the thermo-mechanical control process (TMCP) are typically utilized to achieve proper welding performances. However, since its basic unit price is quite higher than typical hot-rolled steel materials, this study introduced a hybrid BWS section for cost saving with no performance degradation, where high-performance TMCP steel was used in flanges, and conventional hot-rolled steel was adopted in web plate. To verify the tensile performances of a hybrid BWS section with non-uniform properties, split T tension and Charpy impact tests were conducted, and flexural tests were also carried out on hybrid and homogeneous BWS beam members. On this basis, it was confirmed that the structural performance of the hybrid BWS member is comparable with that of the conventional one with a uniform section property.

Recycled aggregate is an environmentally self-sustainable solution that can reduce construction waste and replace natural aggregates. However, there is a disadvantage in concrete such as initial strength drop and long-term strength development. Therefore, the interaction effect of the two materials can be expected by filling the cyclic aggregate concrete in the CFT column. In order to develop a concrete with compressive strength of 50 MPa as a recycled aggregate, we carried out a mixing experiment and fabricated 18 specimens to confirm the compressive behavior of a RCFT (Recycled Concrete Filled Tube) column that can be applied to actual buildings. Variable is the shape and thickness of steel pipe, concrete strength and mixing ratio, and coarse aggregate and fine aggregate are all used as recycled aggregate. The optimum mixing ratio for recycled aggregate concrete to be filled in the CFT filled steel pipe was found through three concrete preliminary mixing experiments. In addition, the compression test of the RCFT column was carried out to observe and analyze the buckling shape of the CFT column. Based on the analysis of the buckling configuration and the experimental data, the load-displacement curves of the specimens were drawn and the compressive behavior was analyzed.

Slim floor system is a method for the pouring concrete after a steel formed deep deck placed on the bottom flange of steel H-beam. Recently As the demand for long span building to secure a parking area increases, the need for development of a long span deep deck without support has emerged. Accordingly, in this study, we proposed improvements to develop of form deep deck applicable to 7.5 m(net length=7.2 m) without supports, then sand loading experimental tests for six specimens were planned to verify the effect on parameters of the end continuity of spans, methods of the end continuity(rebar or cap plate), the thickness of cap plates, lateral trussed girders.

With the improvement of the quality of construction materials and the development of construction technologies, large-scale long-span steel frame buildings have been built recently. The P.E.B system using tapered members is being employed as an economically-efficient long-span structure owing to its advantage of being able to distribute stress appropriately depending on the size of sectional areas of members. However, in December 2005 and in February 2014, P.E.B buildings collapsed due to sudden loads such as snow loads and wind gusts. In this study, the design and construction of the P.E.B system in Korea were analyzed and its structural safety was evaluated using the finite element analysis program to suggest how to improve the P.E.B system in order to promote the efficient and rational application of the system.

A concentric braced steel frame is a very efficient structural system because it requires relatively smaller amount of materials to resist lateral forces. However, primarily developed as a structural system to resist wind loads based on an assumption that the structure behaves elastically, a concentric braced frame possibly experiences the deterioration in energy dissipation after brace buckling and the brittle failure of braces and connections when earthquake loads cause inelastic behavior. Consequently, plastic deformation is concentrated in the floor where brace buckling occurs first, which can lead to the rupture of the structure. This study suggests reinforcing H-shaped braces with non-welded cold-formed stiffeners to restrain flexure and buckling and resist tensile force and compressive force equally. Weak-axis reinforcing members (2 pieces) developed from those suggested in previous studies (4 pieces) were used to reinforce the H-shaped braces in an inverted V-type braced frame. Monotonic loading tests, finite element analysis and cyclic loading tests were carried out to evaluate the structural performance of the reinforced braces and frames. The reinforced braces satisfied the AISC requirement. The reinforcement suggested in this study is expected to prevent the rupture of beams caused by the unbalanced resistance of the braces.

The diagrid structural system has been in the spotlight because of its superiority in terms of its resistance to lateral forces when applied to skyscrapers. In the diagrid structural system, most columns can be eliminated because the vertical loads (gravity loads) and horizontal loads (lateral loads) are delivered simultaneously due to the triangular shape of the diagrid module. Despite this increasing interest, few studies have examined the connection shape and details, which has made it difficult to employ the system to the buildings. In this study, the structural safety of the node connections in a circular steel tube diagrid structural system, which has been considered in the Cyclone Tower in Korea (Seven stories below and fifty-one above the ground), was evaluated using finite element analysis and 4 full-scale specimens. The parameters assessed were the extended length (20, 40, and 60 mm) and thickness (40 and 50 mm)

This paper presents the experimental results for the interfacial bond behaviour between AFRP strip and steel members. The objective of this paper is to examine the interfacial behavior and to evaluate the interfacial bond stress between Aramid FRP strips and steel plates. The test variables were bond length and AFRP thickness. 18 specimens were fabricated and one-face shear type bond tests were conducted in this study. There were two types of failure mode which were debonding and delamination between AFRP strip and steel plates. From the test, the load was increased with the increasing of bond length and AFRP thickness, which was observed that maximum increase of 63 and 86% were also achieved in load with the increasing of bond length and AFRP thickness, respectively. Finally, bond and slip characteristics had the elastic bond-slip model and it was observed that bond strength and fracture energy were not affected by bond length and AFRP thickness.

CFST columns are structurally superior because the concrete inside the steel tubes prevents local buckling at the tubes and the tubes confine the concrete. And, the thickness of steel tube in CFST column has been thinner with development of high-strengh steel. The thinner the steel tube of a square CFST column is, the more local buckling is likely to occur. For this reason, we developed welded built-up square steel tube with stiffeners which are placed at the center of the tube width acts as an anchor. In this study, we conduct experimental test for three specimens of the 4m long span welded built-up square CFT column with parameters of L/D and D/t. And, the test results were compared with the analysis results by M--P Program.

Steel concentrically braced frame is an efficient system that can acquire resistance against the lateral force of buildings with the least amount of quantity. In this study is intended to proceed on the research of schemes for reinforcement by supplementing previously installed H-formed brace with non-welded cold-formed plastic stiffening materials restricting the flexure and buckling and acquire a consistent strength on the tensile and compressive force. As for the measures of supplementing previously-installed inverted V-formed braced frame, stiffening materials in the previous studies were converted to weak-axial supplementing materials to suggest a specific scheme evaluating the structural function through an experiment of members, interpretation of members, and frame-focused experiment. Reinforced brace satisfied the requirement to be prevent AISC brace from being ruptured due to imbalanced strength in the beam.

Other countries(USA, Europe) have performed the fire resistance design of buildings by the alternative performance design methods, which are based on fire engineering theories. However, in Korea, the process on the alternative fire resistance performance design has only suggested without any applications for real steel structures. Therefore, In the case of steel structures stagnant research on refractory measures face difficulties in introducing fire resistance design. In this study, first of all, Intumescent paint was analyze the thermal properties(thermal conductivity, specific heat and density). In Sequence, using the section factor by H-standard section propose of section concrete filled steel tube and hollow. finally presents a reasonable thickness Intumescent paint takes time to target performance of the proposed cross-section steel tube.

Objective Desipramine is a tricyclic antidepressant with a negative side effect of dry mouth. The Na+/H+ exchanger was suggested to be a target of desipramine in salivary gland cells. However, it is unclear whether desipramine has other targets in the salivary secretion pathway. Here, we studied the effect of desipramine on salivary Ca2+ signaling. Materials and Methods Cytosolic free Ca2+ concentration ([Ca2+]i) was determined with the fluorescent Ca2+ indicator fura-2/AM. Aquaporin translocation was analyzed by Western blotting and immunocytochemistry of confocal microscopy. Results Desipramine inhibited the carbachol- and histamine-mediated increase in cytosolic Ca2+ ([Ca2+]i) in a concentration-dependent manner. However, desipramine did not affect increases in [Ca2+]i mediated by extracellular ATP, sphingosine-1-phosphate, or thapsigargin. The adrenergic receptor blockers prazosin and propranolol did not reverse the desipramine-mediated inhibition of carbachol- and histamine-induced increases in [Ca2+]i. We also found that desipramine inhibits the increase in membrane aquaporin-5 level triggered by carbachol and histamine treatments. Conclusions These results imply that desipramine blocks muscarinic and histamine receptor-mediated Ca2+ signaling and the subsequent translocation of aquaporin-5 in human salivary gland cells, suggesting a novel mechanism for the xerogenic effects of desipramine.

As buildings are becoming larger, demand for mega-sized composite columns (over 1-meter diameter) is increased. We have developed and commercialized welded built-up CFT column (ACT Column I) since 2005 which are structurally stable and economical using cold-formed steel with rib. However, there has a limit in size of cross section (618 X 618mm) by a fabrication facilities. And due to charateristics of closed cross section, there has a limit to construction of connection of moment frame. Composite mega column (ACT Column II) has same concept of forming closed cross section. But in order to enlarge cross sectional size, thick plate is inserted between cold-formed steels. Since composite mega column can control thickness and width of thick plate, steel or composite beams can be directly attached to the connection. In this study, we propose strength formula of composite mega column to beam connections with T-shaped stiffener as internal diaphragm and verified through finite element analysis and simple tensile experiment.

This study focuses on mixing steel fiber in the concrete to improve the ductility and toughness of the columns. The purpose of the study is to evaluate the load capacity and deformation capacity associated with the amount of steel fiber and loading condition and to analyze the interplay between the steel fiber reinforced concrete and the welding built-up square tube in terms of structure and fire resistance performance. Reinforcement of concrete with steel fiber, when cross-section shape and boundary condition (load ratio) remained unchanged, improved fire resistance performance by 1.1–1.3 times. It is deemed that the area resisting thermal load increased and fire resistance performance was improved since the concrete reinforced with steel fiber restrained cracking. In addition, the fact that the cross-sections of the concrete were barely damaged indicates that load share capacity was greatly improved.