• Transactions of Materials Processing
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• v.21 no.1
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• pp.36-41
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• 2012

Gas Assisted Injection Molding is a relatively new low-pressure injection molding technique that provides benefits such as reduced part warpage, excellent surface quality without shrink marks, greater design flexibility, etc. In the gas assisted injection molding process, the injected pressurized nitrogen gas flows through designed gas channels and forms hollow sections within the part. However, due to the characteristics of the gas, the design of the gas channels which are the paths for the injected gas is important in order to avoid defects such as gas blowout, fingering, etc. Therefore, in this study, the gas channel design for gas assisted injection molding of exterior display panels was conducted by examining the results of three CAE analyses. The designed gas channel was verified by conducting tryouts using a 450 ton injection molding machine with 3-stage pressure controlled gas kit. In addition, the hollow shapes which were formed by the gas with the installed gas channels were examined by examining the cross sections of the prototypes that were produced. As a result, it was found that exterior display panels can be produced without any defect by applying the gas assisted injection molding technique.

• Steel and Composite Structures
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• v.5 no.6
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• pp.459-484
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• 2005

In recent years, the use of steel tube confined concrete (STCC) columns has been the interests of many structural engineers. The present study is an attempt to study the monotonic and cyclic behaviours of STCC columns. For the monotonic behaviours, a series of tests on STCC stub columns (twenty one), and beam-columns (twenty) were carried out. The main parameters varied in the tests are: (1) column section types, circular and square; (2) tube diameter (or width) to thickness ratio, from 40 to 162, and (3) load eccentricity ratio (e/r), from 0 to 0.5. For the cyclic behaviours, the test parameters included the sectional types and the axial load level (n). Twelve STCC column specimens, including 6 specimens with circular sections and 6 specimens with square sections were tested under constant axial load and cyclically increasing flexural loading. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes. It was found that STCC columns exhibit very high levels of energy dissipation and ductility, particularly when subjected to high axial loads. Generally, the energy dissipation ability of the columns with circular sections was much higher than those of the specimens with square sections. Comparisons are made with predicted column strengths and flexural stiffness using the existing codes such as AIJ-1997, AISCLRFD- 1994, BS5400-1979 and EC4-1994.

• Steel and Composite Structures
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• v.6 no.1
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• pp.71-85
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• 2006

This paper presents the results of a series of tests carried out on cold-formed steel rectangular hollow and concrete infilled beam to column connections and frames. A stub column was chosen such that overall buckling does not influence the connection behaviour. The beam chosen was a short-span cantilever with a concentrated load applied at the free end. The beam was connected to the columns along the strong and weak axes of columns and these connections were tested to failure. Twelve experiments were conducted on cold-formed steel direct welded tubular beam to column connections and twelve experiments on connections with concrete infilled column subjected to monotonic loading. In all the experiments conducted, the stiffness of the connection, the ductility characteristics and the moment rotation behaviour were studied. The dominant mode of failure in hollow section connections was chord face yielding and not weld failure. Provision of concrete infill increases the stiffness and the ultimate moment carrying capacity substantially, irrespective of the axis of loading of the column. Weld failure and bearing failure due to transverse compression occurred in connections with concrete infilled columns. Six single-bay two storied frames both with and without concrete infill, and columns loaded along the major and minor axes were tested to failure. Concentrated load was applied at the midspan of first floor beam. The change in behaviour of the frame due to provision of infill in the column and in the entire frame was compared with hollow frames. Failure of the weld at the junction of the beam occurred for frames with infilled columns. Design expressions are suggested for the yielding of the column face in hollow sections and bearing failure in infilled columns which closely predicted the experimental failure loads.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.3
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• pp.51-65
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• 2009

The seismic design concept of RC bridges is to attain the proper ductility of piers, yielding a ductile failure mechanism. Therefore, seismic design force for moment is determined by introducing a response modification factor (R), and lateral reinforcements to confine core concrete are specified in the current design code. However, these design provisions have irrationality, which results in excessive amounts of lateral reinforcements for columns in Korea, which are generally designed with large sections. To improve on these provisions, a new design method based on seismic performance has been proposed. To apply this to hollow sectional columns, however, further investigations and improvements must be performed, due to the different seismic behaviors and confinement effects. In this study, hollow sectional columns with different lap-splice of longitudinal bars and lateral reinforcements have been tested. Seismic characteristics and performance were investigated quantitatively. These research results can be used to derive a performance-based design for hollow sectional columns.

• Steel and Composite Structures
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• v.46 no.6
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• pp.793-804
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• 2023

In this study, cyclic loading tests were conducted to assess the seismic performance of cast-in-place (CIP) concrete-filled hollow core precast concrete columns (HPCC) constructed using steel ducts and rubber tubes. The outer shells of HPCC, with a hollow ratio of 47%, were fabricated using steel ducts and rubber tubes, respectively. Two combinations of shear studs & long threaded bars or cross-deformed bars & V-ties were employed to ensure the structural integrity of the old concrete (outer shell) and new CIP concrete. Up to a drift ratio of 3.8%, the hysteresis loop, yielding stiffness, dissipated energy, and equivalent damping ratio of the HPCC specimens were largely comparable to those of the solid columns. Besides the similarities in cyclic load-displacement responses, the strain history of the longitudinal bars and the transverse confinement of the three specimens also exhibited similar patterns. The measured maximum moment exceeded the predicted moment according to ACI 318 by more than 1.03 times. However, the load reduction of the HPCC specimen after reaching peak strength was marginally greater than that of the solid specimen. The energy dissipation and equivalent damping ratios of the HPCC specimens were 20% and 25% lower than those of the solid specimen, respectively. Taking into account the overall results, the structural behavior of HPCC specimens fabricated using steel ducts and rubber tubes is deemed comparable to that of solid columns. Furthermore, it was confirmed that the two combinations for securing structural integrity functioned as expected, and that rubber air-tubes can be effectively used to create well-shaped hollow sections.

• Steel and Composite Structures
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• v.19 no.4
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• pp.877-895
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• 2015

Connections to circular hollow steel sections (CHS) are considered one of the most complex and time consuming connections in steel construction. Such connections are usually composed of gusset plates welded to the outside of the steel tube or penetrating the steel tube. Design guides, accounting for the effect of connection configuration on the strength of the connection, are not present. This study aims to investigate, through experimental testing and a parametric study, the influence of connection configuration on the strength of one sided branch plate-to-CHS members. A notable effect was observed on the behavior of the connections due to its detailing changes with respect to capacity, failure mode, ductility, and stress distribution. A parametric study is performed using the calibrated analytical model to include a wider range of parameters. The study involves 26 numerical analyses of finite element models including parameters of the diameter-to-thickness (D/t) ratio, length of gusset plate, and connection configuration. Accordingly, a modification to the formulas provided by the current design recommendations was suggested to include connection configuration effects for the one sided branch plate-to-CHS members.

• International Journal of High-Rise Buildings
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• v.7 no.4
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• pp.313-325
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• 2018

Concrete-filled steel tubular (CFST) members are commonly used as composite columns in modern construction. However, the current guidelines for members' fire design (EN1994-1-2) have been proved to be unsafe in case the relative slenderness is higher than 0.5. In addition, the simplified design methods of Eurocode 4 are limited to circular and square CFST columns, while in practice columns with rectangular and elliptical hollow sections are being increasingly used because of their architectural aesthetics. In the last years a large experimental research has been carried out at Coimbra University on the topic. They have been tested concrete filled circular, square, rectangular and elliptical hollow columns with restrained thermal elongation. Some parameters such as the slenderness, the type of cross-section geometry as well as the axial and rotational restraint of the surrounding structure to the column have been tested in order to evaluate their influence on the fire resistance of such columns. In this paper it is evaluated the influence of the boundary conditions (pin-ended and semi-rigid end-support conditions) on the behavior of the columns in case of fire. In these tests it could not be seen a marked effect of the tested boundary conditions but it is believed that the increasing of rotational stiffness increases the fire resistance of the columns.

• Steel and Composite Structures
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• v.15 no.2
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• pp.131-150
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• 2013

This paper presents the experimental results of axially loaded stub columns of slender steel hollow square section (SHS) strengthened with carbon fiber reinforced polymers (CFRP) sheets. 9 specimens were fabricated and the main parameters were: width-thickness ratio (b/t), the number of CFRP ply, and the CFRP sheet orientation. From the tests, it was observed that two sides would typically buckle outward and the other two sides would buckle inward. A maximum increase of 33% was achieved in axial-load capacity when 3 layers of CFRP were used to wrap HSS columns of b/t = 100 transversely. Also, stiffness and ductility index (DI) were compared between un-retrofitted specimens and retrofitted specimens. Finally, it was shown that the application of CFRP to slender sections delays local buckling and subsequently results in significant increases in elastic buckling stress. In the last section, a prediction formula of the ultimate strength developed using the experimental results is presented.

• Steel and Composite Structures
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• v.10 no.6
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• pp.489-500
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• 2010

The rigid connections of I-beams to Rectangular Hollow Sections (RHS) in steel structures usually behave as semi-rigid connection. This behavior is directly related to the column face deformation. The deformation in the wall of RHS column in the connection zone causes a relative rotation between beam end and column axis, which consequently reduces the rigidity of beam-column connection. In the present paper, the percentages of connection rigidity reduction for serviceability conditions are evaluated by using the finite element analysis. Such percentages for RHS columns without internal stiffeners are considerable, and can be calculated from presented graphs.

• Steel and Composite Structures
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• v.5 no.1
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• pp.49-70
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• 2005

This paper reports on finite element analysis techniques that may be applied to the study of circular hollow structural sections and related bearing connection geometries. Specifically, a connection detail involving curved steel saddle bearings and a Structural Tee (ST) connected directly to a large-diameter Hollow Structural Section (HSS) truss chord, near its open end, is considered. The modeling is carried out using experimentally verified techniques. It is determined that the primary mechanism of failure involves a flexural collapse of the HSS chord through plastification of the chord wall into a well-defined yield line mechanism; a limit state for which a shell-based finite element model is well-suited to capture. It is also found that classical metal plasticity material models may be somewhat limited in their applicability to steels in fabricated tubular members.