• Steel and Composite Structures
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• 제21권2호
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• pp.323-342
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• 2016

To study the effect of collar-plate reinforcement on the static strength of tubular T-joints under axial loading, fundamental research work is carried out from both experimental test and finite element (FE) simulation. Through experimental tests on 7 collar-plate reinforced and 7 corresponding un-reinforced tubular T-joints under axial loading, the reinforcing efficiency is investigated. Thereafter, the static strengths of the above 14 models are analyzed by using FE method, and it is found that the numerical results agree reasonably well with the experimental data to prove the accuracy of the presented FE model. Additionally, a parametric study is conducted to analyze the effect of some geometrical parameters, i.e., the brace-to-chord diameter ratio ${\beta}$, the chord diameter-to-chord wall thickness ratio $2{\gamma}$, collar-plate thickness to chord wall thickness ratio ${\tau}_c$, and collar-plate length to brace diameter ratio $l_c/d_1$, on the static strength of a tubular T-joint. The parametric study shows that the static strength can be greatly improved by increasing the collar-plate thickness to chord wall thickness ratio ${\tau}_c$ and the collar-plate length to brace diameter ratio $l_c/d_1$. Based on the numerical results, parametric equations are obtained from curving fitting technique to estimate the static strength of a tubular T-joint with collar-plate reinforcement under axial loading, and the accuracy of these equations is also evaluated from error analysis.

• Steel and Composite Structures
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• 제2권1호
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• pp.35-50
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• 2002

A series of tests on simple-welded plate specimens (SWPS) and T-stub tension specimens simulating some of the joint details in moment frame connections were conducted in this investigation. The effects of weld strength mismatch and weld metal toughness on structural behavior of these specimens were considered under both static and dynamic loading conditions. Finite element analyses were performed by taking into account typical weld residual stress distributions and weld metal strength mismatch conditions to facilitate the interpretation of the test results. The major findings are as follows: (a) Sufficient specimen size requirements are essential in simulating both load transfer and constraint conditions that are relevant to moment frame connections, (b) Weld residual stresses can significantly elevate stress triaxiality in addition to structural constraint effects, both of which can significantly reduce the plastic deformation capacity in moment frame connections, (c) Based on the test results, dynamic loading within a loading rate of 0.02 in/in/sec, as used in this study, premature brittle fractures were not seen, although a significant elevation of the yield strength can be clearly observed. However, brittle fracture features can be clearly identified in T-stub specimens in which severe constraint effects (stress triaxiality) are considered as the primary cause, (d) Based on both the test and FEA results, T-stub specimens provide a reasonable representation of the joint conditions in moment frame connections in simulating both complex load transfer mode and constraint conditions.

• 한국구조물진단유지관리공학회 논문집
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• 제18권4호
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• pp.10-21
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• 2014

프리캐스트 방식에 의해 제작이 가능한 격자형 강합성 바닥판의 이음부는 콘크리트 전단키와 고장력볼트 체결로 구성될 수 있으며, 이와같은 이음부 자체에 대한 휨 및 전단성능은 부재요소에 대한 실험을 통해 분석된 바 있다. 본 연구에서는 실제 바닥판 구조시스템에서 이음부에 의한 횡방향 하중전달 거동을 분석하고자, 길이 2.5m 및 폭 1m의 단위 바닥판 모듈 한쌍에 이음부를 설치한 실험체를 제작하고 중심 및 편심가력 휨실험을 하였다. 이음부에 하중이 직접 가해지는 중심재하 조건에서 고장력볼트의 설치개수가 30cm 간격 9개에서 60cm 간격 4개로 줄어 들 경우, 재하단계에 따라 이음부의 회전이 비교적 더 크게 증가하고, 이에 따라 바닥판 횡방향으로의 하중전달 정도가 감소함을 알 수 있었다. 그러나, 한쪽 바닥판의 중심에 집중하중이 가해지는 편심재하 조건의 경우에는 횡방향 하중전달 거동에 큰 차이가 없었다. 하중 재하방법별로 이음부의 거동을 비교한 결과, 집중하중에 대한 바닥판 횡방향으로의 하중분배 및 전달량은 이음부 자체의 성능뿐만 아니라 바닥판 슬래브의 펀칭전단에 의해서도 제한되는 것으로 분석되었다. 또한, 펀칭 전단파괴가 발생할 때까지 이음부의 고장력볼트가 항복하지 않은 점을 고려할 때, 이음부 고장력볼트의 설치개수를 4개에서 9개로 증가시키는 것은 실질적으로 강도 보다는 이음부 및 바닥판의 휨강성 성능 증가에 더 큰 영향을 미치는 것으로 사료된다.

• Steel and Composite Structures
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• 제45권5호
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• pp.749-766
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• 2022

This paper investigates the seismic performance of exposed RCFST column-base joints, in which the high-strength steel bars (USD 685) are set through the column and reinforced concrete foundation without any base plate and anchor bolts. Three specimens with different axial force ratios (n = 0, 0.25, and 0.5) were tested under cyclic loadings. Finite element analysis (FEA) models were validated in the basic indexes and failure mode. The hysteresis behavior of the exposed RCFST column-base joints was studied by the parametrical analysis including six parameters: width of column (D), width-thickness ratio (D/t), axial force ratio (n), shear-span ratio (L/D), steel tube strength (f_y) and concrete strength (f_c). The bending moment of the exposed RCFST column-base joint increased with D, f_y and f_c. But the D/t and L/D play a little effect on the bending capacity of the new column-base joint. Finally, the calculation formula is proposed to assess the bending moment capacities, and the accuracy and stability of the formula are verified.

• Steel and Composite Structures
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• 제24권5호
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• pp.615-633
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• 2017

Fatigue crack initiated in welded tubular joints due to cyclic loading may produce harmful effect on the integrity of the tubular structures. To study such effect, both fatigue and static tests on nine circular tubular T-joint specimens made of carbon steel materials were carried out. The specimens were subjected to tensile loading in both fatigue and static tests. The load-displacement relation, the crack propagation and the failure mode of the specimens are all analyzed. The deterioration of the static strength of the cracked T-joints is also investigated and evaluated through an area reduction factor. Experimental results indicate that the static strength of a tubular T-joint with a surface crack seems to decrease slightly while a through crack has relatively remarkable effect on the reduction of the static strength. Additionally, experimental results also show that the toughness of the materials and the geometry of the specimens play an important role on the failure process of cracked tubular T-joints.

• Composites Research
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• 제33권3호
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• pp.115-124
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• 2020

적층복합재료, 특히 탄소섬유 복합재료는 금속에 비해 가벼우며 상대적으로 비강도 및 비강성이 뛰어나기 때문에 항공 우주 산업 및 자동차 산업 등과같이 광범위한 분야에서 사용되고 있다. 그러나, 적층 복합재료는 섬유의 배열이 모두 면내방향으로 배열되어있기 때문에 박리가 발생한다는 큰 단점이 있으며, 이는 적층복합재료의 응용분야를 제한한다. 본 연구에서는 먼저 π-빔과 평판이 결합된 형태의 적층복합재료 T-빔을 개발하고, 구조해석 및 기계적 물성평가를 통하여 설계변수를 최적화하였다. 이후 적층복합재료 T-빔의 설계변수를 3D 직조 프리폼에 동일하게 적용하여 T-빔을 개발하였으며, 적층구조에 비하여 향상된 기계적 강도를 달성할 수 있었다. 이러한 연구결과는 강도향상을 필요로 하는 기존의 적층복합재료 구조물에 적용 가능할 것으로 기대된다.

• Steel and Composite Structures
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• 제21권1호
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• pp.137-156
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• 2016

Due to excellent advantages such as better illuminative effects, considerable material savings and ease and rapidness of construction, the bolted ball-cylinder joint which is a new type joint system has been proposed in space truss structures. In order to reveal more information and understanding on the behaviour of bolted ball-cylinder joints, full-scale experiments on eight bolted ball-cylinder joint specimens were conducted. Five joint specimens were subjected to axial compressive force, while another three joint specimens were subjected to axial tensile force. The parameters investigated herein were the outside diameter of hollow cylinders, the height of hollow cylinders, the thickness of hollow cylinders, ribbed stiffener and axial force. These joint specimens were collapsed by excessive deformation of hollow cylinders, punching damage of hollow cylinders, evulsion of bolts, and weld cracking. The strain distributions on the hollow cylinder opening were mainly controlled by bending moments. To improve the ultimate bearing capacity and axial stiffness of bolted ball-cylinder joints, two effective measures were developed: (1) the thickness of the hollow cylinder needed to be thicker; (2) the ribbed stiffener should be adopted. In addition, the axial stiffness of bolted ball-cylinder joints exhibited significant non-linear characteristics.

• Smart Structures and Systems
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• 제5권4호
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• pp.329-344
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• 2009

Ultrasonic chaotic excitations combined with sensor prediction algorithms have shown the ability to identify incipient damage (loss of preload) in a bolted joint. In this study we examine a physical experiment on a single-bolt aluminum lap joint as well as a three-dimensional physics-based simulation designed to model the behavior of guided ultrasonic waves through a similarly configured joint. A multiple bolt frame structure is also experimentally examined. In the physical experiment each signal is imparted to the structure through a macro-fiber composite (MFC) patch on one side of the lap joint and sensed using an equivalent MFC patch on the opposite side of the joint. The model applies the waveform via direct nodal displacement and 'senses' the resulting displacement using an average of the nodal strain over an area equivalent to the MFC patch. A novel statistical classification feature is developed from information theory concepts of cross-prediction and interdependence. This damage detection algorithm is used to evaluate multiple damage levels and locations.

• Steel and Composite Structures
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• 제21권5호
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• pp.1017-1029
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• 2016

When a welded circular hollow section (CHS) tubular joint is subjected to brace axial loading, failure position is located usually at the weld toe on the chord surface due to the weak flexural stiffness of the thin-walled chord. The failure mode is local yielding or buckling in most cases for a tubular joint subjected to axial load at the brace end. Especially when a cyclic axial load is applied, fracture failure at the weld toe may occur because both high stress concentration and welding residual stress along the brace/chord intersection cause the material in this region to become brittle. To improve the ductility as well as to increase the static strength, a tubular joint can be reinforced by increasing the chord thickness locally near the brace/chord intersection. Both experimental investigation and finite element analysis have been carried out to study the hysteretic behaviour of the reinforced tubular joint. In the experimental study, the hysteretic performance of two full-scale circular tubular T-joints subjected to cyclic load in the axial direction of the brace was investigated. The two specimens include a reinforced specimen by increasing the wall thickness of the chord locally at the brace/chord intersection and a corresponding un-reinforced specimen. The hysteretic loops are obtained from the measured load-displacement curves. Based on the hysteretic curves, it is found that the reinforced specimen is more ductile than the un-reinforced one because no fracture failure is observed after experiencing similar loading cycles. The area enclosed by the hysteretic curves of the reinforced specimen is much bigger, which shows that more energy can be dissipated by the reinforced specimen to indicate the advantage of the reinforcing method in resisting seismic action. Additionally, finite element analysis is carried out to study the effect of the thickness and the length of the reinforced chord segment on the hysteretic behaviour of CHS tubular T-joints. The optimized reinforcing method is recommended for design purposes.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 1995년도 춘계공동학술대회논문집; 전남대학교; 28-29 Apr. 1995
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• pp.787-796
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• 1995

A man model is a useful design tool for the evaluation of man machine systems and products. An arm reach trajectory prediction for such a model will be specifically useful to present human activities and, consequently, could increase the accuracy and reality of the evaluation. In this study, a three-dimensional reach trajectory prediction model was developed using an inverse kinematics technique. The upper body was modeled as a four link open kinematic chain with seven degrees of freedom. The Resolved Motion Method used for the robot kinematics problem was used to predict the joint movements. The cost function of the perceived discomfort developed using the central composite design was also used as a performance function. This model predicts the posture by moving the joints to minimize the discomfort on the constraint of the end effector velocity directed to a target point. The results of the pairwise t-test showed that all the joint coordinates except the shoulder joint's showed statistically no differences at .alpha. = 0.01. The reach trajectory prediction model developed in this study was found to accurately simulate human arm reach trajectory and the model will help understand the human arm reach movement.