• International Journal of Concrete Structures and Materials
• /
• 제11권2호
• /
• pp.215-228
• /
• 2017

A new approach for measuring the specific fracture energy of concrete denoted modified disk-shaped compact tension (MDCT) test is presented. The procedure is based on previous ideas regarding the use of compact tension specimens for studying the fracture behavior of concrete but implies significant modifications of the specimen morphology in order to avoid premature failures (such as the breakage of concrete around the pulling load holes). The manufacturing and test performance is improved and simplified, enhancing the reliability of the material characterization. MDCT specimens are particularly suitable when fracture properties of already casted concrete structures are required. To evaluate the applicability of the MDCT test to estimate the size-independent specific fracture energy of concrete ($G_F$),the interaction between the fracture process zone of concrete andthe boundary of theMDCTspecimens at the end of the test is properly analyzed. Further, the experimental results of $G_F$ obtained by MDCT tests for normal- and high-strength self-compacting concrete mixes are compared with those obtained using the well-established three-point bending test. The procedure proposed furnishes promising results, and the $G_F$ values obtained are reliable enough for the specimen size range studied in this work.

• Journal of Korean Society of Steel Construction
• /
• 제16권5호통권72호
• /
• pp.565-574
• /
• 2004

The purpose of this paper was to investigate the block shear and the fracture in the net section, according to AISC Specifications, by analysing the shear lag effect in the block shear rupture of the single angle with three or four bolt connection. Specimen with three or four bolt connections showed that failure generally went from block shear with some net section failures to classic net section failures. From the test results, showed that the connection length, the thickness of angle, and reduction factor, which affect the block shear rupture, were investigated. According to the test results, it is suggested that the calculation of the net section rupture capacity by using the reduction factor of U, that was suggested by Kulak, is needed.

• Structural Engineering and Mechanics
• /
• 제60권1호
• /
• pp.51-69
• /
• 2016

A large number of welded steel moment-resisting framed (SMRF) structures failed due to brittle fracture induced by ductile fracture at beam-to-column connections during 1994 Northridge earthquake and 1995 Kobe (Hyogoken-Nanbu) earthquake. Extensive research efforts have been devoted to clarifying the mechanism of the observed failures and corresponding countermeasures to ensure more ductile design of welded SMRF structures, while limited research on the failure analysis of the ductile cracking was conducted due to lack of computational capacity and proper theoretical models. As the first step to solve this complicated problem, this paper aims to establish a straightforward procedure to simulate ductile cracking of welded joints under monotonic tension. There are two difficulties in achieving the aim of this study, including measurement of true stress-true strain data and ductile fracture parameters of different subzones in a welded joint, such as weld deposit, heat affected zone and the boundary between the two. Butt joints are employed in this study for their simple configuration. Both experimental and numerical studies on two types of butt joints are conducted. The validity of the proposed procedure is proved by comparison between the experimental and numerical results.

• Journal of Korean Society of Steel Construction
• /
• 제20권2호
• /
• pp.279-288
• /
• 2008

In this study, the slip behavior of high-tension bolted joints subjected to compression force is investigated through 3D finite element analysis and experiments. The relation with sliding load, bolt deformation, and failure load are studied with the metal thickness affecting the bolted joint. The post-sliding behavior considering bolt stiffness is presented and compared with the results by finite element and experiments. The finite element model is constructed by solid elements in ABAQUS, in consideration of all the friction effects between metal plates and bolts. The stress-strain relations in the literature are used, and the sliding displacements and axial stresses around the bolt connection are investigated. The flexural buckling of species happened when the plate thickness is less than the bolt diameter. However, the shear failures of bolt occurred in the opposite case.

• Composites Research
• /
• 제26권2호
• /
• pp.91-98
• /
• 2013

A three-dimensional finite analysis method was proposed to predict the failure of composite double-lap bolted joints, which is based on the stiffness degradation method using damage variables and Hashin's three-dimensional failure criteria. Ladeveze's theory using damage variables to consider the matrix/shear damage was combined with stiffness degradation in fiber direction. Four different failure modes were considered including matrix compression/shear, matrix tension/shear, fiber compression, and tension failures. The friction between bolt and composite and the clamping force were considered using a commercial finite element software ABAQUS. The damage model was incorporated using the user-defined subroutine of the software. The predicted result was verified with the existing test result for bearing tension double shear and showed the deviation ranging 7~16% from test results.

• Transactions of the Korean Society of Mechanical Engineers
• /
• 제19권2호
• /
• pp.382-390
• /
• 1995

Failure of connecting rod in automotive engine may cause catastrophic situation. The corner radius at small end has an effect on stress raising. To investigate the stress distribution in connecting rod during operation, the finite element analysis was used by giving possible maximum tension and compression. Excessive sizing after forging connecting rod may result in the tensile residual stress which lower the fatigue life and cause premature failures. It was shown that when the sizing amount is too large, the location of high tensile residual stress coincide with that of high stress amplitude during operation through the elastic-plastic finite element analysis. The endurance limit moves down due to the surface finish and decarburization, which combines with the movement of resultant stress points to dangerous range. It was concluded that the precise control of sizing and enough corner radius are necessary to a reliability of connecting rod.

• Structural Engineering and Mechanics
• /
• 제24권2호
• /
• pp.181-194
• /
• 2006

The masonry is a complex heterogeneous material and its shear deformation and fracture is associated with very complicated progressive failures in masonry structure, and is investigated in this paper using a mesoscopic mechanical modelling, Considering the heterogeneity of masonry material, based on the damage mechanics and elastic-brittle theory, the newly developed Material Failure Process Analysis (MFPA) system was brought out to simulate the cracking process of masonry, which was considered as a three-phase composite of the block phase, the mortar phase and the block-mortar interfaces. The crack propagation processes simulated with this model shows good agreement with those of experimental observations by other researchers. This finding indicates that the shear fracture of masonry observed at the macroscopic level is predominantly caused by tensile damage at the mesoscopic level. Some brittle materials are so weak in tension relative to shear that tensile rather than shear fractures are generated in pure shear loading.

• The Journal of Korean Academy of Prosthodontics
• /
• 제27권2호
• /
• pp.101-121
• /
• 1989

This study investigated the effects of Silicoating procedure on the tensile bond strength of resin-bonded prostheses. The Rexillium III specimens were treated with electrochemical etching and Silicoating procedure, followed by thermocycling and the NNB, Pors-on 4, and Degudent-U specimens were treated with Silicoating procedure. The specimens were debonded in tension with a Tensilon machine. Also, all specimens were observed with SEM, concentration of Si elements was analyzed with EPMA, and the mode of failure was recorded. The results of this study were obtained as follows: 1. In the Rexillium III specimens, the tensile bond strength of the Silicoated specimens was higher than that of the electrochemically etched specimens, and significant differences were observed (P<0.05). 2. The tensile bond strength of electrochemically etched Rexillium III specimens, significant differences were observed between the thermocycled and nonthermocycled specimens (P<0.05), but no significant differences were observed in the Silicoated specimens (P>0.05). 3. The tensile bond strength of the Silicoated specimens decreased NNB, Pors-on 4, Rexillium III, and Degudent-U in that order named. 4. Unlike the electrochemically etched specimens, the Silicoated specimens showed gap-free metal-resin interfaces with SEM. 5. Compared to the electrochemically etched specimens, the Silicoated specimens showed higher concentration of Si elements at the metal-resin interfaces and resin cement. 6. Photographic evaluation (X2) of the fractured sites revealed mainly cohesive failures with the Silicoated specimens, and adhesive failures with the electrochemically etched specimens.

• Proceedings of the Korean Institute Of Construction Engineering and Management
• /
• 한국건설관리학회 2007년도 정기학술발표대회 논문집
• /
• pp.316-321
• /
• 2007

The casualties due to slope failures such as landslide, rock fall, debris flow etc. are about 24% in total casualties caused by natural disasters for the last 10 years. And these slope failures are focused in the season in which typhoon and torrential rain take place. Not much attention, however, have been put into landslide mitigation research. Meanwhile, USN(Ubiquitous Sensor Network) forms the self-organization network, and transfers the information among sensor nodes that have computing technology ability. Accordingly, USN is embossed a social point technology. The objective of this paper is to develop a prototype system for slope failure monitoring using USN technology. For this we develop module that collects and change slope movement data measured by two tiltermeter and a tension wire, store transferred data in database. Also we develop application program that can easily analyze the data. We apply the prototype system to a test site at KICT for testing and analyzing the system's performance.

• Earthquakes and Structures
• /
• 제15권5호
• /
• pp.453-462
• /
• 2018

Damages to buildings affected by a near-fault strong ground motion are largely attributed to the vertical component of the earthquake resulting in column failures, which could lead to disproportionate building catastrophic collapse in a progressive fashion. Recently, considerable interests are awakening to study effects of earthquake vertical components on structural responses. In this study, detailed modeling and time-history analyses of a 12-story code-conforming reinforced concrete moment frame building carrying the gravity loads, and exposed to once only the horizontal component of, and second time simultaneously the horizontal and vertical components of an ensemble of far-field and near-field earthquakes are conducted. Structural responses inclusive of tension, compression and its fluctuations in columns, the ratio of shear demand to capacity in columns and peak mid-span moment demand in beams are compared with and without the presence of the vertical component of earthquake records. The influences of the existence of earthquake vertical component in both exterior and interior spans are separately studied. Thereafter, the correlation between the increase of demands induced by the vertical component of the earthquake and the ratio of a set of earthquake record characteristic parameters is investigated. It is shown that uplift initiation and the magnitude of tensile forces developed in corner columns are relatively more critical. Presence of vertical component of earthquake leads to a drop in minimum compressive force and initiation of tension in columns. The magnitude of this reduction in the most critical case is recorded on average 84% under near-fault ground motions. Besides, the presence of earthquake vertical components increases the shear capacity required in columns, which is at most 31%. In the best case, a direct correlation of 95% between the increase of the maximum compressive force and the ratio of vertical to horizontal 'effective peak acceleration (EPA)' is observed.