• Journal of the Korean Society of Safety
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• v.9 no.2
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• pp.18-25
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• 1994

In this thesis, the fatigue tests were performed on a series of reinforced concrete to Investigate the variation of strength and the safety of reinforced concrete structures under fatigue load. The specimens were of the same rectangular cross-section, of effective height 24cm and width 30cm and their span was 330cm. The three point loading system is used in the fatigue tests. In these tests, the fracture mode of reinforced concrete structures under fatigue load, relationship between the repeated loading cycles and the mid-span displacement of the specimens were observed. According to the test results, the following fatigue behavior of reinforced concrete specimens were observed. By increasing of the number of repeated loading cycles, the mid-span displacement became greater, however the Incremental amounts of the displacement were reduced. It could be also known that the inelastic strain energy of the doubly reinforced rectangular beams was larger than that of the singly reinforced rectangular beams as increasing the number of repeated loading cycles. Compliance of reinforced concrete structures tended to be reduced as increasing the repeated loading cycles, and the compliance of the doubly reinforced rectangular beams was generally smaller than that of the singly reinforced rectangular beams. Based on the above investigation, it could be concluded that the doubly reinforced rectangular beams under fatigue load were more efficient to resist the brittle fracture than the singly reinforced rectangular beams.

• Geomechanics and Engineering
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• v.14 no.2
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• pp.115-129
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• 2018

This paper presents a set of results of plate load tests that imposed incremental cyclic loading to a sandy soil bed containing multiple layers of granulated rubber-soil mixture (RSM) at large model scale. Loading and unloading cycles were applied with amplitudes incrementally increasing from 140 to 700 kPa in five steps. A thickness of the RSM layer of approximately 0.4 times the footing diameter was found to deliver the minimum total and residual settlements, irrespective of the level of applied cyclic load. Both the total and residual settlements decrease with increase in the number of RSM layers, regardless of the level of applied cyclic load, but the rate of reduction in both settlements reduces with increase in the number of RSM layers. When the thickness of the RSM layer is smaller, or larger, settlements increase and, at large thicknesses may even exceed those of untreated soil. Layers of the RSM reduced the vertical stress transferred through the foundation depth by distributing the load over a wider area. With the inclusion of RSM layers, the coefficient of elastic uniform compression decreases by a factor of around 3-4. A softer response was obtained when more RSM layers were included beneath the footing damping capacity improves appreciably when the sand bed incorporates RSM layers. Numerical modeling using "FLAC-3D" confirms that multiple RSM layers will improve the performance of a foundation under heavy loading.

• Structural Engineering and Mechanics
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• v.1 no.1
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• pp.31-46
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• 1993

The motivations of the application of shakedown analysis to the earthquake-resistant design of ductile moment-resisting steel structures are presented. The problems which must be solved with this application are also addressed. The illustrative results from a series of static and time history nonlinear analyses of one-bay three-story steel frame and the related discussions have shown that the incremental collapse may be the critical design criterion in case of earthquake loading. Based on the findings, it was concluded that the inelastic excursion mechanism for alternation load pattern, such as in earthquake, should be the sidesway mechanism of the whole structure for the efficient mobilization of the structural energy dissipating capacity and that the shakedown analysis technique can be used as a tool to ensure this mechanism.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.4
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• pp.183-193
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• 2006

This study deals with the response of reinforced concrete beams strengthened with carbon fiber sheets. Test beams are subjected to static loading and repeated loading. Based on the static test results of the RC beams strengthened with carbon fiber sheets, repeated loading tests are performed. The variables of repeated loading test are composed of the number of carbon fiber sheets, the existence of U-shaped band at the end for anchoring, and loading rate of repeated loading, etc. Test results show the flexural behavior, the characteristics of strength, the characteristics of ductility, the change of flexural rigidity, and the amount of energy loss of RC beams under monotonic incremental loading and repeated loading. The failure strain of carbon fiber sheets is also estimated under repeated loading. From the experimental results, this work presents a basis of the data needed to analyze and design the static and dynamic flexural response of RC beams strengthened with carbon fiber sheets.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.99-109
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• 2008

The standard consolidation tests using the incremental loading technique test (IL) were performed on remolded normal consolidation and undisturbed clay samples to find out the effects of plastic index and loading period on consolidation in this study. The remolded samples used were prepared by mixing Gunsan-Samangum clay with bentonite so that they may have plasticity indexes of 15, 30, 45, and 60%, respectively. The undisturbed clay samples were collected from Inchon, Kwangyang, and Uoolsan. The samples were tested at the condition of 4 different loading periods (1, 2, 4, and 8 days). Settlement, coefficient of consolidation, compression index, secondary compression index, and pore water pressure characteristics were investigated from the plastic index and loading period aspects, and the compression index, coefficient of consolidation, and secondary compression index were formulated in terms of the plastic index and loading. To verify the applicability of proposed equations, the settlements obtained from Terzaghi's theory, modified Cam-Clay model (elasto-plastic model), and the Sekiguchi model (elasto-viscoplastic mode) were compared with the test results. The comparison indicates that the Sekiguchi model incorporating the secondary consolidation characteristic well predicts the results.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.1070-1077
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• 2005

The purpose of this study is to establish a proper criterion for the constant rate of loading consolidation(CRLC) test which is a kind of the continuous loading consolidation(CLC) and widely used as alternative methods to the incremental loading consolidation(ILC)test. With those results, the preconsolidation pressure estimated by the CRLC test turned out to be comparatively larger than that of the ILC test, and it is increased in proportion to the applied loading rates. However, the compression index in the CRLC test is less influenced on by the loading rates. The coefficient of consolidation and permeability in the CRLC test are dependent on excess pore pressure ratio mainly. In other words, if the pore pressure ratios are too low, the coefficient of consolidation and permeability become smaller than those of the ILC test. On the other hand, if the excess pore pressure ratios are too high, the coefficient of consolidation and permeability become so larger than those of the ILC test. Therefore, loading rates should be carefully determined to generate proper excess pore pressure ratio inside the soil specimen. From this study, good results are obtained from the CRLC test if the excess pore pressure ratios were in the range of 2.5 to 6.0 %, performed with loading rates between 0.0015 and 0.005 $kgf/cm^2/min$.

• Geomechanics and Engineering
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• v.15 no.1
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• pp.695-710
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• 2018

Formation of a soil plug in an open-ended pile is a very important factor in determining the pile behavior both during driving and during static loading. The degree of soil plugging can be represented by the incremental filling ratio (IFR) which is defined as the change in the plug length to the change of the pile embedment length. The experimental tests carried out in this research contain 138 tests that are divided as follows: 36 tests for single pile, 36 tests for pile group ($2{\times}1$), 36 tests for pile group ($2{\times}2$) and 30 pile group ($2{\times}3$). All tubular piles were tested using the poorly graded sand from the city of Karbala in Iraq. The sand was prepared at three different densities using a raining technique. Different parameters are considered such as method of installation, relative density, removal of soil plug with respect to length of plug and pile length to diameter ratio. The soil plug is removed using a new device which is manufactured to remove the soil column inside open pipe piles group installed using driving and pressing device. The principle of soil plug removal depends on suction of sand inside the pile. It was concluded that the incremental filling ratio (IFR) is changed with the changing of soil state and method of installation. For driven pipe pile group, the average IFR for piles in loose is 18% and 19.5% for L/D=12 and 15, respectively, while the average of IFR for driven piles in dense sand is 30% and 20% for L/D=12 and L/D=15 respectively. For pressed method of pile installation, the average IFR for group is zero for loose and medium sand and about 5% for dense sand. The group capacity increases with the increase of IFR. For driven pile with length of 450 mm, the average IFR % is about 30.3% in dense sand, 14% in medium and 18.3% for loose sand while when the length of pile is 300 mm, the percentage equals to 20%, 17% and 19.5%, respectively.

• Smart Structures and Systems
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• v.18 no.1
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• pp.139-154
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• 2016

This paper is concerned with the dynamics of hyperelastic solids and structures. We seek for a smart control actuation that produces a desired (prescribed) displacement field in the presence of transient imposed forces. In the literature, this problem is denoted as displacement tracking, or also as shape morphing problem. One talks about shape control, when the displacements to be tracked do vanish. In the present paper, it is assumed that the control actuation is provided by imposed eigenstrains, e.g., by the electric field in piezoelectric actuators, or by thermal actuators, or via analogous physical effects, such as magneto-striction or pre-stress. Structures with a controlled eigenstrain-type actuation belong to the class of smart structures. The action of the eigenstrains can be conveniently characterized by actuation stresses. Our theoretical derivations are performed in the framework of the theory of small incremental dynamic deformations superimposed upon a statically pre-deformed configuration of a hyperelastic solid or structure. We particularly ask for a distribution of incremental actuation stresses, such that the incremental displacements follow exactly a prescribed trajectory field, despite the imposed incremental forces are present. An exact solution of this problem is presented under the assumption that the actuation stresses can be tailored freely and applied everywhere within the body. Extending a Neumann-type solution strategy, it is shown that the actuation stresses due to the distributed control eigenstrains must satisfy certain quasi-static equilibrium conditions, where auxiliary body-forces and auxiliary surface tractions are to be taken into account. The latter auxiliary loading can be directly computed from the imposed forces and from the desired displacement field to be tracked. Hence, despite the problem is a dynamic one, a straightforward computation of proper actuator distributions can be obtained in the framework of quasi-static equilibrium conditions. Necessary conditions for the functioning of this concept are presented. Particularly, it must be required that the intermediate configuration is infinitesimally superstable. Previous results of our group for the case of shape control and displacement tracking in linear elastic structures are included as special cases. The high potential of the solution is demonstrated via Finite Element computations for an irregularly shaped four-corner plate in a state of plain strain.

• Steel and Composite Structures
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• v.31 no.2
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• pp.187-199
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• 2019

This paper presents the semi-analytical development of the dynamic instability behavior and the dynamic response of functionally graded (FG) cylindrical shallow shell panel subjected to different type of periodic axial compression. First, in prebuckling analysis, the stresses distribution within the panels are determined for respective loading type and these stresses are used to study the dynamic instability behavior and the dynamic response. The prebuckling stresses within the shell panel are the same as applied in-plane edge loading for the case of uniform and linearly varying loadings. However, this is not true for the case of parabolic loadings. The parabolic edge loading produces all the stresses (${\sigma}_{xx}$, ${\sigma}_{yy}$ and ${\tau}_{xy}$) within the FG cylindrical panel. These stresses are evaluated by minimizing the membrane energy via Ritz method. Using these stresses the partial differential equations of FG cylindrical panel are formulated by applying Hamilton's principal assuming higher order shear deformation theory (HSDT) and von-$K{\acute{a}}rm{\acute{a}}n$ non-linearity. The non-linear governing partial differential equations are converted into a set of Mathieu-Hill equations via Galerkin's method. Bolotin method is adopted to trace the boundaries of instability regions. The linear and non-linear dynamic responses in stable and unstable region are plotted to know the characteristics of instability regions of FG cylindrical panel. Moreover, the non-linear frequency-amplitude responses are obtained using Incremental Harmonic Balance (IHB) method.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.179-194
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• 1991

This paper explains outline of a behavior analysis program for underground structures, and its application to a tunnel problem. The program can deal with elasto-plastic behavior of medium and supporting structures, discontinuous behavior due to existing joint, creation and propagation of cracks. in-situ loading condition, and incremental behavior due to stepwise excavation, etc. The program also has additional capabilities such as graphic output of mesh, displacement pattern, stress condition, and safety factor contour, and automatic mesh generation during the excavation steps.