• Journal of the Korean Geotechnical Society
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• v.21 no.10
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• pp.123-131
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• 2005

In the present study, laboratory pull-out tests with screw anchors are carried out to investigate behavior characteristics of the anchors used in foundation system of underground structures which are applied to uplifting seepage forces. Small scaled pull-out tests in sand under saturated condition and dry condition were carried out. For estimating the group effects of the anchors, the upward displacement and the pullout load varied with spacing of the anchor were observed. The test results were compared with theoretical equation for the ultimate pull-out force. Also, the result of tests can be used to the finite element analysis program, $PENTAGON^{2D}$.

• Computers and Concrete
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• v.16 no.5
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• pp.759-774
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• 2015

This study simulates the flexural behavior of ultra-high-performance fiber-reinforced concrete (UHPFRC) beams reinforced with steel and glass fiber-reinforced polymer (GFRP) rebars. For this, micromechanics-based modeling was first carried out on the basis of single fiber pullout models considering inclination angle. Two different tension-softening curves (TSCs) with the assumptions of 2-dimensional (2-D) and 3-dimensional (3-D) random fiber orientations were obtained from the micromechanics-based modeling, and linear elastic compressive and tensile models before the occurrence of cracks were obtained from the mechanical tests and rule of mixture. Finite element analysis incorporating smeared crack model was used due to the multiple cracking behaviors of structural UHPFRC beams, and the characteristic length of two times the element width (or two times the average crack spacing at the peak load) was suggested as a result of parametric study. Analytical results showed that the assumption of 2-D random fiber orientation is appropriate to a non-reinforced UHPFRC beam, whereas the assumption of 3-D random fiber orientation is suitable for UHPFRC beams reinforced with steel and GFRP rebars due to disorder of fiber alignment from the internal reinforcements. The micromechanics-based finite element analysis also well predicted the serviceability deflections of UHPFRC beams with GFRP rebars and hybrid reinforcements.

• Geotechnical Engineering
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• v.11 no.4
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• pp.99-110
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• 1995

In this study, friction angles on the surface of vertical rigid ground anchor in normally consolidated dry sand were measured by model pullout tests in laboratory. Friction angles were obtained from the normal and shear stresses measured along depth of the anchor stir face by attaching several 2-dimensional load cells. Model tests were conducted under the plane strain state and axial symmetric state. From the results of tests, it was concluded that the maximum friction angle on the anchor surface coincides nearly with the maximum angle of stress obliquity on the plane of zero-extension direction obtained by plane strain compression test. This result was made with regard to the strength anisotropy and stress dependency of sand. It showed that when angle of shear resistance of the sand is applied to the friction angle of the anchor surface, the design capacity could be less than the applied force, thus making the anchor unsafe.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.6
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• pp.1388-1398
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• 1994

The fracture toughness and micro-fracture mechanisms of the porous glass and stainless fiber reinforced glass composite were evaluated by using the acoustice mission(AE) technique, fracture toughness $test(K_{IC})$ and the macroscopic observation of the specimen surface which was being under the loading. At initial portion of the loading, the AE signals with low energy, of which origins were considered as the micro-cracks formated at the crack tip, were emitted. With increasing the applied load, AE signals having higher energies were generated due to the coalesence of micro-cracks and fast fracture. Based on the such relationship between AE emission and loading condition, fracture toughness $K_{IAE}$ could be defined successfully be using the $K_I$ value corresponding to an abrupt change of the accumulated AE signal energies emitted during the fracture toughness test. In spite of its brittleness of glass material, nonlinear deformation behavior before maximum load was observed due to the formation of micro-cracks. Further, the stainless fiber may have attributed to the improvement of fracture toughness and the resistance to crack propagation comparing to noncomposited materials Finally, models of the micro-fracture process combined with the AE sources for the porous glass material and its composite were proposed paying attention to the micro-crack nucleation and its coalescence at the crack tip. Fiber fracture and its Pullout, deformation of fiber itself were also delinated from the model.

• Computers and Concrete
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• v.24 no.1
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• pp.73-83
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• 2019

Concrete reinforced with fiber reinforced polymer (FRP) bars (FRP-RC) has attracted a significant amount of research attention in the last three decades. A limited number of studies, however, have investigated the effect of bond slip on the performance of FRP-RC columns under eccentric loading. Based on previous experimental study, a finite-element model of eccentrically loaded FRP-RC columns was established in this study. The bondslip behavior was modeled by inserting spring elements between FRP bars and concrete. The improved Bertero-Popov-Eligehausen (BPE) bond slip model with the results of existing FRP-RC pullout tests was introduced. The effect of bond slip on the entire compression-bending process of FRP-RC columns was investigated parametrically. The results show that the initial stiffness of bond slip is the most sensitive parameter affecting the compression-bending performance of columns. The peak bond stress and the corresponding peak slip produce a small effect on the maximum loading capacity of columns. The bondslip softening has little effect on the compression-bending performance of columns. The sectional analysis revealed that, as the load eccentricity and the FRP bar diameter increase, the reducing effect of bond slip on the flexural capacity becomes more obvious. With regard to bond slip, the axial-force-bending-moment (P-M) interaction diagrams of columns with different FRP bar diameters show consistent trends. It can be concluded from this study that for columns reinforced with large diameter FRP bars, the flexural capacity of columns at low axial load levels will be seriously overestimated if the bond slip is not considered.

• Journal of the Korean Geotechnical Society
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• v.27 no.6
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• pp.17-26
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• 2011

Ground anchor method is one of the most popular reinforcing technology in Korea. For the sound monitoring of slope reinforced by permanent anchor for a long period, monitoring the tension force of ground anchor is very important. However, special technology except conventional load cell has not been developed for this purpose. In this paper, a new method is described to replace the conventional strain gauge and V.W. type load cell which has been commonly used as a prestress force monitoring tool for a short-term and long-term. Four 11.5 m long strain detectable tension type anchors were made using FBG sensor embedded tendon since FBG sensor is smaller than strain gauge type load cell and does not have noise from electromagnetic wave. Each two set strain detectable tension type anchors were installed into the different ground conditions, i.e., soft rock and weathered granite soil. Prestress force of ground anchor was monitored during the loading-unloading step from in-situ pullout test using proposed FBG sensor embedded in the tendon and the conventional load cell Test results show that the prestress force monitored from FBG sensor may well be used practically, for it almost matches with that measured from expensive load cell.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.5
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• pp.79-86
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• 2009

With the substantial increase of the size of structure, the management of excavation becomes more difficult. Therefore, massive collapses which are related to retaining wall recently increase. However, since the study on measuring and monitoring the pre-stressing force of anchor is insufficient, behavior of anchor may not be predicted and monitored appropriately by the existing strain gauge and load cell type monitoring system. FBG Sensor, which is smaller than strain gauge and has better durability and does not have a noise from electromagnetic waves, is adapted to measure the strain and pre-stressing force of 7-wire strand, so called smart tendon. A series of pullout tests were performed to verify the feasibility of smart tendon and find out the load transfer mechanism around the steel wire tendon fixed to rock with grout. Distribution of measured strains and estimated shear stresses are compared with those predicted by theoretical solutions. It was found that developed smart tendon can be used effectively for measuring strain of 7-wire strand anchor and theoretical solutions underestimate the magnitude of shear stress and load transfer depth.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.774-780
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• 1999

The study of bond behavior between concrete and rebar has been performed for a long time. On this study, we tried to analysed variation of bond behaviors quantitatively with varying the strength of concrete. Bond stress which observed below the neutral surface of beam and at connecting part of beam and column is affected by various bond parameters. Resistance of deformed bars which embedded in concrete to the pullout force is divided 1) chemical adhesive force 2) frictional force 3) mechanical resistance of ribs to the concrete and these horizontal components of resistance is being bond strength. We selected the most common and typical variable which is concrete strength among various variables. So we used two kinds of concrete strength like as 25MPa(NSC) and 65MPa(HSC). Tension Test was performed to verify how bond behavior varied with two kinds of concrete strength. Concentration of bond stress was observed at load-end commonly in Tension Test of the initial load stage. At this stage stress distribution was almost coincident at each strength. As tension load added, this stress distribution had difference gradually and movement of pick point of bond stress to free-end and central section was observed. This tendency was observed at first and moving speed was more fast in NSC. At the preceeding result the reason of this phenomenon is considered to discretion of chemical adhesion and local failure of concrete around rebar in load-end direction. Especially, when concrete strength was increased 2.6 times in tension test, ultimate bond strength was increased 1.45 times. In most recent used building codes, bond strength is proportioned to sqare root of concrete compressive strength but comparison of normalized ultimate bond strength was considered that the higher concrete strength is, the lower safety factor of bond strength is in each strength if we use existing building codes. In Tension Test, in case of initial tensile force state, steel tensile stress of central cross section is not different greatly at each strength but tensile force increasing, that of central cross section in NSC was increased remarkably. Namely, tensile force which was shared in concrete in HSC was far greater than that of concrete in NSC at central section.

• Journal of the Korean GEO-environmental Society
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• v.19 no.9
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• pp.5-12
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• 2018

The foundation of the multi-span greenhouse structures is designed with small shallow concrete foundation considering mainly the vertical load. However, recently, due to an abnormal climate such as strong wind, horizontal load and up-lift load over design strength are applied to the foundation, causing safety problems of the greenhouse foundation. In order to reasonably evaluate the safety of greenhouse foundations, rotational and pullout stiffness expressed by the ground-foundation interaction should be evaluated, which also affects the safety of the upper structural members. In this study, three representative basic foundation types were selected by classifying greenhouse standards in Korea according to the shape, and the horizontal loading tests and theoretical calculation were performed for each foundation type. As a result of the comparison and analysis of the test and calculation, it was found that rotational resistance of the foundation is different according to the ratio of the contact area between the foundation and ground when the conditions of the foundation - ground contact surface and the mechanical properties of the ground are the same.

• Journal of Korean Society of Steel Construction
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• v.19 no.3
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• pp.303-312
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• 2007

Steel box girder bridges are being commonly designed for medium-span bridges of span length. Composite truss bridges with steel diagonals instead of concrete webs can be an excellent design alternative, because it can reduce the dead weight of superstructures. One of the key issues in the design of composite truss bridges is the joint structureconnecting the diagonal steel members with the upper and lower concrete slabs. Because the connection has to carry concentrated combined loads and the design provisions for the joint are not clear, it is necessary to investigate the load transfer mechanism and the design methods for each limit state. There are various connection details according to the types of diagonal members. In this paper, the joint structure with group stud connectors welded on a gusset plate is used. Push-out tests for the group stud connectors of were performed. The test results showed that the current design codes on the ultimate strength ofthe stud connection can be used when the required minimum spacing of stud connectors is satisfied. Flexure-shear tests were conducted to verify the applicability of the design provisions for combined load effects to the strength of joint structures. To increase the pullout strength of the connection, bent studs were proposed and utilized for the edge studs in the group arrangement of the joint. The results showed that the details of the joint structure were enhanced. Thereafter, design guidelines were proposed.