• Steel and Composite Structures
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• v.44 no.3
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• pp.371-388
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• 2022

The present study tackles the problem of forced vibration of imperfect axially functionally graded shell structure with truncated conical geometry. The linear and nonlinear large-deflection of the structure are considered in the mathematical formulation using von-Kármán models. Modified coupled stress method and principle of minimum virtual work are employed in the modeling to obtain the final governing equations. In addition, formulations of classical elasticity theory are also presented. Different functions, including the linear, convex, and exponential cross-section shapes, are considered in the grading material modeling along the thickness direction. The grading properties of the material are a direct result of the porosity change in the thickness direction. Vibration responses of the structure are calculated using the semi-analytical method of a couple of homotopy perturbation methods (HPM) and the generalized differential quadrature method (GDQM). Contradicting effects of small-scale, porosity, and volume fraction parameters on the nonlinear amplitude, frequency ratio, dynamic deflection, resonance frequency, and natural frequency are observed for shell structure under various boundary conditions.

• Steel and Composite Structures
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• v.48 no.6
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• pp.649-666
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• 2023

In the current scenario, conventional concrete faces a substantial challenge in the modern era of the construction industry. Today's structures are massive, featuring innovative designs and strict time constraints. Conventional concrete does not provide the required compressive strength, tensile strength, flexural strength, toughness, and cracking resistance. As a result, most of engineers and professionals prefer to use ultra-high-performance concrete (UHPC), based on its wide advantages. Several advantages like mechanical and durability properties of UHPC provides dominant properties than the traditional concrete. Mix proportions of UHPC consists of higher powder content which provides maximum hydration and pozzolanic reaction, thereby contributing to the enhancement of the UHPC properties. Apart from that the nanomaterials provides the filler behavior, which will further improve the density. Enhanced density and mechanical properties lead to improved durability properties against water absorption and other typical chemicals. Nanomaterials are the most adopted materials for various applications, ranging in size from 0.1 nanometers to 100 nanometers. This article explores the effects of nanomaterial application in UHPC as a replacement for cementitious material or as an additive in the UHPC mix. The physical and durability properties modifications and improvements of UHPC, as well as negative effects, limitations, and shortcomings, are also analyzed.

• Computers and Concrete
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• v.33 no.4
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• pp.385-398
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• 2024

As concrete dominates the construction industry, alternatives to traditionally used steel reinforcement are being sought. This study explored the suitability of carbon fiber-reinforced polymer (CFRP) as a substitute within rigid frames, focusing on its impact on section ductility and overall structural durability against seismic events. However, current design guidelines address quasi-static loads, leaving a gap for dynamic or extreme circumstances. Our approach included multiscale simulations, parametric study, and energy dissipation analyses, drawing upon a unique adaptation of modified compression field theory. In our efforts to optimize macro and microparameters to improve yield strength, manage brittleness, and govern failure modes, we also recognized the potential of CFRP's high corrosion resistance. This characteristic of CFRP could significantly reduce the frequency of required repairs, thereby contributing to enhanced durability of the structures. The research reveals that CFRP's durability and seismic resistance are attributed to plastic joints within compressed fibers. Notably, CFRP can impart ductility to structural designs, effectively balancing its inherent brittleness, particularly when integrated with quasi-brittle materials. This research challenges the notion that designing bendable components with carbon fiber reinforcement is impractical. It shows that creating ductile bending components with CFRP in concrete is feasible despite the material's brittleness. This funding overturns conventional assumptions and opens new avenues for using CFRP in structural applications where ductility and resilience are crucial.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.189-195
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• 2024

Buried pipelines can be classified as continuous and segmented pipelines. These infrastructures can be damaged either by ground movement or by seismic wave propagation during an earthquake. Permanent ground deformations (PGD) include surface faulting, liquefaction-induced lateral spreading and landslide. Liquefaction is a major problem for both superstructures and infrastructures. Buyukcekmece lake zone, which is the studied region in this paper, is a liquefaction prone area located near the North Anatolian Fault Line. It is an active fault line in Turkey and a major earthquake with a magnitude of around 7.5 is expected in this investigated region in Istanbul. It is planned to be constructed a new 12" steel natural gas pipeline from one side of the lake to the other side. In this study, this case has been examined in terms of two different support conditions. Firstly, it has been defined as a beam in liquefied soil and has built-in supports at both ends. In the other approach, this case has been modeled as a beam in liquefied soil and has vertical elastic pinned supports at both ends. These models have been examined and some solution proposals have been produced according to the obtained results. In this study, based on this sample, it is aimed to determine the behaviors of buried continuous pipelines subject to liquefaction effects in terms of buoyancy.

• Journal of the Korean GEO-environmental Society
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• v.7 no.2
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• pp.67-76
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• 2006

For a hydro power plant project, the headrace tunnel having a finished diameter of 3.3 m was constructed in volcanic rocks with well-developed vertical joint and high groundwater table. The intake facility was located 20.3km upstream of the powerhouse and headrace tunnel of 20km in length and penstock of 440m in height connected the intake and the powerhouse. The typical caldera lake, Lake Toba set the geology at the site the caving of the ground caused tension cracks in the vertical direction to be developed and initial stresses at the ground to be released. High groundwater table(the maximum head of 20bar) in the area of well-connected vertical joints delayed the progress of tunnel excavation severely due to the excessive inflow of groundwater. The excavation of tunnel was made using open-shield type TBM and mucking cars on the rail. High volume of water inflowraised the water level inside tunnel to 70cm, 17% of tunnel diameter (3.9m) and hindered the mucking of spoil under water. To improve the productivity, several adjustments such as modification of TBM and mucking cars and increase in the number of submersible pumps were made forthe excavation of severe water inflow zone. Since the ground condition encountered during excavation turned out to be much worse, it was decided to adopt PC segment lining instead of RC lining. Besides, depending on the conditions of the water inflow, rock mass condition and internal water pressure, one of the invert PC segment lining with in-situ RC lining, RC lining and steel lining was applied to meet the site specific condition. With the adoption of PC segment lining, modification of TBM and other improvement, the excavation of the tunnel under severe groundwater condition was successfully completed.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.152-160
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• 2021

Converter steel slag(BOF slag) is a vast amount of solid waste generated in the steelmaking process which has very low utilization rate in Korea. Due to the presence of free CaO which can derive bad volume stability in BOF slag, it usually land filled. For recycling BOF and identify its applicability as fine aggregate, this study investigates the fundamental characteristics of mortar with cement replaced ferronickel slag(FNS), which has the potential to be used as a binder. The results suggest that the mineral phases of BOF slag mainly include larnite(CaSiO₄), mayenite(Ca₁₂Al₁₄O₃₃) and wuestite(FeO) while olivine crystallines are shown in FNS. The results of flow and setting time reveals that the flowability and process of hardening increased when the amount of FNS and BOF slag incorporated was increased. The length change shows that the amount of change in the length of the mortar was almost constant regardless of mix proportion while compressive strength was reduced. Micro structure test results revealed that FNS or/and BOF slag mix took a long time to react in the cement matrix to form a complete hydration products. To achieve the efficient utilization of B OF slag as construction materials, proper replacement rate is necessary.

• Journal of the Korean GEO-environmental Society
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• v.16 no.3
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• pp.23-34
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• 2015

In this study, a newly modified soil nailing technology using bamboo is developed. And field tests were performed to confirm applicability of bamboo soil nailing system. For the practical use of bamboo soil nailing system, laboratory tests, field instrumentations and pullout tests were also performed to investigate the applicability. The results of field measurement through field tests were compared with the results of numerical analyses for verifying the field construction. As a result, the results of comparing with the field measurement and numerical analyses shows the similar behavior characteristics. Based on this study, applicability for bamboo soil nailing systems were confirmed for the case of comparatively low scale nailed-soil excavation wall. And it is expected that the bamboo soil nailing system can be used as satisfactory reinforcement technique taking the place of existing steel reinforcement soil nailing system. Hereafter, it needed the research for the applicability for the various types of excavation condition, also the active practical application of bamboo soil nailing system is needed.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.187-194
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• 2013

Fiber reinforced polymer (FRP) has been gathering interest from designers and engineers for its possible usage as a replacement reinforcement of a steel reinforcing bar due to its advantageous characteristics such as high tensile strength, non-corrosive material, etc. Since it is manufactured with various contents ratios, fiber types, and shapes without any general specification, test results for concrete members reinforced with these FRP reinforcing bars could not be systematically used. Moreover, since investigations for FRP reinforced members have mainly focused on short-term behavior, the purpose of this study is to evaluate long-term behaviors of glass FRP (GFRP) reinforcing bar and concrete beams reinforced with GFRP. In this paper, test results of tensile and bond performance of GFRP reinforcing bar and creep behavior are presented. In the creep tests, results showed that 100 years of service time can be secured when sustained load level is below 55% of tensile strength of GFRP reinforcing bar. A modification factor of 0.73 used to calculate long-term deflection of GFRP reinforced beams was acquired from the creep tests for GFRP reinforced concrete beams. It is expected that these test results would give more useful information for design of FRP reinforced members.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.5
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• pp.459-470
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• 2014

Now-a-days, the trend in constructing tunnels is to build more deeper, more longer tunnels of greater cross-sections. That's why, the demand of "Early-high-strength shotcrete" is very high because of their advantage of attaining higher strength immediately after excavation, which controls the ground subsidence. So, this study reveals the supporting phenomena of early-high-strength shotcrete, using three-dimensional numerical analysis. The crux of this study can be applied practically in construction sites also. Support Performance of two different qualities of shotcrete was checked out, by keeping the general shotcrete's thickness constant and comparing it with early-high-strength shotcrete's thickness decreasing it gradually in five steps, and analysing/comparing the support performance in all cases. Effect of using early-high-strength shotcrete was analysed to save the cost of steel sets, which are widely used for supporting the ground before the hardening of general shotcrete. The results of numerical analysis on the performance of early-high-strength shotcrete show that, it behaves more effectively under worse ground conditions and it can support the ground more conveniently than steel sets, before the shotcrete is hardened.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.5
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• pp.431-439
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• 2016

This paper dealt with contents of the quality evaluation method of lattice girder utilizing non-destructive method. Quality evaluation of ordinary lattice girder is performed through the tensile strength test of structural steel and visual inspection. The tensile strength test of structural steel is performed by collecting samples of lattice girder brought into the site, during which lattice girder must be damaged to obtain sample. In addition to such disadvantage, tensile strength tester is not available at the site in most cases, requiring an inconvenient service from test certification agency. In addition, it is substituted by mile sheet issued during the production of structural steel, which inevitably lacks reliability. Furthermore, visual inspection at the site entails a problem of lack of reliability, thereby requiring a method of easily and quickly evaluating the quality of lattice girder without damaging the material. Accordingly, this study comparatively analyzed the yield strength of tensile strength test and the yield strength of instrumented indentation test with same sample. The test results ensured over 95% precision level for the instrumented indentation test, based on which a quality evaluation method based on instrumented indentation test that allowed onsite direct quality evaluation is proposed.