• International Journal of Concrete Structures and Materials
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• v.9 no.1
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• pp.69-88
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• 2015

Self-consolidating concrete (SCC) is a stable and cohesive high consistency concrete mix with enhanced filling ability properties that reduce the need for mechanical compaction. Limited standards and specifications have been reported in the literature on the structural behavior of reinforced self-compacting concrete elements. The significance of the research presented in this paper stems from the need to investigate the effect of enhanced fluidity of SCC on the structural behavior of high strength self-consolidating reinforced concrete beams. To meet the objectives of this research, twelve reinforced concrete beams were prepared with two different generations of superplasticizers and designed to exhibit flexure, shear, or bond splitting failure. The compared beams were identical except for the type of superplasticizer being used (second generation sulphonated-based superplasticizer or third generation polycarboxylate-based superplasticizer). The outcomes of the experimental work revealed comparable resistance of beam specimens made with self-compacting (SCC) and conventional vibrated concrete (VC). The dissimilarities in the experimental values between the SCC and the control VC beams were not major, leading to the conclusion that the high flowability of SCC has little effect on the flexural, shear and bond strengths of concrete members.

• Steel and Composite Structures
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• v.27 no.6
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• pp.661-674
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• 2018

Seismic excitations may impart a significant amount of energy into structures. Modern structural design attitudes tend to absorb some part of this energy through special dissipaters instead of heavy plastic deformations on the structural members. Different types of dissipater have been generated and utilized in various types of structures in last few decades. The expected earthquake damage is mainly concentrated on these devices and they may be replaced after earthquakes. In this study, a low-cost device called energy dissipative steel cushion (EDSC) made of flat mild steel was developed and tested in the Structural and Earthquake Engineering Laboratory (STEELab) of Istanbul Technical University (ITU). The monotonic and cyclic tests of EDSC were performed in transversal and longitudinal directions discretely. Very large deformation capability and stable hysteretic behavior are some response properties observed from the tests. Load vs. displacement relations, hysteretic energy dissipation properties as well as the closed form equations to predict the behavior parameters are presented in this paper.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.865-870
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• 2001

This paper propose a new seismic detail for ductility enhancement by interlocking spiral reinforcement in the potential yield regions of a wall. Through the theoretical consideration and experiment program, confinement with interlocking spirals lead the structural walls to ductile behavior. All specimens show stable hysteretic behavior and good energy dissipation capacity. Also the increase of shear strength mainly induces a flexural failure mode. As interlocking spiral are used in lapped splice region, they increase the bond strength and prevent a early tensile failure caused by the loss of bond stresses. Consequently, the confinement with interlocking spirals may result in a lower value of force reductions factor, newly proposed detail will be provide more economical design.

• Journal of Korean Association for Spatial Structures
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• v.23 no.4
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• pp.89-96
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• 2023

The seismic retrofits of existing structures have been focused on the control of structural responses which can be achieved by providing displacement capacity through inelastic ductile action at supplemental devices. Due to their hysteretic characteristics, it is expected to sustain damage through repeated inelastic behaviors including residual deformation which might increase repair costs. To solve such drawbacks of existing yielding devices, this study proposes a self-centering disc spring brace that sustains large axial deformation without structural damage while providing stable energy dissipation capacity. The hysteretic behaviors of suggested brace are first investigated based on the quasi-static cyclic test procedure. Experimental results present the effective self-centering behavior and an analytical model is then suggested in order to reasonably capture the flag-shaped hysteretic behavior of the disc spring brace.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.8
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• pp.21-28
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• 1997

This paper presents the influence of the process parameters on the change in dynamic behavior of a lathe turning system. With variation of feed rate, depth of cut, direction of tool motion, cutting speed and tool location along the workpiece, the dynamic characteristics of stable cutting, chatter transition and fully developed chatter regions are demonstrated. The workpiece vibration during machining is continuously measured at different tool locations along the workpiece and quantitatively analyzed. Complex linear behavior due to change of process parameter values as well as fundamental wystem nonlinearity due to change of process configuration indicated by a tool path dependence of the locations of chatter onset and disappearance are described. Finally, the structural characteristics of the turning system which can have large and nonlinear effects on system behavior are presented.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.167-174
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• 2001

A shape resistant shell structure is an extremely efficient mechanical creation because it transmits forces mainly by in-plane forces, but at a certain load level it changes from a stable condition to an unstable condition or vise versa. The instability phenomenon of Geiger-type cable dome structure is generated due to the in-plane twisting near critical load level. Therefore the effect of bracing reinforcement is investigated for the Geiger-type model reinforced by bracing. The effect of initial imperfection is also studied since the structural instability behavior characteristic of shell-like structure is significantly sensitive according to the initial condition.

• International Journal of Automotive Technology
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• v.6 no.1
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• pp.45-52
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• 2005

Interrupted creep tests for investigating the structural degradation during creep were conducted for a Mod.9Cr-1Mo steel in the range of stress from 71 to 167 MPa and temperature from 873 to 923 K. The change of hardness and tempered martensitic lath width was measured in grip and gauge parts of interrupted creep specimens. The lath structure was thermally stable in static conditions. However, it was not stable during creep, and the structural change was enhanced by creep strain. The relation between the change in lath width and creep strain was described quantitatively. The change in Vickers hardness was expressed by a single valued function of creep LCR(life consumption ratio). Based on the empirical relation between strain and lath width, a model was proposed to describe the relation between change in hardness and creep LCR. The comparison of the model with the empirical relation suggests that about 65% of hardness loss is due to the decrease of dislocation density accompanied by the movement of lath boundaries. The role of precipitates on subboundaries was discussed in connection with the abnormal subgrain growth appearing in low stress regime.

• Journal of the Korean Society for Precision Engineering
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• v.21 no.2
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• pp.168-176
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• 2004

Interrupted creep tests were carried out on the Mod.9Cr-1Mo steel in order to investigate the structural degradation during creep. The ranges of creep stress and temperature were from 71 to 167MPa and 873 to 923k, respectively. The change of hardness and tempered martensitic lath width were measured in the grip and gauge parts of interrupted specimens. The lath structure was thermally stable in static conditions, but was not stable during creep, and the structural evolution was enhanced by creep strain. The relation between the change in lath width and strain was described in the from, $\delta$W= a ($W_s-W_o$)$cdot;varepsilon$, where $\varepsilon$ is the strain, $W_o$is the initial lath width, $W_s$ is the final lath width depending solely on stress, and a is the constant of the magnitude of 0.67 $\mu$m /strain. The change in Victors hardness was expressed by a one-valued function of creep life consumption ratio. Based on the empirical relation between strain and lath width, a model was proposed to explain the relation between change in hardness and creep life consumption ratio. The model revealed that about 65$%$ of dislocations in lath structures were eliminated by the migration of subboundaries.

• International Journal of High-Rise Buildings
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• v.8 no.2
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• pp.117-123
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• 2019

Tall buildings are prone to wind-induced vibrations due to their slenderness whereby peak structural accelerations may be higher than the recommended maximum value. The common countermeasure is the installation of a tuned mass damper (TMD) near the highest occupied floor. Due to the extremely large modal mass of tall buildings and because of the narrow to broad band type of wind excitation the TMD mass may become inacceptable large - in extreme cases up to 2000 metric tons. It is therefore a need to develop more efficient TMD concepts which provide the same damping to the building but with reduced mass. The adaptive TMD concept described in this paper represents a solution to this problem. Frequency and damping of the adaptive TMD are controlled in real-time by semi-active oil dampers according to the actual structural acceleration. The resulting enhanced TMD efficiency allows reducing its mass by up to 20% compared to the classical passive TMD. The adaptive TMD system is fully fail-safe thanks to a smart valve system of the semi-active oil dampers. In contrast to active TMD solutions the adaptive TMD is unconditionally stable and its power consumption on the order of 1 kW is negligible small as controllable oil dampers are semi-active devices. The adaptive TMD with reduced mass, stable behavior and lowest power consumption is therefore a preferable and cost saving damping tool for tall buildings.

• Geomechanics and Engineering
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• v.34 no.2
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• pp.155-171
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• 2023

Aiming at the grouting treatment of water inflow in karst conduits, a visualized experiment system for conduit-type grouting blocking was developed. Through the improved water supply system and grouting system, and the optimized multisource information monitoring system, the real-time observation of diffusion and deposition of slurry, and the data acquisition of pressure and velocity during the whole process of grouting were realized, which breaks through the problem that the monitoring element is easy to fail due to slurry adhesion in conventional test system. Based on the grouting experiments in static and flowing water, the diffusion and deposition behavior of the quick-setting slurry under different working conditions were analyzed. The temporal and spatial variation behavior of the pressure and velocity were studied, and the blocking mechanism of the grouting were further revealed. The results showed that: (1) Under the flowing water condition, the counter-flow diffusion distance of slurry was negatively correlated with the flow water velocity and the volume ratio of cement and sodium silicate (C-S ratio), and positively correlated with the grouting volume. The slurry deposition thickness was negatively correlated with the flowing water velocity, and positively correlated with the grouting volume and C-S ratio. (2) The pressure increased slowly before blocking of the flowing water and rapidly after blocking in karst conduits. (3) With the continuous progress of grouting, the flowing water velocity decreased slowly first, then significantly, and finally tended to be stable. According to the research results, some engineering recommendations were put forward for the grouting treatment of the conduit-type water inflow disaster, which has been successfully applied in the treatment project of the China Resources Cement (Pingnan) Limestone Mine. This study provided some guidance and reference for the parameter optimization of grouting for the treatment projects of water inflow in karst conduits.