• Smart Structures and Systems
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• v.14 no.2
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• pp.85-104
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• 2014

Damage detection is a challenging, complex, and at the same time very important research topic in civil engineering. Identifying the location and severity of damage in a structure, as well as the global effects of local damage on the performance of the structure are fundamental elements of damage detection algorithms. Local damage detection is essential for structural health monitoring since local damages can propagate and become detrimental to the functionality of the entire structure. Existing studies present several methods which utilize sensor data, and track global changes in the structure. The challenging issue for these methods is to be sensitive enough in identifYing local damage. Autoregressive models with exogenous terms (ARX) are a popular class of modeling approaches which are the basis for a large group of local damage detection algorithms. This study presents an algorithm, called Influence-based Damage Detection Algorithm (IDDA), which is developed for identification of local damage based on regression of the vibration responses. The formulation of the algorithm and the post-processing statistical framework is presented and its performance is validated through implementation on an experimental beam-column connection which is instrumented by dense-clustered wired and wireless sensor networks. While implementing the algorithm, two different sensor networks with different sensing qualities are utilized and the results are compared. Based on the comparison of the results, the effect of sensor noise on the performance of the proposed algorithm is observed and discussed in this paper.

• Structural Engineering and Mechanics
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• v.19 no.2
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• pp.185-198
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• 2005

In the design of reinforced concrete beams, it is a standard practice to use the yield stress of the steel reinforcement for the evaluation of the flexural strength. However, because of strain hardening, the tensile strength of the steel reinforcement is often substantially higher than the yield stress. Thus, it is a common belief that the actual flexural strength should be higher than the theoretical flexural strength evaluated with strain hardening ignored. The possible increase in flexural strength due to strain hardening is a two-edge sword. In some cases, it may be treated as strength reserve contributing to extra safety. In other cases, it could lead to greater shear demand causing brittle shear failure of the beam or unexpected greater capacity of the beam causing violation of the strong column-weak beam design philosophy. Strain hardening may also have certain effect on the flexural ductility. In this paper, the effects of strain hardening on the post-peak flexural behaviour, particularly the flexural strength and ductility, of reinforced normal- and high-strength concrete beams are studied. The results reveal that the effects of strain hardening could be quite significant when the tension steel ratio is relatively small.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.100-115
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• 1993

In this paper, the extent of use of three kinds of the existing idealized structural units, namely the idealized beam-column unit, the idealized unstiffened plate unit and the idealized stiffened plate unit, is expanded to deal with the excessive tension-deformation effects, in which a simplified mechanical model for the stress-strain relation of steel members under tensile load is suggested. The 1/3-scale hull model for a leander class frigate under sagging moment tested by Dow is analyzed, and it is shown that the excessive tension-de-formation is a significant factor affecting the progressive collapse behavior, particularly in the post-collapse range.

• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.243-255
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• 2019

Utilization of fiber beam-column element has gained considerable attention in recent years due mainly to its ability to model distributed plasticity over the length of the element through a number of integration points. However, the relatively high sensitivity of the method to modeling parameters as well as material behavior models can pose a significant challenge. Residual drift is one of the seismic demands which is highly sensitive to modeling parameters and material behavior models. Permanent deformations play a prominent role in the post-earthquake evaluation of serviceability of bridges affected by a near-fault ground shaking. In this research, the influence of distributed plasticity modeling parameters using both force-based and displacement-based fiber elements in the prediction of internal forces obtained from the nonlinear static analysis is studied. Having chosen suitable type and size of elements and number of integration points, the authors take the next step by investigating the influence of material behavioral model employed for the prediction of permanent deformations in the nonlinear dynamic analysis. The result shows that the choice of element type and size, number of integration points, modification of cyclic concrete behavior model and reloading strain of concrete significantly influence the fidelity of fiber element method for the prediction of permanent deformations.

• Environmental Engineering Research
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• v.24 no.3
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• pp.501-512
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• 2019

The seasonal effects on the biostability of drinking water were investigated by comparing the seasonal variation of assimilable organic carbon (AOC) in full-scale water treatment process and adsorption of AOC by three filling materials in lab-scale column test. In full-scale, pre-chlorination and ozonation significantly increase $AOC_{P17\;(Pseudomonas\;fluorescens\;P17)}$ and $AOC_{NOX\;(Aquaspirillum\;sp.\;NOX)}$, respectively. AOC formation by oxidation could increase with temperature, but the increased AOC could affect the biostability of the following processes more significantly in winter than in warm seasons due to the low biodegradation in the pipes and the processes at low temperature. $AOC_{P17}$ was mainly removed by coagulation-sedimentation process, especially in cold season. Rapid filtration could effectively remove AOC only during warm seasons by primarily biodegradation, but biological activated carbon filtration could remove AOC in all seasons by biodegradation during warm season and by adsorption and bio-regeneration during cold season. The adsorption by granular activated carbon and anthracite showed inverse relationship with water temperature. The advanced treatment can contribute to enhance the biostability in the distribution system by reducing AOC formation potential and helping to maintain stable residual chlorine after post-chlorination.

• Earthquakes and Structures
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• v.19 no.6
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• pp.459-469
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• 2020

An external prestressed steel-bar truss unit was developed as a new strengthening technology to enhance the seismic performance of an in-plane masonry wall structure while taking advantage of the benefits of a prestressed system. The presented method consists of six steel bars: two prestressed vertical bars to introduce a prestressing force on the masonry wall, two diagonal bars to resist shear deformation, and two horizontal bars to maintain the configuration. To evaluate the effects of this new technique, four full-scale specimens, including a control specimen, were tested under combined loadings that included constant-gravity axial loads and cyclic lateral loads. The experimental results were analyzed in terms of the shear strength, initial stiffness, dissipated energy, and strain history. The efficiency of the external prestressed steel-bar truss unit was validated. In particular, a retrofitted specimen with an axial load level of 0.024 exhibited a more stable post behavior and higher energy dissipation than a control specimen with an observed complete sliding failure. The four vertical bars of the adjacent retrofitting units created a virtual column, and their strain values did not change until they reached the peak shear strength. The shear capacity of the masonry wall structure with external prestressed steel-bar truss units could be predicted using the model suggested by Yang et al.

• Structural Engineering and Mechanics
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• v.85 no.3
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• pp.407-417
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• 2023

Precast assembled bridge piers with hybrid connection (PASP) use both tendons and socket connections. To study the seismic performance of PASP, a full-scale in-situ test was performed based on an actual bridge project. The elastic-plastic fiber model of PASP was established using finite element software, and numerical analyses were performed to study the influence of prestress degree and socket depth on the PASP seismic performance. The results show that the typical failure mode of PASP under horizontal load is bending failure dominated by concrete cracking at the joint between the column and cushion cap. The cracking of the pier concrete and opening of joints depend on the prestress degree and socket depth. The prestressing tendons and socket connection can provide enough ductility, strength, restoration capability, and bending strength under small horizontal displacements. Although the bearing capacity and post yield stiffness of the pier can be improved to some extent by increasing the prestressing force, ductility is reduced, and residual deformation is increased. Overall, there are reasonable minimum socket depths to ensure the reliability of the socket connection.

• Steel and Composite Structures
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• v.44 no.3
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• pp.423-436
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• 2022

This paper proposes an innovative thin-walled square concrete filled steel tubular (CFST) column with an octagonal/circular lining steel tube, in which the outer steel tube and the inner liner are fabricated independently of each other and connected by slot-weld or self-tapping screw connections. Twelve thin-walled square CFST columns were tested under quasi-static loading, considering the parameters of liner type, connection type between the square tube and liner, yield strength of steel tube, and the axial load ratio. The seismic performance of the thin-walled square CFST columns is effectively improved by the octagonal and circular liners, and all the liner-stiffened specimens showed an excellent ductile behavior with the ultimate draft ratios being much larger than 1/50 and the ductility coefficients being generally higher than 4.0. The energy dissipation abilities of the specimens with circular liners and self-tapping screw connections were superior to those with octagonal liner and slot-weld connections. Based on the test results, both the finite element (FE) and simplified theoretical models were established, considering the post-buckling strength of the thin-walled square steel tube and the confinement effect of the liners, and the proposed models well predicted the hysteretic behavior of the liner-stiffened specimens.

• Steel and Composite Structures
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• v.48 no.5
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• pp.565-582
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• 2023

The present research reports the application of engineered cementitious composites (ECC) as an alternative to conventional concrete to improve the seismic behavior of short columns. Experimental and finite element investigation was conducted by testing five reinforced engineered cementitious composite (RECC) concrete columns (half-scale specimens) and one control reinforced concrete (RC) specimen for different shear-span and transverse reinforcement ratios under cyclic lateral loads. RECC specimens with higher shear-span and transverse reinforcement ratios demonstrated a significant effect on the column lateral load behavior by improving ductility (>5), energy dissipation capacity (1.2 to 4.1 times RC specimen), gradual strength degradation (ultimate drift >3.4%), and altering the failure mode. The self-confinement effect of ECC fibers maintained the integrity in the post-peak region and reserved the transmission of stress through fibers without noticeable degradation in strength. Finite element modeling of RECC specimens under monotonic incremental loads was carried out by adopting simplified constitutive material models. It was apprehended that the model simulated the global response (strength and stiffness) and damage crack patterns reasonably well.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.2
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• pp.49-58
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• 2022

The 2017 Pohang earthquake caused severe damage to low-rise piloti buildings. The damage was caused mainly by column shear failure, and some core walls were as well. The damaged piloti buildings in Pohang City could be relieved if they were designed correctly according to the standards at that time. However, the post-earthquake investigation revealed design, construction, and permission problems. To solve the problems, the Piloti Building Structure Design Guidelines that include strict specifications were published in 2018. Separately, KDS 41 17 00, the seismic design standard for buildings, was enacted in 2019 and it included the guideline contents. Therefore, at least after the publication of the guidelines, piloti buildings, designed by the standard and guidelines, can be expected to possess better seismic performance than existing piloti buildings. To confirm this, the probability of exceedance for several damage state thresholds was estimated for existing and designed piloti buildings. As a result, the probability of damage of designed piloti buildings was very low compared to existing ones. Consequently, it was confirmed that the guideline and standard adequately supplement the structural fragility of existing piloti buildings.