• Korean Journal of Construction Engineering and Management
• /
• v.22 no.3
• /
• pp.21-30
• /
• 2021

This study proposes a 5-month rebar price prediction method using the recursive prediction method of deep learning. This approach predicts a long-term point in time by repeating the process of predicting all the characteristics of the input data and adding them to the original data and predicting the next point in time. The predicted average accuracy of the rebar prices for one to five months is approximately 97.24% in the manner presented in this study. Through the proposed method, it is expected that more accurate cost planning will be possible than the existing method by supplementing the systematicity of the price estimation method through human experience and judgment. In addition, it is expected that the method presented in this study can be utilized in studies that predict long-term prices using time series data including building materials other than rebar.

• Steel and Composite Structures
• /
• v.43 no.1
• /
• pp.91-106
• /
• 2022

This paper has focused on presenting a three dimensional theory of elasticity for free vibration of 3D-graphene foam reinforced polymer matrix composites (GrF-PMC) cylindrical panels resting on two-parameter elastic foundations. The elastic foundation is considered as a Pasternak model with adding a Shear layer to the Winkler model. The porous graphene foams possessing 3D scaffold structures have been introduced into polymers for enhancing the overall stiffness of the composite structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the shell thickness direction. The effective Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary at the curved edges. It is explicated that 3D-GrF skeleton type and weight fraction can significantly affect the vibrational characteristics of GrF-PMC panel resting on two-parameter elastic foundations.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.35 no.6
• /
• pp.381-386
• /
• 2022

This paper details the analytical and experimental studies performed to propose a steel damper based on the flexural yielding mechanism. The damper is composed of a set of damping plates that are designed to yield in flexure. The comparison of experimental and finite element analysis results indicate that the analytical approach adopted in this study should be appropriate to perform sensitivity studies on the geometries of the damping plates. Although the damper is originally proposed to work based on the flexural mechanism, it is observed that the contribution of the tensile behavior of the damping plate could be considerable. As the thickness of the damping plate increases, the plastic energy due to the flexural yield increases. As the thickness of the damping plate decreases, the contribution of the tensile behavior increases, and the shape of the hysteresis loop distorts.

• Journal of the Korea Institute of Information Security & Cryptology
• /
• v.33 no.4
• /
• pp.621-631
• /
• 2023

Adversarial training improves the robustness of deep neural networks for adversarial examples. However, the previous adversarial training method focuses only on the adversarial loss function, ignoring that even a small perturbation of the input layer causes a significant change in the hidden layer features. Consequently, the accuracy of a defended model is reduced for various untrained situations such as clean samples or other attack techniques. Therefore, an architectural perspective is necessary to improve feature representation power to solve this problem. In this paper, we apply an attention module that generates an attention map of an input image to a general model and performs PGD adversarial training upon the augmented model. In our experiments on the CIFAR-10 dataset, the attention augmented model showed higher accuracy than the general model regardless of the network structure. In particular, the robust accuracy of our approach was consistently higher for various attacks such as PGD, FGSM, and BIM and more powerful adversaries. By visualizing the attention map, we further confirmed that the attention module extracts features of the correct class even for adversarial examples.

• International conference on construction engineering and project management
• /
• 2005.10a
• /
• pp.968-973
• /
• 2005

The purpose of this study is to clarify the reality of labor and capital productivity in the construction industry through an industry-level approach and to analyze the relationship between labor and capital productivity using a Cobb-Douglas production function. According to the research results, the construction industry has shown a very high capital productivity, while labor productivity has kept up a low level during the 1980s and 1990s. The reason was because of the lack of skillful construction workers and the decrease of capital. Meanwhile, the construction productivity has greatly increased since 2000 when there was no change in wages. This was because of a large inflow of low-wage foreign workers while the amount of value added has dramatically increased due to the liberalized sale price of apartment buildings. According to the analysis by the Cobb-Douglas production function, the elasticity coefficient of V/L to K/L in the construction industry had decreased from 1.1663 in the 1^st period(1971-1988) to 0.4465 in the 2^nd period(1989-1997), and to 0.1664 in the 3^rd period(1998-2003). Such a result means that the allocation of labor has gradually increased while the allocation of capital has decreased. Moreover there was a big increase in allocation of labor after 1998 due to the excessive deterioration of capital. In conclusion, in order to raise the construction productivity and to avoid labor-intensive production methods, investment for capital should be more increased. In particular, new machinery and equipment that can actually substitute human labor in construction sites should be more developed and applied to construction sites.

• Journal of the Korea Institute of Building Construction
• /
• v.23 no.2
• /
• pp.143-152
• /
• 2023

In this research, the microwave oven drying method was investigated as a potential accurate testing approach for determining the water content of fresh concrete. To do so, water content estimation formulas employed in three prominent oven drying test methods were selected, and the calculation principles for each equation, along with potential error factors arising during the actual testing process, were considered. Moreover, a concrete test was conducted to validate the possible error factors. Consequently, it was confirmed that estimation errors in the water content of fresh concrete can occur due to sample deviations arising during the wet screening process for creating mortar specimens or deviations in the coarse aggregate sampling quantity during the sample collection process.

• Structural Engineering and Mechanics
• /
• v.86 no.6
• /
• pp.715-730
• /
• 2023

Broad studies have addressed the issue of structural element damage identification, however, rubber bearing, as a key component of load transmission between the superstructure and substructure, is essential to the operational safety of a bridge, which should be paid more attention to its health condition. However, regarding the limitations of the traditional bearing damage detection methods as well as few studies have been conducted on this topic, in this paper, inspired by the model updating-based structural damage identification, a two-stage bearing damage identification method has been proposed. In the first stage, we deduce a novel bearing damage localization indicator, called element relative MSE, to accurately determine the bearing damage location. In the second one, the prior knowledge of bearing damage localization is combined with sailfish optimization (SFO) to perform the bearing damage estimation. In order to validate the feasibility, a numerical example of a 5-span continuous beam is introduced, also the noise robustness has been investigated. Meanwhile, the effectiveness and engineering applicability are further verified based on an experimental simply supported beam and actual engineering of the I-40 Bridge. The obtained results are good, which indicate that the proposed method is not only suitable for simple structures but also can accurately locate the bearing damage site and identify its severity for complex structure. To summarize, the proposed method provides a good guideline for the issue of bridge bearing detection, which could be used to reduce the difficulty of the traditional bearing failure detection approach, further saving labor costs and economic expenses.

• International conference on construction engineering and project management
• /
• 2013.01a
• /
• pp.437-443
• /
• 2013

Recently, sustainable building design, a growing field within architectural design, has been emerged in the construction industry as the practice of designing, constructing, and operating facilities in such a manner that their environmental impact, which has become a great concern of construction professionals, can be minimized. A number of different green rating systems have been developed to help assess that a building project is designed and built using strategies intended to minimize or eliminate its impact on the environment. In the United States, the widely accepted national standards for sustainable building design are known as the LEED (Leadership in Energy and Environmental Design) Green Building Rating System. The assessment of sustainability using the LEED green rating system is a challenging and time-consuming work due to its complicated process. In effect, the LEED green rating system awards points for satisfying specified green building criteria into five major categories: sustainable sites, water efficiency, energy and atmosphere, materials and resources, and indoor environmental quality; and sustainability of a project is rated by accumulating scores (100 points maximum) from these five major categories. The sustainability rating process could be accelerated and facilitated by using computer technology such as BIM (Building Information Modeling), an innovative new approach to building design, engineering, and construction management that has been widely used in the construction industry. BIM is defined as a model-based technology linked with a database of project information, which can be accessed, manipulated, and retrieved for construction estimating, scheduling, project management, as well as sustainability rating. This paper will present a framework representing the building knowledge contained in the LEED green building criteria. The proposed building knowledge framework will be implemented into a BIM platform (e.g. Autodesk Revit Architecture) in which sustainability rating of a building design can be automatically performed. The development of the automated sustainability rating system and the results of its implementation will be discussed.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.5
• /
• pp.295-305
• /
• 2023

This study introduces a smoothed finite-element implementation into the phase-field framework. In recent years, the phase-field method has recieved considerable attention in crack initiation and propagation since the method needs no further treatment to express the crack growth path. In the phase-field method, high strain-energy accuracy is needed to capture the complex crack growth path; thus, it is obtained in the framework of the smoothed finite-element method. The salient feature of the smoothed finite-element method is that the finite element cells are divided into sub-cells and each sub-cell is rebuilt as a smoothing domain where smoothed strain energy is calculated. An adaptive quadtree refinement is also employed in the present framework to avoid the computational burden. Numerical experiments are performed to investigate the performance of the proposed approach, compared with that of the finite-element method and the reference solutions.

• Journal of the Korea Institute of Building Construction
• /
• v.24 no.2
• /
• pp.261-271
• /
• 2024

The widespread adoption of aluminum slab formwork in modern construction, evident in both domestic and international projects, offers numerous advantages. However, a critical challenge persists regarding the dismantling process for these slabs. The current industry standard involves dropping the slabs to the ground floor upon removal. This practice raises several concerns, notably the generation of significant noise pollution that disrupts nearby communities. More importantly, the risk of worker injuries due to falls from height during the dismantling process is a serious safety hazard. Additionally, the impact from dropping the slabs can damage the aluminum itself, leading to increased replacement costs. These drawbacks necessitate the exploration of alternative dismantling techniques that prioritize worker safety, material sustainability, and overall process efficiency. Accordingly, in this study, when the entire first-generation slab formwork of an apartment house is simultaneously lowered to a reachable position for workers, it is then disassembled and lifted for transport to the next floor. This approach has the potential to demonstrate improvements in safety, quality, economy, and process efficiency.