• Structural Engineering and Mechanics
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• v.27 no.4
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• pp.501-521
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• 2007

This study presents a model to better understand the shear behavior of reinforced concrete walls subjected to lateral load. The scope of the study is limited to squat walls with height to length ratios not exceeding two, deformed in a double-curvature shape. This study is based on limited knowledge of the shear behavior of low-rise shear walls subjected to double-curvature bending. In this study, the wall ultimate strength is defined as the smaller of flexural and shear strengths. The flexural strength is calculated using a strength-of-material analysis, and the shear strength is predicted according to the softened strut-and-tie model. The corresponding lateral deflection of the walls is estimated by superposition of its flexibility sources of bending, shear and slip. The calculated results of the proposed procedure correlate reasonably well with previously reported experimental results.

• Earthquakes and Structures
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• v.7 no.5
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• pp.647-665
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• 2014

Squat reinforced concrete walls require enough shear strength in order to promote flexural yielding, which creates the need for designers of an accurate method for strength prediction. In many cases, especially for existing buildings, strength estimates might be insufficient when more accurate analyses are needed, such as pushover analysis. In this case, estimates of load versus displacement are required for building modeling. A model is developed that predicts the shear load versus shear deformation of squat reinforced concrete walls by means of a panel formulation. In order to provide a simple, design-oriented tool, the formulation considers the wall as a single element, which presents an average strain and stress field for the entire wall. Simple material constitutive laws for concrete and steel are used. The developed models can be divided into two categories: (i) rotating-angle and (ii) fixed-angle models. In the first case, the principal stress/strain direction rotates for each drift increment. This situation is addressed by prescribing the average normal strain of the panel. The formation of a crack, which can be interpreted as a fixed principal strain direction is imposed on the second formulation via calibration of the principal stress/strain direction obtained from the rotating-angle model at a cracking stage. Two alternatives are selected for the cracking point: fcr and 0.5fcr (post-peak). In terms of shear capacity, the model results are compared with an experimental database indicating that the fixed-angle models yield good results. The overall response (load-displacement) is also reasonable well predicted for specimens with diagonal compression failure.

• Advances in Computational Design
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• v.8 no.1
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• pp.37-59
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• 2023

Squat reinforced concrete (SRC) shear walls are a critical part of the structure for both office/residential buildings and nuclear structures due to their significant role in withstanding seismic loads. Despite this, empirical formulae in current design standards and published studies demonstrate a considerable disparity in predicting SRC wall shear strength. The goal of this research is to develop and evaluate hybrid and ensemble artificial neural network (ANN) models. State-of-the-art population-based algorithms are used in this research for hybrid intelligence algorithms. Six models are developed, including Honey Badger Algorithm (HBA) with ANN (HBA-ANN), Hunger Games Search with ANN (HGS-ANN), fitness-distance balance coyote optimization algorithm (FDB-COA) with ANN (FDB-COA-ANN), Averaging Ensemble (AE) neural network, Snapshot Ensemble (SE) neural network, and Stacked Generalization (SG) ensemble neural network. A total of 434 test results of SRC walls is utilized to train and assess the models. The results reveal that the SG model not only minimizes prediction variance but also produces predictions (with R²= 0.99) that are superior to other models.

• Physical Therapy Korea
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• v.22 no.3
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• pp.71-80
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• 2015

Hip muscle activation and strengthening exercise programs are often used to prevent and treat various lower extremity injuries. Common exercise programs include squat exercises. The purposes of this study were to investigate gluteus medius (GMED) and tensor fasciae latae (TFL) muscle activity, and to assess the GMED/TFL ratio during squat exercises involving different isometric hip contraction conditions. Different types of isometric hip contraction were standard squat without hip contraction, squats with isometric hip adduction, and squats with isometric hip abduction. Twenty (10 males and 10 females) healthy subjects ($23.7{\pm}2.8$ years old) were recruited. Subjects performed the squat exercises with the back supported by a wall and knees flexed to $60^{\circ}$. Surface electromyography (EMG) was used to measure GMED and TFL activity. One-way repeated analysis of variance was used to compare GMED and TFL muscle activity and the GMED/TFL ratio. GMED and TFL EMG activity was significantly higher during squats with isometric hip adduction and abduction compared with the standard squat without hip contraction (p<.05). Between the isometric hip adduction and abduction contraction conditions, only the TFL EMG activity was significantly higher during squats with isometric hip adduction than isometric hip abduction (p<.05). The GMED/TFL ratio was significantly higher during squats with isometric hip adduction than isometric hip abduction (p<.05). Squats with isometric hip adduction and abduction improved GMED and TFL muscle activity. Furthermore, the GMED/TFL ratio was higher during isometric hip adduction than isometric hip abduction. Our data indicate that squat exercises involving isometric hip adduction enhance GMED muscle activity.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.449-449
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• 2008

• Journal of the Korea Concrete Institute
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• v.27 no.5
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• pp.489-499
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• 2015

This study suggested shear strength prediction model for retrofitted single-layered RC squat wall by providing column element as additional boundary element. This model revised existing shear strength prediction model of shear wall to consider detail and shear deformation capacity of column by assuming the length that concentrated shear deformation of the column is occurred. It was able to suggest additional compatibility condition related to shear strain of retrofitted of retrofitted shear wall at the ultimate state by using this length. Therefore, this study proposed a flow chart for predicting shear strength of the retrofitted shear wall considering this additional condition. Moreover, this study also proposed a method for predicting initial stiffness of the retrofitted shear wall by transforming the wall's resisting mechanism against to lateral load to a single diagonal strut mechanism. The proposed methods can predict shear strength and initial stiffness of not only the retrofitted shear wall of this study, also infilled RC shear wall in RC frame.

• Computers and Concrete
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• v.8 no.2
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• pp.143-162
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• 2011

Advanced material models for concrete are not widely available in general purpose finite element codes. Parameters to define them complicate the implementation because they are case sensitive. In addition to this, their validity under severe shear condition has not been verified. In this article, simple engineering plasticity material models available in a commercial finite element code are used to demonstrate that complicated shear behavior can be calculated with reasonable accuracy. For this purpose dynamic response of a squat shear wall that had been tested on a shaking table as part of an experimental program conducted in Japan is analyzed. Both the finite element and material aspects of the modeling are examined. A corrective artifice for general engineering plasticity models to account for shear effects in concrete is developed. The results of modifications in modeling the concrete in compression are evaluated and compared with experimental response quantities.

• Journal of the Korean Society of Physical Medicine
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• v.7 no.4
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• pp.541-550
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• 2012

PURPOSE: The purpose of this study was compare quadriceps femoris muscle activity while performing wall slide squats of four methods. METHODS: Forty subjects, with no history of patellofemoral pain, quadriceps injury, or other knee injury volunteered for this study. Muscle activation of the vastus medialis obliquus, rectus femoris, vastus lateralis muscles were recorded while subjects performed 10 consecutive wall slide squats. Subjects performed the wall slide squats during four different methods: (1) basic wall slide squat, (2) keep back upright against fitness ball, (3) standing of unstable surface, (4) squeezing ball between both knees. Statistical analysis were accomplished by utilizing the one-way ANOVA(Bonferroni's post-hoc test) by SPSS 20.0 program. Significance level was set at p<.05. RESULTS: Muscle activations induced wall slide squats of four methods compared and results showed that there was significant difference only in vastus medialis obliquus and rectus femoris but there was no significant difference in vastus lateralis. The vastus medialis obliquus was significantly different only keep back upright against fitness ball at post-hoc test. The rectus femoris was significantly different keep back upright against fitness ball and standing of unstable surface at post-hoc test. CONCLUSION: Based on these results, we conclude that quadriceps femoris muscle activations are differenced by performing wall slide squats of four different methods in healthy subjects. These data suggest that for quadriceps muscle strengthening, exercise professionals can perform the wall slide squats by altering several task variables. Further research is needed to determine the exact mechanism by which quadriceps function is altered.

• Physical Therapy Rehabilitation Science
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• v.8 no.1
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• pp.45-51
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• 2019

Objective: The purpose of this study was to investigate the muscle activity ratio of the lower limb according to changes in straight leg raise (SLR) test angles on hamstring muscle shortening during squat exercises. Design: Randomized controlled trial. Methods: The subjects were 14 healthy adults who were informed of and agreed to the method and purpose of the study. The participants were classified into SLR groups according to two angles (over $80^{\circ}$ or under $80^{\circ}$) assessed using the SLR tests. After training and practicing the wall squat posture to be applied to the experiment, electromyography (EMG) was used to measure changes in muscle activity during the performance of a wall squat. After stretching, a sequence of pre-stretch tests were performed again, and the active and passive SLR tests were also reconducted; thereafter, a wall squat was performed again by attaching EMG electrodes. The EMG results before and after stretching were compared. Results: The muscle activity of the vastus lateralis oblique muscle increased in both groups. The muscle activity of the vastus medialis oblique muscle decreased in over both group. Rectus femorus activity increased in the under 80-degree groups but decreased in the over 80-degree group. The muscle activity of the biceps femoris muscle decreased after stretching in the over 80-degree group and increased in the under 80-degree group, and the semitendinosus muscle activity after stretching was decreased. The quadriceps-to-hamstring muscle (Q:H) ratio before and after stretching between groups showed that the hamstring muscle ratio decreased after stretching in both groups. Conclusions: The results of this study showed that the Q:H ratio before and after stretching between groups was not significantly different.

• Journal of the Earthquake Engineering Society of Korea
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• v.16 no.5
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• pp.1-11
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• 2012

In this paper, non-linear analysis was performed for Reinforced Concrete (RC) walls using different macroscopic models subjected to cyclic loading, and the analytical results were compared with previous experimental studies of RC walls. ASCE41-06 (American Society of Civil Engineers) specifies that the hysteresis behaviors of RC walls are different due to the aspect ratio of the walls. For a comparison between analytical and experimental results, a slender wall with an aspect ratio exceeding 3.0 and a squat wall with an aspect ratio of 1.0 were selected among previous research works. For the non-linear analysis, each test specimen was modeled using two different macroscopic methods: the first representing the flexural behavior of the RC wall, and the second considering the diagonal shear in the web of the wall. Through nonlinear analysis of the considered RC walls, the analytical difference of a slender wall was negligible due to the different macroscopic modeling methods. However, the squat wall was significantly affected by the considered components of the modeling method. For an accurate performance evaluation of the RC building with squat walls, it would be reasonable to use a macroscopic model considering diagonal shear.