9 research outputs found
A Comparison of Receptive-Expressive Language Profiles between Toddlers with Autism Spectrum Disorder and Developmental Language Delay
PURPOSE:
It is well known that expressive language impairment is commonly less severe than receptive language impairment in children with autism spectrum disorder (ASD). However, this result is based on experiments in Western countries with Western language scales. This study tries to find whether the result above is applicable for toddlers in a non-Western country; more specifically, in Korea with non-Western language scales.
MATERIALS AND METHODS:
The participants were 166 toddlers aged between 20 months and 50 months who visited the clinic from December 2010 to January 2013. The number of toddlers diagnosed as ASD and developmental language delay (DLD) was 103 and 63, respectively. Language development level was assessed using Sequenced Language Scale for Infants (SELSI), a Korean language scale. Using SELSI, each group was divided into 3 sub-groups. Moreover, the group difference by age was observed by dividing them into three age groups. Chi-square test and linear-by-linear association was used for analysis.
RESULTS:
Receptive language ability of the DLD group was superior to that of the ASD group in all age groups. However, expressive language ability in both groups showed no difference in all age groups. A greater proportion of expressive dominant type was found in ASD. The 20-29 months group in ASD showed the largest proportion of expressive language dominant type in the three age groups, suggesting that the younger the ASD toddler is, the more severe the receptive language impairment is.
CONCLUSION:
These findings suggest that receptive-expressive language characteristics in ASD at earlier age could be useful in the early detection of ASD.ope
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νλ λ° λ³΄λ€ ν©λ¦¬μ μ΄λ€.This dissertation aims at estimating the critical crack path dependent shear strength of reinforced concrete beams without web reinforcement and investigating size effect by using the mixed mode fracture in linear elastic fracture mechanics (LEFM) approach. This approach has been supplied the theoretical basis for size effect in shear strength because the stress states at the crack tip can be expressed as a function of crack length.
Even though the efforts of numerous experimental and analytical studies for shear strength and size effect of reinforced concrete beams, a fundamental theory explaining the size effect and shear failure mode of slender and deep beams without web reinforcement considering critical crack path is still missing. Current code provisions and many existing models are based on empirical and statistical considerations.
To determine the shear strength and investigate the size effect of reinforced concrete beams, a failure mechanism based on the critical crack path and crack length was proposed. This study assumes biaxial stress fields at the diagonal critical crack tip in both diagonal tension failure and sliding failure modes. The transition area which is located from uniaxial stress states below the neutral axis of beams to biaxial stress states above the neutral axis requires the change of primary fracture mode. This failure is defined as material failure such as separation and sliding. To provide the deformation dependent strength model, the modified Mohr-Coulomb criteria was used and failure mechanism was investigated by using concrete failure criteria. For investigating the stress states at critical diagonal crack tip, size dependent critical stress intensity factors for mode-I and mode-II fracture expressed in terms of ultimate stresses determined by material failure criteria and crack length were proposed. From the relationship between the stress intensity factor and critical stress intensity factor, it is recognized that size effect is related to the crack length for both mode-I and mode-II fracture.
To obtain the shear strength of slender beams without web reinforcement, failure modes are classified into diagonal tension failure and sliding failure on the basis of critical crack path. And it is assumed that softening occurs at cracked section in the compression zone. In addition a newly flexural-shear behavior of reinforced concrete beams without web reinforcement based on the concrete strain for diagonal tension failure and sliding failure was proposed. The ultimate shear strength is determined at the intersection between flexural behavior curves and shear limit curves represented the softening.
To determine the shear strength of deep beams without web reinforcement, behavior of prismatic body of concrete subjected to uniaxial compression was investigated. Both normal stress and shear stress assume to exist in the prismatic body on the basis of theory of elasticity. As a result, deep beams also showed the size effect for effective depth.
Proposed models are to estimate the shear strength of reinforced concrete slender and deep beams without web reinforcement. The proposed theory accurately predicts the experimental results for the ultimate shear stress of slender and deep beams with various strengths of concrete, steel ratio, shear span-to-depth ratio and effective depth.
Finally, the proposed theoretical models based on the critical crack path and crack length are more reasonable to explain the size effect of reinforced concrete beams than existing models.1. Introduction 1
1.1 Research Background and Problem Statements 1
1.2 Research Objectives and Scope 4
1.3 Organization of the Dissertation 5
2. Literature Review 6
2.1 Current Design Provisions 6
2.1.1 ACI 318-08 Building Code 6
2.1.2 CEB-FIP Model Code 1990 7
2.1.3 Eurocode 2 8
2.1.4 JSCE 10
2.2 Previous Researches 11
2.2.1 Fracture Mechanics Approach 11
2.2.2 Strut-and-Tie Model 16
2.2.3 Deformation based Design 18
2.2.4 Regression Analysis 21
2.3 Review 22
3. Behavior of Concrete 24
3.1 Uniaxial Compression 24
3.2 Uniaxial Tension 24
3.3 Biaxial Stress Behavior 26
3.4 Softening of Concrete 27
3.3 Summary 34
4. Fracture Mechanics of Concrete 35
4.1 Linear Elastic Fracture Mechanics 35
4.2 Stress Intensity Factor 37
4.3 Critical Stress Intensity Factor 42
4.4 Material Properties and Nonlinear Zone 43
4.4.1 Nonlinear Behavior of Concrete 43
4.4.2 Concrete Crack and Fracture Process Zone 45
4.6.3 Fracture Process zone for Mixed Mode Fracture 47
4.5 Size Dependent Critical Stress Intensity Factor 51
4.6 Size Effect 54
4.6.1 Size Effect of Linear Elastic Materials 54
4.6.2 Size Effect of Concrete Structures 55
4.7 Mixed-Mode Fracture of Concrete Beams 58
4.7.1 Introduction 58
4.7.2 Size Dependent Effective Stress Intensity Factors 61
4.8 Summary 67
5. Flexural Behavior of Reinforced Concrete Beams without Web Reinforcement 68
5.1 Introduction 68
5.2 Moment-Curvature Relationship 69
5.3 Depth of neutral axis 72
5.4 Moment Capacity 79
5.5 Summary 82
6. Critical Crack Path Dependent Shear Strength 83
6.1 Introduction 83
6.2 Crack Path Dependent Failure Mechanism 84
6.2.1 Characteristics of Critical Diagonal Crack 84
6.2.2 Failure Mechanisms 86
6.3 Diagonal Cracking Strength 88
6.3.1 General 88
6.3.2 Effective Stress Intensity Factor 88
6.3.3 Critical Stress Intensity Factor 91
6.3.4 Shear Strength of Flexural Tension Zone 96
6.4 Shear Strength for Diagonal Tension Failure 103
6.4.1 General 103
6.4.2 Failure Criteria 103
6.4.3 Effective Stress Intensity Factor 105
6.4.4 Shear Strength 108
6.4.5 Verification and Effect of Primary Parameters 114
6.5 Shear Strength for Sliding Failure 122
6.5.1 Introduction 122
6.5.2 Shear Transfer across a crack 123
6.5.3 Failure Criteria 127
6.5.4 Shear Strength 131
6.5.5 Verification 135
6.5.6 Summary 139
6.6 Shear Strength of Reinforced Concrete Short Beams without Web Reinforcement 141
6.6.1 Introduction 141
6.6.2 Failure Mode of Diagonal Strut 142
6.6.3 Uniaxial Compression 143
6.6.4 Stress Concentrations 144
6.6.5 Concentrated Load at a Point of a Straight Boundary 144
6.6.6 Sliding Failure of Prismatic Body 148
6.6.7 Shear Strength of Short Beams 157
6.6.8 Verification 159
6.6.9 Summary 163
7. Summary and Conclusions 165
7.1 Summary 165
7.2 Conclusions 166Docto