1 Introduction
2 Method
2.1 Details of Test Specimens
Name | Size (mm) | Fire exposure time (min) | Sustained load (tonf) |
---|---|---|---|
P1-60 | 250 × 400 × 5000 (width × depth × length) | 60 | 4.82 |
P1-120 | 120 | 4.82 | |
P2-60 | 60 | 7.23 | |
P2-120 | 120 | 7.23 | |
P3-60 | 60 | 9.56 |
W/C (%) | s/a (%) | Weight per unit volume (kg/m3) | ||||
---|---|---|---|---|---|---|
W | C | S | G | FA | ||
53.4 | 49.8 | 83 | 155 | 913 | 914 | 1.86 |
Concrete | 28-day compressive strength | 28-day tensile strength |
---|---|---|
25 MPa | 3 MPa | |
Steel | Elastic modulus | Tensile strength |
205 GPa | 448 MPa |
2.2 Test Setup and Data Measurements
2.3 The Crack Detection Method
2.3.1 Image Data Acquisition and Pre-processing
2.3.2 Proposed CNN Method
2.3.3 Training and Testing
2.4 Crack Detection
Specimens | (a) The number of pixels obtained from the proposed CNN model | (b) Total crack length obtained from the optical observation (mm) | Ratio (a/b) |
---|---|---|---|
P1-60 | 33,987,368 | 76,316 | 4.45 × 102 |
P1-120 | 39,942,906 | 83,866 | 4.76 × 102 |
P2-60 | 35,924,210 | 75,827 | 4.73 × 102 |
P2-120 | 40,607,469 | 86,856 | 4.67 × 102 |
P3-60 | 37,277,057 | 78,000 | 4.77 × 102 |
Specimens | The number of pixels from the proposed CNN model with using threshold | |||||||
---|---|---|---|---|---|---|---|---|
Threshold = none | Threshold = 100 | Threshold = 180 | Threshold = 200 | |||||
Result | Order | Result | Order | Result | Order | Result | Order | |
P1-60 | 33,987,368 | 5 | 4,318,206 | 4 | 2,016,520 | 4 | 1,532,640 | 4 |
P1-120 | 39,942,906 | 2 | 6,102,724 | 2 | 2,875,649 | 3 | 2,183,620 | 3 |
P2-60 | 35,924,210 | 4 | 3,844,416 | 5 | 1,952,067 | 5 | 1,525,105 | 5 |
P2-120 | 40,607,469 | 1 | 5,652,050 | 3 | 2,986,106 | 2 | 2,372,325 | 2 |
P3-60 | 37,277,057 | 3 | 8,239,397 | 1 | 4,814,109 | 1 | 3,952,994 | 1 |
Specimens | The number of pixels excluding pore edges from the proposed CNN model | Ratio to total crack length obtained from the optical observation | Ratio to heated surfaces (%) |
---|---|---|---|
P1-60 | 11,683,021 | 1.53 × 102 | 4.73 |
P1-120 | 17,638,559 | 2.10 × 102 | 7.14 |
P2-60 | 13,619,863 | 1.79 × 102 | 5.52 |
P2-120 | 18,303,122 | 2.11 × 102 | 7.41 |
P3-60 | 14,972,710 | 1.92 × 102 | 6.06 |
3 Discussion
Specimens | Fire test results | Residual strength test results | The number of pixels excluding pore edges from the proposed CNN model | Ratio of pixel numbers to P1-60 | |||
---|---|---|---|---|---|---|---|
Temperature at mid span (c) | Ratio of temp to P1-60 | Maximum load (kN) | Stiffness (kN/mm) | Ratio of stiffness to P1-60 | |||
P1-60 | 184.7 | 1.00 | 174.6 | 4.05 | 1.00 | 11,683,021 | 1.00 |
P1-120 | 528.9 | 2.86 | 169.9 | 3.28 | 0.81 | 17,638,559 | 1.51 |
P2-60 | 160.8 | 0.87 | 178.8 | 3.69 | 0.91 | 13,619,863 | 1.17 |
P2-120 | 568.8 | 3.08 | 174 | 2.91 | 0.72 | 18,303,122 | 1.57 |
P3-60 | 312.1 | 1.69 | 172.6 | 3.36 | 0.83 | 14,972,710 | 1.28 |