1 Introduction
2 Test Program
2.1 Test Specimens
Specimen groups | Dimensions (mm × mm) | Longitudinal bars | Transverse bars | Splice length (mm) | Concrete strength (MPa) | Hammer mass (kg) | Drop height (m) | Ps/PM |
---|---|---|---|---|---|---|---|---|
S-18-300-L | 250 × 300 | D18 | D8@100 | 300 | 37.72 | 272.3 | 3.15/6.30/12.60 | 2.38 |
597.3 | 5.74 | |||||||
S-18-400-L | 400 | 37.96 | 272.3 | 3.15/6.30/12.60 | 2.38 | |||
597.3 | 5.74 | |||||||
S-18-300 | 300 | 31.16 | 532.3 | 1.58/3.15/4.73 | 2.34 | |||
857.3 | 1.96 | |||||||
S-18-400 | 400 | 30.01 | 532.3 | 1.58/3.15/6.30 | 2.34 | |||
857.3 | 1.96 | |||||||
S-25-300 | D25 | 300 | 34.62 | 532.3 | 1.58/3.15/4.73 | 1.38 | ||
857.3 | 1.96 | |||||||
S-25-400 | 400 | 32.77 | 532.3 | 1.58/3.15/6.30 | 1.38 | |||
857.3 | 1.96 |
2.2 Materials
2.3 Test Setup and Instrumentation
3 Test Results
3.1 Impact Force
Specimens | Drop height (m) | Drop weight (kg) | Impact energy (kJ) | Pp (kN) | δp (mm) | δr (mm) | εu (10−6 mm/mm) | εr (mm/mm) | Strain rate (1/s) |
---|---|---|---|---|---|---|---|---|---|
S-18-300-L | 3.15 | 272.3 | 8.41 | 3518 | 23.1 | 18.3 | 1280 | 450 | 2.91 |
6.30 | 272.3 | 16.83 | 4953 | 86.6 | 75.6 | 2140 | 1680 | 4.14 | |
12.60 | 272.3 | 33.66 | 8002 | 165.6 | 151.7 | 3070 | 1760 | 5.30 | |
5.74 | 597.3 | 33.65 | 6771 | 194.6 | 176.1 | 3100 | 1950 | 5.93 | |
S-18-400-L | 3.15 | 272.3 | 8.41 | 3622 | 12.8 | 5.8 | 1600 | 380 | 2.91 |
6.30 | 272.3 | 16.83 | 5380 | 60.5 | 50.6 | 2150 | 540 | 4.15 | |
12.60 | 272.3 | 33.66 | 8566 | 150.9 | 138.0 | 3140 | 1370 | 5.31 | |
5.74 | 597.3 | 33.65 | 7108 | 167.0 | 159.0 | 3360 | 1580 | 5.93 | |
S-18-300 | 1.58 | 532.3 | 8.22 | 2540 | 55.8 | 52.4 | 1610 | 320 | 3.19 |
3.15 | 532.3 | 16.45 | 4588 | 101.7 | 88.7 | 2160 | 1370 | 4.11 | |
4.73 | 532.3 | 24.67 | 5716 | 159.6 | 144.9 | 2570 | 840 | 4.97 | |
1.96 | 857.3 | 16.45 | 3590 | 137.7 | 135.2 | 2430 | 1380 | 4.16 | |
S-18-400 | 1.58 | 532.3 | 8.22 | 3123 | 38.9 | 34.7 | 2030 | 340 | 3.16 |
3.15 | 532.3 | 16.45 | 4589 | 83.2 | 77.8 | 2210 | 680 | 4.09 | |
6.30 | 532.3 | 32.90 | 6768 | 183.2 | 167.0 | 3430 | 1130 | 5.61 | |
1.96 | 857.3 | 16.45 | 3541 | 104.0 | 100.0 | 2540 | 1050 | 4.14 | |
S-25-300 | 1.58 | 532.3 | 8.22 | 3140 | 32.4 | 30.2 | 1690 | 240 | 2.80 |
3.15 | 532.3 | 16.45 | 4500 | 95.2 | 89.8 | 2170 | 1360 | 3.53 | |
4.73 | 532.3 | 24.67 | 5484 | 134.8 | 118.1 | 3320 | 780 | 4.26 | |
1.96 | 857.3 | 16.45 | – | – | – | – | – | – | |
S-25-400 | 1.58 | 532.3 | 8.22 | 2685 | 23.5 | 15.1 | 2070 | 320 | 2.75 |
3.15 | 532.3 | 16.45 | 4500 | 75.0 | 72.3 | 2290 | 8970 | 3.49 | |
6.30 | 532.3 | 32.90 | 6768 | 193.8 | 185.2 | 3470 | 1520 | 4.70 | |
1.96 | 857.3 | 16.45 | 4410 | 122.8 | 118.4 | 2580 | 320 | 3.52 |
3.2 Mid-span Deflection
3.3 Failure Modes
3.4 Reinforcing Bar Strain
4 Evaluation of Structural Performance Under Impact Load
4.1 Energy Conservation Model
Energy types | Equations |
---|---|
Kinetic energy \(E_{k}\) | \(E_{k} = 0.5m_{h} V_{i}^{2} = m_{h} gh_{d}\) |
Potential energy \(E_{p}\) | \(E_{p} = \left\{ {\begin{array}{*{20}l} {\left( {m_{be} + m_{h} } \right)g\delta } & {{\text{for }}\delta < \delta_{y} } \\ {\left( {m_{be} + m_{h} } \right)g\delta + \left( {m_{bp} + m_{h} } \right)g\left( {\delta - \delta_{y} } \right)} & {{\text{for }}\delta < \delta_{y} } \\ \end{array} } \right.\) |
Deformation energy \(E_{d}\) | \(E_{d} = \int_{0}^{\delta } {P(\delta )} d\delta\) |
Spalling energy \(E_{s}\) | \(E_{s} = \left\{ {\begin{array}{*{20}l} 0 & {{\text{for }}\varepsilon_{c} < \varepsilon_{cu} } \\ {0.2f_{td} bc_{c} k_{s} \left( {L_{p} + 2C_{c} } \right)} & {{\text{for }}\varepsilon_{cs} < \varepsilon_{yd} } \\ \end{array} } \right.\) \(k_{s} = (300/h)^{0.25} \le 1\) |
Energy loss \(E_{l}\) | \(E_{l} = E_{k} - \frac{1}{2}(m_{be} + m_{h} )V_{c}^{2} = \frac{{m_{be} }}{{m_{be} + m_{h} }}E_{k}\) |
4.2 Deformation Energy Ed
Materials | Stress-strain relationship | Strain rate effect |
---|---|---|
Reinforcing bar | \(\sigma_{s} = \left\{ {\begin{array}{*{20}c} {E_{s} \varepsilon_{s} } & {{\text{for}}\left| {\varepsilon_{s} } \right| \le \varepsilon_{yd} } \\ {f_{yd} + E_{h} \left( {\varepsilon_{s} - \varepsilon_{yd} < 1.25f_{yd} } \right)} & {{\text{for}}\left| {\varepsilon_{s} } \right| > \varepsilon_{yd} } \\ \end{array} } \right.\) | \(f_{yd} = f_{y} + 6\ln (10^{5} \left| {\dot{\varepsilon }} \right|/5) \le f_{y} + 6\ln (2 \times 10^{5} ){\text{ (CEB)}}\) |
Confined concrete under compression | \(\sigma_{cc} = \left\{ {\begin{array}{*{20}c} {kf{\prime}_{cd} \left[ {\frac{{2\varepsilon_{c} }}{{\varepsilon_{cod} K}} + \left( {\left[ {\frac{{\varepsilon_{c} }}{{\varepsilon_{cod} K}} + } \right]} \right)^{2} } \right]} & {{\text{for }}\varepsilon_{c} \ge - \varepsilon_{cod} K} \\ {kf{\prime}_{cd} \left[ {1 + Z_{m} \left( {\varepsilon_{c} + \varepsilon_{cod} K} \right)} \right] \ge 0.2f{\prime}_{cd} } & {{\text{for }}\varepsilon_{c} < - \varepsilon_{cod} K} \\ \end{array} } \right.\) \(K = 1 + \rho_{t} f_{yt} /f_{cd}^{'}\) \(Z_{m} = \frac{0.5}{{\frac{{3 + 0.29f_{cd}^{'} }}{{145f_{cd}^{'} - 1000}} + \frac{3}{4}\rho_{t} \sqrt {\frac{{h_{0} }}{s}} - \varepsilon_{cod} K}}\) | \(f_{cd}^{'} = \left\{ {\begin{array}{*{20}c} {f{\prime}_{c} \left( {10^{5} \left| {\dot{\varepsilon }/3} \right|} \right)^{0.014} } & {{\text{for }}\dot{\varepsilon }_{c} {\text{ < 30/s }}} \\ {0.012f^{\prime}\left( {10^{5} \left| {\dot{\varepsilon }/3} \right|} \right)^{01/3} } & {{\text{for }}\dot{\varepsilon }_{c} \ge 3 0 / {\text{s }}} \\ \end{array} } \right.{ (}fib{ 2010) }\) |
Unconfined concrete under compression | \(\sigma_{cu} = f_{cd}^{'} \left[ {\frac{{2\varepsilon_{c} }}{{\varepsilon_{cod} }} + \left( {\frac{{\varepsilon_{c} }}{{\varepsilon_{cod} }}} \right)^{2} } \right]{\text{ for }} - \varepsilon_{cu} \le \varepsilon_{c} \le 0\) | |
Concrete under tension | \(\sigma_{t} = E_{cd} \varepsilon_{c} ,0 < \varepsilon_{c} \le f_{td}^{'} /E_{cd}\) | \(f_{td} = \left\{ {\begin{array}{*{20}c} {f{\prime}_{c} \left( {10^{6} \left| {\dot{\varepsilon }} \right|} \right)^{0.018} } & {{\text{for }}\dot{\varepsilon }_{c} {\text{ < 10/s }}} \\ {0.0062f_{t} \left( {10^{6} \left| {\dot{\varepsilon }} \right|} \right)^{1/3} } & {{\text{for }}\dot{\varepsilon }_{c} \ge 1 0 / {\text{s }}} \\ \end{array} } \right.{ (}fib{ 2010) }\) \(f_{t} = \left\{ {\begin{array}{*{20}c} {0.3f_{c}^{{'2/3}} \quad \quad \quad \quad \quad \quad \quad {\text{for }}f_{c}^{'} < 50{\text{MPa}}} \\ {2.12\ln [1 + 0.1(f_{c}^{'} + 8)]{\text{ }}\;\; {\text{for }}f_{c}^{'} \ge 50{\text{MPa}}} \\ \end{array} } \right.(fib{\text{ }}2010)\) |
4.3 Mid-span Deflection of RC Beam Under Impact Load
Specimens | Drop height (m) | Drop weight (kg) | δtest (mm) | δp (mm) | δp/δtest |
---|---|---|---|---|---|
S-18-300-L | 3.15 | 272.3 | 23.1 | 13.8 | 0.60 |
6.30 | 272.3 | 86.6 | 23.1 | 0.27 | |
12.6 | 272.3 | 165.6 | 42.0 | 0.25 | |
5.74 | 597.3 | 194.6 | 68.2 | 0.35 | |
S-18-400-L | 3.15 | 272.3 | 12.8 | 13.7 | 1.07 |
6.30 | 272.3 | 60.5 | 23.1 | 0.38 | |
12.60 | 272.3 | 150.9 | 42.0 | 0.28 | |
5.74 | 597.3 | 167.0 | 68.1 | 0.41 | |
S-18-300 | 1.58 | 532.3 | 55.8 | 19.3 | 0.35 |
3.15 | 532.3 | 101.7 | 34.6 | 0.34 | |
4.73 | 532.3 | 159.6 | 49.7 | 0.31 | |
1.96 | 857.3 | 137.7 | 44.3 | 0.32 | |
S-18-400 | 1.58 | 532.3 | 38.9 | 19.4 | 0.50 |
3.15 | 532.3 | 83.2 | 34.8 | 0.42 | |
6.30 | 532.3 | 183.2 | 64.3 | 0.35 | |
1.96 | 857.3 | 104.0 | 44.5 | 0.43 | |
S-25-300 | 1.58 | 532.3 | 32.4 | 13.0 | 0.40 |
3.15 | 532.3 | 95.2 | 22.0 | 0.23 | |
4.73 | 532.3 | 134.8 | 31.2 | 0.23 | |
1.96 | 857.3 | – | – | – | |
S-25-400 | 1.58 | 532.3 | 23.5 | 13.1 | 0.56 |
3.15 | 532.3 | 75.0 | 22.2 | 0.30 | |
6.30 | 532.3 | 193.8 | 40.7 | 0.21 | |
1.96 | 857.3 | 122.8 | 28.0 | 0.23 | |
Avg. | 0.38 | ||||
COV. | 0.47 |
5 Prediction for Bar Development Length
5.1 Existing Methods for Bar Development Length
Design methods | Development length (mm) | Splice length lsp | |
---|---|---|---|
ACI 318-19 | \(l_{d} = \frac{{f_{y} d_{b} }}{{1.1\lambda \sqrt {f_{c}^{'} } }}\frac{{\psi_{t} \psi_{e} \psi_{s} }}{{\left( {c_{f} + K_{tr} } \right)/d_{b} }} \ge 300{\text{ mm}}\) | \((c_{f} + K_{tr} )/d_{b} \le 2.5\) \(c_{f} = \hbox{min} (c_{b} ,c_{so} ,c_{si} ) + 0.5d_{b}\) \(K_{tr} = 40A_{tr} /\left( {s_{t} n} \right)\) | 1.0–1.3ld |
ACI 408R-03 | \(l_{d} = \frac{{(f_{y} /\sqrt[4]{{f_{c}^{'} }} - \phi 57.4w)(\psi_{t} \psi_{e} \psi_{s} )d_{b} }}{{\phi 1.83(cw + K_{atr} )/d_{b} }}\) | \((cw + K_{atr} )/d_{b} \le 4.0\) \(w = 0.1(c_{\hbox{max} } /c_{\hbox{min} } ) + 0.9 \le 1.25\) \(K_{atr} = 6\sqrt {f_{c}^{'} } t_{d} A_{tr} /(s_{t} n)\) \(t_{d} = 0.03d_{b} + 0.22\) \(c = c_{\hbox{min} } + d_{b} /2\) \(c_{\hbox{max} } = \hbox{max} (c_{b} ,c_{s} )\) \(c_{\hbox{min} } = \hbox{min} (c_{b} ,c_{s} )\) \(c_{s} = \hbox{min} (c_{so} ,c_{si} + 6.4)\) | ld |
Eurocode 2-04 | \(l_{d} = \alpha_{2} \alpha_{3} \frac{{f_{y} d_{b} }}{{4f_{bd} }} \ge \frac{{l_{0} }}{1.5}\) | \(\alpha_{2} = 0.7 \le 1 - 0.15\left( {c_{d} - d_{b} } \right)/d_{b} \le 1.0\) \(\alpha_{3} = 0.7 \le 1 - K\left( {\sum {A_{tr} - A_{s} } } \right)/A_{s} \le 1.0\) \(f_{bd} = 2.25\eta_{2} \left[ {0.75(0.3)(f_{c}^{'} )^{2/3} } \right]\) \(\alpha_{2} \alpha_{3} \ge 0.7\) \(c_{d} = \hbox{min} (c_{b} ,c_{so} ,c_{si} )\) \(l_{0} = \hbox{max} (0.45d_{b} f_{y} /(4f_{bd} ),15d_{b} ,200mm)\) \(\eta_{2} = (132 - d_{b} )/100 \le 1.0\) | 1.0–1.5ld |
Hwang et al. (2017) | \(f_{s} = \frac{{l_{d} }}{{d_{b} }}[3\tau_{1} + \tau_{2} ] \le f_{y}\) | \(\tau_{1} = \frac{{\tau_{u} }}{1.4}\left[ {\frac{{1 - (\Delta_{f} /s_{1} )^{1.4} }}{{1 - (\Delta_{f} /s_{1} )}}} \right] \le \tau_{u}\) \(\frac{{\Delta_{f} }}{{s_{1} }} = 1 - \frac{{14.7l^{2} }}{{E_{s} d_{b} }}\frac{{\tau_{u} }}{{\sqrt {f_{c}^{'} } }} + 0.007\frac{{l_{d} }}{{\sqrt {f_{c}^{'} } }}\) \(\tau_{u} = 0.91\alpha_{d} \sqrt {f_{c}^{'} } \left[ {\frac{{(cw + K_{atr} )/d_{b} }}{2.5}} \right]\) \(\tau_{2} = \left[ {\frac{{16{ - }6C_{1} \tau_{1} }}{{16 + C_{1} \tau_{u} }}} \right]\tau_{u} \ge \frac{{\tau_{u} }}{2}\) \(C_{1} = l_{d}^{2} /[1 - (\sqrt {0.003f_{c}^{'} } )E_{s} d_{b} ]\) | ld |