- Email: [email protected]
Assessment of the Nonlinear Behavior of Connections in Water Distribution Networks for Their Seismic Evaluation
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Procedia Engineering 00 (2011) 000–000 Procedia Engineering 14 (2011) 2878–2883
Procedia Engineering www.elsevier.com/locate/procedia
The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction
Assessment of the Nonlinear Behavior of Connections in Water Distribution Networks for Their Seismic Evaluation MAHMOOD HOSSEINI1ab and SAMIRA JALILI2 1 Associate Professor, Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran 2 Graduate student, Civil Engineering Department, Tehran South Branch of the Islamic Azad University (IAU), Tehran, Iran
ABSTRACT
Connections, used in water distribution networks, have mostly a nonlinear force – displacement or moment – rotation relationship, subjected to extensive ground deformations due to large earthquakes. On the other hand, to evaluate the seismic functionality of water distribution networks, which should be performed with high reliability for seismic risk reduction purposes, the determination of realistic nonlinear behaviors of connections in water distribution networks is very important. In this study the nonlinear behaviors of various types of connections, have been assessed numerically by using finite element analysis (FEA). For this purpose, different sizes of pipes, elbows, and Tees in various combinations have been considered, and their body has been modeled by solid elements, between them contact conditions have been introduced wherever necessary. Special attention has been paid to the rubber gasket used in Tyton joints. For obtaining the nonlinear relationship in each case, one end of the connected parts has been assumed to be fixed, and a force or a moment has been applied incrementally in an appropriate direction or around an appropriate axis, till reaching the ultimate state, which is when the convergence cannot be achieved in FEA anymore. Results show that for rotation values above 0.005rad most of connections enter the nonlinear range, however, with regard to force – displacement behavior the displacement value at which the connection enter the nonlinear range various form less that a centimeter to a few centimeter depending on the connection type and the parts sizes. © 2011 Published by Elsevier Ltd. Keywords: Socket; Flange; Elbows; Tees; Tyton; Bolted Gland; Finite Element Analysis.
a b
Presenter: Email: [email protected] Corresponding author: Email: [email protected]
1877–7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.362
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MAHMOOD HOSSEINI and SAMIRA JALILI / Procedia Engineering 14 (2011) 2878–2883 Author name / Procedia Engineering 00 (2011) 000–000
1. INTRODUCTION There are various connection types in water distribution networks, which have nonlinear force – displacement or moment – rotation relationships, subjected to extensive ground deformations, which happens in strong earthquakes. Either socket (push-in), commonly used for connecting the pipe segments together, or flanged joints (of both Tyton and Bolted Gland types) used for connecting the pipe segments to either Tees or elbows, are among these connections. On the other hand evaluating the seismic functionality of water distribution networks, which is of great importance for making decision on either upgrading the vulnerable components of the network, or emergency actions for more critical parts of the city in the aftermath of large earthquakes, should be performed with high reliability. Therefore, the determination of realistic nonlinear behaviors of connections in water distribution networks is very important for seismic risk reduction purposes. Although the water distribution networks in most large and earthquake prone cities of the world are several decades old, studies with regard to these systems go back to only a decade ago (Takada et al. 2000; Sekozawa et al. 2000). So far, earthquake damage evaluation of water distribution networks have been done with various methods, including theoretical methods such as the use of artificial neural network (Takada et al. 2003), and also the online methods (Liang 2003). Seismic reliability of water distribution networks has been also studied (Jie 2006). In spite of several studies on seismic evaluation of water systems, the studies which consider the nonlinear behavior of connections are very few. In this study the nonlinear behaviors of various types of connections, used in water distribution networks, have been assessed numerically by using finite element analysis (FEA). For this purpose, different sizes of pipes, elbows, and Tees in various combinations have been considered, and their body has been modeled by solid elements, between them contact conditions have been introduced wherever necessary. Special attention has been paid to the rubber gasket used in Tyton joints. For obtaining the nonlinear force – displacement or moment – rotation relationships in each case, one end of the connected parts has been assumed to be fixed, and a force or a moment has been applied incrementally in an appropriate direction or around an appropriate axis, and the loading in each case has been continued till reaching the ultimate state, which is when the convergence cannot be achieved in FEA anymore. Details of these calculations are described in the next section. 2. NONLINEAR BEHAVIOR OF PIPE CONNECTIONS The connections in water distribution network are mostly of socket (push-in) and/or flanged joints (of both Tyton and Bolted Gland types), the socket joints are commonly used for connecting the pipe segments together, and the flanged joints for connecting the pipe segments to the either Tees or elbows. The material of pipes and connection parts is cast-iron, with Young modulus of 165 GPa, yielding stress of 276 MPa, ultimate tensile stress of 414 MPa, and Poisson ration of 0.275 (ICS 1981). For modeling the network connections nonlinear finite element modeling has been employed in which both geometrical and material nonlinearities have been taken into consideration, and contact elements have been used wherever necessary. It is worth mentioning that to obtain the moment – rotation behavior of various connections one point load, in case of pipes segments and also elbows, and two opposite point loads, in case of Tees, were applied at the cross-sectional center point of the corresponding end(s) of the connecting parts, as shown in Figure 1, and then by assuming one end of the pipe or elbow, or the end of the branch of the Tee, as the fixed end, and increasing the value of the applied load(s) little by little, the nonlinear moment – rotation relationship of the connection, up to the ultimate state, in which the connection fails, was obtained in each case.
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Figure 1- Applying the point load(s) at end(s) of connecting parts for obtaining their moment rotation behavior
100000 90000 80000
force(N)
70000 60000 50000 40000 30000 20000 10000 0 0
2
4
6
ux(mm) Figure 2- Finite element model and nonlinear force – displacement behavior of socket joints of Tyton (or push-in) type in pipe of 150mm diameter subjected to axial load 3.5 3 moment(ton.m)
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2.5 2 1.5 1 0.5 0 0
0.01
0.02
0.03
0.04
0.05
theta
Figure 3- Finite element model and nonlinear moment – rotation behavior of socket joints of Tyton (or push-in) type in pipe of 150mm diameter subjected to lateral load
4
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moment(ton.m)
3.5 3 2.5 2 1.5 1 0.5 0 0
0.01
0.02
0.03
0.04
0.05
theta
Figure 4- Finite element model and nonlinear moment – rotation behavior of flanged joints of Bolted Gland type in pipe of 150mm diameter 8.00E+00 7.00E+00 Moment(ton.m)
6.00E+00 5.00E+00 4.00E+00 3.00E+00 2.00E+00 1.00E+00 0.00E+00 0
0.005
0.01
0.015
0.02
0.025
Theta
Figure 5- Finite element model and nonlinear moment – rotation behavior of flanged elbow of 300mm diameter of Tyton type with a taper at one end 3.5
moment(ton.m)
3 2.5 2 1.5 1 0.5 0 0
0.005
0.01
0.015
0.02
0.025
0.03
theta
Figure 6- Finite element model and nonlinear moment – rotation behavior of flanged Tee of 150mm-250mm diameter of Bolted Gland type with a 200mm-250mm taper at one end
Samples of various pipe connections, including socket and flanged, and also T connections and elbows, modeled by solid elements along with their nonlinear force – displacement or moment – rotation behaviors are shown in Figures 2 to 6. More results of the type shown in Figures 2 to 6 can not be shown here because of lack of space and may be found in the main report of the study (Jalili 2010). Comparing Figures 2 to 6 it can be realized that the amount of nonlinearity is different is various connections depending on their type and the applied action. Of special interest may be the variable stiffness of the connection of Bolted Gland type of 150mm diameter pipe at the beginning of moment – rotation curve, as shown in Figure 4. It can be seen that at start of the curve stiffness is less than the remaining part before reaching the ultimate strength. This is since at the beginning the deformation of the rubber gasket, which is very soft comparing to the pipes
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materials, lets the relatively easy rotation of either side of the joint with respect to each other, while later the outer surface of the male end of the pipe engages the inner surface of the female end. To have a better view at the differences between the moment – rotation curves of Tyton and Bolted Gland connections their corresponding curves for pipes of different diameters are compared in Figure 7.
Figure 7- Comparison of moment – rotation curves of Tyton and Bolted Gland connections in pipes of different diameters from 150mm to 300mm
It can be seen in Figure 7 that, as expected, the Bolted Gland joints are stronger that their counterparts of the Tyton type, and that with increase in the pipe diameter the ultimate strength of the joint increases for both type of joints. It is also seen that in the case of Tyton joints the slope of the curves at the beginning is less that their slope in other parts of the curves. This is due to the softness of the rubber gasket acting between the two metal parts at the beginning, as mentioned before. This slope change is not seen in case of Bolted Gland joints since from the beginning the male and female ends are engaged without the interference of the rubber gasket. In case of socket joints, as expected, the failure occurs in the gasket as the rotation exceeds some specific value, which depends on the pipe diameter and the socket size type, and is given in the corresponding specifications manual. However, in case of flanged joints and also in elbows and Tees failure occurs in pipe section, the inner side of elbows, and the corners of Tees due to stress concentration. In fact, when the strain value in these locations gets close to the yielding strain of the pipe material, its value grows very rapidly up to twenty time because of the imperfections in the part cross-section, which are almost inevitable in manufacturing, or the aging problem (corrosion) (Hosseini et al. 2008). On this basis a strain value of around 0.002 can be considered as the start of rupture. It is obvious that in case of socket joints between pipes and elbow or Tees, the failure occurs in the socket joints, while in case of flanged connections, since the diameter of elbows or Tees is a little smaller than the connecting pipes, failure happens in the elbow’s or Tee’s body.
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3. CONCLUSIONS Results show that, as expected, the socket joints have highly nonlinear behavior, while the bolted joints behave almost linear behavior, as long as the materials behave in the elastic range. It is also observed that with increase in the pipe diameter the ultimate strength of the joint increases for both types of joints. With regard to moment – rotation behavior for rotation values above 0.005rad most of connections enter the nonlinear range, however, with regard to force – displacement behavior the displacement value at which the connection enter the nonlinear range varies form less than a centimeter to a few centimeter depending on the connection type and the part sizes. REFERENCES [1]
Hosseini M, Salek Sh, and Moradi M (2008). The Effect of Corrosion on the Seismic Behavior of Buried Pipelines and a Remedy for Their Seismic Retrofit, Proceedings of 2008 Seismic Engineering International Conference Commemorating the 1908 Messina and Reggio Calabria Earthquake, University of Riggio Calabria, Italy.
[2]
ICS (1981). Iron Castings Handbook, Iron Castings Society (ICS).
[3]
Jalili S. (2009). Modeling of Connections in Water Distribution Networks to Study their Seismic Failures for Estimating the Hydraulic Pressure Drop, Master of Science Thesis in Hydraulic Structures (under supervision of Prof. Mahmood Hosseini), Civil Engineering Department, Graduate School, Tehran South Branch of the Islamic Azad University (IAU), Tehran, Iran.
[4]
Jie L, Shulin W, and Wei, L (2006). Seismic reliability analysis of urban water distribution network, Earthquake Engineering and Engineering Vibration, 5(1), pp. 71-77.
[5]
Liang J (2003). Online location of seismic damage to a water distribution system, Earthquake Engineering and Engineering Vibration, 2(2), pp. 181-187.
[6]
Sekozawa T, Kurisu H, and Kukumoto T (2000). Real-time seismic damage estimation system for water supply control, Confronting Urban Earthquakes: Report of Fundamental Research on the Mitigation of Urban Disasters Caused by NearField Earthquakes; pp. 250-251.
[7]
Takada S, Hassani N, and Kitada T (2000). Relation between damage ratio and burial direction of water distribution pipelines in Kobe city during the Hyogoken-Nanbu earthquake, Confronting Urban Earthquakes: Report of Fundamental Research on the Mitigation of Urban Disasters Caused by Near-Field Earthquakes; pp.193-197.
[8]
Takada S, Hassani N, and Rasti R (2003). Artificial neural network (ANN) modeling for earthquake damage detection in water distribution system, Proceedings of the 2003 Pacific Conference on Earthquake Engineering [electronic resource], 9 pages.
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Procedia Engineering 00 (2011) 000–000 Procedia Engineering 14 (2011) 2878–2883
Procedia Engineering www.elsevier.com/locate/procedia
The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction
Assessment of the Nonlinear Behavior of Connections in Water Distribution Networks for Their Seismic Evaluation MAHMOOD HOSSEINI1ab and SAMIRA JALILI2 1 Associate Professor, Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran 2 Graduate student, Civil Engineering Department, Tehran South Branch of the Islamic Azad University (IAU), Tehran, Iran
ABSTRACT
Connections, used in water distribution networks, have mostly a nonlinear force – displacement or moment – rotation relationship, subjected to extensive ground deformations due to large earthquakes. On the other hand, to evaluate the seismic functionality of water distribution networks, which should be performed with high reliability for seismic risk reduction purposes, the determination of realistic nonlinear behaviors of connections in water distribution networks is very important. In this study the nonlinear behaviors of various types of connections, have been assessed numerically by using finite element analysis (FEA). For this purpose, different sizes of pipes, elbows, and Tees in various combinations have been considered, and their body has been modeled by solid elements, between them contact conditions have been introduced wherever necessary. Special attention has been paid to the rubber gasket used in Tyton joints. For obtaining the nonlinear relationship in each case, one end of the connected parts has been assumed to be fixed, and a force or a moment has been applied incrementally in an appropriate direction or around an appropriate axis, till reaching the ultimate state, which is when the convergence cannot be achieved in FEA anymore. Results show that for rotation values above 0.005rad most of connections enter the nonlinear range, however, with regard to force – displacement behavior the displacement value at which the connection enter the nonlinear range various form less that a centimeter to a few centimeter depending on the connection type and the parts sizes. © 2011 Published by Elsevier Ltd. Keywords: Socket; Flange; Elbows; Tees; Tyton; Bolted Gland; Finite Element Analysis.
a b
Presenter: Email: [email protected] Corresponding author: Email: [email protected]
1877–7058 © 2011 Published by Elsevier Ltd. doi:10.1016/j.proeng.2011.07.362
2
MAHMOOD HOSSEINI and SAMIRA JALILI / Procedia Engineering 14 (2011) 2878–2883 Author name / Procedia Engineering 00 (2011) 000–000
1. INTRODUCTION There are various connection types in water distribution networks, which have nonlinear force – displacement or moment – rotation relationships, subjected to extensive ground deformations, which happens in strong earthquakes. Either socket (push-in), commonly used for connecting the pipe segments together, or flanged joints (of both Tyton and Bolted Gland types) used for connecting the pipe segments to either Tees or elbows, are among these connections. On the other hand evaluating the seismic functionality of water distribution networks, which is of great importance for making decision on either upgrading the vulnerable components of the network, or emergency actions for more critical parts of the city in the aftermath of large earthquakes, should be performed with high reliability. Therefore, the determination of realistic nonlinear behaviors of connections in water distribution networks is very important for seismic risk reduction purposes. Although the water distribution networks in most large and earthquake prone cities of the world are several decades old, studies with regard to these systems go back to only a decade ago (Takada et al. 2000; Sekozawa et al. 2000). So far, earthquake damage evaluation of water distribution networks have been done with various methods, including theoretical methods such as the use of artificial neural network (Takada et al. 2003), and also the online methods (Liang 2003). Seismic reliability of water distribution networks has been also studied (Jie 2006). In spite of several studies on seismic evaluation of water systems, the studies which consider the nonlinear behavior of connections are very few. In this study the nonlinear behaviors of various types of connections, used in water distribution networks, have been assessed numerically by using finite element analysis (FEA). For this purpose, different sizes of pipes, elbows, and Tees in various combinations have been considered, and their body has been modeled by solid elements, between them contact conditions have been introduced wherever necessary. Special attention has been paid to the rubber gasket used in Tyton joints. For obtaining the nonlinear force – displacement or moment – rotation relationships in each case, one end of the connected parts has been assumed to be fixed, and a force or a moment has been applied incrementally in an appropriate direction or around an appropriate axis, and the loading in each case has been continued till reaching the ultimate state, which is when the convergence cannot be achieved in FEA anymore. Details of these calculations are described in the next section. 2. NONLINEAR BEHAVIOR OF PIPE CONNECTIONS The connections in water distribution network are mostly of socket (push-in) and/or flanged joints (of both Tyton and Bolted Gland types), the socket joints are commonly used for connecting the pipe segments together, and the flanged joints for connecting the pipe segments to the either Tees or elbows. The material of pipes and connection parts is cast-iron, with Young modulus of 165 GPa, yielding stress of 276 MPa, ultimate tensile stress of 414 MPa, and Poisson ration of 0.275 (ICS 1981). For modeling the network connections nonlinear finite element modeling has been employed in which both geometrical and material nonlinearities have been taken into consideration, and contact elements have been used wherever necessary. It is worth mentioning that to obtain the moment – rotation behavior of various connections one point load, in case of pipes segments and also elbows, and two opposite point loads, in case of Tees, were applied at the cross-sectional center point of the corresponding end(s) of the connecting parts, as shown in Figure 1, and then by assuming one end of the pipe or elbow, or the end of the branch of the Tee, as the fixed end, and increasing the value of the applied load(s) little by little, the nonlinear moment – rotation relationship of the connection, up to the ultimate state, in which the connection fails, was obtained in each case.
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Figure 1- Applying the point load(s) at end(s) of connecting parts for obtaining their moment rotation behavior
100000 90000 80000
force(N)
70000 60000 50000 40000 30000 20000 10000 0 0
2
4
6
ux(mm) Figure 2- Finite element model and nonlinear force – displacement behavior of socket joints of Tyton (or push-in) type in pipe of 150mm diameter subjected to axial load 3.5 3 moment(ton.m)
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2.5 2 1.5 1 0.5 0 0
0.01
0.02
0.03
0.04
0.05
theta
Figure 3- Finite element model and nonlinear moment – rotation behavior of socket joints of Tyton (or push-in) type in pipe of 150mm diameter subjected to lateral load
4
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moment(ton.m)
3.5 3 2.5 2 1.5 1 0.5 0 0
0.01
0.02
0.03
0.04
0.05
theta
Figure 4- Finite element model and nonlinear moment – rotation behavior of flanged joints of Bolted Gland type in pipe of 150mm diameter 8.00E+00 7.00E+00 Moment(ton.m)
6.00E+00 5.00E+00 4.00E+00 3.00E+00 2.00E+00 1.00E+00 0.00E+00 0
0.005
0.01
0.015
0.02
0.025
Theta
Figure 5- Finite element model and nonlinear moment – rotation behavior of flanged elbow of 300mm diameter of Tyton type with a taper at one end 3.5
moment(ton.m)
3 2.5 2 1.5 1 0.5 0 0
0.005
0.01
0.015
0.02
0.025
0.03
theta
Figure 6- Finite element model and nonlinear moment – rotation behavior of flanged Tee of 150mm-250mm diameter of Bolted Gland type with a 200mm-250mm taper at one end
Samples of various pipe connections, including socket and flanged, and also T connections and elbows, modeled by solid elements along with their nonlinear force – displacement or moment – rotation behaviors are shown in Figures 2 to 6. More results of the type shown in Figures 2 to 6 can not be shown here because of lack of space and may be found in the main report of the study (Jalili 2010). Comparing Figures 2 to 6 it can be realized that the amount of nonlinearity is different is various connections depending on their type and the applied action. Of special interest may be the variable stiffness of the connection of Bolted Gland type of 150mm diameter pipe at the beginning of moment – rotation curve, as shown in Figure 4. It can be seen that at start of the curve stiffness is less than the remaining part before reaching the ultimate strength. This is since at the beginning the deformation of the rubber gasket, which is very soft comparing to the pipes
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MAHMOOD HOSSEINI and SAMIRA JALILI / Procedia Engineering 14 (2011) 2878–2883 Author name / Procedia Engineering 00 (2011) 000–000
materials, lets the relatively easy rotation of either side of the joint with respect to each other, while later the outer surface of the male end of the pipe engages the inner surface of the female end. To have a better view at the differences between the moment – rotation curves of Tyton and Bolted Gland connections their corresponding curves for pipes of different diameters are compared in Figure 7.
Figure 7- Comparison of moment – rotation curves of Tyton and Bolted Gland connections in pipes of different diameters from 150mm to 300mm
It can be seen in Figure 7 that, as expected, the Bolted Gland joints are stronger that their counterparts of the Tyton type, and that with increase in the pipe diameter the ultimate strength of the joint increases for both type of joints. It is also seen that in the case of Tyton joints the slope of the curves at the beginning is less that their slope in other parts of the curves. This is due to the softness of the rubber gasket acting between the two metal parts at the beginning, as mentioned before. This slope change is not seen in case of Bolted Gland joints since from the beginning the male and female ends are engaged without the interference of the rubber gasket. In case of socket joints, as expected, the failure occurs in the gasket as the rotation exceeds some specific value, which depends on the pipe diameter and the socket size type, and is given in the corresponding specifications manual. However, in case of flanged joints and also in elbows and Tees failure occurs in pipe section, the inner side of elbows, and the corners of Tees due to stress concentration. In fact, when the strain value in these locations gets close to the yielding strain of the pipe material, its value grows very rapidly up to twenty time because of the imperfections in the part cross-section, which are almost inevitable in manufacturing, or the aging problem (corrosion) (Hosseini et al. 2008). On this basis a strain value of around 0.002 can be considered as the start of rupture. It is obvious that in case of socket joints between pipes and elbow or Tees, the failure occurs in the socket joints, while in case of flanged connections, since the diameter of elbows or Tees is a little smaller than the connecting pipes, failure happens in the elbow’s or Tee’s body.
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MAHMOOD HOSSEINI and SAMIRA JALILI / Procedia Engineering 14 (2011) 2878–2883 Author name / Procedia Engineering 00 (2011) 000–000
6
3. CONCLUSIONS Results show that, as expected, the socket joints have highly nonlinear behavior, while the bolted joints behave almost linear behavior, as long as the materials behave in the elastic range. It is also observed that with increase in the pipe diameter the ultimate strength of the joint increases for both types of joints. With regard to moment – rotation behavior for rotation values above 0.005rad most of connections enter the nonlinear range, however, with regard to force – displacement behavior the displacement value at which the connection enter the nonlinear range varies form less than a centimeter to a few centimeter depending on the connection type and the part sizes. REFERENCES [1]
Hosseini M, Salek Sh, and Moradi M (2008). The Effect of Corrosion on the Seismic Behavior of Buried Pipelines and a Remedy for Their Seismic Retrofit, Proceedings of 2008 Seismic Engineering International Conference Commemorating the 1908 Messina and Reggio Calabria Earthquake, University of Riggio Calabria, Italy.
[2]
ICS (1981). Iron Castings Handbook, Iron Castings Society (ICS).
[3]
Jalili S. (2009). Modeling of Connections in Water Distribution Networks to Study their Seismic Failures for Estimating the Hydraulic Pressure Drop, Master of Science Thesis in Hydraulic Structures (under supervision of Prof. Mahmood Hosseini), Civil Engineering Department, Graduate School, Tehran South Branch of the Islamic Azad University (IAU), Tehran, Iran.
[4]
Jie L, Shulin W, and Wei, L (2006). Seismic reliability analysis of urban water distribution network, Earthquake Engineering and Engineering Vibration, 5(1), pp. 71-77.
[5]
Liang J (2003). Online location of seismic damage to a water distribution system, Earthquake Engineering and Engineering Vibration, 2(2), pp. 181-187.
[6]
Sekozawa T, Kurisu H, and Kukumoto T (2000). Real-time seismic damage estimation system for water supply control, Confronting Urban Earthquakes: Report of Fundamental Research on the Mitigation of Urban Disasters Caused by NearField Earthquakes; pp. 250-251.
[7]
Takada S, Hassani N, and Kitada T (2000). Relation between damage ratio and burial direction of water distribution pipelines in Kobe city during the Hyogoken-Nanbu earthquake, Confronting Urban Earthquakes: Report of Fundamental Research on the Mitigation of Urban Disasters Caused by Near-Field Earthquakes; pp.193-197.
[8]
Takada S, Hassani N, and Rasti R (2003). Artificial neural network (ANN) modeling for earthquake damage detection in water distribution system, Proceedings of the 2003 Pacific Conference on Earthquake Engineering [electronic resource], 9 pages.
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