REAL the structural health effects on other structural and

 

REAL TIME WIRELESS MONITORING OF AXIAL LOADS AND AXIAL SHORTENING OF COLUMNS IN HIGH-RISE BUILDING

 

B.A.D.C Gunawardhana

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University of moratuwa,[email protected]

Supervisor/s name/s

Suppervisor: Dr Lewangamage, university of Moratuwa.

                                  Co suppervisor: Dr K.J.C Kumara,university of Ruhuna.

 

Abstract: Adequate estimation of column shortening in high rise building is required to estimate the structural health effects on other structural and non-structural element due to the column shortening. The theoretical values of shortening of columns are different from actual values.so field monitoring is the best way to estimate actual shortening. This paper is about, developing a wireless axial shortening monitoring system for high rise building columns, monitoring a high rise building and making a database for loading history of the building. To compare theoretical values and experimental values, monitoring device should install high rise building column and making a database is necessary for analysing results. Selecting suitable sensors, develop a low cost structural health monitoring system, laboratory testing of accuracy of the monitoring system, field monitoring of axial shortening and give recommendations for quality controls are the main objectives.

Keywords:  wireless axial shortening monitoring; low cost structural health monitoring; quality control; data base for loading history

 

1.    Introduction

Structural health monitoring is very important for a good quality construction. Over the years the height of buildings was increased. Now a days high rise buildings are very popular. Structural health of a high rise building is affected on column shortening.it is possible to discuss two kinds of shortening of columns which is affected by structural health of high rise buildings. Total Axial shortening of columns and differential shortening of a column(s) can be discussed separately.

When considering structural health total column shortenings are not very much interested. But the effect of differential shortening can (be) lead bad structural health issues for the building. Some of structural issues between them are slab tilting which caused to turn rotates and distorts non- structural partitions, unacceptable crack width on horizontal directions, potential structural problem to facades, beams and unexpected deformation of interior drywalls and separation of elevator guide rail brackets damage to cladding system can be occurred.

High rise building with not with good structur(al)     

Health, it will definitely effect on its design life and there may be a huge failure on the whole structure.

Therefore, monitoring of structural health can be used for quality control of the structure. Actual axial shortening differential shortening of columns is different from the predicted amount due to idealizations in analysing and assuming material properties. So field monitoring is the best way to monitor axial shortening of columns.

Developing a wireless system which cam used to monitor column shortening for high rise building is a main task in this research. This is a civil engineering research which bond with electronics. This kind of monitoring system can be used to prepare a database for the building which showing the loading history of the building and monitor excessive differential shortenings. By observing shortening history with respect to loads can identify the possibility of excessive differential settlement to occur at initial stages. Then we can prov(ed) the solution by identifying risk using this monitoring system. Further, this kind of long time monitoring data base can be used to make some practical relationships rather than theoretical relationships and capability of comparing practical values and theoretical values are some plus point of this kind of project.     

 

 

 

2. Research gap

Although there are variations of numerical models of predicting axial shortening of a high rise building column there is very few methods and experiment done for field investigation of axial shortening. When considering Sri Lanka there is no field investigation of column shortening done by wireless monitoring. The results of this experiment and usefulness of this kind of implementation will cause(d) a making demands of wireless structural health monitoring.

3. The significance of the research

Differential axial shortening of column in high rise building and its effect have been identified as a major concern.

By developing this kind of monitoring system it is,

Possible to monitor Load time histories associated with the construction process.

·         Capable of Store strain data with respect to time as a database.

·         Capability of Predict axial shortening in future using past actual axial shortening data

4. Range of column shortening in a high rise building.

 Any vertical member in high rise building which carry axial loads are caused elastic deformation and inelastic deformations due to creep and shrinkages. High rise building has high gravity loads. Stresses in columns are also high due to heavy gravity loads which carried by columns.

Both elastic and inelastic deformations are caused for total shortening accumulation in each column in every floor.

For an example, short term shortening of 60-story high rise building interior column due to dead load and live loads is 50mm-76mm and concrete columns are subjected to additional 50-76mm shortening due to creep and shrinkages. (Steel, concrete & composite design of a tall building. New York)

Therefore, strain in columns are in micro scale. The sensor should have the capability of measuring micro scale strains. 

 

 

 

 

5. Efficient sensor selection 

There are two methods which can use(d) to sense shortening of the column. First one is a direct distance measurement with special arranging of columns. Second one is to measure strain in the column directly using strain gauge.

When considering distance measuring there are so many types of sensors such as inductive, capacitive and ultrasonic for distance measurements.

If we select direct strain measuring method best option is the vibrating wire strain gauge.

Sensor selection for structural health monitoring system should be based on following main facts.

Structural property: should select good parameter and scale of the parameter. In our case the strain of a column is the parameter and generally strain in micro scale.   

Natural environment: relationship between changes in environmental factors for the results of sensor.  

 Economic efficiency: cost effectiveness is another factor for success of experimental work.

Capacitive sensors and vibrating wire strain gauges are more reliable for our monitoring system. So further investigation should be done in selecting most suitable sensor.

5.1 Capacitive sensors

Working principle: There are two parallel plates in a capacitor one plate has a positive charge and the other plate is grounded. Following shown is the equation of a capacitor.

A= area of two plates

?= permittivity of medium

d =distance between two plates.

When a change in distance between very small amount capacitance varies by large amount. Therefore, this kind of sensor can be used to measure very small distance changes. Sensitivity of capacitive sensor is in Nano scale and power consumption is micro ampere range   

Figure 1 : Capacitive sensor 1

 

The accuracy is greater in capacitive sensor but there are some difficulties in installing a column(s). Special arrangement in a column is required to use this kind of sensor.

5.2 Vibrating wire strain gauges.

Working principle: Vibrating wire strain gauge working with the principle of resonance frequency. Following picture shows is a general arrangement of a vibrating wire strain gauge.

Figure 2: Vibrating wire strain gauge

 Vibrating wire strain gauge should fix(ed) into a column by both ends of the strain gauge. Due fixity in both ends vibrating wires also shortening when column shortening will occur. Due to changes in the length of the wire, resonance frequency also changes. By identifying the resonance frequency for the new length of vibrating wire, change in length can be determined. Then strain can be calculated.

 6. Wireless sensor network for Monitoring of column shortening

Vibrating wire strain gauge sensors (are) normally use to monitor axial shortening of a column(s). Previously discussed capacitive distance measuring sensors can be used for the purpose of determining changing length of a column. But in the capacitive sensing method, it is necessary to make some changes related to columns for the purpose of installing the sensor. Considering that point, vibrating wire strain gauges are the most suitable.

The system should consist of wireless sensor network and server that stores and manage in real time transmitted data. Sensors, sensor nodes, master nodes and repeater nodes are the main features of sensing network of monitoring system. 

Following shown is the network of sensor and server.

Figure 3 Arrangement of WMS

 

 Sensor nodes directly connect to sensors by wires to get automatic measurements of shortening columns. After that, data obtaining should transfer wirelessly to master node. Function of master node is to transfer data wirelessly to main server. If there are problems in communication between sensor nodes and master nodes due to obstacles such as dry wall, repeater node should be utilized.

Further, this monitoring system should consist of   two major parts. Those are

·         WSN which measure axial shortening automatically

·         Monitoring software which capable of monitoring the real time data collected in the server via an internet connection.

Should develop a simple software which handles and present analysed data by user friendly manner.

7. Comparison of theoretical value and actual value

The theoretical value of axial shortening has governed by following equation.

Where ?0 = initial concrete stress

           Ec(s) =elastic modulus of concrete at age

           f(t,s) = creep coefficient

           ??(t) = stress increment

           ?(t,s) = aging coefficient

           esh,(t) = shrinkage component

After obtaining the results from a real time monitoring system, it should be compared with theoretical values. It can be done by manually by above equation or can be easily evaluated using structural computer modelling of that building.

8. Conclusion

Field monitoring is the best way for monitoring actual axial shortening. Therefore, implement a wireless axial shortening monitoring system will be more accurate and convenient. There is a strong capability of predicting future axial shortening of construction stage high rise building by analysing the variation of strain of columns over some period through this kind of wireless monitoring system.

9. References
Baidya N, M. P. (n.d.). monitoring of a tall building to develop axial shortening medel incorparating high strength concrete. australiya: university of melbourne.
BS, T. (1997). steel,concrete &composite design of tall building. Newyork: McGraw-Hill .
Essam A, A. A. (2017). Axial loaded capacity of alternative strengthned cold-formed channel columns. constructional steel reaserach, 3.
Moragaspitiya, H. p. (2011). Interractive axail shortening of columns and walls in high rise buildings. QUT.
Ruben correia, P. s. (2017). Simplified Assesment of the effect of columns shortening on the response of tall buildings. 2nd international conference on structural integrity, 4-7.
S fragomeni, H. W. (2014). axial shortening in an 80-storey concrete building. 23rd Austrlasian conference on the mechanics of stuctures and materials, 4.
Yun Lee, J.-k. K.-c. (2016). 3D numarical analysis of column shortening and shore sfety under constuction of high rise building. Engineering structures, 2-4.
 

 

 

 

 

 

 

 

 

 

REAL TIME WIRELESS MONITORING OF AXIAL LOADS AND AXIAL SHORTENING OF COLUMNS IN HIGH-RISE BUILDING

 

B.A.D.C Gunawardhana

University of moratuwa,[email protected]

Supervisor/s name/s

Suppervisor: Dr Lewangamage, university of Moratuwa.

                                  Co suppervisor: Dr K.J.C Kumara,university of Ruhuna.

 

Abstract: Adequate estimation of column shortening in high rise building is required to estimate the structural health effects on other structural and non-structural element due to the column shortening. The theoretical values of shortening of columns are different from actual values.so field monitoring is the best way to estimate actual shortening. This paper is about, developing a wireless axial shortening monitoring system for high rise building columns, monitoring a high rise building and making a database for loading history of the building. To compare theoretical values and experimental values, monitoring device should install high rise building column and making a database is necessary for analysing results. Selecting suitable sensors, develop a low cost structural health monitoring system, laboratory testing of accuracy of the monitoring system, field monitoring of axial shortening and give recommendations for quality controls are the main objectives.

Keywords:  wireless axial shortening monitoring; low cost structural health monitoring; quality control; data base for loading history

 

1.    Introduction

Structural health monitoring is very important for a good quality construction. Over the years the height of buildings was increased. Now a days high rise buildings are very popular. Structural health of a high rise building is affected on column shortening.it is possible to discuss two kinds of shortening of columns which is affected by structural health of high rise buildings. Total Axial shortening of columns and differential shortening of a column(s) can be discussed separately.

When considering structural health total column shortenings are not very much interested. But the effect of differential shortening can (be) lead bad structural health issues for the building. Some of structural issues between them are slab tilting which caused to turn rotates and distorts non- structural partitions, unacceptable crack width on horizontal directions, potential structural problem to facades, beams and unexpected deformation of interior drywalls and separation of elevator guide rail brackets damage to cladding system can be occurred.

High rise building with not with good structur(al)     

Health, it will definitely effect on its design life and there may be a huge failure on the whole structure.

Therefore, monitoring of structural health can be used for quality control of the structure. Actual axial shortening differential shortening of columns is different from the predicted amount due to idealizations in analysing and assuming material properties. So field monitoring is the best way to monitor axial shortening of columns.

Developing a wireless system which cam used to monitor column shortening for high rise building is a main task in this research. This is a civil engineering research which bond with electronics. This kind of monitoring system can be used to prepare a database for the building which showing the loading history of the building and monitor excessive differential shortenings. By observing shortening history with respect to loads can identify the possibility of excessive differential settlement to occur at initial stages. Then we can prov(ed) the solution by identifying risk using this monitoring system. Further, this kind of long time monitoring data base can be used to make some practical relationships rather than theoretical relationships and capability of comparing practical values and theoretical values are some plus point of this kind of project.     

 

 

 

2. Research gap

Although there are variations of numerical models of predicting axial shortening of a high rise building column there is very few methods and experiment done for field investigation of axial shortening. When considering Sri Lanka there is no field investigation of column shortening done by wireless monitoring. The results of this experiment and usefulness of this kind of implementation will cause(d) a making demands of wireless structural health monitoring.

3. The significance of the research

Differential axial shortening of column in high rise building and its effect have been identified as a major concern.

By developing this kind of monitoring system it is,

Possible to monitor Load time histories associated with the construction process.

·         Capable of Store strain data with respect to time as a database.

·         Capability of Predict axial shortening in future using past actual axial shortening data

4. Range of column shortening in a high rise building.

 Any vertical member in high rise building which carry axial loads are caused elastic deformation and inelastic deformations due to creep and shrinkages. High rise building has high gravity loads. Stresses in columns are also high due to heavy gravity loads which carried by columns.

Both elastic and inelastic deformations are caused for total shortening accumulation in each column in every floor.

For an example, short term shortening of 60-story high rise building interior column due to dead load and live loads is 50mm-76mm and concrete columns are subjected to additional 50-76mm shortening due to creep and shrinkages. (Steel, concrete & composite design of a tall building. New York)

Therefore, strain in columns are in micro scale. The sensor should have the capability of measuring micro scale strains. 

 

 

 

 

5. Efficient sensor selection 

There are two methods which can use(d) to sense shortening of the column. First one is a direct distance measurement with special arranging of columns. Second one is to measure strain in the column directly using strain gauge.

When considering distance measuring there are so many types of sensors such as inductive, capacitive and ultrasonic for distance measurements.

If we select direct strain measuring method best option is the vibrating wire strain gauge.

Sensor selection for structural health monitoring system should be based on following main facts.

Structural property: should select good parameter and scale of the parameter. In our case the strain of a column is the parameter and generally strain in micro scale.   

Natural environment: relationship between changes in environmental factors for the results of sensor.  

 Economic efficiency: cost effectiveness is another factor for success of experimental work.

Capacitive sensors and vibrating wire strain gauges are more reliable for our monitoring system. So further investigation should be done in selecting most suitable sensor.

5.1 Capacitive sensors

Working principle: There are two parallel plates in a capacitor one plate has a positive charge and the other plate is grounded. Following shown is the equation of a capacitor.

A= area of two plates

?= permittivity of medium

d =distance between two plates.

When a change in distance between very small amount capacitance varies by large amount. Therefore, this kind of sensor can be used to measure very small distance changes. Sensitivity of capacitive sensor is in Nano scale and power consumption is micro ampere range   

Figure 1 : Capacitive sensor 1

 

The accuracy is greater in capacitive sensor but there are some difficulties in installing a column(s). Special arrangement in a column is required to use this kind of sensor.

5.2 Vibrating wire strain gauges.

Working principle: Vibrating wire strain gauge working with the principle of resonance frequency. Following picture shows is a general arrangement of a vibrating wire strain gauge.

Figure 2: Vibrating wire strain gauge

 Vibrating wire strain gauge should fix(ed) into a column by both ends of the strain gauge. Due fixity in both ends vibrating wires also shortening when column shortening will occur. Due to changes in the length of the wire, resonance frequency also changes. By identifying the resonance frequency for the new length of vibrating wire, change in length can be determined. Then strain can be calculated.

 6. Wireless sensor network for Monitoring of column shortening

Vibrating wire strain gauge sensors (are) normally use to monitor axial shortening of a column(s). Previously discussed capacitive distance measuring sensors can be used for the purpose of determining changing length of a column. But in the capacitive sensing method, it is necessary to make some changes related to columns for the purpose of installing the sensor. Considering that point, vibrating wire strain gauges are the most suitable.

The system should consist of wireless sensor network and server that stores and manage in real time transmitted data. Sensors, sensor nodes, master nodes and repeater nodes are the main features of sensing network of monitoring system. 

Following shown is the network of sensor and server.

Figure 3 Arrangement of WMS

 

 Sensor nodes directly connect to sensors by wires to get automatic measurements of shortening columns. After that, data obtaining should transfer wirelessly to master node. Function of master node is to transfer data wirelessly to main server. If there are problems in communication between sensor nodes and master nodes due to obstacles such as dry wall, repeater node should be utilized.

Further, this monitoring system should consist of   two major parts. Those are

·         WSN which measure axial shortening automatically

·         Monitoring software which capable of monitoring the real time data collected in the server via an internet connection.

Should develop a simple software which handles and present analysed data by user friendly manner.

7. Comparison of theoretical value and actual value

The theoretical value of axial shortening has governed by following equation.

Where ?0 = initial concrete stress

           Ec(s) =elastic modulus of concrete at age

           f(t,s) = creep coefficient

           ??(t) = stress increment

           ?(t,s) = aging coefficient

           esh,(t) = shrinkage component

After obtaining the results from a real time monitoring system, it should be compared with theoretical values. It can be done by manually by above equation or can be easily evaluated using structural computer modelling of that building.

8. Conclusion

Field monitoring is the best way for monitoring actual axial shortening. Therefore, implement a wireless axial shortening monitoring system will be more accurate and convenient. There is a strong capability of predicting future axial shortening of construction stage high rise building by analysing the variation of strain of columns over some period through this kind of wireless monitoring system.

9. References
Baidya N, M. P. (n.d.). monitoring of a tall building to develop axial shortening medel incorparating high strength concrete. australiya: university of melbourne.
BS, T. (1997). steel,concrete &composite design of tall building. Newyork: McGraw-Hill .
Essam A, A. A. (2017). Axial loaded capacity of alternative strengthned cold-formed channel columns. constructional steel reaserach, 3.
Moragaspitiya, H. p. (2011). Interractive axail shortening of columns and walls in high rise buildings. QUT.
Ruben correia, P. s. (2017). Simplified Assesment of the effect of columns shortening on the response of tall buildings. 2nd international conference on structural integrity, 4-7.
S fragomeni, H. W. (2014). axial shortening in an 80-storey concrete building. 23rd Austrlasian conference on the mechanics of stuctures and materials, 4.
Yun Lee, J.-k. K.-c. (2016). 3D numarical analysis of column shortening and shore sfety under constuction of high rise building. Engineering structures, 2-4.
 

 

 

 

 

 

 

 

 

 

 

  

 

 

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