A Cyber-Physical System for Girder Hoisting Monitoring Based ... - MDPI

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A Cyber-Physical System for Girder Hoisting Monitoring Based on Smartphones Ruicong Han 1,2 , Xuefeng Zhao 1,2, *, Yan Yu 3 , Quanhua Guan 4 , Weitong Hu 4 and Mingchu Li 4 1 2 3 4

*

State Key Laboratory of Coastal and Offshore Engineering, Dalian University of Technology, Dalian 116000, China; [email protected] School of Civil Engineering, Dalian University of Technology, Dalian 116000, China School of Electronic Science and Technique, Dalian University of Technology, Dalian 116000, China; [email protected] School of Software Technology, Dalian University of Technology, Dalian 116000, China; [email protected] (Q.G.); [email protected] (W.H.); [email protected] (M.L.) Correspondence: [email protected]; Tel.: +86-411-8470-6443; Fax: +86-411-8470-6414

Academic Editor: Mianxiong Dong Received: 18 May 2016; Accepted: 4 July 2016; Published: 7 July 2016

Abstract: Offshore design and construction is much more difficult than land-based design and construction, particularly due to hoisting operations. Real-time monitoring of the orientation and movement of a hoisted structure is thus required for operators’ safety. In recent years, rapid development of the smart-phone commercial market has offered the possibility that everyone can carry a mini personal computer that is integrated with sensors, an operating system and communication system that can act as an effective aid for cyber-physical systems (CPS) research. In this paper, a CPS for hoisting monitoring using smartphones was proposed, including a phone collector, a controller and a server. This system uses smartphones equipped with internal sensors to obtain girder movement information, which will be uploaded to a server, then returned to controller users. An alarming system will be provided on the controller phone once the returned data exceeds a threshold. The proposed monitoring system is used to monitor the movement and orientation of a girder during hoisting on a cross-sea bridge in real time. The results show the convenience and feasibility of the proposed system. Keywords: cyber-physical systems; accelerometer; gyroscope

offshore hoisting monitoring;

smartphone sensors;

1. Introduction Cyber-physical systems (CPS) have recently become an important research field these years [1,2]. It’s a multidisciplinary field involving physics, communication, computation, control, and so on. CPS tries to connect the physical world and information world. It not only serves as the ears and eyes of the information with sensors, but also serves as the hand to change the mode of the physical activity and provide convenient lives for people [3,4]. There have been many CPS applications [5,6], such as medical devices and systems, assisted living, traffic control and safety, advanced automotive systems, process control, distributed sensing command and control, smart structures, autonomous electric vehicle [7] and so on. In recent years, smartphones have become popular on an unprecedented scale and can now be used as effective scientific tools. With an operating system, communication system and built-in sensors, they have already been applied to cyber-physical systems [8], including human health monitoring [9], vehicle maintenance services [10] and accident detection [11], motivation recognition [12–15], and structural health monitoring (SHM) [16–24]. Authors have also applied smartphones in the SHM

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field [25], in uses such as cable force monitoring [26–28], displacement monitoring [29], and earthquake rescue [30,31], etc. These applications allow the people to participate in the structural health perception process through the mobile phone and help people take corresponding measures to be safer. During the construction of cross-sea bridges, each operation faces challenges due to the complexity of the environment, particularly in terms of hoisting [32]. The girders that require hoisting into place are typically bulky and heavy, and the crane performing the hoisting operation is floating on the sea and is thus significantly affected by waves and winds. Therefore, offshore construction is considerably more difficult than construction on land. The hoisting of a heavy structural element is critical to the entire project construction plan; any accident during a hoisting operation could result in considerable property loss or casualties and affect the construction schedule of the entire project. To ensure that a hoisting operation can be completed safely, the orientation and movement of a girder should be monitored in real time, and corresponding measures should be taken based on monitoring results. For monitoring the girder hoisting process, the total station is employed in the traditional method. However, it’s always influenced by landform; some parts can’t be measured because of the block and it’s difficult to place it on the site construction at sea. Thus, a new sensing and monitoring method, which calls for fewer restrictions for landform and more convenient operations, is of great value. As previously mentioned, smartphones represent a mobile technology of the cyber-physical social system, with advantages of lower cost, convenience, easy operation, that may be useful for girder hoisting monitoring. We highlight the features and contributions of our paper as follows: 1.

2.

3. 4.

An iPhone-based monitoring system is developed; this system uses smartphones equipped with internal sensors to obtain girder movement information, which will be uploaded to a server, and then return to controller users. The system consists of a controller and collectors. The controller can send instruments to the collector to control the state of collector, it can also receive monitoring and warning information from the collector in real-time. An alarming function is designed, and once the returned data exceeds a threshold, an alarm will appear on the controller iPhone. The proposed system is used to monitor the movement and orientation of a girder during hoisting on a cross-sea bridge. The site monitoring results validate the data acquisition, data transmission, commands control and alarming functions. This CPS using smartphones and wireless networks in hoisting monitoring can provide more field conditions for operators and help them take corresponding measures to ensure safety.

The remainder of the paper is organized as follows: Section 2 describes the offshore bridge which girder hoisting need to be monitored. Section 3 gives the architecture of the hoisting monitoring system, and calibrates the angle measured by the iPhone. Sections 4 and 5 show the monitoring test on the side-span and middle-span respectively. Section 6 concludes this paper. 2. Engineering Description The primary bridge is a three-span, earth-anchored suspension bridge with a double tower. Its total span is 820 m with a primary span length of 460 m and side span lengths of 180 m each. The stiffening girder is a steel truss with a height of 10 m. There are 43 girders that must be hoisted. All girders are heavy and bulky steel truss structures with weights from 264.18 to 527.19 t. Girders in the side spans must be hoisted using a floating crane, and the girders in the middle span were lifted using two cranes stretched across the two primary cables. The hoisting procedures must be implemented in good weather and calm seas, and hoisting safety is an important factor that must be considered. The monitoring for hoisting is essential to make sure the safety, and can be realized in real-time and more convenient with the developed system. The elevation of the bridge is shown as Figure 1, and the girder numbers are labeled in red. In the following parts, the girders monitored were No. 3 in side-span and No. 22 in mid-span.

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Figure 1. Elevation of the cross-sea bridge investigated in this study. Figure Figure1. 1.Elevation Elevationof ofthe thecross-sea cross-seabridge bridgeinvestigated investigatedin inthis thisstudy. study.

3. HoistingMonitoring MonitoringSystem System 3.Hoisting Hoisting Monitoring System 3.1. Monitoring System Design 3.1. 3.1.Monitoring MonitoringSystem SystemDesign Design The monitoring systemconsists consistsof ofaaacollector collectorprogram program that is installed an iPhone The that isis installed on an (i.e., the The monitoring monitoring system system consists of collector program that installed on on an iPhone iPhone (i.e.,(i.e., the the collector) and a controller program that is installed in another iPhone (i.e., the controller). collector) collector) and and aa controller controller program program that that isis installed installed in in another another iPhone iPhone (i.e., (i.e., the the controller). controller). Additionally, iPhones and Additionally, web server isis used used to gather the data collected by the collector then Additionally, aaa web web server server is used to to gather gather the the data data collected collected by by the the collector collector iPhones iPhones and and then then return data to the controller. return data to the controller. return data to the controller. The The controller sends instructions to collector and observes the collected data. The collector The controller controller sends sends instructions instructions to to aaacollector collectorand andobserves observesthe thecollected collecteddata. data. The The collector collector collects monitoring data through its built-in sensors after receiving instructions from the controller and collects collects monitoring monitoring data data through through its its built-in built-in sensors sensors after after receiving receiving instructions instructions from from the the controller controller returns the data the to controller every 20 s. Once the current data exceeds given threshold and the data every 20 Once the current data aa given and returns returns theto data to the the controller controller every 20 s.s. Once thereturned current returned returned dataaexceeds exceeds given 2 , and the threshold of angle is 10˝ ), an alarm will be (e.g., the threshold of acceleration is 10 m/s 2 2 threshold threshold (e.g., (e.g., the the threshold threshold of of acceleration acceleration isis 10 10 m/s m/s ,, and and the the threshold threshold of of angle angle isis 10°), 10°), an an alarm alarm triggered on the controller iPhone, which then continues collecting collecting and monitoring. The threshold will on iPhone, which then and The will be be triggered triggered on the the controller controller iPhone, which then continues continues collecting and monitoring. monitoring. The can be set on the controller at any time according to operator experience and the requirements of the threshold threshold can can be be set set on on the the controller controller at at any any time time according according to to operator operator experience experience and and the the on-site conditions. The flowchart of this system is presented in Figure 2. requirements requirementsof ofthe theon-site on-siteconditions. conditions.The Theflowchart flowchartof ofthis thissystem systemisispresented presentedin inFigure Figure2. 2.

Figure Figure2.2.Flowchart Flowchartof ofthe themonitoring monitoringand andalarm alarmsystems. systems. Figure 2. Flowchart of the monitoring and alarm systems.

3.2. 3.2.Sensor SensorSubsystem Subsystem 3.2. Sensor Subsystem 3.2.1. 3.2.1.Sensor SensorParameters Parameters 3.2.1. Sensor Parameters Three Three parameters parameters are are primarily primarily considered considered during during aa hoisting hoisting process: process: the the vertical vertical acceleration acceleration Three parameters are primarily considered during a hoisting process: the vertical acceleration and andthe theangles anglesof ofthe thexx-and andy-axes, y-axes,which whichwill will be beintroduced introducedin inSection Section3.5. 3.5.The Thevertical verticalacceleration acceleration and the angles of the x- and y-axes, which will be introduced in Section 3.5. The vertical acceleration is isismonitored monitoredto toavoid avoidthe theoccurrence occurrenceof ofaasudden suddendrop; drop;the theangles anglesnoted notedare areexamined examinedto tomonitor monitorthe the monitored to avoid the occurrence of a sudden drop; the angles noted are examined to monitor locations of four corners of the structure during hoisting. Acceleration is collected by the built-in locations of four corners of the structure during hoisting. Acceleration is collected by the built-in the locations of four corners of the structure during hoisting. Acceleration is collected by the BMA220-type BMA220-typeaccelerometer accelerometer(Bosch, (Bosch,Stuttgart, Stuttgart,Germany), Germany),which whichallows allowsmeasurement measurementof ofacceleration acceleration built-in BMA220-type accelerometer (Bosch, Stuttgart, Germany), which allows measurement of in in three three perpendicular perpendicular axes. axes. This This sensor sensor isis based based on on micro micro electro electro mechanical mechanical systems systems (MEMS). (MEMS). Additionally, the digital resolution is 6 bit. The acceleration sensor can be programmed to optimize Additionally, the digital resolution is 6 bit. The acceleration sensor can be programmed to optimize functionality, functionality, performance performance and and power power consumption consumption in in customer-specific customer-specific applications. applications. The The angle angle isis

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acceleration in three perpendicular axes. This sensor is based on micro electro mechanical systems (MEMS). Additionally, the digital resolution is 6 bit. The acceleration sensor can be programmed to optimize functionality, performance and power consumption in customer-specific applications. The angle is determined by invoking the convert function in the iPhone to read the angular rate of rotation collected by the built-in L3G4200D-type gyroscope (ST, Geneva, Switzerland), which is also a MEMS-based sensor. The gyroscope integrates low- and high-pass filters with a user-selectable bandwidth and incorporates power-down and sleep modes, a temperature sensor, and first-in first-out memory. The basic features of the accelerometer and gyroscope in the iPhone are provided in Table 1. The mechanical characteristics of the accelerometer and gyroscope in the iPhone 5S are presented in Tables 2 and 3, respectively. Table 1. Basic features of the accelerometer and gyroscope in the iPhone.

Supply voltage Low voltage-compatible IOS Data output Selectable full scales Output interface High shock survivability

Accelerometer (BMA220)

Gyroscope (L3G4200D)

1.62–1.98V 1.8 V 16 bit ˘2 g/˘4 g/˘8 g, ˘16 g I2 C/SPI Yes

2.4–3.6 V 1.8 V 16 bit 250 dps/500 dps/2000 dps I2 C/SPI Yes

Table 2. Mechanical characteristics of the accelerometer in the iPhone 5S. Parameter

Conditions

Typical

Measurement range (MR)

˘2, ˘4, ˘8 g, ˘16 g

Sensitivity

˘2.0 g ˘4.0 g ˘8.0 g ˘16.0 g

16 LSB/g 8 LSB/g 4 LSB/g 2 LSB/g

Sensitivity change vs. temperature

˘2.0 g

˘0.01%/˝ C

Typical zero-g offset accuracy

˘2.0 g

˘95 mg ´40 to +85 ˝ C

Operating temperature range Zero-g offset temperature drift

´40 to +85 ˝ C

Bandwidths

˘2 mg/K 32, 64, 125, 250, 500, 1000 Hz

Table 3. Mechanical characteristics of the gyroscope in the iPhone 5S. Parameter

Test Conditions

MR

Type

Unit

˘250, ˘500, ˘2000

dps

Sensitivity

MR is ˘250 dps MR is ˘500 dps MR is ˘2000 dps

8.75 17.50 70

mdps/digit

Sensitivity change vs. temperature

´40 ˝ C to +85 ˝ C

˘2

%

Digital zero-rate level

MR is ˘250 dps MR is ˘500 dps MR is ˘2000 dps

˘10 ˘15 ˘75

dps

Zero-rate level change vs. temperature

MR is ˘250 dps MR is ˘2000 dps

˘0.03 ˘0.04

dps/˝ C

100, 200, 400, 800

Hz

Digital output data rate

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Based on the preceding characteristics, the basic performances of the accelerometer and gyroscope are stable, and these devices can thus satisfy engineering requirements in certain situations. The acceleration direction is specified as follows: regardless of the position of the phone, when the screen faces the user, the horizontal direction (i.e., left to right) is the positive direction of the x-axis, Sensors 2016, 16, 1048 5 of 17 Sensors the 2016,vertical 16, 1048 direction (i.e., bottom to top) is the positive direction of the y-axis. The direction 5 of 17 while Sensors 2016, 16, 1048 5 of 17 that faces the user is the positive direction of the z-axis, which is perpendicular to the phone’s screen. represent the rotation angles around the x-, y-, and z-axes, respectively. The angle-of-rotation represent the rotation angles aroundinthe x-, y-, and z-axes, respectively. The acceleration directions are shown Figure 3. To determine the angle, theThe dataangle-of-rotation obtained by the directions are shown in angles Figure 4. represent the rotation around the x-, y-, and z-axes, respectively. The angle-of-rotation directions are shown in Figure 4. gyroscope is categorized into three groups (i.e., pitch, roll, and yaw), which represent the rotation directions are shown in Figure 4. angles around the x-, y-, and z-axes, respectively. The angle-of-rotation directions are shown in Figure 4.

Figure 3. Acceleration directions. Figure 3. Acceleration directions. Figure 3. Acceleration directions. directions. Figure 3. Acceleration

Figure 4. Angle-of-rotation directions. Figure Figure 4. 4. Angle-of-rotation Angle-of-rotation directions. directions. Figure 4. Angle-of-rotation directions.

3.2.2. Calibration of Angle 3.2.2. 3.2.2. Calibration Calibration of of Angle Angle 3.2.2.In Calibration of Angle order to to validate the the accuracy of of the angle, angle, an angle angle instrument was was applied to to test the the angle In In order order to validate validate the accuracy accuracy of the the angle, an an angle instrument instrument was applied applied to test test the angle angle variation. The experiment photo is shown as Figure 5. In order to validate the accuracy of the angle, an angle instrument was applied to test the angle variation. variation. The The experiment experiment photo photo is is shown shown as as Figure Figure 5. 5. variation. The experiment photo is shown as Figure 5.

Figure 5. Photo of calibration experiment. Figure 5. Photo of calibration experiment. Figure 5. Photo of calibration experiment.

The angle angle instrument is fixed on the table, and the angle can by The can be be changed changed by turning turning the the knob. knob. The angle instrument instrument is is fixed fixed on on the the table, table, and and the the angle angle can be changed by turning the knob. The smartphone is fixed on the instrument, and moved with the instrument. Because of the The angle instrument is fixed on the table, the angle can be changed by turning the knob. The on on the the instrument, and moved with the instrument. Because Because of the dynamic The smartphone smartphoneisisfixed fixed instrument, and moved with the instrument. of the dynamic angle data slow manual angle and low precise, step-by-step The smartphone is acquisition, fixed on the instrument, and loading, moved with the reading instrument. Because of the dynamic angle data acquisition, slow manual angle loading, and low reading precise, step-by-step loading method is adopted in the experiment. Fiveloading, loadingand steps are included in each test, one dynamic angle data acquisition, slow manual angle low reading precise, step-by-step loading method is adopted in the experiment. Five loading steps are included in each test, one degree added every step by in the angle instrument, then keep for several seconds, loading method is adopted experiment. Fiveand loading steps static are included in each test, then one degree added every step by thethe angle instrument, and then keep static for several seconds, then goes to the nextevery step. Take two experiments as examples, the angle around x-axis is shown in Figure 6a, degree added step by the angle instrument, and then keep static for several seconds, then goes to the next step. Take two experiments as examples, the angle around x-axis is shown in Figure 6a, and the angle around y-axis is experiments shown in Figure 6b. goes to the next step. Take two as examples, the angle around x-axis is shown in Figure 6a, and the angle around y-axis is shown in Figure 6b.

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2 2

2 2

0 0

0 0

angle(degree) angle(degree)

angle(degree) angle(degree)

angle data acquisition, slow manual angle loading, and low reading precise, step-by-step loading method is adopted in the experiment. Five loading steps are included in each test, one degree added every step by the angle instrument, and then keep static for several seconds, then goes to the next step. Take two experiments as examples, the angle around x-axis is shown in Figure 6a, and the angle Sensors 2016, 16, 1048 6 of 17 around y-axis is shown in Figure 6b. Sensors 2016, 16, 1048 6 of 17

-2 -2 -4 -4 -6 -6 0 0

20 20

40 60 40time(s) 60 time(s)

80 80

-2 -2 -4 -4 -6 -6 0 0

100 100

20 20

40 60 40time(s) 60 time(s)

(a) (a)

80 80

100 100

(b) (b)

Figure 6. Angle variation with step-by-step method. (a) Angle around x-axis; (b) Angle around Figure 6. Angle Anglevariation variationwith with step-by-step method. (a) Angle around x-axis; (b) Angle Figure 6. step-by-step method. (a) Angle around x-axis; (b) Angle aroundaround y-axis. y-axis. y-axis.

Several Several experiments experiments were were conducted, conducted, and and angle angle steps steps on on smart smart phone phone of of three three experiments experiments are are Several experiments were conducted, and angle steps on smart phone of three experiments are presented presentedin inFigure Figure7.7. presented in Figure 7.

4 4

4 4

Angle(degree) Angle(degree)

5 5

Angle (degree) Angle (degree)

5 5

3 3

3 3

Angle instrument Angle Test 1instrument Test Test12 Test Test23 Test 3

2 2

1 1 1 1

2 2

3

3 times Loading Loading times

(a) (a)

4 4

5 5

2 2

Angle instrument Angle Test 1instrument Test Test12 Test Test23 Test 3

1 1 1 1

2 2

3

3 times Loading Loading times

4 4

5 5

(b) (b)

Figure 7. 7. Angle Angle step step comparison comparison between between smart smart phone phone and and angle angle instrument. instrument. (a) (a) Angle Angle step step around around Figure Figure 7. Angle step comparison between smart phone and angle instrument. (a) Angle step around x-axis; (b) (b) Angle Angle step steparound aroundy-axis. y-axis x-axis; x-axis; (b) Angle step around y-axis

From Figure 7, it can be seen that the angle step coincides better with the instrument loading From Figure 7, it can be seen that the angle step coincides better with the instrument loading step. The error is inevitable because the angle on the instrument is loaded manually, and the step. The The error errorisisinevitable inevitable because angle on instrument the instrument is loaded manually, the because thethe angle on the is loaded manually, and the and reading reading is not so exact. Moreover, the loading in each experiment may be different to some extent, reading not soMoreover, exact. Moreover, the loading each experiment be different some extent, is not soisexact. the loading in each in experiment may bemay different to sometoextent, so the so the dynamic experiment was also conducted in [28]. The angle collected by the smartphone is so the dynamic experiment also conducted in [28]. angle collected by the smartphone is dynamic experiment was alsowas conducted in [28]. The angleThe collected by the smartphone is compared compared to wired acquisition system and wireless sensing system, and the result proved the compared to wired system acquisition system sensing and wireless sensing and the proved the to wired acquisition and wireless system, and thesystem, result proved theresult accuracy of angle accuracy of angle acquisition using smartphone. accuracy of using angle smartphone. acquisition using smartphone. acquisition 3.3. Controller Program 3.3. Controller Program The controllerprogram program workswith with theweb web server to control and observe the data transmitted and observe thethe data transmitted by The controller controller programworks works withthe the webserver servertotocontrol control and observe data transmitted by the online collectors. The controller program can send instructions via the web server and make the online collectors. The controller program can send instructions via the web server and make the by the online collectors. The controller program can send instructions via the web server and make the collectors run based on instructions. these instructions. Three instructions are typically available: “start”, collectors run based on these Three Three instructions are typically available: “start”, “start”, “stop”, the collectors run based on these instructions. instructions are typically available: “stop”, and “upload data”. The “start” instruction automatically prepares the default settings and and “upload data”. The “start” automatically prepares the default the settings andsettings initiatesand the “stop”, and “upload data”. Theinstruction “start” instruction automatically prepares default initiates the collection operation of online data collectors. The “stop” instruction controls online initiates the collection operation of online data collectors. The “stop” instruction controls online collectors, which are currently collecting data. The “upload data” instruction prompts online collectors, which are currently collecting data. The “upload data” instruction prompts online collectors to upload the data to the web server for further analysis. collectors to upload the data to the web server for further analysis. Acting as the primary component of the system, the controller observes the online collectors, Acting as the primary component of the system, the controller observes the online collectors, while the collectors collect data and returns six types of data (i.e., acceleration data of three directions while the collectors collect data and returns six types of data (i.e., acceleration data of three directions

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collection operation of online data collectors. The “stop” instruction controls online collectors, which are currently collecting data. The “upload data” instruction prompts online collectors to upload the data to the web server for further analysis. Acting as the primary component of the system, the controller observes the online collectors, while the collectors collect data and returns six types of data (i.e., acceleration data of three directions Sensors 2016, data 16, 1048 7 of 17 and angle of three directions) to the controller with their ID approximately every 20 s, it’s worth Sensors 2016, 16, 1048 7 of 17 mentioning that the data will be returned to controller immediately once the collected data exceeds given the given threshold. When thethereturned returned collected data exceeds aagiven given threshold, the color of the the a giventhreshold. threshold.When When returnedcollected collecteddata dataexceeds exceedsa given threshold, threshold, the the color color of corresponding monitoring parameter in the interface of the controller will change. interface of of the the controller controller will will change. change. corresponding monitoring parameter in the interface The web web server provides storage and push which information webserver server provides data storage and functions, push functions, functions, which facilitate facilitate information The provides datadata storage and push which facilitate information exchange exchange (e.g., instructions) between the controller and the collectors. The interface of the controller exchange (e.g., instructions) between theand controller and theThe collectors. The of theiscontroller (e.g., instructions) between the controller the collectors. interface of interface the controller shown in is in 8, interface of real-time monitoring system is is shown shown in Figure Figure 8, and and the the interface of the the real-time system monitoring system is shown shown in Figure Figure 9. 9. Figure 8, and the interface of the real-time monitoring is shown in Figure 9. in

Figure 8. Controller Figure 8. Controller interface. interface.

Figure 9. Interface of the real-time monitoring system. Figure Figure 9. 9. Interface Interface of of the the real-time real-time monitoring monitoring system. system.

3.4. 3.4. Collector Collector Program Program The The collector collector program program uses uses the the built-in built-in sensors sensors of of the the iPhone iPhone to to collect collect angle angle and and acceleration acceleration data. Prior to data collection, several variables can be set on a collector, including data. Prior to data collection, several variables can be set on a collector, including the the collection collection frequency, duration, threshold, and data filename. During data collection, a collector continuously frequency, duration, threshold, and data filename. During data collection, a collector continuously accesses accesses its its sensors sensors to to obtain obtain data data and and writes writes their their data data to to aa file. file. A A collector collector can can work work independently independently or under the control of the controller when “network control” is available. Additionally, or under the control of the controller when “network control” is available. Additionally, aa map map

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3.4. Collector Program The collector program uses the built-in sensors of the iPhone to collect angle and acceleration data. Prior to data collection, several variables can be set on a collector, including the collection frequency, duration, threshold, and data filename. During data collection, a collector continuously accesses its sensors to obtain data and writes their data to a file. A collector can work independently or under the control of the controller when “network control” is available. Additionally, a map position interface can be2016, used16, to1048 record the monitoring location. The interface of collector program is shown in Figure Sensors 2016, 16, 1048 of10. 17 Sensors 88 of 17

(a)

(b)

Figure 10. Collector interface of the iPhone. (a) GPS information; (b) Gyroscope interface. Figure 10. Collector interface of the iPhone. (a) GPS information; (b) Gyroscope interface.

3.5. Application of the Proposed System for Monitoring a Hoisting Operation 3.5. Application of the Proposed System for Monitoring a Hoisting Operation The developed system was applied to determine the orientation of a girder during hoisting. A The developed system was applied to determine the orientation of a girder during hoisting. schematic ofof the hoisting be A schematic the hoistingprocess processisisshown shownininFigure Figure11. 11.The Thecollector collectorwas wasfixed fixed on on the the girder girder to to be hoisted, and the controller was positioned in a safe zone (i.e., a boat, on land, a catwalk, or another hoisted, and the controller was positioned in a safe zone (i.e., a boat, on land, a catwalk, or another safe place), where operators can operate the system easily and safely. Instructions were sent from the safe place), where operators can operate the system easily and safely. Instructions were sent from controller to the via the 4Gornetwork. The collector then began to gather data upon the controller to collector the collector via2G, the 3G 2G,or3G 4G network. The collector then began to gather data receiving commands with a sampling frequency of 100 Hz and then returns six data at one time upon receiving commands with a sampling frequency of 100 Hz and then returns six data at one time point (i.e., (i.e., the the acceleration acceleration data data of of three three directions directions and and the the angle angle of of three directions) to to the the controller controller point three directions) every 20 s. The operator can determine the status of the hoisting procedure based on the returned every 20 s. The operator can determine the status of the hoisting procedure based on the returned data data shown on the controller. shown on the controller.

11. Schematic of the hoisting realization realization process. process. Figure 11.

The direction direction of of the the girder girder is is specified specified as as follows: follows: the The the x-axis x-axis runs runs along along the the span span of of the the bridge, bridge, and the y-axis is perpendicular to the bridge. These directions within the construction site are shown and the y-axis is perpendicular to the bridge. These directions within the construction site are shown in Figure Figure 12. 12. in

Figure 11. Schematic of the hoisting realization process.

The direction of the girder is specified as follows: the x-axis runs along the span of the bridge, and the y-axis is perpendicular to the bridge. These directions within the construction site are shown Sensors 2016, 16, 1048 9 of 18 in Figure 12.

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Figure 12. 12. Specified Specified directions. Figure directions.

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4. 4. Monitoring MonitoringofofSide-Span Side-Span Hoisting Hoisting Procedure Procedure 4. Monitoring of Side-Span Hoisting Procedure 4.1.4.1. Monitoring Process Monitoring Process 4.1. Monitoring Process The girder hoisting onon oneone of the side spans waswas performed in this section. TheThe hoisting tooltool used The girder hoisting of the side spans performed in this section. hoisting was a floating crane, and the girder, which is No. 3 in Figure 1, weighed 511.76 t. The location of the usedThe wasgirder a floating crane,onand which No. performed 3 in Figure in 1, weighed 511.76 The location hoisting onethe of girder, the side spansis was this section. Thet. hoisting tool 3# girder iswas shown inisFigure 13. of the 3# girder shown inand Figure used a floating crane, the 13. girder, which is No. 3 in Figure 1, weighed 511.76 t. The location of the 3# girder is shown in Figure 13.

Figure13. 13. Location Location of Figure of the the second secondgirder. girder. Figure 13. Location of the second girder.

During hoisting the girder is lifted by slings that are made of a high-strength fiber. The During hoisting the girder is itlifted by slings that are made of a high-strengththe fiber. The orientation orientation the girder is suspended requires sudden dropThe of Duringofhoisting thewhen girder lifted by slings thatmonitoring are made toofprevent a high-strength fiber. of the girder when it is suspended requires monitoring to prevent the sudden drop of one end, which one end, which would be indicated by a large angle in the front/back or right/left directions. orientation of the girder when it is suspended requires monitoring to prevent the sudden drop of would indicated bythis a large angle in by the afront/back right/left directions. Therefore, to obtain Therefore, to obtain real-time information and then take corresponding measures, thedirections. angle and one be end, which would be indicated large angleor in the front/back or right/left thisacceleration real-time information and then take corresponding measures, the angle and acceleration should be monitored and relayedand to then the operator through themeasures, controller. the Therefore, toshould obtain this real-time information take corresponding theDuring angle and be hoisting monitored and relayed to5S the operator through theoperator controller. the hoisting process, process, an iPhone gathered data as atocollector, whilethrough an During iPhone sent instructions and acceleration should be monitored and relayed the the4S controller. During thean iPhone 5S gathered data as a5S collector, anaiPhone 4Swhile sent instructions received data as a received data as aan controller. The on-sitewhile hoisting procedure is shown in Figure 14. collector (i.e., hoisting process, iPhone gathered data as collector, an iPhone 4S and sentThe instructions and controller. The on-site hoisting procedure is shown in Figure 14. The collector (i.e., the iPhone the iPhone 5S) was fixed on the girder, and the controller (i.e., the iPhone 4S) was operated by a5S) received data as a controller. The on-site hoisting procedure is shown in Figure 14. The collector (i.e., worker on a safe place. The arrangement of the phone is shown in Figure 15. The directions X1 and was on the andonthe (i.e., iPhone 4S) a worker onby a safe thefixed iPhone 5S) girder, was fixed thecontroller girder, and thethe controller (i.e.,was the operated iPhone 4S)bywas operated a Y1 denote the positive directions of the xy-axes the and 15. the The directions and Y2the place. Theon arrangement phone is shown in Figure 15. girder, The directions X1 directions and Y1X2denote worker a safe place. of Thethe arrangement of and the phone isofshown in Figure X1 and represent the ofofthe xand y-axes ofthe thethe collector. the returned data on the Y1 denote thepositive positive the xand y-axes of girder, Thus, andand the directions X2 Y2 positive directions of thedirections x-directions and y-axes of the girder, and directions X2 Y2 represent theand positive angle about the axis of the girder should be considered during hoisting. represent the positive directions of the xand y-axes of the collector. Thus, the returned data on the directions of the x- and y-axes of the collector. Thus, the returned data on the angle about the axis of about the be axisconsidered of the girder should be considered during hoisting. theangle girder should during hoisting.

Figure 14. On-site hoisting. Figure14. 14. On-site On-site hoisting. Figure hoisting.

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Figure 14. On-site hoisting.

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Figure 15. Arrangement of the collector (i.e., the iPhone 5S). Figure 15. Arrangement of the collector (i.e., the iPhone 5S).

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4.2. Related Related Algorithm Algorithm 4.2. In order data collected collected by by collector, collector, the the related In order to to compare compare the the on-site on-site feedback feedback and and original original data related algorithm is the collector phone, and named as algorithm is shown shown in inFigure Figure16. 16.The Thedata dataisiscollected collectedand andstored storedinin the collector phone, and named Angledata.txt and acceleration.txt. The data files can be exported, and then processed by MATLAB to as Angledata.txt and acceleration.txt. The data files can be exported, and then processed by obtain the to time-history In thecurves. data file, thethe sixth column collected time, MATLAB obtain the curves. time-history Inthe thefirst datatofile, first to therepresents sixth column represents they are year, month, day, hour, minute and second respectively. In this test, hour, minute and second collected time, they are year, month, day, hour, minute and second respectively. In this test, hour, are used. In second the accelerationdata.txt file, the seventh to ninth columns the acceleration of minute and are used. In the accelerationdata.txt file, the seventhrepresent to ninth columns represent three axes, so theofvertical acceleration is the ninth columns. In the Angledata.txt seventh to the acceleration three axes, so the vertical acceleration is the ninth columns. Infile, the the Angledata.txt ninth columns represent the angle around three axes. From Figure 15, it can be seen that, angle file, the seventh to ninth columns represent the angle around three axes. From Figure 15, the it can be around x-axis of the girder measured by smartphone is the angle around y-axis. So the eighth and seen that, the angle around x-axis of the girder measured by smartphone is the angle around y-axis. seventh column and is used to calculate the is angle around x-axis and y-axis respectively. The original data So the eighth seventh column used to calculate the angle around x-axis and y-axis in smartphone collected in radians, a transformational relation is used in the data processing. After respectively. The original data in smartphone collected in radians, a transformational relationthe is processing, angle-history curve can be obtained to compare with the used in the the data processing.curve Afterand the acceleration processing, history the angle-history curve and acceleration history on-sitecan feedback. curve be obtained to compare with the on-site feedback.

Figure 16. Algorithm of side-span hoisting.

4.3. Results 4.3. Test Test Results The durationofofthethe hoisting process 3 h. There no warning information on the The duration hoisting process was was 3 h. There was nowas warning information on the controller controller whole procedure. At the beginning, four of corners of themust girder be during theduring wholethe procedure. At the beginning, the four the corners the girder bemust hoisted hoisted simultaneously. Therefore, real-time angle information must be obtained to evaluate the simultaneously. Therefore, real-time angle information must be obtained to evaluate the position of position the to girder andinformation to provide information operators. The vertical-acceleration the girderofand provide to operators.toThe vertical-acceleration time-historytime-history curve of the curve of the collector is shown in Figure 17. collector is shown in Figure 17.

The duration of the hoisting process was 3 h. There was no warning information on the controller during the whole procedure. At the beginning, the four corners of the girder must be hoisted simultaneously. Therefore, real-time angle information must be obtained to evaluate the position of the girder and to provide information to operators. The vertical-acceleration time-history Sensors 2016, 16, 1048 11 of 18 curve of the collector is shown in Figure 17.

Figure 17. Vertical-acceleration time-history curve of the girder during hoisting.

Figure 17. Vertical-acceleration time-history curve of the girder during hoisting. Sensors 2016, 16, 1048

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From the vertical-acceleration vertical-acceleration time-history curves in Figure 17, it is shown that that the acceleration acceleration fluctuated extent whenwhen the girder changed. Additionally, the maximum fluctuated totoa certain a certain extent the state girder state changed. Additionally, theacceleration maximum occurred when the girder is hoisted into its final location; the sudden touch of the girder the acceleration occurred when the girder is hoisted into its final location; the sudden touch of theand girder column major acceleration. Figures 18 and 1918show theshow anglethe about theabout x- andthe y-axes of and the caused columnacaused a major acceleration. Figures and 19 angle x- and the girder. y-axes of the girder.

Figure 18. Angle about the x-axis of the girder during hoisting. Figure 18. Angle about the x-axis of the girder during hoisting.

Figure 19. Angle about the y-axis of the girder during hoisting. Figure 19. Angle about the y-axis of the girder during hoisting.

operator, the the collector collector started started to gather gather data at 9:48; 9:48; the Depending on the records of the field operator, given height height by by 10:45; 10:45; and four four bolts bolts hoisting of the girder began at 10:14; the girder was lifted to a given (i.e., the connection between the cable and girder, which is shown as Figure Figure 20) 20) were were installed installed (i.e., 12:19. The completely by 12:19. The resultant resultant deformation deformation was was severe when workers workers started started to remove the sling. From From Figures Figures 17–19, 17–19, it is shown that the angle changed due to the action of hoisting in every phase of of the the hoisting hoisting procedure. procedure. Before each bolt was secured in its respective hole, the angle angle was was phase match up up each each bolt acceleration and angle angle adjusted to match bolt hole. hole. Throughout the hoisting process, the acceleration marginally, and remained within ranges. Based on the the changed only marginally, and all all disturbances disturbances remained within the the acceptable acceptable ranges. preceding analysis, the girder remained stable during this hoisting operation, which is consistent with the phone investigation.

hoisting of the girder began at 10:14; the girder was lifted to a given height by 10:45; and four bolts (i.e., the connection between the cable and girder, which is shown as Figure 20) were installed completely by 12:19. The resultant deformation was severe when workers started to remove the sling. From Figures 17–19, it is shown that the angle changed due to the action of hoisting in every phase 2016, of the procedure. Before each bolt was secured in its respective hole, the angle Sensors 16, hoisting 1048 12 was of 18 adjusted to match up each bolt hole. Throughout the hoisting process, the acceleration and angle changed only marginally, and all disturbances remained within the acceptable ranges. Based on the preceding stable during thisthis hoisting operation, which is consistent with preceding analysis, analysis,the thegirder girderremained remained stable during hoisting operation, which is consistent the phone investigation. with the phone investigation.

Figure 20. 20. Bolt. Bolt. Figure

5. Monitoring of a Middle-Span Hoisting Procedure 5.1. Monitoring Process Sensors 2016, 16, 1048 The girder which

12 of 17 is No. 22 in Figure 1 on the middle span weighed 372.22 t and was hoisted using two cranes. Two cranes were stretched across the two primary cables and worked together to 5. Monitoring of a Middle-Span Hoisting lift the second girder into place; thus, both Procedure cranes had to raise the girder at the same rate to prevent imbalance. Therefore, the angle of the girder must be determined in real time to ensure a synchronous 5.1. Monitoring Process hoisting operation. In monitoring an iPhone usedspan to collect data372.22 and return Thethis girder which isprocedure, No. 22 in Figure 1 on5S thewas middle weighed t and information was hoisted to the two controller, iPhone 4S served as across a controller to primary receive the returned data and provide using cranes.and Twoancranes were stretched the two cables and worked together to information to the operators. The on-site hoisting procedure is shown in Figure 21. The collector (i.e., lift the second girder into place; thus, both cranes had to raise the girder at the same rate to prevent the iPhone 5S) was fixed the ontoangle the girder to be hoisted, and be the determined controller was by operators imbalance. Therefore, of the girder must inoperated real time to ensureona asynchronous catwalk. Thehoisting arrangement of the collector is shown in Figure 22, and Figure 23 shows the position of operation. the collector and controller at the beginning of the hoisting thisand point during the hoisting In this monitoring procedure, an iPhone 5S was usedoperation; to collect at data return information to procedure, the controller was on4S theserved boat. After girder was raised from the boat, data the controller was the controller, and an iPhone as a the controller to receive the returned and provide taken to a catwalk the remainder of the hoisting procedure. information to the for operators. The on-site hoisting procedure is shown in Figure 21. The collector (i.e., As shown in Figure 22, the collector was pointed toward a direction to the specified the iPhone 5S) was fixed onto the girder to be hoisted, and the controller wassimilar operated by operators direction of theThe trussarrangement girder to allow to judge the monitored directly23 based on the on a catwalk. of operators the collector is shown in Figure situation 22, and Figure shows the feedback information received by the controller. Figure 23 shows the convenience of this method, position of the collector and controller at the beginning of the hoisting operation; at this point during without any procedure, other measurement devices; only arewas required obtain relevant the hoisting the controller was on thetwo boat.smart Afterphones the girder raisedto from the boat, the hoisting information. controller was taken to a catwalk for the remainder of the hoisting procedure.

Figure 21. On-site hoisting of the middle span. Figure 21. On-site hoisting of the middle span.

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Figure 21. On-site hoisting of the middle span. Figure 21. On-site hoisting of the middle span.

Figure22. 22. Arrangement of the Figure thecollector. collector. Figure 22.Arrangement Arrangement of of the collector.

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As shown in Figure 22, the collector was pointed toward a direction similar to the specified direction of the truss girder to allow operators to judge the monitored situation directly based on the Figure 23. Position of collector and controller. feedback information received by the shows the convenience of this method, Figure 23. controller. Position of Figure collector23and controller. Figure 23. Position of collector and controller. without any other measurement devices; only two smart phones are required to obtain relevant hoisting information.

5.2. Related Algorithm

5.2. Related Algorithm

Figure 24 gives the algorithm of the middle-span hoisting monitoring. The detailed accounts are Figure 24 of the the algorithm middle-spaninhoisting Thetwo detailed accounts omitted because of gives whichthe arealgorithm similar to Sectionmonitoring. 4.2 except for aspects. First is the are omitted because of which are similar to the algorithm in Section 4.2 except for two aspects. First about same direction of girder and smartphone, so the seventh column is used to calculate the angle is the same direction of girder and smartphone, so the seventh column is used to calculate the angle x-axis, and the eighth column is used to calculate the angle about y-axis. Second is regarding the size about x-axis, and the eighth column is used to calculate the angle about y-axis. Second is regarding and angle of the girder, the height difference in the front/back and right/left directions can only be the size and angle of the girder, the height difference in the front/back and right/left directions can obtained approximately. The height The difference in the left/right directiondirection can provide some information only be obtained approximately. height difference in the left/right can provide some to theinformation hoisting operators about operators the synchronization of the cranes on the cranes two primary cables. The girder to the hoisting about the synchronization of the on the two primary cables. The in girder 24 m long in the left/right wide in the front/back was 24 m long the was left/right direction and 10direction m wideand in 10 themfront/back direction,direction, so the height so thecan height be calculated according to trigonometric function shown as difference be difference calculatedcan according to trigonometric function shown as Figure 24.Figure 24.

Figure Algorithm of of middle-span monitoring. Figure 24.24.Algorithm middle-spanhoisting hoisting monitoring.

5.3. Test Results The duration of the entire hoisting process was nearly 9 h—from the transmission of the “start” instruction at 9:00 to the transmission of the “stop” instruction at 17:52. The test period is so long and

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5.3. Test Results The duration of the entire hoisting process was nearly 9 h—from the transmission of the “start” instruction at 9:00 to the transmission of the “stop” instruction at 17:52. The test period is so long and the battery in iPhone can function 4 h in working state, while this long field test can be achieved if an additional battery is available. The vertical acceleration collected by the collector is shown in Figure 25 and shows that there is no significant change in the vertical acceleration of the girder. The maximum acceleration occurred at Sensors 2016, 16, 1048 14 of 17 the beginning of the hoisting operation. Sensors 2016, 16, 1048 14 of 17

Figure 25. Vertical-acceleration time-history curve. Figure 25. Vertical-acceleration time-history curve. curve. Figure 25. Vertical-acceleration time-history

Figure 26 shows the angle about the girder’s x-axis; the angle about the y-axis of the girder is Figure 26 shows the angle about the at girder’s x-axis; the angle about the y-axis of the girder is shown in Figure 27. Data began 9:00, and the the hoisting began at 11:31. certain Figure 26 shows the collection angle about the girder’s x-axis; angleprocess about the y-axis of theAgirder is shown in Figure 27. Data collection began at 9:00, and the hoisting process began at 11:31. A certain angle the xy-axes was generated at this During process the initial phase of hoisting, the shownabout in Figure 27.and Data collection began at 9:00, andtime. the hoisting began at 11:31. A certain angle changed about themarginally x- and y-axes was generated at this time. During the sides. initial Additionally, phase of hoisting, the angle to ensure synchronous hoisting of the two the first angle about the x- and y-axes was generated at this time. During the initial phase of hoisting, the angle anglewas changed marginally toatensure synchronous hoisting of thecontinued two sides.toAdditionally, the first bolt placed in position 16:30. The angle about the y-axis change to match the changed marginally to ensure synchronous hoisting of the two sides. Additionally, the first bolt was bolt was placed position at 16:30. The angle about the y-axis continued to change toand match the installation of theinother three the figures, it is shown that the acceleration angles placed in position at 16:30. Thebolts. angleBased abouton the y-axis continued to change to match the installation of installation of theinother three bolts. Based on the figures, it is shown that the acceleration and angles can be reported real time. Lack of synchronization not encountered during hoisting the other three bolts. Based on the figures, it is shown thatwas the acceleration and angles canthis be reported can be reported in real time. Lack of synchronization was not encountered during this hoisting operation. in real time. Lack of synchronization was not encountered during this hoisting operation. operation.

Figure 26. 26. Angle Angle about about the the x-axis x-axis of of the the girder. girder. Figure Figure 26. Angle about the x-axis of the girder.

The height difference recorded in the left/right direction is shown in Figure 28, and the height difference recorded in the front/back direction is shown in Figure 29. It is shown that the height difference in the left/right direction was adjusted to ensure the synchronization of the two cranes. At the end of hoisting process, the height on the left side was 0.7 m higher than that on the right side. The height in the front/back direction was approximately stable throughout the hoisting operation. After the first bolt was installed, the height in the front/back direction continued to increase to allow the installation of the three other bolts. After the installation of all of the pins, the height in the front of

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the girder was 0.75 m higher than that in the back of the girder. No alarm information appears during the on-site monitoring. Thus, the hoisting process was successful, and the last state of the girder had been prepared completely for the construction of the next day, and there is no warning information on the controller during the whole procedure. Figure 26. Angle about the x-axis of the girder.

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the the end end of of hoisting hoisting process, process, the the height height on on the the left left side side was was 0.7 0.7 m m higher higher than than that that on on the the right right side. side. The height in the front/back direction was approximately stable throughout the hoisting operation. The height in the front/back direction was approximately stable throughout the hoisting operation. After After the the first first bolt bolt was was installed, installed, the the height height in in the the front/back front/back direction direction continued continued to to increase increase to to allow allow the the installation installation of of the the three three other other bolts. bolts. After After the the installation installation of of all all of of the the pins, pins, the the height height in in the the front front of the girder was 0.75 m higher than that in the back of the girder. No alarm information appears of the girder was 0.75 m higher than that in the back of the girder. No alarm information appears during during the the on-site on-site monitoring. monitoring. Thus, Thus, the the hoisting hoisting process process was was successful, successful, and and the the last last state state of of the the girder had been prepared completely for the construction of the next day, and there is no warning girder had been prepared completely for the construction of the next day, and there is no warning information during the whole procedure. Angle about the information on on the the controller controller Figure during27. the whole procedure. Figure 27. Angle about the y-axis y-axis of of the the girder. girder. The height difference recorded in the left/right direction is shown in Figure 28, and the height difference recorded in the front/back direction is shown in Figure 29. It is shown that the height difference in the left/right direction was adjusted to ensure the synchronization of the two cranes. At

Figure 28. Height difference in the left/right Figure 28. 28. Height Height difference difference in in the the left/right left/right direction. direction. Figure direction.

Figure 29. Height difference difference in the front/back Figure 29. 29. Height difference in in the the front/back front/back direction. direction. Figure direction.

6. 6. Conclusions Conclusions In In this this study, study, aa CPS CPS iPhone-based iPhone-based system system for for hoisting hoisting monitoring monitoring using using smartphones smartphones was was proposed, including a phone collector, a controller and a server. Field monitoring results of two steel proposed, including a phone collector, a controller and a server. Field monitoring results of two steel girder girder elements elements of of aa cross-sea cross-sea bridge bridge confirmed confirmed the the convenience convenience and and practicability practicability of of this this system. system. The The dynamic dynamic acceleration acceleration and and angle angle data data of of both both hoisting hoisting procedures procedures were were collected collected and and sent sent to to aa web server. The functions of sending instructions to the collectors and real-time monitoring web server. The functions of sending instructions to the collectors and real-time monitoring can can significantly significantly enhance enhance field field hoisting hoisting monitoring monitoring capabilities. capabilities. The The changes changes in in various various angles angles and and height differences obtained during the hoisting procedures were all within normal ranges, and there

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6. Conclusions In this study, a CPS iPhone-based system for hoisting monitoring using smartphones was proposed, including a phone collector, a controller and a server. Field monitoring results of two steel girder elements of a cross-sea bridge confirmed the convenience and practicability of this system. The dynamic acceleration and angle data of both hoisting procedures were collected and sent to a web server. The functions of sending instructions to the collectors and real-time monitoring can significantly enhance field hoisting monitoring capabilities. The changes in various angles and height differences obtained during the hoisting procedures were all within normal ranges, and there is no warning information, which indicates that the girder hoisting process was stable and safe. The real-time monitoring feedback received by the control system can provide important information to operators so that adjustments can be made during hoisting if necessary. The use of smartphone has advantages, including convenience, lower cost, the use of commonly available smartphones, and intuitive operation. Additionally, the proposed monitoring system is simple enough to be operated by any construction worker equipped with an iPhone. The rapid popularity of smart phones has provided the opportunity for researchers and civilians to understand traditional monitoring methods in a new way. For the aforementioned advantages, the use of smartphones will hopefully represent a promising trend in the CPS field. Acknowledgments: This research was financially supported by key Projects in the National Science & Technology Pillar Program during the Twelfth Five-Year Plan Period (2011BAK02B01) and National Natural Science Foundation of China (51278085, 51479031, 51161120359), National Basic Research Program of China (2011CB013705), Program for Liaoning Excellent Talents in University (LJQ2015028), and the Fundamental Research Funds for the Central Universities (DUT15ZD117). Author Contributions: The work presented here was carried out in collaboration between all authors. Ruicong Han, Xuefeng Zhao and Yan Yu contributed the conception and design of the monitoring system. Xuefeng Zhao and Ruicong Han carried out the field hoisting monitoring. Quanhua Guan, Weitong Hu and Mingchu Li Written the program on smartphone. Ruicong Han and Xuefeng Zhao analyzed the test data and prepared the manuscript. Conflicts of Interest: The authors declare no conflict of interest.

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