Abstract FIATECH is a consortium that accelerates the development, demonstration and deployment of existing and emerging technologies throughout the lifecycle of a construction project. This report, Field Study of Wireless Strain Monitoring Technologies, was prepared as part of the FIATECHTM Smart ChipsTM project. The material presented in this publication has been prepared in accordance with generally recognized engineering principles and practices, and is for general information only. This information should not be used without first securing competent advice with respect to its suitability for any general or specific application. The contents of this publication are neither intended nor should be construed to be a standard of FIATECH, and are therefore not intended for reference in purchase specifications, contracts, regulations, statutes, or other legal documents. Reference made in this publication to any specific method, product, process or service do not constitute or imply an endorsement, recommendation, or warranty thereof by FIATECH. FIATECH makes no representation or warranty of any kind, whether expressed or implied, concerning the accuracy, completeness, suitability or utility of any information, apparatus, product, or process discussed in this publication, and assumes no liability thereof. Anyone utilizing this information assumes all liability arising from such use, including but not limited to infringement of any patent or patents. This publication may be purchased from FIATECH. However, no copies may be made or distributed and no modifications made without prior written permission from FIATECH. To purchase this or other FIATECH publications, contact FIATECH at www.fiatech.org or 512232-9600. Copyright Š2006 by FIATECH. All Rights Reserved. Manufactured in the United States of America.
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Acknowledgments The FIATECH consortium prepared this publication and wishes to acknowledge the special contributions of those whose efforts and input have significantly influenced this report. Notably, FIATECH would like to express our appreciation to the following companies who sponsored the Smart Chips project: •
Aramco Services Company
•
Intel Corporation
•
Bechtel Corporation
•
Jacobs Engineering
•
ChevronTexaco
•
KBR
•
The Dow Chemical Company
•
The Procter & Gamble Company
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DuPont
•
Zachry Construction
•
Fluor Corporation
Furthermore, Kamel Saidi of the National Institutes for Standards and Technology (NIST) and Tim Hutcheson of RTKL Associates, Inc. served as consultants to this project and were instrumental in producing this report. FIATECH also wishes to give a special thanks to Bob Hixon and Tom Fontana from the Architect of the Capitol as well as Mike Robinson of MicroStrain Systems. Without their vision and leadership, this project would not have been. Lastly, among the staff who worked on this project, I would like to extend my gratitude to Charles Wood, FIATECH Project Manager, who oversaw and managed this project to completion.
Richard H.F. Jackson, Ph.D. Director FIATECH
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TABLE OF CONTENTS ABSTRACT
I
ACKNOWLEDGMENTS
II
EXECUTIVE SUMMARY
1
INTRODUCTION
2
Motivation for Wireless Sensing on the CVC Project
2
Background
2
Study Goals
7
Scope
7
STRAIN MONITORING PROCESSES
7
Wired vs Wireless Monitoring
7
Technology Used
8
FIELD STUDY
9
Performance Metrics
9
Study Setup
9
Results
13
Operation
17
Interpretation of Results
19
Recommendation for Future Studies
21
Executive Summary Wireless data networks are now common in many office and industrial settings. Wireless data communications offer distinct advantages over wired systems on active construction sites, and the construction industry is starting to adopt such wireless technologies. Wireless systems allow reliable communications in the dynamic and physically harsh construction site environment. In addition wireless data communications systems represent a significant economic savings over traditional systems by eliminating the need to install expensive fixed infrastructure (e.g. fixed cabling and power sources) for the relatively short term duration of a construction project. For these reasons, FIATECH has been interested in investigating construction site application of systems using wireless data communications. The Architect of the Capitol (AoC), who is responsible for all renovation and new construction at the U.S. Capitol complex in Washington, D.C., is overseeing the construction of a Capitol Visitor Center (CVC). During CVC construction, anomalies in steel beam-to-slurry wall connections were observed. These anomalies included embed pull-out, cracked welds, and clip angle deformation. It was believed that these anomalies were the result of cold-weather induced contraction of the beams. Although the observed anomalies were later rectified, the AoC and the contractors working on the project decided to monitor the stresses in the nine affected beams as well as in seven control beams within the same area of the project. The AoC and FIATECH collaborated on a study using wireless strain monitoring technology to monitor strains in these beams during the winter of 2005. This report documents the results of that study. Installing and operating the wireless strain monitoring system on this project was difficult for many reasons. Such a system had not been used in construction before, therefore unanticipated problems were inevitable. The most significant problem was the difficulty in gaining physical access to the data collection computer (and to a lesser extent, the access point). Once a reliable connection was established between the wireless strain monitoring network underground and the data collection computer inside the Capitol building, data collection was initiated. The remote location of the data collection computer and its lack of a network connection meant that data was not gathered continuously over the entire study period. The results of this study indicate that additional field research would be useful in fully assessing the potential for wireless sensing on construction sites. Several recommendations can be distilled from the results of this study into “lessons learned� for future projects. The most important recommendation is to better understand of the sources of radio frequency (RF) interference found on the different types of construction sites. In addition, there are several management issues concerning the implementation of monitoring technologies (whether wired or wireless) in an active construction site that need to be overcome. These management issues include addressing the perception that wireless monitoring is a hindrance or threat to workers, rather than an aid.
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Introduction The Architect of the Capitol (AoC), who is responsible for all renovation and new construction at the U.S. Capitol complex in Washington, D.C., is overseeing the construction of a Capitol Visitor Center (CVC), currently slated for completion in the Summer of 2007. Ground breaking for this project took place on June 20, 2000. In February 2004, when installation of the steel for the Plaza Level was nearly complete, anomalies in steel beam-to-slurry wall connections were observed. These anomalies included embed pull-out, cracked welds, and clip angle deformation. In order to better understand the causes of these anomalies, the AoC and FIATECH collaborated on a pilot project to use wireless strain monitoring technology to track strains in the vicinities of the beams where the anomalies were reported. This report documents the results of that pilot project.
Motivation for Wireless Sensing on the CVC Project Wireless technologies have recently proliferated into many applications beyond voice communications. Wireless data networks are now common in many office and industrial settings. Wireless data communications offer distinct advantages over wired systems on active construction sites, and the construction industry is starting to adopt such wireless technologies. Wireless systems allow reliable communications in the dynamic and physically harsh construction site environment. In addition, wireless data communications systems represent a significant economic savings over traditional systems by eliminating the need to install expensive fixed infrastructure (e.g. cabling and power sources) especially given the relatively short term life cycle of a construction project. Sensing applications (such as strain monitoring) are much more economical when used with wireless data communications. Sensing capabilities are most often needed in locations where wired infrastructure is not available and impractical to install (e.g. existing buildings or structures). The cost of wired communications for sensing systems has been prohibitive for many applications. For these reasons, FIATECH has been interested in investigating construction site application of systems using wireless data communications. As described below, the Capitol Visitor Center project was compelled to implement a strain monitoring sensing application on the construction site in a timely and cost effective manner.
Background The vision for a Capitol Visitor Center (CVC) at the U.S. Capitol originated in the mid 1970’s and developed into its current plan for providing “space for exhibits, visitor comfort, food service, two orientation theaters, an auditorium, gift shops, security, a service tunnel for truck loading and deliveries, mechanical facilities, storage, and much needed space for the House and
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Senate”.1 The artist’s rendition of the completed CVC is shown in Figure 1 below. The CVC will include 580,000 square feet of space on three levels below the East Capitol Grounds.
Figure 1. An artist’s rendition of the completed Capitol Visitor Center.
Construction of the CVC required 196,000 square feet of excavation and into which a steel structure and concrete slurry walls were installed (see Figures 2 and 3). Steel erection began in September of 2003.
Figure 2. An aerial picture of the CVC taken in March 2004 after major excavation work had been completed.
Figure 3. The steel structure being erected and connected to the concrete slurry walls on the NE side of the project (January 2004).
In February of 2004, anomalies were found in nine steel beam-to-slurry wall connections (these are labeled “P” in Figure 4) in the northeast corner (Figure 3) of the project. The beams in question were roof beams meant to support a composite slab made up of layers of concrete and insulation (see Figure 5). The anomalies included cracked welds, embed pull-out, and clip angle deformation (see Figure 6).
1
Architect of the Capitol: http://www.aoc.gov/cvc/index.cfm
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N
Figure 4. Plan view of the beam layout in the area where the anomalies occurred. The inset picture (in the top right corner) is an artist’s rendition of a plan view of the finished CVC with the area in question outlined with a rectangular border.
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Figure 5. Details of the connection between the composite slab, roof beam, and slurry wall.
(a)
(b)
Figure 6. A picture of two roof beams connected to the concrete slurry wall. The beam on the left (a) experienced clip angle deformation, while the beam on the right (b) experienced embed pull out.
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During those winter months of 2003-2004 the lowest temperature was recorded on January 10, 2004, at 8ºF (-13ºC) (see Figure 7).2 This was around the same time that most of the steel roof beams in the northeast corner of the project were erected, but where the roof had not yet been installed (as is clearly shown in Figure 3). Hence the exposed roof beams were exposed to the temperature extremes shown in Figure 7. DC Daily Temperatures (12/01/03 to 03/31/04) 90 80
Temp (Fahrenheit)
70 60 50 40 30 20 10
Date
3/29/2004
3/22/2004
3/15/2004
3/8/2004
3/1/2004
2/23/2004
2/16/2004
2/9/2004
2/2/2004
1/26/2004
1/19/2004
1/12/2004
1/5/2004
12/29/2003
12/22/2003
12/15/2003
12/8/2003
12/1/2003
0
High Low
Figure 7. Chart of the high and low temperatures recorded between December 2003 and March 2 2004 .
The leading theory for explaining the observed anomalies contend that thermal contraction of the beams due to the cold weather, coupled with fabrication errors, resulted in large enough stresses to cause clip angles to deform, bolts embedded in the slurry wall’s concrete cap beams to pull out, and welds to crack. Although the observed anomalies were later rectified, the AoC and the contractors working on the project decided to monitor the stresses in the nine affected beams as well as in seven control beams (labeled “S” in Figure 4) within the same corner of the project.
2
National Weather Service: http://www.erh.noaa.gov/lwx/climate.htm at Reagan National Airport
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Study Goals Between December 2004 and May 2005, the AoC and FIATECH conducted a pilot study with the following three goals: 1. Monitoring strain in selected beams over a 6-month period during the winter of 20042005 (temperature would also be monitored in order to correlate it with the observed strain). 2. Observing and documenting the performance of a wireless strain sensing system in an active and congested construction site. 3. Reporting lessons learned and other critical issues with potential applications of wireless sensing technology in construction.
Scope The scope of this document is limited to reporting on the results of the installation and operation of the wireless strain sensing technology that was chosen for this pilot project in order to record lessons learned. Although one of the goals of the pilot project itself (as stated above) was to examine the effects of temperature on the strain experienced by the nine affected and seven control beams (16 total), the analysis of the collected data and all conclusions about the ultimate cause of the observed anomalies was the responsibility of the AoC and their contractors.
Strain Monitoring Processes Wired vs Wireless Monitoring The current technology used in construction monitoring is to hardwire sensors to a central data logger, or for larger systems, place data loggers at strategic locations. Many of the systems installed to date require that data be downloaded manually in the field. More sophisticated systems are either cabled or wirelessly connected to a host computer on site, and in some rare cases transmit data to offsite locations by means of cell phone. These systems involve cabling from the sensors to the data loggers, and sometimes require additional cabling to the host computer. These systems are difficult and time consuming to install, therefore costly. Cable routing must be carefully planned to ensure that cables are adequately protected. Often the cost of cable exceeds the cost of the sensors, and the cost of protective measures, such as installing the cable inside conduit often exceeds the cost of the cable. In many areas of the country union electricians must be employed to install the cabling. Systems that require on-site download have the ability to provide historical data but offer limited alarm functions based upon embedded processing capability. Systems that provide engineers with real-time data can be used in conjunction with PC-based mathematical and predictive modeling to determine that problems are developing, allowing preventative maintenance to take place before failure occurs. In many instances cabling is the biggest weakness in the system. Cabling is prone to damage by construction equipment, it is easily vandalized, and in some cases not accepted aesthetically. -7-
Wireless systems are easy and fast to deploy, resulting in major cost savings. The removal of cabling from the systems removes not only the cost of the cable and conduit, but also the significant amount of labor involved in planning and installation. Therefore, the time required for wireless installation is significantly less than that of conventional wired installations.
Technology Used The strain sensing system used in this study consists of 16 pairs of strain gauges spot-welded to the structure at critical locations. Each pair of gauges is connected to a V-LINK wireless sensor node. The wireless sensor nodes transmit data to a PC located in the site offices via a base station and repeater installed in the roof of the Visitor’s Center. Strain data from each gauge is transmitted at a rate of 0.25 Hz. Strain Gauges: Two gauges were spot-welded to the structure at each location and connected to a V-LINK wireless sensor node. MicroStrain V-LINK Wireless Sensor Node: The V-LINK addressable wireless sensor nodes are capable of bidirectional communications, enabling the nodes to not only transmit data but to also reprogram offset, gain, and sampling rate, remotely. The V-LINK modules were housed in NEMA rated enclosures with adequate batteries to run for more than two years. Each enclosure was fitted with high-power magnetic mounts to enable rapid deployment. The V-LINKS, featuring two megabytes of on-board, non-volatile memory, can be configured to log data to memory or stream real-time data to a PC. With maximum sampling rates up to 2000 HZ for data logging and 1700 Hz for real-time streaming, the V-LINK is well suited to a host of different applications, and the ability to wirelessly reprogram sampling rates adds to the flexibility of the system. MicroStrain Serial Base Station and Repeater: In most applications, the base station is used as a gateway between MicroStrain wireless sensing nodes and a personal computer. In this deployment, i.e. gathering data underground and then transmitting above ground to the site trailer, an intermediate base station consisting of the MicroStrain base station connected directly to a wireless modem repeater system, was used. The wireless modem repeater can extended the effective communications range of the MicroStrain wireless sensing system from 500 feet to 20 miles. The base station and repeater were also housed in a magnetically mounted, NEMA-rated enclosure. Base Station and PC: A wireless modem was connected to a PC in the site offices.
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Field Study The field study was to commence in December 2004. Sixteen pairs of strain gages were to be installed in early December and data collection was to start later that month. In preparation for the study, the AoC’s contractors were to prepare the steel beam surfaces and install the strain gages onto the 16 beams included in the study. The wireless strain monitoring vendor was then to connect each pair of gages to a wireless node and install an access point through which all nodes would communicate to a base station connected to the data collection computer (supplied by the CVC project). Each node was to be powered by a primary source at each node location, provided by the AoC contractors. Data collection was to continue for a period of six months after which the data would be analyzed by the AoC contractors.
Performance Metrics Although no quantitative performance metrics were selected for this study, there are two general qualitative measures of performance by which this study was evaluated: 1) ease of installation, and 2) ease of operation.
Study Setup The 16 pairs of strain gages were installed in the 16 locations shown in Figure 4 (labeled “P” and “S”). Each pair of gages were installed as shown Figure 8, one gage on either side of the beam web and spaced vertically equidistant from the beam’s neutral axis. Figure 9 is a picture of one side of an actual beam which shows one of the strain gages and the data logging transceiver.
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Front strain gage
Wireless data-logging transceiver
Back strain gage
Figure 8. Schematic diagram of the strain gage locations.
Figure 9. Picture of a strain gage installed on the bottom of a beam web and connected to a wireless data-logging transceiver.
All 16 data logging transceivers communicated wirelessly to an access point (see Figure 10), which in turn relayed all the information to a data collection computer (see Figure 11).
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Figure 10. The wireless access point through which the strain gage nodes communicate to the data collection computer.
Figure 11. The data collection computer.
The data collection computer and the access point’s antenna were separated by a considerable distance since the computer had to be installed in the CVC project’s site office (see Figure 12). - 11 -
Antenna mounted through deck
Data collection PC inside site office
Figure 12. The separation between the access point’s antenna and the site office.
Special software supplied by the wireless strain monitoring system vendor was installed on the data collection computer and was setup to automatically collected data at a fixed interval (see Figure 13).
Figure 13. The data logging software application.
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Results The results of the field study reported in this study are divided into the same two categories as the performance metrics discussed above: 1) installation, and 2) operation.
Installation The wireless technology vendor was responsible for installing the technology and for making sure the system functioned correctly. However, the AoC was responsible for ensuring that sufficient preparations had occurred before the vendor could install the system as discussed below. Preparation - The primary preparations that were to take place before the technology vendor arrived at the site included: a. Clean and prepare the beam surfaces where the strain gages were to be mounted. b. Mount the strain gages to the beams. c. Provide power outlets at each strain gage node. d. Provide a power outlet for the access point. e. Provide an access hole through the roof through which the access point’s antenna cable would be routed. Prior to the technology vendor arriving at the site, the AoC and the vendor together decided to add batteries to all of the sensor nodes since it was determined that the cost and time of installing power outlets at each node would have been too high. Beyond that, none of the other preparation work listed above had been done by the time the technology vendor arrived at the site. In addition, the AoC’s fireproofing contractor inadvertently covered all 16 strain gage locations and the access point’s antenna with spray-on fireproofing material prior to the vendor’s arrival (see Figures 9 and 14).
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Figure 14. The access point’s antenna (which communicates with the sensor nodes) after most of the fireproofing material covering it had been removed.
Consequently, the vendor had to wait onsite while the fireproofing material was removed and the beam surfaces prepared. In addition, the temporary power outlet for the access point and the hole through the roof deck for its antenna cable also had to be installed before the vendor could finish the installation of the system (see Figures 15 and 16).
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Power cable
Access point
Figure 15. The temporary power outlet for the monitoring system’s access point.
Antenna opening thru deck
Antenna cable Access point final location
Access point planned location
Figure 16. The access point in its final location and the opening through the roof deck for the antenna cable.
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Once the beam surfaces had been prepared, the technology vendor installed the strain gages onto the beams. Installation was planned by the AoC using 20 to 30 welds per gage, a process that is faster and easier than traditional gage bonding, but because of relative priorities the AoC was unable to support this task. Therefore, installing and wiring the strain gages consumed more of the technology vendor’s time than any other task. Access to the strain gage locations also proved difficult because the beams are approximately 15 feet off the ground, other structures had been constructed within close proximity to the beam of interest, and several other contractors were onsite performing their job within the same congested area. After the access point’s antenna had been installed for only one day, someone moved it because it was in the way of some other construction activity. The technology vendor then had to make the antenna shorter and less conspicuous. Finally, after the system had been installed and the communication issues seemingly resolved, the technology vendor exited the site. However, the access point’s antenna had to be moved again because of the presidential inauguration ceremonies that took place in January 2005 on top of the CVC project’s site. Subsequently, communication with the data collection computer in the site office became unreliable3. To achieve a reliable connection, the antennae had to be taller and the signal power had to be stronger, both of which were not possible options at this site. Therefore, the data collection computer was moved closer to the access point’s antenna as shown in Figure 17. This move also required that the technology vendor send more parts to be installed by an AoC contractor.
Antenna mounted through deck
Data collection PC inside capitol
Figure 17. The separation between the access point’s antenna and the data collection PC after it was moved to its final location inside the Capitol building. 3
The reliability of the underground wireless connection between the strain gage nodes and the access point was good.
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General Installation Issues - In addition to delays in the technology installation caused by inadequate preparations (as discussed above), whenever the technology vendor needed assistance from the CVC project personnel, such as asking for a ladder or a power outlet, they had to ask multiple contractors who would each direct them to someone else. The lack of a single point of contact to coordinate onsite contractors in order to get things done in a timely fashion caused negative impact. The technology vendor had planned to spend two days for installation and testing, but the actual time onsite was four days. Since the vendor had no experience installing such a system at an active construction site, given the somewhat unstructured environment and typical hectic schedule of this construction site, the vendor found that spending four days to install the wireless strain monitoring system did not seem excessive.
Operation Once a reliable connection was established between the wireless strain monitoring network underground and the data collection computer inside the Capitol building, data collection was initiated. This section describes the performance of the wireless strain monitoring system during the operation phase of the pilot project. During operation several problems occurred that affected the functioning of the wireless strain monitoring system. These problems are discussed below. Due to the unavailability of a network connection in the room where the data collection computer was finally positioned, the computer could not be remotely monitored from the CVC project site office and someone had to physically go to the computer to ensure that it was functioning properly, perform maintenance, fix problems, and retrieve the collected data for analysis. Although one person from the CVC project was designated as the party responsible for overseeing the operation of the strain monitoring system, that person’s busy schedule often meant that problems with the monitoring system did not take precedence and had to wait until time was available before they could be fixed. The problems that required frequent attention are described next. It should also be noted that the final location of the data collection computer was not easily accessible, thereby making the project even more difficult. Periodically, the power cord to the access point shown in Figure 15 would be either accidentally or intentionally disconnected due to activity that was taking place in the area through which the cord was routed. In addition, the access point itself, which was magnetically mounted to a steel column, would also accidentally get knocked off the column by workers in the area. This problem prompted moving the access point to its final location shown in Figure 16, and this location required a ladder for access. These events caused communication between various parts of the system to be lost and also required that someone physically intervene to make the access point operational and to re-establish communication with the data collection computer.
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In addition, communication between the strain gage nodes and the access point as well as between the access point and the data collection computer would be lost sporadically (seemingly at random). Although no definitive explanation for this loss of communication is known, two possible factors could have contributed to this problem. First, there may be certain circumstances that make all forms of wireless communications difficult on this particular project due to the project’s location at the U.S. Capitol. Although some of the CVC contractors reported anecdotally that even cellular telephone communication was intermittent around the U.S. Capitol’s grounds, no independent verification of this claim was provided. Second, the CVC contactor responsible for operating the strain monitoring system noticed that a mobile crane located within the line of sight between the access point’s antenna and the data collection computer’s antenna (see Figure 18) was often in operation whenever there was a loss of communication between the two systems. Once again, although no independent confirmation of this phenomenon was pursued anecdotal information of mobile truss cranes interfering with wireless communications at construction sites has been reported. Antenna mounted through deck
Data collection PC inside capitol
Figure 18. A mobile crane often interfered with the communication between the access point and the data collection PC.
Regardless of the cause for the loss of communication between the various parts of the strain monitoring system, often communication could not be re-established without power cycling the access point and/or the data collection computer, meaning someone had to physically go to the access point and/or the computer to do so. In addition to the communication problems described above, several problems occurred with the data collection computer and software. During most of the time that the system was in - 18 -
operation, only 15 of 16 nodes were reporting data. This may have been due to the non-working node’s remoteness from the access point, but this possibility was not verified. Furthermore, random, non-existent nodes were also periodically detected by the system (no explanation for this phenomenon was available either). Another seemingly random phenomenon was the occurrence of sudden spikes in the reported strain (and sometimes temperature) data as shown in Figure 19. Although the CVC contractor reported that the strain monitoring system often detected changes in strain due to heavy equipment passing over the areas where the gages were installed, the spikes such as those shown in Figure 19 could not be explained because they also occurred outside of working hours, and because instantaneous jumps in temperature underground are highly improbable.
Figure 19. A graph of the strain and temperature data reported by a single node over a period of 24 hours.
Interpretation of Results This section is concerned with the interpretation of the results of the installation and operation of the wireless strain monitoring system. Interpretation of the gathered strain data is outside the scope of this report, however, a brief comment on the conditions under which this data was gathered is appropriate. - 19 -
Data collection was originally planned to commence in December 2004. However, due to the communication problems described earlier, data collection did not start until February 14, 2005. As shown in the graph in Figure 20, the Washington, D.C. area experienced its lowest temperatures of the winter before that date. The temperature did not drop below 20째F after January 28, 2005. In addition, during the winter months of 2004-2005, the composite slab deck had already been installed, and thus the steel beams were largely protected from the temperature extremes they had experienced the year before. Since no strain gages were installed on control beams that were left exposed to the weather, and since steel erection was complete, the recorded strain data is likely not representative of the conditions that were present at the site a year earlier during the winter months of 2003-2004. Furthermore, since little variation in strain and temperature was observed during the first month of data collection, the CVC contractor effectively stopped analyzing the data after March 2005 (although this is also partly due to another reason discussed later).
DC Daily Temperatures (12/01/04 to 03/31/05) 80 70
Temp (dF)
60 50 40 30 20 10
12 /1 /2 00 4 12 /8 /2 00 12 4 /1 5/ 20 04 12 /2 2/ 20 04 12 /2 9/ 20 04 1/ 5/ 20 05 1/ 12 /2 00 5 1/ 19 /2 00 5 1/ 26 /2 00 5 2/ 2/ 20 05 2/ 9/ 20 05 2/ 16 /2 00 5 2/ 23 /2 00 5 3/ 2/ 20 05 3/ 9/ 20 05 3/ 16 /2 00 5 3/ 23 /2 00 5 3/ 30 /2 00 5
0
Date
High Low
Figure 20. Chart of the high and low temperatures recorded between December 2004 and 2 March 2005 .
Although as discussed above, data was ultimately gathered, the installation and operation of the wireless strain monitoring system at the CVC project, an active, congested, and hectic construction site, did not go as planned. Several issues came up that had not been anticipated, but in a sense are part of the motivation for the pilot project. Understanding these issues should help future implementations of similar system in construction. Installing and operating the wireless strain monitoring system on this project was not easy. Such a system had not been used in construction before, therefore unanticipated problems were inevitable. The most significant problem was the difficulty in physically gaining access to the data collection computer (and perhaps to a lesser extent to the access point). The remote location of the computer and its lack of a network connection meant that data was not gathered - 20 -
continuously over the entire study period since problems with the computer could not be immediately resolved right. In addition, the remote location of the computer (and the lack of change in data collected) most likely contributed to a lack of motivation on the part of the CVC contractor responsible for operating the strain monitoring system to keep the system running. Hence, after approximately 6 weeks of gathering data, the system was no longer monitored as closely as before and no data was analyzed after March 2005.
Recommendation for Future Studies There are several recommendations for future projects that can be distilled from the lessons learned through this study. However, the most important recommendation would be the need for a better understanding of the sources of radio frequency (RF) interference found on the different types of construction sites. Since the primary factor that contributed to the communication problems between the strain gage nodes and the access point, and between the access point and the data collection computer seem to have stemmed from RF interference issues, implementation of all sorts of wireless technologies in construction could benefit greatly from a study of the sources of RF interference. Such a study could lead to designs for wireless technologies that are specifically suited for the environments commonly found in construction and to best practices for installing such technologies in construction. In addition, there are several management issues concerning the implementation of monitoring technologies (whether wired or wireless) in an active construction site that need to be identified and understood so that future implementation can be more successful. Anecdotal reports indicate construction personnel usually consider instrumentation used to monitor conditions of an active site a hindrance rather than an aid, and readily tamper with the installed equipment if it is seen to be in their way (as seen in this study). The installation and operation of the wireless strain monitoring technology in this project were not integrated into the construction process, and thus were looked upon as an added burden by those project personnel who were tasked to help install and operate the technology. A study of the management issues concerned with implementing such technologies during the construction phase of a project could greatly benefit future implementations, and some of the problems seen in this study could be avoided altogether. An implementation plan specifically suited for installing instrumentation on an active construction sites to monitor various aspects of the construction process should identify the necessary preparations for installation as well as decommissioning, the resources required, and the parties responsible for operating and maintaining the equipment.
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