The project “SHM for Telecom Towers” aims at developing a remote monitoring service to support the assessment of the structural integrity of assets, as the towers for Radio-TV Broadcasting or other metal infrastructures, in order to increase safety and optimize the maintenance procedures and promote the transition from a time-based maintenance to a condition-based one.
The key point of the proposed solution is the integration of several existing technologies such as structural health monitoring and wireless sensor networks with existing space technologies such as GPS and satcom (when no terrestrial telecommunication is implemented) in order to enhance the proposed service with innovative capabilities
A Structural Health Monitoring system can be a benefit for civil and other engineering industries where visual interval-driven inspections are the main (and in many cases the only) type of checks. Health monitoring can support users in defining and improving maintenance strategies and procedures. Structural health monitoring can give direct data about the actual status of a structure and not just an estimated probability figure based on statistical patterns.
Use of satellite services is a key point for the development of a complete end-to-end service that meets the user requirements. The proposed service is based on a suitable integration of various technologies such as: telecommunication, networking, structural analysis, data transfer, etc.
The objective of the feasibility study is to assess the technical feasibility as well as the commercial viability of such a monitoring service.
Users and their needs
Two major target users have been identified for the SHM for telecom towers service:
Owners and managers of telecom towers: such as Rai Way S.p.A. which is the the major Italian broadcasting company and took part in the feasibility study as the reference user. It uses a large number of telecom towers to transmit TV signals over the Italian territory.
Telecom towers manufacturers such as Calzavara, another reference user and a company operating in the Italian and international markets in the telecommunications and energy fields.
The two companies taking part in the feasibility study (Rai Way S.p.A and Calzavara S.p.A) operate in different markets but show similar needs about the monitoring capabilities for their towers. While taking part in their maintenance programmes, both the companies feel the necessity to increase their capability to assess the structural integrity of their towers without expensive visual inspections. In addition they show the need to record, evaluate and assess the loads and the conditions experienced by the towers during events such as strong winds, for instance.
The proposed service aims at providing the user with updated and meaningful structural data and an early warning service in case of outlier structural responses. The users believe that a monitoring service of the integrity status of the towers can be a premium service or product that could provide a higher-level analysis tool to increase the awareness about the status of the managed infrastructures.
Service/ system concept
Both the users are extremely interested in a structural monitoring service for their towers in order to have data and reports which help the companies to better plan the inspections and to increase the awareness of a current status of a tower.
In addition, the companies could also monitor the tower in special environmental conditions such as storms or snow. The system must be able to provide the user with data that are helpful in the structural assessment of the stable behavior of the tower and to inform the user if the nominal behavior changes. The data provided by the system will be accessible by the companies by means of a protected web-based service.
Space Added Value
The main space assets envisaged in the project are the GPS and satellite communication.
GPS nowadays is normally used to precisely measure structures, for field surveying, GIS and in large-scale constructions. Various services and COTS devices are available, with different level of precision, to support the different needs of these applications. GPS can be used for static monitoring of towers and terrain movements with adequate accuracy.
Terrestrial communication is more relevant in a country such as Italy where the mobile telecommunication infrastructure is well developed and functioning almost everywhere. This solution can cover the necessary data rates at a slightly more advantageous cost with respect to satcom. However satellite telecommunications for the transfer of the monitoring data can be required for TV/Radio broadcast towers that are not equipped with GSM transceivers and located in places where weakly, if none, coverage is provided by the mobile network. The added value of satcom has been outlined for user groups such as Calzavara which, in addition to manufacturing services offers a complete maintenance service for their customers located all around the world. Satellite telecommunication would provide a global coverage and a unified solution for all the data traffic from their worldwide towers (equipped with the proposed SHM service) to their control centre. The satcom solution favours a fast and reliable implementation where ground infrastructures are not present or require a long time to be set in place
The benefits related to SHM for Telecom Towers concern different aspects in the infrastructure management. The proposed service will provide the user with an early warning system suitable for detecting and notifying about the structural status of the tower during its lifetime. Failures and damages will be quickly identified by the user in order to plan an appropriate response action.
The service will track the real load conditions experienced by the towers which can be subjected to special environmental and load conditions such as wind, ice and thermal excursions. By implementing the proposed solution, the user will be able to plan each maintenance intervention based on the actual status of the structure of the tower avoiding, often useless, pre-planned inspections.
The proposed service aims at providing the user with data and reports about the integrity status of its asset. The main added value of this solution is providing the user with data of primary importance to assess the structural behaviour of the asset without the need of a deep and expensive inspection of the site. A remote data acquisition and processing will allow the user to increase the awareness of the status of the assets during the routine operational service and in case of special environmental conditions.
The system will be composed of three integrated segments: a local sensor network, a telecom segment and a data processing station. The main components of such a system can be found in the following figure.
The monitoring of each tower is achieved by using a suitable sensor network that will record some important structural figures such as strain, displacement, environmental and operational conditions that are useful to define the structural integrity of the tower. The sensor network will be installed on the asset and will be equipped with a proper modem to use either a satellite or a terrestrial communication channel to send the acquired data to a data station. All the data coming from the sensor network will be collected and channelled to a data processing station operated by the users’ and located in their premises. The data centre will process the data and will provide the user with the requested output. The user shall be able to access web-based services where the requested data can be found.The consortium will also implement an Assistance & Maintenance (M&A) Centre, which will assist the user in the utilization of the software and carry out software maintenance activities. The M&A Centre will also be responsible for future releases of the software packages.
The main issues of the system regard different technological areas. Firstly, a structural health monitoring system shall be able to discriminate the results related to different load and environmental driven structural responses. The second key issue concerns the integration of different technologies such as networking, low power electronics, satellite and terrestrial communication and data merging. Regarding non-technical aspects, the definition and set-up of a service provider is a key issue.
The Feasibility Study was concluded after the Final Review meeting which took place in June 2014. In the coming months the Consortium will work on solving issues, which are necessary to go to the demonstration project phase; after which, the outline proposal for the demonstration project will be prepared and submitted.
During the Feasibility Study, it was demonstrated that with a reduced set of sensors (among them a piezoelectric transducer, a temperature sensor, an anemometer and two GPS receivers) it was possible to acquire a sufficient amount of raw data to feed into our processing software. The latter was able to output key structural, loading and environmental parameters which were used to support the analysis of the status of the structure under monitoring.
In particular, we were able to identify the resonance frequencies of the tower and monitor its evolution with respect to the environmental conditions. We have been able to estimate and monitor the position of the tower using the GPS receiver with an accuracy in the order of the centimetre. We have also established a link between the instruments (sensor nodes) and the control centre and made available the results of the experimentation in real-time via the internet.
The test performed at Monte Mario tower was successfully conducted for a validity period of a month (from mid-March to mid-April), where the full end-to-end service provision chain was implemented. Aspects related to service provision such as the availability, the quantity and quality of data have met the user requirements as in the case of an operationally running service. As of mid-June 2014, the sensor network was still mounted on the tower of Monte Mario and the data were still being delivered to Raiway.
The sensor network had several advantages w.r.t. to previous installations on the test tower:
- The sensor nodes were compact and easy to install on the target tower.
- The sensor nodes were wireless and therefore there was no need to install bulky long wires on the tower. This property allowed to reduce considerably the installation time and augment the reliability of the system.
- The sensor nodes were independent and autonomous from a power point of view.
The information obtained from the processing of data coming from local sensors could be used, by the customers, for updating the maintenance plan according to the actual condition of the monitored towers. This opportunity represents an improvement with respect to the present situation, where maintenance activities are planned on a pure statistic basis, and consequently subjected to the risks of performing interventions that prove, in the hindsight, to be unnecessary.
The interactions made with potential customers allowed the consortium to identify the business model fitting the customers’ needs: having the most critical infrastructures monitored. The envisaged service consists of a processing system installed within the user control centre, which processes the information acquired by the local sensor networks and displays index and parameters sensitive to the integrity status of the towers. The service includes also assistance for the customers, which will be provided in a customized way, in accordance with specific necessity of any customer.