Advanced Sensors Strain Gages Pave Way For Reversible Traffic Lanes
As ( “Advanced Sensors”*) the old saying goes, two way (reversible) lanes above or below a (full) bridge are often more efficient and safe than set-direction lanes. We will all need more flexibility when designing or renovating infrastructures that will be part of “driving” the new “Normal” post-COVID-19.
As aging infrastructure becomes increasingly prone to failure, each year we are seeing bridge and dam collapses around the world, and road, transmission tower and pipeline failures - all due to invisible external and internal forces. As concerns increase over the possibility of massive property damage and loss of human life, the question arises: “can we identify major and critical infrastructures failures before they happen?”
How do we know when concrete is mature enough to accommodate moderate or even heavy traffic loads given varying environmental conditions including wind loading, thermal expansion and seismic activity. Since the resulting stresses are complex and seldom uniform, how do we know when bending, warping (usually non-uniform) or curling will cause failure? Although many factors influence this process, the general premise is clear: for a variety of economic and safety reasons, new infrastructure design and construction that includes the incorporation of metallic strain gages will contribute to more efficient traffic control. Additionally, these same sensors, when added to existing infrastructure, provide critical data regarding the health of aging structures.
Deploying metal foil strain gages requires bonding them to critical surfaces. For most solid material – including concrete – strain gages can be easily bonded if the surface is properly prepared. For smooth surfaces on nonporous materials, only the basic operations of solvent degreasing, abrading, application of layout lines, conditioning, and neutralizing are required. For concrete and other materials with an uneven, rough, and porous surface, an extra operation must be added to fill the voids and seal the surface with a suitable precoating before the gage is bonded.
In some test applications, weldable strain gages can offer very significant advantages over bondable strain gages. For example, they are ideal for use on large test structures when it is not practicable to apply clamping pressure to the gage installation during the adhesive cure process. Weldable strain gages can also be an excellent substitute for bondable strain gages when the temperature of the test surface is below the minimum required for proper cure of the boding adhesive, and cannot be easily raised.
An even greater challenge comes when the test calls for embedded strain gages—that’s right, embedded! Protecting a delicate strain gage installation from the forces and impact of flowing concrete, as well as the heat of the cure cycle and the flow of water in attempting to permeate every nook and cranny, it requires more attention to detail using well-proven techniques and is easily achieved by experienced strain gauge installers.
The most common approach is to bond Advanced Sensors strain gages to ’sister bars’ which are tie-wired to the rebar prior to pouring the concrete. While this method works well from a strain measurement standpoint, insuring that the installation survives is no small task. Often, there is little chance of doing the job a second time.
One technique involves installing sensors strain gage-based that help engineers know when new concrete is ready to take on heavy traffic loads. With that information, they can prevent tiny stress cracks that lead to expensive repairs if bridges, tunnels or roads are opened prematurely. Fewer maintenance and repair projects to replace or repair the concrete will, in turn, reduce traffic bottlenecks that can lead to preventable road work.
Data from the strain gauge-based sensors (transducers) helps civil engineers monitor structural conditions to optimize traffic loading on new or existing structures. Active monitoring of strain gages throughout the structure allows for monitoring of the concrete curing process as well as the post curing loading from traffic and environmental conditions.
In order to improve the reliability and safety of structures, a technique called Structural Health Monitoring (SHM) has become a critical vehicle to identify potential problems at an early stage. Foil strain gages are widely used in SHM projects and systems because they are inexpensive, easy to install, and provide very precise and accurate measurement. Foil strain gages and the necessary applications accessories are available in configurations for steel, concrete, FRP (fiber reinforced polymer) and for a variety of other materials. These gages are available with resistance values from 120 ohms to 5K ohms for connection to conventional strain gage instrumentation with bridge completion values of 120, 350 and 1K ohms or in the case of battery or RF powered applications, 5K ohm resistance reduces power consumption. These gages are available in uni-axial, bi-axial, and tri-axial rosettes. Both bonded and weldable gages are available along with the Model 700 Portable Welder. Gages are available in ¼, ½ and full bridge configurations. Micro-Measurements also offers concrete embedment gages which eliminates the need for gaging sister bars thus simplifying the gage installation process.
The strain gages that are installed are protected from moisture, corrosion, temperature fluctuations, with special protective coating (coating compounds that have been formulated specifically for use in protecting strain gage installations from damaging environmental conditions) and can be used to collect and transfer data for decades. Being able to monitor concrete strength over a longer period of time helps civil engineers to know if they have over or under designed roads, and would help to better determine the appropriate time to upgrade the infrastructure with replaced concrete.
Another potential benefit of using strain gage sensors as part of road infrastructures, is to allow people to reach their destinations as quickly as possible. We should remember that our commute (traffic) is always directional. To accommodate more traffic, the conventional thinking is to add extra lanes. But creative thinking using artificial intelligence and big data could identify an underused lane and shift traffic into that direction. Using smart transducers based on Advanced Sensors strain gages may allow for better control of traffic without increasing lane count and make the journey more pleasant and safe.
A.I. and Big Data algorithms using on input from transducer based foil strain gages and Micro-Measurements and Pacific instruments DAQ can help make more efficient use of critical traffic infrastructure. These systems allow for continuous monitoring at rates from 1 sample per second up to 1M samples per second to provide both static and dynamic recording of real time loading conditions. From portable strain indicators such as the Micro-Measurements P3 Strain Indicator Recorder (1 sample per second) to System 7100 a high channel count DAQ at 2K samples per second to System 9000 at 50K samples per second, Micro-Measurements offers a wide range of these instruments. Pacific Instruments custom engineered DAQs with record rates of up to 1M samples per second. All these systems are configured for remote monitoring capabilities to allow for long-term data recording and analysis in real time.
Contrary to conventional “concrete” wisdom and many traditional infrastructure design handbooks, reversible direction lane design concepts using sensors and DAQ systems can be more efficient than one set direction road design. We have already seen that smart infrastructure networks, monitored by strain gage transducers, are many times more efficient because they allow engineers and managers to keep more roads and bridges open allowing people to reach their destinations on time. When this is the case, there is a greater incentive from the engineering world to convert traditional infrastructure’s networks to two-way operation based on AI algorithms and strain gage sensors.
(*) Key Advantages of Advanced Sensors Technology
As the foundation of consistently reliable and precise transducers, Micro-Measurements Advanced Sensors strain gages are built on a new manufacturing process using state-of-the-art equipment and tooling. This results in tighter tolerance products with shorter manufacturing lead times as compared to conventional manufacturing techniques. Advanced Sensors Technology was shaped by decades of in-house expert knowledge, experience gained across our global portfolio of successful applications, and sustained attention to customer feedback. Today customers across the world benefit from Advanced Sensors Technology in experimental stress analysis and as the sensing elements in a wide variety of transducers. This technology enables precise measurement of physical variables, including weight, force, torque, pressure and more.