B.Tech. Pre-Project Report
A Reliable Method for Structural Health Health Monitoring
Aijaz Ahmad ( Civ/68/13) Amrendra Pratap Rai ( Civ/49/13) Civ/49/13) Ghulam Haider ( Civ/28/13) Department of Civil Engineering National Institute of Technology Srinagar
Under the guidance of
Prof. Manzoor Ahmad Tantray August 2016-June 2017 A dissertation on structural health monitoring submitted for the partial fulfilment of the requirements of obtaining the Degree of Bachelor of Technology In
Civil Engineering
B.Tech Project report
Certificate This is to certify that this project named A Reliable Method for Structural Health Monitoring has been carried out under the supervision and to best our knowledge, has not been submitted elsewhere as part of the process of obtaining the degree.
May 2017
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Aijaz Ahmad
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Abstract Our work involves developing a simple and reliable method for structural health monitoring . Our aim is to develop a relationship between stress in reinforcement bars and electrical resistance and to find out the damage parameters i.e., permissible stress and deflection limits up to which a structure can be safely used. With this we can know about the health of a structure. We can know about the damaged structural members and necessary measures can be taken to save the structures and human life from catastrophes.
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Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Acknowledgements First and foremost, we are thankful of our guide Prof. Manzoor Ahmad Tantray for having suggested the topic of our project and for his steady support and guidance throughout the project, without which we would not have been able to attempt this project. We are also thankful of lab assistants of concrete lab and structural lab for helping us during casting of beams and testing of beams and bars. We are also thankful of employees of central workshop who helped us to get the th e material, particularly of machine shop who helped us in making mould. Aijaz Ahmad
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Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Contents
1. Introduction 2. Monitoring Items and Techniques 3. Actual 3. Actual Stress Measurement 4. Concrete Stress Measurement 5. Principle of the project 6. Casting of beams
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Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Introduction The job of a civil engineer is to construct new structures, not only that but maintaining old structures is also the duty of a civil engineer. The life of civil engineering structures is limited. The properties of materials (like strength, ductility etc) gets degraded with time and fatigue (loading) due different chemical and physical reactions. So the maintenance of civil engineering structures is equally important as constructing a new one. This maintenance of structures, locating damaging members difficult in visual inspection, commencing a structure unsafe. This need in civil engineering give rise to Structural Health Monitoring (SHM). Structural health monitoring has been one of particular concerns of the engineering community. Effective monitoring, reliable data analysis, rational data interpretation and correct decision making are challenging 6|
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
problems for engineers who specialized in structural health assessment field. Concrete structures were constructed for various purposes in a certain design life in the context of ‘maintenance-free’ construction material. However, in recent years, many concrete structures have been deteriorating even before their design life due to corrosive circumstances, alkali-silica responses, and other environmental effects. In order to maintain sustainability of those infrastructures in which have significant influences to social lifelines, an economical and rational maintenance management is necessary to carry out to evaluate their Life Cycle Cost (LCC). The necessity of a structural monitoring paradigm includes assessment techniques and suitable maintenance management for assessing concrete structures’ health. This structural monitoring paradigm enables to provide necessary data for structural maintenance and safety. In considering a maintenance plan which aims to reduce its LCC, it is requested that the monitoring system should fulfill “AtoE” characteristics, i.e., (A)ccuracy, (B)enefit , (C)ompact, (D)urable and (E)asy to operate. Furthermore, newly developed intelligent measurement technology such as elasto-magnetic-based steel tendon actual-stress sensory technology, mechanical-deformation-based concrete actual-stress measurement technology and acoustic7|
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
emission-based structural health monitoring technology are also used for monitoring.
Structural Health Monitoring is the process of implementing a damage detection and characterisation strategy for engineering structures. SHM involves observation of system over time using periodically sampled dynamic response from an array of sensors, sensitive measurements from these measurements the current state of system, health is determined. SHM is the implementation of improving the maintenance of any structure like building and bridges. It also encompasses damage detection, identification and prevention of structures from natural disasters like earthquake, wind, live loads etc. Monitoring Based Maintenance (MBM) engineering is a civil infrastructure maintenance concept based on input from field monitoring data. The MBM monitoring mo nitoring systems consist of an array of sensors designed to provide desired information to make informed maintenance in order to extend the life of infrastructures.
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Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Monitoring Items and Techniques Table shows the monitoring mon itoring items, techniques and their measurement principle for diagnostic on pre-stressed concrete structures.
D
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Monitoring item Concrete Stress
Technique Slot stress
Steel tendon stress Wire breakage Deflection Crack
Load cell EM sensor AE sensor LVDT Visual inspection Photometry Accelerometer Impact echo test Drilled diagnostic CCD X-ray
Vibration t nI
d
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c
Grout rigidity
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Principle Mechanical deformation Electrical resistance Elasto-magnetic Acoustic emission Mechanical Visual Forced Vibration Elastic wave Visual Electro magnetic wave
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Corrosion
Electric potential Polar resistance
Electric current
Actual Stress Measurement Measurement The elasto-magnetic (EM) sensor that can reliably monitor actual-stress in tendons and cables has been developed. This kind of sensor is a new approach to monitor ferromagnetic steel forces in concrete structures . Based on the physical phenomenon that the permeability of ferromagnetic material is a function of magnetic history and applied fields, stress and temperature, permeability function is characterized at a technical saturation experimentally . Besides fulfilling ‘AtoE’ characteristics, the sensor provides a theoretically unlimited service lifetime, can be applied to any structure built with circular steel reinforcements or cables and does not influence structural integrity in any way . Pre-fabricated EM sensor takes the form of a hollow cylinder in the middle of which the measured element (wire, strand, cable, bar) passes through . It should be slipped onto the measured element beforehand, during the construction. Stress at each stage of loading condition can be monitored accurately. This 10 |
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
manufactured sensor consists of primary, secondary and compensating windings, mounted in a protective steel shield and sealed with an insulating material. EM sensor enables to measure the actual-stress in strands and cables protected by thin-wall steel tube or plastic tube without the need to remove them. This cylindrical EM sensor has no mechanical contact with the measured element so it will not be overloaded, it is resistant to water and mechanical injury, its characteristics does not change with time and its lifetime is closer to unlimited life time. Durability and reliability of the EM sensor depend on a few parts, i.e., (i) the copper wire; (ii) the potting compound; (iii) the steel cover; and (iv) the connecting cable. The copper wire has very high durability, with special insulations maybe hundreds of years. The copper wire is also protected by the potting compound. The steel cover may be plated and protected against corrosion, when the EM sensor is embedded inside the concrete, the steel cover is off course protected against corrosion. The weakest point of the EM sensor is the connecting cable. For heavy duty application, high durability reliable cable is recommended. The measuring unit is not critical, because the measuring conditions are precisely defined and it is possible to replace the damaged measuring unit or after long time replaced by a new type measuring unit. Off course, after 50 years our computers will be replaced by new generation computers 11 |
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
and the electronics parts used in the measuring unit will w ill be no more available, but the physical principle will be the same and the measured steel cable will be also the same. Therefore, lifetime of EM sensor can be predicted to be more than 50 years, even in the industrial environment. The configuration of the windings, number of turns does not change with time. It seems that the EM sensor is one of the most reliable sensors. Comparing with the resistive strain gauges the EM sensor has infinite lifetime. The main advantage of the EM sensor is contactless transfer of the stress from the measured cable to the sensor. No glue, as at resistive strain gauges, no mechanical contact as at vibrating wire gauges and annular dynamometers, only the magnetic field which is infinite. This type of EM sensor enable to measure stress in external tendons in outer cable PC bridge, steel cables in cable stayed bridges and suspension bridges, and steel bars in concrete structures, without the necessity to install the sensor during construction stage.
Concrete Stress Measurement The mechanical-deformation-based technique for measurement of stress in concrete has been derived from the mining industry where it is used to measure stresses in rock masses. The method is also widely used in metals or 12 |
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
plastics. Its principle is simple, the strain field is relieved by coring or slotting the material, the change of the strain in the relieved area is measured and the stress is calculated taking into account the elastic properties of the material and the geometry of the cut. However, in concrete, the modulus of elasticity varies with concrete mix, age, curing and environmental conditions. In order to eliminate the need to know the elastic properties of the concrete, a flat jack can be inserted into the slot and pressurized. As a result the initial strain field will be restored. Extensive evaluations including analytical, laboratories and field studies concluded that the strain relief method combined with the flat jack technique is the most appropriate and practical technique for measurement of stresses in concrete. Recent improvements of the original technique were motivated by the need to achieve better performance and cost efficiency, such as, monitoring of relieved strain, geometry of the slot, flat jack and data acquisition. Depending on the structure to be evaluated, several depths of slot ranging from 60mm to 200mm can be used. For an appropriate access condition, the total process of one measurement can be performed in approximately one hour including installation of displacement monitoring device, core drilling, slot cutting and pressurization of flat jack.
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Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Principle of the project The principle behind our project is that the resistance is directly proportional to length and inversely proportional to area of cross section.
R=ρL/A ρ= resistivity of material L=length between two ends A= area of cross section As the load is applied on the structure, the reinforcement bars deform, with the result the length increases and cross section decreases, both of which favour resistance (increase). By conducting experiments we are able to develop a definite relationship between resistance and the load applied. And we find various stages of loading and corresponding resistances and come up with the permissible loading and corresponding resistance. In structures if the resistance is above that limit, we can take preventive measures to enhance its safety. 14 |
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
Casting of Beams To measure the resistance and the corresponding loads, we cast few beams with different diameter reinforcement bars. In our part we cast beam of size 200mm×175mm×1200mm. Also two reinforcement bars are embedded in tension side. Compression and Shear reinforcement is not provided. Since maximum reinforcement is at centre, we wound copper wire at 25mm from centre on both sides with equal number of turns. Mix used 1:1.5:3 Water cement ratio 0.5 Cement Used Saifco 43 grade Reinforcement bars used 10mmØ Himaliya Platinum 500 15 |
Department of Civil Engineering National Institute of Technology Srinagar
B.Tech Project report
12mmØ Satyam TMT 500 Aggregate used 10mm
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Department of Civil Engineering National Institute of Technology Srinagar