K. Ravisankar

Evaluation of Longitudinal Force on a Railway Bridge Based on Strain Measurements

Evaluation of longitudinal force is very important for the performance evaluation of older bridges and for the design of new bridges. There is a growing demand to increase freight haulage in railway networks, in particular, on the iron ore routes of various zones of Indian railways. This proposed alteration may subject the bridges to higher tractive effort/braking forces together with higher axle loads. It is thus obvious that there is a need to check the performance of the concerned bridges under this proposed increased loading. Hence, as part of evaluating the bridges for higher axle loads, experimental investigations have been carried out on a typical steel plate girder railway bridge. This paper gives the summary of experimental investigations, test setups, and results obtained for the evaluation of longitudinal force. The longitudinal force evaluated based on the experiments for the increased axle loads is found to be within the design limits specified. The special fixtures developed for direct measurement of the longitudinal force are found to give the reliable results compared to the strain gage measurements on the girder. The results show that only part of the rail force is transmitted to the girder.

Performance Evaluation of a Stone Masonry–Arch Railway Bridge under Increased Axle Loads

AbstractMany of the masonry arch bridges in the network of railway bridge stock belong to the civil engineering heritage of the railways. Therefore, their maintenance and management require careful consideration. An effective procedure for performance evaluation should promote solutions that are directed toward preservation and restoration of arch bridges by evaluating their existing structural capacity. In this paper, experimental methodologies adopted for the performance evaluation of a stone masonry–arch railway bridge are presented. One of the primary objectives of the current study was to evaluate the longitudinal force exerted on the bridge due to increased axle loads of freight wagons. An innovative technique using a flat jack was implemented for the evaluation of longitudinal stress due to increased axle load. Three-dimensional numerical modeling and analysis was carried out to identify the critical locations for fixing the flat jacks for evaluation of live-load stresses. A special instrumentation...

Development of a Real-time Remote Structural Monitoring Scheme for Civil Infrastructural Systems

Long-term structural monitoring has become an important requisite to ensure structural and operational safety for critical civil infrastructures. Long-term structural monitoring by acquiring data continuously or at small intervals may be difficult to achieve by employing conventional on-site monitoring methods. In order to overcome these difficulties remote structural monitoring (RSM), an advanced structural monitoring technique, can be used to acquire continuous data from the remotely instrumented structure. RSM methodology requires an interdisciplinary approach integrating areas such as structural engineering, sensor technology, communication technology, statistical mechanics, information technology for online data transmission (over larger distances) and damage detection/ health assessment of the structure. RSM has many advantages like, continuous monitoring, early alarm of any incipient damage, and data acquisition even in adverse climatic/environmental conditions. This article describes the development of an RSM scheme, developed at SERC, Chennai. The article outlines the laboratory and field investigations carried out to validate the developed scheme. Brief information about the observations and modifications made during these trials are also presented. A part of the work carried out for synthesizing online data using Auto Regressive Moving Average model is also presented.

Long-term prestress loss and camber of box-girder bridge

The evaluation of long-term prestress losses and camber, taking into account the effect of creep, shrinkage, and relaxation, is essential for prestressed concrete bridges. An effort has been made in this paper to identify a suitable time-dependent creep coefficient and shrinkage strain models to estimate the long-term prestress losses and camber for an existing box-girder bridge span. Longterm prestress losses and camber are estimated using four different models for creep and shrinkage-ACI 209R-92, CEB MC90-99, GL2000, and B3-And the comparison has been made with field measurements. From the limited studies made, it is seen that for the initial 5 years after the construction of a bridge, the B3 model can be used for estimation of long-term losses, and the CEB MC90-99 model can be used for estimation of long-term camber. However, for a prestressed concrete beam, the ACI 209R-92 model is found to predict closer prestress loss values with laboratory measurements.

Studies on Apparent Strain Using FBG Strain Sensors for Different Structural Materials

Fiber Bragg grating (FBG) sensors are the most recent type of fiber optic sensors, which are gaining importance in the field of structural health monitoring of civil infrastructure. These are proven to be more versatile due to their distinct advantages such as high sensitivity, immunity to electromagnetic interference, ease of multiplexing, and remote sensing. These are suitable for the long-term monitoring of the structures. The FBG sensors are found to be very effective in strain and temperature sensing. However, the FBG sensors are not self-temperature compensated and the total strain obtained using FBG sensor is the sum of the strain induced due to mechanical load and the apparent strain induced due to temperature. In this article a method to calibrate the apparent strain is discussed. A study is carried out on various structural materials such as mild steel, aluminium, concrete, and carbon fiber-reinforced plastic (CFRP) using bonded and unbounded FBG sensors. This article presents the result in the form of a temperature calibration curve, which can be used to find the actual mechanical strain.

Wireless strain sensing system for assessing condition of civil infrastructure facilities

Wireless sensors and sensor networks are emerging as substitutes for traditional structural monitoring systems. Their benefit lies in a lower cost of installation because extensive wiring is no longer required between sensors and the data acquisition system. Studies carried out to evaluate performance of wireless strain measurement units are described in this paper. An example is given of a wireless system used for measuring behaviour of a railway bridge, and comparison with traditional systems is made.

FBG Sensor Technology to Interfacial Strain Measurement in CFRP-Strengthened Concrete Beam

Fiber-reinforced polymer (FRP) composite materials are very attractive for use in strengthening of civil engineering structures because of their high strength to weight and stiffness to weight ratios, being corrosion free, light weight, and potentially high durability. The requirement for any embedded sensor for monitoring strain in FRP-strengthened concrete structures is that the sensor should not be detrimental to the operational requirement of the strengthened structure. Owing to the compatibility with FRP materials, fiber Bragg grating (FBG) sensor is a good choice for embedding at the interface of the FRP-strengthened concrete structures. As the FBG sensors are more flexible and small size (diameter = 250 μm), it may be easily instrumented at the FRP–concrete interface with sufficient surface preparation and suitable adhesive. This article deals with the issues/methods in application of FBG sensors for interfacial strain measurement of reinforced concrete beams strengthened with carbon fiber-reinforced polymer (CFRP). It also describes the experimental studies which were carried out to identify the initiation and propagation of debonding of CFRP from concrete surface using FBG array sensors.

In situ Stress Assessment in Concrete Structures Under Bi-axial Condition by Trepanning Technique

Assessment of in situ stresses in concrete structures which are under bi-axial stress state is complex to handle. In this paper, a trepanning technique is developed to assess the in situ stress. The proposed technique employs a three-element strain gage rosette to measure the strain release due to core drilling. The reliability of the proposed technique is evaluated through laboratory studies.

Fibre optic sensors as a non-destructive tool for structural monitoring

Structural monitoring is a diagnostic tool for detection of defects/ damages and for scheduling maintenance operations. It is essential to determine the safety of the structures by Non-Destructive Testing (NDT) for evaluation of strength/integrity. This assessment is required for the repair, rehabilitation and life extension of the structure. Fibre Optic Sensors (FOS) are attractive sensing devices as an NDT tool, given their small size, light weight, immune to electrical noise and electromagnetic interference. Optical fibres offer the possibility of embedding in cement/concrete without affecting their performance. Sensors can also be surface mounted on concrete/steel members. There are challenging problems/issues in applying FOS for concrete structures. Systematic studies on FOS have been carried out in the laboratory to solve the issues/problems. In this paper, details of the laboratory studies carried out in solving some of the technical challenges and issues in fibre optic sensing technology are covered.

Temperature calibration of fiber optic strain sensor for structural health monitoring

Major civil engineering structures, such as bridges constitute a significant portion of national wealth, and the cost of maintenance of these structures is very high. Structural health monitoring is a cost effective method of maintenance, and it predicts the structural integrity by early detection of degradation of health of the structure. One of the best ways of structural health monitoring is by the use of fiber optic strain sensors, which are eminently suitable for long term monitoring. However, the apparent strain due to variations in temperature at different measurement times may be very large and has to be accounted for. The apparent strain calibration curves of fiber optic strain sensors bonded to three structural materials, namely, steel, aluminum and concrete are obtained from laboratory experiments which can be used for correcting the temperature induced apparent strain from the total strain measured in the structures.