Hyperspectral Endmember Extraction Techniques

Hyperspectral data processing and analysis mainly plays a vital role in detection, identification, discrimination and estimation of earth surface materials. It involves atmospheric correction, dimensionality reduction, endmember extraction, spectral unmixing and classification phases. One of the ultimate aims of hyperspectral data processing and analysis is to achieve high classification accuracy. The classification accuracy of hyperspectral data most probably depends upon image-derived endmembers. Ideally, an endmember is defined as a spectrally unique, idealized and pure signature of a surface material. Extraction of consistent and desired endmember is one of the important criteria to achieve the high accuracy of hyperspectral data classification and spectral unmixing. Several methods, strategies and algorithms are proposed by various researchers to extract the endmembers from hyperspectral imagery. Most of these techniques and algorithms are significantly dependent on user-defined input parameters, and this issue is subjective because there is no standard specificity about these input parameters. This leads to inconsistencies in overall endmember extraction. To resolve the aforementioned problems, systematic, generic, robust and automated mechanism of endmember extraction is required. This chapter gives and highlights the generic approach of endmember extraction with popular algorithm limitations and challenges

Hygrothermal durability of bond in FRP-strengthened masonry

Fiber reinforced polymers (FRPs) are accepted as an efficient material for external strengthening of masonry structures. Previous researches have shown that the bond between FRP and the substrate plays an important role in the effectiveness of this strengthening technique. Extensive investigations have been devoted to the characterization of the short-term bond behavior, while its durability and long-term performance requires further studies. In this regard, a full experimental program for investigating the environmental durability of bond in FRP-strengthened masonry is crucial for understanding the degrading mechanisms. This paper presents the results of an experimental program aimed at investigating the hygrothermal durability of bond in FRP-strengthened bricks. Accelerated ageing tests were performed on the FRP-strengthened brick elements and the bond degradation was periodically investigated by visual inspection and by conventional single-lap shear bond tests. The changes in the properties of material constituents have also been monitored. The obtained results are presented and critically discussed.This work was developed within the framework of the RILEM Technical Committee "223-MSC: Masonry Strengthening with Composite Materials". The financial support from the project FP7-ENV-2009-1-244123-NIKER of the 7th Framework Program of the European Commission is gratefully acknowledged. The first author also acknowledges the financial support of the Portuguese Science Foundation (Fundacao de Ciencia e Tecnologia, FCT), through grant SFRH/BD/80697/2011

FRP-to-masonry bond durability assessment with infrared thermography method

The bond behavior between FRP composites and masonry substrate plays an important role in the performance of externally bonded reinforced masonry structures. Therefore, monitoring the bond quality during the application and subsequent service life of a structure is of crucial importance for execution control and structural health monitoring. The bond quality can change during the service life of the structure due to environmental conditions. Local detachments may occur at the FRP/substrate interface, affecting the bond performance to a large extent. Therefore, the use of expedite and efficient non-destructive techniques for assessment of the bond quality and monitoring FRP delamination is of much interest. Active infrared thermography (IR) technique was used in this study for assessing the bond quality in environmentally degraded FRP-strengthened masonry elements. The applicability and accuracy of the adopted method was initially validated by localization and size quantification of artificially embedded defects in FRP-strengthened brick specimens. Then, the method was used for investigating the appearance and progression of FRP delaminations due to environmental conditions. GFRP-strengthened brick specimens were exposed to accelerated hygrothermal ageing tests and inspected periodically with the IR camera. The results showed environmental exposure may produce large progressive FRP delaminations.Fundação para a Ciência e Tecnologi

Static and Dynamic Testing of a Concrete T-Beam Bridge before and after Carbon Fiber–Reinforced Polymer Retrofit

This paper summarizes the design and execution of field studies to improve the performance of a deteriorated bridge through the use of carbon fiber-reinforced polymer (CFRP) material. The objective of the CFRP retrofit was to extend the life of Bridge 2028 in Cayey, Puerto Rico, by increasing its load rating. Field testing before and after the retrofit was performed to evaluate objectively improvement in load capacity and stiffness. The field testing program included both static load tests and dynamic tests. The first set of field tests was conducted in November 2002 to capture baseline bridge performance characteristics before the retrofit The CFRP retrofit was installed in October 2003, and a second set of nearly identical field tests was performed in August 2004. The test results indicated that the retrofit increased the bending stiffness of the bridge by 15% and decreased the tensile strains in the bottom rebars of the concrete T-beams by about 13%. Furthermore, the maximum rebar strains under a heavy truck load case were only 10% of the yield strength after the retrofit The change in stiffness determined from static deflection measurements was well correlated with the stiffness change determined from the dynamic tests. The field testing program showed that the CFRP retrofit was successful in improving the mechanical behavior of the bridge. The long-term performance and durability of the CFRP retrofit could be affected by a number of parameters such as local environmental conditions. The field testing program is to be periodically repeated; alternatively, a continuous monitoring program could be implemented to evaluate objectively the long-term performance and durability of the CFRP retrofit

Effect of hot-wet aging on the pin-bearing strength of a pultruded material with polyester matrix

This paper presents test results to show the effect of hot-wet conditioning on the pin-bearing strength of a pultruded fiber reinforced polymer material. Knowledge of this strength property, taking account of any reduction over the service lives of structures, is required to reliably calculate bearing strength when designing bolted connections. Pin-bearing strength is determined using an in-house test method with batches of nominally identical specimens, cut from the web of a 203 x 203 x 9.53 mm wide flange shape. This shape is from the 1525 series of Creative Pultrusion Inc., having a polyester based matrix. Specimens were immersed prior to strength testing under water for 3000 hours at the constant temperature of 40° C. The paper discusses the accelerated aging protocol and its relation to service life, and an explanation is given to why the material was aged for an unknown number of service years. Variables in the test matrix are the direction of the bearing force (0°, 45° and 90° to the direction of pultrusion) and plain pin diameter (four sizes from 9.7 mm to 25.4 mm). Comparing aged pin-bearing strengths with equivalent strengths for non-aged material it is found that the average reduction in characteristic strength (calculated in accordance with Eurocode 0) of the 12 batches, is in the range of 18 to 31%. The extent of strength reduction is found to be independent of pin size, except when the diameter is 25.4 mm. For the 0o situation a comparison is made between the characteristic strengths for the four pin diameters determined using BS EN 1990:2002 and ASTM D7290 to show that the latter Weibull distribution values are lower, and by 4 to 18%