Several billion tons of water is annually used as mixing, curing and cleaning around the world, in concrete industry. As there is a scarcity of fresh drinkable water around the world; so there is a need to save fresh water and hence possibilities of using seawater as mixing as well as curing water should be investigated seriously. Additionally, if use of seawater as concrete material is permitted, it will be very convenient and economical in the construction; especially in the coastal works. However; most of the reinforced concrete codes do not permit the use of seawater due to risk of early corrosion of reinforcement. The effect of seawater on concrete deserves special attention as the coastal and offshore structures are exposed to simultaneous action of a number of physical and chemical deterioration processes. Moreover, 80 percent of the earth is covered by seawater either directly or indirectly (e.g. winds can carry sea water spray up to a few miles in land from the coast). Concrete piers, decks, break-water, and retaining walls are widely used in the construction of harbors and docks. The use of concrete offshore drilling platforms and oil storage tanks is already on the increase. This paper illustrates the various research and their results that were carried out earlier on the experimental studies on the strength of concrete in seawater.
Empirical relations have been found out to describe the decay in amplitude with distance of s-waves in the region of Garhwal Himalaya. These functions results from the analysis of spectral amplitudes of three component digital records from 19 local earthquakes obtained from 12-station seismological network deployed in the Garhwal lesser Himalaya. The events lie in a magnitude range from ML 2 to ML 4.5, epi-central distance 5 km to 120 km and focal depth from 5 km to 50 km. To determine the variations of the quality factor Qin the direction of wave propagation (Q anisotropy), independent estimates have been made of the attenuation of SV- and SH-waves using vertically polarized and transversely polarized components, respectively. Frequency analyzed (1-12 Hz) and in the whole distance range, the frequency dependence of Q can be approximated as Qsh = 74.3 f 1.0 for the SH-wave and Qsv = 81.5 f 0.95 for the SV-waves. The small difference between SH and SV spectral decay, suggests that Q anisotropy is negligible. However, In the distance range of 5-50 km, Qsv tends to be significantly greater than Qsh at frequency > 8 Hz. So in this distance range we observed Q anisotropy in the studied region. The dependence of Q value with frequency in this range is Qsh = 110 f 0.94 for SH- wave and Qsv = 134 f1.0 for SV-waves.
Reinforced concrete structures are subjected to damage due to environmental loading and operational conditions. Early detection of damages in reinforced concrete structures is very important. However, this becomes difficult because failure at the micro level in the form of minute cracks, develops much earlier than the visual appearance of actual damages resulting out of coalesce of several such micro level damages. Vibration based damage detection techniques, particularly use of modal testing by exciting a structure dynamically and measuring resulting responses is well established in current practice. Still, real experimental investigation involving a full scale reinforced concrete structure is somewhat rare in current literature. In the present investigation, dynamic responses of a 3.3-metre long reinforced concrete beam were measured experimentally before and after damage. Damage in the form of flexural cracks was inflicted by applying quasi-static load using a universal testing machine of capacity 300 kN under the four-point bending configuration. Broadband roving impact excitation was imparted through an impact hammer and the resulting responses were picked up by a single accelerometer. The time signals of both the force and acceleration responses were Fourier transformed using a spectrum analyser to determine the frequency response functions. The modal parameters e.g. frequencies, mode shapes, modal damping factors are found out through curve fitting. The frequency response function at a particular point has also been investigated for all the load increments and gradual changes into the dynamic properties are noted. Comparison of modal parameters between the undamaged and damaged state including their curvatures indicates that they are sensitive to the crack locations. On the other hand, the differences in frequency response functions including their curvatures were sensitive to the damage intensity in turn. The current experimental investigation provides great insight into the application of vibration-based damage detection technique to reinforced concrete structures.
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