Wimal Suaris

ULTRASONIC PULSE ATTENUATION AS A MEASURE OF DAMAGE GROWTH DURING CYCLIC LOADING OF CONCRETE

The paper presents experimental results of damage growth during cyclic loading of concrete. The damage growth is inferred from the reduction in amplitude of ultrasonic waveforms transmitted through the specimen during the test. The amplitude of the waveform, by virtue of its higher sensitivity to the extent of cracking, is found to be a better indicator of crack growth than the more often used pulse velocity technique. A continuous recording of pulse transmission throughout the tests is obtained by using a pulse generator, a digital oscilloscope, and a microcomputer. A specially constructed frame is used to hold the transducers in contact with the specimen during the test. The damage accumulation during cyclic loading as inferred from the attenuation results is presented by several mix proportions.

Detection of crack growth in concrete from ultrasonic intensity measurements

Results of monitoring crack growth in concrete during uniaxial compression using ultrasonic methods offer the possibility of determining the internal properties of a concrete member both during and after loading without causing any damage. The ultrasonic transducers were designed to monitor pulse transmission in both the axial and lateral directions throughout a uniaxial compression test. The waveforms received at various stages of loading were digitized, stored and analysed after the test. The crack growth was inferred from the intensity of these ultrasonic waveforms. Axial stresses/strains and transverse strains were also recorded by the use of a data acquisition system. Four different mix proportions were tested and the results obtained are discussed and compared with other available results.

Post-fire behavior of GFRP bars and GFRP-RC slabs

AbstractTechnologies developed over the last two decades have introduced the use of glass fiber reinforced polymer (GFRP) composite bars as reinforcement in concrete structures when corrosion of th...

Hadamard's principle for displacement discontinuity modeling of cracks

Abstract It is well known that boundary integral formulations degenerate for a body containing flat cracks. The methods used to analyse fracture problems include multi-region approaches and Greens function formulations. Recently a displacement discontinuity method has also been used to solve fracture problems. In this method the displacement discontinuity along the crack surface is related to the applied traction through an integral equation. The technique adapted for solving this equation requires that the gradient of the displacement discontinuity be continuous across the element boundaries. This can be ensured only if the gradients of the displacement discontinuity is also interpolated in addition to the displacement discontinuities. For two dimensional problems this would result in doubling the number of nodal variables. In the proposed method the integral equation relating the displacement discontinuities to the applied traction is solved directly by using the Hadamards principle. This method requires only that the points at which the stresses are evaluated be distinct from the element nodes. This technique is found to yield satisfactory results for various problems including multi-cracks, non-uniform loading and both infinite space and half space problems.