Fatigue damage assessment of reinforced concrete beam using acoustic emission technique / Noorsuhada Md Nor

Damage due to fatigue loading in a reinforced concrete (RC) beam is a crucial phenomenon that requires assessment. Acoustic emission (AE) technique can be used to identify the fatigue damage progression in the RC beam. Third point loading fatigue test was carried out in the laboratory of heavy structure on a small size RC beam of 150 mm x 150 mm x 750 mm and the actual size of RC beam of 300 mm x 600 mm x 4050 mm. The fatigue test was carried out based on various ranges of maximum fatigue loading, based on the first crack load, Pcr and ultimate static load, Pult. Four objectives were outlined; to investigate the fatigue crack progression of RC beam specimens corresponding to the AE characteristic, to correlate damage classification of the RC beam specimens with respect to intensity analysis, to evaluate the fatigue crack characterization of RC beam specimens based on average frequency and RA value and to develop a new approach in fatigue damage assessment of RC beam specimens based on AE characteristics. RA value is the rise time divided by peak amplitude (μs/v or ms/v). In the review, it was found that the analysis based on AE signal collected from channel basis is generally used. Channel basis is an analysis of AE data at a particular channel

Steel and polypropylene fiber as a mechanism in concrete properties improvement / Soffian Noor Mat Saliah, Noorsuhada Md. Nor

The effects of steel and polypropylene fibers on properties of concrete have been investigated. Concrete mixes with a characteristic strength of 30 MPa at 28 days were prepared. Steel fiber was used at dosage levels of 15, 25 and 45 kg/m3, whereas polypropylene fiber was included at dosage levels of 4.5, 6 and 9 kg/m3. It was found that the inclusion of both types of fibers reduce the workability of concrete with greater reduction at higher fiber dosage. Compressive strength was not significantly affected by the inclusion of fibers, but the inclusion of fibers seemed to reduce the tendency of concrete to undergo brittle failure under compressive load. Both types of fibers significantly enhance the flexural strength of concrete with steel fibers showing greater effect. Concrete containing fibers exhibited greater toughness and residual strength factor. Steel and polypropylene fibers did not have significant effects on splitting tensile strength and interfacial bond strength between steel and concrete. However, observation on failure pattern showed that the inclusion of both types of fibers prevented the concrete from breaking and splitting as well as reduced the tendency of steel reinforcement to undergo debonding

Properties of Controlled Low-Strength Material Mixes Made from Wastepaper Sludge Ash and Recycled Fine Aggregate

As demarcated in the American Concrete Institute (ACI 229R-13), CLSM stands for controlled low-strength material, which is a self-consolidating cementitious material that can be used as a backfill instead of compacted fill. However, the usage of CLSM in the construction industry was limited to backfilling, structural filling, void filling, and erosion control due to low compressive strength. On the other hand, using materials that can replace the material responsible for greenhouse gases has been promoted globally to halt the incidence of global warming instigated by releasing greenhouse gases, mainly CO2, into the atmosphere. Waste paper sludge ash (WPSA) is one among them, and researchers have discovered that it can be used to substitute cement in the manufacture of CLSM effectively. In this research, CLSM were made using recycled fine aggregate (RFA) as fine aggregate and WPSA as cement replacement to determine the plastic and in-services properties of CLSM mixes made from both materials mentioned. For the plastic properties, the test included are flowability, bleeding and hardening test as for in-services properties, including the testing of density and compressive strength of CLSM produced. The testing of CLSM in terms of plastic and in-services properties was influenced by the water-to-cementitious ratio, WPSA replacement and total cementitious material. The flowability of CLSM is influenced by the amount of RFA and WPSA used in the design. The lower the water absorption, the more water will be absorbed and gives less bleeding. Therefore, different proportions of w/cm, WPSA replacement and total cementitious material of CLSM mixtures influence a product's plastic in-service properties. Its compressive strength was between 0.3 MPa to 4 MPa, which satisfied the backfill strength required by ACI 229R-13, and it can also be concluded that samples with higher cement content show higher compressive strength results than others

Analysis of failure mechanisms in fatigue test of reinforced concrete beam utilizing acoustic emission

The acoustic emission technique is used for monitoring the fatigue failure mechanisms in reinforced concrete beam under three point bending. The analysis was conducted by using the bathtub curve method plotted from acoustic emission data. In this study, the fatigue behavior was divided into three stages. The first stage is involved with the decreasing failure rate, known as early life failure or burn-in phase, the second stage is characterized by constant failure rate and the third stage is called the burnout phase which is an increase of failure rate. The three parameters used in analyzing is the fatigue behavior for each stage of failure which are severity, signal strength and the cumulative signal strength. From severity analysis, the range of each stage of failure had been determined while from signal strength analysis, the initiation of distribution of crack had been detected through the fluctuation of signal strength. Cumulative signal strength parameter provides a clearer view of the initiation and distribution of crack

Detection of Uniaxial Fatigue Stress under Magnetic Flux Leakage Signals using Morlet Wavelet

This paper demonstrates the application of continuous wavelet transform technique for magnetic flux leakage signal generated during a uniaxial fatigue test. This is a consideration as the magnetic signal is weak and susceptible to being influenced by an external magnetic field. The magnetic flux leakage signal response of API steel grade X65 is determined using Metal Magnetic Memory under cyclic load conditions ranging from 50% to 85% of the UTS. To facilitate further signal analysis, the magnetic flux gradient, the dH(y)/dx signal were converted from a length base into time series in this study. Magnetic flux leakage readings indicated a maximum UTS load of 56.5 (A/m)/mm at 85%, where a higher load resulted in a higher reading and the signal contained Morlet wavelet coefficient energy of 1.02×106 µe2/Hz. As increasing percentages of UTS loads were applied, the signal analysis revealed an increasing linear trend in the dH(y)/dx and wavelet coefficient energy. The analysis revealed a strong correlation between the wavelet coefficient energy and the dH(y)/dx amplitude, as indicated by the coefficient of determination (R2) value of 0.8572. Hence, this technique can provide critical information about magnetic flux leakage signals that can be used to detect high stress concentration zones

Observing the simulation behaviour of Magnesium alloy metal sandwich panel under cyclic loadings

This study aims to investigate the delamination effect of a metal sandwich panel using a four-point bending simulation under continual spectrum loading. The most recent core designs of the sandwich panel have a cavity that can increase vulnerability in terms of bonding strength under constant cyclic loading. The sandwich panel is simulated under constant cyclic loading using different core design configurations, which are rounded dimple, hemispherical dimple, and smooth surface core design. There are two types of conditions used; no pre-stress and pre-stress loads with variable stress ratios based on Gerber stress life theory. Results showed that dimple core design enhanced mechanical behaviour and fatigue life performance about 33% and 5%, respectively, compared to the sandwich panel with a smooth surface core design. It is highlighted that modification on the surface of core design could be beneficial to enhance the bonding strength performance of sandwich panels and prevent early delamination under extreme conditions such as constant cyclic loading. This study is beneficial to enhance the bonding strength for sandwich panels against extreme conditions such as high impact load and continuous cyclic load

Fatigue Crack Inspection and Acoustic Emission Characteristics of Precast RC Beam under Repetition Loading

Abstract. Fatigue crack of the precast reinforced concrete beam under repetition loading is vital to be examined. Reinforced concrete structures exposed to excessive repetition loading could lead to the failure of the structures. In order to examine the active fatigue crack, the reinforced concrete beams were subjected to three-point repetition maximum loading. Eight phases of maximum fatigue loading with sinusoidal wave, frequency of 1 Hz and 5000 cycles for each phase were performed on the reinforced concrete beams. The inspection was carried out with visual observation of the crack pattern and acoustic emission technique for each load phase. The signal strength of acoustic emission was investigated. It is found that the signal strength of acoustic emission and crack pattern of the reinforced concrete beam subjected to repetition loadings showed promising results for structural health monitoring