Chao-Wei Tang

Dynamic Properties of Lightweight Concrete Beams Made by Sedimentary Lightweight Aggregate

This research aimed to investigate the engineering and dynamic properties, such as unit weight, stiffness, natural frequency and damping ratio, of lightweight aggregate concrete (LWAC) beams made with sedimentary lightweight aggregate (LWA) and to compare with companion normal weight concrete (NWC) beams. The primary design variables included compressive strengths of 20, 40, and 60 MPa and reinforcement ratios of 0%, 1.03%, and 2.32%, respectively. A total of 62 beams were made and tested. Test results showed that the unit weight of LWAC beams was about 16–23% lower than that of NWC beams for the same strength level. In addition, the reduced modulus of elasticity of LWAC resulted in a stiffness decrease of reinforced lightweight concrete (RLC) beams of 5–15% related to the reinforced NWC (RC) beams. Nevertheless, the natural frequency of RLC was still higher by about 1–10% than that of RC. In contrast, it was also found that the porous LWA with high damping capacity enhanced the damping ratio of RLC beams by 13–30% for concrete strength in the range from 20 to 60 MPa. As a whole, the lower the concrete strength is (e.g., 20 MPa), the more effective will be for the lightness of LWAC beam and the damping ratio, which in turn is more favorable to the seismic resistant efficiency of LWAC beam.

Radial Basis Function Neural Network Models for Peak Stress and Strain in Plain Concrete under Triaxial Stress

In the analysis or design process of reinforced concrete structures, the peak stress and strain in plain concrete under triaxial stress are critical. However, the nonlinear behavior of concrete under triaxial stresses is very complicated; modeling its behavior is therefore a complicated task. In the present study, several radial basis function neural network (RBFN) models have been developed for predicting peak stress and strain in plain concrete under triaxial stress. For the purpose of constructing the RBFN models, 56 records including normal- and high-strength concretes under triaxial loads were retrieved from literature for analysis. The K-means clustering algorithm and the pseudoinverse technique were employed to train the network for extracting knowledge from training examples. Besides, the performance of the developed RBFN models was estimated by the method of three-way data splits and K-fold cross-validation. On the other hand, a comparative study between the RBFN models and existing regression models was made. The results demonstrate the versatility of RBFN in constructing relationships among multiple variables of nonlinear behavior of concrete under triaxial stresses. Moreover, the results also show that the RBFN models provided better accuracy than the existing parametric models, both in terms of root-mean-square error and correlation coefficient.

Paper Sludge Reuse in Lightweight Aggregates Manufacturing

The lightweight aggregates used by the civil engineering market are sintered at a high temperature, about 1200 °C. In times of high energy prices and regulation of carbon dioxide emissions, lightweight aggregate products of the high-temperature process in sales marketing are not readily accepted. This study developed a sintered-type paper sludge lightweight aggregate. In order to reduce energy consumption, substitution of some reservoir sediment clay in paper sludge substitutes is to be expected. The study used two types of paper sludge (green clay paper sludge and paper pulp sludge). The sintering temperature was reduced effectively as the green clay paper sludge was substituted for some of the reservoir sediment clay, and the optimum substitute ranges of green clay paper sludge were 10%–50%. The optimum substitute ranges of the paper pulp sludge were 10%–40%. Test results show that the properties of aggregates have a particle density of 0.66–1.69 g/cm3, a water absorption of 5%–30%, and a loss on ignition of 10%–43%. The loss on ignition of aggregate became greater with the increase in paper sludge content. This means that the calorific value provided by the paper sludge will increase as paper sludge content increases. Paper sludge can therefore be considered a good material to provide heat energy for sintering lightweight aggregate.

A New Testing Method for Fatigue of Reinforced Concrete Beam

In this research, a new testing method for fatigue is proposed. The traditional hydraulic machine is replaced by vibrating motors with identical magnitude but higher frequency (12 Hz and 30 Hz) of cyclic loading on the basis of force control. The test results (including midspan deflection and beam stiffness) for both fatigue testing systems are compared. By comparison, preloading for the beam at first cycle and adjustment in frequency of loading are suggested to eliminate the dynamic effects for the vibrating motor system. Under such condition, the time it would take for the fatigue testing could be reduced substantially.