Journal of Materials and Engineering Structures

58-72

Authors: Ghoson Ibrahim DANHASH, Mayada Ahamad Kousa, George Yakoub Wardeh

Post peak tensile behavior of concrete, softening, can be described using bi-linear curve. The area under this curve is the fracture energy GF which is necessary for the structural design. RILEM presented a recommendation for calculating GF but unfortunately the obtained value is size dependent. In this paper a large number of experimental Forces – Crack Mouth Opening Displacement (F-CMOD) curves, obtained from three points bending tests, were analyzed through an inverse analysis procedure to obtain the size independent fracture parameters. The effect of compressive strength, aggregate size, and paste volume on the fracture behavior of concrete were studied and compared with the empirical formulas found in the literature. A new empirical relationship for the prediction of size independent fracture energy of concrete from compressive strength, aggregate size and paste volume was proposed. It is shown that the proposed model can predict the size independent fracture energy with a good accuracy.

89-98

Authors: Zebbiche Toufik, Boun-jad Mohamed, Allali Abderrazak

The presented work is to develop a numerical computation program to determine the geometrical characteristics of arbitrary simply connected planar sections and applications to airfoils. In the literature, there are exact analytical solutions only for some simples’ geometries, such as circular, rectangular and elliptical sections. Hence our interest is focused on the search of approximate numerical solutions for more complex sections used in aeronautics. The used method is to subdivide the section in the infinitesimal triangular sections with a single observer within the area having a suitable position. The characteristics of any triangle, given by the positions of these three nodes are known in the literature. Using the principle of compound surfaces, one can determine the geometric characteristics of the airfoil surface. The analytic function of the airfoil boundary is obtained by using the cubic spline interpolation because the airfoil is given in the form of tabulated points. Error estimation is done to determine the accuracy of the numerical computation.

110-117

Authors: M P Singh, S P Singh, A P Singh

The paper presents results of an investigation conducted to study the compressive strength, split tensile strength and water permeability of fibre concrete mixes containing steel fibres in mono, binary and ternary combinations. Steel fibres of different lengths i.e. 12.5 mm, 25 mm and 50 mm having constant diameter of 0.6 mm were used to obtain mono, binary and ternary combinations. A reference concrete mix with no fibres was also used for comparison purpose. The total fibre volume fraction was kept at 1.0% in all the mixes. Compressive strength, split tensile strength and water permeability tests were conducted of specimens of size 100 x 100 x 100 mm after 28 days of curing. It has been observed that a fibre combination of 33% 12.5 mm + 33% 25 mm + 33% 50 mm long fibres can be adjudged as the most appropriate combination to be employed in HySFRC for compressive strength, split tensile strength and water permeability.

11-21

Authors: Daniel Mensah Boakye, Herbert Chidozie Uzoegbo, Nonhlanhla Mojagotlhe, Moeti Malemona

The results of laboratory studies conducted to evaluate the effects of different curing conditions on the compressive strength development of concrete made with pulverized copper slag as partial replacement for ordinary Portland cement (OPC) is presented. Concrete cube specimens were made with copper slag replacing cement in the following proportions; 2.5, 5, 10 and 15% compared to the control (0%) specimen under normal laboratory conditions and cured in three different conditions, namely; water, solar chamber and ambient air up 90 days. Test performed included X-ray Fluorescence (XRF) and sieve analysis respectively for the chemical oxide composition and fineness for both the pulverized copper slag and ordinary Portland cement. Specimens were tested for compressive strength up to 90 days of curing, with the temperature and humidity of the surrounding curing environment recorded for each of the three curing method used. The experimental results indicate a significant drop in the compressive strength as the copper slag content increases for all curing methods. Moreover, for the control samples, the percentage decrease in the compressive strength for the 3-day curing for water cured sample, compared to the solar chamber and ambient air were respectively 31% and 28%. However, beyond 28 up to 90 days of curing, the water cured samples yielded a higher compressive strength, followed by the solar chamber and ambient air. The percentage increase in the compressive strength up to 90 days of curing for water cured specimen, compared to the solar chamber and ambient air were respectively 8.5% and 12%. This trend was similar for all percentage replacement of cement with the pulverized copper slag

32-45

Authors: Driss Sarsri

In this paper, we propose a method to calculate the first two moments (mean and variance) of the structural dynamics response of a structure with uncertain variables and subjected to random excitation. For this, Newmark method is used to transform the equation of motion of the structure into a quasistatic equilibrium equation in the time domain. The Neumann development method was coupled with Monte Carlo simulations to calculate the statistical values of the random response. The use of modal synthesis methods can reduce the dimensions of the model before integration of the equation of motion. Numerical applications have been developed to highlight effectiveness of the method developed to analyze the stochastic response of large structures.