The use of recycled concrete aggregates (RCA) in high performance concrete (HPC) was analyzed. The paper presents the experimental studies of model reinforced concrete beams with a rectangular section using high-performance recycled aggregates. Two variable contents of recycled aggregate concrete were used in this study: 50% and 100%. The experimental analyses conducted as immediate studies concerned the following issues: short time loads-deflection, load-carrying capacity of beams, deformation of concrete, cracks, and long-term loads-deflection. The comparative analysis involves the behavior of beams made of high performance concrete-high strength concrete (HPC-HSC) recycled aggregates with model control elements made of regular concrete based on natural aggregates. The deflection values for the recycled aggregate beams were 20% higher than in the case of the control beams made of HPC-HSC exclusively. Replacement of aggregate with recycled concrete aggregate resulted in a large decrease in the value of these two parameters, i.e., compression strength by about 42% and modulus of elasticity by about 33%.

The paper presented aimed at examining the effect of a fiber-reinforced concrete layer in the compressed zone on the mechanical properties of composite fiber-reinforced concrete slabs. Steel fibers (SF) and polypropylene fibers (PP) in the amount of 1% in relation to the weight of the concrete mix were used as reinforcement fibers. The mixture compositions were developed for the reference concrete, steel fiber concrete and polypropylene fiber concrete. The mechanical properties of the concrete obtained from the designed mixes such as compressive strength, bending strength, modulus of elasticity and frost resistance were tested. The main research elements, i.e., slabs with a reinforced compression zone in the form of a 30 mm layer of concrete with PP or SF were made and tested. The results obtained were compared with a plate made without a strengthening layer. The bending resistance, load capacity and deflection tests were performed on the slabs. A scheme of crack development during the test and a numerical model for the slab element were also devised. The study showed that the composite slabs with fiber-reinforced concrete with PP in the upper layer achieved 12% higher load capacity, with respect to the reference slabs.

The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high-performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross-section of 120 x 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of highperformance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

The paper summarises the experimental and numerical analysis of flexural capacity and deformability of structural concrete beams prepared as composite members consisting of two concrete layers made of reinforced normal concrete and high‐performance concrete (HPC). The reinforced concrete composite beams used in the tests were prepared in full scale with the cross‐section of 120 × 200 mm and the effective span of 2950 mm. The basic samples were composed in two layers consisting of high‐performance concrete as the top layer, and normal strength concrete. The results of the analyses confirm a significant improvement of structural properties of composite beams in comparison to the beams prepared totally of normal concrete, and in some cases also in comparison with the beam totally made of HPC.

The present paper is the first study on the hygrothermal analysis (i.e., effect of temperature and moisture loadings) of laminated composite skew conoids with reasonable depth and thickness. In order to solve the hygrothermal problem of laminated composite skew conoids, the cubic variation in displacement field, along with cross curvature effects of the shell, were considered. In the present analysis, the shear correction factor is not needed due to the parabolic variation of transverse shear strain. The zero transverse shear stress conditions at the top and bottom of the shell were imposed in the mathematical model. The novelty of our model is reflected by the simultaneous addition of twist curvature in the strain field, as well as the curvature in the displacement field allowing the reasonably thick and deep laminated composite rhombic conoid. The conoid behavior differs from the usual shells, like cylindrical or spherical ones, due to its inherent twist curvature with the complex geometry and different location of maximum deflection. The finite element (FE) implementation of the present realistic mathematical model was carried out using a nine-noded curved isoparametric element with seven unknowns at each node. The C0 FE implementation of the present mathematical model was done and coded in FORTRAN. The present model results were compared and found in good agreement with other solutions published in the literature. Hygrothermal analysis was performed for skew conoids having a different skew angle, temperature, moisture concentration, curvatures, ply orientation, thickness ratio, and boundary conditions.

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The application of recycled coarse aggregates (RCA) in high-performance concrete (HPC) was analyzed in the article. In the paper, the behavior of HPC with coarse recycled aggregate and natural coarse aggregate (NCA) was compared. Short-term experiments were conducted, including concrete deformation, deflection, load bearing capacity, and cracking of beams. The analysis involved reinforced concrete T-beams made in 100% of RCA or NCA. The studies indicated that the beams with recycled aggregate are characterized by greater deflection and 7.6% lower load bearing capacity in comparison to the beams with NCA. Substitution of coarse natural aggregate with RCA reduced the compressive and tensile strengths by 20 and 26 (%), whereas and the modulus of elasticity was decreased by 15%.

In the present work, for the first time, free vibration response of angle ply laminates with uncertainties is attempted using Multivariate Adaptive Regression Spline (MARS), Artificial Neural Network-Particle Swarm Optimization (ANN-PSO), Gaussian Process Regression (GPR), and Adaptive Network Fuzzy Inference System (ANFIS). The present approach employed 2D C0 stochastic finite element (FE) model based on the Third Order Shear Deformation Theory (TSDT) in conjunction with MARS, ANN-PSO, GPR, and ANFIS. The TSDT model used eliminates the requirement of shear correction factor owing to the consideration of the actual parabolic distribution of transverse shear stress. Zero transverse shear stress at the top and bottom of the plate is enforced to compute higher-order unknowns. C0 FE model makes it commercially viable. Stochastic FE analysis done with Monte Carlo Simulation (MCS) FORTRAN inhouse code, selection of design points using a random variable framework, and soft computing with MARS, ANN-PSO, GPR, and ANFIS is implemented using MATLAB in-house code. Following the random variable frame, design points were selected from the input data generated through Monte Carlo Simulation. A total of four-mode shapes are analyzed in the present study. The comparison study was done to compare present work with results in the literature and they were found in good agreement. The stochastic parameters are Young’s elastic modulus, shear modulus, and the Poisson ratio. Lognormal distribution of properties is assumed in the present work. The current soft computation models shrink the number of trials and were found computationally efficient as the MCS-based FE modelling. The paper presents a comparison of MARS, ANN-PSO, GPR, and ANFIS algorithm performance with the stochastic FE model based on TSDT.