Habib Uysal

THE EFFECTS OF DIFFERENT CEMENT DOSAGES, SLUMPS AND PUMICE AGGREGATE RATIOS ON THE COMPRESSIVE STRENGTH AND DENSITIES OF CONCRETE

Abstract Compressive strengths of concretes made up of mixtures of pumice aggregate (PA) and normal aggregate were measured. To determine the effect of PA ratio, different cement dosage and slumps on the compressive strength of concrete, (1) 25%, 50%, 75% and 100% pumice ratios were used instead of normal aggregate by volume, (2) 200, 250, 350, 400 and 500 kg/m 3 cement dosages were used and (3) 3±1, 5±1 and 7±1 cm slumps were also used in this study. The analysis of the test results leads to the conclusion that PA decreased the density of concretes up to 41.5% and reductions occurred due to the increase of the PA ratio in the mixes. With the increase of cement dosage in the mixes, both density and compressive strength of concretes increased up to 3.2% and 265%, respectively, when compared to the control sample that contain 200 kg/m 3 cement dosage. The effect of the slump on the density and compressive strength was varied. Elasticity moduli were decreased with an increase of PA ratio and increased with an increase of cement dosage. Water absorption improved with an increase of cement content.

A FULLY STRESSED DESIGN METHOD TO DETERMINE THE OPTIMUM STRUT-AND-TIE MODEL FOR BEAM–COLUMN CONNECTIONS

Topology optimization and strut-and-tie model methods have a remarkable success in the detailing of reinforced concrete structures, especially for discontinuity regions of the beam–column connections. However, it has always been complicated to determine an optimum design throughout all the offers of an optimization process, since it is not obvious which of the decision variables should be considered in order to select the optimum design. This paper presents the application of a new selection method on topology optimization and strut-and-tie modeling of the beam–column connections. A performance index formulation assists the selection of the optimum design from the process by considering the fully stressed design concept unlikely other performance indices. Former indices take just one of the structural criterions into consideration such as stress, strain energy, displacement, etc. The efficiency and capability of the approach have been demonstrated by the comparison of element removal criterions and different parameter values on several bidimensional design examples.

A computational and experimental study for the optimum reinforcement layout design of an RC frame

Purpose – Compared with conventional design methods, strut-and-tie modeling is a more suitable and even a superior method for the reinforcement layout design of structural members with uncommon geometrical shapes and/or regions essentially subject to shear effects. Because determination of the optimum strut-and-tie model for each of the members is an important task, implementation of a topology optimization method could be useful before the detailing stage. The paper aims to discuss these issues. Design/methodology/approach – Optimum reinforcement layout of a concrete frame was designed by an integrated approach, which consists of topology optimization and strut-and-tie modeling methods. Subsequently, an experimental comparison of the new model with the conventional model was performed based on their structural behaviors. Findings – Depending on the experimental results, it was concluded that the new integrated design method presents more successful results than does the conventional method for the design...

SIZING OF A SPHERICAL SHELL AS VARIABLE THICKNESS UNDER DYNAMIC LOADS

In this paper, optimization of a spherical shell under various dynamic loads is investi- gated. The aim of this optimization problem is to minimize the volume of the shell. Design variables are corner thicknesses of each finite element. Constraints are stresses obtained from von Mises stress criterion not to exceed the yield stress in corner nodal points of each finite element at the top and bottom surfaces of shell and thicknesses are restricted not to be less than 2.5 mm. In addition to shells own weight, the vertical loads with equal intensity are applied at the nodal points on the upper edge of spherical shell, varying with respect to time function P(t). Time varying load vector is considered three different cases such as step, step after ramp and impulse functions.A program is coded with MapleV for optimization of spherical shell and finite element package program ANSYS is used for structural analysis. Obtained results are presented in graphical and tabular form. Finally, concluded remarks are given.