Nildem Tayşi

Temperature Distributions and Variations in Concrete Box-Girder Bridges: Experimental and Finite Element Parametric Studies

In this research, a full-scale, experimental box-girder bridge segment and three dimensional finite element thermal studies were conducted to investigate the temperature distributions and variations in concrete bridges under environmental thermal loads, with particular reference to the influence of the thermal properties of concrete. Applicable ranges of the studied properties were gathered from an extensive literature survey. One-way analysis of variance was used to evaluate the effect of the concrete properties of interest, demonstrating that density and surface emissivity have negligible effects. Parametric studies showed that the combined effects of thermal conductivity, specific heat, and solar absorptivity may increase the maximum bridge temperature by approximately 25%. Analysis of extreme thermal conditions indicated that these combined effects increased the mean bridge temperature by approximately 15 to 20%. Moreover, it may cause vertical temperature gradients exceeding the AASHTOs and the Bridge Manuals vertical gradients by up to 10°C.

Finite element analysis and optimization of bonded post-tensioned concrete slabs

Abstract Optimization techniques may be effective in finding alternative design of post-tensioned slabs to improve their mechanical behaviour, particularly reducing the bending moments. Post-Tensioned (PT) concrete one-way slabs are one of the widely used slabs because of their good performance and cost effectiveness compared with other slab types. The objective of this study is to develop three-dimensional Finite Element (FE) model for the optimization of bonded PT concrete one-way slab. The FE software package ANSYS was used to find the optimum strain energy and area of PT tendons. The interface between PT tendon and the surrounding concretes was also modeled, allowing the tendon to keep its shape during slab deformation. Contact algorithm and material nonlinearity were considered in the FE model. The total strain energy of bonded PT concrete slab was considered as the objective function. The design variables are the area of PT tendons, the initial stress in tendons and the eccentricity of the tendon profile while the constraints are the normal stress in concrete, the stress in steel tendon, the shear stress in concrete and the displacement at mid-span of the slab. The optimization results indicate that the area of PT tendons may be reduced by approximately 38% using an appropriate optimization algorithm. We conclude that the optimization of area of PT tendons of the post tensioned slab is very important because, it enable us to find the optimal area of PT tendon with low cost and suitable service conditions

A COMPUTATIONAL TOOL BASED ON GENETIC ALGORITHM FOR DETERMINING OPTIMUM SHAPES OF VIBRATING PLANAR AND SPACE TRUSSES

This paper deals with the structural optimization of vibrating planar and space trusses. The objective of the present study is to develop a robust and reliable shape optimization tool for vibrating trusses. Natural frequencies are determined using standard finite element matrixdisplacement method. The fundamental concept is to generate structural shapes for trusses in which certain vibration characteristics are improved. The results of comparative studies of the Genetic Algorithm (GA) against other continuous optimization algorithms for truss problems are reported to show the efficiency of the structural optimization.

OPTIMIZATION OF VIBRATING ARCHES BASED ON GENETIC ALGORITHM

The present work is concerned with the structural shape optimization of vibrating arches. Natural frequencies and mode shapes are determined using curved, variable thickness, C(0) continuity Mindlin-Reissner finite elements. The whole shape optimization process is carried out by integrating finite element analysis, cubic spline shape and thickness definition, automatic mesh generation and Genetic Algorithm (GA). An example is included to highlight various features of the optimization procedure.