Apostolos Fafitis

Analysis of thin-walled box girders by parallel processing

Abstract This paper presents a substructuring analysis method for thin-walled box girders. The formulation of the problem and the independent computational tasks of each thin-walled substructure lend themselves to parallel processing. Instead of solving the condensed equilibrium equations in the traditional substructuring method, a mix of compatibility and equilibrium equations are employed. The major unknowns are the shear forces at the interfaces where the thin walls of the substructures join. The proposed substructuring method is general and can be performed by using commercial finite-element analysis software on microcomputers. Numerical examples of a thin-walled box girder are analyzed by the proposed method and the results are compared with classical solutions and other studies. The stresses and shear lag calculated by the proposed method compare favourably with those reported by other investigators. Estimates of reduction in computation time and computer memory for the stiffness matrix operation indicate that the method is numerically efficient.

Structural properties of a new material made of waste paper

Papercrete is a new construction material made most often with waste paper, cement and water. People have been using papercrete to build low cost homes without a clear understanding of its structural properties. The purpose of this study is to obtain some mechanical and physical parameters of papercrete by doing several laboratory tests. The samples tested were made following the most common mixes that papercrete makers are using currently. The experimental setup used to test the samples is briefly described and some test results are tabulated in tables. This will allow us to reach some conclusions and make several recommendations for using papercrete to build homes.

A Stochastic Nonlinear Constitutive Law for Concrete

An incremental three-dimensional stress-strain relationship for concrete with induced anisotropy has been developed. The nonlinearity and path-dependency are modeled by expressing the elastic moduli at each increment as function of the octahedral and deviatoric strains, based on a uniaxial stochastic model developed earlier. Predictions of multiaxial response under proportional and nonproportional loading are in good agreement with experimental results

Analyses of High Grade Strength Steel Bars in the Design of a Five-Storey Reinforced Concrete Structure with Comparison of Energy Consumption and CO2 Emission

Energy consumption and CO2 emissions in buildings is becoming an increasingly important issue. Steel is a major building material with high energy cost. In a reinforced concrete (RC) structure, it accounts for the maximum energy consumption. There is a need to quantify the steel amount in RC for various situations so that reduction or optimization in steel usage can be analyzed. In this paper two different calculations (Calculation-I and Calculation-II) are conducted by using two groups of steel in designing beams, columns and plates for a 20000 m2 five-storeyed frame RC structure. In Calculation-I, or Cal-I in abbreviation, the steel used for beams, columns and plates is HRB335, HRB400 and HPB235 respectively. In Calculation-II, or Cal-II in abbreviation, the steel used for beams, columns and plates is HRB400, HRB500 and CRB550 respectively. The strength of steel used in Cal-II is higher than that in Cal-I. The calculation is carried out by following the standardized concrete structural design code, and the steps involved in calculation are given in certain details as seen necessary. The corresponding energy for producing the steel used in beams, columns and plates is also computed and normalized on per square meter basis. The results show that Cal-II saves 101.76 tons of steel than Cal-I, or 5.09kg/m2, which means a saving of about 64.11 t of standard coal or 1.6×102 t CO2 for the whole structure, or 3.2 kg of standard coal or 7.98kg CO2 for per square meter.

Curvature Ductility of Singly Reinforced CRC Beams (Part-II)

This article (Part-II) continues the work of a previous article (Part-I). It undertakes a theoretical analysis of the curvature ductility factor (CDF) of a singly reinforced CRC (crumb rubber concrete) beam and demonstrates how CRC’s material ductility is transformed into structural ductility of a reinforced CRC beam. The result shows that CDF for a reinforced CRC beam is much higher than that for a conventional concrete reinforced beam.

Transfer of shear tractions along rough cracks

A constitutive model for transfer of shear tractions along rough cracks in strain softening composites like concrete, is presented. The model relates the normal and shearing stresses on the rough crack to the corresponding displacements in terms of the interface strength, contact areas, the contact angle of the rough crack surface, and the crack closing pressure. The initial angle of contact at zero normal stresses, a fundamental property of the rough crack surface, was established by means of statistical and numerical simulations. Using the concepts of critical state soil mechanics, conditions were stipulated for dilation and contraction of the rough crack. The deformability of the asperity was mathematically described in terms of the initial angle of contact and a progression of this angle to a minimum by means of an exponential model. Using idealizöi test results such as constant crack width experiments, a mathematical model was developed for contact area as a function of the crack width and tangential displacement. The performance of the constitutive model was verified by predicting experimental results with varying crack width and normal stress boundary conditions, as well as constant crack width and constant normal stress. The comparison between predicted and experimental results appear to be very satisfactory. INTRODUCTION With the advent of fast computers such as vector processor, nonlinear problems which were hitherto time consuming, can now be solved very quickly on computers. This feature has let researchers and designers to use more sophisticated mathematical models for material description. While a number of mathematical models for continuous media are available, there is a scarcity of constitutive models for media with discontinuities such as cracks, joints and interfaces. In the investigations conducted by Bazant and Gambarova (1,2), stress displacement relations were developed for a rough crack using some idealized test results. Other investigations (3,4,5,6,7) relate shear and normal stresses and displacements of the rough crack by using empirical relations. Most of these constitutive models are based on macroscopic considerations, and so far, there has not been any model which considers the internal structure of the material and nature of the rough crack surface.