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INTRODUCTION

1.1Advantages and Characteristics of Reinforced Concrete

Reinforced concrete is a composite material made of concrete and steel bars, seeFigure 1.1. It merges the advantages of concrete (form, stiffness and durability) with those of steel bars (high tensile strength and ductiltiy) into a single material with excellent physical and mechanical properties. Longitudinal steel in form of reinforcing bars is placed on the tension side of the member to carry flexural tensile stress from bending (in case of beams) or from combined axial laod and bending (in case of columns). Transverse steel in form of stirrups (in beams) or ties (in columns) serves to carry diagonal tension from shear forces.

1.2Composite Action

For composite action to work, adequate load transfer between the steel bars and the surrounding concrete has to be ensured via adequate development length of the steel bars. As such, the steel bar will develop its full tension capacity (yield strength times the bar cross sectional area) before it pullls out of the concrete. That is why reinforcing bars are deformed (Figure 1.2-a) to have adequate load transfer ability. Development length of straight bars ranges from 40-60 times the bar diameter. Using a 90 dgrees or 180 degrees hook (Figure 1.2-b) at the end of the bar can reduce the development length by roughly 50%

1.3Types of Reinforced Concrete Buildings

The most common types of low-rise and mid-rise (up to 20 stories) reinforced concrete buildings are:

1- Frame buildings (Figure 1.3)

2- Wall buildings (Figure 1.4)