# The properties of structural steel for bridge

### The properties of structural steel relevant for its use in bridge construction are

the following:

(1) strength

(2) ductility

(3) weldability

(4) notch toughness

(5) weather resistance.

The strength properties of commonly available structural steels are

represented in the idealized tensile stress–strain behavior in Fig(a).

The slope of the initial linear part is defined as Young’s modulus E. At a stress just

beyond the limit of linearity, the flow of the steel becomes plastic at nearly

constant stress. This stress is called the yield stress (or yield point) Re of the

steel. After the yield is completed the stress increases again until the maximum

stress, called the tensile strength (Rm) is reached. With further straining large

local elongation and reduction in cross-section occur, and the stress falls until

fracture takes place.

With some steel, after the initial limit of linearity, the stress may attain a

maximum, then fall and remain approximately constant during yielding, as

shown in fig (b); the value of the stress at the commencement of yield is

called the upper yield stress ReH. Some steel does not show the yield

phenomenon; beyond the limit of linearity, the strain continues to increase

non-proportionally, as shown in Fig. (c). In such cases a ‘proof stress’ is

measured. Proof stress (total elongation) Rt is measured by drawing a line

parallel to the stress axis and distant from it by the required total elongation;

proof stress (non-proportional elongation) Rp is measured by drawing a line

parallel to the initial straight portion of the behaviour and distant from it by the

required non-proportional elongation. For such steel a 0.5% total elongation

proof stress is regarded as the yield stress. Unloading from any stage of initial

straining occurs along a line approximately parallel to the initial straight

portion of the stress–strain curve.

Idealised stress–strain behaviour of steel.

The Design of

Modern Steel Bridges S.Chatterjee