Lecture 2

Question 1

-About some of the properties of concrete relevant for
designing structural members
• About some of the properties of steel reinforcement
relevant for designing structural members
• Properties of Beams subjected to bending and how to
design them for flexure (bending moments)

Answer 1

.

Question 2

Why do we reinforce concrete with steel

Answer 2

Concrete has a low tensile strength

Question 3

How do we test reinforcement

Answer 3

We use a tensile test on steel

Question 4

Revision: 𝜎 =𝑀𝑦/I

Answer 4

Cross section bending (This is the value of failure)

Question 5

How do we design a concrete beam to resist bending

Answer 5

The Bending strength (Mrd) of the beam is greater than the Ultimate bending load (Med)

Question 6

Ultimate moment capacity

Answer 6

• Remember Equilibrium must always be maintained (SH = 0, SM = 0)
• Step 1 Draw a diagram of strain in the x-section and a diagram of stress
• Step 2 Assume a depth to neutral axis (X)
• Step 3 Calculate es using similar triangles and ecu3 = 0.0035
• Step 4 Calculate the force in the concrete compression zone (Fc
)
• Step 5 Calculate the stress in the reinforcement and subsequently the force in the
reinforcement (Fs
)
• Step 6 if Fc = Fs
then “X” is correct (i.e. SH = 0). If not choose new “X”
• Step 7 when correct “X” has been obtained, calculate internal moment (moments
can be taken about any point, but it is suggested that you take moments about the
reinforcement) MRd= Fc
(d - lx/2)
• Since SM = 0, for equilibrium MRd must be equal to the applied Moment at failure
(i.e. the design moment MEd)