Response of Members Subjected to Axial Load

Question 1

What are the 3 responses to calculate for under axial load?

Answer 1

1. Short term response
2. Linear elastic uncracked response
3. Long term response

Question 2

What is the difference between the short term response and the linear uncracked response?

Answer 2

While both responses are due to short term loading, the short term response deals with all types of linear and non-linear values along the N-ec plot….

The linear uncracked response is only applicable to linear values along the plot, ie the straight part of the N-ec graph where the tension loads are less than the cracking load

Question 3

What is the difference between the long-term and short-term response?

Answer 3

Long term response includes the effect of concrete creep, relaxation of the tendon and temperature effects.

Question 4

What is the stage before failure of an axially loaded prestressed member?

Answer 4

Stage 0; fc

Question 5

According to the failure stages of an axially loaded prestressed member, which stages are in the compression zone?

Answer 5

Stage 0
Stage 1
Stage 2
Stage 3i

Question 6

According to the failure stages of an axially loaded prestressed member, which stages are in the tension zone?

Answer 6

Stage 3ii
Stage 4
Stage 5

Question 7

When do you begin to account for tension stiffening?

Answer 7

After the concerte has cracked ie from stage 3 and beyond

Question 8

At what stages do crack widths matter?

Answer 8

Stage 2, fc=fcr concrete cracks
Stage 3, fs=fy steel yields, concrete is crackin
Stage 4, fp=fpy tendon yields, concrete is cracking

Question 9

How do you calculate the Max Axial load Nmax and ec at stage 5?

Answer 9

1 At crack surface: Exclude the effects of concrete because at the crack there is no concrete only yielded steel and prestressed tendon
2 In between crack: include effect of concrete, tension stiffening and you can find max strain in concrete

Question 10

What is the first stage of failure of an axially loaded prestressed member?

Answer 10

Stage 1 where fc=f’c

Concrete stress reaches yield stress

Question 11

What is the second stage of failure of an axially loaded prestressed member?

Answer 11

Stage 2 where fc=fcr

Concrete stress reaches cracking stress

Question 12

What is the third stage of failure of an axially loaded prestressed member?

Answer 12

Stage 3i where fs=fy in compression
Stage 3ii where fs=fy in tension
Non-prestressed steel yields in compression and tension

Question 13

What is the fourth stage of failure of an axially loaded prestressed member?

Answer 13

Stage 4 where fp=fpy

Prestressed tendon yields (in both compression and tension?)

Question 14

What is the fifth stage of failure of an axially loaded prestressed member?

Answer 14

Stage 5 where fp=fpu

Prestressed tendon ruptures

Question 15

How does a synthetic liner around a prestressed concrete tank affect the maximum failure load

Answer 15

…see Olesya