Bond length/Anchorage of Crack Control Reinforcement

[sybie99]

Hi Everyone,

I have a query on crack control steel. We are working on a massive dam project where most of the reinforcement does not play a structural role, only crack control. My question is, do you need to have full anchorage on your bars as you would for example for a beam for bars in tension? According to BS8110 for example, you must provide a 40 x bar diameter anchorage in 30Mpa concrete to develop the full tensile stress in the bar. But for crack control surely the full tensile capacity is not developed and hense you do not need full anchorage.

What are you thoughts? I am using BS8007 to calculate crack widths and thus steel areas required. I cannot seem to find a way by which I can calculate the tension in the bar as a result of cracking whereby I can calculate the anchorage length required.

Thanks

 

[ishvaaag]

BS8007 has written...

"B.5 Assessment of crack widths in direct tension
Provided that the strain in the reinforcement is limited to 0.8fy/Es,the design crack width should not exceed the appropriate value given in 2.2.3.3 and may be calculated from equation..."

Since all the related evaluation is for control of cracking by placing a minimum amount of reinforcement, and the controlled cracks may appear randomly anywhere, where you dimension the reinforcement according to BS8007 it maybe understood the reinforcement may need to work anywhere at 9.8Fy, a value from which you may dimension your overlap requirement.

 

[dik]

Can the bars be easily laid out so that splice locations are alternated.

Dik

 

[ishvaaag]

to 0.8 Fy, of course..

 

[DST148]

I am neither familiar with Euro Codes nor ever was involved with design of massive concrete structures, but...... ACI 224R-01 Control of cracking in concrete structures, Part of section 3.5.2: Although the use of reinforcement to control cracking in a relatively thin concrete section is practical, it is not needed in massive structures, such as dams, due to low drying shrinkage of these mass structures.
Control of cracking in massive concrete structures can be achieved through correct construction practices. Of course, reinforcement will always supplement that.
ACI 318-05, commentary R7.12.2: Splices and end anchorages of shrinkage and temperature reinforcement are to be designed for the full specified yield strength.
In some of the offices I have worked, we did provide rebars in elements which could be designed using the provisions of structural plain concrete but then we did not attempt to conform to each and every provision of structural reinforced concrete.