Anchorage & Splice Length

8/3/2019 Anchorage & Splice Length

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Ralejs Tepfers 2006-10-30 1

Should the anchorage length and

overlap splice length for reinforcementbe the same in codes?

Ralejs Tepfers


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Stetements

Overlap splice length is situated within themoment envelop and anchors full bar force.The chosen splice length determines the bondstress gradient.

Anchorage length is situated outside themoment envelop and theoretically does notanchor any force. However, anchorages at

supports may partly be within the momentenvelop and may have to anchor considerableforce. There the support pressure and eventual

stirrups help.


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Definition in following tests:

Over length = Anchorage length

On-loading length = has splice length function The anchorage length theoretically does nor anchor any tensilereinforcement force. Practically yes.


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Overlap splice anchors full tensile

reinforcement force

The chosen splice length s determines the anchorage

force gradient. Gradient has to be limited to avoid failure.


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In the following tests the moment shift is

disregarded at anchoring of staggered bars

follows moment on top of beam Beams with in 45o inclined stirrups have no

moment shift. The stirrups are designed to takeall shear according to Mrsch at moment failure.

Beams with vertical stirrups have half lever arm

moment shift. The stirrups are designed to takeall shear according to Mrsch at moment failure.

Bundled bars has favourable force transfer atstaggering points. If distance between bars bond

has to be transferred by shear trough concrete.

T t i A


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Test series A.

Beam A1 to A5: 3 bundles of 38Ks400 bars

Test series A


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Test series ABeams are shear reinforced for full shear force according to Mrsch at moment

failure.

Beams with vertical stirrups have half lever arm moment shift.

Beams with stirrups inclined in 45 degrees have no moment shift.


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There is no over length

= anchorage lengthfor 16 mm bar.

There is full 100% cover of

shear force by stirrups.

The moment envelop shift isdisregarded and of course

it influences the anchorage

performance.


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The reinforcement

in beams Series U.

Beams are shear reinforced fofull shear force according to

Mrsch at moment failure.

Beams with vertical stirrups havhalf lever arm moment shift.

Beams with stirrups inclined in

45 degrees have no momentshift.

B i S i U lt


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Beams in Series U resultsObserve that beams with 45o stirrups and longer on-loading length

can give necessary anchorage without any anchorage length

outside the moment envelop.


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Series U


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Hinged beam test for determination of influence of

transverse pressure on anchorage. Central moment is

shifted to support. Full force anchorage.

.

Magnusson J. Bond and Anchorage of Deformed Bars

in High-Strength Concrete.

Chalmers University of Technology, Division of

Concrete Structures, Licentiate

thesis, Work No. 1113, Publication 97:1, Gteborg,

November 1997. p. 234


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Tensile stress in bars varies between the bars depending on

anchoring conditions for individual bars


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Questions-Statements

Is anchorage length the same as overlap splice length?Some statements. Anchorage length starts where force in bar theoretically already is zero.

Most of the anchoring has been done along the on-loading length. Splice length anchors always full force. The splice length determines the

bond intensity.

Moment envelop

Shear is taken by stirrups, concrete compressive zone and reinforcementdowel action. This influences the moment envelop.

Direction of shear cracks is 45o at 100% of shear force cover by stirrups. Ifless cover, inclination less than 45o.

Covering 100% of shear force, stirrups in 45o give no displacement ofmoment and stirrups in 90o give half lever arm moment displacement. Anychange in relations influence the moment envelop.


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Questions- Statements cont.Anchorage at supports At supports we approach the splice situation because anchorage

starts mostly within moment envelop. Up to full reinforcement forceanchorage has to be secured. In most cases there is transverse

compressive support force and confining stirrups, which helps.Anchorage confinement

For staggered reinforcement with short on-loading lengths there areshear required necessary confining stirrups.

Force redistribution

Force is redistribution from anchored bars with some slip tocontinuous bars without, and other way round if on-loading isintense. The distance between the staggered anchored bars andcontinuous bars influences the redistribution and activation of theanchorage length.


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Is the splice length

=

anchorage length???

No!!!

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Anchorage & Splice Length