Should the anchorage length and overlap splice length for reinforcement be the same in codes? Ralejs Tepfers

Transcription

1 Should the anchorage length and overlap splice length for reinforcement be the same in codes? Ralejs Tepfers Ralejs Tepfers

2 Stetements Overlap splice length is situated within the moment envelop and anchors full bar force. The chosen splice length determines the bond stress gradient. Anchorage length is situated outside the moment envelop and theoretically does not anchor any force. However, anchorages at supports may partly be within the moment envelop and may have to anchor considerable force. There the support pressure and eventual stirrups help. Ralejs Tepfers

3 Definition in following tests: Over length = Anchorage length On-loading length = has splice length function The anchorage length theoretically does nor anchor any tensile reinforcement force. Practically yes. Ralejs Tepfers

4 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. Ralejs Tepfers

5 In the following tests the moment shift is disregarded at anchoring of staggered bars follows moment on top of beam Beams with in 45 o inclined stirrups have no moment shift. The stirrups are designed to take all shear according to Mörsch at moment failure. Beams with vertical stirrups have half lever arm moment shift. The stirrups are designed to take all shear according to Mörsch at moment failure. Bundled bars has favourable force transfer at staggering points. If distance between bars bond has to be transferred by shear trough concrete. Ralejs Tepfers

6 Test series A. Beam A1 to A5: 3 bundles of 3Ø8Ks400 bars Ralejs Tepfers

7 Test series A Beams are shear reinforced for full shear force according to Mörsch at moment failure. Beams with vertical stirrups have half lever arm moment shift. Beams with stirrups inclined in 45 degrees have no moment shift. Ralejs Tepfers

8 There is no over length = anchorage length for 16 mm bar. There is full 100% cover of shear force by stirrups. The moment envelop shift is disregarded and of course it influences the anchorage performance. Ralejs Tepfers

9 The reinforcement in beams Series U. Beams are shear reinforced for full shear force according to Mörsch at moment failure. Beams with vertical stirrups have half lever arm moment shift. Beams with stirrups inclined in 45 degrees have no moment shift. Ralejs Tepfers

10 Beams in Series U results Observe that beams with 45 o stirrups and longer on-loading length can give necessary anchorage without any anchorage length outside the moment envelop. Ralejs Tepfers

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12 Series U Ralejs Tepfers

13 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, Göteborg, November p. 234 Ralejs Tepfers

14 Tensile stress in bars varies between the bars depending on anchoring conditions for individual bars Ralejs Tepfers

15 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 reinforcement dowel action. This influences the moment envelop. Direction of shear cracks is 45 o at 100% of shear force cover by stirrups. If less cover, inclination less than 45 o. Covering 100% of shear force, stirrups in 45 o give no displacement of moment and stirrups in 90 o give half lever arm moment displacement. Any change in relations influence the moment envelop. Ralejs Tepfers

16 Questions- Statements cont. Anchorage at supports At supports we approach the splice situation because anchorage starts mostly within moment envelop. Up to full reinforcement force anchorage 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 are shear required necessary confining stirrups. Force redistribution Force is redistribution from anchored bars with some slip to continuous bars without, and other way round if on-loading is intense. The distance between the staggered anchored bars and continuous bars influences the redistribution and activation of the anchorage length. Ralejs Tepfers

17 Is the splice length = anchorage length??? No!!! Ralejs Tepfers