(1)P Coupling of walls by means of slabs shall not be taken into account, as it is not effective.
(2) The provisions of 5.5.3.1 may only be applied to coupling beams, if either one of the following conditions is fulfilled:
a) Cracking in both diagonal directions is unlikely. An acceptable application rule is:
b) A prevailing flexural mode of failure is ensured. An acceptable application rule is: l/h > 3.
(3) If neither of the conditions in (2) is met, the resistance to seismic actions should be provided by reinforcement arranged along both diagonals of the beam, in accordance with the following (see Figure 5.12):
a) It should be ensured that the following expression is satisfied:
where
VEd is the design shear force in the coupling element (VEd = 2MEd/l); Asi is the total area of steel bars in each diagonal direction; a is the angle between the diagonal bars and the axis of the beam.
b) The diagonal reinforcement should be arranged in column-like elements with side lengths at least equal to 0,5bw; its anchorage length should be 50% greater than that required by EN 1992-1-1:2004.
c) Hoops should be provided around these column-like elements to prevent buckling of the longitudinal bars. The provisions of 5.5.3.2.2(12) apply for the hoops..
d) Longitudinal and transverse reinforcement should be provided on both lateral faces of the beam, meeting the minimum requirements specified in EN 1992-1-1:2004 for deep beams. The longitudinal reinforcement should not be anchored in the coupled walls and should only extend into them by 150 mm.
5.6 Provisions for anchorages and splices
5.6.1 General
(1)P EN 1992-1-1:2004, Section 8 for the detailing of reinforcement applies, with the additional rules of the following sub-clauses.
(2)P For hoops used as transverse reinforcement in beams, columns or walls, closed stirrups with 135° hooks and extensions of length 10dbw shall be used.
(3)P In DCH structures the anchorage length of beam or column bars anchored within beam-column joints shall be measured from a point on the bar at a distance 5dbL inside the face of the joint, to take into account the yield penetration due to cyclic post-elastic deformations (for a beam example, see Figure 5.13a).
(1)P When calculating the anchorage or lap length of column bars which contribute to the flexural strength of elements in critical regions, the ratio of the required area of reinforcement over the actual area of reinforcement Asreq/As,prov shall be assumed to be 1.
(2)P If, under the seismic design situation, the axial force in a column is tensile, the anchorage lengths shall be increased to 50% longer than those specified in EN 1992-11:2004.
(1)P The part of beam longitudinal reinforcement bent in joints for anchorage shall always be placed inside the corresponding column hoops.
(2)P To prevent bond failure the diameter of beam longitudinal bars passing through beam-column joints, dbL, shall be limited in accordance with the following expressions:
a) for interior beam-column joints:
hc Y Rd • fyd 1 + 0 75kD •P' / pmax b) for exterior beam-column joints:
hc Y Rd • fyd where hc is the width of the column parallel to the bars; fctm is the mean value of the tensile strength of concrete; fyd is the design value of the yield strength of steel;
vd is the normalised design axial force in the column, taken with its minimum value for the seismic design situation (vd = NEd/fcd-Ac);
kD is the factor reflecting the ductility class equal to 1 for DCH and to 2/3 for DCM;
p' is the compression steel ratio of the beam bars passing through the joint;
pmax is the maximum allowed tension steel ratio (see 5.4.3.1.2(4) and 5.5.3.1.3(4));
YRd is the model uncertainty factor on the design value of resistances, taken as being equal to1,2 or 1,0 respectively for DCH or DCM (due to overstrength owing to strain-hardening of the longitudinal steel in the beam).
The limitations above (expressions (5.50)) do not apply to diagonal bars crossing joints.
(3) If the requirement specified in (2)P of this clause cannot be satisfied in exterior beam-column joints because the depth, hc, of the column parallel to the bars is too shallow, the following additional measures may be taken, to ensure anchorage of the longitudinal reinforcement of beams.
a) The beam or slab may be extended horizontally in the form of exterior stubs (see Figure 5.13a).
b) Headed bars or anchorage plates welded to the end of the bars may be used (see Figure 5.13b).
c) Bends with a minimum length of 10dbL and transverse reinforcement placed tightly inside the bend of a group of bars may be added(see Figure 5.13c).
(4)P Top or bottom bars passing through interior joints, shall terminate in the members framing into the joint at a distance not less than /cr (length of the member critical region, see 5.4.3.1.2(1)P and 5.5.3.1.3(1)P) from the face of the joint.
A anchor plate; B hoops around column bars
Figure 5.13: Additional measures for anchorage in exterior beam-column joints
5.6.3 Splicing of bars
(1)P There shall be no lap-splicing by welding within the critical regions of structural elements.
(2)P There may be splicing by mechanical couplers in columns and walls, if these devices are covered by appropriate testing under conditions compatible with the selected ductility class.
(3)P The transverse reinforcement to be provided within the lap length shall be calculated in accordance with EN 1992-1-1:2004. In addition, the following requirements shall also be met.
a) If the anchored and the continuing bar are arranged in a plane parallel to the transverse reinforcement, the sum of the areas of all spliced bars, EAsL, shall be used in the calculation of the transverse reinforcement.
b) If the anchored and the continuing bar are arranged within a plane normal to the transverse reinforcement, the area of transverse reinforcement shall be calculated on the basis of the area of the larger lapped longitudinal bar, AsL;
c) The spacing, s, of the transverse reinforcement in the lap zone (in millimetres) shall not exceed s = min {h/4; 100} (5.51)
where h is the minimum cross-sectional dimension (in millimetres).
(4) The required area of transverse reinforcement Ast within the lap zone of the longitudinal reinforcement of columns spliced at the same location (as defined in EN
1992-1-1:2004), or of the longitudinal reinforcement of boundary elements in walls, may be calculated from the following expression:
where
Ast is the area of one leg of the transverse reinforcement; dbL is the diameter of the spliced bar; ^ is the spacing of the transverse reinforcement;
fyld is the design value of the yield strength of the longitudinal reinforcement; fywd is the design value of the yield strength of the transverse reinforcement.
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