Aci 318-11 Boundary Elements of Shear Walls

21.9.6 — Boundary elements of special structural walls 21.9.6.1 — The need for special boundary elements at the edges of structural walls shall be evaluated in accordance a ccordance with 21.9.6.2 or 21.9.6.3 21.9.6.3.. The requirements of 21.9.6.4 and 21.9.6. also shall be satis!ed. 21.9.6.2 — This section applies to walls or wall piers that are e"ectively continuous from the base of structure to top of wall and designed to have a single critical section for #e$ure and a$ial loads. %alls not satisfying these requirements shall be designed by 21.9.6.3 21.9.6.3.. &a' (ompression )ones shall be reinforced reinforced with special boundary elements where

c in *q. &21+,' corresponds &21+,'  corresponds to the largest neutral a$is depth calculated for the factored a$ial force and nominal moment strength consistent with the design displacement u. -atio u / hw in *q. &21+,' shall &21+,' shall not be taen less than /.//0  &b' %here special boundary elements are required required by 21.9.6.2&a' 21.9.6.2&a' the special boundary element reinforcement reinforcement shall e$tend vertically from the critical section a distance not less /4V u than the larger of lw or Mu/4V 

21.9.6.3 — tructural walls not designed to the provisions of 21.9.6.2 21.9.6.2 shall  shall have special boundary elements at boundaries and edges around openings of structural walls where the ma$imum e$treme e$treme !ber compressive stress corresponding to load combinations 0.2f c. The special boundary element including earthquae e"ects E e$ceeds 0.2f  shall be permitted to be discontinued where the calculated compressive stress is 0.15f c . tresses shall be calculated for the factored less than 0.15f  fa ctored forces forces using a linearly elastic model and gross section properties. or walls with #anges an e"ective #ange width as de!ned in 21.9..2 21.9..2 shall  shall be used. 21.9.6.4 — %here special boundary elements are required by 21.9.6.2 or 21.9.6.3 &a' through &e' shall be satis!ed5 &a' The boundary element shall e$tend hori)ontally from the e$treme compression compression 0.1lw  and c/2 where c is the !ber a distance not less than the larger of c – 0.1l largest neutral a$is depth calculated for the factored a$ial force and nominal moment strength consistent with δu.  &b' n #anged sections the boundary element shall include the e"ective #ange width in compression and shall e$tend at least 3// mm into the web

&c' The boundary element transverse reinforcement shall satisfy the requirements of 21.6.4.2 through 21.6.4.4 e$cept *q. &21+4' need not be satis!ed and the transverse reinforcement spacing limit of 21.6.4.3&a' shall be one+third of the least dimension of the boundary element

21.6.4 — Transverse reinforcement 21.6.4.2 — Transverse reinforcement shall be provided by either single or overlapping spirals satisfying 0.1/.4 circular hoops or rectilinear hoops with or without crossties. (rossties of the same or smaller bar si)e as the hoops shall be permitted. *ach end of the crosstie shall engage a peripheral longitudinal reinforcing bar. (onsecutive crossties shall be alternated end for end along the longitudinal reinforcement. pacing of crossties or legs of rectilinear hoops h x  within a cross section of the member shall not e$ceed 3/ mm on center. 21.6.4.3 — pacing of transverse reinforcement along the length lo of the member shall not e$ceed the smallest of &a' &b' and &c'5 &a' 7ne+quarter of the minimum member dimension &b' i$ times the diameter of the smallest longitudinal bar and &c' so as de!ned by *q. &21+2'

 The value of s shall not e$ceed 1/ mm and need not be taen less than 1// mm.

21.6.4.4 — The amount of transverse reinforcement required in &a' or &b' shall be provided unless a larger amount is required by 21.6.. &a' The volumetric ratio of spiral or circular hoop reinforcement ρs shall not be less than required by *q. &21+3'

and shall not be less than required by *q. &1/+'.

&b' The total cross+sectional area of rectangular hoop reinforcement Ash shall not be less than required by *q. &21+4' and &21+'

&d' The boundary element transverse reinforcement at the wall base shall e$tend into the support at least ld , according to 21.9.2.3 of the largest longitudinal reinforcement in the special boundary element unless the special boundary element terminates on a footing mat or pile cap where special boundary element transverse reinforcement shall e$tend at least 3// mm into the footing mat or pile cap

&e' 8ori)ontal reinforcement in the wall web shall e$tend to within 1/ mm of the end of the wall. -einforcement shall be anchored to develop f y  in tension within the con!ned core of the boundary element using standard hoos or heads. %here the con!ned boundary element has sucient length to develop the hori)ontal web reinforcement and Av  f y   / s of the web reinforcement is not greater than Ash f yt  / s of the boundary element transverse reinforcement parallel to the web reinforcement it shall be permitted to terminate the web reinforcement without a standard hoo or head.

21.9.6.5 — %here special boundary elements are not required by 21.9.6.2 or 21.9.6.3 &a' and &b' shall be satis!ed5 &a' f the longitudinal reinforcement ratio at the wall boundary is greater than 2. /f y  boundary transverse reinforcement shall satisfy 21.6.4.2 and 21.9.6.4&a'.  The ma$imum longitudinal spacing of transverse reinforcement in the boundary shall not e$ceed 2// mm. &b' *$cept when V u in the plane of the wall is less than 0.03 Acv  λ f c0.5 hori)ontal reinforcement terminating at the edges of structural walls without boundary elements shall have a standard hoo engaging the edge reinforcement or the edge reinforcement shall be enclosed in :+stirrups having the same si)e and spacing as and spliced to the hori)ontal reinforcement.

!.10 — "rans#erse reinforcement for compression mem$ers !.10.1 — Transverse reinforcement for compression members shall conform to the provisions of 0.1/.4 and 0.1/. and where shear or torsion reinforcement is required shall also conform to provisions of (hapter 11. !.10.4 — %pirals !.10.5 — "ies  Tie reinforcement for compression members shall conform to the following5 !.10.5.1 — ;ll nonprestressed bars shall be enclosed by transverse ties at least