180
offset. In the corners of columns, bars are usually offset on the diagonal which requires that the offset be increased accordingly.
For any offset between column faces less than 3 in., the vertical bar shall be shop offset bent. When the offset is 3 in. (75 mm) or more, the vertical bars in the column below shall be terminated at the floor slab and separate straight dowels shall be provided.
Lapped splices
Typical arrangement of bars at a lapped splice is shown. Unless special details are provided on the engineering drawings, all column verticals to be lap spliced in square or rectangular columns must be shop offset.
There are no limits on the ratio of column cross-section dimensions.
However, reductions prescribed for slender columns effectively limit the minimum size of practicable columns. Tables exist for short columns with specific loads, sizes, shapes, reinforcement concrete strengths and eccen-tricities. A number of computer programs and software are available for structural design and detailing of concrete structures.
IV.3.2.2. Spirals Pitch or spacing of spirals should be given to the nearest quarter inch.
According to ACI 318-83 (revised 1986), the clear spacing between spiral turns should not exceed 3 in. (75 mm) or be less than 1 in. or 113 times the maximum size of coarse aggregate used. Spirals should be provided with 112
(37 mm) extra turns at both top and bottom. If necessary to splice a spiral, it should be done by welding or by a tension lap splice of 48db.
Minimum diameters to which standard spirals can be formed and minimum diameters which are considered collapsible are shown in Table IV.3 for various sizes of spiral bars (1 in.25·4 mm).
IV.3.3. Reinforced concrete walls IV.3.3.1. Introduction
Reinforced concrete solid walls
A reference is made to ACI-318-2000 version for concrete walls. Concrete walls are defined (Section 2.1) as elements, usually vertical, used to enclose or separate spaces. Minimum reinforcement requirements given for walls in Section 14.3 of the code apply to walls which are used to separate spaces and which function in the structure as compression members. The provisions of Sections 14.4 and 14.5 of the code apply to walls which function as compression members. It should be noted that all minimum reinforcement requirements for walls in Chapter 14 of the code may be disregarded ‘where structural analysis shows adequate strength and stability’ (Section 14.2.7 of the code).
The required analysis for flexural strength (ACI 318.1, Section 7.1) can be employed. Temperature and shrinkage reinforcement can be likewise reduced (ACI 318.1. Section 6.3). The design of such walls must be based on lateral forces or any other loads to which they may be subjected (Section 14.2.1). A rational method of design for walls subject to flexure or both flexure and axial compression is provided (Section 14.4). An empirical method of design for Table IV.3.
Minimum outside Minimum outside diameter which can diameter of collapsible Spiral bar diameter: in. be formed: in. spiral: in.
3/8 9 14
1/2 12 16
5/8 15 24
3/4 (special) 30 —
bearing walls with small moment (resultant compressive force within the middle-third of the wall thickness) is permitted (Section 14.5.1). The empirical design method is explained in detail (Section 14.5). Non-loadbearing walls whether precast or cast-in-place, ordinary reinforced or prestressed, must be designed by the rational method, taking into account all loading conditions (Sections 14.4, 16.3, and 18.1.3 of the code).
Special walls
Walls which principally resist horizontal shear forces (shear walls in low-rise buildings) in the plane of the wall and parallel to the length of the wall must conform to the requirements for shear (Section 11.10 of the code). Shear walls which resist forces from seismic accelerations must conform to the seismic requirements (Section A.5). Special requirements for walls designed as grade beams are provided (Section 14.7). In addition to the general provisions (Section 14.4) of the code, precast concrete wall panels must conform to requirements for precast concrete wall panels (Section 16.3). Cantilever retaining walls are designed for flexure under Chapter 10 (Section 14.1.2) of the code.
When bars larger than #5 are used, the minimum vertical and horizontal reinforcement must be increased 25% (Sections 14.3.2-b and 14.3.3-b of the code). The code does not require that minimum reinforcement be placed in the two faces of a wall (Sections 14.1.2, 14.2.7 and 14.4 of the code).
Table IV.4.
In single layer only* In both faces†
Thickness, Horizontal Vertical Horizontal Vertical h: in. p0·0020 p0·0012 p0·0020 p0·0012
* Bars arranged in two-way mat, usually centred in wall.
† Bars arranged in identical two-way mats, one near each face of wall.
Sheet No. IV.24 shows typical wall details. Note: when steel is placed in two layers, maximum spacing limitations apply separately, but minimum steel requirements () apply to the sum of steel areas in both faces. For wall panel detailing a reference is made to the separate section under precast concrete detailing in this text.
Different types of walls exist in order to perform different functions. The well knowns are lever retaining walls, area enclosure walls, exterior precast panel walls, tilt-up walls and cast-in-place walls for hydraulic structures. Such walls are subjected primarily to flexure or to flexure and relatively small axial compression loads with the resultant compressive forces outside the kern (eh/6) of the section and must be designed by the rational method (Section 14.4 of the ACI code 318-83 (revised 2000)). Design for shear forces perpendicular to the face of such walls must conform to the requirements for slabs (Section 11.11 of the ACI code 318-83 (revised 2000)).
182
TYPICAL WALL DETAILS SHEET NO. IV.24