Name : ____________________________ Date: ___________Course/Year: ____________________________ Rating:___________

GENERAL REQUIREMENTS OF REINFORCED CONCRETE STRUCTURES

I. Objectives:The students must be able to:1. enumerate the general requirements that apply to all concrete structures,2. explain the importance of bending of reinforcement and when bending should be

avoided,3. explain the importance of following the building code requirements

II. Discussions:

BAR SPACING AND CONCRETE COVER FOR STEEL:Steel bars are usually placed as close as possible to the outside surface of concrete members in order to be most effective in resisting flexure or to help in the reduction of surface cracking. The distance between the edge of the bars and the outside surface of the concrete is called the cover. General requirements for cover are as follows:

FOR BEAMS AND GIRDERS:X >diameter of main barsX > 1-1/3 x maximum aggregate size X > 1” (25 mm)Z > diameter of main bars, always

When not exposed to weather or earth, Z > 1-1/2” (40 mm)

When exposed to weather or earth, Z > 1-1/2” (40 mm), bars No. 5 (15M) or smallerZ > 2” (50 mm), bars larger than No. 5 (15 M)

Columns with spirals or tiesX > 1-1/2 diameter of vertical barsX > 1-1/3 x maximum aggregate sizeX > 1-1/2’ (40 mm)Z > diameter of vertical bars, always

When not exposed to weather or earth,Z > 1-1/2” (40 mm)Z > 1-1/3 x maximum aggregate sizeWhen exposed to weather or earth,Z > 2” (50 mm), unless local building code requires greater clearance

FOOTINGSX > 2” (50 mm) when side forms are usedX > 3” (75 mm) without side formsWhen exposed to weather or earth,Z > 2” (50 mm) (formed surfaces)Z or X is always greater than the bar diameter and exceeds 1-1/3 times the maximum aggregate size.

SLABS, WALLS, and JOISTSY < 3hY < 18” (460 mm)

Y > bar diameter Y > 1-1/3x maximum aggregate sizeY > 1” (25 mm)When exposed to weather,Z > 1-1/2” (40 mm), bars No. 5 (15 M) or smallerZ > 2” (50 mm), for bars larger than No. 5 (15 M)When not exposed to weather,Z > ¾” (20 mm), bars No. 11 (35 M) or smallerZ > 1-1/2” (40 mm), bars No. 14 and No. 18 (45 M and 55M)When S > 30” (750 mm), consider the joist as a beam

WALLSY < 5h (Temperature Reinforcement)Y < 3h (Main reinforcement)Y < 18” (460 mm)Y > bar diameterY > 1-1/3” x maximum aggregate sizeY > 1” (25 mm) When not exposed to weather earth,Z > ¾” (20 mm)When exposed to weather or earth,Z > 1-1/2” (40 mm), bars No. 5 (15M) or smallerZ > 2” (50 mm), bars larger than No. 5 (15M)

BENDING OF REINFORCEMENT

In various situations, it is sometimes necessary to bend reinforcing bars. Bending is done preferably in the fabricating shop instead of at the job site, and the bend diameters should be adequate to avoid cracking the bar. Bending of bars is sometimes done in order to provide anchorage for the bars. The code defines such a bend as a “standard hook,” and the requirements for the details of this type of bend are given in the following figure.

Minimum bend requirements

Requirements for standard hook

Standard hooks consist of one of the following:a.) A 180 degree turn plus an extension of at least 4 bar diameters. The extension

must be at least 2 ½ in. (64 mm) long.b.) A 90 degree turn plus an extension of at least 12 bar diameters.c.) For stirrups and ties, a 90 degree or 135 degree turn plus an extension of at

least 6 bar diameters. The extension must be at least 2 ½ in. (64 mm) long. The inside radius of bend shall at least 1 bar diameter.