Requirements for the recommended minimum distance between reinforcing bars in concrete structures
Requirements for the minimum distance between the reinforcement bars are given in section 10.3 of the joint venture 63.13330.2012 Concrete and reinforced concrete structures. The main provisions. Updated edition of SNiP 52-01-2003. (section 10.3 SP 63.13330.2018) [Russian building standards]
Why is it necessary to ensure a minimum distance between the rods in a reinforced concrete structure:
- ensuring the joint work of reinforcement with concrete;
- high-quality manufacture of structures (laying and compaction of concrete mix)
According to clause 10.3.5 (SP 63.13330.2012, SP 63.13330.2018), the minimum distance between the reinforcement bars should be:
1. Not less than the largest diameter of the rod!
2. When the rods are horizontal or inclined in one or two rows during concreting:
- for bottom reinforcement not less than 25 mm;
- for upper reinforcement not less than 30 mm;
3. With the horizontal or inclined position of the rods in more than two rows during concreting:
- for the bottom reinforcement of at least 50 mm (except for the rods of the two lower rows).
4. With the vertical position of the rods during concreting.
- not less than 50 mm;
5. Under constrained conditions, it is allowed to arrange the rods in groups — beams (without a gap between them).
In this case, the distances in the light between the beams must also be not less than the reduced diameter of the rod, equivalent in cross-sectional area to the reinforcement beam, taken equal to by the formula:
- dsi is the diameter of one reinforcing bar in the beam,
- n is the number of reinforcing bars in the beam.
Requirements for the recommended maximum distance between reinforcing bars in concrete structures
The requirements for the maximum distance between the reinforcement bars are given in section 10.3 of the joint venture 63.13330.2012 Concrete and reinforced concrete structures. The main provisions. Updated edition of SNiP 52-01-2003 [Russian building standards].
For longitudinal reinforcement
In accordance with clauses 10.3.8 — 10.3.10 SP 63.13330.2012 (SP 63.13330.2018), the maximum distance between the axes of the rods of longitudinal reinforcement is:
1. in reinforced concrete beams and slabs:
- no more than 200 mm — with a cross-sectional height h≤150 mm;
- not more than 400 mm or 1.5 h — with a cross-sectional height h> 150 mm;
2. in reinforced concrete columns:
- no more than 400 mm — in the direction perpendicular to the plane of bending;
- no more than 500 mm — in the direction of the bending plane.
3. In reinforced concrete walls:
- no more than 400 and no more than 2t (t- wall thickness) — between the bars of vertical reinforcement;
- no more than 400 — between the rods of horizontal reinforcement.
- In beams and ribs with a width of more than 150 mm, the number of longitudinal working stretched rods in the cross section must be at least two.
- In beams and ribs with an element width of 150 mm or less, it is allowed to install one longitudinal rod in cross section.
- In the beams, the rods of the longitudinal working reinforcement with a cross-sectional area of at least 1/2 the cross-sectional area of the rods in the span and at least two rods should be brought to the support.
- In plates, the rods of the longitudinal working reinforcement should be brought up to support per 1 m of plate width with a cross-sectional area of at least 1/3 of the cross-sectional area of the rods per 1 m of plate width in the span.
For transverse reinforcement
In accordance with clause 10.3.11-10.3.20- SP 63.13330.2012 (SP 63.13330.2018), the maximum distance between the axes of the rods of longitudinal reinforcement is:
Transverse reinforcement is installed on all surfaces of reinforced concrete elements, near which longitudinal reinforcement is placed.
It is established with the aim of perceiving efforts, as well as restricting the development of cracks, holding longitudinal rods in the design position and securing them from lateral buckling in any direction.
The diameter of the transverse reinforcement (clamps) in knitted frames of eccentrically compressed elements (columns, racks, etc.) take at least 0.25 of the largest diameter of the longitudinal reinforcement and at least 6 mm.
The diameter of the transverse reinforcement in knitted frames of bent elements (beams, crossbars, etc.) is taken at least 6 mm.
In welded frames, the diameter of the transverse reinforcement is not less than the diameter established from the conditions of welding with the largest diameter of the longitudinal reinforcement.
Maximum distance for transverse reinforcement:
- not more than 0.5 h0 and not more than 300 mm — in reinforced concrete elements in which the transverse force cannot be perceived by concrete only by concrete.
- not more than 0.75 h0 and not more than 500 mm — in beams and ribs with a height of 150 mm or more, as well as in often-ribbed slabs with a height of 300 mm or more, in areas of the element where the transverse force is calculated only by concrete.
- can not be installed — in solid slabs, as well as in often-ribbed slabs with a height of less than 300 mm and in beams (ribs) with a height of less than 150 mm in areas of the element where the shear force is calculated only by concrete.
- not more than 15d and not more than 500 mm — in eccentrically compressed linear elements, as well as in bent elements in the presence of compressive longitudinal reinforcement necessary for the calculation in order to prevent buckling of longitudinal reinforcement (d is the diameter of the compressed longitudinal reinforcement).
- If the cross-sectional area of the compressed longitudinal reinforcement installed at one of the faces of the element is more than 1.5%, the transverse reinforcement should be installed in increments of not more than 10d and not more than 300 mm.
- The design of the clamps (transverse rods) in eccentrically-compressed linear elements should be such that the longitudinal rods (at least through one) are located in the places of the bends, and these bends — at a distance of not more than 400 mm along the width of the face. With the width of the face not more than 400 mm and the number of longitudinal rods at this face not more than four, it is allowed to cover all longitudinal rods with one clamp.
- In elements subject to torques, transverse reinforcement (clamps) should form a closed loop.
- The transverse reinforcement in the plates in the punching zone in the direction perpendicular to the sides of the design loop is set in increments of not more than 1/3h0 and not more than 300 mm. The rods closest to the cargo area circuit are positioned no closer than 1/3h0 and no further than 1/2h0 from this circuit. In this case, the width of the zone of setting transverse reinforcement (from the contour of the cargo area) should be at least 1/3h0. It is allowed to increase the pitch of transverse reinforcement to 1/ 2h0. In this case, one should consider the most unfavorable location of the bursting pyramid and in the calculation take into account only reinforcing bars crossing the bursting pyramid.
- The distances between the rods of the transverse reinforcement in a direction parallel to the sides of the design circuit take no more than 1/4 of the length of the corresponding side of the design circuit.
- The transverse reinforcement provided for the perception of transverse forces and torques must have reliable anchoring at the ends by welding or covering longitudinal reinforcement, ensuring equal strength of joints and transverse reinforcement.
- At the ends of prestressed elements, additional transverse or indirect reinforcement must be installed.
h0 — working section height in m, calculated by the formula
h0 = h-a ‘, where
- h — section height in m
- a’ is the distance from the center of gravity of the tensile reinforcement to the nearest section edge
The working height of the section is the distance from the compressed face of the element to the center of gravity of the stretched longitudinal reinforcement (paragraph 3.22 SP63).