Strengthened Concrete Beam Detailing In line with ACI Code

Clearly, the detailing of the bolstered concrete members is the important thing to good design and execution of labor on the website.That's the reason poor detailing of reinforcement makes the construction endure cracking, extreme deflection, and even collapse.

Reinforcements resist tensile forces. They could even be required within the compression zones to extend the compression capability, improve ductility, to cut back long-term deflections, or enhance the flexural capability for beams.

Added to that, they forestall cracking of concrete as a result of shrinkage and temperature stresses.

Lastly, totally different facets of bolstered concrete beam detailing based mostly on ACI Code is defined within the following sections.

Kinds of reinforcement in a beam

  • Major bars (backside steels)- take care of rigidity drive
  • Prime bars (anchor bars)-hold stirrups of their place
  • Reduce off bars- take care of rigidity forces
  • Stirrups with totally different spacing-tackle vertical and diagonal shear.

Hooked anchors

The perform of hooked anchors is the availability of extra anchorage when there's insufficient straight size accessible to develop a bar.

Generally, customary hooks described in ACI Code Part 7.1 utilized other than the case the place it's particularly specified.

The ACI customary hooks are as follows:

ACI customary hooks for major reinforcement

  • 180-degree bend plus 4db extension, however not lower than 65 mm at free finish of bar.
  • 90-degree bend plus 12db extension at free finish of bar.

Fig.1: Customary hook, 180diploma

Standard hook, 90degree

Fig.2:Customary hook, 90diploma

ACI customary hooks for stirrups

  • 16 bar and smaller, 90-degree bend plus 6db extension at free finish of bar.
  • 19, No. 22, and No. 25 bar, 90-degree bend plus 12db extension at free finish of bar
  • 25 bar and smaller, 135-degree bend plus 6db extension at free finish of bar.

Stirrup hooks

Fig.3:Stirrup hooks

seismic stirrup, 135degree

Fig.4:seismic stirrup, 135diploma

Minimal bend diameters

Customary bends in reinforcing bars are described by way of the within diameter of bend as a result of that is simpler to measure than the radius of bend.

The first elements which management the minimal bend diameter are feasibility of bending with out breakage and avoidance of crushing the concrete contained in the bend.

  • Diameter of bend measured on the within of the bar, apart from for stirrups in sizes No. 10 by No. 16, shall not be lower than the values in Desk 1.
  • Inside diameter of bend for stirrups shall not be lower than 4db for No. 16 bar and smaller. For bars bigger than No. 16, diameter of bend shall be in accordance with Desk 1.
  • Inside diameter of bend in welded wire reinforcement for stirrups shall not be lower than 4db for deformed wire bigger than MD40 and 2db for all different wires. Bends with inside diameter of lower than 8db shall not be lower than 4db from nearest welded intersection.

Desk 1 minimal inside diameter of hooks based mostly on the scale of the bars

Bar dimensionMinimal diameter
No.10 to No.256db
No.29, No.32, and No.368db
No.43 and No.5710db
db is the diameter of the bar

Inside diameter of hooked bar

Fig.5:Inside diameter of hooked bar


In beam detailing, the detailer or designer shall present sizes, spacing, location, and kinds of all stirrups which embrace open and closed stirrups. stirrups could also be vertical or inclined.

Various stirrup configurations

Fig.5:Varied stirrup configurations

Furthermore, the place the design requires closed stirrup for shear, the closure might include overlapped, customary 90finish hooks of 1 or two-piece stirrups, or correctly spliced pairs of U-stirrups.

Moreover, when the design requires closed ties for torsion, the closure might include overlapped, customary 135hooks of one- or two-piece ties enclosing a longitudinal bar.

Lastly, there are totally different strategies for anchorage of stirrups, however the most typical is to make use of one of many customary hooks as proven in determine Three and determine 4.

Improvement size (ld)

The event size (ld) is the shortest size of bar through which the bar stress can enhance from zero to the yield power (fy). It's totally different in rigidity and compression, and primary equation for every case are as comply with:

Improvement size in rigidity

Use the next expression to calculate improvement size in rigidity, however at least 30.48cm.

The place:

cb: issue that represents the smallest of the aspect cowl. the duvet over the bar or wire (in each circumstances measured to the middle of the bar or wire)

Ktr: issue which denotes the contribution of confining reinforcement throughout potential splitting planes.

: the standard reinforcement location issue to mirror the hostile results of the highest reinforcement casting place.

: coating issue reflecting the consequences of epoxy coating. The product of shouldn't exceed 1.7.

: reinforcement dimension issue that displays the extra favorable efficiency of smaller diameter reinforcement.

: issue reflecting the decrease tensile power of light-weight concrete and the ensuing discount of the splitting resistance, which will increase the event size in light-weight concrete.

(cb+ Ktr)/db equal to 2.5 if the results of (cb + Ktr)/db is lower than 2.5.

db: bar diameter

Atr: complete cross-sectional space of all transverse reinforcement throughout the spacing s.

n: variety of bars or wires being developed alongside the airplane of splitting

Consider improvement size equationInstancesValues
Horizontal reinforcement so positioned that greater than 30cm of contemporary concrete forged within the member under the event size or splice1.3
Different reinforcement1
Epoxy-coated bars or wires with cowl lower than 3db or clear spacing lower than 6db1.5
All different epoxy-coated bars or wires1.2
Uncoated and galvanized reinforcement1
No. 19 and smaller bars and deformed wires0.8
No. 22 and bigger bars1
For lightweight-aggregate concrete utilization0.75
when the splitting tensile power is specified, it is the same as fc’^0.5/1.8fct however no more1
for normal-weight concrete1

Improvement size in compression

improvement size will be calculated utilizing the best of the next formulation, but it surely shall not be smaller than 20.32cm.

ldc=(0.02fy / )db  Equation 3

ldc=( (0.0003fy)db  Equation 4

the place

ldc: improvement size in compression bars

fy: yield power of bars

db: bar diameter

Improvement of bundled bars

Particular person bar improvement size inside a bundle, in rigidity or compression, shall be that for the person bar, elevated 20 % for three-bar bundle, and 33 % for four-bar bundle.

Improvement Size ldh for normal hooks in rigidity

The event size, ldh, for normal hooks in rigidity is given as:

The place:

= 1.2 for epoxy-coated reinforcement

= 1.Three for light-weight combination concrete.

For different circumstances,  and   are equal to 1.0.

development length in end hooks

Fig.5:improvement size in finish hooks

Bar minimize off in beams and improvement size in flexural reinforcement

Bar minimize off in beams

Generally, reinforcements are supplied near the underside of beams in order to counter act tensile forces on the beam.

Furthermore, these reinforcements computed based mostly on most moments at mid spans and at face of helps.  these moments scale back in beam areas apart from mid span and help faces.

Subsequently, it's doable to chop off bars in zones the place they're not required. therefore, minimize off bars present financial benefits.

Nonetheless, bar minimize off shall be stored as minimal as doable to say no design and building complexities.

Moreover, it is very important lengthen the minimize off bars past minimize off level by improvement size (ld) to make sure enough bond between bar and concrete. Improvement size might be mentioned within the part under.

Lastly, the placement of factors the place bars are not wanted is a perform of the flexural tensions that outcomes from the bending moments and the consequences of shear on these tensile forces.

Cut off bars

Fig.6:Reduce off bars

Improvement size in flexural reinforcement in beams

In beams, improvement size is supplied at factors of vital stress. The vital stress factors in beams are Factors of most constructive and unfavorable moments are vital sections, from which enough anchorage ld have to be supplied.

Furthermore, vital factors are additionally at factors throughout the span the place adjoining reinforcement minimize off; persevering with bars should have enough anchorage ld from the theoretical cut-off factors of terminated bars.

Added to that, minimize off bars shall lengthen past the theoretical cut-off factors to withstand flexure for a distance equal to d or 12db.

Improvement of constructive second reinforcement

For easy members, minimal one-third of constructive second reinforcement and one-fourth of constructive second reinforcement in steady members should lengthen alongside the aspect face into the help.

These reinforcements in beams shall lengthen into the help no less than 152.3mm.

Improvement of unfavorable second reinforcement

Adverse second reinforcement in a steady, restrained, or cantilever member, or in any member of a inflexible body, shall be anchored in or by the supporting member by embedment size, hooks, or mechanical anchorage.

Moreover, no less than one-third the entire rigidity reinforcement supplied for unfavorable second at a help shall have an embedment size past the purpose of inflection not lower than d, 12db, or clear span /16, whichever is larger.

Anchorage of negative moment reinforcement

Fig.6:Anchorage of unfavorable second reinforcement

Typical reinforcement details of non perimeter beams with open stirrups

Fig.7:Typical reinforcement particulars of non perimeter beams with open stirrups

Typical reinforcement details of non perimeter beams with closed stirrups

Fig.8:Typical reinforcement particulars of non perimeter beams with closed stirrups

Typical reinforcement details of perimeter beams

Fig.9:Typical reinforcement particulars of perimeter beams

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