Overview
i)Bending-anchorage type shear reinforcement
(Stirrup) constructed for shear reinforcement in plate-type
concrete members (underground structures such as slabs,
foundations, walls, etc.) those have to be satisfied the
anchorage requirements presented in KDS 14 20 52 (4.4). This
is a typical process that takes a relatively large amount of
time and manpower at the construction site as an
installation rule that requires to surround the longitudinal
bending rebar (for shear reinforcement).
Meanwhile, other shear reinforcement methods that replace
Stirrups include ⅱ)Shear-head type , which
arranges steel-beams in a grid form, and
ⅲ)Enlarged-head type which was newly introduced
in Korean Concrete Institute's 2012 revised domestic
structural standards.
As a technology to improve the construction method of shear reinforcement, SRD (Shear Reinforcement of Dual anchorage) shear reinforcement of the enlarged head type that replaces bending-anchorage shear reinforcement (Stirrup) equivalently: Technology certification by the Korea Concrete Institute (2020)
SRD is used for shear reinforcement of plate-type members
such as concrete slabs, foundations, and walls, and the
shear performance of reinforced concrete members follows the
following general formula according to the concrete design
code- compressive strength
shear reinforcement amount
and placement interval s .
| SRD13 | SRD16 | SRD19 | note | |
|---|---|---|---|---|
|
cross-sectional area (m㎡) |
185 | 290 | 418 | SS275 |
| 144 | 225 | 324 | SM355A | |
| height(max) | · member size − concrete cover(min) | |||
| notation | · [ex] SRD13, SRD13@100, 3-SRD13@100 | |||
| other specifications | · SRDs of different sizes or strengths are specified separately | |||
Workability
In order to secure the shear reinforcement performance,
Stirrup must firmly surround the upper and lower bending
rebar at the same time according to design codes.
However, such reinforcing requirements are by no means a
simple task in the construction of plate-type members
(slabs, foundations, walls). In addition, this often leads
to friction between contractors, supervisors, and design
managers in the field on the method of reinforcement work.
The shear reinforcement method using SRD has the advantage of easily installing the SRD through post-installation (or sequential construction) after completing the construction of the upper and lower bending rebars. In addition, SRD has another very advantageous feature in the construction method that, unlike Stirrup, there is no need to surround the upper and lower bending rebars.Due to these characteristics, unlike when constructing Stirrup, shear reinforcing work using SRD greatly shortens the on-site placement process of rebar.
“Shortening process, Reducing costs”
In the reinforced concrete structure process, there is often
a need to shorten the work time due to delays in the
previous steps. In addition, in the recently changed
environment, on-site work processes such as rebar assembly
are facing increasing pressure on labor costs.
Therefore, such a solution to reduce labor and
construction costs by shortening the work time has become a
very important technical interest in design-construction VE.
Economics
Based on the standard market price “rebar processing and assembly” steps, the direct construction costs when using co-working Stirrup and when doing post-construction SRD are as follows. According to the existing ‘rebar processing and assembly’ unit-price standard, bending and shear rebar are compared per unit weight (ton). (In this case, shear reinforcement is usually about 10%)
In general, when Stirrup is replaced equally with SRD, material costs increase partially. ([ex] Material cost increases by about 12% compared to the existing direct construction cost)
In the case of post-construction with SRD instead of Stirrup, the labor cost of ‘rebar processing and assembly’ is lowered by 1-level from the existing ‘Type-Ⅱ’ to ‘Type-Ⅰ’, and the labor cost is partially reduced. ([ex] Labor costs for the ‘rebar processing and assembly’ process using SRD are reduced by approximately 10% compared to conventional costs)
In the "rebar processing and assembly" steps, Stirrup (B)
must surround the bending rebars (A), so there is an
inconvenience in the arrangement that requires two tasks to
be constructed simultaneously. This is a typical cause of
consuming a lot of field work-time in the rebar assembly.
In contrast, in the' steps using SRD(C), the bending
rebar (A) is first placed independently, and then in the
subsequent process, the SRD(C) is installed between the
placed bending rebars. And then tied, the rebar assembly
process is completed.
From the aspect of shortening the construction period, this
makes it possible to separate the shear reinforcement
process (B) from the main (critical path) and construct it
in a subsequent process. Accordingly, the main process work
time can be significantly shortened, and a distinct
construction period reduction effect can be expected.
Performance and Durability
The performance of shear reinforcement is ultimately
determined by anchorage features. (The examples below show
the characteristics of each anchorage type compared through
analysis data to evaluate the performance of various types
of shear reinforcement.)
Conventional bending anchorage methods such as ‘Stirrup’
correspond to ‘B’, and enlarged head methods such as ‘SRD’
correspond to ‘H’.As shown in the figure, it can be seen
that the enlarged head method (H) not only has the best
anchorage performance (=tensile force) but also has the
smallest slip (=minimizing crack width) compared to the
bending anchorage method (B)
Quotations : R. Beutel, J. Hegger / Germany / Cement & Composiete 24 (2002) 539-549
『Concrete Structure Standard Design Commentary KDS 14 20 22, 4.11.5 (1)』
~ According to the results of an experimental study (Joint
ACI-ASCE Committee 421 1999), the studs with mechanical
anchorage that are as close as possible to the top and
bottom of the slab effectively resist punching shear.
Compared to shear reinforcing bars with hooks at the ends,
the enlarged heads of shear studs have less slip, so the
shear crack width is relatively small.
The enlarged
head method has the advantage of stably maintaining the
performance of the structure even after cracking or peeling
of the structure due to the characteristic of stably
maintaining anchoring performance with little deformation
(slip) of the anchoring part.
· Plate-type concrete members such as flat plate slab, foundation, walls
· Shear reinforcement of concrete structures such as underpasses, subways, and tunnels (entrances and exits)
Shear reinforcement, SRD download
