Detailing Cut and Bend Reinforcing Steel
Getting it Right First Time
Jan 14, 2020
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Wondering why the Cut and Bend ordered is different to what was originally quoted or requires modification to do the job?
We often get customer queries on why changes have occurred or requesting changes to what is supplied.
Our detailers observed some common reasons for change, which include:
- Initial detail is done from unconsented plans
- Errors & gaps in plans
- Gaps & errors in the specification
- Plans don’t align with site conditions
At United Steel we understand that designing and specifying reinforcing is not always straightforward, specifying everything upfront can be difficult and mistakes happen. We also appreciate, our attempts to communicate uncertainties in plans, and the assumptions we subsequently make in detailing, may not always be fully understood. This article looks to demystify some of this.
While there will always be a level of uncertainty, and the odd mistake by us all, we are always looking for ways to improve, and there is much to be said for check twice, measure twice and cut once.
In the remainder of this article we discuss examples of the above reasons for change and provide ways to minimise changes and uncertainty.
Initial detailing and quoting is often done from a combination of the architectural drawings and structural drawings. Inconsistencies in information can occur due to a lack of:
- coordination between the various parties working on a design. An example is shown below, where the architectural and structural drawings specify different types of mesh
- knowledge around the site-specific conditions, such the depth of hard strata, and the length & height of site retaining walls.
The consenting process often removes much of this ambiguity, although in some cases this uncertainty is not removed until work begins on site.
Architectural Drawing – Mesh SE73
|Structural Drawing – Mesh SE62|
The lack of knowledge around site specific conditions can affect the depth of the foundation, which impacts both starter and stirrup lengths, and in some cases can impact the number of bars in the footing. An increase in the number of bars in a footing, as shown below, can have a significant impact on cost, as this additional bar may be required around the full perimeter of the footing. Further discussion on site specific conditions and examples of uncertainty in starter and stirrup length can be found here
|Prior to Consent||After Consent|
We often find that plans we receive are incomplete, contain errors, or have issues with readability.
Some common issues observed include:
- Missing dimensions in foundation plans, such as lengths and widths of footings, and offsets such as Bay Window projections & those related to Concrete Stair levels or heights.
- Missing dimensions in sections of the foundation, such as the depths and widths of isolated or pad footings used to support columns, strip footings used to support walls and slab thickenings.
- Missing height dimensions, for items such as chimneys, retaining walls, windows, and step changes in floor level.
- Missing information for interfaces such as control joints or where an extension attaches to an existing building. This missing information can be either the location of the joint or the detail of the interface reinforcing.
- A series of incremental dimensions do not sum to the overall dimension provided
- Illegible hand annotated plans
- A mismatch between drawn and written information in the drawings and vice versa. Example shown below.
|Foundation dimensions missing in architectural drawing||Same foundation dimensions missing in structural drawing|
|Control joint indicated with no details||Illegible writing|
|Shows one but mentions two bars - 2/HD12||Top bar drawn but grade and diameter no specified|
|Mentions D10 stirrups but not drawn in footing|
Incomplete plans often result from an approach during the design process to complete the detail at a later time, but the intent to come back and finish the detail is forgotten. Common examples are window details, rebate details at openings, nib or raised threshold details, wing wall details and construction joint details in slabs.
Gaps and errors in the Specification
The drawn component of the plans, including the drawn reinforcing detail within these plans, only contain some of the information required to fully detail the reinforcing required. These plans are usually supplemented by written information either on the plans themselves or in a separate specification document, to define the type, shape and quantity of reinforcing.
The gaps and issues we have observed around the specification of reinforcing include:
- The spacing of the reinforcing and its components are not specified, this includes bar spacing, and the regular spacing interval required for starters, stirrups, and links. During detailing we will often make assumptions on the spacing of these items based on typical practice and state these assumptions in the detailing notes – see below.
- Inconsistencies between the drawn information and written information in the schedules or specifications – see below
|Assumptions required on bar type and spacing||Specification & drawing inconsistency|
The ground conditions, site-levels and existing building details are often not fully understood until more detailed investigations are done on site or even until construction commences.
The key issues we observe with the plans not aligning with the conditions on site, include
- The depth of hard Strata being unknown at the time of design, with the plans simply stating the foundation must bear on good ground and the dimensions of the foundation are subject to these ground conditions. The size & quantity of reinforcing cannot be fully determined until the depth of the good ground is determined. As is shown below this uncertainty can impact the height of both stirrups and starters.
- Heights and lengths of retaining & block walls, which often require assumptions to be made about dimensions by:
- taking the nearest measurement of a related structure and scaling
- scaling from site plans
- counting the standard dimensions of blocks & bricks
- taking the floor to floor heights
- using the maximum height where an embankment of retaining walls is specified – this results in an over estimation
|Uncertainty in stirrup height||Uncertainty in number of bars|
|Missing height - Counted Blocks||Missing height - Scaled|
|Maximum height details opted for external retaining wall|
With the need to estimate costs early in the build process it will not always be possible to resolve all uncertainty in the plans prior to quoting commencing. As a consequence, it is just as important to understand where the uncertainty lies in the plans, what assumptions have been made in detailing and quoting, and what can be done to remove the uncertainty.
To minimise changes and reduce uncertainty:
- Quote & order from consented plans. This should ensure dimensions in the architectural and engineering drawings align, which in turn should remove uncertainty in offsets, floor area and floor level
- Come back to us as soon as possible if we contact you with queries on the plans, and we will work together to resolve the identified uncertainties.
- Check C&B specified for retaining walls and block-walls with site specific conditions – we will provide a marked-up set of plans with assumed wall heights.
- We will send you annotated plans and notes after fully detailing an order, if we have remaining questions, have made assumptions or if missing information prevented detailing a specific aspect of the plans. A site visit may then be required to check assumptions and remove the uncertainty.
In some cases where the uncertainty cannot be resolved prior to delivery, we may supply straight or partially bent bar, with the instruction to make the final bend(s) on site. An example, where this could happen is where extra-long starters are supplied, or crank bars are supplied with one bend, and the remaining bend is put in on site once final dimensions are determined.