Building information modelling is to date under used when it comes to designing and constructing in reinforced concrete. NCE outlines the benefits to be gained.
The debate on concrete or steel as the material of choice for construction projects will continue for years to come. However, the steel industry’s approach to design and fabrication has been consistently ahead of their concrete rival, through the use of 3D building information modelling software.
While the benefits of BIM software for steel may be more immediately obvious from a fabrication perspective, there are still many positive reasons to implement it on concrete projects as well.
Design versus construction BIM
BIM is still seen by many as a design solution, which sees it primarily used by architects and consulting engineers as a visualisation and design coordination tool. Design models will tend to concentrate more on aesthetic and structural design considerations than the practicalities of assembly. But for the construction BIM phase, specialist subcontractors and manufacturers then perform the detailed design, adding all the relevant detail required to physically manufacture and construct the project.
We are now able to 3D model and detail all of the concrete and rebar in a project, enabling a complete virtual prototyping of the planned design
Dr Sarah Williamson, Laing O’Rourke
However, for concrete projects the 3D workflow typically ends at the structural design stage, with detailed reinforcement design reverting to a traditional 2D process.
But that doesn’t need to be the case. For example, Laing O’Rourke has chosen Tekla Structures because it gives it the capability to rapidly model concrete, steel reinforcement, embeds and all construction detail in a 3D environment and then produce drawings and schedules directly from the model.
“At Laing O’Rourke we strive to improve processes and reduce rework through Digital Engineering, using modern technology in innovative ways, says Laing O’Rourke structural engineering leader Dr Sarah Williamson.
“We are now able to 3D model and detail all of the concrete and rebar in a project, enabling a complete virtual prototyping of the planned design, including reinforcement and the detection and elimination of clashes and associated construction problems.
In addition, these models are linked to the related data and can be used directly to generate production information in the form of machine readable cutting and bending schedules further improving efficiency, reducing errors and enabling our approach of design for manufacture and assembly.
“To do this we carried out desktop research, identified and engaged with potential technology providers, defined requirements, trialled, tested and evaluated potential solutions in terms of their ability to meet the technical requirements and technological readiness.
We are able to take a preconstruction model into estimating, logistics, and pricing very efficiently
Eric Lindquist, Tekla
“Tekla was chosen as the provider of the best overall technical solution and because of their demonstrable capability and willingness to work with us to improve and configure the software to meet our specific needs.”
If a change is made to the model, all associated outputs will update automatically, reducing the amount of manual work and checking that is required to update a set of disparate 2D drawings and schedules.
In addition, users can instantly see whether there are clearance issues with rebar embeds, voids or penetrations, removing the need for clash detection after the fact.
Model, plan, pour
The benefits of having a detailed digital model do not stop at the engineering and detailing phase. With the reinforcement fully modelled in 3D, the contractor can be sure that it will fit when the time comes to fix on site.
Using Tekla for example, intricate areas of reinforcement can be reviewed in detail as an accurate digital representation before it is ordered from the fabricator and complex cages can even be assembled off site.
The reinforcement fabricator can take data directly from the model to its machinery rather than relying on manual input from paper schedules.
Data from the model can then be passed to the field, allowing contractors to perform model-based layout using robotic total station devices and also track rebar and materials, identifying where and when they are required.
On site, the fixers can take a look at the rebar in the model environment, giving them an instant and clear appreciation of what is required, rather than relying on interpreting traditional 2D drawings.
Reinforcement is only one part of the concrete process. Specialist concrete contractors can draw a number of benefits from creating their own
In Tekla, users can create an accurate 3D model for quantity take off of elements, concrete and formwork, with the confidence that any changes made to that model will be instantly reflected in their bill of materials.
When the project is won, the model can then be taken beyond the estimating stage and not just discarded only for the same information to be re-created elsewhere in a different format.
Construction level of detail and a host of other data can be accumulated in the same model for use by the entire project team.
On site personnel can also use the model to plan daily work schedules, safe access routes, plant and crane positioning.
Tekla has also developed pour management capabilities, enabling contractors to break a model into individual pours and more accurately plan and manage concrete deliveries.
Lift drawings and complex section details can again be created instantly from the model and either produced on a drawing or visualised using the firm’s free collaboration software solution, Tekla BIMsight.
It is therefore clear that engineers, detailers, specialist subcontractors, main contractors and clients can all benefit from having a 3D digital model with construction level of detail for concrete projects.
Tekla customers all over the world are changing the face of concrete construction in their markets.
Take the United States, for example. Illinois-based concrete subcontractor Adjustable Forms typifies the approach there. It is using Tekla software to streamline many of its business functions.
“The ability to leverage the model for other uses is the primary benefit. We are able to take a preconstruction model into estimating, logistics, and pricing very efficiently,” explains project manager Eric Lindquist.
“Then when we are awarded work, we can leverage the model further into field coordination, shop drawings, and layout.”
“The possibilities keep expanding as the software and hardware improve.”
CASE STUDY 1:
PONT DU BOIS, CANADA
The spillway facilities at Pointe du Bois, a hydro power plant located on the Winnipeg River, approximately 160km northeast of Winnipeg, Canada, needed wholesale repair. The plant had been producing electricity for more than 100 years and the spillway required replacement to maintain dam safety and provide a modern and safe working environment for staff.
The owner Manitoba Hydro chose KGS Group to design this innovative project, and KGS selected Tekla Structures as the optimum tool to perform cast-in-place concrete modelling and deliver construction drawings.
The replacement posed unique challenges for KGS as the Pointe du Bois Spillway involved major earthworks. Since it was a replacement project, it needed to take into account existing structures in order to ensure the replacement spillway fit perfectly. The team used several topographic models from
Autodesk’s Civil 3D as well as scans and point clouds for planning. As a result, they were able to cut the underside of concrete pours to match the terrain accurately.
Pointe du Bois Spillway Replacement was KGS Group’s first cast-in-place reinforced concrete project designed and detailed with Tekla Structures. A team of just three users, two of them new to the software, completed steel reinforcement and concrete modelling, drawings and schedules while the experienced steel detailing department took care of structural steel requirements. As a result, KGS modelled every single piece of reinforcing steel with Tekla Structures. The software allowed KGS to accurately model the reinforcement, allowing the identification of potential clashes or mistakes early in the design process.
“At KGS, we benefited from the effective, full-blown modelling approach. We had control over the contents and precision in the model”, says James Tapper, KGS’ Tekla administrator. “As a variety of disciplines added numerous components to the model, clash detection proved to be the biggest benefit. KGS’ team solved many problems in the design stage, which saves a lot of time and money compared to finding fixes on site.”
So while there were clear advantages for the engineering team in this case, the construction level of detail in the model also benefited the contractor by reducing the likelihood of costly issues in the field.
SPILLWAY REPLACEMENT FACTS
● Cast in place components include 30,000m3 of concrete and 145t of reinforcing steel
● Estimated total cost of the project $300M (£186M)
● The model includes everything for construction: concrete pours and curbs, electrical conduit, electrical cable trays, steel intake gates & stoplogs, waterstop profiles, all structural steel, all rebar and all embedded steel.
CASE STUDY 2:
LONDON BRIDGE STATION DEVELOPMENT
Work now underway at London Bridge has been described by Network Rail as “the most ambitious station redevelopment in a generation”.
Between now and 2018, London Bridge will be rebuilt in nine phases at a cost of around £400M, while the station remains operational.
Starting on the south west side, successive sections running the length of the station and about the width of three platforms, are being cordoned off, demolished and rebuilt.
The main contractor on the job is Costain, with reinforcing steelwork fabricated by Midland Steel.
Midland Steel tendered for the project last year after a search to find the most suitable 3D modelling software. The company chose Tekla to design the reinforcing steel and submitted the initial model as part of its pitch.
The centrepiece of the new station design is a huge street-level concourse, 70m by 150m, that will increase the space by two thirds, creating room for new stores and allowing passengers to access all of the station’s platforms from one place for the first time.
This feat will be achieved by raising the tracks at the station and supporting them on 24 reinforced concrete pillars and cross bars. Passengers will access the platforms by lifts and escalators.
With the project ongoing and given its complex nature, the revisions to the design are likely to stop only when the concrete starts pouring
Tony Woods, Midland Steel
The steelwork for the supports is unique as not one of the 451 reinforcing bars in each column is in the same angle, plane or orientation, making 3D modelling the only logical choice to ensure accuracy and constructability.
The software was critical to planning the project and bringing the models to fruition but also helped Midland Steel with the delivery process, proving to be both cost and time effective and a worthwhile investment to mitigate project risks.
The advantages of having a 3D reinforcement model for the London Bridge project were obvious during the detailing phase and beyond to construction. Tekla Structures is able to automatically identify where reinforcement detailed in the engineering drawings cannot be physically placed, saving significant time and countless revisions to the design and remedial costs in the field.
Additionally, the software is helping to coordinate frequent revision by all parties involved with the refurbishment, while maintaining a consistent model and continually updating schedules, drawings and other traditional 2D outputs in the background as changes are made.
All three parties use the software to highlight, annotate and alter the model, with any change immediately highlighted and identified for other users.
“With the project ongoing and given its complex nature, the revisions to the design are likely to stop only when the concrete starts pouring,” notes Midland Steet director Tony Woods.