Case Studies

Central Park Tower

 

 

The Central Park Tower in Broomfield Colorado provides excellent examples of measurable return on investment (ROI).

This case study reports how general contractor, The Weitz Company, combined Integrated Project Delivery (IPD) process to streamline the delivery of the entire structural system and maximise the use of data/deliverables that could be extracted from the fully coordinated building information models.

A Vision of Innovation
At the Weitz Company, deployment and use of Virtual Design Construction (VDC) and Building Information Modelling (BIM) is part of a corporate driven strategy of process innovation. This strategy is built upon owner-driven value creation, the minimisation of waste and effective cost/schedule control, using lean project management in combination with BIM technology.

Weitz initially committed to company-wide use of VDC/BIM in June 2007. Their initial implementation activities represented the standard use cases for BIM in construction, including coordination between the steel and mechanical sub-contractor’s existing 3D models for conflict detection. Early attempts to springboard past design coordination, in the 3D environment, revealed a variety of constraints, (for example, late arrival of information, inconsistency between models and drawing integrity, as well as the duplication of work between 3D and 2D environments).

These early efforts led the Weitz VDC–BIM team to make difficult decisions, such as abandoning various design/construction models and reverting back to traditional means and methods to continue work. As Chris Allen manager of VDC & Operational Excellence, explained:

‘Initially the technology was deployed without an inherent process understanding’.

In an effort to align their deployment of VDC-BIM with actual construction process, Weitz further identified opportunities that would yield greater benefits than the standard use cases for BIM in construction. This investigation led them to examine several areas that would yield immediate tangible benefits to both new and existing projects. The primary criteria were to reduce both cost and risk in operations, together with optimising schedule - without compromising quality.

Project Overview
Location – Broomfield, Colorado
Area – 305,331 square feet
Pursuing LEED Gold Certification
Height – 11 stories with 1 level below grade
Below Grade Parking Level: Precast horizontal system to CIP pilasters
Quantities

  • 2,849 cubic yards concrete
  • 358 tons reinforcing steel
  • 1,400 tons structural steel
  • 2,470 shop drawing sheets, 47 erection
  • 150,000 square feet exterior wall panels

The Delivery Model
Project delivery can be broadly summarised under two primary activities – Cast in Place (CIP) concrete and Structural and Miscellaneous Steel, including Glass Fibre Reinforced Polymer (GFRP) Exterior Panels.

Beyond simply establishing a corporate vision, Weitz seized the opportunity at Central Park Tower to streamline the delivery of the entire structural system and maximize the use of data and deliverables that could be extracted out of fully coordinated building information models. Doing this paved the way for Weitz to effectively mitigate the risk associated with the structure by ensuring design-to-construction coordination, maximising off-site fabrication, and facilitating ahead-of-schedule performance of the trades on site.

The delivery model was Construction Management (CM) at risk (as defined in the previous articles of this issue), incorporating IPD as a process perspective.

Progressing the model from design to construction
Structural Consultants Incorporated (SCI) was hired by Weitz to provide the design, drawings and modelling for both the structural and miscellaneous steel package and the exterior skin. Their scope went beyond design interpretation and constructability review to more effectively increase the benefits provided to the project.

SCI served as the IPD Structural Engineer. Figures 1 and 2 below show how the structural relationship network for the project changed from the traditional and illustrate the inclusion of an IPD Structural Engineer and Structural Design/Build Subcontractor. From a social standpoint, these team members were created to assist Weitz in bridging the critical gaps between the Architect and Engineer of record and the fabrication/construction teams

The Virtual Design and Construction Process
With the delivery model and structural relationship network in place, the project was able to effectively undertake a VDC-BIM deployment.

Using a fully co-ordinated building information model as a point of focus facilitates the VDC process and enables key project stakeholders (Owner/Developer, Design and Contractors) to share the same information at the same time in both a virtual and live environment.

This in turn enabled the benefits of the process to be fully realised. The key benefits can be summarised as follows:

• Earlier involvement in project – commitments made at Schematic Design phase
• Overlapping of design and construction activities
• An accurate structural model maintained throughout design/construction phases
• Extracted supplementary structural drawings from the structural model

BIM technology was deployed over the lifecycle of the project to perform and inform the following critical activities:

Design – Modelling of the entire structure including the exterior GFRP
Coordination - Designed and modelled all concrete embed plates for attachment of steel and precast
Detailing – plus full Constructability analysis
Fabrication – The model produced embed and formwork layout plus Grade Beam Rebar Shop Drawings
Erection/Place Work – Including comprehensive lift drawings

Project results and benefits
By adopting the aforementioned delivery model and process, the project realised significant benefits, some of which are summarised as follows:

1. Cast in Place
Comprehensive lift drawings were crucial to achieve the required quality, productivity and performance of the cast.

The model delivered drawings for individual concrete pours to aid field crews. Details provided included pour dimensions, concrete mix and volumes, placing equipment requirements, formwork considerations, finishing work, and location/quantity of the required embed, conduit and reinforcement material. This enabled easy adaptation of the programme to meet user requirements.

In standard construction projects, the number of embedded items (for example, lifts and stairs) in concrete pours can total thousands, while the number of reinforcing steel members is in the order of tens of thousands. The use of a single building information model facilitated accurate coordination of embeds and reinforcements realising tremendous benefits in comparison to the traditional error prone and fragmented process.

The results confirmed the benefits. There were practically no approval comments required from the EOR (Engineer of Record), the construction schedule was reduced by two weeks, 26.1% reduction of reinforcing materials (actual versus budget), waste of reinforcement materials estimated at 0.07% - and ZERO RFIs.

2. Structural and Miscellaneous Steel
SCI were responsible for design and detailing of structural steel superstructure and participated in design team meetings from the earliest phase. The structural model was designed for constructability and GRFP compatibility.

From the model it was possible to extract all supplementary contract documents and a detailed calculated data package similar to that summarised above for CIP.

There was continuous coordination of steel, CIP concrete, precast and GFRP panels. Structural and Mechanical/Plumbing models were coordinated at end of Design Development and then at two weekly intervals.

Timely correction of the model at all stages facilitated detailing work and resulted in a reduction of detailing hours from 1,600 to 1,050 (planned versus actual).

To support fabrication, there was a concurrent design/detailing process allowing seamless interaction between the construction and shop drawings. This advanced the fabrication start date by five weeks (56%) and the initial steel delivery time by eight weeks (50%)

All of this work impacted on the erection phase which produced only two RFIs and ZERO change orders in erection cost.

3. GRFP Exterior panels
Design, fabrication and erection of the GRFP panels were all enhanced by the interoperable BIM process.

The GRFP panel outline was modelled for coordination with the structural frame and this identified many conflicts that could be corrected before the design was handed over to the fabricator.

The model included x.y.z target coordinates for bracket locations of the GFRP panel connections to the structure. The automatically extracted erection drawings and survey data were interoperable with a total station to enable accurate placement on site.

Project ROI
The efficiency and value generated by the delivery model and process and interoperability of the technologies deployed were summarised by Weitz as follows:

CIP:

  • Two weeks off schedule
  • 21.6% of materials savings = $104,306
  • RFI Savings (compared to a similar project completed 12 months earlier) = $97,549 - $161,549

Steel:

  • Eight weeks off schedule
  • $49,000 reduction in detailing costs
  • $250,000 materials savings
  • Two RFI + ZERO Change Orders

In total – 10 weeks off the schedule and >$500,000 reduction in costs.

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