Industry Spotlight: The Structural Hierarchy Effect

July 18th, 2013

We don’t just build highways in construction; we often force people down them.
Truth is, we have all experienced the attitude of, “it’s my way or the highway.” The team player in us bristles at this claim and immediately communication starts to break down.

During coordination of the interstitial space or exterior skin, there is a dominant notion that the structural stays. All the other trades need to work around structural; it is top dog and cannot be challenged. For how long has this attitude been established? What drives the hierarchy of trades; is it size or importance? Here is the typical hierarchy I see on jobs:

  1. Architectural
  2. Concrete
  3. Steel
  4. Gravity Lines
  5. Mechanical Duct Work
  6. Mechanical Piping
  7. Plumbing
  8. Electrical
  9. Fire Protection
  10. Data Telecom

This hierarchy does work in getting building systems to fit and work as designed, but concrete and steel are not immobile and I should not get a pass during coordination. For years I have experienced the structural engineer and structural subcontractors absent during coordination meetings because we were on their highway. Forget the highway; in order for us all to share in the reward of successful coordination we need the entire design team and necessary subcontractors present.  

The benefit? TIME.

Typically our subcontractors attend in person and the Design Team calls in via GoTo. Instead of writing 30+ RFI’s from issues discussed in the meeting, they are discussed in real time and solutions are created with a think-tank group versus in a vacuum.

Below are some experiences my team and others have had working with great structural engineers and subcontractors:

Roof drains have high precedence because of slope and routing, yet they rarely go where the original intent indicates. Rather than spend weeks going back and forth we can get input from the architect, structural engineer and steel subcontractor adjusting the roof locations, the wall size that the drains are located in and the building exit.

Existing site conditions. These three words always cause stress and cost money. On one particular job, the existing conditions of the site required additional footing depth to meet the 30” frost depth coverage. During coordination, weeks before the concrete pour this condition was discovered, leaving ample time for planning. In addition steps were needed to maintain the coverage and provide an economical location of the steps for the owner.  Below are images of the site conditions and the original versus new layout.

Footing versus underground utilities often presents a best guess situation. Unless we have a 3D model or pipes with RFID tags we never know the exact location of the underground systems until they are unearthed. Where we connect in and how we route is often a field activity, but it impacts the construction document directions. When coordinating the underground utilities, having the structural engineer present allowed us to discuss either dropping certain footings or changing the size as in the case shown below where the spread of the footing weight would crush the storm sewer pipe.

Catwalks get the maintenance crew close enough to the MEPF systems to service them, which often leads to these systems going right through it. During the coordination of the project shown below, the effort took 4 weeks, but without design team and subcontractor collaboration it would have taken 10. It is not as simple as the structural engineer going back to the drawing board. The MEPF systems have changed during coordination with subcontractor input. Those changed models need to get into the hands of the design team to reevaluate the catwalk based on the latest information. The most complicated condition was a large exhaust duct cutting off the North loop of the catwalk (image 3). Some issues can be resolved in the meeting, some take weeks of calculations. The key is keeping the entire team in the loop (no pun intended).

Bracing keeps a structure rigid, but it cuts through duct and pipe like a knife. Thank goodness there are multiple options for bracing. In some situations it is the steel bracing for exterior skin, but in recent years the challenge is bracing interior walls. Whether it is king studs, door headers or diagonal bracing we need the structural engineer present to discuss options. Below is an image of walls (green) and duct (red) overlay that demonstrates the challenge in bracing certain internal walls.

Roof and floor joists are prime real estate when we have short interstitial spaces. We want to fit as much up there as possible. Among some challenges is VAV access. It is difficult to get a 36” clearance and the code is ambiguous between high and low voltage. A disconnect is possible for a smaller clearance, but it is not as high-quality as some owners would like. Coordinating the mechanical and structural prior to CD’s helps eliminate this issue.

Shear walls have a unique name. You would think they are transparent wafers for aesthetics. Yet they are the core strength of buildings. That most structural engineers prefer not be penetrated. Oops. We have to more times than not. Some walls turn into swiss cheese. Having the presence of the architect and consultants helps not only determine where we can go, the size of the opening but whether the shear wall is even necessary. Can we bolster another wall to compensate for the difference?

Hail to coordination meetings and the attendees who make it all work!

 

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About the Authors

Jennifer Lanzetti

Jennifer Lanzetti is the BIM Director for Jacobsen Construction and international construction company. With a passion for lean construction, the integrity of information and trusting relationships she understands the need for a different approach to construction. As a BIM advocate, she is a big part of an industry shift away from the ‘hard-bid’ mentality to an Integrated Project Delivery process.

Working with her team at Jacobsen Construction as well as owners and trade contractors she assists teams in 3D Spatial coordination, 3D Exterior Skin coordination, 3D Laser Scanning, 4D scheduling, 5D estimating, Virtual Mock-ups and other BIM tools. BIM presents many opportunities and challenges but is nothing short of a paradigm shift for the industry that has far reaching social, cultural, contractual, cost, and building performance implications.  If it is worth doing, she believes it is worth doing well with enthusiasm.

 

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