Deliberate Clashing in Urban Infill Projects

Written by Microdesk’s Architecture Solutions Specialist, Jason Stevens  
Originally published in Informed Infrastructure.

A partial 3D axonometric section portraying the representation of an existing railyard below, the structural platform built around it and the potential massing of a building above.

As urban populations grow and demand for housing increases, vacant or under-utilized land is at a premium leading to a rise in urban infill projects. These developments take advantage of huge facilities built in the last century such as transportation hubs and industrial centers.

In the United States and Europe, there are notable examples of ongoing urban industrial/transportation infill projects. Brownfield projects such as London’s Battersea Power Station begun in 2012, Kings Cross development in 2007, and Paris’ Rive Gauche project in 1995 are designed to infill the urban voids left by old industrial complexes in inner cities.

In other locations, metropolitan passenger railyards are also drawing interest. Although still very much in use, they occupy just a fragment of the hundreds of acres of prime real estate. Portions of these tracts are either not developed, or contain inactive industrial sites. These areas create open voids within our inner cities as well as opportunities. The trains at these sites provide a major mode of transportation for the daily commute of millions of people. Careful advance planning is essential because it would not be economically feasible to shutter these transportation services for lengthy periods during construction.

Developers, local governments and public entities can draw upon and evaluate the successes of transforming underutilized urban railyards. As New York City’s Hudson Yards, Pacific Park, and Sunnyside Yards projects are tested, proven and refined, cities including Washington D.C. with Union Station, Chicago with the South Loop and Philadelphia with Schuylkill Yards are studying their own plans for constructing around and over the tops of their railyards.

Planning Plus 3D Technology

A section of a typical train car, its dynamic or moving envelope and its clearance envelope.

Redevelopment of these types of properties is complicated. However, with the advent of new, accurate 3D modeling software, architects and engineers are able to replicate not only the existing site conditions of these railyards but also the complex transportation systems that use them. For example, think how and where a train moves along a track through a railyard. By merging those concepts with new structure and architecture built around and above railyards and deliberately clashing them, they can carefully plan and design these unique sites in an artificial 3D environment far in advance of construction commencing.

The purpose of utilizing technology to detect clashes in the design phase is to streamline the project process overall. The main difference from how Navisworks software is most often used in these examples is in mixing new and existing site elements. Usually, elements being clashed early in the design process are using hypothetical digital representations of the building design from multiple disciplines, i.e. structure/MEP/architecture and are easily modified if caught early enough. With an existing transportation system, this is not the case.

By using new mobile 3D laser scanning technologies, survey engineers are able to precisely measure and document existing site conditions. They can translate the generated point cloud data using Autodesk’s Recap software to visualize and ultimately recreate that geometry in CAD or Revit.

Designing for Deliberate Clashes

Left: a potential ‘clearance’ clash between train envelope and structural column, as opposed to a ‘hard’ clash where solid geometry might intersect. Right: potential ‘clearance’ and ‘hard’ clashes between train envelopes and structural beams.

With Navisworks’ clash detection analysis and using accurately modeled geometry from Revit, engineers can identify dimensions down to less than an inch revealing avoidable real-world conflicts between existing and new objects. An example of this deliberate clash detection is an existing moving train potentially colliding with a new structural column. Train designs are comprised of not only the physical cab we ride in, but also two invisible and hypothetical spatial offsets from the physical train. Other built objects should not enter these zones in order to avoid physical clashes.

These invisible clearance envelopes can be modeled as solid geometry in Revit and clashed in Navisworks. There is a static clearance envelope and a dynamic or non-static moving clearance that must be considered. When a train moves along a railway there is an expected but very slight ‘wobble’ centered on the train’s axles at the bottom to the top of the train cab. Something as unassuming as the XYZ coordinates of an existing, in-use train track can have a domino effect on everything above and around it. Studying these concepts digitally in advance is invaluable for the design process.

Using previous construction methods, this conflict would be discovered in the field manually. It would halt progress for weeks while the incident was documented and sent back to architects and engineers to study and modify the design to resolve the issue.

Identifying Fire Safety Issues

Another example singularly unique to constructing on top of railyards is fire safety. While these sites have been open to the air for the past 100-plus years, the concern has been minimal. With planning to enclose a railyard, the risks of fire and smoke ventilation need to be carefully considered to meet even the most basic of local fire codes, often requiring special variances of cities’ fire laws. Using computer simulations and the aforementioned accurately modeled building and site geometry, precise spatial areas can be calculated to analyze air volumes. This will guide planning for the complex ventilation systems required to safely enclose these spaces and build over the top of them.

Looking to the Future

A partial 3D axonometric section portraying the representation of an existing railyard below and structural platform built above and around it.

With advanced, detailed planning and phasing, construction costs and times can potentially be cut in half while the transportation systems experience minimal impact and continue to function normally. Compare Paris’ Rive Gauche redevelopment, which is still under construction more than 20 years later, with Hudson Yards’ whose first phase started in 2012 and is already complete. The difference in the progress of these projects is largely due to improvements in design software.

There are positives and negatives to using new technology to deliberately clash design elements before construction. On the negative side, there is a learning curve as with all new technology and periods of trial and error. On the other hand, the positives are cost and time savings if implemented early enough and incorporated into a project’s overall design and construction processes. The utilization of these technologies has only scratched the surface of their total potential impact on the construction industry.  The in-progress redevelopment projects have already demonstrated how technology accelerates construction. These projects bring construction jobs which spur local economies, deliver more modern housing and office buildings and expand the tax base by attracting world-class populations.