Clear-Span Rigid Frame Buildings Near Boulder

Column-free means every load in the building has to reach the ground through the frames and the footings at their edges, and the design effort goes into those two places. A rigid frame is a portal: the rafter and the column act together, and the haunch where they meet carries a large bending moment. At the base, the column does not just push down, it also pushes outward, and the foundation must resist that thrust.

Owners usually want the open interior for a practical reason. An aircraft needs room to turn, an indoor arena needs a clear playing field, a municipal shop needs to move large equipment without bumping a column, and a bulk storage building needs to maximize usable area. We build clear-span frames in steel, from modest 60 foot spans to long-span hangars, and we plan them as an integrated system of frame, foundation, floor and door.

Aviation work near Boulder and Longmont adds airspace and ownership rules that ordinary commercial projects do not face, and the planning for a typical aircraft hangar starts with those rules, not with the frame. We handle them early so they do not surprise the owner at the permit stage. A hangar owner also needs to know early whether the ground is leased or owned, because that decides who approves the design.

What the work includes

The scope begins with site preparation and foundations, often with grade beams or tie rods across the slab to resist frame thrust, then proceeds to frame erection, secondary framing, roof and wall enclosure, doors and the slab. We often finish with utilities and fire protection. Frame components are fabricated off site and arrive in sections sized for road transport, and splices are bolted on the ground before the pieces are lifted into place.

Tall door openings change the wall design considerably. A large bifold or hydraulic door needs headers, jambs and a tracked threshold, and the structure around it may require extra bracing. For the largest openings we coordinate the door supplier early so the framing is designed around the actual dimensions. The frame erection method is outlined in structural steel erection.

Airfields and airspace

Several public airports sit within the metro. Vance Brand Airport in Longmont has a 4,800 by 75 foot concrete runway, and the city says more than 40 acres on the southwest side of the airport are available for development or expansion. Erie Municipal Airport, serving the town of Erie, has a runway listed at 4,700 feet, and Boulder's municipal airport occupies 136 acres northeast of the city. Each is city or town owned, which means ground leases and design standards come from the owner before the building department reviews anything. See the Vance Brand Airport area for the Longmont site.

Height, setbacks, drainage and utility capacity all enter the leasing conversation. The city of Longmont notes that a preliminary planning study covers utility and drainage infrastructure and that it is willing to discuss development incentives with tenants, though specific zoning and lease terms should be confirmed directly. We help prospective tenants prepare a feasibility sketch before approaching the airport sponsor.

Frame design, wind and snow

Because a clear-span frame has few redundant members, the design loads must be right. In unincorporated Boulder County, snow loads come from the county map and wind speeds from the county wind map, with separate gust data for other risk categories. A hangar is often a Risk Category II building, but a public shelter or emergency facility can be classified higher, which increases both snow and wind loads.

Frost depth, drainage and soil conditions drive the footings, and the building official can ask for a geotechnical report. Because the thrust at the base of the frame is large, we use a structural engineer who specializes in these systems, and we have the foundation designer and frame manufacturer coordinate directly. If the project's ground conditions call for deep foundations, our work in deep drilled pier foundations applies.

Owners who need open space

Public agencies are a major source of clear-span work in the valley: cities and towns that own airports, school and recreation districts that need gymnasiums and field houses, and utilities with large vehicle or equipment bays. We serve government and public sector owners with documented bids, prevailing-wage procedures where they apply, and clear closeout records.

Private owners include general aviation tenants, aircraft maintenance shops, equipment dealers, recreation operators and agricultural users. For education institutions, the typical project is an athletic or maintenance building where the spans are long and the budget is fixed, so we look for the simplest frame that meets the use.

Planning the interior around the frame

We ask owners to define the interior before the frame is engineered: the widest vehicle or aircraft, door height and width, the crane or hoist loads, the mezzanine plan and the mechanical equipment. A hangar that must house a specific aircraft needs a tail clearance that dictates the eave height. A shop that will install an overhead crane needs frame columns designed for the crane reactions, which leads to crane buildings.

The floor is part of the plan. Hangar slabs need a slope to drains, radiant heat or heat-mat options, and joints placed to match the door tracks. Equipment bays need a heavier slab. We discuss each with the owner using sketches rather than catalog language, so choices are made once. Truck-heavy tenants look at truck terminals and cross-docks, which use many of the same ideas.

Define the opening first

Give us the span, door size and the use. We will return a frame concept with foundation approach, a cost range and the approvals your site is likely to need.

Questions Owners Ask

How wide can a clear-span building be?

Pre-engineered frames can span well over 100 feet, and custom steel frames can span much more. The practical limit is cost and the thrust the foundation can resist. We help owners find the span where the use is satisfied without paying for extra width.

Do airport buildings need a separate approval?

Usually the airport sponsor, which is the city or town, must approve the lease, the site plan and often the building design before the building department sees the permit application. Height near a runway may also require airspace review.

Why are tie rods or grade beams used across the floor?

They resist the horizontal thrust at the frame base so the footings do not spread. Whether to use them depends on soil, frame geometry and the owner's floor needs. We discuss alternatives with the engineer before the slab is finalized.

Can a clear-span building be expanded?

Yes, if planned in advance. The end frames are designed to be removed or replaced by interior frames, and utilities and foundations are sized for the future addition. This is cheaper than retrofitting.

How does snow affect the roof?

The county uses a ground snow load map, and drifting at roof steps or near neighboring buildings can increase local loads. We assess drift conditions with the engineer and avoid creating step conditions where possible.

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