July 01, 2016
As one of Iowa’s largest life care communities, Oaknoll Retirement Residence has served retired citizens in Iowa City, IA, since 1966. Providing independent and assisted living, as well as healthcare options, the Oaknoll community has experienced tremendous growth due to the wide variety of choices it offers.
As a true testament to its evolution, Oaknoll has completed two large expansion projects in the last decade, including the recent Oaknoll Spring Street expansion. Providing independent housing for 100 active seniors, this $46 million, six-floor, 69-unit addition is Oaknoll’s largest project to date, adding 235,965 square feet of usable space. A glass skywalk allows residents to safely and easily access the amenities in the main building year-round – including a movie theater, game rooms, a library, a coffee shop and an internet café – while also enjoying the sports pub, restaurant, art studio and exhibition area in the new Oaknoll Spring Street facility.
The expansion also gave the organization an opportunity to showcase its commitment to sustainable, environmentally friendly practices. Two levels of underground, climate-controlled parking not only provide protection for vehicles, but also reduce storm water runoff and the maintenance costs associated with snow removal, lawn care and leaf blowing.
Plenty of daylighting, along with energy-efficient LED lighting, radiant floor heating and a geothermal heating and cooling system, help keep residents comfortable, reduce long-term operating costs and maximize energy efficiency (not to mention the $900,000 energy rebate Oaknoll received from its local utility).
Structural steel also played an important role in the building’s green design. As one of the most sustainable building materials in the world, steel contains recycled content, and can be recovered and recycled again in the future. The structural steel used in the Oaknoll Spring Street project was also locally sourced, fabricated just a few miles from the jobsite. Although the building was designed using U.S. Green Building Council LEED principles, Oaknoll chose not to invest in the certification. (The use of steel would have provided LEED credits if the organization had decided to pursue it, however.)
The use of structural steel also helped solve several jobsite challenges, including the accommodation of 100-foot (and longer) spans, winter construction timelines and a skywalk with floor-to-ceiling walls of glass. Compared to precast beams, it was the more cost-effective material; it also provided more control over the building’s design, allowing flexibility with structural shapes beyond hollow core plank.
An Easy Choice
Oaknoll residents voiced their desires about the living and community spaces. They wanted to feel a connection to the outdoors while inside. This was accomplished through extensive use of large windows and public areas that flow from inside to outside.
The $1 million, glass-enclosed pedestrian skywalk is one example of how residents’ wishes were carried out – the skywalk reaches from the existing Oaknoll facility to the new addition, spanning two walkways and a two-lane street with parking. Situated in a residential neighborhood with houses on all sides, the goal was to complete the skywalk with minimal disruption to pedestrian and vehicle traffic – especially before and after school. Controlling impact on neighbors traveling to and from work, and children walking to and from school, was crucial in order to ensure a warm welcome from the surrounding community once the building was complete.
For design and fabrication, structural steel was an obvious choice to support the skywalk. As compared to other building materials, the steel could be fabricated offsite, delivered on a truck in manageable loads from just a few miles away, picked off with a tower crane and erected quickly so the street only needed to be closed for short periods of time.
With structural steel, the skywalk is able to accommodate directional and elevation changes between the existing facility and the new addition. The skywalk is hung from an upper girder, which supports the weight of the structure plus 100 pounds per square foot of live load on the walkway below.
Steel also provided flexibility in choosing connection types. Wanting to stay away from large concrete sections, the skywalk design had an ambitious vision: clean lines and an all-glass enclosure. Concealing connections was a key part of making this vision a reality.
Wide Open Spaces
To give residents and their families a place to gather, Oaknoll Spring Street wanted its upper-level meeting and community rooms to house as many people as possible with as few obstructions as possible. Structural steel beams and long span joists lend themselves to creating open spaces that minimize interior columns.
Perimeter columns were concealed within the exterior wall, which also helped open the interior spaces. Intumescent paint was used on steel column sections to provide fire resistance.
Because of the construction timeline, bad weather couldn’t slow the Oaknoll Spring Street project down. Steel was a natural choice that allowed the team to work through Iowa’s snow, rain and ice. The material’s inherent ability to resist damage from winter weather conditions, unlike cast-in-place concrete, meant that the project could forge ahead as long as there were no strong winds. Nothing had to be tented, nothing had to cure, and the steel beams could be erected despite below-freezing temperatures. Building through all four seasons in central Iowa also meant dealing with large temperature swings (-20 degrees F to more than 100 degrees F) on building materials that were not yet enclosed. Special connections were detailed to allow the steel beams to change length through the seasons and still provide integrity to the not-yet-complete structure.
Although structural steel was the star of the project, the Oaknoll Spring Street building used precast concrete as well. Through this project, valuable lessons were learned about erection stability when combining the two materials.
When beams are designed with loads from both directions, they work just fine. But if erection isn’t complete – for example, if erection must be stopped at a certain point before it’s finished – the beam or girder needs to be braced for potential rotational issues when the load is only on one side.
When the erection sequence drawings were established for the Oaknoll Spring Street project, some of the girders were only going to be loaded on one side – even though they’re designed to be braced with precast on both sides. To accommodate this in the erection sequence, temporary bracing solutions were used for interim stability and stiffness until all structural elements were assembled. Working closely with the contractor can help define the correct erection sequence so rotational issues associated with one-sided girder loading are avoided.
More than 100 16-inch-deep and larger tube steel beams were used – more than what would typically be utilized – so that the beam depth could be hidden within the depth of the floor slab rather than placing the beam below the slab. The floor-to-floor height and the floor-to-ceiling height limitations presented a challenge to find a structural system shallow enough to fit the space; the overall building height was limited due to City of Iowa City zoning and the U.S. Federal Aviation Administration (FAA) regulations on building height.
The system needed to allow the beam to be placed within the depth of the floor structure rather than below it. Using precast planks, the plank would typically be placed on top of the W-section, but that couldn’t be done in this situation. The team also wanted to steer clear of placing a precast plank on the bottom flange or putting an angle in the web of a W-section, which would render the system un-erectable. Instead, tube steel beams were chosen with bearing angles on each side.
Building for the Future
As Iowa City’s senior population continues to grow, the Oaknoll Spring Street addition offers a unique alternative to traditional nursing homes and assisted-living facilities. The expansion welcomed its first residents on June 29, 2015, and is now fully occupied.
The "Creating Home" article originally appeared in the July 2016 issue of Modern Steel Construction.