The dramatic, curved architectural facade of 1200 Intrepid takes first place in ACI Excellence Awards
The American Concrete Institute (ACI) recognized High Concrete Group LLC at its annual ACI Excellence in Concrete Construction Awards. The precast company produced the innovative architectural precast concrete system for 1200 Intrepid, the office building that claimed the top prize in the Mid-Rise Buildings category.
1200 Intrepid won against an impressive group of 13 other outstanding entrants from the U.S., France, Canada, and Qatar. The award was presented at the ACI’s 2018 Awards Gala in Las Vegas, https://youtu.be/tjeEoFjj--U.
Location: Cincinnati, Ohio
Size: 236,000 sq. ft. – 8 stories, 5 stories above ground, 63,120 square feet of precast architectural cladding
Architect: Bernard Tschumi Architects
Architect of Record: glaserworks
Design Engineer: Arup Partners
Engineer of Record: THP Ltd.
General Contractor: Turner Construction Company
Owner: University of Cincinnati
A Dramatic Turn: The Richard E. Lindner Athletic Center
The Lindner Center is the focal point for the University of Cincinnati’s Varsity Village athletic complex. The project represents an innovative use of precast concrete to accomplish a design that, given its complexity, was unfeasible with other materials. Designed by Bernard Tschumi Associates of New York, and working with Glaserworks of Cincinnati, the Lindner Center in a dramatic infill project that consolidates all athletic functions and other facilities under one roof.
Striving to architecturally unify the many facilities of Varsity Village, Tschumi conceived of a unique boomerang-shape building that turns 90 degrees within an alley-sized space between a new arena and the school’s football field, creating in his words “a linchpin between athletics and academics.” This dramatic shape is “precise, muscular, eventful” and epitomizes UC’s athletic traditions. It is built on top of a smaller building that already occupied part of the infill space. The narrow site leaves room on either side for foot traffic and not much else.
The “Diagrid” and Project Complexities
The Lindner Center project brought to life a new frame design concept that Tschumi had had in development for several years. This idea was the “diagrid,” a latticework of diagonal lines converging to form a network of triangle-shaped windows. The diagrid was wrapped into the shape of the building, forming an exoskeleton that supports the weight of the building’s interior.
The Lindner Center has a dynamic feel, with a free-flowing ribbon-like exterior. The flowing lines sought by Tschumi were realized through the diagrid, but with a complexity that would challenge and ultimately stretch the envelope of precast concrete technology.
The design and construction team involved the precaster early on to ensure that they could achieve their aesthetic, cost, performance and schedule objectives.
On paper – in two dimensions – the diagrid had same-size windows all the way around. But in three dimensions it was a different story. The objects making up the diagrid became distorted as they conformed to the building’s boomerang shape. This created triangular windows of different sizes and curved returns. Adding to the complexity was a multiplicity of curves and radii to be captured and reproduced in a series of tight-fitting panels on the exterior.
Beyond the complex design, the building site presented challenges of its own. Two existing buildings – Nippert Field and the new Fifth Third Arena – flanked it on either side, limiting the staging area for the erection phase of the project. The site had a drop of approximately 40 feet. Further, the existing building over which the Lindner Center was to be built had to be kept open during the entire construction process.
Varsity Village Lindner Center Highlights (link to pop up)
The Lindner Center at Varsity Village features:
Demonstrating the Strength of a BIM Approach
Because all the project data was loaded into the model, users several steps removed from the project could import the details they needed to create steel forms. Drawings and dimensioning of members was simplified, and the model served as a trouble-shooting tool during erection.
However, the various programs also presented several implementation challenges. Normal checking conventions were no longer useful, and though the data needed to do the checking was in the model, the software did not have an appropriate utility built in. This meant independent checking was required using other software. File sizes prevented the model from being exported in its entirety, so spatial conflict review excluded details such as nuts and bolts which would become an issue on the job site. Model versioning also was important, as data updated in one program needed to be updated in another.
Critical to the project’s success was appropriate modeling expertise, and not only familiarity with the software, but also with the methods of creating and connecting precast concrete components. For everyone on the team, the drawings themselves were no longer the documents that determined how the building was to be built, but they were merely reports. A new way of thinking took root as the model was to be the place where all information was to be kept. If the data didn’t exist there, it wasn’t in the project.
Creative engineering and design—coupled with innovative forming and installation techniques developed during the design phase—made Varsity Village a reality. The application of BIM components to the Linder project demonstrated value in terms of cost, quality, and schedule. And, it was the only way practical way to accomplish such a complex, forward-thinking design.
BIM and Precast (link to pop up)
The BIM ideal is a single building information model for the entire construction industry that delivers:
BIM captures vast amounts of data early on, allowing designers and engineers to work together to fully interpret plans, foresee difficulties, and collaborate on ways to execute. . The software speeds information flow, facilitates the checking process, and smoothes typically contentious processes.
Possibly BIM’s greatest potential is in reducing uncertainty and cost by sharing information quickly and completely among owners, designers, contractors, fabricators, and suppliers. Precast is particularly suited to BIM because design, MEP, and other requirements already must be captured much earlier in the process. BIM amplifies the schedule compression advantage of precast by reducing the lead time for components, and then further enabling the complex geometries of today’s leading designs.
Information Flow (link to pop up)
The Tschumi design team used 3D Studio Viz to present the concept and support early decision making. The diagrid was rendered in RAM Steel.
When the project was passed to glaserworks, Form-Z, a construction-accurate 3D modeling program, was used. The precast fabricator subcontracted with the architect to further define the model and translate it into 2D shop drawings using AutoCAD.
The Form-Z model was exported in dxf format and given to the mold manufacturer, who used AutoCAD Inventor to interpret the 3D model pieces and reconstruct them as parametric objects form which the molds were made.
The steel fabricator contracted to have the RAM steel model translated into Tekla X-Steel so the pieces could be detailed.
Conforming the Precast to the Design
The precast work began as the steel did, with the diagrid. The precast panels and covers were mapped onto the diagrid superstructure by the 3D software. Before the project began, the architect had mapped out the different types of precast panels required in 2D, and calculated the number of variations within each type for the bidders.
The 3D model was used to develop the specific dimension drawings for bid. The steel form manufacturer used the 3D model, including parametric data, to accurately create the steel forms and variations within them.
Because of the multiple curvature and helical warp unique to the columns, the column covers were handled by High Concrete directly. These panels required a much higher level of detail, such as diagonal dimensions, side form profiles and cross-section templates, to assure matching joints in helical multi-level “V” columns. The spandrels, too, had their own complexities with curved rear closure panels.
High Concrete created wood forms for the column covers, which were fewer in number and more complex than the panels. The column covers were cast in High Concrete's form shop. The accuracy of the form cross section at each end was checked by plywood template and/or diagonal dimensions. The templates were reused to cast any adjacent panels.
For approval purposes, High Concrete created mock ups based on the 3D model. The first mock up was fashioned out of foam and supplied early in the project for review and approval of the overall features and installation details of the production panels to follow.
While the foam mock up method was accurate, it proved to be unsuitable. Stripping the foam mold was too time consuming and messy due to the many negative draft surfaces created by the multiple curves and radii of the building design.
So for approval of shape, finish, and color, High Concrete produced a second mock up made from a steel form. Following approvals, this mock up was used by the window manufacturer to install and test their windows. Window water and air penetration tests were performed at High Concrete’s Springboro plant. After it passed, the test unit became a QC reference during panel casting.
Precast is Chosen
The Lindner Center’s exoskeleton had to have a smooth, consistent aesthetic while keeping the building water tight and thermally controlled. Early on, the structural engineer, Arup, determined that the metal panels originally envisioned for the building’s skin would not be suitable for the project. Though they were pliable to allow conformity to the building’s unusual curvatures, the metal panels would leave too many seams for water to leak through. The metal panels had another, more important disadvantage: high cost.
Instead, Arup chose precast concrete as the natural alternative because it had the ability to conform plus thermal mass to preserve the interior temperature. And costs were substantially lower.
Precast mixes can be designed, cast in a variety of shapes, and finished to closely match virtually any cut stone—from polished granite to limestone to marble. The Lindner Center was finished with light gray, light sandblasted precast concrete panels. However, unlike any precast project before it, the complex geometry of the Lindner Center required the creation of 145 unique shapes out of 567 total precast concrete panels.
Because of space limitations on site, there was limited staging room which made assembly of components difficult. This again played to the strengths of precast because the panels were fabricated off-site while the steel frame was erected, then brought on site for installation.
This project is LEED Registered with the US Green Building Council for LEED Certification. The architect of record, Glaserworks, is currently preparing the documentation for submittal to the US Green Building Council. The University of Cincinnati intends to apply for base certification.
Triangular Window Panels
The precast panels were made with one downward pointing triangle window in the middle. The sides of the panels and the bottom of the panel above framed the upward pointing triangle windows. To accommodate flat glass, and to facilitate their removal from the precast molds, the panels were designed with non-radial window returns. Panel bottoms had a curved, 30 degree slope.
Inside, windows were installed with two pieces of right angled triangular glass each, framed to form an isosceles triangle. Having two pieces of flat glass accommodated the building’s curvature while keeping control of costs. The frames were recessed 14 to 15 inches into each panel. Inverted flat-pane triangle windows are contained within the precast panels; upright triangle windows are fitted between the precast panels. Solid panels continued the triangular theme at the lecture hall auditorium and other areas requiring solid wall treatments.
“V” columns were a logical extension of the diagrid design theme, and minimized the number of columns required to support the structure. The columns were of differing lengths and some were lengthened and doubled as walkway supports on the west side of the building. Column covers completely enclosed the steel columns.
Since the spandrels cut across the curvature of the building, the dimensions of the plan cross-sections vary throughout their height to maintain their helical shape. The returns are planar surfaces and are not radial, to avoid warped surfaces and to provide adequate draft.
Fitting the Precast to the Diagrid
With the steel diagrid in place, the precast panels began arriving on site for staging and installation. Since the 3D model originated both the steel diagrid and the precast layout, the components were expected to match or be close enough that they could be adapted to fit. As a precaution, High Concrete tried to make all the panel connections easily adjustable. These drawings show the bolts, washers, and brackets used to affix the panels to the steel superstructure. However, connections inside the panel returns often required additional adjustment plates because the space between the fireproofed columns and the panel return was too tight to get a hand inside.
According to the bid specification, the precast panels were to be tilted up directly from the trailer when they arrived from the precast factory. Due to the top edge lifting stresses and the curved 30-degree slope at the base of most panels, High Concrete performed an erection test to verify that it could be done without cracking or spalling the panel. Most of the panels passed the test, through a few of the longer panels at the lecture hall auditorium required steel strongbacks for the tilt up to work successfully.
A Homemade Theodolite
Once lifted into place, the panels had to be securely installed. Due to the tight construction site, the large number of layout points, the alternating panel layout at each floor, and the curvatures involved, the precast fabricator developed a system and tool to expedite installation.
High Concrete obtained the coordinates for the layout points from the 3D model and furnished them to the erector’s surveyors. The layout points were marked on the steel superstructure. In open interior spaces where no floor was present, a ground laser marked the radial line when the panel was lifted into place.
To allow the crew to have direct control of the panel layout, High Concrete custom-made a panel alignment tool. The erection crew placed the tool over two survey marks that oriented the tool along the radial line at each panel joint. It projected over and through the column “X” intersection to locate the centerline and face of the panel joint on the far side of the steel column., enabling the crew to accurately locate the face of each panel at the joint when it was lifted into place. They loved it, calling it their homemade theodolite, and used it to install every panel around building’s perimeter. This method eliminated the need for a layout man on the ground and the communications involved.
How Spatial Conflicts Were Handled
Most of the steel beam splices are located at the mid-span, at the panel joint between the panel bearings. However, 30 splices were offset and fell directly under one of the bearings of the two panels that were to be installed there resulting in a clearance problem.
To allow the panels to be installed properly, the erection crew had to reverse the orientation of the top splice bolts and raise the panel bearings 2”. No alteration or remake of panels was required.
This spatial conflict existed in the 3D model, but was not found during conflict checking because the steel model was too large to import into the precast model fully defined with bolts and washers. Instead, the detailing practice and problem solving approach of the people involved. Because they Caught and corrected the fit-up error, 30 panels did not have to be remade.
A walkway steel conflict also was not fully defined in the 3D model. The adjusted walkway panels fit perfectly, as the model had predicted. However, the panels later had to be sawed to allow the finished walkway width dimensions to meet interior finish code requirements. Finer details such as connection problems and other interference may not be found until the time of installation.
After the panels were installed it became clear that the extreme geometry had created an effect unanticipated by the 3D model. The model had utilized curves that were not tangential and, as a result, a scalloped surface became evident in several panels at the southern end of the building, at the transition between curves. Visible only at certain sun angles, the scallop measures -4 degrees at the southeast elevation compound radius; on the southwest elevation a corresponding +7 degree scallop shows at the compound radius.