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Home arrow Archives   The American Surveyor     

A New Star Over Milan Print E-mail
Written by John Stenmark, LS   
Friday, 05 December 2008

A 1.730Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

Innovation and precise surveying bring complex architecture to life. They are meant to impress. Designed by cutting-edge architects, today's office buildings, commercial complexes and public buildings are taking on new and exciting forms. With glittering facades and compelling interior spaces, they communicate the prestige and confidence of their occupants. Today's new buildings are futuristic and gorgeous. They are designed to be an important part of a business's image.

The new architecture presents a completely new challenge for surveying engineers. The complex designs and shapes must move from the architect's design system onto the construction site, where materials, costs and schedules are the driving forces. The work requires sophisticated computation and modeling, aggressive quality control and close interaction with construction contractors and suppliers.

To address the opportunity, the engineering bureau IU Plan in Hachenburg, Germany, has developed practical solutions using cutting-edge measuring and software technology from Trimble. IU Plan has combined high-accuracy surveying with software solutions used in road construction and civil engineering planning to support a new specialty. It's called Digital Facade Surveying, and it's opening a lot of doors.

IU Plan applied this expertise during the construction phase of the new Mercedes-Benz Sales Centre in Milan. Planned as their largest sales center in southern Europe, Mercedes-Benz wanted the Italian center to stand out. In addition to housing sales, service, parts depot and customer support activities, the new building needed to impress. It does.

There is nothing simple about the project. The footprint of the three-story building is 600 x 413 feet. Offices and showrooms are arranged around the `brand core'­a conical structure that dominates the front of the building. It houses several vehicle showrooms, conference areas, even a cafe. A multi-functional event area offers room for up to 2,000 people. The customer service area, workshop and parts storage occupy the west side of the building. The basement contains an underground garage, mechanical equipment and facilities for vehicle preparation. Constructed in just 21 months, the building was handed over to the owner in autumn 2007. "This was the highlight of the year 2007 for our bureau," confirms Jürgen Weber, a director of IU Plan.

The brand core is the centerpiece, designed as an inclined cone truncated to produce a flat, circular floor and roof. It is 62 feet high and tapers from a diameter of 62 feet at the base to 56 feet at the top. The vertical axis is inclined by 13 degrees and the center of the circle of the roof is offset by 14.3 feet from the center of the main floor. The structure is built of cast-in-place concrete with steel girder construction for the roof. The exterior (and many interior surfaces) of the building is covered with custom-fabricated panels made of glass and aluminum, and a curved roof connects the brand core with the rectangular building wings behind and to each side. To project the MercedesBenz brand "feel," the design required tight joints between the panels and very high quality overall. For Weber and the IU Plan team, the project was a real challenge. They had done projects involving cone-shape facades­ notably for a wastewater treatment plant in Munich. But this one was much more complex, involving the unusual geometry of an asymmetrically inclined, truncated cone, plus exacting tolerances for measurement and construction.

The tight tolerances were on everyone's mind throughout the project. The facade panels would have horizontal and vertical spacing of 3/8 inch along all joints. Yet there was less than 3/16 inch of adjustment once they were mounted in the frame. Both the initial survey and the stakeout work had to be exactly correct.

Calculations
The architectural and design work was done using CATIA (ComputerAided Three-Dimensional Interactive Application) developed by Dassault in France. Initially developed for aerospace design, CATIA has found a home in architecture, notably the complex curvilinear designs of many new buildings. The calculations for the survey work were done using Trimble Geomatics Office software. IU Plan used the coordinate geometry and road alignment functionality in Trimble Geomatics Office to compute the points needed by the survey crews. Weber's team transferred information from CATIA to Trimble Geomatics Office using DXF and DWG files. The data transferred smoothly, although CATIA does not support layer structures common in AutoCAD files. And Weber noted that the point IDs in Trimble Geomatics Office were lost when the data arrived in CATIA.

The building was defined on a conventional rectangular grid with intervals of 17.2 feet. Center points for the cone were defined relative to the grid. One center point was set at the center of the base of the cone. The second was defined at the top of the cone, including the offset and smaller radius from the base. Initially, the base and top of the brand core were modeled as circles. But as the work progressed, those assumptions would need to change.

A series of axes was computed running up the exterior walls of the cone. A total of 48 axes were defined, with spacing of 7.5 degrees along the top and bottom rings. As the axes moved around the cone, their inclination changed as a function of the offset distance between the center points of the floor and ceiling. The axes served as the baselines for inspections and as-built measurements. They would also become the lines for mullions supporting the panels of the finished facades. These calculations were repeated for the core's interior.

A staircase on the west side of the core presented further challenges. While it would appear to be parallel to the core, this structure had its own geometry. It was a different height than the core, and required different center points. By the time the calculations were complete, the team had defined 96 axes on the core structures that needed to be surveyed.

Surveying the Site
Two survey crews from IU Plan were assigned to the project. Equipped with Trimble S6 Total Stations and Trimble CU Controllers running Trimble Survey Controller software, the crews worked in parallel to gather detailed information about the building. As the rough construction was already in place, there was no need to tie to the local cadastral coordinate grid. Instead, the surveyors used a minimally constrained coordinate system referenced to the building itself. Points and markers for the coordinate system were constantly maintained and updated by the surveyors. As existing points were covered or destroyed by construction, new points were set into walls and floors and marked with waterproof labels.

With the concrete and steel framework for the building already in place, the crews focused on collecting details. They used surface and line scan routines to measure the building and cone structure. With the endpoints of the 96 axis lines on the cone already defined and stored in the data collectors, the crews could quickly scan each axis line along the entire height of the cone.

The predefined points and lines helped the crews catch any errors in the scans while still on site. Point separations between measured and computed lines provided information on the tolerances in the existing rough construction. Any incorrect entry of an axis line definition could be recognized immediately. "A host of functions for quality control were available even during the survey of the rough construction," says Weber.

In addition to the conic axis lines, the surveyors took measurements on all windows, doors, stairwells and other openings in the building. Additional measurements were taken on the structural elements such as wall and roof abutments and steel girders. Measurements were required in the interior as well as exterior of the building, and the construction project plan did not allow scaffolding. So the crews used hydraulic lift platforms to access these points.

Measuring the roof areas presented challenges in positioning the total stations. The team needed to place the instruments in a location that provided stability for the precision measurements, visibility to the points and security on the busy construction site. As construction progressed, insulation and finish surfaces were installed on the roof of the buildings. These soft surfaces made it impossible to set up the total station close to the core. So the surveyors placed the instrument on the roof of a wing of the building about 210 feet away from the roof of the core. In one instance, a crane hoisted a concrete slab three feet square and16 inches thick to the roof to provide a temporary, stable setup. Careful measuring procedures and the high accuracy of their Trimble S6 enabled the surveyors to complete the measurements to the required accuracy. Most of this work was done using the instrument in full robotic mode, with both members of the crew working on the roof or hydraulic platforms.

Mr. Weber stated that it was essential to have the pre-computed information available to the crews. They could quickly compare a measurement with a computed position, catching errors or blunders while still on site. "We anticipated difficulties even during the initial survey, for example while selecting where to place the total stations for measuring and marking out in the roof area," he says. But after transfer of the survey information into Trimble Geomatics Office, any incorrect detail points could be quickly filtered out.

3D Modeling
With the initial measurement data complete and checked, the surveyors produced 3D models of the rough structure. The models consisted of measured coordinates for the rough structure, building openings and break lines. The models let the teams determine the dimensions of the structure and compare to the initial design plans.

The 3D models were provided to Ebener Fassaden-Profiltechnik GmbH in Bad Marienberg (Westerwald), Germany. Ebener used the models to fabricate the 283 panels that covered the cone. The panels varied widely in size with the largest at 48 square feet and the smallest at about six square feet. To fit the cone, the panels had to be curved, with radiuses decreasing as they moved higher up the structure. There was not any single 90-degree angle to be found anywhere. Each panel had a different shape and dimensions, and it was imperative that the 3D models from the surveyors were accurate. Using the tools in Trimble Geomatics Office, the IU Plan team carried out visual and analytical inspection of the data before passing it on to the fabricators.

The smooth flow of accurate data from the construction site to the production facility is crucial when constructing with prefabricated facade sections. Using the data supplied by the surveyors, Ebener's fabrication facility could design, fabricate and finish the panels in a process that takes about four weeks. Working indoors with CNC machines and specialized tools, the panels are assembled faster and with better precision than it could be achieved on site. The result is lower cost, higher quality, and faster installation.

Setting Out for the Panels
As preparation for the precise setting out of the joints and construction axes, the crews needed to measure the exact heights of over 320 attachment points for the panels. Because the axes ran up the sides of the cone, every change in height resulted in a displacement of horizontal position of the marking points. When this work was complete, IU Plan had coordinates for each point where the panels and their supports would attach to the structure.

A series of preassembled brackets would be attached to the top and bottom of the cone at the designated spacing. Using data and models from the initial surveys, the surveyors first marked the location for the mounting brackets at the top and bottom of each of the axis lines. After the brackets were installed, they marked the precise 3D location for the connection points on each bracket. The points had to have an accuracy of better than 1/8 inch. To assemble the frame, wires were stretched between the brackets, indicating the subsequent spatial positions of the joints or facade panels. As a troubleshooting exercise, IU Plan created some incorrect points for stakeout. The survey teams spotted the errors quickly and the work gained confidence. When working on the roof, the accuracy of the initial surveys paid off. Key setup points had been covered with insulation and had to be recovered so the connection points could be marked. Using the Trimble S6 in robotic mode, the surveyors reestablished exposed total station setup points for the construction.

The endpoints of the axes were now in place and installation of the fabricated panels could begin. To keep the lines straight, the surveyors marked points along the cone for the mullions, again using hydraulic lift platforms to access the high areas. The lack of scaffolding was helpful here, as the sight lines from the total stations to the working points could be kept clear. The entire process was repeated in the interior of the building. Panels for the interior facades required the same precision as the exterior faces.

Borrowing from road stakeout techniques, IU Plan utilized the station/offset method in marking many points. They ran into trouble when marking attachment points on the facade brackets in the ceiling. The marked points began drifting away from the center of the brackets, and would soon not fall on the brackets at all. The team found that the circular model used for the stakeout did not exactly match the values used in the design software. The single large circle needed to be dissolved into smaller circular segments that fit the plan and existing structure. It was recomputed and the station and offset work could resume. A number of points had been marked incorrectly based on the original circular model. The next day­in a driving rain­the crews fixed the incorrect markings and finished the layout. With the roof insulation already in place, the crew could not set the total station nearby. So they placed the Trimble S6 on the adjacent building wing and used robotic operation to complete the job.

On the roof, the arched roof met the sloping, curved walls of the cone. The panels from Ebener needed to fit precisely into the steel framework. To ensure a tight fit, IU Plan surveyed the core walls at 1.6 foot intervals, with each point taken at a fixed distance above the roof surface. The surveyors marked the attachment points for each panel and structural support on the steel girders. Even though this part of the work ran on schedule, the complexity was daunting. It was one of the most stressful parts of the project for the survey team.

The results are remarkable. The building is open for business and has achieved its goal of instilling the "Mercedes-Benz Experience" into their customers. The construction installation of the facade elements drew applause from the architects, project managers and clients. Jürgen Weber sees digital facade measurement as a welcome challenge. Despite­or perhaps because of­the accuracy and care required in the calculation and measurements, he sees it as an interesting change in the day-to-day work of surveying and planning.

The trend toward complex facades is continuing. Buildings are becoming even more imaginative and complex. In the United States, the Disney Concert Hall in Los Angeles and new Denver Art Museum are prime examples of how the new architecture is taking hold. Without the precise models created by digital surveying, constructing the facades of modern buildings would be possible only with complex and expensive craftsmanship. Providing accurate information and measurement services on these projects is a superb opportunity for new work and profits for surveying organizations.

John Stenmark is a writer and consultant working in the AEC and technical industries. He has more than 20 years experience in applying advanced technology to surveying and related disciplines. 

A 1.730Mb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

 
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