For example, the primary contractor decided to use components called
“PCs Corbels”—adjustable elements that connect floor girders to the
concrete load-bearing components. By using the PCs Corbels, it was
possible to use self-climbing forms and rapid continuous pours to
construct the concrete load-bearing elements and floor supports. The
self-climbing technology works without additional cranes because it
climbs independently by means of a hydraulic climbing system. But
the increased speed of construction placed special demands on the
"Due to the lack of space on site, prefabricated concrete elements were
installed directly from the delivery trucks,” Almesberger said. “This made
a multi-shift operation necessary from 6 am to 10 pm, 6 days per week.
In addition, special surveying tasks were required to watch for any
deformation or unexpected motion of the building under construction.”
IGL’s project managers Tina Sängerlaub and Alexander Stein had to co-
ordinate the on-site team of surveying engineers, technicians, assistants
and a construction technician. "In order to meet the project’s survey
demands and respond at short notice when required, we created five
survey crews,” said Sängerlaub.
Surveying equipment included four Trimble S6 robotic total stations
with Trimble TSC2® controllers and two Trimble DiNi® 07 digital levels.
The required accuracy for stakeout points was ±6 mm horizontal and
±5 mm in height. "Controlling the total stations remotely via the TSC2
controller significantly contributed to our fast, efficient measurements.”
Sängerlaub said. “Instead of being at the instrument, we could work at a
measuring point and quickly make necessary adjustments."
The surveying tasks for the IGL team started with the erection of
a geodetic control network of fixed points, created by transferring
control from the TaunusTurm coordinate system into the building. On
the basement floor, 12 points were determined using total stations and
analysis software. Control points on the ground floor were set up and
established as fixed points within the local construction site coordi-
nate system. These so-called “plumbing points” would be transferred
vertically as the building rose. With the measurements complete, the
surveyors could consider the field of points located on the building’s
foundation (concrete slab) as positionally stable and avoided the ef-
fect of surveying variations in the geodetic fixed-point field. After that,
continuous control surveys were carried out to check relative variations
between points and to investigate and compensate for significant
variations of the points.
Extending the local coordinate system to each new floor was necessary
during the entire construction progress. Starting from the plumbing
points on the ground floor, a surveying party transferred the horizontal
coordinates by means of plumbing onto the respective working level.
In addition, openings with a diameter of at least 15 cm (0.5 ft) had to
be left in the concrete surface directly through the plumbing points
and kept open during further construction progress. The introduction
of reference planes every 50 m (160 ft) helped minimize the influence of
surveying uncertainties in the progressing construction height.