DRAFT CONCEPT DESIGN REPORT UNIVERSITY OF CALGARY ...

8.5 Structural
� Overview
The McKimmie Library Tower, Block and Link represent three distinct structures due
to differences in their original design and construction. The Tower structure is
largely able to accommodate a multitude of uses and occupancies while meeting
current building codes, but is limited in flexibility with respect to modifications of the
existing structure. The Block is similarly able to accommodate a multitude of uses
and occupancies to meet current building codes, but is somewhat flexible in
accommodating revisions to the existing structure. This may include removal of
some columns and floor slabs to created two storey spaces, and relocation of stairs
and elevators. Finally, the Link is a much smaller structure that has negligible
additional capacity to accommodate revisions to use and occupancy, revisions to
the structure, or to meet current building codes.
� Tower
The McKimmie Library Tower consists of primarily cast-in-place concrete
construction. Concrete floor slabs span over concrete beams and joists, which in
turn span from perimeter concrete columns to the interior concrete core. This interior
core contains the elevator shafts, concrete stairs and mechanical shafts. This
central core also provides the lateral load (wind and seismic) resistance of the
structure. The perimeter columns protrude beyond the edge of the floor slabs, and
taper from larger columns at the base to smaller columns at the top of the building.
The concrete construction and the limited number of vertical load carrying elements
in the Tower limit the potential for significant structural modification. However, this is
largely compensated as the lack of columns does leave an open floor plate that
allows flexibility for architectural and interior design.
The Tower’s original design loading for a typical floor slab was 7.2 kPa (kilopascals),
which is equal to150 psf (pounds per square foot). This is a relatively high loading
that was due to the use as a library, and the high floor loading that results from
stacking of books. For comparison, a typical design loading for an assembly use is
4.8 kPa, and for administration and office areas a typical design loading is 2.4 kPa.
Additionally, it has been proposed that the existing pre-cast concrete exterior panels
be replaced with a lighter curtain-wall system. This combination of factors serves to
decrease the expected vertical loading on the existing core, columns and foundation
piles for a re-purposed Tower when compared to the original design.
This reduced loading is important when investigating the lateral stability of the
Tower under seismic conditions. The lateral stability of the Tower is provided by the
concrete walls that form the central core. Seismic design requirements as specified
by National and Provincial design codes have increased significantly in recent
editions, and are currently much more stringent that was the case during the original
design of the Tower. Increased lateral loading on the Tower structure translates to
increased loading on vertical structural elements (columns and core walls). Of
particular concern are the foundation piles. The foundations are the lowest loadbearing
elements in a structure, and as such vertical loading is compounded to its
highest degree. Additionally, foundation piles are very difficult to access should any
reinforcing work be necessary. A preliminary lateral stability analysis of the Tower
indicates that the increased vertical loads due to seismic loading applied per current
building codes is offset by the reduction in gravity loading due to revised use and
occupancy and a lighter building envelope. The only seismic upgrading of the Tower
structure currently identified would be strengthening the lowest level of the core
walls, from the basement level to the underside of the main level. This could be
accomplished by either application of external steel bracing, or placing of an
additional thickness of concrete adjacent to the existing wall.
There is potential that the decrease in vertical loading on the Tower structure as
described below may actually cause the structure to rebound from the soil. This
would be realized as an upward vertical movement of the structure as load is
released from the soil at the foundations, and the soil elastically returns toward its
pre-loading location. The actual extent of this rebound would require further
investigation at the detailed design phase. However, it is not expected that the
overall rebound value would be a significant cause for concern. Of more concern
would be the potential for differential rebound. This may be caused by a non-uniform
reduction of the loading. This could then cause adjacent structural members to
move differentially and cause local structural damage. The best way to
accommodate this would be to conduct a carefully sequenced demolition of heavy
elements, particularly the existing pre-cast building envelope. The demolition would
be sequenced such that the reduction in load occurs uniformly across each
foundation pile.
The Tower has a structural steel framed mechanical penthouse on the roof level.
This penthouse could relatively easily be modified or re-constructed to
accommodate new mechanical equipment installed with the re-purposing of the
Tower.
� Block
The McKimmie Block structure consists of structural steel beam, joist and column
framing with concrete floor slabs. The current lateral load resisting system of the
Block consists of rigid frames formed by the beams and columns. The structural
steel construction will allow for simpler and more cost effective removal and
replacement of structural members.
The proposed re-purposing of the Block includes some significant structural
revisions, including removal of existing stair and elevator shafts and removal of
some columns to allow for larger classroom areas.
As discussed above with regards to the Tower, the Block will also be subject to
higher lateral loads due to seismic events as specified by current codes when
compared to the original structural design. This will likely require an upgrade to the
lateral load resisting system. It is proposed that this be accomplished by installation
of structural steel cross-bracing. This cross-bracing would consist of relatively slim
steel members, which would have some flexibility in its layout and location. The
bracing may be placed at the Block’s perimeter, forming part of a new building
envelope, or placed within interior walls. The interior walls at the large lecture
theatres and the mechanical shafts are likely locations.
This upgrade of the existing lateral load resisting system would allow for the removal
and relocation of elevator and stair shafts, as their lateral stability properties could
be made redundant. The existing shafts could be infilled with a typical floor slab
structure to become useable space.
CONCEPT DESIGN REPORT
UNIVERSITY OF CALGARY
MacKimmie Tower and Block I Repurposing and Renewal
8. CONCEPT DESIGN
Generally, columns can not be removed from exisiting buildings as the resultant
span between remaining columns will increase, often to double the initial span. This
requires an increased floor beam depth and strength. Additionally, this applies a
higher load on the remaining columns and foundations. The removal of columns for
the large classrooms in the Block is made possible by two primary factors. The first
is the reduction of the design live load on the floor slabs due to use and occupancy.
Similar to the Tower as discussed previously, the Block was originally designed for a
relatively high live loading of 8.1 kPa. It is expected that this may be reduced to 4.8
kPa for academic and student areas. The second factor is that the large classrooms
will essentially be two stories in height. This would result in the removal of large
portions of the existing second and third floors. Therefore, the longer spans resulting
from the removal of some columns are generally offset by the combined reduction in
live load and floor area. However, removal of the columns will require replacement
of the floor beams, both to accommodate the increased span and the slope of the
classroom theatre. From preliminary analysis, this is expected to be either a steel
beam or truss, approximately one metre in depth. Refer to Figures
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