The Reconstruction of Pennichuck Junior High School

1
The Reconstruction of Pennichuck Junior High
School

• 170 Days from Collapse to Occupancy
• presented by

Architect BanwellArchitects Design
Engineers Rist-Frost Shumway Consulting
Engineers Foley Buhl Engineers Construction
Manager Fulcrum Associates, Inc.
2

• On March 10, 2001, the roof over two classrooms
  at Pennichuck Junior High School collapsed under
  the weight of a recent snowfall. Subsequent
  investigation of the roof system identified
  numerous flaws in the roof system.
• A decision was made to replace the roof system in
  its entirety. The design and construction team
  was charged with opening the school on August
  28, 2001. It was an ambitious date, but through
  the efforts of the designers, construction
  manager and hundreds of dedicated tradesmen and
  women, we made it. This is how we did it.

3
The Design Challenge
The roof frame consisted of two truss halves
joined in the middle, and supported by the
exterior walls and interior classroom corridor
walls.
4
The Design Challenge
Bottom chord of truss to remain
Acoustic ceiling grid to remain
Mechanical and electrical chase
In order to meet the demanding schedule, it was
critical to protect and reuse the mechanical and
electrical systems to the greatest extent
possible. Most of these components were located
above the acoustic ceiling attached to the
underside of the truss
5
The Solution
Continuous shoring installed through ceiling grid
and supporting bottom chord of truss.
It was determined that the existing ceiling along
with the mechanical and electrical infrastructure
could be safely supported using continuous
temporary shoring to allow the removal of the
roof frame.
6
The Solution
Once the shoring was complete, the roof structure
could be safely removed to make room for the new
trusses. After the trusses were installed, the
ceiling would be reattached to the new truss.
7
Shoring and Bracing
Shoring is in place prior to removal of the roof
frame. As anticipated, this preserved most, but
not all, mechanical and electrical systems for
reuse.
8
Truss Removal
Once the truss bottom chord was braced, the
trusses were supported overhead by crane while
they were being cut free from the ceiling below.
9
Truss Removal
Once free, roof sections were hoisted from the
building to the parking lot.
10
Truss Removal
There, a waiting demolition crew cut the section
up and placed it in dumpsters.
11
New Truss Installation
New trusses were flown into place one at a time
as soon as a section was opened up.
12
New Truss Installation
New roof
Old roof
To minimize the possibility of water damage,
installation followed removal closely.
13
New Truss Installation
Once in place, trusses were anchored, braced and
sheathed. The existing ceiling was attached to
the new truss bottom chord.
14
New Truss Installation
Existing ceiling supported from below
15
New Truss Installation
In the area where the roof collapsed, there was
no existing ceiling to salvage. All systems and
finishes required replacement.
16
New Truss Installation
Existing roof
New roof with waterproofing
New roof with sheathing
17
Truss Bracing
Considerable attention was paid to permanent
bracing of the roof structure. The engineers
report identified inadequate bracing as a major
contributing factor in the collapse.
18
Truss Bracing
Bracing at the end wall required a maze of
intersecting members.
19
Roofing
After the trusses were sheathed, new asphalt
shingles were installed over the entire roof.
20
Removal of Shoring
With roofing complete and the ceiling supported
by the new roof frame, the shoring was removed to
make way for interior repairs.
21
System Upgrades
Many systems needed to be upgraded due to changes
in the building code. Fire alarm and ventilation
systems were substantially modified to meet new
requirements.
22
Completed Classrooms
Most classrooms received new ceiling tile, new
tile floors and a fresh coat of paint. The
classrooms in the collapsed area received all new
furniture and casework.
23
Wall Reconstruction
While demolishing walls in the collapse area, it
was noticed that masonry walls were not grouted
as required by design. This hole shows
reinforcing bars, but no grout.
24
Wall Coring
Using a combination of electromagnetic detection,
coring and visual borescope imaging, over 2,000
required reinforcing locations were investigated.
This example lacks grout and reinforcing.
25
Wall Coring
This example has reinforcing, but no grout.
26
Video Wall Cavity Investigation
This video image was taken inside one of the wall
cavities. The reinforcing was present, but the
cell was not grouted. Because there were several
variations of the problem (grout without rebar,
rebar without grout and no grout or rebar), as
well as differing performance requirements, there
was no single design solution.
27
Interior Walls
Interior walls only needed to be reinforced
against uplift. One of the solutions was to
install threaded rod from the top of the wall,
grout in place, and anchor at the top of the
wall. Here you can see the rod in place and
grouted.
28
Interior Walls
The threaded rod is then secured to the truss
bearing plate at the top of the wall.
29
Interior Walls
Over 1,000 bags of fluid grout mix was pumped
into wall cavities.
30
Interior Walls
Walls of 12 masonry afforded more room to get
traditional reinforcing in from the mid-point
without having to disturb the top of the wall.
Here, reinforcing has been installed through
access holes, then grouted solid. Decorative wall
panels will be applied to conceal the holes.
31
Interior Walls
In areas where it was not possible to gain access
to the wall cavity, flat straps were applied to
anchor the top of the wall to the foundation
below.
32
Exterior Walls
Reinforcing of exterior walls was more difficult
because the walls needed to withstand wind loads
in addition to uplift resistance. After
exploring dozens of solutions, the design team
settled on an exoskeleton of steel columns and
channels.
33
Exterior Walls
Vertical columns spaced on 8 centers are welded
to continuous horizontal channels, which are
bolted to the top of the wall. The base of the
column is anchored to the foundation wall,
providing the necessary uplift resistance as well
as transmitting wind loads to the foundation
system.
34
Gable End Walls
Channels cut to receive rebar and grout
The height of the gable end walls presented yet
another design challenge. Using the same
exoskeleton as the low walls would have required
larger columns spaced more closely. In these
areas, removal of the veneer brick allowed
installation reinforcing.
35
Gable End Walls
Here, grout is being pumped into the wall
cavities. The channel openings have been sealed
off with plywood forms.
36
Construction Facts

• Over 30 miles of lumber used for trusses and
  bracing.
• Over 35,000 hours of labor in 12 weeks.
• Over one acre of asphalt shingle roofing.
• Over 1,000 bags of fluid grout pumped.
• Over one mile of masonry walls inspected and
  reinforced
• Over 2,000 inspection holes drilled in masonry
  walls