Capstone: the pavilion roof and the pump house walls

The final lesson brings the course together. Priya asks Owen to assemble the design of the training pavilion roof and the pump house walls into a single design package for review: a load summary, a member schedule with every governing check, the connection and detailing decisions, the fire and durability measures, and the drawings and specification items that will make sure the building is built as designed. The review is the last chance to catch an error before the drawings go to tender, so the team checks not only the numbers but the assumptions behind them.

The design basis

The design basis records the codes, loads and materials, so that a reviewer can check every number against a stated assumption. For the pavilion and the pump house it lists the National Building Code edition adopted in Ontario, CSA O86 for wood and S304 for masonry, the importance category of each building (normal for the pavilion, post-disaster for the pump house, which serves the wastewater system), the specified snow load of 2.6 kPa, the wind pressures, the roof dead loads, and the materials: 24f-EX and 16c-E glulam, E1 CLT, S-P-F No.1/No.2 lumber, 20 MPa block with Type S mortar for \(f'_m = 10\) MPa, and Grade 400 bars.

Design summary

Sofia's last script collects the governing checks from every lesson into one table, so that the reviewer sees at a glance which members are close to their limits and why.

# Lesson 12: design summary for the training pavilion roof and the pump house walls (SI)
import math
checks = []
def add(member, check, demand, capacity, unit):
    checks.append((member, check, demand, capacity, unit))

# CLT roof panel, 3-ply 105 mm, 3.0 m span (lesson 4)
add("CLT roof panel", "bending", 6.08, 38.2, "kN.m/m")
add("CLT roof panel", "fire, 60 min", 2.08, 8.28, "kN.m/m")
# Glulam beam 175 x 532, 24f-EX, 9.0 m (lessons 2 and 4)
add("Glulam beam", "bending", 170, 216, "kN.m")
add("Glulam beam", "snow deflection (L/360)", 24, 25, "mm")
add("Glulam beam", "fire, 60 min", 61, 142, "kN.m")
# Interior column 175 x 190, 16c-E, 4.5 m (lesson 3)
add("Interior column", "compression", 153, 320, "kN")
# Beam-to-column knife plate, six 19 mm bolts in two rows (lesson 5)
add("Knife-plate connection", "bolts, perpendicular to grain", 75.4, 6 * 17.5, "kN")
# Pump house wall, 190 mm block, 15M @ 800 (lessons 8 and 9)
add("Pump house wall", "wind + P-delta, 1.25D + 1.4W + 0.5S", 4.01, 8.69, "kN.m/m")
add("Pump house wall", "wind + P-delta, 0.9D + 1.4W", 3.69, 8.07, "kN.m/m")
# Wash-bay shear wall, lw 7.2 m (lesson 10)
add("Wash-bay shear wall", "in-plane shear", 150, 371, "kN")
add("Wash-bay shear wall", "in-plane flexure", 900, 2944, "kN.m")

print(f"{'Member':24s} {'Check':38s} {'Demand':>8s} {'Resist.':>8s}  Ratio")
for m, c, d, r, u in checks:
    print(f"{m:24s} {c:38s} {d:8.1f} {r:8.1f}  {d/r:5.2f}  {u}")
worst = max(checks, key=lambda x: x[2] / x[3])
print(f"\nHighest ratio: {worst[0]}, {worst[1]} at {worst[2]/worst[3]:.2f}")

# Roof quantities for the 18 m x 18 m pavilion: seven lines of beams at 3.0 m, two 9 m spans each
area = 18.0 * 18.0
clt_m3 = area * 0.105
glulam_m3 = 14 * 0.175 * 0.532 * 9.0
print(f"Timber volume: CLT {clt_m3:.1f} m3, glulam beams {glulam_m3:.1f} m3")
print(f"Timber mass at about 480 kg/m3: {(clt_m3 + glulam_m3) * 0.48:.1f} t")

Member                   Check                                    Demand  Resist.  Ratio
CLT roof panel           bending                                     6.1     38.2   0.16  kN.m/m
CLT roof panel           fire, 60 min                                2.1      8.3   0.25  kN.m/m
Glulam beam              bending                                   170.0    216.0   0.79  kN.m
Glulam beam              snow deflection (L/360)                    24.0     25.0   0.96  mm
Glulam beam              fire, 60 min                               61.0    142.0   0.43  kN.m
Interior column          compression                               153.0    320.0   0.48  kN
Knife-plate connection   bolts, perpendicular to grain              75.4    105.0   0.72  kN
Pump house wall          wind + P-delta, 1.25D + 1.4W + 0.5S         4.0      8.7   0.46  kN.m/m
Pump house wall          wind + P-delta, 0.9D + 1.4W                 3.7      8.1   0.46  kN.m/m
Wash-bay shear wall      in-plane shear                            150.0    371.0   0.40  kN
Wash-bay shear wall      in-plane flexure                          900.0   2944.0   0.31  kN.m

Highest ratio: Glulam beam, snow deflection (L/360) at 0.96
Timber volume: CLT 34.0 m3, glulam beams 11.7 m3
Timber mass at about 480 kg/m3: 22.0 t

The highest ratio, 0.96, is the snow deflection of the glulam beams, which is exactly what lesson 2 found: stiffness, not strength, governs the long timber members. Everything else sits between 0.16 and 0.79. The connection at 0.72 includes only the bolt path; with the beam also bearing on the saddle seat, the connection has two load paths. The masonry walls are lightly stressed, at 0.46 or less, because minimum reinforcement and detailing govern a building of this size.

Member schedule

The review

Owen presents the package and Priya works through her review list. It is the same list she uses on every timber and masonry project, and each item corresponds to a lesson in this course.

Loads and combinations come first: are the snow load and its drifting at the step between the pavilion and the taller garage accounted for? The pavilion roof is lower than the garage roof next to it, so snow can drift against the garage wall. Owen had used the uniform snow load; the review adds a drift check on the two beams nearest the garage, which pushes their deflection over the limit. Those two beams are increased to 175x608 (6-3/4 x 24). This is the kind of error a review is meant to catch: not a mistake in arithmetic but a missing load case.

Material assumptions come next: are the service conditions right? The salt shed posts were designed with dry-service values on the strength of a protective finish and an enclosed shed. Priya asks for a moisture survey of the existing shed before the design is final, and a note on the drawings requiring the finish to be maintained, because a design that depends on a finish depends on maintenance.

Connections and details: is every connection designed for the right direction of load relative to grain, and are bolts placed so that the wood can shrink? The knife-plate connection passes, with the bolts low in the beam ends and slotted holes in the plate. The drawings must show the bolt positions exactly, because a fabricator who moves them to the middle of the beam would reduce the splitting resistance by more than half.

Fire: the pavilion meets a one-hour rating without protection, but its connections must be concealed, so the saddles are recessed into the column tops and the bolt heads plugged. Durability: the column shoes lift the end grain above the slab, the CLT roof has a continuous membrane and the glulam is wrapped until the roof is closed in. Movement: the block walls have control joints, the annex veneer has expansion joints and the shrinkage gaps are shown. Inspection: the specification calls for field review of the glulam connections, of the masonry reinforcement before each grout lift, of the shear wall nailing and of the hold-downs.

Drawings and specifications

The design is only as good as the information that reaches the site. Timber and masonry drawings carry information that steel and concrete drawings often leave to shop drawings: the grade and appearance class of each glulam member and its camber; the moisture content of lumber at delivery; the nail sizes and spacings of every shear wall and diaphragm; the type and spacing of every hold-down and tie; the unit strength, mortar type and grout of every masonry wall; the location of every control and expansion joint; and the flashing and weep details. The specification adds the quality assurance requirements: prism tests for \(f'_m\), inspection of reinforcement and grouting, and protection of materials from weather.

The engineer of record reviews the shop drawings of the glulam fabricator and the CLT manufacturer, including the connection hardware, and the contractor's erection procedure, which must include the temporary bracing of the beams until the deck is fixed. Under Ontario practice the engineer also carries out general review during construction and reports on it to the building department.

During construction

The design does not end at tender. On site, the glulam and CLT arrive wrapped and are inspected for damage and moisture before erection; members with dents at the connection zones or with moisture content above the specified limit are rejected or dried. The masonry contractor builds a sample panel showing the units, mortar colour, joint tooling, control joint and flashing details, and the panel becomes the standard for the work. Cold-weather procedures are reviewed before the first block is laid, because the pump house walls will go up in November. The team keeps a record of every change, such as a fabricator's request to substitute a different bolt or hanger, and checks each one against the design basis before accepting it. Finally, the as-built drawings record what was actually built, so that whoever alters the buildings in thirty years knows what they are working with.

Choosing between timber and masonry

The phase 3 buildings show where each material fits. Timber suits the pavilion, a long-span, lightweight public roof where warmth, appearance, speed of erection and low embodied carbon matter, and the salt shed, where salt would corrode steel and concrete. Masonry suits the pump house and the wash bay, small, robust buildings where impact, fire, moisture and long maintenance-free life matter more than span. Both materials demand attention to moisture, movement and connections, and both reward designers who understand how they are made and built.

The timber volume Sofia's script reports, about 46 m³ (1,650 ft³) for the pavilion roof, stores very roughly one tonne of carbon dioxide per cubic metre, a rough rule for softwood, so about 40 tonnes (45 tons) of CO₂. The city's sustainability office will include it in its reporting, with the caveat that the full life cycle, including the steel, concrete and masonry in the rest of the project, needs a proper assessment.