Irregular buildings shall have an engineered lateral-force resisting system designed in accordance with accepted engineering practice.
A building shall be considered
to be irregular when one or more of the following conditions occur:
a) When exterior shear panels or reinforced frame is not in one plane
vertically from the foundation to the uppermost story in which they are
required. (See Framed structure)
b) When a section of floor or roof is not laterally supported by shear panel
or reinforced frame on all edges.
c) When an opening in a floor or roof exceeds the lesser of 3.60m or 50% of
the least floors or roofs dimension.
d) When portions of a floor level are vertically offset.
e) When shear panel or reinforced frame is do not occur in two perpendicular
directions.
f) When shear panel or reinforced frame are constructed of dissimilar
bracing systems on any one-story level above grade.
3.2.1.3 Limit of this code.
When a building of otherwise
conventional construction contains structural elements, which exceed the limits
of this code, those elements shall be designed in accordance with accepted
engineering practice.
Fig A2-2 Trinidad & Tobago winds Table 1 Design pressure for winds Design
pressure
Trinidad
Central
Trinidad
Coastal
Tobago
Basic
wind speed
Km/hr
72
92
101
Wall
(horizontal load) kN/m2
0.70
0.90
1.00
Roof
(uplift) kN/m2
1.00
1.30
1.45
3.2.4 Live load.
Table 2 Minimum uniformly distributed
live loads
3.2.5 Roof load
Table 3 Minimum roof live loads
(kN/m2)
Roof slope
Tributary
loaded area for any structural members
Area (m2)
0 to 20m2
20 to 55m2
over 55m2
Flat or rise less than (20°) 33% slope
1
0.75
0.6
Rise (20°) 33% to (45°) 100%
0.75
0.7
0.6
Rise greater than (45°) 100%
0.6
0.6
0.6
3.2.6.1
Rafters and purlins
L/180
Interior walls and partitions
H/180
Floors and ceilings
L/360
All others structural members
L/240
NOTES:
L = span length
H = span height
3.2.2 Engineered design.
3.2.2.1 General
Buildings shall be constructed
in accordance with the provisions of this code as limited by the provisions of
this section.
3.2.2.2 Wind design.
The
requirements in this document are based on design wind speed over open water at
equivalent elevation of 10m average over 10 minutes with a recurrence of one in
50 year. (See figure A2-2 Trinidad and Tobago Winds)
3.2.2.3 Seismic design.
All buildings shall be
constructed in accordance with the provisions of this section.
3.2.2.3.1 Seismic design category.
3.2.2.3.1.1 Ground acceleration
The requirements in this document are based on maximum
ground acceleration associated with 10% probability of occurrence in 50 years.
For Trinidad & Tobago 0.3 g
(g refers to the gravity and g = 9.81m/s2)
3.2.2.3.1.2 Amplification factor
Where the soil is 100% saturated
(low land, reclaimed land, etc.) an amplification factor of 2 shall be applied
to the ground acceleration. See
calculation for shear load.
3.2.2.3.1.3 Soil liquefaction
To prevent any soil liquefaction
on the same type of land than above a special attention shall be carried out
with an engineer specialist for the choice of the appropriate type of
foundation. See calculation for shear load.
3.2.2.3.2 Weights of applied finishes
Dead load finishes shall not
exceed 1 kN/m2 for roofs or 0.5 kN/m2 for floors.
Dead load finishes for walls
above grade shall not exceed:
a- light-frame walls 0.75 kN/m2 for exterior
0.50 kN/m2 for interior
b- masonry walls.
2.50 kN/m2 for 150mm thick masonry wall.
3.80 kN/m2 for 200 mm thick masonry wall.
c- concrete walls.
4.10 kN/m2 for 150 mm thick concrete walls.
3.2.2.3.3 Height limitations.
The design applied to any
construction is limited to two stories with a maximum of 9m to the top of the
building.
3.2.2.4 Flood plain construction.
Buildings and
structures constructed in flood prone areas as established in Fig. A2-1 shall be
designed and constructed in accordance with Clause Flood resistant construction
and Clause Coastal high hazard areas of Part "Minimal requirements".
3.2.3 Dead load.
The actual weights of materials and construction shall be used for
determining dead load with consideration for the dead load of fixed service
equipment.
The minimum uniformly distributed live load shall be as provided in Table 2.
Use
Live loads
(kN/m2)
Exterior balconies
5
Domestic floor / All rooms, stairs and corridors
1.5
Office floor
2.5
Small industrial and storage
5
Use
Horizontal
loads (kN/m)
Guard rails and handrails
1
Fig A2-3 Trinidad flood prone areas
Roof shall be designed for the live load indicated in Table
3.
Preamble
Wind and earthquake introduce
horizontal loads in the superstructure that are transferred to the foundation.
We have to consider 2 steps:
a) Transfer of the horizontal
load from
- wind to
vertical wall and roof
-
acceleration of mass located everywhere in the superstructure
to the
appropriated wall or framed structure.
b) Transfer of the load from the
top to the bottom of the wall or superstructure and the foundation.
According to this code
- horizontal transfer is done by
horizontal diaphragm or horizontal
beam
- vertical transfer is one by shear
panel, cross, or framed structure
3.2.6.2 Diaphragm
Floor, roof or ceiling
assemblies may be constructed with the necessary stiffness and load path
continuity to distribute lateral loads (wind and earthquake) to lateral support
subsystems. In this role, floor, roof or ceiling surface act as horizontal beams
(also called a diaphragm) spanning lateral supports points.
Use of floor, roof or ceiling
assembly, as a diaphragm requires both strength and stiffness properties and
development of connections to transfer the diaphragm force.
Fig B6-2 Shear panel - Horizontal core blocks
3.2.6.3 Shear panel
3.2.6.3.1
Concrete wall
A shear panel (see figures B-6-1
and B-6-2 Shear panel) is a portion or section of a 150mm exterior wall that
performs the function of resisting lateral earthquake or wind forces.
3.2.6.3.2 Timber
See paragraph "Wall
bracing".
3.2.7 Load factors.
All structures shall resist combined loads as follows;
3.2.7.1
Gravity
1.40 D + 1.70
L
3.2.7.2
Earthquake a) 0.75 (1.40
D + 1.70 L +/- 1.87 E)
and
b) 0.90 D +/-
1.43 E
3.2.7.2.1
Shear load calculation
A simplified formula, for this code is
V =
0.05 x S x W total shear in kN
Whereas :
The 0.05 coefficient integrated the Z = ground acceleration, C =
amplification factor due to structure frequency, I = Importance factor =1 in
this code and Rw = Ductility factor related with respect to the column design
reinforcement used in the normal practice formula.
S = site factor
S = 1 For good soil (rock, gravel)
S = 1.2 For softer material
(clay, fill )
S = 1.5 For deep alluvial
deposits
S = 2.5 maximum for reclaimed
land and saturated soils (due to the amplification factor)
W = total load
in kN
3.2.7.3
Wind
1.40 D + 1.70
L + 1.75 W
Note:
D = dead load
L = live load
E = earthquake load
W = wind load
3.2.8 Deflection.
The allowed deflection of any structural member under the live load shall
not exceed the following values in Table
4
Table 4 – Maximum deflection
authorised.