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A: Zone acceleration coefficient according to the seismic zone and the using group of the building (See Table 1, Fig. 1)
D: Average dynamic amplification factor, depending on the site category, the damping correction factor η and the fundamental period of the structure T (See Fig.2)
T2: Characteristic period associated to the category of the site
(See Table 2)
η: Damping correction factor given by the following formula:
ξ: Critical damping ratio (%) depending on constitutive material, structure type and importance of infill (See Table 3)
R: Global behavior coefficient of the structure according to the lateral force resisting system (See Table 4). In case of different lateral force resisting systems in two considered directions, the smallest value of R must be used.
Q: Quality factor of the structure given by the following formula:
Pq: Penalty to be applied depending on whether the criteria of quality q "is satisfied or not" (See Table 5)
W: Total weight of the structure that is equal to the sum of the weights Wi calculated at every floor I
WGi: weight due to the dead loads and loads of the eventual fixed equipment attached to the structure
WQi: Live loads
β: Weighting coefficient depending on the nature and the duration of the live load (See Table 6)
Category S1 (rocky site): Rock or other geological formation characterized by an average shear wave velocity Vs ≥ 800 m/s
Category S2 (firm site): Very dense gravel or sand and/or over consolidated clay deposits with a thickness of 10 to 20 meters and
Vs ≥ 400 m/s from a depth of 10 meters
Category S3 (soft site): Thick deposits of moderately dense gravel andsand or moderately stiff clay with Vs ≥ 200 m/s from a depth of
10 meters.
Category S4 (very soft site):
-Loose sands deposits with or without
soft clay with Vs < 200 m/s within the 20 first meters
-Soft to moderately stiff clay with Vs < 200 m/s within the 20 first meters
Any building treated by the present rules should be classified in one of the four groups provided
the lateral load
resisting structural systems
A) Reinforced concrete structures
1.a : Moment resisting space frames without rigid masonry infill walls
The concerned buildings should not exceed five (05) stories or 17m in height in Zone I, four (04) stories or 14m in height in Zone IIa, and three (03) stories or 11m in height Zone IIb and III.
1.b : Moment resisting space frames with rigid masonry infill walls
The concerned buildings should not exceed five (05) stories or 17m in height in Zone I, four (04) stories or 14m in height in Zone IIa, three (03) stories or 11m in height in Zone IIb and two (02) stories or 8m in height in Zone III.
Note:
In the case, where a ground floor is programmed for a commercial use or other services and then,
at the initial stage of the conception, contains a low density of partition walls and/or story's height is larger than
for other stories, leading to a "soft story", it is required that the building lateral resistance should be ensured by an
other system containing shear walls in both orthogonal (or equivalent) directions (with a combined frame-shear walls system
or with a reinforced concreate core for example).
It is reminded that the soft story is the one which has a lateral rigidity less than 70% compared to that of the immediate above story or less than 80% of the average lateral rigidity of the immediate three above stories.
12. Tied (confined) bearing masonry structures
This structural system concern bearing structures achieved in rubble masonry
or small manufactured elements and including strengthening reinforced concrete bands cast-in place after execution
of the mansonry. These structures resist both the vertical and horizontal loads.
The building concerned by this structural system category are limited to 5 stories or 17m in height in seismic zone I,
4 stories or 14m in height in seismic zone IIa and 3 stories of 11m in seismic zone IIb and III.
17. System including transparencies (soft stories)
The most illustrative examples are given by the reception levels or lobbies of hotels
(rareseparation walls or story height more important than for the current stories,...) or absence of separation walls at some
stories for some specified reasons (computer rooms, special equipment, etc..)
In general, these systems should be avoided. Otherwise, besides the procedures preciously recommended for the system Ia and Ib
for the specific case of the ground floor (change of dual systems), all the arrangements to decrease the unfavorable effects
should be taken.
In this respect, the procedure to increase the rigidity should be adopted in order to decrease or attenuate the phenomena
(see the definition of the soft story given previously as remarks for systems Ia and Ib).
concrete structures
For the main elements, the concrete must have the strength fc28 not less than 20 Mpa and less than 45 Mpa.
The value of Elasticity modulus must be according the rule C.B.A.
Formwork
The columns must doing in all the height in one time, the heel-piece is forbidden.
Min(b1,h1) ≥ 25 cm in Zone I an IIa
Min(b1,h1) ≥ 30 cm in Zone IIb an III
Min(b1,h1) ≥ he/20
1/4 < b1/h1 < 4
For the cylindrical column, the diameter D must satisfy those conditions:
D ≥ 25 cm en Zone I
D ≥ 30 cm en Zone IIa
D ≥ 35 cm en Zone IIb and III
D ≥ he/15.
The section of the columns in the side or the corner must be comparable than the central column.
Rebar of reinforcement
Longitudinal rebar
Minimum ratio
0.8% in Zone IIa
0.9% in Zone IIb and III
Maximum ratio
3% in current zone
6% in recovery zone