Page 43 - Design of Reinforced Masonry Structures

1.12 CHAPTER ONE

The following are exceptions to the above load combinations:
1. The load factor on L in combinations (3), (4), and (5) is permitted to equal 0.5 for all
occupancies in which floor live load L in ASCE 7-05 Table 4-1 is less than or equal to
o
100 psf, with the exception of garages or areas occupied as places of public assembly.
2. The load factor on H shall be set equal to zero in combinations (6) and (7) if the struc-
tural action due to H counteracts that due to W or E. Where lateral earth pressure pro-
vides resistance to structural actions from other forces, it shall not be included in H but
shall be included in the design resistance.
3. In combinations (2), (4), and (5), the companion load S shall be taken as either the flat
roof snow load (p ) or the sloped roof snow load (p ).
f
s
A designer should investigate each limit state, including the effects of one or more loads
not acting on the structure or its components. In case of wind and earthquake loads, the
most unfavorable effects from each should be investigated and accounted for in design, but
they need not be considered acting simultaneously.
In addition to the above load combinations, there are additional load combinations
which should be investigated for structures subjected to floods (ASCE 7-05 Section 2.3.3)
and to atmospheric ice loads (ASCE 7-05 Section 2.3.4).
Attention should be paid to load factors associated with the earthquake load, E (load
factor = 1.0), and the wind load, W (load factor = 1.6), even though both are lateral loads
acting on the structure. The reason for this difference in load factors is the fact that W repre-
sents the allowable stress-level wind load (hence load factor 1.6 to convert it into a factored
load), whereas E represents strength-level load (hence load factor = 1.0).

1.8.3 Load Combinations for Allowable Stress Design

The following are the load combination which should be investigated when using allowable
stress design.
1. D + F
2. D + H + F + L + T
3. D + H + F + (L or S or R)
r
4. D + H + F + 0.75 (L + T) + 0.75(L or S or R)
r
5. D + H + F + (W or 0.7E)
6. D + H + F + 0.75(W or 0.7E) + 0.75L + 0.75(L or S or R)
r
7. 0.6D + W + H
8. 0.6D + 0.7E + H

In combinations (4) and (6), the companion load S shall be taken as either the flat roof snow
load (p ) or the sloped roof snow load (p ).
f
s
In addition to the above load combinations, there are additional load combinations
which should be investigated for structures subjected to floods (ASCE 7-05 Section 2.4.2)
and to atmospheric ice loads (ASCE 7-05 Section 2.4.3).
As with strength design load combinations, a designer should investigate each load
combination, including the effects of one or more loads not acting on the structure or its
components. In case of wind and earthquake loads, the most unfavorable effects from each
should be investigated and accounted for in design, but they need not be considered acting
simultaneously.