Civil Engineering Reference
In-Depth Information
and cracks; for enclosure structure systems, according to service function, sub-items include:
roof system, walls, doors and windows, underground waterproof facilities, and protective fa-
cilities.
Table 2.7
Grading of slenderness ratio of steel brace
Types of
Slenderness ratio of brace members
factory
Types of brace members
d
a
b
c
buildings
Tension
members
400
>
400
,
425
>
425
,
450
>
450
With medium
or light
Compression
members
Ordinary brace
200
>
200,
225
>
225,
250
>
250
cranes
,
or
without crane
Tension
members
Lower column bracing
300
>
300,
325
>
325,
350
>
350
Compression
members
>
150,
200
>
200,
250
>
250
150
Tension
members
350
>
350
,
375
>
375
,
400
>
400
With heavy
crane
Compression
members
Ordinary brace
200
>
200
,
225
>
225
,
250
>
250
or with
hammers
rating
5t
Tension
members
Lower column bracing
200
>
200
,
225
>
225
,
250
>
250
Compression
members
150
>
150,
175
>
175,
200
>
200
Notes: 1) The ordinary brace listed in the table refers to all braces except lower column bracing.
2) For the bracing systems resisting dynamic load directly or indirectly, the least radius of gyration of the
angle steel should be used in calculation of the slenderness ratio of the tension member. But the axis of the
radius of gyration should be parallel to the leg of angle steel in calculation of the out-of-plane slenderness
ratio of the cross tension member.
3) In a factory building with crab crane or rigid crow crane, the slenderness ratio of bracing tension
members should generally be assessed according to the slenderness of the tension member of the lower
column bracing in the factory “with medium or light duty cranes, or no crane” in the table.
4) For the factory building bearing greater dynamic load, the assessment of slenderness ratio of brace
members should be stricter.
5) With adequate experience, the assessment of slenderness ratio of lower column bracing in the factory
building can be relaxed.
6) When the slenderness ratio of compression member of lower inter-column cross brace is compara-
tively great, it is feasible to check the computations according to the tension member and make assessment
according to the slenderness ratio of tension members.
Since the grading of each sub-item is based on the limit state of certain function, as-
sessment of sub-items is based on whether structural members satisfy the single functional
requirement (reliability requirement), which is expressed as a, b, c, or d. In addition, ac-
cording to impact on reliability of item, sub-items can be divided into principal sub-items
and secondary sub-items.
Sub-items (bearing capability, deformation of structures or members, slenderness ratio of
steel brace, etc.) can be graded according to Table 2.7-Table 2.18.
b. Item or combined item.
Item or combined item is the second level in structural reliability assessment, which can be
divided into basic item and combined item according to composition. Ground foundation,
structure and structure members are basic items; load-bearing system, structural layout,
bracing system and enclosure structure system are combined items. All the items, except
structural layout and bracing system that have no sub-items are evaluated by the second
level assessment, according to the evaluated results of sub-items. Therefore, the assessment
