MEP-Technical Manual CDN 0408.qxd - Hambro

18
DESIGN PRINCIPLES AND CALCULATIONS
4.8 MINI-JOISTS
4.8.1 H SERIES
The standard Hambro section, being 95 mm (3 3 /4”) deep,
possesses sufficient flexural strength to become the major
steel component of the mini-joist series. The three sizes
that are currently being used are illustrated in the figure
below and spans beyond 2 400 mm (8’) can be achieved
with the heavier SRTC unit. Other sizes are also available.
The composite capacities of the TC, RTC & SRTC units are
calculated on the basis of “elastic tee beam analysis”.
The effective flange width, b, equals the lesser of span/4,
or joist spacing. With the mini-joist spaced at 1 251 mm
TABLE 10: Mini-joist H Series Span Chart
TC RTC SRTC
PROPERTIES
Fig. 18
(4’-1 1 /4”), b is dictated by span/4. The load table lists
total unfactored load capacity in kN/m (plf) for span up to
2.64 m (8’-8”).
Full scale tests have demonstrated consistently that shoe
plates are not required for TC and RTC - the section is
simply notched at each bearing end with the lower horizontal
portion of the becoming the actual bearing surface.
Note that where the non-composite end reaction
exceeds 4.5 kN (1.0 kip) the notched ends are reinforced
with a 12.7 mm ( 1 /2”) diameter bar 200 mm (8”) long.
This is to prevent the section from “straightening out”at the
bearing ends. It is interesting to note that this is not a problem
during the composite service stage, even with its higher total
loads, as the 70 mm (2 3 /4”) slab carries the vertical shears.
TYPE CONDITIONS I S MAXIMUM CLEAR SPAN (m)
mm 4 x 10 6 mm 3 x 10 3
TC COMPOSITE 0.950 9.8
NON-COMP. 0.275 4.8 UP TO 1.25 m
RTC COMPOSITE 2.120 21.5
NON-COMP. 0.597 11.5 UP TO 1.68 m
SRTC COMPOSITE 4.830 41.8
NON-COMP. 1.660 26.2 UP TO 2.44 m
TABLE 11: Mini-joist H Series Span Chart
PROPERTIES
TYPE CONDITIONS I S MAXIMUM CLEAR SPAN (ft.)
in. 4 in. 3
TC COMPOSITE 2.29 0.60
NON-COMP. 0.66 0.29 UP TO 4’-1”
RTC COMPOSITE 5.09 1.31
NON-COMP. 1.63 0.75 UP TO 5’-6”
SRTC COMPOSITE b = 12” 9.84 2.55
NON-COMP. b = 24” 11.60 1.60 UP TO 8’-0”