UFC 4-023-03
25 January 2005
B-3.1
Reinforced Concrete Tie Forces.
A review of the 1972 British Standard Code of Practice CP110 is provided in
Burnett 1975 who discusses the origins or logic used to develop the reinforced concrete
tie force requirements. The British Buildings Standards have evolved somewhat since
this time, but the basic approach and most of the requirements are the same today.
B-3.1.1
Internal Ties.
B-3.1.1.1 Upper Limit of the Basic Strength.
In SI units, the equation for internal tie forces is:
a)
(1.0D + 1.0L)
lr Ft
(kN/m)
7.5
5
or
b)
1.0 Ft
(kN/m)
= Dead Load (kN/m2)
where:
D
= Live Load (kN/m2)
L
lr
= Greater of the distances between the centers of
the columns, frames or walls supporting any two
adjacent floor spaces in the direction of the tie
under consideration (m)
Ft
= "Basic Strength" = Lesser of (20 + 4 no) or 60
no
= Number of stories
Burnett indicates that the upper limit of Ft (60) can be derived from two
scenarios. First, this magnitude is equivalent to the internal member force created by
catenary action of the floor after an intermediary load-bearing element is removed, as
shown in Figure B-1, assuming a sag of 10%. Second, the upper limit of Ft can be
related to the forces applied to a typical wall panel loaded with a 34 kN/m2 (5 psi) static
pressure, which is notionally equivalent to the overpressure that was thought to exist in
the Ronan Point gas explosion. Discussions with British engineers suggest that the first
approach (catenary action) is the mechanism that the internal tie forces were intended
to resist.
The determination of lr for framed and spine wall construction are
demonstrated in Figures B-2 and B-3, respectively.
B-3
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