Indicadores multidimensionales

Some useful information on particular uses of welding in precast concrete work generally can be found in references 519—5.21

I

IIII

member is

iLl

^I

[7””~”T

(billet. r.s.j.,

generally L etc.) Which

(bi END&IJVArcN WOEIL5VA11~

Figure HS. 9: Basic types of connection using structural steel inserts.

5.3.5 Connections other than those involving continuity of reinforcement 5.3.5.1 Joints with structural steel inserts

A clear distinction has to be drawn at the design stage between the two basic types of possible connection. These are illustrated in Figure HS.9 which shows a narrow plate embedded in a column, to which a smaller plate in the end of the supported beam will be bolted or otherwise connected. In considering the design of this connection, it is best to refer to the specialist literature (notably reference 5.22); the behaviour is somewhat analogous to the behaviour of end blocks with low Ypo/Yo ratios, in that it is dominated by the tendency of the narrow steel plate to split the column. However, it has been shown15’~1 that an end block approach is not very successful for design as the strength is also influenced by shrinkage effects at the bottom of the plate and by the precise location of transverse links in the column.

The behaviour of the more common type of connection shown in Figure H5.9 (b) is controlled by distribution of bearing stresses underneath the steel insert. An excellent general treatment of the design problems associated with this type of connection is given in reference 5.23 which is based on American design practice and on certain simplifying assumptions. If the insert protrudes from two opposite sides of the column and the imposed loads on each side are equal, design is relatively simple. since 5.2.3.4 permits a uniform bearing stress of up to 0.8

J~

under the ultimate loads. Consideration should be given to the loads imposed on the concrete in the column from the structure above the joint and, if designing to the upper stress limitation, the provision of additional column links immediately beneath the steel insert should also be considered.

The rigorous design of a single steel insert of the type shown in Figure H5.9 (b) can be complex because the distribution of bearing stress in the concrete under the insert is not known. However, a simple design solution can be obtained from the assumed force system shown in Figure HS. 10 where the bearing stresses are taken to be uniform along the lengths l~ and 13. The values of V~, l~, (from 5.3.5.1) and b (from practical considerations) will be known initially andl~ may be calculated from:

=

vii

b1x0.8f~

SlOE ELF~~TAOS

This enables the steel insert to be designed (i.e. h, to be determined) to resist a 119

Handbook to BSSJIO:I%S

centre-line of main column steel

structural steel insert

~, ~ aoditional steel sect:on provide more ~eanng

~ effective beanng wioth area if reouireo: :rie then Decomes i2b.—x.l

sac-7~oNA-A

Figure H5. 10: Force system for design of single steel inserts for columns.

moment equal to V~(lt-~-l2):shear at the column face would also require checking. It is then necessary to calculate V-~ and L. This may be done by taking moments about the line of action of V., thus:

This gives a quadratic equation in terms of 13. The design max’ then be considered satisfactory ifl~<0.6(l~—1I2 13). i.e. if the bearing stress areas do not overlap. Note that.

in lightly loaded columns. it may be necessary to provide the tying-down force V~ by welding vertical reinforcing bars to the steel insert and anchoring them in the column underneath. The widthb will generally be governed by practical considerations: i.e. it

must fit inside the column reinforcement cage and allow the concrete to be placed and compacted and the width should not exceed one-third of the column ‘vidth. If there is then insufficient bearing area to satisfy the inequality given above. additional bearing may be provided by welding on additional steel sections as sho~vn in Figure HS.10 (Section A-A).

In practice, many types of structural steel insert can be used and each should be considered carefully in the light of the above general comments. It is considered that.

with many of these, higher bearing stresses could be carried successfully, especially if additional column links were provided.

A common design problem is that of a billet protruding from each side of a column carrying different loads on each side. This would occur if spans are not equal on each side of the column. In this case the stiffness of the insert is of importance and the design

or slab

I

F 1, C

C

I I2

.column or wail

U

L L

effective joint area in bedding of mortar for precast

compression 6.3.6) floor units

assumed to be not greater than 90% of the cross-sectional area of the wall or column

Figure 1-15.11: Effective joint area for compression joints ^f5.3.6~i.

L

F U

l1)

K - KK. . .~. . . - - ~. .. - K - . - - - — K

Part 1: Section5 problem becomes statically indeterminate. Very stiff inserts will carry the load in bearing with a variable but linear stress across the column.- like a pad foundation. Flexible billets may impose vertical bearing stresses in the upward direction in the centre of the column.

More research is required in this area and design should have experimental backing.

5.3.5.2 Resin adhesives

In document límites alternativas estratificación Los de la en busca de Carlos Eduardo Sepúlveda Rico Denis López Camacho Juan Miguel Gallego Acevedo (página 107-111)