105

1. The stirrup size or yield strength is changed.

2. The stirrup spacing is changed as in current design procedure.

It is reasonable to suggest that the stirrup spacing be changed.

Fig. 4.3b shows a typical truss model for the case of members subjected

to distributed loads. The same principles are applied in this case.

The directions of the compression diagonals are obtained directly from

the shear diagrams shown in Fig. 4.3a. The inclination of the diagonals

has to be within the limits 25 0 ~ a ~ 650 •

Once the truss model has been selected the design procedure is

the same as the one presened in the previous section. The determination

of the sectional forces that should be used in the design procedure for

the case of bend ing and shear in reinforced and prestressed concrete

members subjected to distributed loads has been illustrated in Sec.

2.2.1 of Report 248-3.

4.2.3 Truss Model for the Flange Region of Inverted T -Bent

Caps. Figures 4.4a and 4.4b show the case of a simply supported

inverted T-bent cap loaded on its bottom chord. Figures 4.5b and 4.5c

show the transverse truss systems selected to design the transverse

reinforcement for the flange region of the inverted T-bent cap loaded

through the bottom flange.

The same basic concepts have to be app1 ied in this case. Again

the direction of the compression diagonals is obtained directly from the

shear diagram shown in Fig. 4.5a. The inclination of the compression

diagonals has to be within the limits 25 0 ~ a~ 65 0 , where a is the

angle of inclination of the truss compression diagonals (see Fig. 4.5b).

106

Shear

Diagram

Moment

Diagram

I I I tit , t * t * I t * I I

v1 ~v d~c ~d t tv<-a b a~b ~aVi __ ~~~.rT-~~--a

free ed (+

(8) Shear and moment diagrams

Compression Fan - - - - Tension Fan

I /

(b) Truss model

Fig. 4.3 Truss model in the area of a simply supported member with distributed loading

( (

(a) End view

~p ~p

(b) Longitudinal view

Fig. 4.4 Simply supported inverted T-bent CAp

subjected to bending and shear

107

108

V-Diagram

M-Diagram

(a)

p a

~ I I

Z I I I I I ~::~ "'L __ "\!!;

(b) Truss model

0.5 :s a/z :s 2.0

h II- of bent cop.

I't.

~pa

Flange shear and moment diagr~ms

«(}~:}}:) Compression

--- Tension -- - Supplementary Reinforcement

p

,,-I 1--~­I

(c) Truss mode 1

p,/z ;:;;: 0.5

Fig. 4.5 Truss model for the flange region of an inverted T-bent cap loaded on the bottom flange