Continuous deep beams - Reinforced Concrete Deep Beams - page 97

clear span to effective depth ratios greater than 5 (and loaded at the top or
compression face) be treated as deep beams. The ACI deep beam definition
is based on shear behaviour while CEB definition is based on flexural
behaviour. It is important to recognise the different definitions when
reviewing design recommendations. In reality the deep beam problem is a
coupled problem. This chapter will provide a review of the literature and
attempt to present a coupled or integrated solution which addresses both
shear and flexure with one consistent model.
4.2 Distinguishing behaviour of continuous deep beams
4.2.1 Previous tests
There are very few tests of continuous deep beams available in the literature.
Nylander and Holst (1946) reported perhaps the first test. They reported the
results of a test for a two span specimen with an elaborate arrangement of
truss bars. The specimen was part of a general investigation of reinforced
concrete beams, hence no general conclusions could be drawn.
Leonhardt and Walther (1966) conducted a well known and extensive
series of tests on deep beams. The tests included different loading
conditions, different reinforcement arrangements and different support
conditions including some two span beams. These tests formed the basis for
the CEB-FIP (1970) recommendations.
Rogowsky, MacGregor and Ong (1986) conducted a series of tests on
17 large-scale two span deep beams. Both spans were brought to failure,
providing a total of 34 test results. The tests covered span to depth ratios
ranging from approximately 5 to 2 and had various amounts of horizontal
and vertical web reinforcement (none; minimum ACI vertical stirrups for
deep beams; four times minimum stirrups; about half ACI minimum
horizontal shear reinforcement for deep beams; and 1.5 times minimum
horizontal reinforcement). All beams were loaded by and supported by
monolithic concrete columns. For comparison purposes, six additional
companion simple span deep were also tested. Both ends of the simple
spans were brought to failure, providing a total of 12 large-scale simple
shear span test results. These tests formed the basis for some of the deep
beam recommendations in the current Canadian concrete code (CSA
A23.3 M84) and proposed revisions to the American concrete code (ACI
318-86).
A brief description of the behaviour of a typical deep beam test
specimen is now presented. Figure 4.2 illustrates the key events in the life
of a continuous deep beam. In general, deep beams develop little initial
flexural cracking. For the beams tested by Rogowsky et al. (1986),
midspan flexural cracks tended to form before negative cracks over the
interior support. The first significant event during loading of a deep beam
is the development of diagonal, inclined or shear cracks which occur