Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 1. *Types of reinforced...

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges

1. *Types of reinforced concrete bridges1.1 Slab bridges;1.2 Girder and slab (T-beam) bridge;1.3 Hollow (box) girder bridges;1.4 Balanced cantilever bridges;1.5 Rigid frame bridge;1.6 Arch bridges (bow string arch bridges);2. *T-beam Bridges2.1 Most commonly adopted type in span range of 10—25

m;2.2 The main longitudinal girders are T-beams integral wit

h part of the deck slab monolithically cast with the girders.

2.3 Simply supported T-beam spans of over 25m are rare as the dead load then becomes too heavy .

1 Tuesday, April 18, 2023


3. * Hollow Girder Bridges3.1 Components:3.1.1 the cantilever portion including the kerb;3.1.2 the roadway slab;3.1.3 the bottom slab;3.1.4 the girder webs; and3.1.5 the diaphragms. 3.2 Design of the hollow girder3.2.1 very similar to that for a T-beam superstructure, exce

pt that the tensile bars are spread over a large area on the base slab;.

3.2.2 the webs of the girder are designed to carry the shear; 3.2.3 vertical stirrups can be provided to take care of the re

quirements for shear.



3. Hollow Girder Bridges3.3 Features and usage:3.3.1 economical in the span range of 25 to 30m;3.3.2 the main feature: the additional torsional rigidity beca

use of the closed box section and the convenience in varying the depth along the length;

3.3.3 particularly suited for grade separations, where the alignment of bridges are normally curved in plan

3.3.4 (of cells) rectangular or trapezoidal, the latter being used increasingly in prestressed concrete elevated roadways

3.3.5 multi-cellular in shape and in continuous and balanced cantilever types;



4. * Balanced Cantilever Bridges A balanced cantilever: a combination of supported spa

ns, cantilevers and suspended spans 4.1 Design4.1.1 Articulation: the connection between the suspended sp

an and the edge of the cantilever;4.1.2 The expansion joint is filled with mastic filling at the

wearing coat level with the other parts left open; 4.1.3 The cantilever span is usu. about 0.20 to 0.25 of the su

pported span;4.1.4 The suspended span is designed as a simply supported

span with supports at the articulations.



4.1.5 Moment for the design of the main span: __ the maximum negative moment at the support would

occur when the cantilever and suspended spans are subjected to full live load with no live load on the main span;

__ the maximum positive moment at the mid-span would occur with full live load on the main span and no live load on the cantilever or suspended span.

4.1.6 The governing shears at the different sections are computed using influence lines;

4.1.7 The bearings at the piers will be alternatively of fixed and expansion types;

4.1.7 The cross section can be of T-beam or hollow girder type;



4.1.8 the depth at support will be greater than at mid-span because the negative moments are usually larger than the positive moment;

4.1.9 The soffit can be a parabolic profile or two inclined with a central horizontal line.

4.2 Features and usages4.2.1 minimized governing bending moments in continuous

spans and hence the increased individual span lengths;4.2.2 unyielding supports are required for continuous const

ruction;4.2.3 for medium spans in the range of about 35 to 60m;



5. *Continuous Girder Bridges5.1 This type, not connected monolithically to supports, is s

uitable when unyielding supports available. 5.2 The spans can be equal, but usually the end spans are a

bout 16% to 20 % smaller than the intermediate spans.

5.3 The decking can be of slab, T-beam or box section. 5.4 The bending moments and shears are evaluated by usin

g influence lines. 5.5 The negative bending moment at the support induces te

nsion at the top.5.6 The bending moment will in general be larger at the sup

port than at mid-span. 5.7 A haunched profile or a curved soffit is normally used, t

o strengthen the section at the support with compression reinforcement besides provision of thickened webs and a cross beam.



5.8 In the case of continuous slab bridges, the thickness of slabs at support will be approximately 1.3 to 1.8 times the minimum thickness at mid-span and the length of haunched portion will be about 0.20 to 0.25 of the span.

5.9 All but one of the bearings will be of the expansion type .

6. *Rigid Frame Bridges6.1 Rigid frame bridges are structures consisting of a numb

er of parallel girders (or slabs) rigidly connected to the supporting columns or piers.

6.2 Types of rigid frame bridges6.2.1 single span openings as for bridges over railway track

s;



6.2.2 a two-span bridge with the base of the column fixed (downward tapered column for a hinged base), and bridges with greater number of spans by adding the required number of intermediate columns;

6.2.3 a pleasing structure over restricted access highways expressways.

6.3 The decking and substructure are cast monolithically .7. Arch Bridges Most pleasing appearance and aesthetic elegance 7.1 * Types of arches 7.1.1 the fixed arch;7.1.2 the two-hinged arch: __ the bow-string arch bridge in which a tie member conne

cting the two ends of the arch carries the horizontal thrust from the arch and permits the reactions to be vertical as in the case of girder bridges

7.1.3 the three-hinged arch. 9 Tuesday, April 18, 2023

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 1. *Types of reinforced...

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