Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges *Types of reinforced concrete bridges 1.1 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); *T-beam Bridges 2.1 Most commonly adopted type in span range of 10—25 m; 2.2 The main longitudinal girders are T-beams integral with 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 Saturday, April 15, 2017 French. 1989. Introduction to soil mechanics and shallow foundations design, pp 2-3 Canadian Geotechnical Society: 1992. Canadian Foundation Engineering Manual (3rd Ed.)

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 3. * Hollow Girder Bridges 3.1 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; and 3.1.5 the diaphragms. 3.2 Design of the hollow girder 3.2.1 very similar to that for a T-beam superstructure, except 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 requirements for shear.   2 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 3.  Hollow Girder Bridges 3.3 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 because 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;   3 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 4. * Balanced Cantilever Bridges A balanced cantilever: a combination of supported spans, cantilevers and suspended spans 4.1 Design 4.1.1 Articulation: the connection between the suspended span 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 supported span; 4.1.4 The suspended span is designed as a simply supported span with supports at the articulations.   4 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 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;   5 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 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 usages 4.2.1 minimized governing bending moments in continuous spans and hence the increased individual span lengths; 4.2.2 unyielding supports are required for continuous construction; 4.2.3 for medium spans in the range of about 35 to 60m;   6 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 5. *Continuous Girder Bridges 5.1 This type, not connected monolithically to supports, is suitable when unyielding supports available. 5.2 The spans can be equal, but usually the end spans are about 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 using influence lines. 5.5 The negative bending moment at the support induces tension at the top. 5.6 The bending moment will in general be larger at the support than at mid-span. 5.7 A haunched profile or a curved soffit is normally used, to strengthen the section at the support with compression reinforcement besides provision of thickened webs and a cross beam.    7 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 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 Bridges 6.1 Rigid frame bridges are structures consisting of a number of parallel girders (or slabs) rigidly connected to the supporting columns or piers. 6.2 Types of rigid frame bridges 6.2.1 single span openings as for bridges over railway tracks;   8 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分

Bridge Engineering (7) Superstructure – Reinforced Concrete Bridges 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 connecting 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 Saturday, April 15, 2017 Stirrup: A part or device shaped like an inverted U in which something is supported, held, or fixed. 箍筋; 用来支撑或固定象一个内弯U型的工具或部分