Bridge Engineering (5) Substructure – Abutments and Piers The portion of the bridge structure below the level of the bearing and above the foundation is generally referred to as substructure. 1.1 Piers: the support, usually of concrete or masonry, for the superstructure of a bridge. 1.2 Abutments: the support for the end of a bridge span or lateral support for the soil or rock on which the roadway rests immediately adjacent to the bridge, functioning as a pier and a retaining wall 1.3 Bed blocks over the piers and abutments Piers 2.1 * Types of piers 2.1.1 solid: common for railroad bridges;  1 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 2.1.2 cellular; 2.1.3 trestle; 2.1.4 hammer-headed: avoiding skew spans in passing over existing highways or railroad tracks. 2.2 *Design requirements of piers 2.2.1 The general shape and features of a pier depend to a larger extent on the type, size and dimensions of the superstructure and on the environment. 2.2.2 Solid and cellular piers should be provided with semicircular cut waters to facilitate streamlined flow and to reduce scour; 2.2.2 Solid piers are of masonry or mass concrete; 2.2.3 Cellular, hammer-head and trestle piers are of reinforced concrete;  2 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 2.2.4 It is permissible to use stone masonry for the exposed portions and to fill the interior with lean concrete, which would save expenses on shuttering and would also enhance appearance; 2.2.5 The cellular type permits saving in the quantity of concrete, but usually requires difficult shuttering and additional labor in placing reinforcements; 2.2.6 The trestle type consists of columns (usu. circular or octagonal ) with a bent cap at the top. 2.2.7 In some recent designs , concrete hinges have been introduced between the top of columns and the bent cap in order to avoid moments being transferred from the deck to the columns;   3 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 2.2.8 For tall trestles as in flyovers and elevated roads, connecting diaphragms between the columns may also be provided; 2.2.9 Trestle design leads to minimum restriction of waterway. 2.2.10 The top width of piers depends on the size of the bearing plates on which the superstructure rests. It is usually kept at a minimum of 600mm more than the out-to-out dimension of the bearing plates , measured along the longitudinal axis of the superstructure; 2.2.10 The length of piers at the top should be not less than 1.2m in excess of the out-to-out dimension of the bearing plates, measured perpendicular to the axis of the superstructure. 2.2.11 The bottom width of piers is usually larger than the top width so as to restrict the net stresses within the permissible values;   4 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 2.2.12 It is normally sufficient to provide a batter of 1 in 25 on all sides for the portion of the pier between the bottom of the bed block and the top of the well or pile cap or foundation footing; 2.2.13 The main advantage in use of reinforced concrete framed type of piers is due to reduced effective span lengths for girders on either side of the center line of the pier leading to economy in the cost of superstructure. 2.2.14 Caution in wide adoption of framed type of piers: __ such framework would be conducive to accumulation of debris and especially floating trees if used in rivers subjected to sudden floods near hills and forests; __ such designs call for two expansion joints at close intervals of about 1 to 2m on each pier, resulting in riding discomfort besides maintenance problems;  5 Saturday, April 22, 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 (5) Substructure – Abutments and Piers __ the ends of the decking on either side of the pier center line should be cantilevered beyond the bearings so that one expansion joint would be adequate . 3. *Abutments 3.1 An abutment is the substructure which supports one terminus of the superstructure of a bridge and, at some time, laterally supports the embankment which serves as an approach to the bridge. 3.2 The abutment can of masonry, plain concrete or reinforced concrete . 3.3 An abutment generally consists of the following three distinct structural elements: 3.3.1 the breast wall which directly supports the dead and live loads of the superstructure, and retains the filling of the embankment in its rear;   6 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 3.3.2 the wing walls, which act as extensions of the breast wall in retaining the fill though not taking any loads from superstructure; and 3.3.3 the back wall, which is a small retaining wall just behind the bridge seat, preventing the flow of material from the fill on to the bridge seat . 3.4 Design requirements of abutments 3.4.1 consisting in assuming preliminary dimensions depending on the type of the superstructure and foundation , and checking the stresses at the sill level; 3.4.2 the front face of the breast wall should have a batter of not less than 1 in 25 , preferably at 1 in 12.  7 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 3.5 *Typical forms of reinforced concrete abutments 3.5.1 gravity abutments with wing walls; 3.5.2 U-abutment; 3.5.3 spill-through abutment 3.5.4 pile-bent abutment with stub wings; 3.5.5 others 3.5.5.1 with a gravity type breast wall; 3.5.5.2 the counterfort type; 3.5.5.3 the types to reduce the overturning moment due to earth pressure; 3.5.5.4 the type for overpasses over expressways to enhance aesthetics; 3.5.5.5 the buried types more adaptable for overpasses with side spans and sloping cuts.  8 Saturday, April 22, 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 (5) Substructure – Abutments and Piers 3.6 Failure of bridge abutments 3.6.1 The breast wall may fail by tensile cracks, crushing or shear; 3.6.2 The wall may tilt forward due to excessive overturning moment due to earth pressure; 3.6.3 The wall may slide forward due to earth pressure if the vertical forces are inadequate; 3.6.4 Failures may occur along a curved surface by rupture of the soil due to inadequate shear resistance.  9 Saturday, April 22, 2017 French. 1989. Introduction to soil mechanics and shallow foundations design, pp 2-3 Canadian Geotechnical Society: 1992. Canadian Foundation Engineering Manual (3rd Ed.)