1. Bridge Engineering (1) Introduction(1-2) Table of Contents 8. Location of piers and abutmentsLocation of piers and abutments 9. Vertical clearance above H.F.LVertical clearance above H.F.L 10. Subsoil explorationSubsoil exploration 11. Choice of bridge typeChoice of bridge type 12. Standard Specifications for Road BridgesStandard Specifications for Road Bridges 1 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

2. Bridge Engineering (1) Introduction(1-2) 8. * Location of piers and abutments Principles to locate piers and abutments 8.1 the best use of the foundation conditions available; 8.2 the navigational or aesthetic requirements; 8.3 the minimal number of spans; 8.4 an odd number of span preferable to even ones; 8.5 Ratio of span to pier or abutment height; 8.5.1 Small bridges with open foundations and solid masonry piers and abutments, the economical span is approximately 1.5 times the total height of the pier or abutments, 2 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

3. Bridge Engineering (1) Introduction(1-2) 8.5.2 The span for masonry arch bridges is about 2.0 times the height of the keystone above the foundation. 8.5.3 For major bridges with more elaborate foundations, the question has to be examined in greater detail. 9. Vertical clearance above H.F.L 9.1 Vertical clearance is the difference in level between H.F.L. and the lowest point of the superstructure. 9.2 For high level bridges: a vertical clearance should be allowed between the H.F.L. and the lowest point of the superstructure to allow for any possible error in the estimation of the H.F.L., and the design discharge and also to allow floating debris to pass under the bridge without damaging the structure. Requirements for Minimum Vertical ClearanceRequirements for Minimum Vertical Clearance 3 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

4. Bridge Engineering (1) Introduction(1-2) 9.3 For arched bridges: the clearance below the crown of the intrados of the arch should not be less than one- tenth of the maximum depth of the water plus one- third of the rise of the arch intrados. 9.4 For structures provided with metallic bearings: the clearance between the base of the bearings and the highest flood level taking afflux into account is not to be less than 500 mm. 10. *Subsoil exploration 10.1 The aim in preliminary exploration is to get a general idea about the nature of soil strata. 10.2 The determination of a reasonably accurate soil profile at each of the proposed bridge sites is essential for correctly deciding the location and type of foundation. 4 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

5. Bridge Engineering (1) Introduction(1-2) 10.3 Availability of correct and reliable data would enable the construction contractors to estimate their costs correctly and to plan their work intelligently, resulting in a better job at a lower cost. 10.4 Defects in bridge structures attributable to serious errors in subsoil exploration cannot be easily rectified later. 10.5 Borings have to be taken over the length of the bridge and approaches at suitable intervals, including preferably at the probable locations of abutments and piers. 10.6 The data required are: 10.6.1 nature of soil deposit, 10.6.2 depths and thickness of soil strata, 10.6.3 location of groundwater table, 5 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

6. Bridge Engineering (1) Introduction(1-2) 10.6.4 depth to rock bed, and 10.6.5 engineering properties of soils and rock. 10.7 Methods used for the study of subsoil conditions: 10.7.1 sounding rods ( 测深杆 ),10.7.1 sounding rods ( 测深杆 ) 10.7.2 auger borings( 螺旋钻孔 ),10.7.2 auger borings( 螺旋钻孔 ), 10.7.3 wash borings( 冲冼钻孔 ),10.7.3 wash borings( 冲冼钻孔 ), 10.7.4 geophysical methods,10.7.4 geophysical methods, 10.7.5 test (trial) pits, and core drilling,10.7.5 test (trial) pits, and core drilling, 11. *Choice of bridge type Factors influencing the choice of the bridge type and its basic features are as follows: 11.1 The overall construction cost: a road-cum-rail bridge in two tiers across a very wide river, e.g., the Nangjing Yangtze Bridge, the Nangjing Yangtze Bridge 6 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

7. Bridge Engineering (1) Introduction(1-2) 11.2 Large navigational clearances: arches, cantilever bridges, cable stayed construction or suspension bridgesarches 11.3 A plain coastal area for a railway line with low traffic: a low level structure with a movable (bascule, swing or lift) span to cater to navigation more desirable than long and high approachesmovable 11.4 A high level structure with uninterrupted traffic as on a National Highway and the need to reduce the number of piers: a cantilever or cable stayed bridge or a series of simply supported trusses. 11.5 The climatic and environmental conditions would preclude the use of some types and require some others. 7 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015teaching

8. Bridge Engineering (1) Introduction(1-2) 11.6 highway traffic: deck bridge preferred to through bridges for because of the better view of the surrounding scenery, e.g., the Wanxian Yangtze Bridgedeck bridge 11.7 The topographic and soil conditions at a site may limit the choice to a few general possibilities, e.g., a rocky valley area is ideal for an arch bridge. 11.8 Weak subsoil conditions: simply supported spans instead of continuous spans, e.g., bridges in areas subject to mining subsidence 11.9 Availability of funds: the adoption of a submersible bridge instead of a high level bridge on a road with less traffic, and this in turn may result in reinforced concrete slab decking 8 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

9. Bridge Engineering (1) Introduction(1-2) 11.10 The type of traffic: for railway traffic, steel trusses or steel cantilever types are preferable to suspension bridges. 11.11 The personal preferences or company specialization of the designer/construction firm 12. Standard Specifications for Highway Bridges 12.1 Width of carriageway 12.1.1 Factors determining the width of carriageway: the intensity and volume of traffic anticipated to use the bridge. The width of carriageway is expressed in terms of traffic lanes, each lane meaning the width required to accommodate one train of Class A vehicles. 9 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

10. Bridge Engineering (1) Introduction(1-2) 12.1 Width of carriageway 12.1.2 The minimum width: 4.25 m for a one-lane bridge; 7.5 m for a two-lane bridge; 3.5m for every additional lane 12.1.3 The number of lanes: Bridges must have carriageways of two or four lanes or multiples of two lanes. Three lane bridges should not be constructed, as these will be conducive to the occurrence of accidents. 12.1.4 A central verge: In the case of a wide bridge, it is desirable to provide a central verge of at least 1.2 m width in order to separate the two opposing lines of traffic. 12.2 Clearances Horizontal and vertical clearances 10 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

11. Bridge Engineering (1) Introduction(1-2) 12.3 *Loads For highway bridges and culverts, the following loads, forces and stresses should be considered, where applicable: 12.3.1 dead load; live load (impact or dynamic effect of the live load; wind load; longitudinal forces caused by the tractive effort of vehicles or by braking of vehicles; longitudinal forces due to frictional resistance of expansion bearings; centrifugal forces due to curvature; horizontal forces due to curvature; horizontal forces due to water currents; buoyancy; earth pressure; temperature stresses; secondary stresses; erection stresses; seismic forces [forces and effects due to earthquake]). 11 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015

12. Bridge Engineering (1) Introduction(1-2) 12.3 Loads 12.3.2 Dead load: The dead load carried by a bridge member consists of its own weight and the portions of the weight of the superstructure and any fixed loads supported by the member. The dead load can be estimated fairly accurately during design and can be controlled during construction and service. 12.3.3 Live load: live loads are those caused by vehicles which pass over the bridge and are transient in nature. These loads cannot be estimated precisely, and the designer has very little control over them once the bridge is opened to traffic. However hypothetical loadings which are reasonably realistic need to be evolved and specified to serve as design criteria. 12 Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015Friday, October 30, 2015