Bridge Engineering (1) Introduction(1-1)

1. Bridge Engineering (1) Introduction(1-1) Table of Contents Definition Components of a bridge Classification Investigation for Bridges 5. Selection of Bridge Site 6. Preliminary data to be collected Preliminary drawings Location of piers and abutments 9. Vertical clearance above H.F.L 10. Subsoil exploration 11. Choice of bridge type 12. Standard Specifications for Road Bridges 1Thursday, October 9, 2014

2. Bridge Engineering (1) Introduction(1-1) *Definition A bridge is a structure providing passage over an obstacle without closing the way beneath. The required passage may be for a road, a railway, pedestrians, a canal or a pipeline. The obstacle to be crossed may be a river, a road, railway or a valley. 2. * Components of a bridge The main parts of a bridge structure are as follows: 1) Decking, consisting of a slab, girders, trusses, etc.; 2) Bearings for the decking; 3) Abutments and piers; 4) Foundations for the abutments and piers; 5) River training works, like revetment for slopes at abutments, aprons at bed level, etc; 2Thursday, October 9, 2014

3. Bridge Engineering (1) Introduction(1-1) 6) Approaches to the bridge to connect the bridge proper to the roads on either side; and 7) Handrails, guard stones, etc. The components above the level of bearing are grouped as superstructure, while the parts below the bearing level are classed as substructure. 3. * Classification (1—6) Bridges may be classified in many ways, as below: 1)  According to function as aqueduct (canal over a river), viaduct (road or railway over a valley), pedestrian, highway, railway, road-cum-rail or pipe-line bridge. 3Thursday, October 9, 2014

4. Bridge Engineering (1) Introduction(1-1) 2) According to the construction material of super-structure as timber, masonry, iron, steel, reinforced concrete, prestressed concrete, composite or aluminum bridge. 3) According to the form or type of superstructure as slab, beam, truss, arch or suspension bridge. 4) According to the interspan relations as simple, continuous or cantilever bridge. 5) According to the position of the bridge floor relative to the superstructure as deck, through, half-through or suspended bridge. 4Thursday, October 9, 2014

5. Bridge Engineering (1) Introduction(1-1) 6)  According to span length as culvert (less than 8 m), minor bridge (8 to 30 m), major bridge (above 30 m) or long span bridge (above 120). 7) According to the method of clearance for navigation as high-level, movable-bascule, movable-swing or transporter bridge. 8) According to the method of connections of the different parts of the superstructure, particularly for steel construction, as pin-connected, riveted or welded bridge. 9) According to the degree of redundancy as determinate or indeterminate bridge. 10) According to the anticipated type of service and duration of use as permanent, temporary, military (pontoon, Bailey) bridge. 5Thursday, October 9, 2014

6. Bridge Engineering (1) Introduction(1-1) 4.   Investigation for Bridges 4.1 Need for investigation To consider many factors such as the need for a bridge, the present and future traffic, stream characteristics, subsoil conditions, alternative sites, aesthetics, cost, etc. 4.2 Aim of the investigation To select a suitable site at which a bridge can be built economically, at the same time satisfying the demands of traffic, the stream, safety and aesthetics. 5. *Selection of Bridge Site The characteristics of an ideal bridge site are: 5.1  A straight reach of the river; 5.2 Steady river flow without serious whirls and cross currents; 6Thursday, October 9, 2014

7. Bridge Engineering (1) Introduction(1-1) 5.3    A narrow channel with firm banks; 5.4   Suitable high banks above high flood level on each side; 5.5 Rock or other hard inerodible strata close to the river bed level; 5.6 Economical approaches which should not be very high or long or liable to flank attacks of the river during floods; the approaches should be free from obstacles such as hills, frequent drainage crossings, sacred places, graveyards, or built up areas or troublesome land acquisition; 5.7  Proximity to a direct alignment of the road to be connected; 7Thursday, October 9, 2014

8. Bridge Engineering (1) Introduction(1-1) 5.8  Absence of sharp curves in the approaches; 5.9 Absence of expensive river training works; 5.10 Avoidance of excessive underwater construction; and 5.11 Right angles to the river is more desirable than skew angles because the latter poses more difficulties in design, construction and maintenance. A skew bridge can avoid costly land acquisition or sharp curves on the approaches. 6. * Preliminary data to be collected The engineer should collect the following information: 6.1 Name of the river, road, and location of the probable bridge sites; 8Thursday, October 9, 2014

9. Bridge Engineering (1) Introduction(1-1) 6.2 Location of the nearest G.T.S (Great Trigonometric Survey) bench mark with its reduced level; 6.3 Present and future volume and nature of traffic on the road at the bridge site; 6.4  Hydraulic data pertaining to the river, including the highest flood level, ordinary flood level and low water level, site, shape, slope, and nature of the catchment, intensity and frequency of rainfall in the catchment, and probability of large trees or rolling debris floating down the stream; 6.5  Soil profile along the probable bridge sites over the length of the bridge and approaches; 6.6 Navigational requirements, if any, for the stream; 6.7 Need for large scale river training works; 9Thursday, October 9, 2014

10. Bridge Engineering (1) Introduction(1-1) 6.8 Liability of the site to earthquake disturbances; 6.9 Availability, quality and location of the nearest quarries for stones for masonry and for concrete aggregates; 6.10 Nearest place of availability of cement, steel and timber; 6.11 Means of transport for materials; 6.12 Availability of unskilled and skilled labor for different trades required for construction; 6.13 Facilities required for housing labor during construction; 6.14 Important details of the bridges, if any, crossing the same river within a reasonable distance of the proposed bridge; 10Thursday, October 9, 2014

11. Bridge Engineering (1) Introduction(1-1) 6.15   Availability of electric power; and 6.16 Details of any utilities and services to be provided for (e.g. telephone cables, power cables, water supply pipes) along with relevant information on size and arrangement. 7. *Preliminary drawings The following drawings should be prepared at the time of investigation: 7.1  An index map drawn to a suitable scale (usually 1/50,000) showing the proposed location of the bridge, the alternative sites investigated and rejected, the existing communications, the general topography of the area, and the important towns, etc., in the vicinity. 11Thursday, October 9, 2014

12. Bridge Engineering (1) Introduction(1-1) 7.2  A contour survey plan of the stream to a suitable scale, such as 1/1000 to 1/5000(All sites worth considering should be indicated on the plan); 7.3 A site plan to suitable scale showing the details of the selected site and the details of the stream to a distance of 100 to 200 meters upstream and downstream of the selected site. It should include the following details: 7.3.1 Name of the stream, road and nearest distance marker; 7.3.2 Approximate outlines of the banks and channels at high water level and low water level; 7.3.3   Direction of flow; 7.3.4 The alignment of existing approaches and the proposed crossing with its approaches; 12Thursday, October 9, 2014

13. Bridge Engineering (1) Introduction(1-1) 7.3.5 The angle and direction of skew, if the proposed alignment is on a skew; 7.3.6 The name of the nearest inhabited identifiable locality at either end of the crossing on the roads leading to the site; 7.3.7   Location and reduced level of the bench mark used as datum; 7.3.8 Location of the longitudinal section and cross-sections of road and stream taken within the area of the plan; 7.3.9   The locations of trial pits and borings with their identification numbers; 7.3.10 The locations of all nullahs, buildings, outcrops of rocks and other possible obstructions to a road alignment; 13Thursday, October 9, 2014

14. Bridge Engineering (1) Introduction(1-1) 7.4 A cross-section of the river at the proposed bridge site to a scale of about 1/1000 horizontally and about 1/100 vertically. It should include the following information: 7.4.1 The name of the stream, road, and chainage; 7.4.2 The river bed line with banks up to a level above the highest flood level; 7.4.3   The nature of subsoil; 7.4.4  The low water level, ordinary flood level and the highest flood level; 7.4.5   If the stream is tidal, lowest and highest tide levels and mean seal level. 14Thursday, October 9, 2014

15. Bridge Engineering (1) Introduction(1-1) 7.5 A longitudinal section of the stream showing the site of the bridge with the H.F.L, O.F.L, L.W.L. and the bed levels at suitably spaced intervals along the approximate center line of the deep water channel. 7.6 Additional cross-sections of the stream at suitable distance both upstream and downstream of the proposed bridge site indicating the distance from the bridge site and showing the flood levels and L. W. L. 7.7 Catchment area map tracing the line of the ridge of the watershed from the topographical maps to a scale of 1/50,000. 7.8 Soil profile for each of the probable bridge alignments showing the bed and banks as well as the classification and levels of the layers of the subsoil and clearly marking the levels of the rock or other hard soil suitable for resting foundations 15Thursday, October 9, 2014

16. Bridge Engineering (1) Introduction(1-1) Aqui(a/e)-Water: Aquaculture n.水产业 Aquafarm n.水产养殖场 Aquakinetics [复]n.[用作单]婴幼儿深水漂浮训练法 Aquamarine n.绿玉, 碧绿色 Aquarium n.养鱼池, 玻璃缸, 水族馆 Aquashow n.水上技艺表演 Aquatel n.<英>水上旅馆(由停泊在船坞的若干游艇组成) Aquicultural adj.(=aquacultural)溶液培养的, 水栽法的 back 16Thursday, October 9, 2014