1. Bridge Engineering (2) Bridge Forms 1. *Introduction 1.1 Beam bridges (Dongming YR Brdg)Dongming YR Brdg 1.2 Arch BridgesArch Bridges 1.3 Cable-supported bridges (cable-stayed, suspension) 1.4 Rigid frame CQ No. 1 Yangtze Brdg(cable-stayedsuspensionCQ No. 1 Yangtze Brdg 2. * Beam Bridges 2.1 Beam A ny member that carries a transverse load, i.e. ， one that causes bending, as distinct from bowing, or buckling. 2.2 Simple and continuous bridges 2.2.1 A simple single-span bridge may be of steel ( probably a plate girder), reinforced concrete or prestressed concrete. 1 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016

2. Bridge Engineering (2) Bridge Forms 2.2.2 A continuous girder is adopted for spans over 100 ft. 2.3 Truss bridges 2.3.1 Truss: a number of components joined by their ends to form a framework (usu. of small triangles) to span a gap. 2.3.2 The Warren truss: a popular frame in which all members are of the same length, making a series of equilateral triangles. 2.3.3 The Pratt, or N-girder: another commonly encountered type, easily recognized. 2.3.4 Other types of trussesOther types of trusses 2 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016

3. Bridge Engineering (2) Bridge Forms 2.3.5 The truss often erected for spans between supporting piers above 150 ft. 2.4 Cantilever bridges 2.4.1 Cantilever: A beam that "sticks out", supported at one end only. Cantilever beams may be seen in pairs, with their thick ends joined, sitting on a pier in a river. 2.4.2 The feature of a cantilever is the zero bending moment at the "free" end, and maximum at the thick end. 2.4.3 The suspended span: the middle portion between the two free ends, usu. prefabricated. 2.4.4. For larger spans, steel trusses (trussed girders) are used to reduce the depth of the bridge.trussed girders 3 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016

4. Bridge Engineering (2) Bridge Forms 3. * Arch Bridges 3.1 Terminologies 3.1.1 Arches: curved members or structures, using material in compression, the center part rising above the level of the ends. 3.1.2 Keystone: the stone which completes an arch. 3.1.3 Spring point: the end where the spring arch meets the abutment and the thrust is the greatest 3.1.4 Spandrel: the part above the arch ring when the deck is at a higher level than the crown of the arch 3.1.5 Arch (box) rib 3.1.6 Rise: 4 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016

5. Bridge Engineering (2) Bridge Forms 3.2 Arches may be pinned at one end, at both ends, or at both ends and in the center to ensure that there is no bending effect at that point, and permit movement to accommodate alterations of dimensions due to temperature changes. This is known as hinging. 3.3 The chief feature of an arch bridge, apart from it being a handsome structure, is that at the abutments there are horizontal forces as well as vertical ones, so that the resultant reactions at the abutments are inclined to the vertical. 4. *Suspension Bridges 4.1 The pylons are the tall towers that stick up above the roadway. 5 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016

6. Bridge Engineering (2) Bridge Forms 4.2 The cables are of layers of strands. 4.3 At the top the cables may be either fixed to the pylons themselves or to a kind of trolley that can move a little along the top so that there is no sideways force on the pylon. 4.4 The roadway is hung from the cables by hangers at many points along the whole length. 4.5 Suspension cables generally are in the shape of a parabola or catenary. 4.6 One feature of the suspension bridge which has given trouble in the past is the effect of wind on the roadway. Suggested Reading: www.media.uwe.ac.uk/masoud/projects/bridges/text/contents.ht m 6 Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016Wednesday, March 16, 2016