A Self-Learning Manual - Institution of Engineers Mauritius

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A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU 12. Why is the span length ratio of end span/approach span to its neighboring inner spans usually about 0.75? (SA3) From aesthetic point of view, an odd number of spans with a decrease in length in the direction of abutment is desirable. Moreover, spans of equal length are found to be boring. However, the arrangement of irregular span lengths is not recommended because it gives a feeling of uneasiness. From structural point of view, for a multi-span bridge with equal span length, the sagging moment at the mid-span of the end span/approach span is largest. In order to reduce this moment, the span length of end span/approach span is designed to be 0.75 of inner spans. However, this ratio should not be less than 0.40 because of the effect of uplifting at the end span/approach span support. Note: End span refers to the last span in a continuous bridge while approach span refers top the first span of a bridge. 13. What is the consideration in selecting the orientation of wing walls in the design of bridge abutments? (BA1) There are three common arrangements of wing walls in bridge abutments based on Dr. Edmund C Hambly (1979): (i) Wing walls parallel to abutments This is the simplest and shortest time to build but is not the most economical design. This design has the advantage that it has least disturbance to existing slope embankment. (ii) Wing walls at an angle to abutments This is the most economical design among the three options in terms of material cost. (iii) Wing walls perpendicular to abutments Though it is not the most economical design, the wing walls provide a continuous alignment with bridge decks which provide supports to parapets. However, they cause disturbances to adjacent structures and utility services during construction. Moreover, if the bridge is curved, the wing walls may hinder the road curvature. One the other hand, when the wing walls are structurally connected to the 18
A Self-Learning Manual Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU abutment, then structural advantage can be taken by the stability of box structure. Fig. Different orientation of wing walls. 14. What is the significance of null point in bridge deck? (BDD3) The null point is the position of zero movement in the bridge deck. When the bridge deck is pinned at a single pier, it provides the location of null point with no deck movement. However, when the bridge deck is pinned to more piers, the position of null point has to be calculated. The 19
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A Self-Learning Manual - Institution of Engineers Mauritius

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