VIII Overview Of Design Guidelines A Bridge Design

VIII. Overview Of Design Guidelines A. Bridge Design Tips: n Use Computerized step-backwater model such as HEC-2, HEC-RAS or WSPRO n Take cross sections 1) far downstream 2) at the face of the bridge 3) at the bridge opening 4) far upstream n Utilize guidance (such as Hydraulics of Bridge Waterways) produced by Federal Highway Administration and/or the U. S. Army Corps of Engineers n Utilize Scour Countermeasures: such as provision of deep toe-downs on bridge piers and abutments or construction of spur dikes and jetties n Meet minimum freeboard requirements listed in the literature See these resources: Various City/County Design Manuals and CCDC-01 (5. 4), CCDM-99 (1005), CTDM-89 (9. 5), FITD Class CD 1

Example Large Scale Bridge 2

Example Small Scale Bridge 3

VIII. Overview Of Design Guidelines B. Culvert Design Tips: n n n n Consider Step-by-Step Procedures for Sizing Culverts See Literature for Explanations/Equations of Culvert Hydraulics Determine whether a culvert is under inlet or outlet control See Guidance for Culvert Inlet/Outlet Design and Protection Consider Countermeasures for Culvert Sedimentation and Erosion See Nomographs to simplify equation solving See guidance equations to evaluate the appropriateness of using a culvert in lieu of a bridge See guidance for culvert material selection See these resources: Various City/County Design Manuals and CCDC-01 (5. 1 to 5. 3), CCDM-99 (1001 to 1004), CTDM-89 (11), YCDM-98 (8. 2 to 8. 4), FITD Class CD 4

Example Small Culverts 5

Example Culvert Inlet and Outlet Protection 6

Example Culvert Inlet and Outlet Control Diagrams 7

Example Culvert Flow Types 8

Example Culvert Nomograph 9

VIII. Overview Of Design Guidelines C. Dip Crossing Design Tips: Definition: “Crossings of watercourses which are designed to allow drainage to flow across roadways at-grade are commonly referred to as either ‘at-grade’ or ‘dip’ crossings” (CTDM-89). n Design Dip Crossings to have a 4% minimum cross-slope to reduce roadway sedimentation n At a minimum, place a two-foot-deep cutoff wall along the upstream side of the dip crossing to protect against general scour n Place a minimum 3 -foot-deep cutoff wall downstream of the dip crossing to protect against local scour and channel degradation See these resources: Various City/County Design Manuals, CTDM-89, FITD Class CD 10

Examples of Dip Crossings 11

VIII. Overview Of Design Guidelines D. Low-Flow Channel Crossing Design Tips: Definition: When “the bottom of the channel cross section is too wide to efficiently convey the low-flow discharges [which instead] creates an incised low-flow channel that may meander back and forth across the bed of the channel. . . ” And, “the meandering process can cause frequent and unnecessary scouring at the toe of the primary banks…[which can] even destabilize totally lined channels. ” (CTDM-89). n Possibly construct a low-flow channel within any larger channel in order to restrict the low flows to a designated area within the primary channel. n The designed low-flow channel should be designed such that the unit discharge associated with the 2 -year storm event is the same as pre-construction conditions. See these resources: Various City/County Design Manuals, CTDM-89, FITD Class CD 12

Example Low Flow Channel 13

VIII. Overview Of Design Guidelines E. Other Design Topics n Design Guidance are Similarly Available for the Following – Levee Systems See this resources: FITD Class CD 14

VIII. Overview Of Design Guidelines E. Other Design Topics n Levee System: Illustration Streams with well-developed natural levees tend to be of constant width and have low rates of lateral migration. Well-developed levees usually occur along the lower courses of streams or where the floodplain is submerged for several weeks or months a year. If the levee is breached, the stream course may change through the breach. 15

VIII. Overview Of Design Guidelines E. Other Design Topics n Design Guidance are Similarly Available for the Following – Levee Systems l FEMA Requirements See this resources: FITD Class CD 16

VIII. Overview Of Design Guidelines E. Other Design Topics n Design Guidance are Similarly Available for the Following – Levee Systems l n FEMA Requirements Channelization See this resources: FITD Class CD 17

Channelization Illustration 18

VIII. Overview Of Design Guidelines E. Other Design Topics n n n Design Guidance are Similarly Available for the Following – Levee Systems Channelization Super-Elevation See this resources: FITD Class CD 19

VIII. Overview Of Design Guidelines E. Other Design Topics n n n Levee System Channelization Super-Elevation: Illustrations Because of the change in flow direction which results in centrifugal forces, there is a superelevation of the water surface in bends. The water surface is higher at the concave bank than the convex bank. 20