![]() ![]() Prestressed pre-tensioned inverted T beams with insitu fill. Other topics which need to be considered are: i.Įxisting services (Gas, Electricity, Water, etc) Rivers and streams (liability to flood) Existing property and rights of way Access to site for construction traffic Selection of Bridge Type The following table is intended to be a rough guide to the useful span ranges of various types of deck. It is important to determine the condition of the bridge site by carrying out a comprehensive site investigation.ĮN 1997-2: Ground investigation and testing covers the requirements for the Soil Survey. If the bridge is to cross a road that is on a curve, then the width of the opening may have to be increased to provide an adequate site line for vehicles on the curved road. The Eurocode Standard (EN 19911-7 clause 4.3.2(1) quotes clearances from roadway surfacing to the underside of the deck to avoid impact damage. #Bs 5400 Part 2 Pdf manual#Headroom requirements have to be maintained below the deck the minimum standards for UK Highway bridges are given in TD 27 of the Design Manual for Roads and Bridges. The economic implications of raising or lowering any approach embankments should then be considered.īy lowering the embankments the cost of the earthworks may be reduced, but the resulting reduction in the construction depth may cause the deck to be more expensive. The structure must be pleasing to look at.ĭecisions about form and materials are made at preliminary design stage the sizes of individual members are finalised at detailed design stage.Ĭonstraints The construction depth available should be evaluated. The structure must make minimal demands on labour and capital it must cost as little as possible to build and maintain.Īt preliminary design stage it means choosing the right types of material for the major elements of the structure, and arranging these in the right form.Īppearance. ![]() The ideal structure must not suffer from local deteriorationfailure, from excessive deflection or vibration, and it must not interfere with sight lines on roads above or below it.ĭetailed design cannot correct faults induced by bad preliminary design.Įconomy. This is more significant at detailed design stage as generally any sort of preliminary design can be made safe. It must be capable of carrying the loading required of it with the appropriate factor of safety. The ideal structure must not collapse in use. Since concrete is weak in tension in normal reinforced concrete construction cracks develop in the.ĭecisions taken at preliminary design stage will influence the extent to which the actual structure approximates to the ideal, but so will decisions taken at detailed design stage.Ĭonsideration of each of the ideal characteristics in turn will give some indication of the importance of preliminary bridge design. ![]()
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