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Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Pier Design for Bridges in BS Eurocode II and BD 37/01 Sandipan Goswami B.Sc, BE, M.Tech, FIE, C.Eng, PE (M) Abstract: This chapter describes the step wise design procedure Bridge Pier on Pile Foundation in BS Eurocode 2, for Calculation of Dead Load of Super-Structure, Super Imposed Dead Load (SIDL), Reactions on Applications of Live Load over Pier, Longitudinal Forces, Seismic Component of Super-Structure Dl and SIDL at LWL Condition, Seismic Component of Live Load LLW Condition, Water Current Forces, Hydrodynamic Forces, Summary of Forces, Maximum Pile Capacity, Maximum and Minimum Reaction over Pile, Horizontal Capacity of Pile, Forces at Pile Cap Bottom for Design of Pile and Pile Cap at ULS, Design Forces for Pile Cap at ULS, Bending Moment for Design of Pile Cap in Transverse Direction at ULS, Punching Shear, Pile Moment Capacity at ULS, Shear Force at ULS, Stress Check for Pile at SLS, Un-factored Forces for Design of Shaft, Load Combination for Forces at Base of Pier Shaft at ULS, Check for Pier Shaft Slenderness Ratio and obtain Second Order Forces, Construction of Interaction Diagram, Load Combination Forces at Base of Pier Shaft at SLS, Check for Crack Width at SLS, Design of Pier Cap Transverse Direction, Design of Pier Cap for Shear and Torsion Reinforcements, Load Combination Definition for Pile Capacity 8.0 General Slender piers should be used wherever that is possible allowing sufficient flexibility to allow temperature, shrinkage and creep effects to be transmitted to the abutments even without the need for bearings at the piers, or intermediate joints in the deck A slender bridge deck usually looks best when supported by slender piers without the need for a downstand crosshead beam It is the proportions and form of the bridge as a whole which are vitally important rather than the size of an individual element viewed in isolation The overall configuration of the bridge pier determines the combination of loads and movements that have to be designed for For example if the pier has a bearing at its top, corresponding to a structural pin joint, then the horizontal movements will impose moments at the base, their magnitude will depend on the pier flexibility Sometimes there are special requirements by rail or river authorities if piers are positioned within their zone of influence In the case of river authorities a 'cut water' may be required to assist the river flow, or independent fenders to protect the pier from impact from boats or floating debris A similar arrangement is often required by the rail authorities to prevent any significant damage of the pier by minor derailments striking the pier Although the piers are designed to resist major derailments and if demolished completely by a train derailment then the deck should not collapse Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II 8.1 Pier Design in BS Eurocode II and BD 37/01 8.1.1 User's General Design Data Span c/c of brg From C/L of brg To C/L of exp J Exp Gap Overall span = = = = Left Span 26.52 m 0.5 m 40 mm 27.52 m Depth of super-structure Wearing Coat thickness Depth of Bearing + Pedestal (minimum) = = = 1.42 65 500 Overall carriageway width Clear carriageway width Cross Camber = = = 11.85 m 10.0 m 2.50% m mm mm Right Span 26.52 m 0.5 m 40 mm 27.52 m 1.42 65 500 m mm mm Material Used and There Properties Concrete Grade of Concrete, fck Mean value of concrete compressive strength, fcm Design Concrete compressive strength, fcd Secant Modulus of Elasticity, Ecm Mean axial tensile strength, fctm = = = = = M 35 Mpa 45 Mpa 0.447 x fck = 15.63 MPa 32308.249 MPa 2.77 Mpa Reinforcing Steel Grade of Reinforcement, fyk Design yield strength of reinforcement, fyd Modulus of Elasticity, Es RCC Density Dry density of earth = = = = = Fe 500 Mpa 0.870 x fyk = 434.78 Mpa 200000 Mpa 2.5 t/m3 t/m3 Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Analyses Assumption Environmental parameters Relative humidity Exposure condition Modulus of Elasticity for Concrete For short Term loading, Ecm For long Term loading , Ecm' φ Creep coefficient for Foundation, φ Ecm' = = = = = = = Creep for pier shaft Cross-sectional Area, Ac Perimeter in contact with atmosphere u Notational size, ho, 2Ac/u Age of concrete at the time of loading to t∞ considered φ (∞, 90) 32308.24972 Mpa Ecm/ (1+ φ) Creep coefficient ( As ho = ∞ , For foundations) 16154.124 Mpa = = = = = = Ecm' Creep for pier cap Cross-sectional Area, Ac Perimeter in contact with atmosphere, u Notational size ho, 2Ac/u Age of concrete at the time of loading to t∞ considered φ (∞, 90) Ecm' 45 % Moderate = = = = = = = = = 7.73 m 14.77 m 1046.854 mm 90 days 25550 days = 1.66 (Refer Appendix B) 1.82 x (Increased by 10% on the conservative side) 11441.7 N/mm 2.50 m 7.00 m 714.285 mm 90 days 25550 days 1.74 (Refer Appendix B) 1.91 x (Increased by 10% on the conservative side) 11086.3 N/mm Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Serviceability Limit State : Max permissible Stress in Concrete Rare Combination Quasi permanent Combination = = 0.48 x fck 0.36 x fck Max permissible Stress in Steel (rare) Permissible crack width, wk, max = = 300 0.3 Seismic Parameter Seismic Zone Type of soil Zone factor, Z Importance factor, I Response Reduction Factor, Rlong Response Reduction Factor, Rtrans Response Reduction Factor, Rvert = = = = = = = IV medium 0.24 1.2 3 Level Details Formation level Ground Level Pile Cap Top Level Pile Cap Bottom Level Length of pile below pile cap bottom Pile Founding Level HFL = = = = = = = 100.900 m 93.435 m (Min Bed Level) 92.935 m 91.135 m 20.000 m 71.135 m 96.000 m (As per Hydrological Calculation) 87.835 m 1.2 m 275.0 Tonne (Non-Seismic case) 343.8 Tonne (Seismic Case) Min of Scour Pile Diameter Pile capacity = = = = = = 16.8 12.6 Mpa Mpa Mpa mm Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Pier Components Figure 8.1 (1) - Pier Component Figure 8.1 (2) - Pier at Left or Tight Row of Pile Centre Line Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Figure 8.1 (3) - Pier Cap Figure 8.1 (4) – Layout of Piles at Pile Cap Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Forces due to Self weight of Sub-Structure and Foundation Forces @ pile cap bottom (L-T) Axis eL = CG from c/L of pile group (along L-L axis) eT = CG Form c/L of pile group ( along T-T axis) eY = CG From CG of pile group Table 8.1 – Calculating Self Weight of Sub-Structure Table 8.2 – Calculating Self Weight of Pile Cap Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Total Weight of sub-structure & foundation Lever arm from cg of pile cap (along LL axis) Moment MTT = = = 365.09 T 0.00 m 0.00 Tm Lever arm about c/L base (along TT axis) Moment MLL = = 0.00 m Tm Table 8.3 – Calculating Self Weight of Back Fill Total Weight of Earth fill Lever arm from cg of pile cap (along X'X' axis) Moment MZ'Z' Lever arm about c/L base (along Z'-Z' axis) Moment MX'X' = = = = = 36.64 0.00 0.00 0.00 0.00 T m Tm m Tm Buoyancy Volume of pile cap Volume of pier shaft Buoyant weight over pile cap & pier shaft Buoyant weight over pier shaft = = Total = = = 79.87 m3 23.695 m3 103.56 m3 -103.561 Tonne -23.695 Tonne Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II 8.1.2 Dead Load Calculation of Super-Structure Table 8.4 - Dead Load Reaction from Super-structure 8.1.3 Calculation of Super Imposed Dead Load (SIDL) Table 8.5 - Forces at Centre Line of Pile Cap 8.1.4 Reactions on Applications of Live Load over Pier Figure 8.2 – Lengths of Girder-Deck on Either Side of Pier Detail Design of Bridge Piers on Pile Foundations in BS Eurocode II Table 8.6 – Axle Loads and Distance of Vehicle Live Loads Table 8.7 – Support Reactions for Live Loads CG above FRL = 1.20 m 10