SUPERSTRUCTURESUPERSTRUCTURE( INTRODUCTION , ANALYSIS AND DESIGN CONCEPTS )( INTRODUCTION , ANALYSIS AND DESIGN CONCEPTS )

TABLE OF CONTENTS

• Introduction- Definition- Classification of Superstructures- Some Construction Methods

• Analysis of Superstructures- Loads- Statical Models for Analysis- Various Methods for Analysis- Grillage Method for Analysis (in detail)

• Design of Superstructures- In Detail for R.C. Solid Slab (by effective width method)

• Reinforcement Detailing- In Detail for Solid Slab

INTRODUCTION

• Superstructure consists of the deck structure itself -support the direct loads due to traffic and all other permanent and variable leads.

• Connection between the substructure and the superstructure – usually bearings, However, rigid connections between pier / abutments (frame bridges)

CLASSIFICATION OF SUPERSTRUCTURES

• According to materials of construction : (i) Reinforced Concrete

(a) Solid Slab/Voided Slab

(b) Slab and Girder (T-beam)

(c) Hollow Box Girder

(ii) Pre-stressed Concrete

(a) Voided Slab

(b) Slab and Girder (T/I – Beam) (Post-tension/Pre-tension)

(c) Hollow Box Girder (Post-tension/Pre-tension)

Classification of Superstructures (continued)……..

(iii) Steel – Truss, Arch, Plate Girder, Box Girder

(iv) Composite construction using steel and reinforced concrete, or reinforced and pre-stressed concrete

(a) Longitudinal and transverse beams, with concrete slab

(b) Longitudinal Plate girders, transverse beams & concrete

slab

(c) Longitudinal Box girder with concrete slab

Classification of Superstructures (continued)……..

• According to Structural Arrangement : (i) Slab – Solid/Voided

(Cast-in-situ/Pre-cast)

(ii) T/I – Girder + Slab (Girder-Pre-cast/cast-in-situ & Slab-Cast-in-situ)

(iii) Hollow Box Girder –( Single Cell/Twin Cell - Cast-in-situ / Pre-cast - segmental )

Classification of Superstructures (continued)……..

• According to inter-span relation :

(i)

(ii)

(iii)

SOME CONSTRUCTION METHODS

• Segmental Construction by incremental Launching ( cast in situ)

• Launching and Sliding Girder (Pre-cast)

• Construction of Pre-stressed Cast-in-situ girders

• Construction of Pre-stressed pre-cast girders

ANALYSIS PART

LOADS ON SUPERSTRUCTURE

• Live Load

(i) Class A – wheeled

Class 70R – wheeled / Tracked / Bogie

(ii) Braking Load

(iii) Impact Load

• Self Weight• Temperature • Creep/shrinkage • Seismic/wind

VARIOUS METHODS OF ANALYSIS

• Simple beam theory of analysis• Effective width method of analysis• Distribution factors method of analysis

(i) Morice and Little method(ii) Curbon’s method

• Grillage analysis• Orthotropic plate method of analysis• Finite element method of analysis

GRILLAGE ANALYSIS OF SUPERSTRUCTURE

DESCRIPTION

• A computer-aided method for analysis• Deck - idealized as a series of ‘beam’ elements

(or grillages), connected and restrained at their joints.

• Each element - given an equivalent bending and torsional inertia to represent the portion of the deck which it replaces.

• Restraints and supports - applied at the joints and members framing into a joint may be at any angle.

GRILLAGE ANALYSIS PROGRAM

Essentially five steps of analysis :-

• Idealization of physical deck into equivalent grillage• Evaluation of equivalent elastic inertia of members of

grillage• Application of loads to grillage• Determination of force responses and design

envelopes• Interpretation of results.

GRILLAGE MESH

Bridge Deck Idealized Model (Deflected)

SKEW DECKS

• Orientation of longitudinal members -always be to the free edges.

• Transverse members - parallel to the supports.

SLAB IDEALIZATION– Bending & Torsional Inertia of Grillage Members

• For calculation of flexural and torsional inertia - the effective width calculation of slab needed - Codal provisions

• After calculation of the effective width of slab - the deck is divided into number of T or L-beams (as the case may be)

SECTIONAL PROPERTIES OF GRILLAGE MEMBERS

• The section properties of grid lines representing the slab -calculated by :-

I = bd3/12and J = bd3/6.

• If construction materials have different properties in the longitudinal and transverse directions - correction needed

• For example - in a reinforced concrete slab on precast prestressed concrete beams or on steel beams - the inertia of the beam element ( I or J) is multiplied by the ratio of moduli of elasticity of beam Eb and also Es materials to convert it into the inertia of slab material.

SOLID SLAB – subdivision of deck slab cross-section for longitudinal grillage beams

d

b1 b2 b3 b4 b5 b6

VOIDED SLAB

d

Longitudinal beams Longitudinal beams –– for shaded region about NAfor shaded region about NA

Transverse beams Transverse beams –– at at CLCL of voidof void

DESIGN PART

DESIGN OF SOLID SLAB

Design of Solid Slab (continued)…..

Design of Solid Slab (continued)…..

Design of Solid Slab (continued)…..

Design of Solid Slab (continued)…..

Design of Solid Slab (continued)…..

TYPICAL REINFORCEMENT DETAILING

PLAN OF DECK SLAB

SECTIONS OF DECK SLAB

Reinforcement Detailing- Plan

Reinforcement Detailing- Sections

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