Concrete Road Bridges

Dr. Lakshmy Parameswaran, Chief Scientist, Bridges & Structures Division CSIR-CRRI, New Delhi

Planning, design and construction of bridges and flyovers is very challenging at places with space constraints. There has been rapid development with the availability of high strength steel and concrete. With the increasing span of these structures large number of continuous bridge is being constructed especially using precast segmental construction. There has been improvement in code of practices in India with the introduction of limit state design method, Special Vehicle (SV) loading and fatigue load for bridge design. This has led to the design of bridge bearing as well. In this paper an attempt has been made to discuss these developments and some of their implications.

Introduction

There has been advancement in the area of bridge engineering in India with the introduction of limit state design philosophy, new special vehicle loads and fatigue vehicle for bridge design and usage of construction materials with high strength. Considering these developments and giving importance to durability aspects, it is possible to achieve target design life of 100 years for concrete bridges. With increase in span length of the bridges, more number of continuous bridges (three of four span units) is being built during the last two decades which has led to the development of high capacity bridge bearings, POT bearing, POT-PTFE bearing sand spherical bearings. Also, modular expansion joints have replaced the widely used strip seal expansion joints in many bridges.

Precast segmental construction technology gained popularity as they are used to achieve accelerated bridge construction, better quality control, low life cycle cost and elements with difficult shapes and congested reinforcement can be handled at ground level. This technology demands no formwork at site and therefore, minimal disruption to existing traffic during construction. With only erection work at site, this leads to reduction of noise and dust pollution. When this technology is adopted for large projects, the segments can be standardized which helps in cost saving.

Another development was the use of Reinforced Earth (RE) technology for abutments instead of conventional retaining walls. In RE wall construction, precast concrete panels are stacked without any bond with adjacent units. Each Panel is tied back to earth fill by straps that are buried in retained embankment during construction and results in lighter structure. This is useful even in ground not suitable to construct foundation for retaining wall.

This paper highlights the features of IRC: 112-2011 and new loads introduced for bridge design in IRC: 6, i.e., Special vehicle loading and Fatigue vehicle for bridge design.

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