ABSTRACT
Many countries have medium span length structures built during the 70’s and designed for very low seismic forces. The evolution of the code regulations and the age of the bridges require to evaluate the seismic vulnerability.
Most of bridges are reinforced or prestressed concrete structures that according to current code regulations have insufficient seismic capacity. One alternative to reduce the vulnerability of the bridges is by increasing the stiffness and the strength of the piers or by incorporating control devices to reduce the seismic demand.
Bridges located in high earthquake prone areas have usually important displacement demands in piers. Bridges designed before current regulations normally considered low seismic base-shear coefficients that conduct to small lateral forces. Additionally, limited lap splice lengths in piers and small amount of transverse reinforcement conducted to several failures. One column pier bridges are particularly affected by insufficient lap spice length in the zone of plastic hinge formation.
One of the most common techniques to retrofit bridges substructures is the use of reinforced concrete jacketing. In this paper, we assess the expected capacity, demand and damage of seismically deficient medium-length highway bridges, supported in frame-type piers and retrofitted with reinforced concrete jacketing.
A parametric study considering all the variables involved are conducted. The seismic demand is defined with a suite of twenty accelerograms recorded close to the Pacific Coast in Mexico and generated in interplate seismic sources. The original structures consist of five 30-m span simple supported bridges with five pier heights of 5 m, 10 m, 15 m 20 and 25 m; the analyses include three jacket thickness and three steel ratios.
The bridges are composed of five simple supported 30-m long spans. Four models with different pier height are analyzed; 5-m, 10-m, 15-m, 20-m and 25-m. high bridges. Most of the bridges designed in the 70’s have columns with small longitudinal reinforcement ratios product of designs for gravitational loads. In this study, the column longitudinal reinforcement ratio was of 0.5%.
The bridge deck is a reinforced concrete slab resting on prestressed concrete AASTHO type IV girders (Figure 1). At each span end and at intermediate span length, exist diaphragms to provide lateral stiffness to the superstructure. The substructure consists of frame type piers with four circular prismatic columns and wall type RC abutments. The girders rest on elastomeric bearings located on top of the bent cap and over the abutments. Deck transverse section and pier columns. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315207681/cd556cd4-4dcf-4efe-8e29-56fc67b8bfbd/content/fig249_1.tif"/>
Non-linear static analyses and non-linear dynamic analyses of the bridges subjected to the seismic records were carried out. Results allow selecting the reinforced concrete jacketing that better improves the expected seismic behavior of the bridge models.
