Improvement in seismic configuration of slender Reinforced Concrete wall piers on isolated footings
Published on Jan 1, 2010
In the current seismic design practice, capacity design of slender Reinforced Concrete (RC) wall piers without enlarged boundary elements and on shallow footing considers plastic hinge to occur at the base along with prevention of other modes of failure during strong earthquake shaking. However, the re-entrant corner of wall pier-footing junction makes it vulnerable to significant damages during strong earthquake shaking. This may require costly seismic retrofitting of bridge footing after every earthquake. The present study investigates a new geometric configuration at wall pierfooting junction concerned with smooth flow of forces from the pier to the footing. A wall pier from a continuous bridge is provided with linear and curvilinear tapered configurations at the bottom. Linear elastic finite element analysis is carried out in SAP2000 program using 8-noded solid elements for modeling both the wall pier and the footing, and smeared spring elements for soil flexibility. Actual vertical forces and maximum possible lateral forces are estimated during the formation of plastic hinge at the base of the wall pier. Under these forces, the proposed wall pier-footing system exhibits rigid block-type behaviour irrespective of soil flexibility. It is observed that curvilinear taper with a particular profile ensures the most favorable stress distribution and prevents damage in footing below ground level. The region of damage is located above the tapered region and this can be located above normal ground level. Strategies are presented to suitably proportion the tapered wall pier-footing portion. These strategies are based on three criteria, namely (a) geometry of the curvilinear taper, (b) bearing failure of the underlying soil, and (c) length of footing in contact with the soil. In most of the cases, bearing failure criterion of soil governs the dimensioning of the wall pier-footing system. The detailed parametric study shows the necessity of stress-based design philosophy of tapered wall pier-footings.