Numerical Analysis and Full-Scale Tests of Concrete Underground Ductbanks for Assessment of their Seismic Vulnerability

The paper focuses on full-scale experimental and numerical study of underground concrete ductbanks. The concrete ductbanks are commonly used in many seismic regions throughout the world with the U.S.A. and New Zealand being representative examples. The main purpose of the concrete ductbanks is to provide protection for buried high-voltage transmission cables from environmental and mechanical effects. Therefore, structural integrity of concrete ductbanks is crucial for uninterrupted power supply to large cities that is especially important in providing emergency services after an earthquake and avoiding massive blackouts. Design of concrete ductbanks varies from simple unreinforced concrete covering plastic conduits to well-engineered reinforced concrete with special hold downs supporting the conduits. The structural integrity can be compromised by the many major events, including seismic impact, liquefaction and soil settlement. To assess structural capacity of the ductbanks and develop new design recommendations a number of full-scale ductbanks was tested in static loading at the Pacific Earthquake Engineering Research Center, the University of California at Berkeley. Performance of ductbanks in pure shear and bending tests was studied. The full-scale tests were accompanied by extensive component test program that included compression/tension of polymer conduits with and without joints and tension/compression slippage tests of conduits embedded into concrete. Information obtained from the tests provided a suitable opportunity for the calibration of a detailed FE model which was in turn used in dynamic and static analytical simulations. Based on this sophisticated model capturing replicating performance of tested full-scale specimens a simplified model for design work of utility engineers was developed.