The Collapse of Fukae (Hanshin Expressway) Bridge, Kobe, 1995: The Role of Soil and Soil-Structure Interaction

The paper investigates the role of soil in the collapse of a 630m segment (Fukae section) of the elevated Hanshin Expressway during the severe Kobe earthquake of 1995. From a geotechnical viewpoint, the earthquake has been associated with extensive liquefactions (notably of reclaimed ground), lateral soil spreading, and damage to waterfront structures. However, there is evidence that soil-foundation-structure interaction (SFSI) in non-liquefied ground played a detrimental role in the seismic performance of local structures, including the one under investigation. The bridge consisted of single circular concrete columns monolithically connected to a concrete deck, founded on pile groups in alluvium sand and gravel. There were 18 spans in total, all of which suffered a spectacular pier failure and transverse overturning. Several factors associated with poor structural design have already been identified. The scope of this paper is to complement the earlier studies by examining the role of soil in the collapse. Specifically, the following issues are discussed: (1) seismological and geotechnical information pertaining to the recorded ground- motions; (2) soil amplification; (3) response of soil-foundation-superstructure system; (4) response of nearby structures that did not collapse. Results indicate that the role of soil in the collapse was triple: First, it modified the bedrock motion so that the frequency content of the resulting surface ground motion became disadvantageous for the particular structure. Second, the compliance of soil and foundation altered the vibrational characteristics of the bridge and moved it to a region of stronger response. Third, ductility demand on the pier was higher than the ductility demand of the system. The increase in seismic demand on the piers may have exceeded 100% in comparison with piers fixed at their base. The results of the study contradict the widespread view of an always-beneficial role of soil-foundation-structure interaction on seismic response

Chacao Channel Bridge – the Design Challenges

The Chacao Channel bridge, a planned privatized/concession bridge project, is to link the island of Chiloé with continental Chile through the Chacao Channel. When completed, it will be the longest suspension bridge in South America (2,365 m) with two approximately equal spans linking three pylons. The location of the bridge presents a combination of unprecedented challenges in the design and construction making it very unique, including: extreme seismicity with the largest earthquake recorded to date anywhere in the world having occurred very close to the envisioned bridge location (the 1960 Valdivia Earthquake with a moment magnitude of 9.5!); extremely strong sea currents and tide fluctuations within the channel (up to 5-6 meters/sec and 6 meters, respectively); the general area being surrounded by active volcanoes; and a history of Tsunamis. The above extreme challenges resulted in construction cost escalations; inevitably, in 2006, after a significant portion of the investigations and design was completed, the Chilean ministry of Public Works put the project on hold. The above extreme physical challenges were the main reason for the cost escalation. This paper provides an overview of the design of the envisioned bridge, discusses the methodology to overcome the unique challenges of the bridge location and focuses on the geotechnical and seismic aspects of the design

Kinematic Winkler modulus for laterally-loaded piles

© 2017 Beam-on-dynamic-Winkler-foundation models are widely used to study kinematic soil-pile interaction. Winkler models consider the pile as a flexural beam and simulate the restraining and dissipative action of soil through independent springs and dashpots along its axis. Their performance is related to the proper selection of the spring stiffness and dashpot coefficient which depends on parameters such as pile geometry, pile-soil stiffness ratio and boundary conditions. Expressions for static and dynamic Winkler moduli from literature were implemented in a Winkler model to assess its ability to predict the curvature ratio and kinematic response factors for various pile boundary conditions. Based on an existing static expression, a frequency-dependent, logarithmic-based Winkler modulus is proposed. This modulus offers an attractive and versatile alternative to existing mathematically complex formulations as it is capable of capturing resonant effects and can be used for both inertial and kinematic analyses, while all other frequency-independent expressions from literature are limited by their unique application to kinematic problems. A comprehensive graphical comparison is given between the results from the Winkler model, using existing and proposed moduli, and the more accurate FE solution to guide the user in selecting the most appropriate modulus for the problem to be analyzed