The nonlinear behavior of shallow foundations under large amplitude earthquake-induced loading can result in dissipation of seismic energy through the mechanism of soil yielding beneath the foundation. In addition, foundation uplifting may shift the period of the soil-foundation-structure system away from the damaging energy content of most earthquakes. However, this yielding and uplifting may lead to excessive transient and permanent deformations (settlement, rocking, and sliding). Therefore, modeling procedures that account for foundation nonlinearity and uplift are needed before these benefits can be realized in performance based earthquake engineering (PBEE) practice. This paper adopts a beam-on-nonlinear-Winkler-foundation (BNWF) simulation methodology for modeling shallow foundation-structure systems, where seismically-induced rocking plays a predominant role in their response. Numerical results demonstrate that reasonable comparison between the nonlinear Winkler-based approach, and experimental response in terms of moment-rotation, settlement-rotation, and shear-sliding displacement can be obtained, given an appropriate selection of model and soil properties.
Uplifting of and yielding below shallow foundations supporting rigid lateral force-resisting elements can provide additional nonlinearity into a system's overall force-deformation behavior. While this nonlinearity may be advantageous, potentially reducing seismic demands, displacement compatibility may result in overstress of lateral and/or gravity-resisting elements. Incorporating this balance of benefit versus consequence in structural design is one goal of performance-based earthquake engineering ͑PBEE͒. There are a variety of approaches in design codes for estimating seismic demands and incorporating "performance" as a design goal. Such methods generally account for the displacement of an equivalent SDOF system by reducing the design strength, however, not explicitly for the case of foundation uplift. To address this shortcoming, this paper investigates the relationship between the strength ratio R and the displacement ratio C 1 using the beam on nonlinear Winkler foundation ͑BNWF͒ concept. Numerical models were constructed considering a range of soil-structure natural periods and a range of design R values. Nineteen ground motions with a broad range of characteristics are used to conduct nonlinear time-history analyses. Results from these simulations indicate that current suggestions for C 1 -R relations are highly unconservative when uplifting foundations are anticipated. Revised C 1 -R relations for uplifting foundations are presented and an example numerical comparison provided.
This paper details the novel combination of a population-based swarm intelligence algorithm, structure mechanics, geotechnical variability, and a specific construction staging methodology, to propose an autonomous construction system which can erect a bridge over arbitrary crossing geometry while satisfying project constraints and conventional design code requirements (the Proposal). The fields of metaheuristic applications in structures (MAS), unmanned aerial systems (UAS), and additive manufacturing are all independent innovations in the transportation industry. The Proposal brings these fields together, with a vision that independent drone robots with very basic programming could construct a bridge with no user interruption and without performing a conventional structural design. A simulation as proof-of-concept is compared with a modern bridge design; the result is a modest increase in materials with an anticipated dramatic saving in labor. The paper also studies the effects of geotechnical variability for insight into preparation for possible future construction methodologies and algorithms. The Proposal has promise where socio-economic issues may be a factor, such as construction of infrastructure in remote locations or developing nations, and emergency repair or replacement of bridges. With recent U.S. policy supporting a permanent lunar presence and expanding Moon to Mars exploration through the Artemis program, the Proposal may also assist infrastructure development in advance of human missions.
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