Abstract
Structural analysis and construction control of staged construction process is a major subject for modern long-span bridges. This paper introduces the concept of stress-free-state variable of structural elements and deduces the mechanical equilibrium equations and geometric shape governing equations for staged construction structures utilizing the minimum potential energy theorem. As the core of stress-free-state theory, the two aforementioned equations demonstrate following principles, 1) when the stress-free-state variable of a structural element is set, the internal force and deformation of the element are unique at the completion state of the structure regardless of its construction process; 2) the stress-free length of a cable is independent of its external loads, change in stress-free length of the cable corresponds to a unique variation of the cable force when load is constant; and 3) the internal force of a structural element can be independent from its geometric shape within the completion state of a staged construction structure through an active manipulation of stress-free-state variables of the element. Stress-free-state theory establishes the stage-to-stage and stage-to-completion relationships for staged construction bridges, provides a direct and efficient method for theoretical calculations and a flexible and convenient approach for the control of staged construction, and makes parallel construction and auto-filtering of thermal and temporary loading effect possible.
Highlights
Staged construction, as well as the one-step scaffold supported bridge construction, are two commonly used methods in bridge construction
3 Basic principles of stress-free-state theory Principle 1: when the stress-free-state variable of a structural element is set, the internal force and deformation of the element are unique at the completion state of the structure regardless of its construction process (Qin 2007; Qin 2003; Qin 2008b)
Principle 3: The internal force of a structural element can be independent from its geometric shape within the completion state of a staged construction structure through an active manipulation of stress-free-state variable of the element
Summary
As well as the one-step scaffold supported bridge construction, are two commonly used methods in bridge construction. In 2008, Qin derived the mechanical equilibrium equation of staged construction structures with energy method by introducing the stress-free-state variables of structural elements, further explained the relationship between the internal force and deformation of completion state of staged construction structures and their formation processes (Qin 2008b). The internal force and deformation of the structure at its completion state can be obtained by calculating and adding up the incremental variables for each step of staged construction These incremental structural analysis methods generally have three disadvantages, including: 1) the computational complexity from modified construction process, 2) the inability to consider temperature inconsistency between the design and construction site, and 3) the inability to accommodate parallel construction operations when temporary construction loads are present (Qin 2007; Qin 2008a).
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