Investigating the Behavior of Modular Truss and Lattice Bridges with Hybrid System and Internal Redundancy

This research advances two steel modular bridge approaches, exploring the concept of modularizing nodal connectors while using standard sections as members. Modularity and redundancy are integrated, offering reduced cost and construction time as well as enhanced safety. The modular joint, a concept developed in prior research and advanced in this dissertation, is a built-up steel nodal connector that joins standard wide-flange members through moment-resisting connections to form a truss-like bridge which can tolerate the loss of a diagonal member. These flexural connections enable incremental launching, a rapid erection method that avoids heavy machinery and temporary supports. Feasibility is demonstrated through a logistics study and staged construction analyses. A hybrid redundancy approach is introduced, where the moment-resisting connections provide system redundancy (i.e., the structure can tolerate diagonal loss) and built-up chords, end diagonals, and floor beams provide internal redundancy (i.e., fracture does not propagate through bolted components). Performance is evaluated through (1) explicit dynamic analyses, evaluating the strain rates as the high-velocity stress wave from the fracture is propagated and (2) static analyses considering redundancy load combinations prescribed in the American bridge design code. The lattice joint, a built-up nodal connector comprised of welded plates inspired by the Système Eiffel, is used to from a lattice topology with WT sections as members. Hybrid redundancy is achieved through flexural connections and back-to-back bolted WT chords. Behavior numerically investigated under sudden diagonal and chord loss. A stress-based design tool was developed to guide the selection of lattice topologies for enhanced structural efficiency, reduced construction complexity, and modularity, and is demonstrated through a parametric study of 2450 geometries. Research objectives include: (1) evaluating incremental launching of truss bridges composed of modular joints, (2) introducing and investigating a hybrid approach to redundancy (i.e., internal redundancy for the chords, end diagonals, and floor beams and system redundancy for the diagonals), for truss bridges composed of modular joints and (3) investigating the behavior of modular lattice bridges and developing a stress-based design tool to select an efficient lattice topology. Ultimately, this research demonstrates that the modular and lattice joint technologies create efficient, cost-effective, and highly redundant bridges.本研究提出了两种钢制模块化桥梁设计方案，探索了将节点连接器模块化、以标准型材作为桥梁构件的设计理念。该方案整合了模块化与冗余性两大特性，可有效降低建造成本与施工周期，同时提升结构安全性。模块化节点（modular joint）为前期研究提出、本论文进一步优化的装配式钢制节点连接器，通过抗弯连接（moment-resisting connection）将标准宽翼缘构件拼接为桁架式桥梁，可实现单根斜杆失效后的结构容错。这类抗弯连接支持顶推施工法（incremental launching）——一种无需重型工程机械与临时支撑的快速架设工艺。本研究通过施工后勤调研与分阶段施工分析验证了方案的可行性。研究引入了混合冗余设计方案：抗弯连接提供体系冗余（即结构可耐受斜杆失效），而装配式弦杆、端部斜杆与横梁则提供内部冗余（即断裂不会在螺栓连接构件中扩散）。性能评估通过两类分析完成：(1) 显式动力学分析（explicit dynamic analysis），用于评估断裂产生的高速应力波传播过程中的应变率；(2) 考虑美国桥梁设计规范（American bridge design code）规定的冗余荷载组合的静力分析。格构式节点（lattice joint）是受埃菲尔体系（Système Eiffel）启发的装配式焊接钢板节点连接器，以WT型钢（WT section）作为构件组成格构拓扑结构。该方案通过抗弯连接与背对背螺栓连接的WT型钢弦杆实现混合冗余，研究团队对斜杆与弦杆突发失效工况下的结构性能进行了数值模拟。本研究开发了一款基于应力的设计工具，可用于指导格构拓扑结构的选型，以提升结构效能、降低施工复杂度并实现模块化设计，并通过涵盖2450种几何构型的参数化分析验证了该工具的实用性。本研究的目标包括：(1) 评估由模块化节点组成的桁架桥梁的顶推施工可行性；(2) 针对模块化节点桁架桥梁，提出并研究混合冗余设计方案（即弦杆、端部斜杆与横梁采用内部冗余，斜杆采用体系冗余）；(3) 研究模块化格构桥梁的结构性能，并开发基于应力的设计工具以选型高效格构拓扑结构。最终，本研究证明模块化节点与格构式节点技术可打造兼具结构效能、成本效益与高冗余性的桥梁结构。