Michael Chi Ho Yam

A new type of Fe–Mn–Si alloy damper is developed in this study to enable significant enhancement of the low-cycle fatigue (LCF) resistance compared with conventional metal dampers. A set of material tests was conducted first to foster a good understanding of the basic mechanical properties of the Fe–Mn–Si alloy, followed by a comprehensive experimental study on 18 shear damper specimens, considering different materials, connection types, restraining conditions, and loading protocols. A numerical investigation was also conducted to help interpret the test results. Among other important findings, the study reveals that the Fe–Mn–Si alloy exhibits a non-obvious yield plateau followed by noticeable strain hardening under monotonic loading. The fracture strain attains 57.4%, showing good ductility. Under cyclic loading, the Fe–Mn–Si alloy dampers exhibit different failure modes compared with their normal steel counterparts. The former mainly fails in fracture near the center of the plate, whereas the fracture of the latter tends to initiate from the edge. Importantly, the Fe–Mn–Si alloy dampers show fatigue life and total energy dissipation capacity up to 10 times that of their steel counterparts. Using buckling-restraining plates brings further benefits to the fatigue resistance and energy dissipation capacity. A combined kinematic/isotropic hardening model is shown to adequately capture the hysteretic behavior of the Fe–Mn–Si alloy material, where calibrated parameters are given. Finally, building on the findings from the present study, future research opportunities regarding the analysis and design of Fe–Mn–Si components, including their weld and heat affected zones, are highlighted.

Logistics planning and management are integral to the successful management of construction projects. Although on-site logistics are critical to efficient project delivery, they receive less attention in terms of research. This research introduces a new method for planning on-site logistics operations utilizing vertical supply systems (VSS) in high-rise projects. This method challenges the limitations of using critical path method and Resource Constrained Project Scheduling Problem in scheduling high-rise projects. The presented method treats lifting operations as activities with durations. The method presents a new classification of lifting activities based on their relation to other works, and it prioritizes the assignment of VSS to lifting activities based on the flexibility of VSS choice for each task. These two novel contributions allow planning construction works to match the capacity of available VSS, and it allows an efficient distribution of lifting tasks among available VSS. This method was applied to two towers in an ongoing project. The application to the first tower was during construction which allowed measuring tangible improvements on site and the other applied during the planning stage. The application of this method resulted in shorter floor cycles by 20% to 30%, less idle workers and more efficient cost control.

Although steel moment resisting frame (MRF) systems had long been recognized as effective seismic resistant structures, recent earthquake events and seismic loss estimations indicated that uniform damages of structural members and significant residual deformations would be expected after even a moderate earthquake event for steel MRF systems designed following the conventional ductility‐based design philosophy, and this incompleteness produced the impetus for overhaul of design methodologies and developing innovative systems. With the goal of enhancing the seismic performance of steel MRF structures in low‐to‐moderate seismic regions, this research explored the seismic behavior of high‐strength‐steel (HSS) frame with energy dissipation bays (EDBs) equipped with buckling hinge beams, denoted as the HSSF‐BHEDB system. In particular, the HSS frame is composed of steel with the nominal yield strength higher than 460 MPa, and the buckling hinge beams in the EDBs are constructed with cross‐sections classified as Class 3 or Class 4 by Eurocode 3. The motive of the novel design concept was to improve the structural nonlinearity of steel MRF systems with encouraging damage evolution mode and controllable residual deformations under earthquakes, and the limited energy dissipation of both the buckling hinge beams composed of slender cross‐sections and HSS members can provide a solution for structures in low‐to‐moderate seismic regions. In this work, the design concept and the rationale of the HSSF‐BHEDB were explored in detail. Then, a large‐scale quasi‐static test of a structure was conducted to provide experimental evidence and assess the feasibility of the design concept, and the behavior of the specimen from inception of yielding to failure was completely investigated. The test results showed that the system was characterized by the damage‐control behavior that diverted inelastic damages in the buckling hinge beams of the energy dissipation bay (EDB) in a wide deformation range. In the stage where the HSS frame initiated inelasticity and the energy dissipation of buckling hinge beams deteriorated, a ductile manner was still achieved. In addition, the controllable residual deformations of the specimen highlighted the satisfactory recentering behavior of the HSSF‐BHEDB structure. Lastly, the applicability of the bilinear hysteretic model of significant post‐yielding stiffness ratio and trilinear hysteretic model for featuring the hysteretic behavior of the HSSF‐BHEDB system in different yielding stages were validated by the test results.