Optimization of Steel Panel Damper for Moment Resisting Frame Designs

Autor: Chu-Hung Chang, 張舉虹
Rok vydání: 2018
Druh dokumentu: 學位論文 ; thesis
Popis: 106
The strength, stiffness and ductility of the lateral force resisting frame can be enhanced by incorporating the steel panel dampers (SPDs) into a moment resisting frame (SPD-MRF). The proposed 3-segment SPD is a steel wide-flange section,which consists of one middle inelastic core (IC) and two end elastic joints (EJs). During the earthquake, the two EJs of the same cross-sectional property, are designed to remain elastic while the IC could undergo large inelastic shear deformation thereby dissipating seismic energy. In order to sustain a large deformation and delay the shear buckling of the IC web, stiffeners must be properly deviced. The shear strength of the SPD can be determined from the shear area and yield stress of the IC web. Therefore, the stiffness and strength of SPD can be decoupled. The lateral stiffness of the SPD-MRF can be enhanced by either increasing the stiffness of the SPD or boundary beams. Thus, the stiffness of the two half-height SPDs connected to the boundary beam subassembly can be defined and analyzed by using the four inflection points. In this study, optimization algorithm is adopted to design the SPD-MRF members, and to achieve the minimum steel weight design. The results, comply with the seismic design requirements and the specified lateral stiffness enhancement of SPD-to-beam subassembly for a wide range of SPD strengths and beam spans. In this study, it is assumed that two identical SPDs are attached to the mid-span of the boundary beam. The focus of the study is the designs of the SPD, the boundary beam and the SPD-to-beam panel zone. The MATLAB optimization toolbox combined the simulated annealing algorithm with the gradient descent method is adopted to find the minimum steel weight design. The objective function is the total weight of the SPD, the boundary beam and the panel zone. The design variables are SPD’s sectional properties of the SPD, the boundary beam and the doubler plate thickness. Constraints must be the capacity design of the SPD, boundary beam and panel zone, the stiffeners of the IC web, compact section and lateral torsional buckling limit state design requirements. While consider the story height, beam clear span, unbraced beam length, SPD shear strength, steel grade of SPD and beam as given parameters, the lightest SPD and beam sections meeting the aforementioned constraints can be found through optimization algorithm. These lightest sections which regarded as the ‘‘basic design’’. Then, the inter story drift ratio (IDR) of the PD-to-beam subassembly taken form the “basic design” are evaluated at a shear when the SPD reaches yield strength. Subsequently, an increace of 50% more stiffness of the subassembly as the new constraints, the optimization designs were conducted again. Results are defined as the‘‘1.5 times stiffened designs’’. While complying with the aforementioned constraints, steel weight is increased by about 13% to achieve a 50% stiffened design. The stiffness of subassembly is found enhanced mostly by increasing beam depth and web thickness. However, this also leads to an increase of the beam flexural strength by about 40%. This obviously is not favorable to the strong column weak beam design. Thus, as an additional constraint, beam strength is limited to no greater than 1.25 times of that in the basic design. As the result, the steel weight would increase by about 20% to achieve the specified 50% stiffened design. In addition, it may also result in a 1200 mm deep beam depth, which could impact the ceiling height. Thus, limit the beams to the specified depths for different SPDs are set as a constraint. The resulting steel weight increases by 34% to achieve the 50% stiffeded subassembly. Taking the 9-meter long beam and the 1500-kN SPD for example, beam strength would be 1.4 times of the basic design, beam depth would be 1200 mm to achieve the 50% stiffened subassembly, and the stiffnes to weight ratio (SWR) is 5.5/mm. When the constraint of no greater than 1.25 times the basic beam strength is imposed, beam depth would be 1175 mm to achieve 50% stiffened subassembly, and the SWR would be 5.4/mm. While constraining the beam depth to 800 mm, beam strength would be 1.2 times of the basic design to achieve the 50% stiffened design, but the SWR would be only 3.4/mm. Finally, optimized designs using discrete design variables are discussed. Taking the 9-meter long beam and the 700-kN SPD for example, the steel weight increases by 44% to achieve the 50% stiffened subassembly. Effects of the gravity loads on the capacity design of the boundary beam is also investigated. According to the five different configurations of SPDs in the MRFs, gravity beams frame into the boundary beam could result in a large gravity moment in the boundary beam. Therefore, it is suggested that gravity beams be oriented parallel to the boundary beam.
Databáze: Networked Digital Library of Theses & Dissertations
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