傳統上群樁基礎均採用試誤法的程序來設計，雖能符合規範中強度與位移上的要求，卻無法保證造價的經濟性。本研究的目的便是利用遺傳演算法則來進行預鑄混凝土群樁基礎的低價化設計。 本文的目標函數是群樁基礎之總造價，包含土方開挖費用、樁帽費用和基樁費用等三部分；其設計主要包括樁徑、樁數、樁長、基樁間距和樁帽的尺寸，且均視為離散變數來處理。而預鑄混凝土基樁的尺寸，則由國內廠商已生產之尺寸所建立的資料庫來選取。 群樁基礎之強度與位移束制條件是參考國內建築物基礎構造設計規範來建立，包括基樁間距、穿孔剪力、撓曲剪力、樁頭位移、基樁承載力、樁帽的尺寸等。 遺傳演算法則的效率將透過數個設計例來說明，而影響群樁基礎造價的主要設計參數，亦將透過數值演算結果來探討，以供工程設計之參考。 Conventional design of pile groups is based on the trial-and-error procedures. Although the design results can satisfy strength and displacement requirements that stipulated in code provisions, it is not a minimum cost design. The purpose of this study is to apply the genetic algorithm (GA) for searching the minimum cost design of precast concrete pile groups. The objective function of the problem is the total cost of the foundation, including the costs of soil excavation, cap and piles. The design variables are pile diameter, pile nummers, pile length, pile spacing , and dimensions of cap, which are all considered as discrete design variables. The size of precast concrete piles is selected from the available sections in the engineering market. The strength and displacement constraints for the minimum cost design of pile groups are formulated according to the foundation design code provisions of Taiwan. Size constrains, such as the spacing of piles, punching shear, bending shears, and dimensions of the pile cap are also considered in the formulation. The application of GA to the minimum cost design of pile groups is shown by a number of design examples. The efficiency of GA and sensitivity analyses of design variables on the cost of pile groups are also discussed.
