本文目的為藉著「個案研究」提出「支撐先進工法系統模板可靠度分析」。可靠度分析中，面對的條件包括材料性質、材料強度、構件尺寸、靜態載重、移動載重、風向風壓、地震強度等等。這些相關的物理量隨地點、隨時間而改變，是些不確定條件（Uncertainties），即是隨機變數（Random Variables）。可靠度理論歷經五十年的演進，是用來處理這些含有隨機變數的問題。可靠度分析基於概率的應用，提供了一個客觀的評估標準。合理評估「維護整建現有設施、或是設計全新建設」，有助於提出最後的決策。
　　本文分析所選用的個案為，作者曾參與監造的「第八號國道高速公路」高架橋。其混凝土大梁施工時所採用的系統模板為，承包商向挪威訂製的所謂「支撐先進工法工作車」，主體為兩支巨型鋼梁。按照傳統的結構分析「設計規範」，工作車所受的載重，可以定出巨型鋼梁的尺寸。另一方面，按照「可靠度分析」的原則，系統模板的可靠度被定義為，工作車的使用期間內維持有效（Serviceability）的機率，有效即為巨型鋼梁的內應力均低於降服強度。換言之，如果內應力會高過降服強度則為無效（Unserviceability）。
　　「工作車」可靠度初步分析，選用兩種極限狀態（Limit States）。其一為「工作車定位時」，兩支鋼梁互相聯結提供的平台上，承擔整個跨間混凝土梁體的施工載重。其二為「工作車滑行時」，由此一跨間前進至下一跨間，兩支鋼梁互不相聯，每支鋼梁須承擔自身質量移位所造成的載重。
　　介入可靠度分析的隨機變數，包含有：鋼的彈性模數、鋼的降服強度、構件尺寸、靜態載重、移動載重、風速風壓、以及地震強度。其他變數，包含有：混凝土單位質量、鋼料單位質量、鋼梁長度、橋墩位置，均假定為定數（Deterministic）。依據各項隨機變數的統計特性，模擬以各自的機率模式。根據作者個人歷年來參與工程監造，所蒐集的資料，「構件尺寸、靜態載重、以及移動載重」之統計性質，被模擬成常態分布。根據中央氣象局公佈的每月最大風速及最大地震級數，「風速風壓、以及地震強度」之統計性質，被模擬成第一型極值分布。
　　以數值分析方法運用蒙地卡羅模擬法，執行可靠度分析。可靠度即為「工作車維持為有效」的機率，也可以用「可靠度指標（Reliability Index）」來量計。計算結果顯示，工作車「定位時」因地震與風作用時之可靠度指標，分別為0.68與11。所代表的有效機率，分別為75.2%與100%。工作車「定位時」可靠度較「滑行時」低，分析結果與實際經驗相吻合。計算結果為可靠度分析可以提出量化數據，有助於工作車的設計與評估。

　The variables in the reliability evaluation of systematic formworks include the material modulus, yielding strength, member dimension, dead load, live load, wind, earthquake and others. These related physical quantities change with place and time, so they are uncertainties, or called random variables. The probability-based reliability theory, developed in the last 50 years, dealing the problems that include random variables, provides the best criteria of objective evaluation. Either for the maintenance of existing facilities or for the construction of new designed ones, a rational approach of objective evaluation is necessary to reach the best decision.
　The case study selected for the evaluation is the formwork system, the so-called advancing shoring method “wagon” which the contractor ordered and manufactured in Germany, for constructing the project of continuous prestressed concrete bridge girders of the viaduct in freeway number 8 in Taiwan, while the author ever participated in supervising. According to the traditional procedure, the main part of the “wagon,” a pair of giant box girders of steel plate, are designed to meet the required loads of code specification. However, the reliability of the wagon is defined as the probability of the wagon staying serviceable, that is, the stresses occurred in the steel plate are always below the yielding strength. In word, the wagon is unserviceable if any stress has ever been above the yielding strength.
　Two limit states are assumed in the preliminary analysis for the wagon. One is for the wagon fixed in place, where the two box girders are connected each other to provide a platform, subjected to the loads in constructing a whole span of concrete bridge. The other is for the wagon in advancing from a span to the next, while the two box girders are disconnected, subjected to its own weights in sliding.
　The random variables in the study included the elasticity modulus, yielding strength, plate thickness, dead load, live load, wind speed pressure, and earthquake intensity. Other variables, such as concrete unit mass, steel unit mass, girder length, and pier location were assumed to be deterministic. Each random variable is assigned with an appropriate distribution model according to its statistical characteristics. Based on the field collection from the projects the author ever experienced, normal distributions are for the plate thickness, dead load, and live load. Distributions for wind speed pressure, and earthquake intensity, are extreme type I, according to the monthly statistics of maximal wind speed and earthquake scale from Central Bureau of Weather in Taiwan.
　The probabilities of the wagon in serviceability, in terms of reliability indexes, were integrated numerically using Monte Carlo simulations. Calculations show that the reliability indexes are 0.65 and 11 , respectively, for the wagon fixed in place, and for the wagon in advancing. The corresponding probabilities are 75.2% and 100%, respectively. Quantitative results of the study agree with the practical experience. They might be useful for the design or for the evaluation of the wagon.

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