توسعه‌ي روش‌هاي ضريب انحنا آسيب (CDF)، تغيير در نرمي (CFM) و تغيير در انحنا نرمي (CFCM) براي تشخيص آسيب در وسط دهانه‌ي عرشه‌ي پل‌ها

Development of CDF, CFM and CFCM Methods for Damage Detection in the Middle of Bridge Deck

روش‌ ضريب انحنا آسيب(CDF) ، كه بر پايه‌ي تغيير در انحنا شكل مودي است، و روش هاي تغيير در نرمي (CFM) و تغيير در انحنا نرمي (CFCM)، كه بر پايه‌ي تغيير در ماتريس نرمي سازه هستند، در شناسايي مقطع طولي آسيب ديده در وسط دهانه‌ي عرشه‌ي پل ها قادر به تشخيص مقطع طولي آسيب ديده نيستند و در برخي موارد، مقطع عرضي آسيب ديده را نيز به‌درستي تشخيص نمي دهند. در اين پژوهش، ابتدا ضعف روش هاي ذكرشده نشان داده شده و سپس روشي جديد براي تشخيص آسيب در عرشه‌ي پل از طريق توسعه‌ي روش‌هاي مذكور ارايه شده است. براي اين منظور، مدل عددي پل 3 دهانه‌ي بزرگمهر اصفهان، كه از طريق آزمايش‌هاي ميداني تاييد شده و مدل يك پل 5 دهانه‌ي 25 متري استفاده و آسيب ايجادشده روي عرشه‌ي پل از طريق كاهش مدول كشساني يك المان در وسط دهانه‌ي مدل پل ها تعريف شده است.

Structural damage detection has gained increased attention from the scientific community since unpredicted major hazards, most with human losses, have been reported. Aircraft crashes and catastrophic bridge failure are some examples. Security and economic aspects are important motivations for increasing research into structural health monitoring. Since damage alters the dynamic characteristics of a structure, namely, its Eigen properties (natural frequencies and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. In this article, a new method, based on developing the curvature damage factor method (CDF), change in flexibility method (CFM) and change in flexibility curvature method (CFCM) is presented. For this purpose, the three span Bozorgmehr Bridge, located in Esfahan, Iran, and a five-span bridge previously designed by an expert are used. The numerical model of the Bozorgmehr Bridge is verified by comparing the five primary natural frequencies with those obtained from experimental testing. In applying these methods, the mode shapes and natural frequencies of the damaged and undamaged bridges, are used. Damage is created on an element located in the middle of the deck. The four levels of damage considered are 15%, 30%, 70% and 90% reduction in the module of elasticity. It is shown that if mode shapes, as previously are simply extracted from one longitudinal section, the methods cannot always detect the damaged cross sections or the damaged longitudinal sections. But, if as shown in this article, the mode shapes are obtained from several longitudinal sections, these methods will be able to assess the damaged cross sections as well as the damaged longitudinal sections. It is also concluded that, when using the CDF method, the maximum content of CDF calculated for cross sections on itself cannot always show the damage locations. and it is necessary to consider the changes in value of CDF for several longitudinal sections too and, then, decide about damage locations.