混凝土既有應力之非破壞檢測技術開發

Development of a Non-destructive Technique for the Measurement of Existing Stress in Prestressed Concrete

陳嘉佑(Chia-You Chen)

指導教授 ： 王仲宇

國立中央大學/工學院/土木工程學系/碩士(2007年)

摘要

本研究運用非破壞檢測方法量測混凝土結構既有應力，首先針對殘餘應力理論作了回顧，並對單軸軸壓應力理論作了一個簡單分析，此一分析結果發現軸應力和波速之間存在一最高階為4次方之關係，為了解混凝土於不同軸壓應力下之力學與聲學性質的變化情形，一共製作了66個不同材料強度之試體進行試驗，每一試體在不同等級之軸壓力作用下，均使用先進之乾點式超音波檢測儀量測各種波傳角度下之穿透縱波、穿透橫波、表面縱波、表面橫波之波速。量測結果顯示穿透縱波量測方式，可較明顯地見到軸壓比和波速比之相關性。將所有實驗結果進行回歸分析，可以得到一條平均之迴歸公式。由實驗結果可以發現當應力比達0.5時，波速開始明顯下降，隨著應力比的遞增，約達0.8時，波速即快速衰減。這個發現剛好與AE量測之結果相互呼應。由音洩量測可以看出當應力比達0.5和0.8時，其混凝土內部因微裂縫之生成，而導致音洩事件數量遞增。本文應用最佳化之和聲搜尋法配合聲彈理論進行既有應力反算，並於文中展示了應用迴歸公式進行現地既有應力量測之流程。

關鍵字

非破壞檢測 ； 混凝土 ； 殘餘應力 ； 超音波

並列摘要

In this thesis, the nondestructive testing method to measure the existing stresses
of concrete component is studied. Basic theories for the measurement of residual
stresses were reviewed. A simple one-dimensional theory is derived which shows a
fourth order power relationship between the un-axial stress and velocity of the
material. Totally 66 concrete specimens of material strength ranged from 210 kg / cm2
to 420 kg / cm2 were tested and measured their mechanical and acoustic properties.
For each specimen, the longitudinal wave speeds and transverse wave speeds of
through-transmission mode and surface mode in various directional angles with
respect to the direction of compressive stress were measured by an advanced
dry-contact type ultrasonic instrument at different compression stress level. From
the experimental results, it is found that the through-transmission mode can provide
better signals to distinguish the variation of wave speed ratio due to the change of
stress ratio. A regression formula of the existing stress and wave speed is obtained
from all the tested specimens. It is also found that the wave speed ratio starts
decreasing at the stress ratio of 0.5 and decreases drastically when the stress ratio reaches 0.8. This observation is verified by the acoustic emission (AE) method.
The AE events have obvious variation at the stress levels of
σ / fc′ =0.5 and 0.8
which are corresponding to the growth and extension of micro cracks inside the
concrete specimen. The harmony search method was applied to back calculate the
material properties and the existing stress of each specimen. A procedure of
applying the regression formula to measure the existing stress of concrete component
in field is also presented.

並列關鍵字

Ultrasonic ； Nondestructive testing ； Residual Stress ； Concrete

參考文獻

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