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本文是对本刊1964年第6期王伟生同志所写“拱桥計算中的一点体会”一文中有关“如何选择无鉸拱的合理拱軸”一节的討論。本文同意王文的結論,但認为王文論証欠完整。因此,本文重新作了比較系統的論証。对实腹拱来說,本文的論証是正确的。但对空腹拱,尤其是拱上纵梁的跨度較大而跨数又少时,拱軸綫如仍按三鉸拱来选择,則不一定是合理的。因空腹式无鉸拱的拱上結构的重量对拱肋来說是比較大的集中荷載所以拱的恒載压力綫是一折綫;而拱軸綫只可能是一平滑的曲綫,此二者不可能完全重合。因此,在拱的某些截面內仍存在力矩和剪力,故在拱頂和拱脚处仍有可能产生比較大的力矩。所以,对空腹式无鉸拱当用三鉸拱定出其軸綫以后,最后用其他办法再核算拱頂和拱脚的力矩值。据此,可以进一步修正拱軸綫,或仍用原三鉸拱拱軸綫,但在計算各截面恒载內力时,应将此力矩計算在內。
This article is a discussion of the section entitled “How to Choose a Rational Arch Axis with Hingeless Arches” in his article “Some Experiences in Calculating Arch Bridges” by Comrade Wang Weisheng in Issue 6, 1964. This article agrees with the conclusion of Wang Wen, but believes Wang Wen argumentation is not complete. Therefore, this article re-made a more systematic argument. For real abdominal arch, the argument of this article is correct. However, it is not always reasonable for the fasting arch, especially if the span of the longitudinal arch of the arch is large and the number of spans is small. Due to the weight of the arch structure of the fasting hingeless arch is a relatively large concentrated load on the arch ribs, the constant load pressure line of the arch is a broken line; and the arch axis may only be a smooth curve, both of which It is impossible to completely coincide. As a result, there are still moments and shear forces in some cross-sections of the arch, so large torques may still be generated at the dome and arch. Therefore, when the three-hinged arch is used to determine the axis of an open abdominal hinge-free arch, the torque value of the dome and arch should be calculated by other means. Accordingly, the arch axis may be further modified or the arch axis of the original three-hinged arch is still used, but this moment should be taken into account when calculating the internal force of constant load of each section.