öλÔÓéÀֵǼÈë¿ÚÏÂÔØ

7)    Amount of bonded non-prestressed reinforcing.
            Ó°ÏìÎÞÕ³½áµÄÁºµÄ¼«ÏÞÍä¾ØÄÜÁ¦£¬µ«²»Ó°Ïì»òÕ߸ù±¾²»Ó°ÏìÏàͬ·½Ê½ÏµÄÓÐÕ³½áµÄÁºµÄ±äÁ¿°üÀ¨ÈçÏ£º
1)    ¸Ö½îÊøÖеÄÓÐЧӦÁ¦´óС£»
2)    ¿ç¸ß±È£»
3)    ²ÄÁÏÌØÐÔ£»
4)    ¼ÓºÉ·½Ê½£¨Íä¾ØͼµÄÐÎ×´£©£»
5)    Ê©¼ÓÔ¤Ó¦Á¦µÄ¸Ö½îÊøµÄ¶ÏÃ棻
6)    ÔÚÊ©¼ÓÔ¤Ó¦Á¦µÄ¸Ö½îºÍµ¼¹ÜÖ®¼äµÄĦ²ÁϵÊý£»
7)    ÓÐÕ³½áµÄ·ÇÔ¤Ó¦Á¦¸Ö½îµÄÊýÁ¿¡£
           A method of computing the ultimate strength of prestressed members (with unbonded tendons) that takes into account£¨¿¼ÂÇ£©the variables listed above has been proposed by Pannell. This method is based upon experimental data and is considered slightly conservative.
            PannellÒѾ­½¨ÒéÓÃÒÔ¼ÆË㿼ÂÇÉÏÊöÁгö±äÁ¿µÄ£¨¾ßÓÐÎÞÕ³½áµÄ¸Ö½îÊøµÄ£©Ô¤Ó¦Á¦¹¹¼þ¼«ÏÞÇ¿¶ÈµÄ·½·¨¡£¸Ã·¨ÊÇ»ùÓÚÊÔÑéÊý¾Ý£¬²¢ÇÒ¿¼ÂÇʱÉÔÓб£ÊØ¡£
             It should be recognized that the ultimate moment capacity of a member stressed with unbonded tendons, unlike members with bonded tendons, may be adversely£¨·´¹ýÀ´£©affected by unintentional£¨²»¾­ÒâµÄ£©variations in the effective prestress. Hence, it is considered prudent£¨½÷É÷µÄ£©to exert£¨¸øÓ裩more care in estimating the losses of prestress and in supervising£¨¼à¿Ø£©the stressing£¨¼Óѹ£©of unbonded members than would be considered necessary for bonded members, in order to assure the desired results are obtained.
            Ó¦¸Ã³ÐÈÏ£¬²»Ïó¾ßÓÐÓÐÕ³½áµÄ¸Ö½îÊøµÄ¹¹¼þ£¬Êܵ½ÎÞÕ³½áµÄ¸Ö½îÊøÊ©¼ÓÓ¦Á¦µÄ¹¹¼þµÄ¼«ÏÞÍä¾ØÄÜÁ¦£¬¿ÉÄܻᷴ¹ýÀ´Êܵ½ÓÐЧӦÁ¦²»¾­ÒâµÄ±ä»¯µÄÓ°Ïì¡£Òò´Ë£¬ÎªÁËÈ·±£»ñµÃÆÚÍûµÄ½á¹û£¬±ÈÆðÐè½÷É÷¿¼ÂÇÓÐÕ³½áµÄ¹¹¼þ¶øÑÔ£¬ÔÚ¹À¼ÆÔ¤Ó¦Á¦ËðʧºÍ¼à¿ØÎÞÕ³½áµÄ¹¹¼þ¼Óѹʱ¸ü¼ÓÓèÒÔСÐĽ÷É÷£¬Õâ±»ÈÏΪÊǽ÷É÷µÄ£¨×ö·¨£©¡£

Unit 10 µÚÊ®µ¥Ôª
Structure Steel
½á¹¹¸Ö
Advantages of Steel as a Structural Material
¸Ö²Ä×÷Ϊ½á¹¹²ÄÁϵÄÓŵã
           A person traveling in the United States might quite understandably decide£¨Çå³þµØ¶Ï¶¨£©that steel was the perfect structural material. He or she would see an endless number of£¨ÎÞÇîÎÞ¾¡µÄ£©steel bridges, buildings, towers, and other structures comprising, in fact, a list too lengthy to enumerate£¨Áо٣©. After seeing these numerous steel structures this traveler might be quite surprised to learn£¨Á˽⣩that steel was not economically made in the United States until late in the nineteenth century and the first wide-flange beams were not rolled£¨ÔþÖÆ£©until 1908.
һλÔÚÃÀ¹úÂÃÐеÄÈË¿ÉÄÜ»áºÜÇå³þµØ¶Ï¶¨¸Ö²ÄÊÇÀíÏëµÄ½á¹¹²ÄÁÏ¡£Ëû»òËý½«¿´µ½ÎÞÇîÎÞ¾¡µÄ¸ÖÇÅ¡¢¸ÖµÄ½¨ÖþÎï¡¢¸ÖËþÒÔ¼°ÆäËüµÄ¸Ö½á¹¹£¬Êµ¼ÊÉÏ°üº¬µÄÃûµ¥Ì«³¤ÁËÒÔÖÁÓÚÎÞ·¨ÁоÙ¡£ÔÚ¹Û¿´ÁËÕâЩÊýÁ¿ÖÚ¶àµÄ¸Ö½á¹¹ºó£¬ÕâλÂÃÐÐÕß¿ÉÄÜ»á·Ç³£¾ªÑȵØÁ˽⵽ÔÚÃÀ¹úÖ±µ½19ÊÀ¼ÍºóÆڸֲIJű»¾­¼ÃµØÖÆÔ죬²¢ÇÒÖ±µ½1908Äê²ÅÔþÖƳöµÚÒ»¸ù¿íÒíÔµµÄÁº¡£
           The assumption of the perfection£¨ÍêÃÀ£©of this metal, perhaps the most versatile£¨Í¨Óõģ©of structural materials, would appear to be even more reasonable£¨ºÏÀíµÄ£©when its great strength, light weight, ease of fabrication£¨ÖÆ×÷£©, and many other desirable£¨ÀíÏëµÄ£© properties are considered£¨¿¼ÂÇ£©. These and other advantages of structural steel are discussed in detail£¨ÏêϸµØ£©in the following paragraphs.

µ±¿¼ÂÇÕâÖÖ½ðÊô¾ßÓиßÇ¿¡¢ÇáÖÊ¡¢Ò×ÖÆ×÷ÒÔ¼°ºÜ¶àÆäËüÀíÏëµÄÐÔÄÜʱ£¬ÈÏΪÆäÍêÃÀµÄ¼Ù¶¨ÉõÖÁÏԵøüºÏÀí£¬»òÐíËüÊÇ×îͨÓõĽ¨Öþ²ÄÁÏ¡£ÕâЩºÍÆäËüµÄ½á¹¹¸ÖµÄÓÅÊƽ«ÔÚÏÂÃæµÄ¶ÎÂäÖÐÏêϸµØÌÖÂÛ¡£
    High Strength¡¡¡¡The high strength of steel per unit of weight means that structure weights will be small. This fact is of great importance for long-span bridges, tall buildings, and structures having poor foundation conditions£¨±¡ÈõµØ»ùÌõ¼þ£©.

    ¸ßÇ¿¶È¡¡¡¡¸Ö²Äÿµ¥Î»ÖØÁ¿µÄ¸ßÇ¿¶ÈÒâζ׎ṹµÄÖØÁ¿½«ÊÇСµÄ¡£Õâ¸öÊÂʵ¶Ô´ó¿çµÄÇÅÁº¡¢¸ß²ã½¨ÖþÒÔ¼°ÓÐ×ű¡ÈõµØ»ùÌõ¼þµÄ½á¹¹¾ßÓÐÖØÒªÒâÒå¡£
    Uniformity¡¡¡¡The properties of steel do not change appreciably£¨Ã÷ÏԵأ©with time, as do those of reinforced-concrete structure.

    Ò»ÖÂÐÔ¡¡¡¡¸Ö²ÄµÄÐÔÄÜËæʱ¼äµÄ±ä»¯²»Ã÷ÏÔ£¬ÕýÈç¸Ö½î»ìÄýÍÁ½á¹¹µÄÐÔÄÜÒ²Ëæʱ¼ä±ä»¯²»Ã÷ÏÔ¡£
    Elasticity¡¡¡¡Steel behaves closer to£¨¸ü½Ó½üÓÚ£©design assumptions than most materials because it follows£¨×ñÑ­£©Hooke’s law up to fairly high stresses. The moments of inertia£¨¹ßÐԾأ©of a steel structure can be definitely£¨È·Çеأ© calculated, while the value obtained for a reinforced-concrete structure are rather indefinite£¨²»È·ÇУ©.

    µ¯ÐÔ¡¡¡¡±ÈÆð´ó¶àÊý²ÄÁÏ£¬¸Ö²ÄµÄÔËÐиü½Ó½üÓÚÉè¼ÆµÄ¼Ù¶¨£¬ÒòΪËüÖ±µ½Ï൱¸ßµÄÓ¦Á¦ÈÔÈ»×ñÑ­»¢¿Ë¶¨Àí¡£Ò»¸ö¸Ö½á¹¹µÄ¹ßÐԾؿÉÒÔÈ·Çеر»¼ÆË㣬¶ø¸Ö½î»ìÄýÍÁ½á¹¹µÃµ½µÄ¸ÃÖµÊǷdz£µÃ²»È·ÇС£