INTRODUCTION TO DESIGN (±¸Á¶)¼³°èÀÇ ´ëÇÑ ¼Ò°³
Summary ¿ä¾à
1.1 What is design? - Inputs, design process, scope of course.
1.2 Design
philosophy - permissible stress design, load factor method, limit state design.
1.1 What is design? ¼³°è¶õ ¹«¾ùÀΰ¡?
The task of the structural engineer is to design
a structure which satisfies the needs of the client and the user. Specifically
the structure should be safe, economical to build and maintain, and aesthetically
pleasing. But what does the design process involve?
±¸Á¶±â¼úÀÚ°¡ ÇؾßÇÒ ÀÏÀº °ÇÃàÁÖ¿Í »ç¿ëÀÚÀÇ ¿ä±¸»çÇ×µéÀ» ¸¸Á·½ÃÅ°´Â ±¸Á¶¹°À»
¼³°èÇÏ´Â °ÍÀÌ´Ù. ƯÈ÷ ±× ±¸Á¶¹°Àº ¾ÈÀüÇÏ°í, ½Ã°ø°ú °ü¸®À¯Áö¿¡ °æÁ¦ÀûÀ̸ç, ¹ÌÀûÀ¸·Î
¸¸Á·À» ÁÖ¾î¾ß ÇÑ´Ù. ±×·¯¸é ¼³°è°úÁ¤Àº ¹«¾ùÀ» Æ÷ÇÔÇϴ°¡?
Design is a word that means different things
to different people. In dictionaries the word is described as a mental plan,
preliminary sketch, pattern, construction, plot or invention. Even amongst those
closely involved with the built environment there are considerable differences
in interpretation. Architects, for example, may interpret design as being the
production of drawings and models to show what a new building will actually
look like. To civil and structural engineers however, design is taken to mean
the entire planning process for a new building structure, bridge, tunnel, road
etc., from outline concepts and feasibility studies through mathematical calculations
to working drawings which could show every last nut and bolt in the project.
Together with the drawings there will be bills of quantities, a specification,
and a Contract, which will form the necessary legal and organisation framework
within which a contractor, under the supervision of engineers and architects,
can construct the scheme.
¼³°è¶ó´Â ¸»Àº °¢±â ´Ù¸¥ »ç¶÷¿¡°Ô ¼·Î ´Ù¸¥ °ÍÀ» ÀǹÌÇÏ´Â ´Ü¾îÀÌ´Ù. »çÀü »ó¿¡´Â
¼³°è¶õ ´Ü¾î´Â ÀÏÂ÷ÀûÀ¸·Î´Â ½ºÄÉÄ¡, ÆÐÅÏ, ½Ã°ø, ±¸¼ºÀ̳ª ¹ß¸í°ú °°Àº Á¤½Å»óÀÇ
°èȹÀ¸·Î ±â¼úµÇ¾î ÀÖ´Ù. ½ÉÁö¾î °Ç¼³È¯°æ°ú ¾ÆÁÖ °¡±õ°Ô ¿¬°üµÈ ºÎºÐµé¿¡µµ Á¶Â÷µµ
±× ¹ø¿ª¿¡ ÀÖ¾î¼ »ó´çÇÑ Â÷ÀÌ°¡ ÀÖ´Ù. ¿¹ÄÁµ¥, °ÇÃà°¡´Â ¼³°è¶õ ¸»À» »õ·Î¿î °Ç¹°ÀÌ
½ÇÁ¦·Î º¸¿©Áö´Â °ÍÀ» °¡½ÃȽÃÅ°´Â µµ¸éÀ̳ª ¸ðµ¨À» ¸¸µå´Â °ÍÀ¸·Î Çؼ®ÇÒ °ÍÀÌ´Ù.
±×·¯³ª ½Ã°ø±â¼úÀÚ³ª ±¸Á¶±â¼úÀÚ¿¡°Ô À־ »õ·Î¿î ±¸Á¶¹°, ±³·®, ÅͳÎ, µµ·Î
µîÀÇ ´ë·«ÀûÀÎ °³³äÀ̳ª ¼öÇÐÀû °è»êÀ» ÅëÇÑ Å¸´ç¼º Á¶»ç¿¡¼ºÎÅÍ ±× ÇÁ·ÎÁ§Æ®ÀÇ
¸ðµç ÃÖÈÄÀÇ ³ÊÆ®¿Í º¼Æ®¸¦ º¸¿©ÁÖ´Â ½Ã°øµµ¿¡ À̸£±â±îÁöÀÇ ÀüüÀûÀÎ °èȹ°úÁ¤À»
ÀǹÌÇÑ´Ù. µµ¸é°ú °°ÀÌ ±â¼úÀÚ³ª °ÇÃà°¡ÀÇ °ü¸®ÇÏ¿¡ µµ±ÞÀÚ°¡ °èȹÀ» ¼¼¿ì´Â ÇÊ¿äÇÑ
¹ý·ü»óÀÇ ±×¸®°í Á¶Á÷»óÀÇ Ã¼°è¸¦ ±¸¼ºÇÏ´Â ¼ö·®°è»ê¼, ±ÔÁØ, ±×¸®°í °è¾à¼¸¦ ÀǹÌÇÒ
¼öµµ ÀÖ´Ù.
There are many inputs into the engineering design
process as illustrated by Figure 1.1 including
´ÙÀ½°ú °°ÀÌ ±×¸²1.1¿¡¼ º¸¿©ÁöµíÀÌ °øÇÐÀûÀÎ ¼³°è°úÁ¤¿¡ µé¾î°¡´Â ¸¹Àº ÀÎÀÚµéÀÌ
ÀÖ´Ù.
(a) Client brief °ÇÃàÁÖÀÇ ¿ä±¸»çÇ×
(b)
Experience °æÇè
(c) Imagination »ó»ó·Â
(d) A site investigation ÇöÀå
Á¶»ç
(e) Model and laboratory tests ¸ðµ¨À» ÅëÇØ ±×¸®°í ½ÇÇè½Ç¿¡¼ ÀÌ·ç¾îÁö´Â
Å×½ºÆ®
(f) Economic factors °æÁ¦Àû ¿äÀεé
(g) Environmental factors
ȯ°æÀû ¿äÀεé
Figure 1.1 - Inputs into the design process ¼³°è°úÁ¤¿¡ Æ÷ÇԵǴ ÀÎÀÚµé
The starting point for the designer is normally
a conceptual brief from the client, who may be a private developer or perhaps
a government body. The conceptual brief may simply consist of some sketches
prepared by the client or perhaps a detailed set of architects drawings.
¼³°èÀÚÀÇ Ãâ¹ßÁ¡Àº ÀϹÝÀûÀ¸·Î ¹Î°£°³¹ß¾÷ÀÚ³ª ¾Æ¸¶µµ Á¤ºÎ±â°üÀÌ µÉ ¼öµµ ÀÖ´Â °ÇÃàÁַκÎÅÍÀÇ
°³³äÀûÀÎ ¿ä±¸»çÇ×µéÀÌ´Ù. °³³äÀûÀÎ ¿ä±¸»çÇ×Àº ´Ü¼øÈ÷ °ÇÃàÁÖ¿¡ ÀÇÇØ ÁغñµÈ ¾à°£ÀÇ
½ºÄÉÄ¡³ª ȤÀº °ÇÃ൵¸éµé·Î ´Ü¼øÈ÷ ±¸¼ºµÈ´Ù.
Experience is crucially important, and a client
will always demand that the firm he is employing to do the design has previous
experience designing similar structures.
°æÇèÀº ¸Å¿ì Áß¿äÇϸç, °ÇÃàÁÖ´Â Ç×»ó ¼³°è¸¦ ÇϱâÀ§ÇØ °í¿ëÇÏ°í Àִ ȸ»ç°¡ ÀÚ½ÅÀÌ
»ý°¢ÇÏ°í ÀÖ´Â ±¸Á¶¹°°ú À¯»çÇÑ ±¸Á¶¹°µéÀ» ÀÌÀü¿¡ °æÇèÇØ º» ÀûÀÌ ÀÖ´ÂÁö¸¦ ¿ä±¸Çϱâ
¸¶·ÃÀÌ´Ù.
Although imagination is thought by some to be
entirely the domain of the architect, this is not so. For engineers and technicians
an imagination of how elements of structure inter-relate in three dimensions
is essential, as is an appreciation of the loadings to which structures might
be subject in certain circumstances. In addition, imaginative solutions to engineering
problems are often required to save money, time, or to improve safety or quality.
ºñ·Ï »ó»ó·ÂÀÌ ÀϺΠ»ç¶÷µé¿¡ ÀÇÇØ ÀüÀûÀ¸·Î °ÇÃà°¡ÀÇ ¿µ¿ªÀ̶ó°í »ý°¢µÇ¾îÁúÁö¶óµµ,
½ÇÀº ±×·¸Áö ¾Ê´Ù. °øÇÐÀÚ³ª ±â¼úÀڵ鿡°Ô ÀÖ¾î¼ ±¸Á¶¹°ÀÇ ±¸¼º¿ä¼ÒµéÀÌ ¾î¶»°Ô
»ïÂ÷¿øÀûÀ¸·Î »óÈ£°ü°è¸¦ °¡Áö´Â°¡¿¡ ´ëÇÑ »ó»ó·ÂÀº ÇʼöÀûÀÌ´Ù. ±¸Á¶¹°ÀÌ ¾î¶² ÀÏÁ¤ÇÑ
ȯ°æ ¾Æ·¡¼ ÁÖ¾îÁö´Â ÇÏÁßÀ» Æò°¡ÇÏ´Â °Íµµ ¸¶Âù°¡ÁöÀÌ´Ù. °Ô´Ù°¡, °øÇÐÀû ¹®Á¦¿¡
´ëÇÑ »ó»ó·ÂÀÌ Ç³ºÎÇÑ ÇØ°á¾ÈÀº Á¾Á¾ µ·, ½Ã°£À» Àý¾àÇϰųª ¾ÈÀü¼ºÀ̳ª Ç°ÁúÀ» Çâ»ó½ÃÅ°±â
À§ÇØ ¿ä±¸µÇ¾îÁø´Ù.
A site investigation is essential to determine
the strength and other characteristics of the ground on which the structure
will be founded. If the structure is unusual in any way, or subject to unusual
loadings, model or laboratory tests may also be used to help determine how the
structure will behave.
ÇöÀåÁ¶»ç´Â ±¸Á¶¹°ÀÌ ¼°ÔµÉ Áö¹ÝÀÇ °µµ¿Í ´Ù¸¥ Ư¼ºµéÀ» °áÁ¤Çϱâ À§Çؼ ÇʼöÀûÀÎ
ºÎºÐÀÌ´Ù. ¾î¶°ÇÑ ÀÌÀ¯·ÎÇؼ ±¸Á¶¹°ÀÌ Æ¯¼öÇÑ °ÍÀ̰ųª Ư¼öÇÑ ÇÏÁßÀ» ¹Þ´Â °æ¿ì¶ó¸é,
¸ðµ¨À» ÅëÇϰųª ½ÇÇè½Ç¿¡¼ÀÇ Å×½ºÆ®µµ ±¸Á¶¹°ÀÌ ¾î¶»°Ô °Åµ¿ÇÒ °ÍÀÎÁö¸¦ °áÁ¤Çϴµ¥
µµ¿òÀ» Áֱ⠶§¹®¿¡ »ç¿ëµÇ¾îÁø´Ù.
In today's economic climate a structural designer
must be constantly aware of the economic implications of his or her design.
On the one hand design should aim to achieve economy of materials in the structure,
but over-refinement can lead to an excessive number of different sizes and components
in the structure, and labour costs will rise. In addition the actual cost of
the designers time should not be excessive, or this will undermine the employers
competitiveness. The idea is to produce a workable design achieving reasonable
economy of materials, while keeping manufacturing and construction costs down,
and avoiding unnecessary design and research expenditure.
¿À´Ã³¯ÀÇ °æÁ¦ÀûÀΠȯ°æ¿¡¼ ±¸Á¶±â¼úÀÚ´Â ÀÚ±âÀÚ½ÅÀÇ ¼³°è°¡ Áö´Ï´Â °æÁ¦ÀûÀÎ ÇÔÀǸ¦
Ç×»ó ÀǽÄÇÏ°í ÀÖ¾î¾ß¸¸ ÇÑ´Ù. ¹Ý¸é¿¡ ¼³°è´Â ±¸Á¶¹°¿¡¼ Àç·áÀÇ °æÁ¦¼ºÀ» ȹµæÇϱâ
À§ÇØ ÃÊÁ¡ÀÌ ¸ÂÃß¾îÁ®¾ß ÇÏÁö¸¸, Áö³ªÄ¡°Ô Á¤Á¦µÈ ¼³°è¸¦ ÇÒ °æ¿ì ±¸Á¶¹°¿¡¼ Áö³ªÄ¡°Ô
¸¹Àº ±Ô°Ý°ú ºÎÀçµéÀ» ÇÊ¿ä·Î ÇÏ°Ô µÇ¾î ³ë¹«ºñ°¡ Ä¿Áú °ÍÀÌ´Ù. ¼³°èÀÚÀÇ ½ÇÁ¦ ºñ¿ë»Ó¸¸¾Æ´Ï¶ó
½Ã°£µµ Áö³ªÄ¡°Ô ¸¹À¸¸é ¾ÈµÇ¸ç, ±×·²°æ¿ì °æÀZ¿¡¼ µÚ¶³¾îÁö±â ¸¶·ÃÀÌ´Ù. °á·ÐÀº
Á¦ÀÛºñ¿ë°ú ½Ã°øºñ¿ëÀ» ÁÙÀÌ°í, ºÒÇÊ¿äÇÑ ¼³°è¿Í ¿¬±¸³ë·ÂÀ» ÇÇÇϸ鼵µ ÇÕ¸®ÀûÀÎ
Àç·á»óÀÇ °æÁ¦¼ºÀ» Áö´Ñ ½Ã°ø°¡´ÉÇÑ ¼³°è¸¦ ¸¸µé¾î³»´Â °ÍÀÌ´Ù.
Designers must also understand how the structure
will fit into the environment for which it is designed. Today many proposals
for engineering structures stand or fall on this basis, so it is part of the
designers job to try to anticipate and reconcile the environmental priorities
of the public and government.
¼³°èÀÚ´Â ¶ÇÇÑ ±¸Á¶¹°ÀÌ ±× ¾È¿¡¼ ¼³°èµÇ¾îÁö´Â ȯ°æ¿¡ ¾î¶»°Ô Àß µé¾î¸Â´ÂÁö¸¦
ÀÌÇØÇؾ߸¸ ÇÑ´Ù. ¿À´Ã³¯ ¸¹Àº °øÇÐÀû ±¸Á¶¹°µé¿¡ ´ëÇÑ Á¦¾ÈµéÀÌ ÀÌ·± »çÇ×ÀÌ ±Ù°Å¸¦
µÎ°í ¼ö¶ôµÇ±âµµ ÇÏ°í °ÅÀýµÇ±âµµ ÇÑ´Ù. µû¶ó¼ °ø°ø ´ëÁß°ú Á¤ºÎÀÇ È¯°æ»óÀÇ ¿ì¼±±ÇÀ»
¿¹ÃøÇÏ°í ÀÌ¿¡ ŸÇùÁ¡À» ã¾Æ³»µµ·Ï ³ë·ÂÇÏ´Â °ÍÀÌ ¼³°èÀÚÀÇ ¾÷¹«ÀÇ ÇÑ ºÎºÐÀÌ´Ù.
The engineering design process can often be
divided into two stages:
(1) a feasibility study involving a comparison of the alternative forms of structure,
and selection of the most suitable type and
(2) a detailed design of the
chosen structure.
°øÇлóÀÇ ¼³°è°úÁ¤Àº Á¾Á¾ Å©°Ô µÎ ´Ü°è·Î ³ª´µ¾îÁú ¼ö ÀÖ´Ù :
(1) ±¸Á¶¹°ÀÇ
´Ù¸¥ ´ë¾Èµé°úÀÇ ºñ±³¸¦ ÅëÇÑ Å¸´ç¼ºÁ¶»ç¿Í ±×¿¡ µû¸¥ °¡Àå ÀûÇÕÇÑ À¯ÇüÀÇ ¼±ÅÃ
(2) ¼±ÅÃµÈ ±¸Á¶¹°¿¡ ´ëÇÑ »ó¼¼¼³°è
The success of stage 1, the conceptual design,
relies to a large extent on engineering judgement and instinct, both of which
are the outcome of many years experience of designing structures. Stage 2, the
detailed structural design, also requires these attributes but is usually more
dependent upon a thorough understanding of the codes of practice for structural
design, eg. BS8110 and BS5950. These documents are based on the amassed experience
of many generations of engineers, and the results of research. They help to
ensure safety and economy of construction, and that mistakes are not repeated.
For instance, after the infamous disaster at the Ronan Point block of flats
in Newham, London, when a gas explosion caused a serious partial collapse, research
work was carried out, and codes of practice were amended so that such structures
could survive such a gas explosion, with damage being confined to one level.
1´Ü°èÀÎ °³³äÀû ¼³°èÀÇ ¼º°øÀº °øÇÐÀû ÆÇ´Ü°ú º»´É¿¡ ¸Å¿ì Å©°Ô ÀÇÁ¸Çϴµ¥, ÀÌ µÑ
¸ðµÎ ±¸Á¶¹°À» ¼³°èÇÑ ¼ö½Ê³â°£ÀÇ °æÇèÀÇ »êÃâ¹°ÀÌ´Ù. 2´Ü°èÀÎ »ó¼¼ ±¸Á¶¼³°èµµ ¶ÇÇÑ
ÀÌ·± ¸éµéÀ» ¿ä±¸ÇÏÁö¸¸, ÀϹÝÀûÀ¸·Î BS8110À̳ª BS5950°ú °°Àº ±¸Á¶¼³°è¿¡ ´ëÇÑ
½Ç¹« ±ÔÁØ¿¡ ´ëÇÑ ±íÀÌÀÖ´Â ÀÌÇØ¿¡ ´õ¿í ÀÇÁ¸ÇÑ´Ù. ÀÌ·± ¹®¼µéÀº ¼ö¼¼´ë¿¡ °ÉÄ£
±â¼úÀÚµéÀÇ ÃàÀûµÈ °æÇè¿¡ ±âÃÊÇÏ°í ÀÖÀ¸¸ç, ¿¬±¸ÀÇ °á°ú¹°µéÀÌ´Ù. ¶ÇÇÑ ½Ã°øÀÇ ¾ÈÀü¼º°ú
°æÁ¦¼ºÀ» È®½ÅÇϴµ¥ µµ¿òÀ» ÁÖ¸ç, ½Ç¼öµéÀÌ ¹Ýº¹µÇÁö ¾Ê°Ô µÈ´Ù. ¿¹¸¦ µé¸é, ·±´ø
´ºÇÜ¿¡¼ ÀÖ¾ú´ø °¡½ºÆø¹ßÀÌ ½É°¢ÇÑ ºÎºÐÀûÀÎ ºØ±«¸¦ ¾ß±âÇÑ Ronan Point ºí·°ÀÇ
¾ÆÆÄÆ®¿¡¼ ÀÏ¾î³ ¾Ç¸í³ôÀº ÀçÇØ ÀÌÈÄ¿¡ ¿¬±¸ÀÛ¾÷ÀÌ ¼öÇàµÇ¾ú°í, ½Ç¹«±ÔÁصéÀÌ ±¸Á¶¹°ÀÌ
±×·¯ÇÑ °¡½ºÆø¹ß ¾Æ·¡¼µµ ºØ±«µÇÁö ¾Ê°í ¼Õ»óÀÌ ÇÑ Ãþ¿¡¸¸ ±¹Çѵǵµ·Ï Àç¼öÁ¤µÇ¾ú´Ù.
1.2 Design Philosophy ¼³°èöÇÐ
Table 1.1 illustrates some risk
factors that are associated with activities in which people engage. It can be
seen that some degree of risk is associated with air and road travel. However
people normally accept that the benefits of mobility outweigh the risks. Staying
in buildings, however, has always been regarded as fairly safe. The risk of
death or injury due to structural failure is extremely low, but as we spend
most of our life in buildings this is perhaps just as well.
Ç¥ 1.1Àº Àΰ£ÀÌ ¿µÀ§ÇÏ´Â ÇàÀ§¿¡ °ü·ÃµÈ ÀÏÁ¾ÀÇ À§Çè¿äÀÎÀ» º¸¿©ÁØ´Ù. ¾î´À Á¤µµÀÇ
À§ÇèÀÌ Ç×°ø¿©Çà°ú µµ·Î¿©Çà¿¡ °ü·ÃµÇ¾î ÀÖÀ½ÀÌ º¸¿©Áø´Ù. ±×·¯³ª »ç¶÷µéÀº Åë»óÀûÀ¸·Î
¿î¼Û±â´ÉÀÇ ÀÌÁ¡ÀÌ À§Çè¿äÀÎÀ» ´É°¡ÇÑ´Ù°í ÀÎÁ¤ÇÑ´Ù. ±×·¯³ª °Ç¹°¿¡ ¸Ó¹°·¯ÀÖ´Â °ÍÀº
Ç×»ó ¸Å¿ì ¾ÈÀüÇÏ´Ù°í ¿©°ÜÁ®¿Ô´Ù. ±¸Á¶¹°ÀÇ Æı«·Î ÀÎÇÑ Á×À½À̳ª ºÎ»óÀÇ À§ÇèÀº
¸Å¿ì ³·Áö¸¸, ¿ì¸®°¡ ¿ì¸® ÀλýÀÇ ´ëºÎºÐÀÇ ½Ã°£À» °Ç¹°¿¡¼ º¸³»±â ¶§¹®¿¡ ÀÌ·±
°æ¿ìµµ ¾Æ¸¶ ¸¶Âù°¡ÁöÀÌ´Ù.
Mountaineering (International) µî»ê(±¹Á¦Àû)
2700
Air Travel (International) Ç×°ø¿©Çà(±¹Á¦Àû)
120
Deep Water Trawling ½ÉÇØÆ®·Ñ¾î¾÷ 59
Car Travel ÀÚµ¿Â÷ ¿©Çà 56
Coal Mining ź±¤ÀÛ¾÷
21
Construction Sites °Ç¼³ÇöÀå 8
Manufacturing Á¦Á¶¾÷ 2
Accidents at Home Áý¾È»ç°í
2
Fire at Home Áý¾ÈÈÀç 0.1
Structural Failures ±¸Á¶¹° ºØ±« 0.002
Table 1.1 - Comparative Death
Risk per 108 Persons Exposed
Ç¥ 1.1 - ³ëÃâµÈ 108¸íÀÇ »ç¶÷µé¿¡ ´ëÇÑ ºñ±³ »ç¸Á À§Çè
As far as the design of structures for safety is concerned, it is seen as the
process of ensuring that stresses due to loading at all critical points in a
structure have a very low chance of exceeding the strength of materials used
at these critical points. Figure 1.2 illustrates this in statistical terms.
¾ÈÀü¿¡ ´ëÇؼ ±¸Á¶¼³°è°¡ °ü°èµÇ´Â ÇÑ, ±¸Á¶¼³°è´Â ±¸Á¶¹°¿¡ ÀÖ´Â ¸ðµç À§ÇèºÎÀ§µé(critical
pointsÀÇ ¹ø¿ª)¿¡¼ ¹Þ´Â ÇÏÁßÀ¸·Î ÀÎÇÑ ÀÀ·ÂÀÌ ±× ºÎºÐµé¿¡ »ç¿ëµÈ Àç·áÀÇ °µµ¸¦
ÃÊ°úÇÒ È®·üÀÌ ¸Å¿ì ³·¾Æ¾ß¸¸ ÇÑ´Ù. ±×¸² 1.2´Â Åë°èÀûÀÎ Ãø¸é¿¡¼ ÀÌ·± Á¡À» ³ªÅ¸³½´Ù.
Figure 1.2 - Relationship
between stress and strength ÀÀ·Â°ú °µµÀÇ °ü°è
In design there exist within the
structure a number of critical points (eg beam midspans) where the design process
is concentrated. The normal distribution curve on the left of Figure 1.2 represents
the actual maximum material stresses at these critical points due to the loading.
Because loading varies according to occupancy and environmental conditions,
and because design is an imperfect process, the material stresses will vary
about a modal value - the peak of the curve. Similarly the normal distribution
curve on the right represents material strengths at these critical points, which
are also not constant due to the variability of manufacturing conditions.
¼³°è¿¡´Â ±¸Á¶¹° ÀÚü¿¡ ¼³°è°úÁ¤ÀÌ ÁýÁߵǾîÁö´Â ¸¹Àº À§ÇèºÎÀ§µé(¿¹ÄÁµ¥, º¸ÀÇ
°¡¿îµ¥ ½ºÆÒ)ÀÌ Á¸ÀçÇÑ´Ù. ±×¸² 1.2ÀÇ ¿ÞÂÊ¿¡ ÀÖ´Â Á¤±ÔºÐÆ÷°î¼±Àº ÇÏÁß¿¡ ±âÀÎÇÑ
ÀÌ·± À§ÇèºÎÀ§µé¿¡¼ÀÇ ½ÇÁ¦·Î Àç·á¿¡ »ý±â´Â ÃÖ´ëÀÀ·ÂÀ» ³ªÅ¸³½´Ù. ÇÏÁßÀº »ç¶÷ÀÇ
±¸Á¶¹°¿¡¼ÀÇ È°µ¿°ú ȯ°æÀû Á¶°Ç¿¡ µû¶ó¼ º¯Çϸç, ¼³°è¶õ ºÒ¿ÏÀüÇÑ ÇϳªÀÇ °úÁ¤À̱â
¶§¹®¿¡, Àç·á¿¡ »ý±â´Â ÀÀ·ÂÀº °î¼±ÀÇ °¡¿îµ¥°¡ ³ôÀº ¸ð´Þ°ªÀ» Áß½ÉÀ¸·Î º¯ÈÇÑ´Ù.
ÀÌ¿ÍÀ¯»çÇÏ°Ô ¿À¸¥ÂÊÀÇ Á¤±ÔºÐÆ÷°î¼±Àº ÀÌ·± À§ÇèºÎÀ§µé¿¡¼ÀÇ Àç·áÀÇ °µµ¸¦ ³ªÅ¸³»´Âµ¥,
Á¦Á¶ Á¶°ÇÀÇ º¯µ¿¼º¿¡ ±âÀÎÇØ ÀÏÁ¤ÇÑ °ªÀ» °®Áö ¾Ê´Â´Ù.
The overlap between the two curves represents
a possibility that failure may take place at one of the critical points, as
stress due to loading exceeds the strength of the material. In order for the
structure to be safe the overlapping area must be kept to a minimum. The degree
of overlap between the two curves can be minimised using one of three distinct
design philosophies, namely
ÀÌ µÎ °î¼±ÀÌ °ãÄ£ºÎÀ§´Â ±×·± À§ÇèºÎÀ§µé ÁßÀÇ ÇÑ °÷¿¡¼ Æı«°¡ ÀϾ È®·üÀ»
³ªÅ¸³»´Âµ¥, ÀÌ´Â ÇÏÁßÀ¸·Î ÀÎÇÑ ÀÀ·ÂÀÌ Àç·áÀÇ °µµº¸´Ù Ŭ °æ¿ì¿¡ ¹ß»ýÇÑ´Ù. ±¸Á¶¹°ÀÌ
¾ÈÀüÇϱâ À§Çؼ´Â ÀÌ °ãÄ£ ºÎºÐÀÇ ³ÐÀÌ°¡ ÃÖ¼Ò°¡ µÇµµ·Ï À¯ÁöµÇ¾î¾ß¸¸ ÇÑ´Ù. µÎ
°î¼± »çÀÌÀÇ °ãÄ£ Á¤µµ´Â ¼¼ °¡ÁöÀÇ ¼·Î ´Ù¸¥ ¼³°èöÇеé ÁßÀÇ ÇÑ °¡Áö¸¦ »ç¿ëÇÔÀ¸·Î½á
ÃÖ¼ÒȵǾîÁú ¼ö ÀÖ´Ù, Áï
(a) permissible stress design Çã¿ëÀÀ·Â¼³°è
(b) load factor method ÇÏÁß°è¼ö¹æ¹ý
(c) limit state design ÇÑ°è»óż³°è
1.2.1 Permissible Stress Design Çã¿ëÀÀ·Â¼³°è
In permissible stress design, sometimes referred to as modular ratio or elastic
design, the stresses in the structure at working loads are not allowed to exceed
a certain proportion of the yield stress of the construction material, ie. the
stress levels are limited to the elastic range. By assuming that the stress-strain
relationship over this range is linear, it is possible to calculate the actual
stresses in the material concerned. Such an approach formed the basis of the
design methods used by CP114 (the forerunner of BS8110), and BS449 (the forerunner
of BS5950).
Á¾Á¾ ¸ðµâ·¯ºñ³ª ź¼º¼³°è¶ó°í ºÒ¸®´Â Çã¿ëÀÀ·Â¼³°è¿¡¼´Â »ç¿ëÇÏÁßÀ» ¹Þ´Â ±¸Á¶¹°ÀÇ
ÀÀ·ÂÀÌ ½Ã°øÀç·áÀÇ Ç׺¹ÀÀ·ÂÀÇ ÀÏÁ¤ ºñÀ²Ä¡¸¦ ÃÊ°úÇؼ´Â ¾ÈµÈ´Ù, Áï ÀÀ·Â ¼öÁØÀÌ
ź¼º¹üÀ§¿¡ Á¦ÇѵȴÙ. ÀÌ·± ¹üÀ§¿¡¼´Â ÀÀ·Â-º¯Çüµµ °ü°è°¡ ¼±ÇüÀ̶ó°í °¡Á¤ÇÔÀ¸·Î½á,
°ü°èµÈ Àç·á¿¡ »ý±â´Â ½ÇÁ¦ ÀÀ·ÂÀ» °è»êÇÏ´Â °ÍÀÌ °¡´ÉÇÏ´Ù. ÀÌ·± Á¢±Ù¹ýÀÌ CP114(BS8110ÀÇ
¼±±¸ÀÚÀûÀÎ ±ÔÁØ)³ª BS449¿¡ ÀÇÇØ »ç¿ëµÈ ¼³°è¹æ¹ýÀÇ ±Ù°£À» ÀÌ·ç¾ú´Ù.
However this philosophy had two major drawbacks. Firstly permissible design
methods sometimes tended to over-complicate the design process and also lead
to conservative solutions. Secondly, as the quality of materials increased and
the safety margins decreased, the assumption that the stress-strain curve was
linear became unjustifiable for materials such as concrete, making it impossible
to estimate the true factors of safety.
±×·¯³ª ÀÌ·± ¼³°èöÇÐÀº µÎ °¡Áö Áß¿äÇÑ Ãë¾àÁ¡À» °¡Áø´Ù. ¸ÕÀú Çã¿ë¼³°è¹ýÀº Á¾Á¾
¼³°è°úÁ¤À» Áö³ªÄ¡°Ô º¹ÀâÇÏ°Ô ÇÏ´Â °æÇâÀÌ ÀÖÀ¸¸ç ¶ÇÇÑ ³Ê¹« º¸¼öÀûÀÎ(Áö³ªÄ¡°Ô
¾ÈÀüÃøÀ¸·Î) ÇØ°á¾ÈÀ» ³»³õ´Â °æÇâÀÌ ÀÖ´Ù. ´ÙÀ½À¸·Î´Â Àç·áÀÇ Ç°ÁúÀÌ Çâ»óµÇ°í ¾ÈÀüÀ²ÀÌ
ÁÙ¾îµê¿¡ µû¶ó, ÀÀ·Â-º¯Çüµµ °ü°è°¡ Á÷¼±À̶ó´Â °¡Á¤ÀÌ ÄÜÅ©¸®Æ®¿Í °°Àº Àç·á¿¡ À־Â
Á¤´çȵÇÁö ¸øÇÏ°Ô µÊÀ¸·Î½á, ½ÇÁ¦ ¾ÈÀüÀ²À» ÃøÁ¤ÇÏ´Â °ÍÀÌ ºÒ°¡´ÉÇÏ°Ô µÈ´Ù.
1.2.2 Load Factor Design ÇÏÁß°è¼ö¼³°è
Load factor or plastic design was developed to take account of the behaviour
of the structure once the yield point of the construction material had been
reached. This approach involved calculating the collapse load of the structure.
The working load was derived by dividing the collapse load by a load factor.
ÇÏÁß°è¼ö¼³°è ȤÀº ¼Ò¼º¼³°è´Â ½Ã°øÀç·á°¡ Ç׺¹Á¡¿¡ µµ´ÞÇßÀ» ¶§ÀÇ ±¸Á¶¹°ÀÇ °Åµ¿À»
°í·ÁÇϱâ À§Çؼ °³¹ßµÇ¾ú´Ù. ÀÌ Á¢±Ù¹ýÀº ±¸Á¶¹°ÀÇ Æı«ÇÏÁßÀ» °è»êÇÏ´Â °úÁ¤À»
Æ÷ÇÔÇÑ´Ù. »ç¿ëÇÏÁßÀº Æı«ÇÏÁßÀ» ÇÏÁß°è¼ö·Î ³ª´®À¸·Î½á ¾Ë ¼ö ÀÖ´Ù.
This approach simplified methods of analysis and allowed actual factors of safety
to be calculated. It was in fact permitted in CP114 and BS449 but was slow in
gaining acceptance and was soon superseded by the more comprehensive limit state
approach.
ÀÌ Á¢±Ù¹ýÀº Çؼ®¹æ¹ýÀ» °£´ÜÇÏ°Ô ÇßÀ¸¸ç ½ÇÁ¦ÀÇ ¾ÈÀüÀ²À» °è»êÇÏ´Â °ÍÀ» °¡´ÉÄÉ
ÇÏ¿´´Ù. ¼Ò¼º¼³°è´Â CP114¿Í BS449¿¡¼ ½ÇÁ¦·Î Çã¿ëµÇ¾úÀ¸³ª ÀϹÝÀûÀÎ ÀÎÁ¤À» ¾ò´Âµ¥´Â
¾ÆÁ÷ ¹ÌÈíÇÏ¸ç ´õ¿í Á¤±³ÇÑ ±ØÇÑ»óÅ Á¢±Ù¹ý¿¡ ÀÇÇØ °ð ±× ºûÀÌ ¹Ù·¡Á³´Ù.
The difference between these two approaches is illustrated below.
ÀÌ µÎ Á¢±Ù¹ýÀÇ Â÷ÀÌÁ¡ÀÌ ¾Æ·¡¿¡ ¿¹½ÃµÇ¾îÀÖ´Ù.
Example 1.1 - Comparison of Approaches to
Design ¼³°èÁ¢±Ù¹ýµéÀÇ ºñ±³
Consider the case of a solid rectangular beam, b wide by d deep, with a span
of 10 metres. In example (a) the beam is simply supported, and in example (b)
it is built in at each end. Assuming a safety factor of 1.5 calculate the minimum
width of beam using permissible stress and load factor approaches.
ÆøÀÌ bÀÌ°í ÃãÀÌ dÀ̸ç, ½ºÆÒÀÌ 10mÀÎ Á÷»ç°¢Çü º¸°¡ 12kN/mÀÇ µîºÐÆ÷ÇÏÁßÀ» ¹Þ°í
ÀÖ´Â °æ¿ì¸¦ »ý°¢Çغ¸ÀÚ. ¿¹ÄÁµ¥, (a) º¸´Â ´Ü¼øÁöÁöµÇ¾î ÀÖÀ¸¸ç, (b) º¸ÀÇ ¾ç´Ü¿¡¼
ÁöÁöµÇ°í ÀÖ´Ù. 1.5ÀÇ ¾ÈÀüÀ²À» °í·ÁÇؼ Çã¿ëÀÀ·Â¼³°è¿Í ÇÏÁß°è¼ö¼³°è¸¦ »ç¿ëÇÏ¿©
º¸ÀÇ ÃÖ¼ÒÆøÀ» °è»êÇ϶ó.
Figure 1.3 - Simply supported
beam ´Ü¼øÁöÁöº¸
Permissible stress approach Çã¿ëÀÀ·Â¼³°è¹ý
M = W*l*l/8 = 12(kN/m)*10(m)*10(m)/8=150 (kNm)
S perm = S ult/1.5
Elastic beam theory gives ź¼º º¸ÀÌ·ÐÀº ´ÙÀ½°ú °°´Ù.
Mc = S perm*Z
150 = (S ult/1.5)*(bd2/6)
b = 1350/(S ult*d2)
Load factor approach ÇÏÁß°è¼ö¼³°è¹ý
°è¼öÇÏÁß = 12 x 1.5 = 18 kN/m
M = W*l*l/8 = 18(kN/m)*10(m)*10(m)/8=225 (kNm)
Plastic beam theory gives ¼Ò¼º º¸ÀÌ·ÐÀº ´ÙÀ½°ú °°´Ù.
Mc = S ult*S
225 = S ult*(bd2/4)
b = 900/(S ult*d2)
¿©±â¼,
S perm = Permissible stress Çã¿ëÀÀ·Â;
S ult = Ultimate
or failure stress ±ØÇÑÀÀ·Â ȤÀº Æı«ÀÀ·Â;
M = Effective bending moment À¯È¿ÈÚ¸ð¸àÆ®;
Mc = Moment capacity ¸ð¸àÆ® Ä¿ÆнÃƼ;
S = Plastic section modulus ¼Ò¼º´Ü¸é°è¼ö;
Z = Elastic section modulus ź¼º´Ü¸é°è¼ö
For the special case of a rectangular beam it
can be seen that the permissible stress method gives a relatively conservative
solution compared with the load factor method, although the same safety factor
is used. However the permissible stress method does model behaviour under working
loads, and realistic predictions of behaviour in service can be calculated.
The load factor method only models failure, however, and no information on behaviour
in service can be obtained.
Á÷»ç°¢Çüº¸ÀÇ Æ¯¼öÇÑ °æ¿ì¿¡´Â ºñ·Ï °°Àº ¾ÈÀüÀ²ÀÌ
»ç¿ëµÇ´õ¶óµµ, Çã¿ëÀÀ·Â¼³°è°¡ ÇÏÁß°è¼ö¼³°è¹ý¿¡ ºñÇؼ »ó´ëÀûÀ¸·Î º¸¼öÀûÀÎ ÇØ°á¾ÈÀ»
»êÃâÇÑ´Ù. ±×·¯³ª Çã¿ëÇÏÁß¼³°è´Â »ç¿ëÇÏÁßÀ» ¹ÞÀ» ¶§ÀÇ °Åµ¿À» ¸ðµ¨ÈÇÑ °ÍÀ̱â
¶§¹®¿¡ »ç¿ëÇÏÁßÀ» ¹Þ´Â ±¸Á¶¹°ÀÇ °Åµ¿À» Çö½ÇÀûÀ¸·Î ¿¹ÃøÇÏ¿© °è»êÇÒ ¼ö ÀÖ´Ù. ±×·¯³ª
ÇÏÁß°è¼ö¼³°è´Â ´ÜÁö Æı«¸¦ ¸ðµ¨ÈÇÑ °ÍÀ̱⠶§¹®¿¡ »ç¿ëÇÏÁßÀ» ¹ÞÀ» ¶§ÀÇ °Åµ¿¿¡
´ëÇؼ´Â ¾Æ¹«·± Á¤º¸µµ ÁÖÁö ¸øÇÑ´Ù.
1.2.3 Limit state design ÇÑ°è»óż³°è
Originally formulated in Russia in the 1930's and
developed in Europe in the 1960's, limit state design can perhaps be seen as
a compromise between the permissible stress and load factor methods. It is in
fact a more comprehensive approach which takes into account both methods in
appropriate ways. Most modern structural codes of practice are now based on
a limit state approach. BS8110 for concrete, BS5950 for structural steelwork,
BS5400 for bridges, and BS5628 for masonry are all limit state codes. The principal
exceptions are the code of practice for design in timber, BS5268, and the old
(but still current) structural steelwork code, BS449, both of which are permissible
stress codes.
1930³â´ë¿¡ ·¯½Ã¾Æ¿¡¼ ÃÖÃÊ·Î °í¾ÈµÇ¾úÀ¸¸ç
1960³â´ë¿¡ À¯·´¿¡¼ ¹ßÀüµÈ ÇÑ°è»óż³°è´Â Çã¿ëÀÀ·Â¼³°è¿Í ÇÏÁß°è¼ö¼³°è »çÀÌÀÇ
ÀÏÁ¾ÀÇ Å¸ÇùÁ¡À¸·Î º¼ ¼ö ÀÖ´Ù. »ç½Ç ÇÑ°è»óż³°è´Â Àû´çÇÑ ¹æ½ÄÀ¸·Î µÎ °¡Áö ¼³°è¹ýÀ»
¸ðµÎ °í·ÁÇÑ Á»´õ ¼¼·ÃµÈ Á¢±Ù¹ýÀÌ´Ù. ÇöÀç »ç¿ëµÇ°í ÀÖ´Â ´ëºÎºÐÀÇ ±¸Á¶¼³°è±ÔÁصéÀº
±ØÇÑ»óż³°è¿¡ ±âÃʸ¦ µÎ°í ÀÖ´Ù. ÄÜÅ©¸®Æ®¿¡ ´ëÇؼ´Â BS8110, ö°ñ¿¡ ´ëÇؼ´Â
BS5950, ±³·®¿¡ ´ëÇؼ´Â BS5400, Á¶ÀûÁ¶¿¡ ´ëÇؼ´Â BS5628ÀÌ »ç¿ëµÇ°í Àִµ¥ À̵éÀÌ
¸ðµÎ ±ØÇÑ»óż³°è¿¡ ±Ù°ÅÇÑ ±ÔÁصéÀÌ´Ù. ¸ñ±¸Á¶ ¼³°è±ÔÁØÀ¸·Î »ç¿ëµÇ´Â BS5268¿Í
ö°ñÁ¶¿¡ »ç¿ëµÇ´Â BS449¿¡´Â ¿¹¿ÜÀûÀ¸·Î ÇÑ°è»óż³°è°¡ Àû¿ëµÇÁö ¾Ê°í Çã¿ëÀÀ·Â¼³°è¿¡
±Ù°ÅÇÑ ±ÔÁØÀÌ »ç¿ëµÈ´Ù.
Two limit states are examined. µÎ °³ÀÇ ÇÑ°è»óÅ´Â
´ÙÀ½°ú °°´Ù.
(a)
Ultimate limit state ±ØÇÑÇÑ°è»óÅÂ
Similar to load factor design, failure of the structure
is "modelled" with appropriate safety factors on loading. In addition
partial safety factors are also applied to material strengths. The ultimate
limit state is concerned with the maximum load-carrying capacity of the structure
and plastic analysis methods are appropriate, if they can be applied.
ÇÏÁß°è¼ö¼³°è¿Í À¯»çÇÏ°Ô ±¸Á¶¹°ÀÇ Æı«´Â ÇÏÁß¿¡
´ëÇÑ ÀûÀýÇÑ ¾ÈÀüÀ²À» °¡Áö°í ¸ðµ¨ÈµÈ´Ù. ¶ÇÇÑ ºÎºÐÀûÀÎ ¾ÈÀüÀ²ÀÌ Àç·áÀÇ °µµ¿¡µµ
Àû¿ëµÈ´Ù. ±ØÇÑÇÑ°è»óÅ´ ±¸Á¶¹°ÀÇ ÃÖ´ë ÇÏÁßÁöÁö´É·Â°ú °ü°èµÇ¸ç ¼Ò¼ºÇؼ®¹ýÀÌ
Àû¿ëµÉ ¼ö ÀÖ´Ù¸é ÀûÀýÇÏ´Ù.
(b)
Serviceability limit state »ç¿ë¼ºÇÑ°è»óÅÂ
The serviceability limit state is concerned with
certain aspects of the structure at working loads, in particular deflection
and cracking. Normally behaviour of members at serviceability limit state is
elastic.
»ç¿ë¼ºÇÑ°è»óÅ´ »ç¿ëÇÏÁßÀ» ¹Þ´Â ±¸Á¶¹°ÀÇ Æ¯¼º¿¡
°ü°èµÇ´Âµ¥, ƯÈ÷ ÈÚÀ̳ª ±Õ¿ÀÌ »ý±â´Â °æ¿ì°¡ ±×·¸´Ù. ÀϹÝÀûÀ¸·Î »ç¿ë¼ºÇÑ°è»óÅ¿¡
ÀÖ´Â ºÎÀçÀÇ °Åµ¿Àº ź¼ºÀÌ´Ù.
As this approach forms the basis of the design
methods in most modern codes of practice for structural design, it is essential
that the design methodology is fully understood.
ÀÌ·± Á¢±Ù¹ýÀº ±¸Á¶¼³°è¿¡ ´ëÇÑ ´ëºÎºÐÀÇ Çö´ëÀûÀÎ
½ÇÁ¦ ±ÔÁصéÀÇ ±Ù°£À» ÀÌ·ç±â ¶§¹®¿¡, ¼³°è¹æ¹ý·Ð¿¡ ´ëÇÑ ¿Ïº®ÇÑ ÀÌÇØ´Â ÇʼöºÒ°¡°áÇÏ´Ù.
1.2.3.1
Characteristic and design values Ư¼º°ú ¼³°è°ªµé
As stated at the outset, when checking whether
a particular member is safe, the designer cannot be certain about either the
strength of the material composing the member or, indeed, the load which the
member must carry. The material strength may be less than intended
À§¿¡¼ °³·«ÀûÀ¸·Î ¸»ÇßµíÀÌ, ¾î¶² ºÎÀç°¡ ¾ÈÀüÇÑÁö¸¦
È®ÀÎÇÒ ¶§, ¼³°èÀÚ´Â ºÎÀ縦 ±¸¼ºÇÏ´Â Àç·áÀÇ °µµ¿Í ½ÇÁ¦ ºÎÀç°¡ ÁöÁöÇÏ´Â ÇÏÁßÀÇ
±× ¾î´À °Í¿¡ ´ëÇؼµµ È®½ÅÀ» ÇÒ ¼ö°¡ ¾ø´Ù. Àç·á°µµ´Â ¿¹»óÇß´ø °Íº¸´Ù ÀÛÀ» ¼öµµ
Àִµ¥,
(a) because of it's variable composition,
and
(a) Àç·á ±¸¼º»óÀÇ º¯µ¿¼º ¶§¹®¿¡
±×·¯Çϸç,
(b) because of the variability of manufacturing
conditions during construction, and other effects such as corrosion.
(b) ½Ã°øÇÏ´Â µ¿¾È Á¦Á¶Á¶°ÇÀÇ º¯µ¿¼º°ú ºÎ½Ä°ú °°Àº ´Ù¸¥
¿äÀÎµé ¶§¹®¿¡ ±×·¯ÇÏ´Ù.
Similarly the load in the member may be greater
than anticipated
¸¶Âù°¡Áö·Î ºÎÀç°¡ ÁöÁöÇÏ´Â ÇÏÁßµµ ¿¹ÃøÇß´ø °Íº¸´Ù
´õ Ŭ ¼ö°¡ Àִµ¥,
(a) because of the variability of the occupancy
or environmental loading, and
(a) »ç¿ëÀÚÀÇ
°ÅÁÖ»óÅÂ¿Í ÁÖÀ§ ÇÏÁßÀÇ º¯µ¿¼º ¶§¹®¿¡ ±×·¯Çϸç,
(b) because of unforeseen circumstances which
may lead to an increase in the general level of loading, errors in the analysis,
errors during construction etc.
(b)
ÀϹÝÀû ¼öÁØÀÇ ÇÏÁßÀ» ÃÊ°úÇÒ ¼ö ÀÖ´Â ¿¹ÃøÄ¡ ¸øÇÑ È¯°æ¿äÀÎ, Çؼ®»óÀÇ ½Ç¼ö, ½Ã°øÁßÀÇ
¿ÀÂ÷ µî ¶§¹®¿¡ ±×·¯ÇÏ´Ù.
In each case, item (a) is allowed for by using
a characteristic value. The characteristic strength is the value below which
the strength lies in only a small number of cases. Similarly the characteristic
load is the value above which the load lies in only a small percentage of cases.
In the case of strength the characteristic value is determined from test results
using statistical principles, and is normally defined as the value below which
not more than 5% of the test results fall. However, at this stage there is insufficient
data available to apply statistical principles to loads. Therefore the characteristic
loads are normally taken to be the design loads from previous codes of practice.
°¢°¢ÀÇ °æ¿ì¿¡, (a) »çÇ×Àº Ư¼ºÄ¡¸¦ »ç¿ëÇÔÀ¸·Î½á
°í·ÁµÉ ¼ö ÀÖ´Ù. ÀϹÝÀûÀ¸·Î °µµ´Â ¸Å¿ì ÀûÀº °æ¿ì¿¡ Ư¼º°µµº¸´Ù ÀÛ°Ô µÈ´Ù. ¸¶Âù°¡Áö·Î
ÀϹÝÀûÀ¸·Î ÇÏÁßÀº ¸Å¿ì ÀûÀº È®·üÀ» °¡Áö°í¼ Ư¼ºÇÏÁߺ¸´Ù Å©°Ô µÈ´Ù. °µµÀÇ °æ¿ì¿¡
Ư¼ºÄ¡´Â Åë°èÇÐÀûÀÎ ¿ø¸®¸¦ ÀÌ¿ëÇÑ ½ÇÇè°á°ú·ÎºÎÅÍ °áÁ¤ÀÌ µÇ¸ç, ÀϹÝÀûÀ¸·Î ½ÇÇè°á°úÄ¡°¡
Ư¼ºÄ¡º¸´Ù ³·Àº È®·üÀÌ 5%º¸´Ù ³·°Ô µÈ´Ù. ±×·¯³ª ÀÌ ´Ü°è¿¡¼ Åë°èÇÐÀûÀÎ ¿ø¸®¸¦
ÇÏÁß¿¡ Àû¿ëÇϱ⿡ ºÒÃæºÐÇÑ Á¡ÀÌ ÀÖ´Ù. µû¶ó¼ Ư¼ºÇÏÁßÀº ÀϹÝÀûÀ¸·Î ÀÌÀü ±ÔÁص鿡¼
»ç¿ëµÈ ¼³°èÇÏÁßÀ» ÃëÇÑ´Ù.
Thus the characteristic dead load (Gk), which
represents the weight of the structure including finishes, fixtures and partitions,
can be estimated using BS648: Schedule of Weights for Building Materials and
BS6399: Design Loads for Buildings, Part 1: Code of Practice for Dead and Imposed
Loads. Similarly typical design values of the characteristic imposed load (Qk),
which represents the load due to the proposed occupancy, are given in BS6399.
The characteristic wind loads (Wk) are obtained using BS6399 Part 3, formerly
CP3: Chapter 5: Part 2.
µû¶ó¼ ¸¶°¨Àç, º®Ã¼ºÎÂø¹°, ºñ³»·Âº®À» Æ÷ÇÔÇÏ´Â
±¸Á¶¹°ÀÇ ¹«°Ô¸¦ ³ªÅ¸³»´Â Ư¼º°íÁ¤ÇÏÁßÀº ´ÙÀ½ÀÇ ±ÔÁصéÀ» ÀÌ¿ëÇؼ ÃßÁ¤ÇÒ ¼ö ÀÖ´Ù
: BS648: Schedule of Weights for Building Materials and BS6399: Design Loads
for Buildings, Part 1: Code of Practice for Dead and Imposed Loads. ¸¶Âù°¡Áö·Î,
°¡Á¤ÇÑ °ÅÁÖ¼º¿¡ ±âÀÎÇÑ ÇÏÁßÀ» ³ªÅ¸³»´Â Ư¼ºÄ¡¸¦ Æ÷ÇÔÇÑ ÇÏÁßÀÇ ¼³°èÄ¡´Â BS6399¿¡¼
±¸ÇÒ ¼ö ÀÖ´Ù. Ư¼ºÇ³ÇÏÁßÀº ´ÙÀ½ ±ÔÁØÀ» ÀÌ¿ëÇؼ ±¸ÇÒ ¼ö ÀÖ´Ù : BS6399 Part 3,
formerly CP3: Chapter 5: Part 2
The overall effect of items under (a) and
(b) is allowed for using a partial safety factor, gm for strength, gf for load.
The design strength is obtained by dividing the characteristic strength by the
partial safety factor for strength
(a)¿Í (b)¿¡ ÇØ´çÇÏ´Â Ç׸ñµéÀÇ ÀüüÀûÀÎ ¿µÇâÀº
ºÎºÐ¾ÈÀüÀ²À» »ç¿ëÇÔÀ¸·Î½á °í·ÁÇÒ ¼ö ÀÖ´Ù. °µµ¿¡ ´ëÇؼ´Â gmÀ», ÇÏÁß¿¡ ´ëÇؼ´Â
gf¸¦ »ç¿ëÇÑ´Ù. ¼³°è°µµ´Â Ư¼º°µµ¸¦ °µµ¿¡ ´ëÇÑ ºÎºÐ¾ÈÀüÀ²gm·Î ³ª´®À¸·Î½á ¾ò¾îÁú
¼ö ÀÖ´Ù.
ie design strength = characteristic
strength/gm
¼³°è°µµ = Ư¼º°µµ/ºÎºÐ¾ÈÀüÀ²
The choice of values for gm depend on the material
being considered. For instance, the strength of in-situ concrete is more likely
to be affected by the nature of the construction process than the strength of
the reinforcing steel. This is accounted for in limit state design by assigning
a higher factor of safety to concrete (1.5) than reinforcing steel (1.15).
°µµ¿¡ ´ëÇÑ ºÎºÐ¾ÈÀüÀ² gmÀÇ °ªÀ» ¼±ÅÃÇÏ´Â °ÍÀº
°í·ÁµÇ´Â Àç·á¿¡ ´Þ·ÁÀÖ´Ù. ¿¹ÄÁµ¥, ÇöÀ埼³ ÄÜÅ©¸®Æ®ÀÇ °µµ´Â ö±ÙÀÇ °µµº¸´Ù
½Ã°ø°úÁ¤ÀÇ ¼º°Ý¿¡ ÀÇÇØ ´õ Å« ¿µÇâÀ» ¹Þ±â ¸¶·ÃÀÌ´Ù. ÇÑ°è»óż³°è¿¡¼´Â ÀÌ·± Çö»óÀ»
ö±Ù¿¡ »ç¿ëµÇ´Â 1.15ÀÇ ¾ÈÀüÀ²º¸´Ù ÄÜÅ©¸®Æ®¿¡¼ ´õ Å« 1.5¶õ ¾ÈÀüÀ²À» »ç¿ëÇÔÀ¸·Î¼
ÇØ°áÇÑ´Ù.
The design load is obtained by multiplying the
characteristic load by the partial safety factor for load
¼³°èÇÏÁßÀº Ư¼º°µµ¿¡ ÇÏÁß¿¡ ´ëÇÑ ºÎºÐ¾ÈÀüÀ²À»
°öÇÔÀ¸·Î½á ¾òÀ» ¼ö ÀÖ´Ù.
ie design load = characteristic
load x gf
¼³°èÇÏÁß = Ư¼ºÇÏÁß x ºÎºÐ¾ÈÀüÀ²
The value for gf depends on several factors
including the limit state under consideration and the accuracy of predicting
the loads on the structure. For instance, at the ultimate limit state dead loads
are multiplied by 1.4 and imposed loads by 1.6. However at the serviceability
limit state these factors reduce to 1.0.
ÇÏÁß¿¡ ´ëÇÑ ºÎºÐ¾ÈÀüÀ²ÀÇ °ªÀº °í·ÁÇÏ´Â ÇÑ°è»óÅ¿Í
±¸Á¶¹°¿¡ ÀÛ¿ëÇÏ´Â ÇÏÁß¿¹ÃøÀÇ Á¤È®¼ºÀ» Æ÷ÇÔÇÏ´Â ¿©·¯ ¿äÀε鿡 ±Ù°ÅÇØ °áÁ¤µÈ´Ù.
¿¹ÄÁµ¥, ±ØÇÑÇÑ°è»óÅ¿¡¼´Â °íÁ¤ÇÏÁßÀº 1.4¶õ ºÎºÐ¾ÈÀüÀ²À» °öÇÏ°í À̵¿ÇÏÁß¿¡ ´ëÇؼ´Â
1.6À» °öÇÑ´Ù. ±×·¯³ª »ç¿ë¼º ±ØÇÑ »óÅ¿¡¼´Â ÀÌ °ªµéÀÌ ¸ðµÎ 1.0ÀÌ µÈ´Ù.
In general, once a preliminary assessment of the
design loads has been made it is then possible to calculate the maximum bending
moments, shear forces and deflections in the structure.
ÀϹÝÀûÀ¸·Î ÀÏ´Ü ¼³°èÇÏÁß¿¡ ´ëÇÑ Ãʱâ Æò°¡°¡ ÀÌ·ç¾îÁö¸é,
±¸Á¶¹°ÀÇ ÃÖ´ë ÈÚ¸ð¸àÆ®¿Í Àü´Ü·Â, ±×¸®°í ÈÚÀ» °è»êÇÏ´Â °ÍÀÌ °¡´ÉÇÏ´Ù.
The construction material must be capable
of withstanding these forces otherwise failure of the structure may occur. Simplified
procedures for calculating the moment, shear and axial capacities of the members
together with acceptable deflection limits are described in the appropriate
codes of practice. These allow the designer to rapidly assess the suitability
of the proposed elements of structure. The aim of the following lectures then
is to discuss these procedures in respect of reinforced concrete, steelwork
masonry and timber structures.
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¸ð¸àÆ®, Àü´Ü·Â, ±×¸®°í Ãà·ÂÀ» °è»êÇÏ´Â ´Ü¼øÈµÈ °úÁ¤Àº ÀûÀýÇÑ ±ÔÁØÀ» ã¾Æº¸¸é
±â¼úµÇ¾î ÀÖ´Ù. ÀÌ´Â ¼³°èÀÚ·Î ÇÏ¿©±Ý Á¦¾ÈµÈ ±¸Á¶¹° ºÎÀçÀÇ ÀûÇÕ¼ºÀ» »¡¸® Æò°¡ÇÒ
¼ö ÀÖµµ·Ï ÇØÁØ´Ù. ´ÙÀ½¿¡ ÀÌ·¯Áö´Â °ÀÇÀÇ ¸ñÀûÀº ÀÌ·± °úÁ¤µéÀ» ö±ÙÄÜÅ©¸®Æ®,
ö°ñÁ¶, Á¶ÀûÁ¶, ±×¸®°í ¸ñÁ¶ÀÇ Ãø¸é¿¡¼ ÅäÀÇÇÏ´Â °ÍÀÌ´Ù.