Design of Concrete Arches for Residential Buildings India

8/12/2019 Design of Concrete Arches for Residential Buildings India

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DESIGN OF CONCRETE ARCHES FOR RESIDENTIALBUILDINGSBy.T.Rangarajan,B.E,M.Sc(struct.engg),F.I.E,C.E.,Consulting Structuralengineer,Coimbatore,Tamilnadu.tirumalaicettiar!yaoo.com
mailto:[email protected]:[email protected]


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DIFFERENT ARCH SHAPES:

STR"CT"R#$ BRIC% #RC&ES

'#C% #RC&


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M"TICETERE #RC&

SE*MET#$ #RC&


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SEMICIRC"$#R #RC&

TRI#*"#$R #RC&


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T"+R #RC&

EETI# #RC&


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B"$$SE-E#RC&


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*+T&IC #RC&

*+T&IC #RC&

ITR+"CTI+.

#rcitects alays is to add beauty and elegance to buildings. #lso te /ublicli0e te ay in ic it loo0s as attracti1e and beauti2ul it res/ect to tesurroundings. It became customary to add arces 2or te o/enings not onlyoutside te building but also 2or te door and oter o/enings. 3en tese add


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sa/es are added it becomes a callenge to structural engineers it res/ectte dimensional design as/ect.

In olden days te arces are made use in building bridges as at tat timeneiter te concrete nor rein2orcement ere in1ented. It is te idea tat tese

arces are in1ert o2 Bending moment diagram erein tere is no tension in temember. So by in1erting te BM diagram te structural engineer can eitedesign an arc or a roo2 truss ere te member ill a1e no tension but onlycom/ression 2orces only. Te sa/e o2 te member can be circular , /arabolacatenary or an elli/se. In te olden days many masonry structures ere eiteone o2 te sa/es mentioned.

#s tere are no te4t e4/laing or co1ering te detailed design o2 a Rein2orcedConcrete #rces an attem/t is made to e4/lain te design by re2ering manyboo0s.

ARCH TERMS:

Extrados: The curve which bounds the upper edge of the arch.

Intrados: The curve which bounds the lower edge of the arch. The distinction between soffit andintrados is that the intrados is a line, while the soffit is a surface.

Crown:The apex of the arch's extrados. In symmetrical arches, the crown is at the midspan.


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Rise:The maximum height of the arch soffit above the level of its spring line.

Soffit:The surface of an arch or vault at the intrados.

Span: The horizontal clear dimension between abutments.

Spandrel: The masonry contained between a horizontal line drawn through the crown and a verticalline drawn through the upper most point of the skewback.

Springing: The point where the skewback intersects the intrados.

Springer: The first voussoir from a skewback.

Spring Line: horizontal line which intersects the springing.

Voussoir: One masonry unit of an arch.

CHARACTERISTICS OF ARCH ACTION:Te main caracteristics o2 arces common to all is te /resence at te su//orto2 &ori5ontal trust induced tere, because o2 unyiedling su//orts /re1ent tecur1ed beams 2rom straigtening under 1ertical loads. Te ori5ontal trustacts toards te arc. It /roduces com/ression stresses at all sections o2 tearc.

Te ori5ontal trust also /roduces 61e BMs at all sections o2 te arc iccounteract te 71e BMS due to te loads. Tus te second caracteristic o2arc action is tat in adition to te BMs eac section is subjected to a directtrust and also tat at all sections te static BMS due to load is considerablyreduced by te BM due to ori5ontal trust.

Te abo1e caracteristic are common to FI8E as ell as &I*E arces.

Design of R.C.C..ArchIS !"!#$"%&.

C'()se *.+.$.+

Lo(, on (rch:Re2erence is made to IS9:;:6 in ic te clause ?.@.


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Te rise o2 te arc generally be beteen


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e/ending u/on te s/an o2 te arces tey are classi2ied as MI+R and M#'+Rarces.Minor (rchesare tose oe s/ans do not e4ceed =6:G and it ma4imumrise to s/an ratios o2 :.


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Minor (rch 'o(,ings:

Te loads 2alling u/on a minor arc may consists o2 $IE loads and E# loads2rom 2loors, roo2s, alls and oter structural elements. Tese are a//lied as

/oint loads or as uni2orm loads 2ully or /artially distributed.

Te ead load o2 a all abo1e an arc may be assumed to be te eigt o2 alcontained itin a triangule immediately abo1e te o/ening. Te sides o2 tistriangle are at 9?6degree angles to te base. Tere2ore, its eigt is K o2 tes/an. Suc trangular loading may be assumed to be eJui1alent to a uni2ormlyistributed load o2


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be eigt o2 te all abo1e cron o2 te arc u/to a ma4imum eigt o2$@


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(or vertical uniform load over the entire arch:

+ and 0 are zero at any section of the arch.

-hen x /:

Notation. In these e1uations, the subscripts 2 and / denote the left and right supports respectively.

The subscript x denotes values at any horizontal distance, x, from the origin. is the angle, at any

point, whose tangent is the slope of the arch axis at that point. 3$ee Table 4.5

+ 6 moment

) 6 axial force

0 6 shearing force

f 6 rise of the arch

- 6 total load under consideration

! 6 horizontal thrust

7 6 vertical reaction

6 span of the arch


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$ and T are load constants 3see Table 85.

Ste/sH


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Design of Concrete Arches for Residential Buildings India