Beton Examen

7/29/2019 Beton Examen

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16. Types of shear failure:shear bond failure, dowel failure, shear compression failure, diagonal tensionfailure, flexural failure

P P

45

Shear bond failure

dowel action

Dowel failure

P P

crushing concrete

Shear compression failure

P P

Diagonal tension failure

P P

Flexural failure

Fig.11.23. Types of shear failure


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2. Distana maxim ntre armturi:

- 200 mm (cel puin 5 bare/metru) pentru plci cu mm300hp

- 250 mm (cel puin 4 bare/metru) pentru plci cu mm400h300 p

- 200mm pentru plase sudate

Distana minim dintre bare este:

- 80 mm (maxim 12 bars/metru)

- 50 mm pentru plase sudate.

6. The transversal shape of monolith beams is generally T section. For prefabricated beams the

transversal section can be realized in a big variation that monolith ones, Fig. 16.7.


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3.

a) One way spanning slabs )0,2l( oyox >

The main reinforcement is placed parallel with the small span of the slab. Perpendicular is placed

constructive reinforcement, Fig. 16.18.

For taking over the local bending moments on support from the big span, there are placed riders, that

are m/65 (PC 52, PC 60) or m/85 (OB 37); they are prolonged outer the support with ox25,0 .

b) Two way spanning slabs

The reinforcement is placed respecting on every direction the provisions, Fig. 16.18.b

a) One-way spanning slab b) Two-way spanning slab

c) Two-way spanning slab

Fig. 16.18. Reinforcement arrangement


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3. When the reinforcement is realized of welded meshes, it must respect the same rules as in the case

of independent bars.

In fig. ....there are presented some examples of reinforcing with welded meshes.

a1) span reinforcing a2) support reinforcing

b1) span reinforcing superposed meshes b2) support reinforcing

Fig.. Slab reinforcing with welded meshes


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8. Doubly reinforced rectangular section

Doubly reinforced is necessary when lim> , the steel areas are determined with the relations:

12.

Dac 5wb

b n general axa neutr trece prin plac, fhx sau dac este satisfcut condiia:

=

d

h

d

h

b

b

fdb

M ff

wcdw

Eds 5.012

n aceast situaie dimensionarea seciunilor n form de T se face cu relaiile de la seciunile

dreptunghiulare, nlocuind limea grinzii cu limea plcii, fig.1

Fig.1 Seciunea T simplu armat


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13.

Detrminarea limii efective a plcii n calculul la toate strile limit se face pe baza distanei l0 dintrepunctele de efort nul din diagrama de momente ncovoietoare.Limea efectiv rezult din relaia:

bbbbb weffeffeff ++= 2,1Unde:

++

+

= b

bieff

eff bbb

bb

b 21

,

min

Unde : 002,12,1 2,01.02.0 llbbeff


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14.

Dac lim1 s este necesar dubla armare:

yd

cd

w

f

w

f

sf

f

dbdd

d

h

b

b

d

h

A2

2

lim

2

5.011

=

( )[ ] 2lim1 syd

cdfwws A

f

fhbbdbA +

+=

Fig. 2. Seciunea T dublu armat

29.

The slenderness ratio is defined by:

r

lfo =

fl - is the effective length of the member

r is the radius of gyration

A

Ir=

30.Function of slenderness ratio we have:

- for 10 (short columns), the second-order moments can be ignored

- for 3010 < (slender columns), it is necessary to consider the second-order moments

- for 30> (very slender columns) the failure of columns, under an continuous increasing of the

axial force will take place by loosing the stability (buckling).


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17.

Mecanismul de transfer la elemente fr armtur pentru fora tietoare:(a)efect de pan; (b)legturaagregatelor;(c)beton nefisurat

a) b)

c)

Mecanismul de transfer al forei tietoare la elementele cu armtur pentru for tietoare

Vs este fora tietoare preluat de etrieri


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18.

Modelul grinzii cu zbrele pentru grinda din beton armat: a) fisurare a grinzii; (b) zone decompresiune ntre fisuri;(c) Modelul grinzii cu zbrele.

19.

Shear strength of members with shear reinforcement

For slabs, it is not necessary to provide any shear reinforcement provided Q > Qb. However, where

links are to be provided, a minimum quantity should be used. The minimum quantity of reinforcement arespecified in terms of the shear reinforcement ratio, w. For vertical stirrups in prismatic members, this is the

ratio of the cross-sectional area of stirrup to the area of concrete in plan see Fig.11.27, that is:

a) b)

Fig. 11.27 Definition of w: (a) pictorial view; (b) section X-X (plan view)

where Ae = area of shear reinforcement within length, ae; for stirrups with two

legs each, the combined area from both legs is used in the calculation of Aet;

ae = spacing of shear reinforcement;

b = web breadth or, in the case of rectangular sections, actual breadth.


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20.Equilibrium torsion is that which is required to maintain equilibrium of the member. In such situation,the external load has no other option but to be carried by torsion. Examples of equilibrium torsion,illustrated in Fig. 6.2a are an eccentrical loaded beam and a beam in which there is a change in the directionof its longitudinal axis Fig. 6.2b.Equilibrium torsion is of primary interest in design because failure of the member is inevitable if it hasinsufficient torsional strength.

Fig.12.2. Equilibrium torsion

Compatibility torsion occurs in structures having rigidly connected members Fig. 6.3

Fig. 12.3 Compatibility torsion


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22. Provisions for beams subjected to bending and torsion

Torsional reinforcement is composed of bars of two types: transverse stirrups and additional

longitudinal reinforcement or spiral.

The transverse stirrups used for torsional reinforcement must be of closed form, since principaltensile stress results on each of the form faces of a beam in torsion Fig.16.16. Good anchorage is provided

by hooking the stirrups bar ends around the longitudinal reinforcement.

In order to control spiral cracking properly, the maximum spacing of torsional stirrups should not

exceed4

thba

ssl < .

The spacing of the longitudinal bars should not exceed b

3

1a l < , and they should be well distributed

around the perimeter of the cross-section to control cracking; at least one bar must be placed in each corner

of the stirrups fig. 16.16. Careful attention must be paid to the anchorage of longitudinal torsional

reinforcement so that it is able to develop its yield strength at the face of the supporting columns, where

torsional moments are often maximum.

Fig. 16.16. Reinforcing of beams subjected to bending and torsion

26.

Failure of member subjected to compression plus bending.


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27.

Modul de rupere a stlpilor

Fig. Ruperea stlpilor funcie de excentricitate

28.

Still, some steel reinforcement is always provided for various reasons. For one, very few members are truly

axially loaded; steel is essential for resisting any bending that may exist; For another, if part of the total load

is carried by steel with its much greater strength, the cross-sectional dimensions of the member can be

reduced, the more so the larger the amount of reinforcement.

The two chief forms of reinforced-concrete columns are shown in Fig. 14.5


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(1) (2) (3)

Fig.14.5 Reinforced concrete columns: (1) - longitudinal rods and spiral hooping; (2)

longitudinal rods and lateral ties; (3) structural steel.

Armarea stlpilor se realizeaz cu armatur longitudinal i transversal.

a)Armtura longitudinal

n fig.7.23 sunt prezentate cteva moduri de armare a stlpilor.

Distana liber ntre bare trebuie sa fie be 50 mm, iar distana interax nu trebuie s

depeasc 250 mm.

Se admite armarea cu patru bare n colurile seciunii n urmtoarele situaii: Stlpul face parte din grupa A cu dimensiuni < 350 mm;

Stlpul face parte din grupa B i C cu dimensiuni < 400 mm;


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b)Armtura transversal

n cazul stlpilor armtura transversal sub form de etrieri se utilizeaz pentru mpiedicarea

flambajului barelor longitudinale, pentru confinarea betonului comprimat i pentru a prelua

eforturile transversale n zonele de nndire ale armturilor longitudinale.

Etrierii trebuie realizai cu ciocuri i lungimea dreapt de cel puin 10d.

Diametrul minim al etrierilor se alege

1. How shape has the computed section of the slab.2. What are the minimum and maximum number of bars in a slab section?3. The slab can be with resistant reinforcement on one or both directions?4. How type of reinforcing can be used for slab?5. What members of a structure a subjected to bending and shear force?6. What type of sections the beams have?7. When the rectangular section of a beam is singly reinforced?8. Where are placed the reinforcements in the case of doubly reinforced section?9. What represent x?10. In which stage of working the design of the steel is made?11. What types of stress (produced by what?) are taking over the longitudinal reinforcement in a beam?12. In the case of T section when the neutral axis passes through the flange?13. How is determined the width of the flange (beff)?14. The T section can be doubly reinforced?15. What type of reinforcement can be provided for shear?16. Types of shear failure?17. Mechanisms of shear transfer? For member without shear reinforcement? For members with shear

reinforcement (stirrups)?18. What method is used in order to quantify the behavior and strength of members with shear

reinforcement?19. What method is used for determining the resistance of elements provided with shear steel? (draw)20. How can obtained the lengths of zones on which the distance among stirrups is computed?21. How many types of torsion do you know?22. How can be increased the torsion strength?

8mm}6mm;;4/1{ dde


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23. In which stage of working the limit state of cracking is verified?24. In which stage is done the checking to limit state of cracking?25. The cracks widths are limited by norms?26. The columns are subjected to?27. Depending on the force eccentricity the failure of columns is how?28. The columns are reinforced with what type of reinforcement?29. What is slenderness ratio?30. Depending on the slenderness ratio how the columns are classified?31. Methods of prestressing-32. Prestressing force (tract, transfer, notations)33. Losses of prestress (only tupes)34.Provisions for prestress concrete

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