REINFORCEMENT DETAILING IN NON ENGINEERING AND ENGINEERING E

8/14/2019 REINFORCEMENT DETAILING IN NON ENGINEERING AND ENGINEERING E

1/17

REINFORCEMENT DETAILING IN NON ENGINEERING AND

ENGINEERING EARTHQUAKE RESISTANT STRUCTURES

ABSTRACT

Most losses of life and property during earthquakes have occurred due to collapse of structure. Lack

of understanding of earthquake resistant features reinforcement detailing, developments in the philosophy of

ductility bases design has aggravated the problem. One of the most important factor causing damage to

structure during earthquakes is lack of adequate structural connections along with the other factors. The

observations of structural performance in earthquake damaged areas in the past also identifies the need for

proper reinforcement detailing in non engineering as well as Engineering structures.

This paper is aimed to discuss and describes the reinforcement detailing in earthquake resistant Non

Engineering and Engineering Structures. The material requirements, I.S. code provisions for designing andreinforcement detailing in the different component parts of structure along with illustrations are briefly

discussed.

1) INTRODUCTION

Amongst all the natural disasters, earthquakes can prove most deadly as it has the leastduration of occurance but causing huge loss to human lives and property. Increasing magnitude of

seismic risk to the life could be imagined by the fact that in India more than 55 % of areas lies inactive seismic zones.

Considering the fact that in future we have to live with the earthquake tremors it becomesessential to introduce earthquake resistant features in the construction of structures. The main factors

contributing to the damage of structures during earthquakes have been their heavy weight, low tensileand shearing resistance, lack of adequate structural connections, poor quality of construction and

deterioration of strength with the passage of time.

This paper highlights one of the major aspect of inadequate detailing of reinforcement and

describes the designing and detailing consideration in non engineering and engineering construction

along with I.S.code provisions, material requirements, and general design consideration.The term Non engineering building may only be vaguely defined as a building whose analysisfor lateral earthquake forces would defy reasonable mathematical solutions and the design will be

based mostly on a set of specifications derived from observed behaviour of such buildings during past

earthquakes and trained engineering judgement. Load bearing masonary wall buildings studwalls and

brick nogged constructions in wood composite constructions using load bearing walls and piers inmasonary, reinforced concrete, steel or wooden posts are the examples of Non Engineering

constructions. Where as Reinforced concrete or steel frame buildings, tall buildings using differenttypes of structural system involving the dynamic analysis for seismic loads and ductility design

considerations can be termed as Engineering constructions.

2 WHAT HAPPENS TO BUILDING AND STRUCTURES IN AN EARTHQUAKE

1) Seismic forces are very irregular and buildings are variously affected due to complex nature ofstructures. Therefore, standardization of seismic forces which act and provisions required to bemade in structures to withstand them are very difficult.

2) Seismic forces act horizontally, vertically and in a vibratory and oscillatory manner. The result isthat unless the structure is well-knit, homogeneous and all its components securely anchored and

connected with one another, it is shaken to pieces to a degree depending on the severity of the

seismic forces.

1


2/17


3/17

iv) Proper detailing with regard to anchorage, splicing, minimum reinforcement, bending,termination, extension etc.

3.3. Materials

Reinforcement and concrete

Ductility requires the use of low grades of steel having well defined and longer yield plateau so

that plastic hinges formed will have larger rotation capacities leading to greater energy dissipation. Aslower the grade of steel the higher is the ratio of the ultimate tensile strength to yield strength. A

higher ratio is desirable as it results in increased length of plastic hinge and thereby increased plasticrotation capacity. From these considerations mild steel ( Fe250) is best suited for flexural

reinforcement in earthquake resistant design but will require larger cross sections. I.S.code 13920 -

1993 permits use of Fe415 steel but prohibits the use of higher grades than Fe415.

I.S. code limits the minimum grade of concrete to M20, use of very high strength isundesirable due to it's lower compressive strain which inturn affect ductility. The ACI and Canadian

codes limits cylinder strength to 30 Mpa.

4. REINFORCEMENT DETAILING IN NON ENGINEERING CONSTRUCTION

Non engineering constructions can be made enough earthquake resistant through some simple principles of planning and reinforcing techniques. In this paper discussion is limited to only

reinforcement details at critical sections in the structures. The extent of reinforcing depends upon the

seismic intensity.4.1. Horizontal Reinforcement in masonary Walls.

For imparting horizontal bending strength against plane action for out of plane inertia load andfor tying the perpendicular walls together. The following reinforcing arrangements are provided.

3

Fig No. 1


4/17

4.1.1. Horizontal Band or Ring Beam.

The most important horizontal reinforcing is through reinforced concrete bands provided

continuously through all load bearing longitudinal and transverse Walls. A band consists of two orfour longitudinal steel bars with links embedded in thick concrete ( fig No.1). The steel bars are

located closed to the Wall faces and full continuity is provided at corners and junctions. Such bands

are provided at critical levels of the buildings i.e. plinth lintel, roof and gables according to

requirements.

4.1.2 Dowels at Corners and Junctions

As an alternative to the bands, steel dowel bar may be used at corners and T. junctions to

integrate the box action of Walls. Dowels are placed in every fourth course or at about 50 cm interval

and taken into the Walls to sufficient length to provide full bond strength (fig No 2 a,b,c,)

4

Fi 2a


5/17

5

Fi 2b


6/17

6

Fig 2c


7/17

4.1.3. Reinforcement of partitions and Infills.

Partitions and infill panels are necessarily thin Walls and reinforcement is needed for there out

of plane stability. Thin steel mesh or Welded Wire fabric is provided every fourth course or 30 cmheight.( fig No.3)

4.2. Vertical reinforcement in Walls

The vertical reinforcing steel shall be provided at the critical sections i.e. at jambs of opening

and corners of the Walls. The amount of vertical reinforcing steel will depend upon number of factorslike number of storeys, storey height, seismic Zone importance of building, soil foundation type etc.

Typical arrangements of placing the vertical steel in brickwork are shown in fig No 4. The total

arrangement of providing reinforcing steel in masonary wall construction is illustrated in fig No.5.

7

Fig No. 3


8/17

8

Fig No.4


9/17

4.3 Framing of thin masonry walls

When masonory walls are thinner than 20 cm, then provision of columns and collar beams

becomes necessary as shown in fig No 6. The columns are located at all the corners and junctions of

walls as well as both sides of door openings. The collar beams are provided at top and bottom of

storeys. The fig No 7 illustrates typical reinforcing details between beams and columns.

9

Fig No. 5

Fig No. 6


10/17

10Fig No. 7


11/17


12/17

v) When lap splices are provided transverse reinforcement for confining concrete and to supportlongitudinal bars, in the form of closed stirrups or 'hoops' ( with 1350 hook and 10 extension) should be provided over entire splice length at spacing not exceeding 150 mm

(fig 9)

vi) The bar extensions must provide for possible shifts in the inflection points which may occur

under the combined effects of gravity and seismic loadings.

12

Fig No.8 : End support detailing for earthquake moment (a) Both top and bottom bars are taken up

(b) Top bars down and bottom bars up (c) Top bars down and bottom bars up but within the beam depth

Fig. No.9


13/17

vii) Inclined bars are not allowed as effective shear reinforcement due to changing direction ofdiagonal stress.

viii) Web reinforcement must be in the form of closed stirrups (hoops) placed perpendicular tolongitudinal reinforcement and must be provided throughout the length of member. Hoops

should have minimum diameter of 8 mm in beams with clear span more than 5 m (Fig No 10).

ix) The spacing of hoops should be in accordance with fig No.11.x) Fig No. 12 gives the typical bar details for special ductile moment resisting frames.

13

Fig No. 10

Fig No.11

Fig No. 12


14/17

Fig No. 13

5.2. Columns subjected to Axial load and bending.

i) Minimum dimension should be 200 mm with the ratio of the shortest dimension to

perpendicular dimension not less than 0.4. When unsupported length exceeds 4 m, minimum

dimension should not be less than 300 m m.ii) Lap splices are not permitted near the ends of column. They are permitted in the central half of

member length. Hoops should be provided over the entire splice length at spacing notexceeding 150 mm. At any section not more than 50 percent of the bars should be spliced (fig

13)

iii) Special confining reinforcement must be provided near the joints and on both sides (extending

over a length Lo from joint face) ( fig No 14a). The length Lo should not be less than

larger lateral dimension of the member at section where yielding may occur 1/6 of clearheight of member (c) 450 mm. The hoop spacing should not exceed 1/4 of minimum member

dimension but need be less than 75 mm or more than 100 mm.iv) The area of cross section of the bar to be used as special confining should be taken as

Ash 0.09 s Dk fck Ag - 1fy Ak

for circular hoops/spiral

Ash 0.18 s Dh fck Ag - 1fy Ak

for rectangular hoops

Where S = spacing of hoops, Dk = Core diameterDh = longer dimension of the rectangular hoop not more than 300 mm

Ag = gross area of column, Ak = area of concrete core.

v) Special confining reinforcement shall be provided at the locations as shown in fig 14(b,c,d).

14


15/17

5.3. Beam - column connections

i) The special confining reinforcement near column ends should be extended through the joint aswell (fig No.14a). If the joint is externally confined the spacing of hoops in joint region may

be taken as twice that required at the end of the column but limited to 150 mm.ii) The beam and column bars must be well anchored in the compression zone so as to achieve

full strength. (fig No. 8)

15


16/17

6. CONCLUSION

Considering the fact that in future we have to live with earthquake tremors it becomes

important to study, learn and incorporate in actual practice, the simple principles of reinforcement

detailings, in Non engineering and Engineering earthquake resistant constructions to avoid huge lossesof properties and human lives during an earthquake.

7. REFERENCES1) I.S. 1893 : 1984 - Criteria for Earthquake Design of structures, Bureau of Indian standards, NewDelhi 1984.

2) A Manual of earthquake resistant non engineered construction, Indian society of earthquake

Technology Roorkee 1981.

3) I.S. 4236 : 1976 . code of practice for earthquake resistant design and construction of buildings.

Bureau of Indian standards New Delhi 1976

4) I.S. 13920 : 1993 - Ductile detailing of Reinforced

Concrete structures subjected to Seismic forces - Code of practice, Bureau of Indian standards New

Delhi 1993.5) S.P : 34 - 1987 Handbook on concrete reinforcement and detailing. Bureau of Indian standards New

Delhi - 1987

6) SP 22 : 1982 Explanatory handbook for Earthquake Engineering, Bureau of Indian Standards New

Delhi 1982.

7) S. Unnikrishna Pillai and Devdas Menon.

Reinforced concrete Design, Tata - McGraw Hill publishing Company Ltd. New Delhi 1998.

8) U.H. VARYANI. Structural Design of multi-storeyed buildings, South Asian publishers New Delhi

1999.

9) SIPOREX publication, B.G. Shirke and Company Pune, Dec 1993.

10) PROJECT REPORT submitted by C.O & E.T. final years students under guidance of Prof.P.S.Lande "To study the impact of earthquake on structure damage repair and rehabilitation in Latur"

1995-1996.

16


17/17

17

REINFORCEMENT DETAILING IN NON ENGINEERING AND ENGINEERING E

Documents

Transcript of REINFORCEMENT DETAILING IN NON ENGINEERING AND ENGINEERING E