effective construction of concrete...

Seminar on

Earthquake Resilient Construction for School Buildings

Naveed Anwar, PhD

Post-earthquake School Reconstruction Project

Effective Construction of Concrete Structures

Day-2Session 1

2

•Reinforced Concrete structures rely on on-site “Monolithic” construction• Seismic loads resisted by continuity

•Making RC structures is a complex process• Finding the right basic materials

• Mixing, placing, adding rebars, curing

3

Structural Performance

Structural Displacement

Load

ing

Seve

rity

Resta

urant

Resta

urant

Resta

urant

School

4

Ductility is the key to good seismic performance of Structures.

Confinement is the Key for Ductility in Reinforced Concrete Members

Closed ties and stirrups are the key providing proper confinement

.

5

Modal response (K,m) is the pulse of the structure .

Avoiding irregularity in the structure is the key to the stable response of the structure.

Control the demand (energy dissipation) is the key to the seismic design.

Correct way of modelling is the key to predict the behavior of the structure close to the practical conditions.

6

RebarsConcrete

Reinforced Concrete Structure

Water

Cement

Sand

Aggregate

Concrete RebarsFormwork and

FalseworkFinishing

Steel

Cutting

Bending

Binding

Formwork

Wood

Steel

Making

Fixing

Removing

Curing

7

RebarsConcrete


Water

Cement

Sand

Aggregate


FalseworkFinishing

Steel

Cutting

Bending

Binding

Formwork

Wood

Steel

Making

Fixing

Removing

Curing

8

RebarsConcrete


Water

Cement

Sand

Aggregate


FalseworkFinishing

Steel

Cutting

Bending

Binding

Formwork

Wood

Steel

Making

Fixing

Removing

Curing

9

RebarsConcrete


Water

Cement

Sand

Aggregate


FalseworkFinishing

Steel

Cutting

Bending

Binding

Formwork

Wood

Steel

Making

Fixing

Removing

Curing

Materails

11

Basic Materials & Finishes for Safe School

Innovate l Integrate l Collaborate

Construction Material

Foundation

Brick on mud

Brick on cement

Stone on mud

Stone on cement

Concrete isolated footing

Wall

Brick on mud

Brick on cement

Stone on mud

Stone on cement

Interlocking Habitech blocks

Floor

RCC Slab

Wooden

Precast System

Openings

Timber

Aluminum

UPVC

CGI

Roof

CGI sheet on wooden joists

CGI sheet on steel truss

RCC slab

Roofing tiles on wooden joists

Roofing tiles on steel truss

Staircase

RCC

Timber

Steel

12

Sand• From rivers/quarries• Clean, free of mud &

organic materials

Gravel • From rivers/quarries• Clean, free from mud and

organic materials• Diameter 1-2 cm

Cement• Portland Cement• Not hardened• Dry• Uniform color• Not mixed with other

materials

Burnt Bricks• Completely burnt• Flat, not warping• Doesn’t break easily• Uniform size• Corners not damaged• Over-burnt, under-burnt &

deformed bricks should be avoided.

CRITERIA FOR CHOOSING APPROPRIATE CONSTRUCTION MATERIALS IN NEPAL

13

Timber•Dry•Straight•No cracks•No notch•Treated against termite

Water• Clean • Clear and no smell• No oil, acid, alkali, salt, organic

materials that can affect the R.C. bars

• Potable

Concrete Block

• Best from concrete mix• No cracks• Corners not damaged

Habitech interlocking block

• Dry• Flat, not warping• Undamaged frogs• Corners not damaged• No cracks


14

Steel Bars• Uniform size• Conform with standard bars• Not rusted• Straight• Diameter in accordance with

drawings

Rubble Stone

• Size as uniform as possible• Hard, tough, compact

grained, uniform in texture

• Rough surface (not smooth)

CGI Sheet• Uniform corrugation• Not rusted• Thickness according to

drawing

Steel Bars• Uniform size• Not rusted• Straight• Diameter in accordance

with drawings


15

Quarry Stones• Easily breakable soft stones

should be avoided.• Only solid & strong quarry

stones with no obvious fractures should be used.

Boulder Stone• Round boulders don't provide

uniform binding when used in wall construction, resulting in movement of individual boulders and ultimate failure of the wall during earthquake.

• Round boulders should be avoided or broken into angular pieces.

Mud Mortar • Mud for mortar should be free from organic

materials, pebbles & other hard materials which will upset the mortar thickness.

• Dry mud should be thoroughly kneaded with water to prepare a dense paste.


16

Do’s & Don’ts

Mortar Do’s:

• Use clean sand for mortar and concrete

construction.

• Use fresh and lump-free cement for mortar

and concrete.

• Mix the dry ingredients (sand and

cement) together before adding water.

• Protect the mortar or concrete-mixing

area from wind, rain, and sunshine.

Mortar Don’ts:

• Don’t use excessively thick mortar joints.

• Don’t use or re-use mortar that has

already

• hardened. As cement mortar sets

relatively quickly (in approximately 30

minutes), it should never be mixed in huge

quantities.

• Don’t use sea sand or sand containing a

large amount of silt or clay.

• Don’t use cement that has already set.

17

Do’s & Don’ts

Concrete Do’s

• Calculate how much finished concrete is

required and estimate the amount of

cement, sand, coarse aggregate, and

water required for construction.

• Use clean sand and aggregates.

• Use measuring boxes.

• Mix the dry ingredients (sand, cement, &

aggregates) together before adding

water.

• Inspect the formwork to ensure its stability,

dimensions, water-tightness, and

placement of reinforcement before

placing concrete.

• Concrete, stone masonry, brick masonry,

plasterwork, cement flooring work, etc.

should be cured for seven days.

Concrete Don’ts

• Don’t place concrete more than one hour

after adding water to the mix.

18

Do’s & Don’ts

Steel Reinforcement Do’s

• Bending diameter of reinforcement

should be more than six times the

bar diameter.

Steel Reinforcement Don’ts

• Don’t store the steel bars directly on

the ground. Avoid using bars which

show signs of corrosion or are

covered by dirt.

• Don’t use straightened and re-bent

reinforcement in reinforced

concrete construction.

Placing Reinforced Concrete

20

Plain/Reinforced Concrete Construction

• Concrete: Composite construction material made up of cement, sand,

aggregate & water.

• Low tensile strength, so used to resist tension in the structures/structural members

where there is tensile force steel reinforcing bars

• Concrete used with steel reinforcement bars = Reinforced Cement

Concrete(RCC) & that without reinforcement is Plain Cement Concrete (PCC)

• PCC is generally used in foundation base, floors, road pavement etc. and RCC is

used in beams, columns, slabs and other main structures.

21

Plain/Reinforced Concrete Construction

• Concrete is generally categorized by its strength (like M15, M20 etc.) but

also categorized by mix proportion of the constituent materials ( like 1:2:4,

1:3:6 etc.)

• For PCC, concrete should be of less than M10 or mix not leaner than 1:3:6

and for RCC, it should not be less than M15 or mix not leaner than 1:2:4

• For columns – not less than M20 or 1:1.5:3 and for beams and slabs – not

less than M15 or 1:2:4.

22

Form Work/Centering and Shuttering

Formwork is used to achieve required shape of the concrete products.

Quality of timber for formwork

• Hard, durable, enough thickness and required size

• Water tight, to prevent bleeding

• Should not absorb water from concrete

• Water free

• Smooth surface

• In true line and level

• Able to withstand the concrete load

• Proper horizontal bracings, props and runners

23

Reinforcement Placement

• Reinforcement should be erected as per detailed design and

drawing

• All horizontal bars should be truly straight on line and level

• Splicing should be as specified

• Stirrups should be as specified and placed truly vertical, tied all with

longitudinal reinforcement

• Distribution bars should be placed below the top bars

24


• Top bars and bottom bars should be perfectly separated by

using chairs

• Clear cover on all the sides, top and bottom as specified, use

cover blocks

• Cover block should be placed before placing the concrete for

maintaining clear cover properly

25


• Clear cover for concrete elements

• Slab – 15 mm

• Beam – 25mm but not less than the dia of large bar

• Column – 40mm but not less than the dia of larger bar

• Foundation – 75mm

• For other cases – as per the instruction of Engineer

26

Concrete Batching

• All required materials of appropriate quality and quantity should

be ready at site before proceeding to concreting work

• Batching should be done by weight for good quality of concrete

• Standard cube box (size 300*300*375mm i.e volume of 1 bag of

cement) should be used for batching, where weighing is not

possible.

• Materials should never be batched by empty

cement bags or by the means other than

standard batching cube box as specified.

Batching Cube Box

27

Concrete Mixing

Machine mixing

• The batched materials should be properly mixed in concrete mixer till the mix is

homogeneous

Manual Mixing

• In the cases where machine mixing is not possible, concrete can be mixed manually.

• Add 10% cement extra in case of manual mixing

• Batching should be restricted to maximum 5 bags of cement

• The batched materials should be mixed in dry till it gets homogeneous, then water should

be added. It should again be mixed thoroughly at least 2 times till gets homogeneous

• Control water cement ratio

• Mix the concrete thoroughly till it is uniform and place within 45-60 minutes of mixing

28

Concrete Mixing

Concrete MixerManual Mixing of Concrete

29

Concrete Mixing

Machine Mixing of Concrete at site

30

Concrete Placing

• Mixed concrete should be placed

within 45-6 minutes of mixing with

water

• Start placing the concrete from one

end to complete another end

• Concrete should not be spread out or

dropped from more than 1.5m in

height

31

Concrete Placing

• Should not be segregated while

placing

• Should be compacted and leveled

immediately after placing

• Should not be compacted or

vibrated after 5 minutes of placing

32

Equipments

Needle VibratorCompactor

33

Compacting the Concrete

• Concrete placed as specified and compacted

as soon as possible after placing

• Various means of

compaction

• Over vibration should not

be allowed, so as to

prevent bleeding and

segregation

34

Concrete Curing


Curing is most important in order to

maintain the quality of work-

• Concrete surface should be kept wet or

moist at least for a week

• It can be done by pounding or covering

by jute bags

• Water for curing should be as used for

concrete mixing.

35

Formwork removal

Removal of forms for different elements

• For vertical members – not earlier than 48 hours

• For sides of beams, slabs etc. after hours

• For beams span up to 4.5m – after 13 days and above 4.5m span – after 17 days

• Slab – up to 4.5m span : after 11 days

• Over 4.5m to 6m span : after 14 days

• Over 6m span : after 17 days as approval from engineer

• Cantilevers – after 7 days

36

Service lines

1. Electricity line

2. Plumbing (Water supply and sewerage)

3. Telephone cabling

4. Gas pipe line

37

Power supply line

• Control boards: As per design, of higher quality, height not to reach by

children, protected from moisture

• Auto fuse system

• Switches, sockets and all the fixture – not to reach by children

• Be sure of well functioning

• Maintain alarming system in case of short circuit, fires etc.

38

Plumbing/Water supply and Sewerage

• Good quality of materials such as pipes, fittings, couplings etc.

• Properly connected, no water leakage

• Maintain proper head for water supply, bed slope and sufficient cushion for

drainage pipes

• Sufficient pressure resisting capacity

• Proper clamping of pipes

• Maintaining flexible joint connections at critical locations

• Construct chambers at every bend for sewerage line to reduce chance of blocking

39

Plumbing/Water supply and Sewerage

• Be sure of well functioning

• Provide pressure and air release valves for water supply pipe lines

• Maintain air vents for sewerage lines

• Overhead water storage tanks should have of standard quality

• Tanks resting on the roof should be fixed and clamped properly

• Water pumps properly fixed and clamped should be protected from rain,

maintain proper air circulation and cables well insulated

• Provide rain water outlet pipe to protect walls from dampness

41

RCC Structure

Foundation Beam Column Joint Detail

Slope Roof Construction

Pillar

Foundation Beam

RCC

PCC

Brick Soling

Foundation Width

Foundation Mat

Min. 8” Fo

un

da

tio

n D

ep

th

Corner ColumnIntermediate Column

Beam

Column

Beam

Min. 2 Stirrups

Min. 2 Stirrups

BeamColumn

De

ve

lop

me

nt

Len

gth

Sill Band

Lintel Band

Pillar

Wall Construction

Diagonal Bracing of Roof

Slab Beam Connection

Top Bar

Bottom Bar Chair Bar

Elevation

42

Connect all isolated footings at foundation lever or ground level or just below plinth level

FOUNDATION

• Column terminating into a footing or a mat,

extend special confining reinforcement (at

least 300 mm) into the footing or mat.

• The spacing of confining reinforcement

should not be more than 100 mm.

SPECIAL CONFINING REINFORCEMENT >300 MM

43

Good foundation resting on a Firm Base foundation

:

Quality of foundation and the base

on which the foundation rests

Fig. Structural Foundation

44

Good foundation resting on a Firm Base


: Quality of foundation and the base on which the foundation rests

Fig. Foundation consisting of flexible & rigid spread footings

45

Good foundation

Fig. Foundation consisting of flexible spread footings and connecting beams

46

Pillar

Foundation Beam

RCC

PCC

Brick Soling

Foundation Mat

Min. 8”

Fou

nd

atio

n D

ep

th

Column in boundary

Strap Beam

Column

Eccentric Footing

Isolated Footing

ColumnColumn

Strap Beam

Eccentric Footing Isolated Footing

FOUNDATION - Frame Structure

47

CONNECTION OF STEEL COLUMN WITH RC COLUMN

Steel column connection with RC column

CONNECTION DETAIL OPTIONS

48

COLUMN

Two stirrups

Beam

Beam

2 ft. min.

2 ft. min.

60

x D

iao

f

Co

lum

n B

ar

60

x D

iao

f C

olu

mn

Ba

r

Columns and Joints – Very important

Transverse reinforcement in column

49

BEAM

Stirrups at 4”

Lower Rod

Stirrups at 4”Stirrups at 6”

Upper Rod

1/7 L1/7 L135°

hStirrups for

Beam

Length (L)

Ties and Stirrups

Beam Web Reinforcement

50

BEAM

Overlaps and Splices – The weak link

Anchorage beam bar Lap splice in beam

51

BEAM COLUMN JOINT – Most Critical

Lap splice in column

Hoop stirrups for joints Stirrups for joints

60 x Ф

2 FT.

2 FT.

52

BEAM COLUMN JOINT – Most Critical

Weak Joints

REBARS OF BEAM

REBARS OF COLUMN

60 x

DIA

. O

F R

EB

AR

53

Roof or Slab Structure

Diagonal Bracing of Floor

Wooden Flat roof or slab construction

Tie Beam at Top of WallCantilever

RCC Flat roof or slab construction

Reference: National Building Code (NBC), Nepal & NSET

54

Top Bar

Bottom Bar Chair

Bar

¼ of L ¼ of L ¼ of L 1/7 of L

Length (L) Length (L)

BeamCantilever

Projection

RC SLAB

Reference: National Building Code (NBC), Nepal

55

PRECASE SLAB WITH RC TOPPING

56

RCC Structure

PRECAST SLAB WITH RC TOPPING

57

Lintel Band

Column

Sill Band

Lintel Band

Sill Band

U-Hook

2 Hor. Rods

SILL & LINTEL BAND

Reference: National Building Code (NBC), Nepal

58

SILL & LINTEL BAND

REBAR TO CONSTRUCT LINTEL BAND

CONSTRUCTION WITHOUT BANDS

Quality OF COnstruction

60

Quality Control Concept

Quality Control

Covers all activities from

DesignDevelopm

entProduction Installation Servicing

Documentation

61


• Special care is needed in construction to ensure that the

elements meant to be ductile are indeed provided with

features that give adequate ductility.

• Strict adherence to prescribed standards of construction

materials and construction processes is essential in assuring an

earthquake-resistant building.

62


Elements of Good Quality Control

i. Regular testing of construction materials at qualified

laboratories (at site or away)

ii. Periodic training of workmen at professional training houses

iii. On-site evaluation of the technical work

63

Quality Control

Need for Mason Training

• Key actors in every type of construction

• No awareness of earthquake resistant technology

• Unknown about reducing the earthquake risk

• Who recommend owner on materials selection & construction process.

• Have greater role in building production in terms of quantity and quality

64


Quality is compared with

applicable standards

Verifies if the product meets

pre-defined standards

Implements the process

Verifies if specific attributes are in a

specific product or service specific

product or service

Identifies defects

Defects, reports & correction

Determine defect in the

functionalitiesImprovement

Quality Assurance

65


4 important levels

Level 1: Quality Manual – Quality Policy, Quality Objectives, Requirement Standard

& Other Statutory and Regulatory Requirement

Level 2: Quality Procedures – Control of Documents, Control of Records, Internal Quality

Audits, Control of Non-conforming Products, Corrective Action & Preventive Action

Level 3: Quality Plan – Incoming Inspection Plan, In-Process Inspection Plan, Final Test

Report/Inspection Plan and Work Instruction

Level 4: Forms/Formats/Records – Testing report forms, Commissioning Report Forms,

Inspection forms, Check sheets/Check list and Miscellaneous Documentation forms

66

Quality of Cement

Good Quality

• Hardens/sets within appropriate duration

• Achieves required compressive strength within specified time period

• Absorbs appropriate quantity of moisture

• Fully powder form like talcum powder in well packed slacks

Bad Quality

• Doesn’t get strength within specified time duration

• Absorbs more moisture

• Not in fully powder form, contains some already hardened particles

• Defects in packing, transporting and storage

67

Selection and Handling of Cement

• Should fulfill the design requirements

• For RCC and structural elements – cement should not be of less than 42 grade

• Age < 2 months of the time of construction

• Air tight bags without any holes should be selected

• Should be free from pebbles or any hardened cement contents

• Handling and storing

• Bags should be handled with care during transportation so that they will not be torn out by

hooks and will not come into contact with moisture/water

• Stored in dry, air and water tight and moisture free place

68

Sand

• Known as fine aggregate, size < 4.75 mm

• Naturally available material, found in river beds, river banks

and sand quarries

• Not used alone , mixed for making mortar and concrete

69

Quality of Sand

• Many unnecessary and organic things may be mixed with sand since its

obtained from river or quarries.

• Should be carefully selected and used.

• Should be coarse river sand, well graded grains, clean and fresh

• Should be free from foreign particles and mineral (soil, organics)

• Moisture should contain to maintain minimum bulking

70

Coarse Aggregate

• Obtained from the stones crushed to various sizes or natural

sedimentation on river banks

• Used for cement concrete works, pavements, etc.

• Should be hard enough, durable, clean and granule in shape

• Minimum abrasion

• Should not contain minerals and foreign materials

• Should be well graded to various sizes

71

Size of Aggregate

• Size depends on the thickness of the concrete members, specification

and design requirement

• Size of aggregate for RCC and PCC work

• For the members having thickness > 100 mm - 40mm down

• For the members having thickness 40 to 100 mm - 20mm down

• For the member having thickness < 40mm - 12mm down

• For the members other than specified above - as per design & specification

• Well graded aggregates should always be used (aggregates consisting of

different size in the mix)

72

Steel Reinforcement Bars

• Concrete and masonry have very low tensile strength, so they can not resist

tensile forces

• However, buildings and different elements are frequently subjected to tension.

• Steel reinforcement bars are provided to resist the tensile forces.

• Steel bars have very high tensile strength, but have low compressive strength

as compared to concrete or masonry.

• Steel bars are characterized by their strength such as MS 230, Fe 415, Fe 500

etc.

73

Quality of Steel Bars

• Free from rusting

• Assured standard quality and marked

• Should not break while bending

• Un-cracked, uniform thickness (dia.) throughout the whole length

• Size of rebar depends on the design of structural components

74

Water

• Water is most important nutrition for all the living beings

• Similarly, its is an important material in the construction also.

• Water is required in almost every stage of any type of construction from starting to

the end

• Water is used to make mortar, concrete as well as for curing of masonry and

concrete

• As man needs pure and good quality water; concrete, mortar etc. Also need

pure and drinkable water

• Impurities in water may lower down the quality of concrete and mortar

75

Quality of Construction Work

• A building to be strong, durable and earthquake resistant, good planning

and design and selection of quality materials are not only sufficient,

quality of construction process is also equally important

• Good quality of workmanship at every stage of construction can only

assure the final quality of a building

• Quality and process of each construction work should be in accordance

with the standard practice as outlined in specification and guidelines