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12/2016 CONSTRUCTING WITH CONCRETE BLOCK CONFINED MASONRY

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12/2016

CONSTRUCTING

WITH CONCRETE

BLOCK CONFINED

MASONRY

Presentation Outline

Introduction to confined masonry

General concepts

Comparison with unreinforced masonry and RC frame with infill

Review of confined masonry house designed by Build Change

Introduction to Confined Masonry

Why Confined Masonry?

Poor performance of unreinforced masonry and non-ductile reinforced concrete (RC) frame

construction caused unacceptably high human and economic losses in past earthquakes

This prompted a need for developing and/or promoting alternative building technologies

Confined masonry is an opportunity for improved seismic performance both for unreinforced

masonry and reinforced concrete frame construction in low and medium rise buildings.

The goal is to achieve enhanced seismic performance using technologies which require

similar level of construction skills and are economically viable

Development of Confined Masonry

Evolved though an informal process based on its satisfactory

performance in past earthquakes

The first reported use in the reconstruction after the 1908

Messina, Italy earthquake (M 7.2) - death toll 70,000

Practiced in Chile and Columbia since 1930’s and in Mexico

since 1940’s

Currently practiced in several countries/regions with high

seismic risk, including Latin America, Mediterranean Europe,

North Africa, Middle East, Southeast Asia, and the Far East

Development of Confined Masonry

Large scale testing of confined masonry walls have been

conducted in Mexico (UNAM), Peru (PUCP), India (IIT Kanpur),

and other universities

Tests have shown acceptable performance of properly

constructed confined masonry walls

2009 study by Riahi, Elwood & Alcocer (published by ASCE)

reviewed 102 tests and develop a ductility curve that

confirmed that the confined masonry walls are a ductile

system

Standards for Confined Masonry

Provisions included in several

building codes

Mexico, Chile, Peru, Eurocode,

Algeria, China

EERI and IAEE published guidelines

for design and construction of 1-2

story CM buildings

Engineering design guidelines are

currently being developed

CM guidelines for India are currently

being developed

Performance of Confined Masonry

Confined masonry buildings have been subjected to

large earthquakes, most recently in Chile and China

For example, a six-storey confined masonry

building remained undamaged in the August 2007

Pisco, Peru earthquake (M 8.0) while many other

masonry buildings experienced severe damage or

collapse

In the February 2010 Chile earthquake (M 8.8),

there were 521 deaths. Only 24 of those were due

to damage to confined masonry buildings

Performance of Confined Masonry

Performance of confined masonry buildings in the

2008 Great Wenchuan, China earthquake (M 8.0):

In areas of Intensity 7 (31-50% expected damage),

57.6% of CM buildings remained almost intact, 24.2%

lightly damaged (18% actual damage)

In areas of Intensity 8 (51-70% expected damage),

24.3% of CM buildings remained almost intact, 43.6%

lightly damaged (32% actual damage)

In areas of Intensities 10 & 11, there was extensive

damage to CM buildings but few reported collapses

Figures from the China institute of Engineering Mechanics

Key Components of a Confined Masonry Building

Masonry walls made either of burnt clay brick or

concrete block units

Tie-columns: vertical RC confining elements similar

to columns in reinforced concrete frame construction

Tie-columns occur at wall intersections, ends of shear

walls, and wall openings

Tie-columns are typically tied to the walls with

staggered joints (“toothing”) or dowels in the masonry

mortar joints

Tie-beams: horizontal RC confining elements similar

to beams in reinforced concrete frame construction

Tie-beams occur at each floor level and wall openings

Confined Masonry vs. RC Frame with Infill

Both use concrete frames and unreinforced masonry walls. However, the

primary difference is the construction sequence:

Confined Masonry = The masonry wall is built first, then the concrete beams and

columns are placed

RC Frame with Infill = The concrete frame is built first, then the masonry infill is

placed

Confined Masonry vs. RC Frame with Infill

Because the concrete is poured on top of

the masonry wall and is tied to the columns

at the ends of the wall, a bond develops

between the concrete and masonry

This bond transfers the lateral shear loads

from the concrete to the masonry, since no

gaps develop between the two elements

when loaded

Thus confined masonry is a shear wall

system rather than a frame system

Confined Masonry vs. RC Frame with Infill

Because the concrete elements are not the primary

support system, the load on them is much lower &

the ductility requirements are much less

Thus the size of the columns and the amount of

reinforcing steel required is much less than a

comparable RC frame

Meanwhile, the size of the masonry wall is similar

to infill, primarily because the wall thickness is

often dictated by other factors common to both

systems (e.g. out-of-plane forces, insulation,

standard unit sizes)

Confined Masonry vs. Unreinforced Masonry

Both use unreinforced masonry units that are built the same way. The difference

is what happens when the walls are loaded.

When cracks develop in an unreinforced wall (either in-plane or out-of-plane),

the wall quickly loses its ability to resist loads and falls apart

When cracks develop in a confined wall, the confining frame keeps the wall

together, allowing it to continue to resist loads

Confined Masonry vs. Unreinforced Masonry

Analogous to a stack of books on a table:

A stack of books that are not tied together falls apart when the table is shaken.

But when the books are tied together by a string, the stack stays together unless

the string breaks or the pages rip apart

Confined Masonry House Design

Minimum Criteria for Building a Confined Masonry Building

Geological fault or Ruptured Area

Area susceptible to landslide

Steep slope > 20%

Filled Area

River bank ad water logged area

Maximum

number of

stories Two

Span of wall Largest span of the room should not be more than 3.5 metres

Height of

wall Maximum height of wall should not be more than 2.5 metres

ProportionThe house shall be planned in square, rectangular. External length to

width ratio of the building should not exceed 3

General The foundation trench shall be of uniform width. The foundation bed

shall be on the same level troughout the foundation in the flat area

Depth The depth of footing should not be less than 900mm depending on

the soil sub strata

WidthThe width of footing should not be less than 900 mm in medium soil

condition.

A building shall not be constructed if the site is:

Site Selection1

Shape of house2

Foundation3

Minimum Criteria for Building a Confined Masonry Building

General Provide a reinforced concrete band at plinth level, as shown in detail drawings. The plinth

height should not be less than 300mm from existing ground level.

Depth of beam Depth of plinth beam shall be greater than or equal to 150mm

Width of beam Width of plinth beam shall be greater than or equal to 200mm

ReinforcementMain reinforcement should be 4-10mm dia. Bars. Use 7mm diameter rings at 150mm center to

center. Hook length should be 50mm. Bars shall have a clear cover of 25mm concrete

General Masonry should be laid staggered in order to avoid continuous vertical joints. The wall should

have toothing at the wall-tiecolumn interface to facilitate good connection

Hollow Block unitsThe hollow blocks used shall be of good quality and shall adhere to the Nepal Standards of

block production

Mortar joints and

ratio

Mortar joints should be between 20mm to 10mm in thickness. The mortar shall be 1: 5

(cement:sand) or richer

Span of wallThe length of wall shall be less than or equal to 3.5 metres. The length of wall between

vertical reinforcing members (tie column or vertical grouted reinforcement) shall be less than

or equal to 1.5 metres.

Width The thickness of wall shall be greater than or equal to 150mm

Location Openings are to be located away from inside corners by a clear distance of at least 600mm.

Only one opening is allowed in a pannel

SizeArea of the opening shall not exceed 10% of the area of confined wall panel including the

confining tie columns and beams.

Distance The horizontal distance between two openings shall not be less than 600mm

Lintel level The lintel level should be kept same for all doors and windows

Plinth4

Walls5

Openings6

Minimum Criteria for Building a Confined Masonry Building

LocationTie columns should be placed at each corner and intersection of the walls as

well as on either side of the door.

Size The size of the tie-column shall be equal to the width of the wall

Spacing The spacing of tie-column shall be less than or equal to 3.5 metres.

ReinforcementThe minimum reinforcement to be used is 4-12mm dia. Longitudnal bars and

7mm dia. Stirrups at 150mm c/c

LocationVertical reinforcement in the blocks is placed on either side of the window

Reinforcement Minimum 12mm dia. Bar centred in the Hollow block cell and grouted with

cement mortar

General Horizontal bands should be provided throughout the entire wall

Sill band A continuous sill band shall be provided throughout the entire wall at the

bottom level of the openings. The minimum depth of the band shall be 75mm

Lintel band A continuous lintel band shall be provided throughout the entire wall at the

top level of the openings. The minimum depth of the band shall be 75mm

Floor/Roof bandA continuous floor/roof band shall be provided throughout the entire wall at

the top of the walls at floor/roof level. The minimum depth of the band shall

be 200mm. The minimum width of the band shall be 200mm.

Reinforcement

Main reinforcement should be 4-10mm dia. Bars. Use 7mm diameter rings at

150mm. Hook length should be 50mm. Bars shall have a clear cover of 25mm

concrete

Vertical Tie

columns and

reinforcements

7

Horizontal

band9

Vertical

reinforcement

grouted in

blocks

8

Light roof Use light roof comprising wooden or steel truss covered with CGI sheets

ConnectionAll members of the timber truss or joints should be properly connected as

shown in detail drawings

Cross-tieTrusses should be properly cross tiesd with wooden braces as shown in detail

drawings

TimberWell seasoned Khote salla wood without knots should be used for roofing,

timber treatment such as use of coal tar or any other preservative can

prevent timber from being decayed and attacked by insects

MortarCement sand mortar should not be leaner than 1:5 (cement:sand) for masonry

and 1:6 for plaster

ConcreteConcrete mix for seismic bands should not be leaner than 1:1.5:3

(cement:sand:aggregates)

Reinforcement High strength deformed bars - Fe415

12 Roof Span The center to center span of the truss shall not be greater than 3.5m

RaftersThe size of the rafters shall be greater than 50mm x 100mm and shall be

provided at a spacing of 1138mm or lesser

Purlins

The size of the purlins shall be greater than 50mm x 50mm and shall be

provided at a spacing of 350mm center to center at the porch and at a

spacing of 500mm center to center at the roof

Roof10

Materials11

Minimum Criteria for Building a Confined Masonry Building

Blocks available in the market and their corresponding strengths

District Gross compressive strength (Mpa)

Sindupalchowk 1.97

Kavrepalanchowk 1.66

Gwarko (Kathmandu) 1.75

United Cements (Kathmandu) 5.01

Prefab (Bhaktapur) 7.20

The table shows the gross compressive strength of random block samples collected

from different districts.

Description of the building

Building type: ResidentialNumber of storeys: 2Ground floor storey height: 2.475mFirst floor storey height: 2.475 mWall thickness: 150 mm (without plaster)

Length of the building: 9.66 mWidth of the building: 3.5 mHeight of the building: 6.043m

Hollow Concrete Block (HCB) size: 400 mm x 200mm x 150mm

Plan of the Building

Elevation of the Building

Elevation of the Building

Section of the Building

Roof Framing Plan

Graphical View of the Building

Material Properties

The Hollow block must be compliant to NS Standard.

Design Methodology

- Dead loads were taken as per IS 875 Part I

- Imposed loads were taken as per IS 875 Part II

- The lateral load demand was calculated based on IS 1893:2002 Part I

• Lump mass calculation

• Seismic load calculation based on seismic coefficient method: Z = 0.36; I = 1; R = 2.5

• Calculation of center of mass and center of stiffness

- Check for torsion by calculation of eccentricity due to difference in center of mass and center of stiffness: should be less than 30% of thelength for corresponding direction

- In-Plane Pier analysis was done by manual calculation

• Calculation of Net stress = bending stress + overturning stress + Vertical stress

• Calculation of length of tension zone

• Calculation of rebar for tension

- Out of Plane Pier analysis

• Check height/thickness ratio of the wall

• Stress check of beams at floor and lintel levels:

o Calculation of bending moment due to lateral loads

o Calculation of required depth and reinforcement for the above moment

Design Methodology

- The following stress checks were made based on IITK GSDMA and IS 1905: 1987

• Shear Stress Check:

o Calculation of shear stress due to lateral load demand

o Calculation of permissible shear stress as per IS 1905: 1987

• Compressive stress check

o Calculation of compressive stress based on dead load and live load

o Calculation of permissible compressive stress as per IS 1905: 1987

- To match the demand with the capacity of the masonry, addition of confining reinforced concrete ties were provided as deemed necessary to meet the above stress demands

Quantity and Cost Estimation

Skilled Unskilled Stone Bricks

Hollow

Block Cement Sand

Aggregate

Wood

Ply WoodLocal

Wood for

form work Glass Bar

Binding

Wire Soil Water

CGI

Sheet

Unit Md Md Cum. Nos. Nos. Bags Cum. Cum. Cum. Sq.m Cum. Sq.m kg Kg Cum. lit. Bundle

Upto Plinth Level 39.00 74.00 21.12 0.00 0.00 72.00 9.20 1.14 0.00 2.97 0.07 0.00 274.37 2.74 13.09 2227.93 0.00

Super Structure 220.00 263.00 6.78 0.00 1330.00 160.00 15.14 11.81 2.11 38.31 0.57 3.28 1487.42 14.87 0.00 3597.77 0.00

Roof 36.00 12.00 0.00 0.00 0.00 0.00 0.00 0.00 1.67 0.00 0.00 0.00 0.00 0.00 0.00 0.00 5.00

Total 295.00 349.00 27.90 0.00 1330.00 232.00 24.34 12.95 3.78 41.28 0.64 3.28 1761.79 17.62 13.09 5825.69 5.00

From the District Rate of Sindhupalchowk the Total Building Cost

15% overhead

Total 1,651,796.75

Manpower Material

Nepal Housing Reconstruction Programme

SUMMARY OF QUANTITY

MODEL HOLLOW CONCRETEBLOCK

1,436,345.00

215,451.75

Structural Detail of toothing and mortar grouting

The toothing length is one third of the length of the block.

The window opening is grouted with cement mortar with a

single rebar.

Section showing wall section with toothing

Roof Truss Detail

Roof Truss Detail

Roof Truss Detail

Connection Detail

Questions?